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www.huawei.com
Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA RAN Fundamental
Page1Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Objectives
Upon completion of this course, you will be able to:
Describe the development of 3G
Outline the advantage of CDMA principle
Characterize code sequence
Outline the fundamentals of RAN
Describe feature of wireless propagation
Page2Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
Page3Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
Page4Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Different Service, Different Technology
AMPS
TACS
NMT
Others
1G 1980sAnalog
GSMGSM
CDMA CDMA IS-95IS-95
TDMATDMAIS-136IS-136
PDCPDC
2G 1990sDigital
Technologies drive
3G IMT-2000
UMTSUMTSWCDMAWCDMA
cdmacdma20002000
Demands drive
TD-SCDMA
TD-SCDMA
3G provides compositive services for both operators and subscribers
The first generation is the analog cellular mobile communication network in the time period from the middle of 1970s to the middle of 1980s. The most important breakthrough in this period is the concept of cellular networks put forward by the Bell Labs in the 1970s, as compared to the former mobile communication systems. The cellular network system is based on cells to implement frequency reuse and thus greatly enhances the system capacity.
The typical examples of the first generation mobile communication systems are the AMPS system and the later enhanced TACS of USA, the NMT and the others. The AMPS (Advanced Mobile Phone System) uses the 800 MHz band of the analog cellular transmission system and it is widely applied in North America, South America and some Circum-Pacific countries. The TACS (Total Access Communication System) uses the 900 MHz band. It is widely applied in Britain, Japan and some Asian countries.
The main feature of the first generation mobile communication systems is that they use the frequency reuse technology, adopt analog modulation for voice signals and provide an analog subscriber channel every other 30 kHz/25 kHz.
However, their defects are also obvious:
Low utilization of the frequency spectrum
Limited types of services
No high-speed data services
Poor confidentiality and high vulnerability to interception and number embezzlement
High equipment cost
To solve these fundamental technical defects of the analog systems, the digital mobile communication technologies emerged and the second generation mobile communication systems represented by GSM and IS-95 came into being in the middle of 1980s. The typical examples of the second generation cellular mobile communication systems are the DAMPS of USA, the IS-95 and the European GSM system.
The GSM (Global System for Mobile Communications) is originated from Europe. Designed as the TDMA standard for mobile digital cellular communications, it supports the 64 kbps data rate and can interconnect with the ISDN. It uses the 900 MHz band while the DCS1800 system uses the 1800 MHz band. The GSM system uses the FDD and TDMA modes and each carrier supports eight channels with the signal bandwidth of 200 kHz.
The DAMPS (Digital Advanced Mobile Phone System) is also called the IS-54 (North America Digital Cellular System). Using the 800 MHz bandwidth, it is the earlier of the two North America digital cellular standards and specifies the use of the TDMA mode.
The IS-95 standard is another digital cellular standard of North America. Using the 800 MHz or 1900 MHz band, it specifies the use of the CDMA mode and has already become the first choice among the technologies of American PCS (Personal Communication System) networks.
Since the 2G mobile communication systems focus on the transmission of voice and low-speed data services, the 2.5G mobile communication systems emerged in 1996 to address the medium-rate data transmission needs. These systems include GPRS and IS-95B.
The CDMA system has a very large capacity that is equivalent to ten or even twenty times that of the analog systems. But the narrowband CDMA technologies come into maturity at a time later than the GSM technologies, their application far lags behind the GSM ones and currently they have only found large-scale commercial applications in North America, Korea and China. The major services of mobile communications are currently still voice services and low-speed data services.
With the development of networks, data and multimedia communications have also witnessed rapid development; therefore, the target of the 3G mobile communication is to implement broadband multimedia communication.
The 3G mobile communication systems are a kind of communication system that can provide multiple kinds of high quality multimedia services and implement global seamless coverage and global roaming. They are compatible with the fixed networks and can implement any kind of communication at any time and any place with portable terminals.
Page6Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
3G Evolution
Proposal of 3G
IMT-2000: the general name of third generation mobile
communication system
The third generation mobile communication was first proposed
in 1985,and was renamed as IMT-2000 in the year of 1996
Commercialization: around the year of 2000
Work band : around 2000MHz
The highest service rate :up to 2000Kbps
Put forward in 1985 by the ITU (International Telecommunication Union), the 3G mobile communication system was called the FPLMTS (Future Public Land Mobile Telecommunication System) and was later renamed as IMT-2000 (International Mobile Telecommunication-2000). The major systems include WCDMA, cdma2000 and UWC-136. On November 5, 1999, the 18th conference of ITU-R TG8/1 passed the Recommended Specification of Radio Interfaces of IMT-2000 and the TD-SCDMA technologies put forward by China were incorporated into the IMT-2000 CDMA TDD part of the technical specification. This showed that the work of the TG8/1 in formulating the technical specifications of radio interfaces in 3G mobile communication systems had basically come into an end and the development and application of the 3G mobile communication systems would enter a new and essential phase.
The 3GPP is an organization that develops specifications for a 3G system based on the UTRA radio interface and on the enhanced GSM core network.
The 3GPP2 initiative is the other major 3G standardization organization. It promotes the CDMA2000 system, which is also based on a form of WCDMA technology. In the world of IMT-2000, this proposal is known as IMT-MC. The major difference between the 3GPP and the 3GPP2 approaches into the air interface specification development is that 3GPP has specified a completely new air interface without any constraints from the past, whereas 3GPP2 has specified a system that is backward compatible with IS-95 systems.
Page7Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
3G Spectrum Allocation
ITU has allocated 230 MHz frequency for the 3G mobile communication system IMT-2000: 1885 ~ 2025MHz in the uplink and 2110~ 2200 MHz in the downlink. Of them, the frequency range of 1980 MHz ~ 2010 MHz (uplink) and that of 2170 MHz ~ 2200 MHz (downlink) are used for mobile satellite services. As the uplink and the downlink bands are asymmetrical, the use of dual-frequency FDD mode or the single-frequency TDD mode may be considered. This plan was passed in WRC92 and new additional bands were approved on the basis of the WRC-92 in the WRC2000 conference in the year 2000: 806 MHz ~ 960 MHz, 1710 MHz ~ 1885 MHz and 2500 MHz ~ 2690 MHz.
Page8Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Bands WCDMA UsedMain bands
1920 ~ 1980MHz / 2110 ~ 2170MHz
Supplementary bands: different country maybe different1850 ~ 1910 MHz / 1930 MHz ~ 1990 MHz (USA)
1710 ~ 1785MHz / 1805 ~ 1880MHz (Japan)
890 ~ 915MHz / 935 ~ 960MHz (Australia)
. . .
Frequency channel number=central frequency×5, for main band:
UL frequency channel number :9612~9888
DL frequency channel number : 10562~10838
The WCDMA system uses the following frequency spectrum (bands other than those specified by 3GPP may also be used): Uplink 1920 MHz ~ 1980 MHz and downlink 2110 MHz ~ 2170 MHz. Each carrier frequency has the 5M band and the duplex spacing is 190 MHz. In America, the used frequency spectrum is 1850 MHz ~ 1910 MHz in the uplink and 1930 MHz ~ 1990 MHz in the downlink and the duplex spacing is 80 MHz.
Page9Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
3G Application Service
Time Delay
Error Ratio
background
conversational
streaming
interactive
Compatible with abundant services and applications of 2G, 3G system has an open integrated service platform to provide a wide prospect for various 3G services.
Features of 3G Services
3G services are inherited from 2G services. In a new architecture, new service capabilities are generated, and more service types are available. Service characteristics vary greatly, so each service features differently. Generally, there are several features as follows:
Compatible backward with all the services provided by GSM.
The real-time services (conversational) such as voice service generally have the QoS requirement.
The concept of multimedia service (streaming, interactive, background) is introduced.
Page10Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
The Core technology of 3G: CDMA
CDMA
WCDMAWCDMACN: based on MAP and GPRS
RTT: WCDMA
TD-SCDMACN: based on MAP and GPRS
RTT: TD-SCDMA
cdma2000CN: based on ANSI 41 and MIP
RTT: cdma2000
Formulated by the European standardization organization 3GPP, the core network evolves on the basis of GSM/GPRS and can thus be compatible with the existing GSM/GPRS networks. It can be based on the TDM, ATM and IP technologies to evolve towards the all-IP network architecture. Based on the ATM technology, the UTRAN uniformly processes voice and packet services and evolves towards the IP network architecture.
The cdma2000 system is a 3G standard put forward on the basis of the IS-95 standard. Its standardization work is currently undertaken by 3GPP2. Circuit Switched (CS) domain is adapted from the 2G IS95 CDMA network, Packet Switched (PS) domain is A packet network based on the Mobile IP technology. Radio Access Network (RAN) is based on the ATM switch platform, it provides abundant adaptation layer interfaces.
The TD-SCDMA standard is put forward by the Chinese Wireless Telecommunication Standard (CWTS) Group and now it has been merged into the specifications related to the WCDMA-TDD of 3GPP. The core network evolves on the basis of GSM/GPRS. The air interface adopts the TD-SCDMA mode.
Page11Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
Page12Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Multiple Access and Duplex Technology
Multiple Access Technology
Frequency division multiple access (FDMA)
Time division multiple access (TDMA)
Code division multiple access (CDMA)
In mobile communication systems, GSM adopts TDMA; WCDMA, cdma2000 and TD-SCDMA adopt CDMA.
Page13Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Multiple Access Technology
Frequency
Time
Power
FDMA
FrequencyTime
Power
TDMA
Power
Time
CDMA
Frequency
Frequency Division Multiple Access means dividing the whole available spectrum into many single radio channels (transmit/receive carrier pair). Each channel can transmit one-way voice or control information. Analog cellular system is a typical example of FDMA structure.
Time Division Multiple Access means that the wireless carrier of one bandwidth is divided into multiple time division channels in terms of time (or called timeslot). Each user occupies a timeslot and receives/transmits signals within this specified timeslot. Therefore, it is called time division multiple access. This multiple access mode is adopted in both digital cellular system and GSM.
CDMA is a multiple access mode implemented by Spreading Modulation. Unlike FDMA and TDMA, both of which separate the user information in terms of time and frequency, CDMA can transmit the information of multiple users on a channel at the same time. The key is that every information before transmission should be modulated by different Spreading Code to broadband signal, then all the signals should be mixed and send. The mixed signal would be demodulated by different Spreading Code at the different receiver. Because all the Spreading Code is orthogonal, only the information that was be demodulated by same Spreading Code can be reverted in mixed signal.
Page14Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Multiple Access and Duplex Technology
Duplex Technology
Frequency division duplex (FDD)
Time division duplex (TDD)
In third generation mobile communication systems, WCDMA and cdma2000 adopt frequency division duplex (FDD), TD-SCDMA adopts time division duplex (TDD).
Page15Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Duplex Technology
Time
Frequency
Power
TDD
USER 2
USER 1
DLUL
DLDL
UL
FDD
Time
Frequency
Power
UL DL
USER 2
USER 1
Page16Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
Page17Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Network Architecture
RNS
RNC
RNS
RNC
Core Network
Node B Node B Node B Node B
Iu-CS Iu-PS
Iur
Iub IubIub Iub
CN
UTRAN
UEUu
CS PS
Iu-CSIu-PS
CSPS
WCDMA including the RAN (Radio Access Network) and the CN (Core Network). The RAN is used to process all the radio-related functions, while the CN is used to process all voice calls and data connections within the UMTS system, and implements the function of external network switching and routing.
Logically, the CN is divided into the CS (Circuit Switched) Domain and the PS (Packet Switched) Domain. UTRAN, CN and UE (User Equipment) together constitute the whole UMTS system
A RNS is composed of one RNC and one or several Node Bs. The Iu interface is used between RNC and CN while the Iub interface is adopted between RNC and Node B. Within UTRAN, RNCs connect with one another through the Iur interface. The Iur interface can connect RNCs via the direct physical connections among them or connect them through the transport network. RNC is used to allocate and control the radio resources of the connected or related Node B. However, Node B serves to convert the data flows between the Iub interface and the Uu interface, and at the same time, it also participates in part of radio resource management.
Page18Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Network Version Evolution
3GPP Rel993GPP Rel4
3GPP Rel5
2000 2001 2002
GSM/GPRS CNWCDMA RTT
IMSHSDPA 3GPP Rel6
MBMSHSUPA
2005
CS domain change to NGN
WCDMA RTT
The overall structure of the WCDMA network is defined in 3GPP TS 23.002. Now, there are the following three versions: R99, R4, R5.
3GPP began to formulate 3G specifications at the end of 1998 and beginning of 1999. As scheduled, the R99 version would be completed at the end of 1999, but in fact it was not completed until March, 2000. To guarantee the investment benefits of operators, the CS domain of R99 version do not fundamentally change., so as to support the smooth transition of GSM/GPRS/3G.
After R99, the version was no longer named by the year. At the same time, the functions of R2000 are implemented by the following two phases: R4 and R5. In the R4 network, MSC as the CS domain of the CN is divided into the MSC Server and the MGW, at the same time, a SGW is added, and HLR can be replaced by HSS (not explicitly specified in the specification).
In the R5 network, the end-to-end VOIP is supported and the core network adopts plentiful new function entities, which have thus changed the original call procedures. With IMS (IP Multimedia Subsystem), the network can use HSS instead of HLR. In the R5 network, HSDPA (High Speed Downlink Packet Access) is also supported, it can support high speed data service.
In the R6 network, the HSUPA is supported which can provide UL service rate up to 5.76Mbps. And MBMS (MultiMedia Broadcast Multicast Service) is also supported.
Page19Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Network Version Evolution
Features of R6
MBMS is introduced
HSUPA is introduced to achieve the service rate up to 5.76Mbps
Features of R7
HSPA+ is introduced, which adopts higher order modulation and MIMO
Max DL rate: 28Mbps, Max UL rate:11Mbps
Features of R8
WCDMA LTE (Long term evolution) is introduced
OFDMA is adopted instead of CDMA
Max DL rate: 50Mbps, Max UL rate: 100Mbps (with 20MHz bandwidth)
Page20Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. 3G Overview
2. CDMA Principle
3. WCDMA Network Architecture and protocol structure
4. WCDMA Wireless Fundamental
Page21Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Processing Procedure of WCDMA System
SourceCoding
Channel Coding& Interleaving Spreading Modulation
SourceDecoding
Channel Decoding& Deinterleaving Despreading Demodulation
Transmission
Reception
chip modulated signalbit symbol
ServiceSignal
Radio Channel
ServiceSignal
Receiver
Source coding can increase the transmitting efficiency.
Channel coding can make the transmission more reliable.
Spreading can increase the capability of overcoming interference.
Through the modulation, the signals will transfer to radio signals from digital signals.
Bit, Symbol, Chip
Bit : data after source coding
Symbol: data after channel coding and interleaving
Chip: data after spreading
Page22Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Source Coding
AMR (Adaptive Multi-Rate) Speech
A integrated speech codec with 8 source rates
The AMR bit rates can be controlled by the RAN depending on the system load and quality of the speech connections
Video Phone ServiceH.324 is used for VP Service in CS domain
Includes: video codec, speech codec, data protocols, multiplexing and etc.
5.15AMR_5.15
4.75AMR_4.75
5.9AMR_5.90
6.7 (PDC EFR)AMR_6.70
7.4 (TDMA EFR)AMR_7.40
7.95AMR_7.95
10.2AMR_10.20
12.2 (GSM EFR)AMR_12.20
Bit Rate (kbps)CODEC
AMR is compatible with current mobile communication system (GSM, IS-95, PDC and so on), thus, it will make multi-mode terminal design easier.
The AMR codec offers the possibility to adapt the coding scheme to the radio channel conditions. The most robust codec mode is selected in bad propagation conditions. The codec mode providing the highest source rate is selected in good propagation conditions.
During an AMR communication, the receiver measures the radio link quality and must return to the transmitter either the quality measurements or the actual codec mode the transmitter should use during the next frame. That exchange has to be done as fast as possible in order to better follow the evolution of the channel’s quality.
Page23Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Processing Procedure of WCDMA System
Transmitter
SourceCoding
Channel Coding& Interleaving Spreading Modulation
SourceDecoding
Channel Decoding& Deinterleaving Despreading Demodulation
Transmission
Reception
chip modulated signalbit symbol
ServiceSignal
Radio Channel
ServiceSignal
Receiver
Source coding can increase the transmitting efficiency.
Channel coding can make the transmission more reliable.
Spreading can increase the capability of overcoming interference.
Scrambling can make transmission in security.
Through the modulation, the signals will transfer to radio signals from digital signals.
Bit, Symbol, Chip
Bit : data after source coding
Symbol: data after channel coding and interleaving
Chip: data after spreading
Page24Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Block Coding - CRC
Block coding is used to detect if there are any uncorrected
errors left after error correction.
The cyclic redundancy check (CRC) is a common method of
block coding.
Adding the CRC bits is done before the channel encoding
and they are checked after the channel decoding.
During the transmission, there are many interferences and fading. To guarantee reliable transmission, system should overcome these influence through the channel coding which includes block coding, channel coding and interleaving.
Block coding: The encoder adds some redundant bits to the block of bits and the decoder uses them to determine whether an error has occurred during the transmission. This is used to calculate Block Error Ratio (BLER) used in the outer loop power control.
The CRC (Cyclic Redundancy Check) is used for error checking of the transport blocks at the receiving end. The CRC length that can be inserted has four different values: 0, 8, 12, 16 and 24 bits. The more bits the CRC contains, the lower is the probability of an undetected error in the transport block in the receiver.
Note that certain types of block codes can also be used for error correction, although these are not used in WCDMA.
Page25Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Channel Coding
Effect
Enhance the correlation among symbols so as to recover the signal when interference occurs
Provides better error correction at receiver, but brings increment of the delay
Types
No Coding
Convolutional Coding (1/2, 1/3)
Turbo Coding (1/3)
Code Block of N Bits
No Coding
1/2 Convolutional Coding
1/3 Convolutional Coding
1/3 Turbo Coding
Uncoded N bits
Coded 2N+16 bits
Coded 3N+24 bits
Coded 3N+12 bits
UTRAN employs two FEC schemes: convolutional codes and turbo codes. The idea is to add redundancy to the transmitted bit stream, sO that occasional bit errors can be corrected in the receiving entity.
The first is convolution that is used for anti-interference. Through the technology, many redundant bits will be inserted in original information. When error code is caused by interference, the redundant bits can be used to recover the original information. Convolutional codes are typically used when the timing constraints are tight. The coded data must contain enough redundant information to make it possible to correct some of the detected errors without asking for repeats.
Turbo codes are found to be very efficient because they can perform close to the theoretical limit set by the Shannon’s Law. Their efficiency is best with high data rate services, but poor on low rate services. At higher bit rates, turbo coding is more efficient than convolutional coding.
In WCDMA network, both Convolution code and Turbo code are used. Convolution code applies to voice service while Turbo code applies to high rate data service.
Note that both block codes and channel codes are used in the UTRAN. The idea behind this arrangement is that the channel decoder (either a convolutional or turbo decoder) tries to correct as many errors as possible, and then the block decoder (CRC check) offers its judgment on whether the resulting information is good enough to be used in the higher layers.
Page26Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Interleaving
Effect
Interleaving is used to reduce the probability of consecutive bits error
Longer interleaving periods have better data protection with more delay
⎥⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢⎢
⎣
⎡
11101........................0000100
0 0 1 0 0 0 0 . . . 1 0 1 1 1
⎥⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢⎢
⎣
⎡
11101........................0000010
0 0 … 0 1 0 … 1 0 0 … 1 0 … 1 1 Inter-column permutation
Output bits
Input bits
Interleaving periods: 20, 40, or 80 ms
Channel coding works well against random errors, but it is quite vulnerable to bursts of errors, which are typical in mobile radio systems. The especially fast moving UE in CDMA systems can cause consecutive errors if the power control is not fast enough to manage the interference. Most coding schemes perform better on random data errors than on blocks of errors. This problem can be eased with interleaving, which spreads the erroneous bits over a longer period of time. By interleaving, no two adjacent bits are transmitted near to each other, and the data errors are randomized.
The longer the interleaving period, the better the protection provided by the time diversity. However, longer interleaving increases transmission delays and a balance must be found between the error resistance capabilities and the delay introduced.
Page27Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Processing Procedure of WCDMA System
SourceCoding
Channel Coding& Interleaving Spreading Modulation
SourceDecoding
Channel Decoding& Deinterleaving Despreading Demodulation
Transmission
Reception
chip modulated signalbit symbol
ServiceSignal
Radio Channel
ServiceSignal
Receiver
Source coding can increase the transmitting efficiency.
Channel coding can make the transmission more reliable.
Spreading can increase the capability of overcoming interference.
Scrambling can make transmission in security.
Through the modulation, the signals will transfer to radio signals from digital signals.
Bit, Symbol, Chip
Bit : data after source coding
Symbol: data after channel coding and interleaving
Chip: data after spreading
Page28Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Correlation
Correlation measures similarity between any two arbitrary signals.
Identical and Orthogonal signals:
Correlation = 0Orthogonal signals
-1 1 -1 1⊗
-1 1 -1 1
1 1 1 1
+1
-1+1
-1
+1
-1
+1
-1
Correlation = 1Identical signals
-1 1 -1 1⊗
1 1 1 1
-1 1 -1 1
C1
C2+1
+1
C1
C2
Correlation is used to measure similarity of any two arbitrary signals. It is computed by multiplying the two signals and then summing (integrating) the result over a defined time windows. The two signals of figure (a) are identical and therefore their correlation is 1 or 100 percent. In figure (b) , however, the two signals are uncorrelated, and therefore knowing one of them does not provide any information on the other.
Page29Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Orthogonal Code Usage - Coding
UE1: +1 -1
UE2: -1 +1
C1 : -1 +1 -1 +1 -1 +1 -1 +1
C2 : +1 +1 +1 +1 +1 +1 +1 +1
UE1×c1: -1 +1 -1 +1 +1 -1 +1 -1
UE2×c2: -1 -1 -1 -1 +1 +1 +1 +1
UE1×c1+ UE2×c2: -2 0 -2 0 +2 0 +2 0
UE1: +1 -1
UE2: -1 +1
C1 : -1 +1 -1 +1 -1 +1 -1 +1
C2 : +1 +1 +1 +1 +1 +1 +1 +1
UE1×c1: -1 +1 -1 +1 +1 -1 +1 -1
UE2×c2: -1 -1 -1 -1 +1 +1 +1 +1
UE1×c1+ UE2×c2: -2 0 -2 0 +2 0 +2 0
By spreading, each symbol is multiplied with all the chips in the orthogonal sequence assigned to the user. The resulting sequence is processed and is then transmitted over the physical channel along with other spread symbols. In this figure, 4-digit codes are used. The product of the user symbols and the spreading code is a sequence of digits that must be transmitted at 4 times the rate of the original encoded binary signal.
Page30Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Orthogonal Code Usage - Decoding
UE1×C1+ UE2×C2: -2 0 -2 0 +2 0 +2 0
UE1 Dispreading by c1: -1 +1 -1 +1 -1 +1 -1 +1
Dispreading result: +2 0 +2 0 -2 0 -2 0
Integral judgment: +4 (means+1) -4 (means-1)
UE2 Dispreading by c2: +1 +1 +1 +1 +1 +1 +1 +1
Dispreading result: -2 0 -2 0 +2 0 +2 0
Integral judgment: -4 (means-1) +4 (means+1)
UE1×C1+ UE2×C2: -2 0 -2 0 +2 0 +2 0
UE1 Dispreading by c1: -1 +1 -1 +1 -1 +1 -1 +1
Dispreading result: +2 0 +2 0 -2 0 -2 0
Integral judgment: +4 (means+1) -4 (means-1)
UE2 Dispreading by c2: +1 +1 +1 +1 +1 +1 +1 +1
Dispreading result: -2 0 -2 0 +2 0 +2 0
Integral judgment: -4 (means-1) +4 (means+1)
The receiver dispreads the chips by using the same code used in the transmitter. Notice that under no-noise conditions, the symbols or digits are completely recoveredwithout any error. In reality, the channel is not noise-free, but CDMA system employ Forward Error Correction techniques to combat the effects of noise and enhance the performance of the system.
When the wrong code is used for dispreading, the resulting correlation yields an average of zero. This is a clear demonstration of the advantage of the orthogonal property of the codes. Whether the wrong code is mistakenly used by the target user or other users attempting to decode the received signal, the resulting correlation is always zero because of the orthogonal property of codes.
Page31Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Spectrum Analysis of Spreading & Dispreading
Spreading code
Spreading code
Signal Combination
Narrowband signalf
P(f)
Broadband signal
P(f)
f
Noise & Other Signal
P(f)
f
Noise+Broadband signal
P(f)
f
Recovered signal P(f)
f
Traditional radio communication systems transmit data using the minimum bandwidth required to carry it as a narrowband signal. CDMA system mix their input data with a fast spreading sequence and transmit a wideband signal. The spreading sequence is independently regenerated at the receiver and mixed with the incoming wideband signal to recover the original data. The dispreading gives substantial gain proportional to the bandwidth of the spread-spectrum signal. The gain can be used to increase system performance and range, or allow multiple coded users, or both. A digital bit stream sent over a radio link requires a definite bandwidth to be successfully transmitted and received.
Page32Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Spectrum Analysis of Spreading & Dispreading
Max allowed interference
Eb/No Requirement
Power
Max interference caused by UE and others
Processing Gain
Ebit
Interference from other UE Echip
Eb / No = Ec / No ×PG
Page33Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Process Gain
Process Gain
Process gain differs for each service.
If the service bit rate is greater, the process gain is smaller, UE needs more power for this service, then the coverage of this service will be smaller, vice versa.
)rate bitrate chiplog(10Gain ocessPr =
For common services, the bit rate of voice call is 12.2kbps, the bit rate of video phone is 64kbps, and the highest packet service bit rate is 384kbps(R99). After the spreading, the chip rate of different service all become 3.84Mcps.
Page34Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Spreading Technology
Spreading consists of 2 steps:
Channelization operation, which transforms data symbols into chips
Scrambling operation is applied to the spreading signal
scramblingchannelization
Data symbol
Chips after spreading
Spreading means increasing the bandwidth of the signal beyond the bandwidth normally required to accommodate the information. The spreading process in UTRAN consists of two separate operations: channelization and scrambling.
The first operation is the channelization operation, which transforms every data symbol into a number of chips, thus increasing the bandwidth of the signal. The number of chips per data symbol is called the Spreading Factor (SF). Channelizationcodes are orthogonal codes, meaning that in ideal environment they do not interfere each other.
The second operation is the scrambling operation. Scrambling is used on top of spreading, so it does not change the signal bandwidth but only makes the signals from different sources separable from each other. As the chip rate is already achieved in channelization by the channelization codes, the chip rate is not affected by the scrambling.
Page35Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Channelization Code
OVSF Code (Orthogonal Variable Spreading Factor) is used as
channelization code
SF = 8SF = 1 SF = 2 SF = 4
Cch,1,0 = (1)
Cch,2,0 = (1,1)
Cch,2,1 = (1, -1)
Cch,4,0 = (1,1,1,1)
Cch,4,1 = (1,1,-1,-1)
Cch,4,2 = (1,-1,1,-1)
Cch,4,3 = (1,-1,-1,1)
Cch,8,0 = (1,1,1,1,1,1,1,1)
Cch,8,1 = (1,1,1,1,-1,-1,-1,-1)
Cch,8,2 = (1,1,-1,-1,1,1,-1,-1)
Cch,8,3 = (1,1,-1,-1,-1,-1,1,1)
Cch,8,4 = (1,-1,1,-1,1,-1,1,-1)
Cch,8,5 = (1,-1,1,-1,-1,1,-1,1)
Cch,8,6 = (1,-1,-1,1,1,-1,-1,1)
Cch,8,7 = (1,-1,-1,1,-1,1,1,-1)
……
Orthogonal codes are easily generated by starting with a seed of 1, repeating the 1 horizontally and vertically, and then complementing the -1 diagonally. This process is to be continued with the newly generated block until the desired codes with the proper length are generated. Sequences created in this way are referred as “Walsh” code.
Channelization uses OVSF code, for keeping the orthogonality of different subscriber physical channels. OVSF can be defined as the code tree illustrated in the following diagram.
Channelization code is defined as Cch SF, k,, where, SF is the spreading factor of the code, and k is the sequence of code, 0≤k≤SF-1. Each level definition length of code tree is SF channelization code, and the left most value of each spreading code character is corresponding to the chip which is transmitted earliest.
Page36Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Channelization Code
SF = chip rate / symbol rate
High data rates → low SF code
Low data rates → high SF code
16Data 128 kbps DL8Data 128 kbps UL
32Data 64 kbps DL16Data 64 kbps UL
8Data 384 kbps DL4Data 384 kbps UL
16Data 144 kbps DL8Data 144 kbps UL
128Speech 12.2 DL64Speech 12.2 UL
SFRadio bearerSFRadio bearer
The channelization codes are Orthogonal Variable Spreading Factor (OVSF)codes. They are used to preserve orthogonality between different physical channels. They also increase the clock rate to 3.84 Mcps. The OVSF codes are defined using a code tree.
In the code tree, the channelization codes are individually described by Cch,SF,k, where SF is the Spreading Factor of the code and k the code number, 0 ≤ k ≤ SF-1.
A channelization sequence modulates one user’s bit. Because the chip rate is constant, the different lengths of codes enable to have different user data rates. Low SFs are reserved for high rate services while high SFs are for low rate services.
The length of an OVSF code is an even number of chips and the number of codes (for one SF) is equal to the number of chips and to the SF value.
The generated codes within the same layer constitute a set of orthogonal codes. Furthermore, any two codes of different layers are orthogonal except when one of the two codes is a mother code of the other. For example C4,3 is not orthogonal with C1,0and C2,1, but is orthogonal with C2,0.
SF in uplink is from 4 to 256.
SF in downlink is from 4 to 512.
Page37Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Purpose of Channelization Code
Channelization code is used to distinguish different physical
channels of one transmitter
For downlink, channelization code ( OVSF code ) is used to
separate different physical channels of one cell
For uplink, channelization code ( OVSF code ) is used to
separate different physical channels of one UE
For voice service (AMR), downlink SF is 128, it means there are 128 voice services maximum can be supported in one WCDMA carrier;
For Video Phone (64k packet data) service, downlink SF is 32, it means there are 32 voice services maximum can be supported in one WCDMA carrier.
Page38Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Purpose of Scrambling Code
Scrambling code is used to distinguish different transmitters
For downlink, scrambling code is used to separate different
cells in one carrier
For uplink, scrambling code is used to separate different UEs
in one carrier
In addition to spreading, part of the process in the transmitter is the scrambling operation. This is needed to separate terminals or base stations from each other.
Page39Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Scrambling Code
Scrambling code: GOLD sequence.
There are 224 long uplink scrambling codes which are used for
scrambling of the uplink signals. Uplink scrambling codes are
assigned by RNC.
For downlink, 512 primary scrambling codes are used.
Different scrambling codes will be planned to different cells in downlink.
Different scrambling codes will be allocated to different UEs in uplink.
The scrambling code is always applied to one 10 ms frame.
In UMTS, Gold codes are chosen for their very low peak cross-correlation.
Page40Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Primary Scrambling Code Group
Primary scrambling codes for downlink physical channels
Group 0
…
Primary scrambling code 0
……
Primary scrambling code
8*63
……
Primary scrambling code
8*63 +7512 primary scrambling
codes
……
……
Group 1
Group 63
Primary scrambling code 1
Primary scrambling code 8
64 primary scrambling code
groupsEach group consists of 8
primary scrambling codes
There are totally 512 primary scrambling codes defined by 3GPP. They are further divided into 64 primary scrambling code groups. There are 8 primary scrambling codes in every group. Each cell is allocated with only one primary scrambling code.
Page41Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Code Multiplexing
Downlink Transmission on a Cell Level
Scrambling code
Channelization code 1
Channelization code 2
Channelization code 3
User 1 signal
User 2 signal
User 3 signal
NodeB
Page42Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Code Multiplexing
Uplink Transmission on a Cell Level
NodeB
Scrambling code 3
User 3 signalChannelization code
Scrambling code 2
User 2 signal
Channelization code
Scrambling code 1
User 1 signal
Channelization code
Page43Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Processing Procedure of WCDMA System
SourceCoding
Channel Coding& Interleaving Spreading Modulation
SourceDecoding
Channel Decoding& Deinterleaving Despreading Demodulation
Transmission
Reception
chip modulated signalbit symbol
ServiceSignal
Radio Channel
ServiceSignal
Receiver
Source coding can increase the transmitting efficiency.
Channel coding can make the transmission more reliable.
Spreading can increase the capability of overcoming interference.
Scrambling can make transmission in security.
Through the modulation, the signals will transfer to radio signals from digital signals.
Bit, Symbol, Chip
Bit : data after source coding
Symbol: data after channel coding and interleaving
Chip: data after spreading
Page44Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Modulation Overview
1 00 1
time
Basic steady radio wave:
carrier = A.cos(2πFt+φ)
Amplitude Shift Keying:
A.cos(2πFt+φ)
Frequency Shift Keying:
A.cos(2πFt+φ)
Phase Shift Keying:A.cos(2πFt+φ)
Data to be transmitted:Digital Input
A data-modulation scheme defines how the data bits are mixed with the carrier signal, which is always a sine wave. There are three basic ways to modulate a carrier signal in a digital sense: amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK).
In ASK the amplitude of the carrier signal is modified by the digital signal.
In FSK the frequency of the carrier signal is modified by the digital signal.
The PSK family is the most widely used modulation scheme in modern cellularsystems. There are many variants in this family, and only a few of them are mentioned here.
Page45Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Modulation Overview
Digital Modulation - BPSK
1
t
1 10
1
t-1
NRZ coding
fo
BPSKModulated
BPSK signal
Carrier
Information signal
φ=0 φ=π φ=0
1 102 3 4 9875 6
1 102 3 4 9875 6
Digital Input
High FrequencyCarrier
BPSK Waveform
In binary phase shift keying (BPSK) modulation, each data bit is transformed into a separate data symbol. The mapping rule is 1 −> + 1 and 0 − > − 1. There are only two possible phase shifts in BPSK, 0 and π radians.
NRZ means none return zero.
Page46Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Modulation Overview
Digital Modulation - QPSK
-1 -1
1 102 3 4 9875 6
1 102 3 4 9875 6
NRZ Input
I di-Bit Stream
Q di-Bit Stream
IComponent
QComponent
QPSK Waveform
1
1
-1
1
-1
1
1
-1
-1
-1
1 1 -1 1 -1 1 1 -1
The quadrature phase shift keying (QPSK) modulation has four phases: 0, π/2, π, and 3π/2 radians. Two data bits are transformed into one complex data symbol; A symbol is any change (keying) of the carrier.
Page47Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Modulation Overview
NRZ coding
90o
NRZ coding
QPSK
Q(t)
I(t)
fo
±A
±A ±Acos(ωot)
±Acos(ωot + π/2)
φ
1 1 π/41 -1 7π/4-1 1 3π/4-1 -1 5π/4
)cos(2: φω +oAQPSK
Page48Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Demodulation
QPSK Constellation Diagram
1 102 3 4 9875 6
QPSK Waveform
1,1
-1,-1
-1,1
1,-1
1 -11 -1 1 -1-11-1 1
-1,1
NRZ Output
Page49Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Modulation
Different modulation methods corresponding to different
transmitting abilities in air interface
HSDPA: QPSK or 16QAMR99/R4: QPSK
The UTRAN air interface uses QPSK modulation in the downlink, although HSDPA may also employ 16 Quadrature Amplitude Modulation (16QAM). 16QAM requires good radio conditions to work well. As seen, with 16QAM also the amplitude of the signal matters.
As explained, in QPSK one symbol carries two data bits; in 16QAM each symbol includes four bits. Thus, a QPSK system with a chip rate of 3.84Mcps could theoretically transfer 2 × 3.84 = 7.68 Mbps, and a 16QAM system could transfer 4 ×3.84 Mbps = 15.36 Mbps. In 3GPP also the usage of 64QAM with HSDPA has been studied.
Page50Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Processing Procedure of WCDMA System
SourceCoding
ChannelCoding Spreading Modulation
SourceDecoding
ChannelDecoding Despreading Demodulation
Transmission
Reception
chip modulated signalbit symbol
ServiceSignal
Radio Channel
ServiceSignal
Transmitter
Receiver
Source coding can increase the transmitting efficiency.
Channel coding can make the transmission more reliable.
Spreading can increase the capability of overcoming interference.
Scrambling can make transmission in security.
Through the modulation, the signals will transfer to radio signals from digital signals.
Bit, Symbol, Chip
Bit : data after source coding
Symbol: data after channel coding and interleaving
Chip: data after spreading
Page51Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Wireless Propagation
ReceivedSignal
TransmittedSignal
Transmission Loss:Path Loss + Multi-path Fading
Time
Amplitude
A mobile communication channel is a multi-path fading channel and any transmitted signal reaches a receive end by means of multiple transmission paths, such as direct transmission, reflection, scatter, etc.
Page52Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Propagation of Radio SignalSignal at Transmitter
Signal at Receiver
-40-35-30-25-20-15-10-5
dB
0
0
dBm
-20-15-10-5
5101520
Fading
Page53Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Fading Categories
Fading Categories
Slow Fading
Fast Fading
Furthermore, with the moving of a mobile station, the signal amplitude, delay and phase on various transmission paths vary with time and place. Therefore, the levels of received signals are fluctuating and unstable and these multi-path signals, if overlaid, will lead to fast fading. Fast fading conforms to Rayleigh distribution. The mid-value field strength of fast fading has relatively gentle change and is called “slow fading”. Slow fading conforms to lognormal distribution.
Page54Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Diversity Technique
Diversity technique is used to obtain uncorrelated signals for combining
Reduce the effects of fadingFast fading caused by multi-path
Slow fading caused by shadowing
Improve the reliability of communication
Increase the coverage and capacity
Diversity technology means that after receiving two or more input signals with mutually uncorrelated fading at the same time, the system demodulates these signals and adds them up. Thus, the system can receive more useful signals and overcome fading.
Page55Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Diversity
Time diversity
Channel coding, Block interleaving
Frequency diversity
The user signal is distributed on the whole bandwidth
frequency spectrum
Space diversity
Polarization diversity
Diversity technology is an effective way to overcome overlaid fading. Because it can be selected in terms of frequency, time and space, diversity technology includes frequency diversity, time diversity and space diversity.
Time diversity: Channel coding
Frequency diversity: WCDMA is a kind of frequency diversity. The signal energy is distributed on the whole bandwidth.
Space diversity: using two antennas
Page56Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Principle of RAKE Receiver
Receive set
Correlator 1
Correlator 2
Correlator 3
Searcher correlator Calculate the time delay and signal strength
CombinerThe
combined signal
tt
s(t) s(t)
RAKE receiver help to overcome on the multi-path fading and enhance the receive performance of the system
The RAKE receiver is a technique which uses several baseband correlators to individually process multipath signal components. The outputs from the different correlators are combined to achieve improved reliability and performance.
When WCDMA system is designed for cellular system, the inherent wide-bandwidth signals with their orthogonal Walsh functions were natural for implementing a RAKE receiver. In WCDMA system, the bandwidth is wider than the coherence bandwidth of the cellular. Thus, when the multi-path components are resolved in the receiver, the signals from different paths are uncorrelated with each other. The receiver can then combine them using some combining schemes. So with RAKE receiver WCDMA system can use the multi-path characteristics of the channel to get signal with better quality.
Page57Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Summary
In this course, we have discussed basic concepts of WCDMA:
Spreading / Despreading principle
UTRAN Voice Coding
UTRAN Channel Coding
UTRAN Spreading Code
UTRAN Scrambling Code
UTRAN Modulation
UTRAN Transmission/Receiving
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Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Radio Interface Physical Layer
Page1Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Foreword
The physical layer offers data transport services to higher layers.
The physical layer is expected to perform the following functions in
order to provide the data transport service, for example: spreading,
modulation and demodulation, despreading, Inner-loop power
control and etc.
Page2Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Objectives
Upon completion of this course, you will be able to:
Outline radio interface protocol Architecture
Describe structure and functions of different physical channels
Describe UMTS physical layer procedures
Page3Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Physical Layer Overview
2. Physical Channels
3. Physical Layer Procedure
Page4Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Physical Layer Overview
2. Physical Channels
3. Physical Layer Procedure
Page5Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
UTRAN Network Structure
RNS
RNC
RNS
RNC
Core Network
NodeB NodeB NodeB NodeB
Iu-CS Iu-PS
Iur
Iub IubIub Iub
CN
UTRAN
UEUu
CS PS
Iu-CSIu-PS
CSPS
UTRAN: UMTS Terrestrial Radio Access Network.
The UTRAN consists of a set of Radio Network Subsystems connected to the Core Network through the Iu interface.
A RNS consists of a Radio Network Controller and one or more NodeBs. A NodeB is connected to the RNC through the Iub interface.
Inside the UTRAN, the RNCs of the RNS can be interconnected together through the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed over direct physical connection between RNCs or virtual networks using any suitable transport network.
Page6Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Uu Interface Protocol Structure
L3co
ntro
l
cont
rol
cont
rol
cont
rol
C-plane signaling U-plane information
PHY
L2/MAC
L1
RLC
DCNtGC
L2/RLC
MAC
RLCRLCRLC
Duplication avoidance
UuS boundary
L2/BMC
control
PDCPPDCP L2/PDCP
DCNtGC
RRC
RLCRLCRLCRLC
BMC
radio bearer
logical channel
transport channel
The layer 1 supports all functions required for the transmission of bit streams on the physical medium. It is also in charge of measurements function consisting in indicating to higher layers, for example, Frame Error Rate (FER), Signal to Interference Ratio (SIR), interference power, transmit power, … It is basically composed of a “layer 1 management” entity, a “transport channel” entity, and a “physical channel” entity.
The layer 2 protocol is responsible for providing functions such as mapping, ciphering, retransmission and segmentation. It is made of four sub-layers: MAC (Medium Access Control), RLC (Radio Link Control), PDCP (Packet Data Convergence Protocol) and BMC (Broadcast/Multicast Control).
The layer 3 is split into 2 parts: the access stratum and the non access stratum. The access stratum part is made of “RRC (Radio Resource Control)” entity and “duplication avoidance” entity. “duplication avoidance” terminates in the CN but is part of the Access Stratum. The higher layer signalling such as Mobility Management (MM) and Call Control (CC) is assumed to belong to the non-access stratum, and therefore not in the scope of 3GPP TSG RAN. In the C-plane, the interface between 'Duplication avoidance' and higher L3 sub-layers (CC, MM) is defined by the General Control (GC), Notification (Nt) and Dedicated Control (DC) SAPs.
Not shown on the figure are connections between RRC and all the other protocol layers (RLC, MAC, PDCP, BMC and L1), which provide local inter-layer control services.
The protocol layers are located in the UE and the peer entities are in the NodeB or the RNC.
Many functions are managed by the RRC layer. Here is the list of the most important:
Establishment, re-establishment, maintenance and release of an RRC connection between the UE and UTRAN: it includes an optional cell re-selection, an admission control, and a layer 2 signaling link establishment. When a RNC is in charge of a specific connection towards a UE, it acts as the Serving RNC.
Establishment, reconfiguration and release of Radio Bearers: a number of Radio Bearers can be established for a UE at the same time. These bearers are configured depending on the requested QoS. The RNC is also in charge of ensuring that the requested QoS can be met.
Assignment, reconfiguration and release of radio resources for the RRC connection: it handles the assignment of radio resources (e.g. codes, shared channels). RRC communicates with the UE to indicate new resources allocation when handovers are managed.
Paging/Notification: it broadcasts paging information from network to UEs.
Broadcasting of information provided by the non-access stratum (Core Network) or access Stratum. This corresponds to “system information” regularly repeated.
UE measurement reporting and control of the reporting: RRC indicates what to measure, when and how to report.
Outer loop power control: controls setting of the target values.
Control of ciphering: provides procedures for setting of ciphering.
The RRC layer is defined in the 25.331 specification from 3GPP.
The RLC’s main function is the transfer of data from either the user or the control plane over the Radio interface. Two different transfer modes are used: transparentand non-transparent. In non-transparent mode, 2 sub-modes are used: acknowledged or unacknowledged.
RLC provides services to upper layers:
data transfer (transparent, acknowledged and unacknowledged modes).
QoS setting: the retransmission protocol (for AM only) shall be configurable by layer 3 to provide different QoS.
notification of unrecoverable errors: RLC notifies the upper layers of errors that cannot be resolved by RLC.
The RLC functions are:
mapping between higher layer PDUs and logical channels.
ciphering: prevents unauthorized acquisition of data; performed in RLC layer for non-transparent RLC mode.
segmentation/reassembly: this function performs segmentation/reassembly of variable-length higher layer PDUs into/from smaller RLC Payload Units. The RLC size is adjustable to the actual set of transport formats (decided when service is established). Concatenation and padding may also be used.
error correction: done by retransmission (acknowledged data transfer mode only).
flow control: allows the RLC receiver to control the rate at which the peer RLC transmitting entity may send information.
MAC services include:
Data transfer: service providing unacknowledged transfer of MAC SDUsbetween peer MAC entities.
Reallocation of radio resources and MAC parameters: reconfiguration of MAC functions such as change of identity of UE. Requested by the RRC layer.
Reporting of measurements: local measurements such as traffic volume and quality indication are reported to the RRC layer.
The functions accomplished by the MAC sub-layer are listed above. Here’s a quick explanation for some of them:
Priority handling between the data flows of one UE: since UMTS is multimedia, a user may activate several services at the same time, having possibly different profiles (priority, QoS parameters...). Priority handlingconsists in setting the right transport format for a high bit rate service and for a low bit rate service.
Priority handling between UEs: use for efficient spectrum resources utilization for bursty transfers on common and shared channels.
Ciphering: to prevent unauthorized acquisition of data. Performed in the MAC layer for transparent RLC mode.
Access Service Class (ACS) selection for RACH transmission: the RACH resources are divided between different ACSs in order to provide different priorities on a random access procedure.
PDCP
UMTS supports several network layer protocols providing protocol transparency for the users of the service.
Using these protocols (and new ones) shall be possible without any changes to UTRAN protocols. In order to perform this requirement, the PDCP layer has been introduced. Then, functions related to transfer of packets from higher layers shall be carried out in a transparent way by the UTRAN network entities.
PDCP shall also be responsible for implementing different kinds of optimization methods. The currently known methods are standardized IETF (Internet Engineering Task Force) header compression algorithms.
Algorithm types and their parameters are negotiated by RRC and indicated toPDCP.
Header compression and decompression are specific for each network layer protocol type.
In order to know which compression method is used, an identifier (PID: Packet Identifier) is inserted. Compression algorithms exist for TCP/IP, RTP/UDP/IP, …
Another function of PDCP is to provide numbering of PDUs. This is done if lossless SRNS relocation is required.
To accomplish this function, each PDCP-SDUs (UL and DL) is buffered and numbered. Numbering is done after header compression. SDUs are kept until information of successful transmission of PDCP-PDU has been received from RLC. PDCP sequence number ranges from 0 to 65,535.
BMC (broadcast/multicast control protocol)
The main function of BMC protocol are:
Storage of cell broadcast message. the BMC in RNC stores the cell broadcast message received over the CBC-RNC interface for scheduled transmission.
Traffic volume monitoring and radio resource request for CBS. On the UTRAN side, the BMC calculates the required transmission rate for the cell broadcast service based on the messages received over the CBC-RNC interface, and requests appropriate .CTCH/FACH resources from from RRC
Scheduling of BMC message. The BMC receives scheduling information together with each cell broadcast message over the CBC-RNC interface. Based on this scheduling information, on the UTRAN side the BMC generates schedule message and schedules BMC message sequences accordingly. On the UE side ,the BMC evaluates the schedule messages and indicates scheduling parameters to RRC, which are used by RRC to configure the lower layers for CBS discontinuous reception.
Transmission of BMC message to UE. The function transmits the BMC messages according to the schedule
Delivery of cell broadcast messages to the upper layer. This UE function delivers the received non-corrupted cell broadcast messages to the upper layer
The layer 1 (physical layer) is used to transmit information under the form of electrical signals corresponding to bits, between the network and the mobile user. This information can be voice, circuit or packet data, and network signaling.
The UMTS layer 1 offers data transport services to higher layers. The access to these services is through the use of transport channels via the MAC sub-layer.
These services are provided by radio links which are established by signaling procedures. These links are managed by the layer 1 management entity. One radio link is made of one or several transport channels, and one physical channel.
The UMTS layer 1 is divided into two sub-layers: the transport and the physical sub-layers. All the processing (channel coding, interleaving, etc.) is done by the transport sub-layer in order to provide different services and their associated QoS. The physical sub-layer is responsible for the modulation, which corresponds to the association of bits (coming from the transport sub-layer) to electrical signals that can be carried over the air interface. The spreading operation is also done by the physical sub-layer.
These two parts of layer 1 are controlled by the layer 1 management (L1M) entity. It is made of several units located in each equipment, which exchange information through the use of control channels.
Page13Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
RAB, RB and RL
RAB
RB
RLNodeB
RNC CNUE
UTRAN
RAB: The service that the access stratum provides to the non-access stratum for transfer of user data between User Equipment and CN.
RB: The service provided by the layer 2 for transfer of user data between User Equipment and Serving RNC.
RL: A "radio link" is a logical association between single User Equipment and a single UTRAN access point. Its physical realization comprises one or more radio bearer transmissions.
Page14Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Physical Layer Overview
2. Physical Channels
3. Physical Layer Procedure
Page15Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
2. Physical Channels
2.1 Physical Channel Structure and Functions
2.2 Channel Mapping
Page16Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Radio Interface Channel Definition
Logical Channel = information container
Defined by <What type of information> is transferred
Transport Channel = characteristics of transmission
Described by <How> and with <What characteristics> data is transmitted over the radio interface
Physical Channel = specification of the information global content
providing the real transmission resource, maybe a frequency , a specific set of codes and phase
In terms of protocol layer, the WCDMA radio interface has three types of channels: physical channel, transport channel and logical channel.
Logical channel: Carrying user services directly. According to the types of the carried services, it is divided into two types: control channel and service channel.
Transport channel: It is the interface between radio interface layer 2 and layer 1, and it is the service provided for MAC layer by the physical layer. According to whether the information transported is dedicated information for a user or common information for all users, it is divided into dedicated channel and common channel.
Physical channel: It is the ultimate embodiment of all kinds of information when they are transmitted on radio interface. Each channel which uses dedicated carrier frequency, code (spreading code and scramble) and carrier phase (I or Q) can be regarded as a physical channel.
Page17Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Logical Channel
Control channel
Traffic channelDedicated traffic channel (DTCH)
Common traffic channel (CTCH)
Broadcast control channel (BCCH)
Paging control channel (PCCH)
Dedicate control channel (DCCH)
Common control channel (CCCH)
As in GSM, UMTS uses the concept of logical channels.A logical channel is characterized by the type of information that is transferred.As in GSM, logical channels can be divided into two groups: control channels for control plane information and traffic channel for user plane information.The traffic channels are:
Dedicated Traffic Channel (DTCH): a point-to-point bi-directional channel, that transmits dedicated user information between a UE and the network. That information can be speech, circuit switched data or packet switched data. The payload bits on this channel come from a higher layer application (the AMR codec for example). Control bits can be added by the RLC (protocol information) in case of a non transparent transfer. The MAC sub-layer will also add a header to the RLC PDU. Common Traffic Channel (CTCH): a point-to-multipoint downlink channel for transfer of dedicated user information for all or a group of specified UEs. This channel is used to broadcast BMC messages. These messages can either be cell broadcast data from higher layers or schedule messages for support of Discontinuous Reception (DRX) of cell broadcast data at the UE. Cell broadcast messages are services offered by the operator, like indication of weather, traffic, location or rate information.
Page18Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Logical Channel
Control channel
Traffic channelDedicated traffic channel (DTCH)
Common traffic channel (CTCH)
Broadcast control channel (BCCH)
Paging control channel (PCCH)
Dedicate control channel (DCCH)
Common control channel (CCCH)
The control channels are:
Broadcast Control Channel (BCCH): a downlink channel that broadcasts all system information types (except type 14 that is only used in TDD). For example, system information type 3 gives the cell identity. UEs decode system information on the BCH except when in Cell_DCH mode. In that case, they can decode system information type 10 on the FACH and other important signaling is sent on a DCCH.
Paging Control Channel (PCCH): a downlink channel that transfers paging information. It is used to reach a UE (or several UEs) in idle mode or in connected mode (Cell_PCH or URA_PCH state). The paging type 1 message is sent on the PCCH. When a UE receives a page on the PCCH in connected mode, it shall enter Cell_FACH state and make a cell update procedure.
Dedicated Control Channel (DCCH): a point-to-point bi-directional channel that transmits dedicated control information between a UE and the network. This channel is used for dedicated signaling after a RRC connection has been done. For example, it is used for inter-frequency handover procedure, for dedicated paging, for the active set update procedure and for the control and report of measurements.
Common Control Channel (CCCH): a bi-directional channel for transmitting control information between network and UEs. It is used to send messages related to RRC connection, cell update and URA update. This channel is a bit like the DCCH, but will be used when the UE has not yet been identified by the network (or by the new cell). For example, it is used to send the RRC connection request message, which is the first message sent by the UE to get into connected mode. The network will respond on the same channel, and will send him its temporary identities (cell and UTRAN identities). After these initial messages, the DCCH will be used.
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Transport Channel
Dedicated Channel (DCH)
Broadcast channel (BCH)
Forward access channel (FACH)
Paging channel (PCH)
Random access channel (RACH)
High-speed downlink shared channel (HS-DSCH)
Common transport channel
Dedicated transport channel
In order to carry logical channels, several transport channels are defined. They are:
Broadcast Channel (BCH): a downlink channel used for broadcast of system information into the entire cell.
Paging Channel (PCH): a downlink channel used for broadcast of control information into the entire cell, such as paging.
Random Access Channel (RACH): a contention based uplink channel used for initial access or for transmission of relatively small amounts of data (non real-time dedicated control or traffic data).
Forward Access Channel (FACH): a common downlink channel used for dedicated signaling (answer to a RACH typically), or for transmission of relatively small amounts of data.
Dedicated Channel (DCH): a channel dedicated to one UE used in uplink ordownlink.
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Physical Channel
A physical channel is defined by a specific carrier frequency, code (scrambling code, spreading code) and relative phase.
In UMTS system, the different code (scrambling code or spreadingcode) can distinguish the channels.
Most channels consist of radio frames and time slots, and each radio frame consists of 15 time slots.
Two types of physical channel: UL and DL
Physical Channel
Frequency, Code, Phase
Now we will begin to discuss the physical channel. Physical channel is the most important and complex channel, and a physical channel is defined by a specific carrier frequency, code and relative phase. In CDMA system, the different code (scrambling code or spreading code) can distinguish the channel. Most channels consist of radio frames and time slots, and each radio frame consists of 15 time slots. There are two types of physical channel: UL and DL.
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Downlink Physical ChannelDownlink Dedicated Physical Channel (DL DPCH)
Downlink Common Physical Channel
Primary Common Control Physical Channel (P-CCPCH)
Secondary Common Control Physical Channel (S-CCPCH)
Synchronization Channel (SCH)
Paging Indicator Channel (PICH)
Acquisition Indicator Channel (AICH)
Common Pilot Channel (CPICH)
High-Speed Physical Downlink Shared Channel (HS-PDSCH)
High-Speed Shared Control Channel (HS-SCCH)
The different physical channels are: Synchronization Channel (SCH): used for cell search procedure. There is the primary and the secondary SCHs.Common Control Physical Channel (CCPCH): used to carry common control information such as the scrambling code used in DL (there is a primary CCPCH and additional secondary CCPCH).Common Pilot Channels (P-CPICH and S-CPICH): used for coherent detection of common channels. They indicate the phase reference.Dedicated Physical Data Channel (DPDCH): used to carry dedicated data coming from layer 2 and above (coming from DCH).Dedicated Physical Control Channel (DPCCH): used to carry dedicated control information generated in layer 1 (such as pilot, TPC and TFCI bits).Page Indicator Channel (PICH): carries indication to inform the UE that paging information is available on the S-CCPCH.Acquisition Indicator Channel (AICH): it is used to inform a UE that the network has received its access request.High Speed Physical Downlink Shared Channel (HS-PDSCH): it is used to carry subscribers BE service data (mapping on HSDPA) coming from layer 2.High Speed Shared Control Channel (HS-SCCH): it is used to carry control message to HS-PDSCH such as modulation scheme, UE ID etc.
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Uplink Physical Channel
Uplink Dedicated Physical Channel
Uplink Dedicated Physical Data Channel (Uplink DPDCH)
Uplink Dedicated Physical Control Channel (Uplink DPCCH)
High-Speed Dedicated Physical Channel (HS-DPCCH)
Uplink Common Physical Channel
Physical Random Access Channel (PRACH)
The different physical channels are:
Dedicated Physical Data Channel (DPDCH): used to carry dedicated data coming from layer 2 and above (coming from DCH).
Dedicated Physical Control Channel (DPCCH): used to carry dedicated control information generated in layer 1 (such as pilot, TPC and TFCI bits).
Physical Random Access Channel (PRACH): used to carry random access information when a UE wants to access the network.
High Speed Dedicated Physical Control Channel (HS-DPCCH): it is used to carry feedback message to HS-PDSCH such CQI,ACK/NACK.
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Function of Physical Channel
NodeB UE
P-CCPCH-Primary Common Control Physical ChannelP-CCPCH-Primary Common Control Physical Channel
P-CPICH--Primary Common Pilot ChannelSCH--Synchronisation ChannelP-CPICH--Primary Common Pilot ChannelSCH--Synchronisation Channel
Cell Search Channels
DPDCH--Dedicated Physical Data ChannelDPDCH--Dedicated Physical Data Channel
DPCCH--Dedicated Physical Control ChannelDPCCH--Dedicated Physical Control Channel
Dedicated Channels
Paging ChannelsPICH--Paging Indicator ChannelPICH--Paging Indicator Channel
SCCPCH--Secondary Common Control Physical ChannelSCCPCH--Secondary Common Control Physical Channel
PRACH--Physical Random Access ChannelPRACH--Physical Random Access ChannelAICH--Acquisition Indicator ChannelAICH--Acquisition Indicator Channel
Random Access Channels
HS-DPCCH--High Speed Dedicated Physical Control ChannelHS-DPCCH--High Speed Dedicated Physical Control Channel
HS-SCCH--High Speed Share Control ChannelHS-SCCH--High Speed Share Control Channel
HS-PDSCH--High Speed Physical Downlink Share ChannelHS-PDSCH--High Speed Physical Downlink Share Channel
High Speed Downlink Share Channels
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Synchronization Channels (P-SCH & S-SCH)
Used for cell search
Two sub channels: P-SCH and S-SCH
SCH is transmitted at the first 256 chips of every time slot
Primary synchronization code is transmitted repeatedly in each time slot
Secondary synchronization code specifies the scrambling code groups of the cell
Primary SCH
Secondary SCH
Slot #0 Slot #1 Slot #14
acsi,0
pac pac pac
acsi,1 acs
i,14
256 chips2560 chips
One 10 ms SCH radio frame
When a UE is turned on, the first thing it does is to scan the UMTS spectrum and find a UMTS cell. After that, it has to find the primary scrambling code used by that cell in order to be able to decode the BCCH (for system information). This is done with the help of the Synchronization Channel.
Each cell of a NodeB has its own SCH timing, so that there is no overlapping.
The SCH is a pure downlink physical channel broadcasted over the entire cell. It is transmitted unscrambled during the first 256 chips of each time slot, in time multiplex with the P-CCPCH. It is the only channel that is not spread over the entire radio frame. The SCH provides the primary scrambling code group (one out of 64 groups), as well as the radio frame and time slot synchronization.
The SCH consists of two sub-channels, the primary and secondary SCH. These sub-channels are sent in parallel using code division during the first 256 chips of each time slot. P-SCH always transmits primary synchronization code. S-SCH transmits secondary synchronization codes.
The primary synchronization code is repeated at the beginning of each time slot. The same code is used by all the cells and enables the mobiles to detect the existence of the UMTS cell and to synchronize itself on the time slot boundaries. This is normally done with a single matched filter or any similar device. The slot timing of the cell is obtained by detecting peaks in the matched filter output.
This is the first step of the cell search procedure. The second step is done using the secondary synchronization channel.
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Secondary Synchronization Channel (S-SCH)
slot number Scrambling Code Group #0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14
Group 0 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16 Group 1 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10 Group 2 1 2 1 15 5 5 12 16 6 11 2 16 11 15 12 Group 3 1 2 3 1 8 6 5 2 5 8 4 4 6 3 7 Group 4 1 2 16 6 6 11 15 5 12 1 15 12 16 11 2
… Group 61 9 10 13 10 11 15 15 9 16 12 14 13 16 14 11 Group 62 9 11 12 15 12 9 13 13 11 14 10 16 15 14 16 Group 63 9 12 10 15 13 14 9 14 15 11 11 13 12 16 10
……..acp
Slot # ?
P-SCH acp
Slot #?
16 6S-SCH
acp
Slot #?
11 Group 2Slot 7, 8, 9
256 chips
The S-SCH also consists of a code, the Secondary Synchronization Code (SSC) that indicates which of the 64 scrambling code groups the cell’s downlink scrambling code belongs to. 16 different SSCs are defined. Each SSC is a 256 chip long sequence.
There is one specific SSC transmitted in each time slot, giving us a sequence of 15 SSCs. There is a total of 64 different sequences of 15 SSCs, corresponding to the 64 primary scrambling code groups. These 64 sequences are constructed so that one sequence is different from any other one, and different from any rotated version of any sequence. The UE correlates the received signal with the 16 SSCs and identifies the maximum correlation value.
The S-SCH provides the information required to find the frame boundaries and the downlink scrambling code group (one out of 64 groups). The scrambling code (one out of 8) can be determined afterwards by decoding the P-CPICH. The mobile will then be able to decode the BCH.
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Primary Common Pilot Channel (PCPICH)
Primary PCPICH
Carrying pre-defined sequence
Fixed channel code: Cch, 256, 0, Fixed rate 30Kbps
Scrambled by the primary scrambling code
Broadcast over the entire cell
A phase reference for SCH, Primary CCPCH, AICH, PICH and downlink DPCH, Only one PCPICH per cell
Pre-defined symbol sequence
Slot #0 Slot #1 Slot # i Slot #14
Tslot = 2560 chips , 20 bits
1 radio frame: Tr = 10 ms
The Common Pilot Channel (CPICH) is a pure physical control channel broadcasted over the entire cell. It is not linked to any transport channel. It consists of a sequence of known bits that are transmitted in parallel with the primary and secondary CCPCH.
The PCPICH is used by the mobile to determine which of the 8 possible primary scrambling codes is used by the cell, and to provide the phase reference for common channels.
Finding the primary scrambling code is done during the cell search procedure through a symbol-by-symbol correlation with all the codes within the code group. After the primary scrambling code has been identified, the UE can decode system information on the P-CCPCH.
The P-CPICH is the phase reference for the SCH, P-CCPCH, AICH and PICH. It is broadcasted over the entire cell. The channelization code used to spread the P-CPICH is always Cch,256,0 (all ones). Thus, the P-CPICH is a fixed rate channel. Also, it is always scrambled with the primary scrambling code of the cell.
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Primary Common Control Physical Channel (PCCPCH)
Carrying BCH transport channel
Fixed rate, fixed OVSF code (30kbps,Cch, 256, 1)
The PCCPCH is not transmitted during the first 256 chips of eachtime slot
PCCPCH Data18 bits
Slot #0
1 radio frame: T f = 10 ms
Slot #1 Slot #i
256 chips
Slot #14
T slot = 2560 chips,20 bits
SCH
The Primary Common Control Physical Channel (P-CCPCH) is a fixed rate (SF=256) downlink physical channel used to carry the BCH transport channel. It is broadcasted continuously over the entire cell like the P-CPICH.
The figure above shows the frame structure of the P-CCPCH. The frame structure is special because it does not contain any layer 1 control bits. The P-CCPCH only hasone fix predefined transport format combination, and the only bits transmitted are data bits from the BCH transport channel. It is important to note that the P-CCPCH is not transmitted during the first 256 chips of the slot. In fact, another physical channel (SCH) is transmitted during that period of time. Thus, the SCH and the P-CCPCH are time multiplexed on every time slot.
Channelization code Cch,256,1 is always used to spread the P-CCPCH.
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Paging Indicator Channel (PICH)
Carrying Paging Indicators (PI)
Fixed rate (30kbps), SF = 256
N paging indicators {PI0, …, PIN-1} in each PICH frame, N=18, 36, 72, or 144
One radio frame (10 ms)
b1b0
288 bits for paging indication 12 bits (undefined)
b287 b288 b299
The Page Indicator Channel (PICH) is a fixed rate (30kbps, SF=256) physical channel used by the NodeB to inform a UE (or a group of UEs) that a paging information will soon be transmitted on the PCH. Thus, the mobile only decodes the S-CCPCH when it is informed to do so by the PICH. This enables to do other processing and to save the mobiles’ battery.
The PICH carries Paging Indicators (PI), which are user specific and calculated by higher layers. It is always associated with the S-CCPCH to which the PCH is mapped.
The frame structure of the PICH is illustrated above. It is 10 ms long, and always contains 300 bits (SF=256). 288 of these bits are used to carry paging indicators, while the remaining 12 are not formally part of the PICH and shall not be transmitted. That part of the frame (last 12 bits) is reserved for possible future use.
In order not to waste radio resources, several PIs are multiplexed in time on the PICH. Depending on the configuration of the cell, 18, 36, 72 or 144 paging indicators can be multiplexed on one PICH radio frame. Thus, the number of bits reserved for each PI depends of the number of PIs per radio frame. For example, if there is 72 PIs in one radio frame, there will be 4 (288/72) consecutive bits for each PI. These bits are all identical. If the PI in a certain frame is “1”, it is an indication that the UE associated with that PI should read the corresponding frame of the S-CCPCH.
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Secondary Common Control Physical Channel (SCCPCH)
Carrying FACH and PCH, SF = 256 - 4
Pilot: used for demodulation
TFCI: Transport Format Control Indication, used for describe data
format
DataN bits
Slot #0 Slot #1 Slot #i Slot #14
1 radio frame: T f = 10 ms
T slot = 2560 chips,
DataPilot
N bitsPilotN bitsTFCITFCI
20*2 k bits (k=0..6)
The Secondary Common Control Physical Channel (S-CCPCH) is used to carry the FACH and PCH transport channels. Unlike the P-CCPCH, it is not broadcasted continuously. It is only transmitted when there is a PCH or FACH information to transmit. At the mobile side, the mobile only decodes the S-CCPCH when it expects a useful message on the PCH or FACH.
A UE will expect a message on the PCH after indication from the PICH (page indicator channel), and it will expect a message on the FACH after it has transmitted something on the RACH.
The FACH and the PCH can be mapped on the same or on separate S-CCPCHs. If they are mapped on the same S-CCPCH, TFCI bits have to be sent to support multiple transport formats
The figure above shows the frame structure of the S-CCPCH. There are 18 different slot formats determining the exact number of data, pilot and TFCI bits. The data bits correspond to the PCH and/or FACH bits coming from the transport sub-layer. Pilot bit are typically used when beamforming techniques are used.
The SF ranges from 4 to 256. The channelization code is assigned by the RRC layer as is the scrambling code, and they are fixed during the communication. They are sent on the BCCH so that every UE can decode the channel.
As said before, FACH can be used to carry user data. The difference with the dedicated channel is that it cannot use fast power control, nor soft handover. The advantage is that it is a fast access channel.
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Physical Random Access Channel (PRACH)
Carrying uplink signaling and data, consist of two parts:
One or several preambles: 16 kinds of available preambles
10 or 20ms message part
Message partPreamble
4096 chips10 ms (one radio frame)
Preamble Preamble
Message partPreamble
4096 chips 20 ms (two radio frames)
Preamble Preamble
The Physical Random Access Channel (PRACH) is used by the UE to access the network and to carry small data packets. It carries the RACH transport channel. The PRACH is an open loop power control channel, with contention resolution mechanisms (ALOHA approach) to enable a random access from several users.
The PRACH is composed of two different parts: the preamble part and the message part that carries the RACH message. The preamble is an identifier which consists of 256 repetitions of a 16 chip long signature (total of 4096 chips). There are 16 possible signatures, basically, the UE randomly selects one of the 16 possible preambles and transmits it at increasing power until it gets a response from the network (on the AICH). That preamble is scrambled before being sent. That is a sign that the power level is high enough and that the UE is authorized to transmit, which it will do after acknowledgment from the network. If the UE doesn’t get a response from the network, it has to select a new signature to transmit.
The message part is 10 or 20 ms long (split into 15 or 30 time slots) and is made of the RACH data and the layer 1 control information.
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PRACH Message Structure
PilotN bits
Slot # 0 Slot # 1 Slot # i Slot # 14
Message part radio frame T = 10 ms
Tslot = 2560 chips, 10*2
Pilot
TFCIN bitsTFCI
DataN data bitsData
Control
k bits (k=0..3)
The data and control bits of the message part are processed in parallel. The SF of the data part can be 32, 64, 128 or 256 while the SF of the control part is always 256. The control part consists of 8 pilot bits for channel estimation and 2 TFCI bits to indicate the transport format of the RACH (transport channel), for a total of 10 bits per slot.
The OVSF codes to use (one for RACH data and one for control) depend on the signature that was used for the preamble (for signatures s=0 to s=15: OVSFcontrol= Cch,256,m, where m=16s + 15; OVSFdata= Cch,SF,m, where m=SF*s/16.
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PRACH Access Timeslot Structure
#1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14
5120 chips
radio frame: 10 ms radio frame: 10 ms
Access slot #0 Random Access Transmission
Access slot #1
Access slot #7
Access slot #14
Random Access Transmission
Random Access Transmission
Random Access TransmissionAccess slot #8
The PRACH transmission is based on the access frame structure. The access frame is access of 15 access slots and lasts 20 ms (2 radio frames). To avoid too many collisions and to limit interference, a UE must wait at least 3 or 4 access slots between two consecutive preambles.The PRACH resources (access slots and preamble signatures) can be divided between different Access Service Classes (ASC) in order to provide different priorities of RACH usage. The ASC number ranges from 0 (highest priority) to 7 (lowest priority).
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Acquisition Indicator Channel (AICH)
Carrying the Acquisition Indicators (AI), SF = 256
There are 16 kinds of Signature to generate AI
AS #14 AS #0 AS #1 AS #i AS #14 AS #0
a1 a2a0 a31 a32a30 a33 a38 a39
AI part Unused part
20 ms
The Acquisition Indicator Channel (AICH) is a common downlink channel used to control the uplink random accesses. It carries the Acquisition Indicators (AI), each corresponding to a signature on the PRACH (uplink). When the NodeB receives the random access from a mobile, it sends back the signature of the mobile to grant its access. If the NodeB receives multiple signatures, it can sent all these signatures back by adding the together. At reception, the UE can apply its signature to check if the NodeB sent an acknowledgement (taking advantage of the orthogonality of the signatures).
The AICH consists of a burst of data transmitted regularly every access slot frame. One access slot frame is formed of 15 access slots, and lasts 2 radio frames (20 ms). Each access slot consists of two parts, an acquisition indicator part of 32 real-valued symbols and a long part during which nothing is transmitted to avoid overlapping due to propagation delays.
s (with values 0, +1 and -1, corresponding to the answer from the network to a specific user) and the 32 chip long sequence <bs,j> is given by a predefined table. There are 16 sequences <bs,j>, each corresponding to one PRACH signatures. A maximum of 16 AIs can be sent in each access slot. The user can multiply the received multi-level signal by the signature it used to know if its access was granted.
The SF used is always 256 and the OVSF code used by the cell is indicated in system information type 5.
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Uplink Dedicated Physical Channel (DPDCH&DPCCH)
Uplink DPDCH and DPCCH are I/Q code division
multiplexed (CDM) within each radio frame
DPDCH carries data generated at Layer 2 and higher layer,
the OVSF code is Cch,SF,SF/4, where SF is from 256 to 4
DPCCH carries control information generated at Layer 1,
the OVSF code is Cch,256,0
There are two kinds of uplink dedicated physical channels, the Dedicated Physical Data Channel (DPDCH) and the Dedicated Physical Control Channel (DPCCH).The DPDCH is used to carry the DCH transport channel. The DPCCH is used to carry the physical sub-layer control bits.
Each DPCCH time slot consists of Pilot, TFCI,FBI,TPC
Pilot is used to help demodulation
TFCI: transport format control indicator
FBI:used for the FBTD. (feedback TX diversity)
TPC: used to transport power control command.
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Uplink Dedicated Physical Channel (DPDCH&DPCCH)
Frame Structure of Uplink DPDCH/DPCCH
PilotNpilot bits
TPCNTPC bits
DataNdata bits
Slot #0 Slot #1 Slot #i Slot #14
Tslot = 2560 chips, 10*2k bits (k=0..6)
1 radio frame: Tf = 10 ms
DPDCH
DPCCH FBINFBI bits
TFCINTFCI bits
On the figure above, we can see the DPDCH and DPCCH time slot constitution. The parameter k determines the number of symbols per slot. It is related to the spreading factor (SF) of the DPDCH by this simple equation: SF=256/2k. The DPDCH SF ranges from 4 to 256. The SF for the uplink DPCCH is always 256, which gives us 10 bits per slot. The exact number of pilot, TFCI, TPC and FBI bits is configured by higher layers. This configuration is chosen from 12 possible slot formats. It is important to note that symbols are transmitted during all slots for the DPDCH
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Downlink Dedicated Physical Channel (DPDCH+DPCCH)
Downlink DPDCH and DPCCH is time division multiplexing
(TDM).
DPDCH carries data generated at Layer 2 and higher layer
DPCCH carries control information generated at Layer 1
SF of downlink DPCH is from 512 to 4
The uplink DPDCH and DPCCH are I/Q code multiplexed. But the downlink DPDCH and DPCCH is time multiplexed. This is main difference.
Basically, there are two types of downlink DPCH. They are distinguished by the use or non use of the TFCI field. TFCI bits are not used for fixed rate services or when the TFC doesn’t change.
Page37Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Downlink Dedicated Physical Channel (DPDCH+DPCCH)
Frame Structure of Downlink DPCH (DPDCH+DPCCH)
One radio frame, Tf = 10 ms
Slot #0 Slot #1 Slot #i Slot #14
Tslot = 2560 chips, 20*2k bits (k=-1..6)
Data2Ndata2 bits
DPDCH
TFCINTFCI bits
PilotNpilot bits
Data1Ndata1 bits
DPDCH DPCCH DPCCH
TPCNTPC bits
We have known that the uplink DPDCH and DPCCH are I/Q code multiplexed. But the downlink DPDCH and DPCCH is time multiplexed. This is main difference. The parameter k in the figure above determines the total number of bits per time slot. It is related to the SF, which ranges from 4 to 512. The chips of one slot is also 2560.
Downlink physical channels are used to carry user specific information like speech, data or signaling, as well as layer 1 control bits. Like it was mentioned before, the payload from the DPDCH and the control bits from the DPCCH are time multiplexed on every time slot. The figure above shows how these two channels are multiplexed. There is only one DPCCH in downlink for one user.
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High-Speed Physical Downlink Shared Channel (HS-PDSCH)
Bearing service data and layer 2 overhead bits mapped from the transport channel
SF=16, can be configured several channels to increase data service
Slot #0 Slot#1 Slot #2
Tslot = 2560 chips, M*10*2k bits (k=4)
DataNdata1 bits
1 subframe: Tf = 2 ms
HS-PDSCH is a downlink physical channel that carries user data and layer 2 overhead bits mapped from the transport channel: HS-DSCH.
The user data and layer 2 overhead bits from HS-DSCH is mapped onto one or several HS-PDSCH and transferred in 2ms subframe using one or several channelization code with fixed SF=16.
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High-Speed Shared Control Channel (HS-SCCH)
Carries physical layer signalling to a single UE ,such as modulation scheme (1 bit) ,channelization code set (7 bit), transport block size (6bit),HARQ process number (3bit), redundancy version (3bit), new data indicator (1bit), UE identity (16bit)
HS-SCCH is a fixed rate (60 kbps, SF=128) downlink physical channelused to carry downlink signalling related to HS-DSCH transmission
Slot #0 Slot#1 Slot #2
Tslot = 2560 chips, 40 bits
DataNdata1 bits
1 subframe: Tf = 2 ms
HS-SCCH uses a SF=128 and has q time structure based on a sub-frame of length 2 ms, i.e. the same length as the HS-DSCH TTI. The timing of HS-SCCH starts two slot prior to the start of the HS-PDSCH subframe.
The following information is carried on the HS-SCCH (7 items)
Modulation scheme(1bit) QPSK or 16QAM
Channelization code set (7bits)
Transport block size ( 6bits)
HARQ process number (3bits)
Redundancy version (3bits)
New Data Indicator (1bit)
UE identity (16 bits)
In each 2 ms interval corresponding to one HS-DSCH TTI , one HS-SCCH carries physical-layer signalling to a single UE. As there should be a possibility for HS-DSCH transmission to multiple users in parallel (code multiplex), multiplex HS-SCCH may be needed in a cell. The specification allows for up to four HS-SCCHs as seen from a UE point of view .i.e. UE must be able to decode four HS-SCCH.
Page40Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
High-Speed Dedicated Physical Control Channel (HS-DPCCH )
Carrying information to acknowledge downlink transport blocks and feedback information to the system for scheduling and link adaptation of transport block
CQI and ACK/NACK
Physical Channel, Uplink, SF=256
Subframe #0 Subframe #i Subframe #n
One HS-DPCCH subframe ( 2ms )
ACK/NACK
1 radio frame: Tf = 10 ms
CQI
Tslot = 2560 chips 2 × Tslot = 5120 chips
The uplink HS-DPCCH consists of:
Acknowledgements for HARQ
Channel Quality Indicator (CQI)
As the HS-DPCCH uses SF=256, there are a total of 30 channel bits per 2 ms sub frame (3 time slot). The HS-DPCCH information is divided in such a way that the HARQ acknowledgement is transmitted in the first slot of the subframe while the channel quality indication is transmitted in the rest slot.
Page41Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
2. Physical Channels
2.1 Physical Channel Structure and Functions
2.2 Channel Mapping
Page42Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Mapping Between ChannelsLogical channels Transport channels Physical channels
BCCH BCH P-CCPCH
FACH S-CCPCH
PCCH PCH S-CCPCH
CCCH RACH PRACH
FACH S-CCPCH
CTCH FACH S-CCPCH
DCCH, DTCH DCH DPDCH
HS-DSCH HS-PDSCH
RACH, FACH PRACH, S-CCPCH
This page indicates how the mapping can be done between logical, transport and physical channels. Not all physical channels are represented because not all physical channels correspond to a transport channel.
The mapping between logical channels and transport channels is done by the MAC sub-layer.
Different connections can be made between logical and transport channels:
BCCH is connected to BCH and may also be connected to FACH;
DTCH can be connected to either RACH and FACH, to RACH and DSCH, to DCH and DSCH, to a DCH or a CPCH;
CTCH is connected to FACH;
DCCH can be connected to either RACH and FACH, to RACH and DSCH, to DCH and DSCH, to a DCH or a CPCH;
PCCH is connected to PCH;
CCCH is connected to RACH and FACH.
These connections depend on the type of information on the logical channels.
Page43Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Physical Layer Overview
2. Physical Channels
3. Physical Layer Procedure
Page44Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Synchronization Procedure - Cell Search
Frame synchronization & Code Group Identification
Scrambling Code Identification
UE uses SSC to find frame synchronization and identify the code group of the cell found in the first step
UE determines the primary scrambling code through correlation over the PCPICH with all codes within the identified group, and then detects the P-CCPCH and reads BCH information。
Slot Synchronization
UE uses PSC to acquire slot synchronization to a cell
The purpose of the Cell Search Procedure is to give the UE the possibility of finding a cell and of determining the downlink scrambling code and frame synchronization of that cell. This is typically performed in 3 steps:
PSCH (Slot synchronization): The UE uses the SCH’s primary synchronization code to acquire slot synchronization to a cell. The primary synchronization code is used by the UE to detect the existence of a cell and to synchronize the mobile on the TS boundaries. This is typically done with a single filter (or any similar device) matched to the primary synchronization code which is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output.
SSCH (Frame synchronization and code-group identification): The secondary synchronization codes provide the information required to find the frame boundaries and the group number. Each group number corresponds to a unique set of 8 primary scrambling codes. The frame boundary and the group number are provided indirectly by selecting a suite of 15 secondary codes. 16 secondary codes have been defined C1, C2, ….C16. 64 possible suites have been defined, each suite corresponds to one of the 64 groups. Each suite of secondary codes is composed of 15 secondary codes (chosen in the set of 16), each of which will be transmitted in one time slot. When the received codes matches one of the possible suites, the UE has both determined the frame boundary and the group number.
PCPICH (Scrambling-code identification): The UE determines the exact primary scrambling code used by the found cell. The primary scrambling code is typically identified through symbol-by-symbol correlation over the PCPICH with all the codes within the code group identified in the second step. After the primary scrambling code has been identified, the Primary CCPCH can be detected and the system- and cell specific BCH information can be read.
Page45Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Random Access Procedure
START
Choose a RACH sub channel fromavailable ones
Get available signatures
Set Preamble Retrans Max
Set Preamble_Initial_Power
Send a preamble
Check the corresponding AI
Increase message part power by p-m based on preamble power
Set physical status to be RACHmessage transmitted Set physical status to be Nack
on AICH received
Choose a access slot again
Counter> 0 & Preamble power < maximum allowed power
Choose a signature and increase preamble transmit power
Set physical status to be Nackon AICH received
Get negative AI
No AI
Report the physical status to MAC
END
Get positive AI
The counter of preamble retransmit Subtract 1, Commanded preamble power
increased by Power Ramp Step
N
Y
Send the corresponding message part
Physical random access procedure
1. Derive the available uplink access slots, in the next full access slot set, for the set of available RACH sub-channels within the given ASC. Randomly select one access slot among the ones previously determined. If there is no access slot available in the selected set, randomly select one uplink access slot corresponding to the set of available RACH sub-channels within the given ASC from the next access slot set. The random function shall be such that each of the allowed selections is chosen with equal probability ;
2. Randomly select a signature from the set of available signatures within the given ASC. ;
3. Set the Preamble Retransmission Counter to Preamble_ Retrans_ Max
4. Set the parameter Commanded Preamble Power to Preamble_Initial_Power
5. Transmit a preamble using the selected uplink access slot, signature, and preamble transmission power.
6. If no positive or negative acquisition indicator (AI ≠ +1 nor –1) corresponding to the selected signature is detected in the downlink access slot corresponding to the selected uplink access slot:
A: Select the next available access slot in the set of available RACH sub-channels within the given ASC;B: select a signature;C: Increase the Commanded Preamble Power;D: Decrease the Preamble Retransmission Counter by one. If the Preamble Retransmission Counter > 0 then repeat from step 6. Otherwise exit the physical random access procedure.
7. If a negative acquisition indicator corresponding to the selected signature is detected in the downlink access slot corresponding to the selected uplink access slot, exit the physical random access procedure Signature
8. If a positive acquisition indicator corresponding to the selected signature is detected , Transmit the random access message three or four uplink access slots after the uplink access slot of the last transmitted preamble
9. exit the physical random access procedure
Page46Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Transmit Diversity ModeApplication of Tx diversity modes on downlink physical channel
––applied–AICH
––applied–HS-SCCH
–appliedapplied–HS-PDSCH
––applied–PICH
appliedappliedapplied–DPCH
––applied–S-CCPCH
–––appliedSCH
––applied–P-CCPCH
Mode 2Mode 1STTDTSTD
Closed loop modeOpen loop modePhysical channel type
Transmitter-antenna diversity can be used to generate multi-path diversity in places where it would not otherwise exist. Multi-path diversity is a useful phenomenon, especially if it can be controlled. It can protect the UE against fading and shadowing. TX diversity is designed for downlink usage. Transmitter diversity needs two antennas, which would be an expensive solution for the UEs.
The UTRA specifications divide the transmitter diversity modes into two categories: (1) open-loop mode and (2) closed-loop mode. In the open-loop mode no feedback information from the UE to the NodeB is available. Thus the UTRAN has to determine by itself the appropriate parameters for the TX diversity. In the closed-loop mode the UE sends feedback information up to the NodeB in order to optimize the transmissions from the diversity antennas.
Thus it is quite natural that the open-loop mode is used for the common channels, as they typically do not provide an uplink return channel for the feedback information. Even if there was a feedback channel, the NodeB cannot really optimize its common channel transmissions according to measurements made by one particular UE. Common channels are common for everyone; what is good for one UE may be bad for another. The closed-loop mode is used for dedicated physical channels, as they have an existing uplink channel for feedback information. Note that shared channels can also employ closed loop power control, as they are allocated for only one user at a time, and they also have a return channel in the uplink. There are two specified methods to achieve the transmission diversity in the open-loop mode and two methods in closed-loop mode
Page47Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Transmit Diversity - STTD
Space time block coding based transmit antenna diversity
(STTD)
4 consecutive bits b0, b1, b2, b3 using STTD coding
b0 b1 b2 b3 Antenna 1
Antenna 2Channel bits
STTD encoded channel bitsfor antenna 1 and antenna 2.
b0 b1 b2 b3
-b2 b3 b0 -b1
The TX diversity methods in the open-loop mode are
space time-block coding-based transmit-antenna diversity (STTD)
time-switched transmit diversity (TSTD).
In STTD the data to be transmitted is divided between two transmission antennas at the base station site and transmitted simultaneously. The channel-coded data is processed in blocks of four bits. The bits are time reversed and complex conjugated, as shown in above slide. The STTD method, in fact, provides two brands of diversity. The physical separation of the antennas provides the space diversity, and the time difference derived from the bit-reversing process provides the time diversity.
These features together make the decoding process in the receiver more reliable. In addition to data signals, pilot signals are also transmitted via both antennas. The normal pilot is sent via the first antenna and the diversity pilot via the second antenna.
The two pilot sequences are orthogonal, which enables the receiving UE to extract the phase information for both antennas.
The STTD encoding is optional in the UTRAN, but its support is mandatory for the UE’s receiver.
Page48Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Transmit Diversity - TSTD
Time switching transmit diversity (TSTD) is used only on
SCH channel
Antenna 1
Antenna 2
i,0
i,1
acsi,14
Slot #0 Slot #1 Slot #14
i,2
acp
Slot #2
(Tx OFF)
(Tx OFF)
(Tx OFF)
(Tx OFF)
(Tx OFF)
(Tx OFF)
(Tx OFF)
acp acp
acsacs
acp
acs(Tx OFF)
Time-switched transmit diversity (TSTD) can be applied to the SCH. Just like STTD, the support of TSTD is optional in the UTRAN, but mandatory in the UE. The principle of TSTD is to transmit the synchronization channels via the two base station antennas in turn. In even-numbered time slots the SCHs are transmitted via antenna 1, and in odd-numbered slots via antenna 2. This is depicted in above Figure. Note that SCH channels only use the first 256 chips of each time slot (i.e., one-tenth of each slot).
Page49Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Closed Loop Mode
Used in DPCH and HS-PDSCH
The closed-loop-mode transmit diversity can only be applied to the downlink channel if there is an associated uplink channel. Thus this mode can only be used with dedicated channels. The chief operating principle of the closed loop mode is that the UE can control the transmit diversity in the base station by sending adjustment commands in FBI bits on the uplink DPCCH. The UE uses the base station’s common pilot channels to estimate the channels separately. Based on this estimation, it generates the adjustment information and sends it to the UTRAN to maximize the UE’s received power.
There are actually two modes in the closed-loop method. In mode 1 only the phase can be adjusted; in mode 2 the amplitude is adjustable as well as the phase. Each uplink time slot has one FBI bit for closed-loop-diversity control. In mode 1 each bit forms a separate adjustment command, but in mode 2 four bits are needed to compose a command.
This functions can be configured by LMT command ADD CELLSETUP.
Page50Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
ReferencesTS 25.104 UTRA (BS) FDD Radio Transmission and Reception
TS 25.201 Physical layer-general description
TS 25.211 Physical channels and mapping of transport channels onto physical channels (FDD)
TS 25.212 Multiplexing and channel coding (FDD)
TS 25.213 Spreading and modulation (FDD)
TS 25.214 Physical layer procedures (FDD)
TS 25.308 UTRA High Speed Downlink Packet Access (HSDPA)
TR 25.877 High Speed Downlink Packet Access (HSDPA) - Iub/Iur Protocol Aspects
TR 25.858 Physical layer aspects of UTRA High Speed Downlink Packet Access
Page51Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
This course mainly introduces the basic concept, key
technology and procedures of WCDMA physical layer.
These knowledge is very important for understanding Uu
interface and further study.
Summary
Thank youwww.huawei.com
www.huawei.com
Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA UTRAN Interface and Signaling Procedure
Page1Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Objectives
Upon completion of this course, you will be able to:
Understand UTRAN interface and structure
Understand the definitions about UTRAN network elements
Understand UTRAN signaling procedure
Page2Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. UTRAN Network Overview
2. Basic Concepts about UTRAN
3. UTRAN Signaling Procedure
Page3Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. UTRAN Network Overview
2. Basic Concepts about UTRAN
3. UTRAN Signaling Procedure
Page4Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
UMTS Network Structure
RNS
RNC
RNS
RNC
Core Network
NodeB NodeB NodeB NodeB
Iu-CS Iu-PS
Iur
Iub IubIub Iub
CN
UTRAN
UEUu
CS PS
Iu-CSIu-PS
CSPS
UTRAN (UMTS Terrestrial Radio Access network) structure
The UTRAN consists of one or several Radio Network Subsystem ( RNS ), each containing one RNC and one or several NodeB
Interface
Iu interface: the Iu interface connects the UTRAN to the CN and is split in two parts. The Iu-CS is the interface between the RNC and the circuit switched domain of the CN. The Iu-PS interface is the interface between the RNC and the packet switched domain of the CN.
Uu interface: the Uu interface is the WCDMA radio interface with in UMTS. It is the interface through which the UE accesses the fixed part of the network.
Iub interface: the Iub interface connects the NodeB and the RNC. Contrarily to GSM, this interface is fully open in UMTS and thus more competition is expected.
Iur interface: the RNC-RNC interface was initially designed in order to provide inter RNC soft handover, but more features were added during the development.
Page5Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Uu Interface
L3co
ntro
l
cont
rol
cont
rol
cont
rol
C-plane signaling U-plane information
PHY
L2/MAC
L1
RLC
DCNtGC
L2/RLC
MAC
RLCRLCRLC
Duplication avoidance
UuS boundary
L2/BMC
control
PDCPPDCP L2/PDCP
DCNtGC
RRC
RLCRLCRLCRLC
BMC
radio bearer
logical channel
transport channel
The layer 1 supports all functions required for the transmission of bit streams on the physical medium. It is also in charge of measurements function consisting in indicating to higher layers, for example, Frame Error Rate (FER), Signal to Interference Ratio (SIR), interference power, transmit power, … It is basically composed of a “layer 1 management” entity, a “transport channel” entity, and a “physical channel” entity.
The layer 2 protocol is responsible for providing functions such as mapping, ciphering, retransmission and segmentation. It is made of four sublayers: MAC (Medium Access Control), RLC (Radio Link Control), PDCP (Packet Data Convergence Protocol) and BMC (Broadcast/Multicast Control).
The layer 3 is split into 2 parts: the access stratum and the non access stratum. The access stratum part is made of “RRC (Radio Resource Control)” entity and “duplication avoidance” entity. The non access stratum part is made of CC, MM parts.
Not shown on the figure are connections between RRC and all the other protocol layers (RLC, MAC, PDCP, BMC and L1), which provide local inter-layer control services.
The protocol layers are located in the UE and the peer entities are in the NodeB or the RNC.
Page6Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
General Protocol Mode for UTRAN Terrestrial Interface
The structure is based on the principle that the layers and planes are logically independent of each other.
Application Protocol
Data Stream(s)
ALCAP(s)
Transport Network
Layer
Physical Layer
Signaling Bearer(s)
Control Plane User Plane
Transport NetworkUser Plane
Transport Network Control Plane
Radio Network
Layer
Signaling Bearer(s)
Data Bearer(s)
Transport NetworkUser Plane
Protocol structures in UTRAN terrestrial interfaces are designed according to the same general protocol model. This model is shown in above slide. The structure is based on the principle that the layers and planes are logically independent of each other and, if needed, parts of the protocol structure may be changed in the future while other parts remain intact. Horizontal Layers
The protocol structure consists of two main layers, the Radio Network Layer (RNL) and the Transport Network Layer (TNL). All UTRAN-related issues are visible only in the Radio Network Layer, and the Transport Network Layer represents standard transport technology that is selected to be used for UTRAN but without any UTRAN-specific changes.
Vertical Planes
Control Plane
The Control Plane is used for all UMTS-specific control signaling. It includes the Application Protocol (i.e. RANAP in Iu, RNSAP in Iur and NBAP in Iub), and the Signaling Bearer for transporting the Application Protocol messages. The Application Protocol is used, among other things, for setting up bearers to the UE (i.e. the Radio Access Bearer in Iu and subsequently the Radio Link in Iur and Iub). In the three plane structure the bearer parameters in the Application Protocol are not directly tied to the User Plane technology, but rather are general bearer parameters. The Signaling Bearer for the Application Protocol may or may not be of the same type as the Signaling Bearer for the ALCAP. It is always set up by O&M actions.
User Plane
All information sent and received by the user, such as the coded voice in a voice call or the packets in an Internet connection, are transported via the User Plane. The User Plane includes the Data Stream(s), and the Data Bearer (s) for the Data Stream(s). Each Data Stream is characterized by one or more frame protocols specified for that interface.
Transport Network Control Plane
The Transport Network Control Plane is used for all control signaling within the Transport Layer. It does not include any Radio Network Layer information. It includes the ALCAP protocol that is needed to set up the transport bearers (Data Bearer) for the User Plane. It also includes the Signaling Bearer needed for the ALCAP. The Transport Network Control Plane is a plane that acts between the Control Plane and the User Plane. The introduction of the Transport Network Control Plane makes it possible for the Application Protocol in the Radio Network Control Plane to be completely independent of the technology selected for the Data Bearer in the User Plane.
About AAl2 and AAL5
Above the ATM layer we usually find an ATM adaptation layer (AAL). Its function is to process the data from higher layers for ATM transmission.
This means segmenting the data into 48-byte chunks and reassembling the original data frames on the receiving side. There are five different AALs (0, 1, 2, 3/4, and 5). AAL0 means that no adaptation is needed. The other adaptation layers have different properties based on three parameters:
Real-time requirements;
Constant or variable bit rate;
Connection-oriented or connectionless data transfer.
The usage of ATM is promoted by the ATM Forum. The Iu interface uses two AALs: AAL2 and AAL5.
AAL2 is designed for the transmission of connection oriented, real-time data streams with variable bit rates.
AAL5 is designed for the transmission of connectionless data streams with variable bit rates.
Page8Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
RNL Control Plane Application Protocol
NBAP Node B Application Part
RANAP Radio Access Network Application Part
RNSAP Radio Network Subsystem Application Part
RRC Radio Resource Control
NodeB
RNC
CN
UE
RANAP
NBAP
RNSAPRRC RNC
RANAP is the signaling protocol in Iu that contains all the control information specified for the Radio Network Layer.
RNSAP is the signaling protocol in Iur that contains all the control information specified for the Radio Network Layer.
NBAP is the signaling protocol in Iub that contains all the control information specified for the Radio Network Layer.
RRC is the signaling protocol in Uu that locate in the Uu interface layer 3.
Page9Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Iu-CS Interface
ALCAPALCAP
Control Plane
Transport NetworkControl Plane
User planeRadioNetworkLayer
Transport NetworkUser Plane
TransportNetworkLayer
A B
RANAP
AAL2 PATH
ATM
Physical Layer
SAAL NNI
SCCPMTP3-B
Iu UP
SAAL NNI
MTP3-B
Transport NetworkUser Plane
Protocol Structure for Iu CS
The Iu CS overall protocol structure is depicted in above slide. The three planes in the Iu interface share a common ATM (Asynchronous Transfer Mode) transport which is used for all planes. The physical layer is the interface to the physical medium: optical fiber, radio link or copper cable. The physical layer implementation can be selected from a variety of standard off-the-shelf transmission technologies, such as SONET, STM1, or E1.
Iu CS Control Plane Protocol Stack
The Control Plane protocol stack consists of RANAP, on top of Broadband (BB) SS7 (Signaling System #7) protocols. The applicable layers are the Signaling Connection Control Part (SCCP), the Message Transfer Part (MTP3-b) and SAAL-NNI (Signaling ATM Adaptation Layer for Network to Network Interfaces).
Iu CS Transport Network Control Plane Protocol Stack
The Transport Network Control Plane protocol stack consists of the Signaling Protocol for setting up AAL2 connections (Q.2630.1 and adaptation layer Q.2150.1), on top of BB SS7 protocols. The applicable BB SS7 are those described above without the SCCP layer.
Iu CS User Plane Protocol Stack
A dedicated AAL2 connection is reserved for each individual CS service.
Page10Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Iu-PS Interface
Control Plane User planeRadioNetworkLayer
Transport NetworkUser PlaneTransport
NetworkLayer
Transport NetworkUser Plane
C
RANAP
ATM
SAAL NNI
SCCP
MTP3-B
Iu UP
AAL Type 5IP
UDP
GTP-U
Physical Layer
Protocol Structure for Iu PS
The Iu PS protocol structure is represented in above slide. Again, a common ATM transport is applied for both User and Control Plane. Also the physical layer is as specified for Iu CS.
Iu PS Control Plane Protocol Stack
The Control Plane protocol stack consists of RANAP, on top of Broadband (BB) SS7 (Signaling System #7) protocols. The applicable layers are the Signaling Connection Control Part (SCCP), the Message Transfer Part (MTP3-b) and SAAL-NNI (Signaling ATM Adaptation Layer for Network to Network Interfaces).
Iu PS Transport Network Control Plane Protocol Stack
The Transport Network Control Plane is not applied to Iu PS. The setting up of the GTP tunnel requires only an identifier for the tunnel, and the IP addresses for both directions, and these are already included in the RANAP RAB Assignment messages.
Iu PS User Plane Protocol Stack
In the Iu PS User Plane, multiple packet data flows are multiplexed on one or several AAL5 PVCs. The GTP-U (User Plane part of the GPRS Tunneling Protocol) is the multiplexing layer that provides identities for individual packet data flow. Each flow uses UDP connectionless transport and IP addressing.
Page11Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Iub Interface
ALCAPALCAP
Control Plane
Transport NetworkControl Plane
User planeRadioNetworkLayer
Transport NetworkUser Plane
TransportNetworkLayer
Transport NetworkUser Plane
NBAP
AAL2 PATH
ATM
Physical Layer
SAAL UNI
Iub FP
SAAL UNI
NCP CCP
The Iub interface is the terrestrial interface between NodeB and RNC. The Radio Network Layer defines procedures related to the operation of the NodeB. The Transport Network Layer defines procedures for establishing physical connections between the NodeB and the RNC.
The Iub application protocol, NodeB application part ( NBAP ) initiates the establishment of a signaling connection over Iub . It is divided into two essential components, CCP and NCP.
NCP is used for signaling that initiates a UE context for a dedicated UE or signals that is not related to specific UE. Example of NBAP-C procedure are cell configuration , handling of common channels and radio link setup
CCP is used for signaling relating to a specific UE context.
SAAL is an ATM Adaptation Layer that supports communication between signaling entities over an ATM link.
The user plane Iub Frame Protocol ( FP ), defined the structure of the frames and the basic in band control procedure for every type of transport channel. There are DCH-FP, RACH-FP, FACH-FP, HS-DSCH FP and PCH FP.
Page12Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Iur Interface
ALCAPALCAP
Control Plane
Transport NetworkControl Plane
User planeRadioNetworkLayer
TransportNetworkLayer
A B
RANAP
AAL2 PATH
ATM
Physical Layer
SAAL NNI
SCCPMTP3-B
Iur Data Stream
SAAL NNI
MTP3-B
Transport NetworkUser Plane
Transport NetworkUser Plane
Iur interface connects two RNCs. The protocol stack for the Iur is shown in above slide.
The RNSAP protocol is the signaling protocol defined for the Iur interface.
Page13Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. UTRAN Network Overview
2. Basic Concepts about UTRAN
3. UTRAN Signaling Procedure
Page14Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
SRNC / DRNC
SRNC and DRNC are concepts for a connected UE.The SRNC handles the connection to one UE, and may borrow radio resources of a certain cell from the DRNC. Drift RNCs support the Serving RNC by providing radio resourcesA UE in connection state has at least one and only one SRNC, but can has 0 or multiple DRNCs
CN
SRNC DRNC
Iu Iur
Inside the UTRAN, the RNCs of the Radio Network Subsystems can be interconnected together through the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed over direct physical connection between RNCs or virtual networks using any suitable transport network .
For each connection between User Equipment and the UTRAN, One RNC is the Serving RNC. When required, Drift RNCs support the Serving RNC by providing radio resources. The role of an RNC (Serving or Drift) is on a per connection basis between a UE and the UTRAN.
Page15Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
RAB, RB and RL
RAB
RB
RLNodeB
RNC CNUE
UTRAN
RAB: The service that the access stratum provides to the non-access stratum for transfer of user data between User Equipment and CN.
RB: The service provided by the layer2 for transfer of user data between User Equipment and Serving RNC.
RL: A "radio link" is a logical association between single User Equipment and a single UTRAN access point. Its physical realization comprises one or more radio bearer transmissions.
Page16Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
UE Working Modes and States
Idle Mode
Connected Mode
CELL_DCH
CELL_FACH
CELL_PCH
URA_PCH
If RRC connection does not exit between UE and RNC, then the UE is in idle mode.
If RRC connection exits between UE and RNC, then the UE is in connected mode.
Based on UE mobility and activity UE in connected mode may be allocated to four different states: CELL_DCH, CELL_FACH, CELL_PCH and URA_PCH.
The UE leaves the connected mode and returns to idle mode when the RRC connection is released or at RRC connection failure.
Page17Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Idle Mode
The UE has no relation to UTRAN, only to CN. For data
transfer, a signaling connection has to be established.
UE camps on a cell
It enables the UE to receive system information from the PLMN
UE can monitor PICH of a cell for paging
The idle mode tasks can be divided into three processes:
PLMN selection and reselection
Cell selection and reselection
Location registration
When a UE is switched on, a public land mobile network (PLMN) is selected and the UE searches for a suitable cell of this PLMN to camp on.
The UE searches for a suitable cell of the chosen PLMN and chooses that cell to provide available services, and tunes to its control channel. This choosing is known as "camping on the cell". The UE will, if necessary, then register its presence, by means of a NAS registration procedure, in the registration area of the chosen cell.
If the UE finds a more suitable cell, it reselects onto that cell and camps on it. If the new cell is in a different registration area, location registration is performed.
Page18Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Connected Mode
When UE is in connected mode
The UE position can be known on different levels:
Cell level (CELL_DCH/CELL_FACH/CELL_PCH)
UTRAN Registration Area (URA) level (URA_PCH)
The UE can use different types of channels in connected mode
Dedicated transport channels (CELL_DCH)
Common transport channels (CELL_FACH)
Assuming that there exists an RRC connection, there are two basic families of RRC connection mobility procedures, URA updating and handover. Different families of RRC connection mobility procedures are used in different levels of UE connection (cell level and URA level):
URA updating is a family of procedures that updates the UTRAN registration area of a UE when an RRC connection exists and the position of the UE is known on URA level in the UTRAN;
Handover is a family of procedures that adds or removes one or several radio links between one UE and UTRAN when an RRC connection exists and the position of the UE is known on cell level in the UTRAN.
Which type of transport channel is used by UE in connected mode is decided by RNC according to the UE activity.
Page19Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Connected Mode
Cell-DCH
In active state
Communicating via its dedicated channels
UTRAN knows which cell UE stays in
If there is huge data to be transmitted, it must allocate dedicated channel. Thus UE will be in Cell-DCH. UE in Cell-DCH state is communicating via DCH (downlink and uplink) with UTRAN.
Page20Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Connected Mode
Cell-FACH
In active state
Few data to be transmitted both in uplink and in downlink.
There is no need to allocate dedicated channel for this UE
Downlink uses FACH and uplink uses RACH
UE needs to monitor the FACH for its information
UTRAN knows which cell the UE stays in
If there is only few data to be transmitted, there is no need to allocate dedicated channel. Thus UE will be in Cell-FACH. UE in Cell-FACH state is communicating via FACH (downlink) and RACH (uplink) with UTRAN. UE need to monitor the FACH for its relative information because FACH is shared for all users in the cell.
Page21Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Connected Mode
Cell-PCH
No data to be transmitted or received
Monitor PICH, to receive its paging
UTRAN knows which cell the UE stays in
UTRAN has to update cell information of UE when UE roams
to another cell
Lower the power consumption of UE
If UE has no data to be transmitted or received, UE will be in Cell-PCH or URA-PCH. In these two states, UE needs to monitor PICH,to receive its paging. UTRAN knows which cell or URA UE is now in. The difference between Cell-PCH and URA-PCH is that UTRAN update UE information only after UE which is in URA-PCH state has roamed to other URA.
UTRAN have to update cell information of UE when UE roams to another cell. UE migrates to cell-FACH state to complete the cell update. If there is also no data to be transmitted or received, UE is back to CELL-PCH state after cell update. If the cell update times in a fixed time reach a preset value, UTRAN will let UE migrate to URA-PCH. URA is an area of several cells.
Page22Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Connected Mode
URA-PCH
No data to be transmitted or received
Monitor PICH, to receive its paging
UTRAN only knows which URA (which consists of multiple cells) that UE stays
UTRAN updates UE information only after UE has roamed to other URA
A better way to reduce the resource occupancy and signaling transmission
It is the same as the CELL-PCH state. UE should migrate to CELL-FACH state to complete the URA update.
Page23Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
UE Working Modes and States
CELL_DCH CELL_FACH
CELL_PCHURA_PCH
IDLE
DEAD - Scan networks (PLMN)- Camp on a cell
- Monitor paging channel- Cell re-selection
- Dedicated channel- Common service, such as voice
- Reduce activity, DTX,and save powerRRC Connection
- Common channel- PS service with few
data to transmit
- Reduce activity further- Avoid unnecessary signaling
This is the UE states figure. These states are significant only for UTRAN and UE. They are transparent to CN. Let’s focus on the switch between the states.
Page24Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. UTRAN Network Overview
2. Basic Concepts about UTRAN
3. UTRAN Signaling Procedure
Page25Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
3. UTRAN Signaling Procedure
3.1 System Information Broadcast
3.2 Paging
3.3 Call Process
3.4 Handover
Page26Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
System Information Broadcast Flow
3. BCCH: System Information
1. System Information Update Request
UE Node B RNC
NBAPNBAP
RRCRRC
4. BCCH: System InformationRRCRRC
5. BCCH: System Information RRCRRC
2. System Information Update ResponseNBAPNBAP
Page27Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Introduction of System Information
MIB:
PLMN tag
Scheduling information for SB (Scheduling Block)
Scheduling information for SIB (System Information Block)
SB1: scheduling information for SIB
SB2: scheduling information for SIB (extended)
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Introduction of System Information
SIB1: System information for NAS and the timer/counter for UE
SIB2: URA information
SIB3: Parameters for cell selection and cell re-selection
SIB4: Parameters for cell selection and cell re-selection while UE is in connected mode
SIB5: Parameters for the common physical channels of the cell
SIB6: Parameters for the common physical channels of the cell while UE is in connected mode
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Introduction of System Information
SIB7: uplink interference level and the refreshing timer
SIB8: the CPCH static information
SIB9: the CPCH dynamic information
SIB10: information to be used by UEs having their DCH controlledby a DRAC procedure
SIB11: measurement controlling information
SIB12: measurement controlling information in connected mode
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Introduction of System Information
SIB13: ANSI-41 system information
SIB14: the information in TDD mode
SIB15: the position service information
SIB16: the needed pre-configuration information for handover from other RAT to UTRAN
SIB17: the configuration information for TDD
SIB18: the PLMN identities of the neighboring cells to be used in shared networks to help with the cell reselection process
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System Information Block Type 1
System information type 1
The NAS system information
CS domain DRX: K=6, then DRX period is 2^k= 2^6= 64TTI=640 ms
PS domain DRX: K=6, then DRX period is 2^k=2^6=64TTI =640 ms
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System Information Block Type 2
System info type 2
URA information
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System Information Block Type 3
The references for cell selection and re-selection
Qhyst2s
Sintrasearch
Sintersearch
Sinterratsearch
Qqualmin
Qrxlemin
T reselection
Max Allowed UE TX power
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System Information Block Type 5
The configuration information for the following physical channels and the counterpart transport channels
PCCPCH
SCCPCH
PICH
AICH
PRACH
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System Information Block Type 7 and 11
System info type 7
Including the UL interference level which is used for open loop power control
Including the Expiration Time Factor which is used for refreshing the SIB7 periodically
System info type 11
The neighbor cell information for cell re-selection in IDLE mode
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Contents
3. UTRAN Signaling Procedure
3.1 System Information Broadcast
3.2 Paging
3.3 Call Process
3.4 Handover
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Paging Initiation
CN initiated paging
Establish a signaling connection
UTRAN initiated paging
Trigger the cell update procedure
Trigger reading of updated system information
For CN originated paging:
In order to request UTRAN connect to UE, CN initiates the paging procedure, transmits paging message to the UTRAN through Iu interface, and UTRAN transmits the paging message from CN to UE through the paging procedure on Uu interface, which will make the UE initiate a signaling connection setup process with the CN.
For UTRAN originated paging:
UE state transition: In order to trigger UE in the CELL_PCH or URA_PCH state to carry out state transition (for example, transition to the CELL_FACH state), the UTRAN will perform a paging process. Meanwhile, the UE will initiate a cell update or URA update process, as a reply to the paging.
When the cell system message is updated: When system messages change, the UTRAN will trigger paging process in order to inform UE in the idle, CELL_PCH or URA_PCH state to carry out the system message update, so that the UE can read the updated system message.
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Paging Type 1
If UE is in CELL_PCH,URA_PCH or IDLE state,the paging message will be transmitted on PCCH with paging type 1
CN RNC1 RNC2 NODEB1.1 NODEB2.1 UE
RANAPRANAP
RANAP RANAP
PCCH: PAGING TYPE 1
PAGING
PAGING
PCCH: PAGING TYPE 1
Paging type 1:
The message is transmitted in one LA or RA according to LAI or RAI.
After calculating the paging time, the paging message will be transmitted at that time
If UE is in CELL_PCH or URA_PCH state, the UTRAN transmits the paging information in PAGING TYPE 1 message to UE. After received paging message, UE performs a cell update procedure to transit state to CELL_FACH.
As shown in the above figure, the CN initiates paging in a location area (LA), which is covered by two RNCs. After receiving a paging message, the RNC searches all the cells corresponding to the LAI, and then calculates the paging time, at which it will send the PAGING TYPE 1 message to these cells through the PCCH.
Page39Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Paging Type 2
If UE is in CELL_DCH or CELL_FACH state,the paging message will be transmitted on DCCH with paging type 2
CN SRNC UE
RANAPRANAP
PAGING
RRCRRCDCCH: PAGING TYPE 2
Paging type 2:
If UE is in CELL_DCH or CELL_FACH state,the paging message will be transmitted on DCCH with paging type 2
The message will be only transmitted in a cell
As shown in the above figure, if the UE is in the CELL_-DCH or CELL_FACH state, the UTRAN will immediately transmit PAGING TYPE 2 message to the paged UE on DCCH channel.
Page40Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
3. UTRAN Signaling Procedure
3.1 System Information Broadcast
3.2 Paging
3.3 Call Process
3.4 Handover
Page41Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Introduction of Call Process
In WCDMA system, a call process includes the following basic signaling flows:
RRC connection flow
Direct transfer message flow
Authentication flow (optional)
Security flow (optional)
RAB establish flow
Call proceeding
NAS signaling before correlative bearer release
Correlative bearer release
Page42Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
RRC Connection Establishment Flow (CCCH)
UE Serving RNC
RRCRRC
RRCRRC2. CCCH: RRC Connection Set up
RRCRRC3. DCCH: RRC Connection Setup Complete
1. CCCH: RRC Connection Request
In the idle mode, when the non-access layer of the UE requests to establish a signaling connection, the UE will initiate the RRC connection procedure. Each UE has up to one RRC connection only.
When the SRNC receives an RRC CONNECTION REQUEST message from the UE, the Radio Resource Management (RRM) module of the RNC determines whether to accept or reject the RRC connection request according to a specific algorithm. If accepting the request, the RRM module determines whether to set up the RRC connection on a Dedicated Channel (DCH) or on a Common Channel (CCH) according to a specific RRM algorithm.
Description:
The UE sends an RRC CONNECTION REQUEST message to the SRNC through the uplink CCCH, requesting the establishment of an RRC connection.
Based on the RRC connection request cause and the system resource state, the SRNC decides to establish the connection on the common channel.
The SRNC sends an RRC CONNECTION SETUP message to the UE throughthe downlink CCCH. The message contains the information about the CCH.
The UE sends an RRC CONNECTION SETUP COMPLETE message to the SRNC through the uplink CCCH.
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RRC Connection Establishment Flow (DCCH)
5. Downlink Synchronization
UE Node B Serving RNC
DCH - FP
Allocate RNTISelect L1 and L2parameters
RRCRRC
NBAPNBAP3. Radio Link Setup Response
NBAPNBAP2. Radio Link Setup Request
RRCRRC7. CCCH: RRC Connection Set up
Start RX
Start TX
4. ALCAP Iub Data Transport Bearer Setup
RRCRRC9. DCCH: RRC Connection Setup Complete
6. Uplink Synchronization
NBAPNBAP8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
1. CCCH: RRC Connection Request
Typically, an RRC connection is set up on the DCH.
Description:
The UE sends an RRC Connection Request message via the uplink CCCH to request to establish an RRC connection.
Based on the RRC connection request cause and the system resource state, the SRNC decides to establish the connection on the dedicated channel, and allocates the RNTI and L1 and L2 resources.
The SRNC sends a Radio Link Setup Request message to Node B, requesting the Node B to allocate specific radio link resources required by the RRC connection.
After successfully preparing the resources, the Node B responds to the SRNC with the Radio Link Setup Response message.
The SRNC initiates the establishment of Iub user plane transport bearer with the ALCAP protocol and completes the synchronization between the RNC and the Node B.
The SRNC sends an RRC Connection Setup message to the UE in the downlink CCCH.
The UE sends an RRC Connection Setup Complete message to the SRNC in the uplink DCCH.
DCH_3.4K_SIGNALLINGSpare RRC establishDEFAULTEST
FACHTerminating cause unknownTERMCAUSEUNKNOWN
FACHTerminating Low Priority SignalingTERMLOWPRIORSIGEST
DCH_13.6K_SIGNALLINGTerminating High Priority SignalingTERMHIGHPRIORSIGEST
DCH_3.4K_SIGNALLINGCall re-establishmentCALLREEST
FACHOriginating Low Priority SignalingORIGLOWPRIORSIGEST
DCH_13.6K_SIGNALLINGOriginating High Priority SignalingORIGHIGHPRIORSIGEST
FACHDetachDETACHEST
DCH_13.6K_SIGNALLINGRegistrationREGISTEST
DCH_3.4K_SIGNALLINGInter-RAT cell change orderINTERRATCELLCHGORDEREST
DCH_3.4K_SIGNALLINGInter-RAT cell re-selectionINTERRATCELLRESELEST
DCH_13.6K_SIGNALLINGEmergency Call RRC establish typeEMERGCALLEST
DCH_13.6K_SIGNALLINGTerminating Background CallTERMBKGCALLEST
DCH_13.6K_SIGNALLINGTerminating Interactive CallTERMINTERCALLEST
DCH_13.6K_SIGNALLINGTerminating Streaming CallTERMSTREAMCALLEST
DCH_13.6K_SIGNALLINGTerminating Conversational CallTERMCONVCALLEST
DCH_13.6K_SIGNALLINGOriginating Subscribed traffic CallORIGSUBSTRAFFCALLEST
DCH_13.6K_SIGNALLINGOriginating Background CallORIGBKGCALLEST
DCH_13.6K_SIGNALLINGOriginating Interactive CallORIGINTERCALLEST
DCH_13.6K_SIGNALLINGOriginating Streaming CallORIGSTREAMCALLEST
DCH_13.6K_SIGNALLINGOriginating Conversational CallORIGCONVCALLEST
Recommended valueNameID
Page45Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Direct Transfer Message Flow
In Iu interface, radio network layer reports the RANAP
information and NAS information. NAS information is
taken as directed message in RANAP information.
UE NodeB RNC CN
RRC RRC
SCCP SCCP
SCCP SCCP
Initial DT
Connect Request
Connect Confirm
RRC
RANAP RANAPInitial UE Message
RANAP RANAPCommon ID
After the RRC connection between the UE and the UTRAN is successfully set up, the UE sets up a signaling connection with the CN via the RNC for NAS information exchange between the UE and the CN, such as authentication, service request and connection setup. This is also called the NAS signaling setup procedure.
For the RNC, the signaling exchanged between the UE and the CN is a direct transfer message. After receiving the first direct transfer message, that is, the Initial Direct Transfer message, the RNC sets up a signaling connection with the CN on the SCCP. The procedure is shown in the above figure:
The specific procedure is given as follows:
After the RRC connection is established, the UE sends the Initial Direct Transfer message to the RNC via the RRC connection. This message carries the NAS information content sent to the CN by the UE.
After receiving the Initial Direct Transfer message from the UE, the RNC sends the SCCP Connection Request (CR) message to the CN via the Iu interface. The message content is the Initial UE Message sent from the RNC to the CN, and carries the message content sent from the UE to the CN.
If the CN is ready to accept the connection request, then it returns the SCCP Connection Confirm (CC) message to the RNC. The SCCP connection is successfully set up. The RNC receives the message and confirms the signaling connection setup success.
If the CN cannot accept the connection request, then it returns the SCCP Connection Reject (CJ) message to the RNC. The SCCP connection setup fails. The RNC receives the message and confirms the signaling connection setup failure. Then it initiates the RRC release procedure.
After the signaling connection is successfully set up, the message sent by the UE to the CN is forwarded to the RNC via the Uplink Direct Transfer message, and the RNC converts it into the Direct Transfer message to send to the CN. The message sent by the CN to the UE is forwarded to the RNC via the Direct Transfer message, and the RNC converts it into the Downlink Direct Transfer to send to the UE.
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Common ID
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Authentication and Security FlowUE RNC CN
RRC Connection Setup Initial DT Initial UE Message
(CM Service Request)
DL DT (Authentication Request)DL DT (Authentication Request)
DL DT (Authentication Response)DL DT (Authentication Response)
Common ID
Security Mode CommandSecurity Mode Command
Security Mode Command Complete Security Mode Command Complete
RAB Assignment
UL Direct Transfer (Setup) Direct Transfer (Setup)
Direct Transfer (Call Proceeding)DL Direct Transfer (Call Proceeding)
Authentication is used for the validity of CN and UE. Security flow includes the encrypt process and integrity protection.
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RAB Establishment FlowNodeBUE CNRNC
RANAPRANAPRAB Ass Req
Q.AAL2 Q.AAL2
Q.AAL2Q.AAL2
NBAPNBAP
AAL2 Setup Req
RL Recfg Prep
AAL2 Setup Rsp
NBAPNBAPRL Recfg Ready
Q.AAL2Q.AAL2 AAL2 Setup Req
Q.AAL2Q.AAL2 AAL2 Setup Rsp
FPFPDL Sync
FPFPUL Sync
RRC RRCRB Setup
NBAPNBAPRL Recfg Commit
RRC RRCRB Setup Complete
RANAPRANAPRAB Ass Rsp
RAB is the carrier which is provided by AS for NAS.
RAB is the carrier in user plane, which is for transferring the voice service, data service or multiple media service between UE and CN.
RAB establishment flow mainly includes the AAL2 PATH establishment of Iu and Iub interface, also includes the reconfiguration process of radio resource.
The RAB refers to the user plane bearer that is used to transfer voice, data and multimedia services between the UE and the CN. The UE needs to complete the RRC connection establishment before setting up the RAB.
The RAB setup is initiated by the CN and executed by the UTRAN. The basic procedure is as follows:
1. First the CN sends the RAB assignment request message to the UTRAN, requesting the UTRAN to establish the RAB.
2. The SRNC in the UTRAN initiates the establishment of the data transport bearer between the Iu interface and the Iub interface (Iur interface).
3. The SRNC sends the RB setup request to the UE.
4. After completing the RB establishment, the UE responds to the SRNC with the RB setup complete message.
5. The SRNC responds to the CN with the RAB assignment response message and the RAB setup procedure ends.
When the RAB is successfully established, a basic call is set up and the UE enters the conversation process.
Page50Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
NAS Signaling (CS)UE MSC
CM Service Request
RRC and NAS signaling Connection Setup
Authentication Request
Authentication Response
Security Mode Command
Security Mode Command Complete
RAB Assignment
SetupCall Proceeding
Alerting
Connect Connect ACKDisconnect
ReleaseRelease Complete
UE Outgoing Call UE Terminating Call
UEMSC
Paging Response
Authentication Request
Authentication Response
Security Mode Command
Security Mode Command Complete
RAB Assignment
SetupCall Confirmed
Alerting Connect
Connect ACKDisconnect
ReleaseRelease Complete
Paging
RRC and NAS signaling Connection Setup
Authentication and security flow are optional.CN does not need to the CM Service Response if the security mode is used.
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NAS Signaling (PS)UE SGSN
Service Request
RRC and NAS signaling Connection Setup
Authenticate and Ciphering Req
Security Mode Command
Security Mode Command Complete
RAB Assignment
Service Accept
Activate PDP Context Req
Activate PDP Context Accept
Deactivate PDP Context Req
Deactivate PDP Context Accept
UE Outgoing Call
Authenticate and Ciphering Rsp
UE Terminating Call
UE
Service Request
Authenticate and Ciphering Req
Security Mode Command
Security Mode Command Complete
RAB Assignment
Request PDP Context Activation
Activate PDP Context Req
Activate PDP Context Accept
Deactivate PDP Context Req
Deactivate PDP Context Accept
Paging
RRC and NAS signaling Connection Setup
SGSN
Authenticate and Ciphering Rsp
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UE to UE CS Call Process (1)
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UE to UE CS Call Process (2)
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UE to UE CS Call Process (3)
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UE to UE CS Call Process (4)
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UE to UE CS Call Process (5)
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UE to UE CS Call Process (6)
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UE to UE CS Call Process (7)
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Activate PDP Context from UE (1)
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Activate PDP Context from UE (2)
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Activate PDP Context from Network (1)
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Activate PDP Context from Network (2)
Page63Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
3. UTRAN Signaling Procedure
3.1 System Information Broadcast
3.2 Paging
3.3 Call Process
3.4 Handover
Page64Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Concepts about Soft Handover
Soft handover: the signals from different NodeBs are
merged in RNC
Softer handover: the signals from different cells, but from
the same NodeB are merged in NodeB
In the WCDMA system, since the intra-frequency exists among neighboring cells, the UE can communicate with the network via multiple radio links, and can select one with good signal quality by comparison when these radio links are merged, thus optimizing the communication quality. The soft handover can be conducted only in the FDD mode. The soft handover falls into the following cases according to the locations of the cells. The first case is the soft handover among difference cells of the Node B. In this case, the radio links can be merged within the Node B or the SRNC. If they are merged within the Node B, it is called softer handover. The second case is the soft handover among different Node Bs within the same RNC and among different RNCs.
An important issue during the soft handover is the merge of multiple radio links. In the WCDMA system, the MACRO DIVERSITY technology is adopted for the merge of the radio links, that is, the system compares the data from different radio links based on certain standards (such as BER), and selects the data with better quality to send to the upper layer.
Soft handover:
Selection combination in uplink
Maximum combination in downlink
Softer handover
Maximum combination in uplink and downlink
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Soft Handover Flow (Intra-RNC)
Before Handover After Handover
SRNC
NodeBNodeB
SRNC
NodeBNodeB
SRNC
NodeBNodeB
During Handover
CNCN CN
During the soft handover, two or more radio links are connected with UE, and data in each RL are same.
The following are some key concepts about the neighboring cell in the soft handover:
Active set: The set of cells currently used by the UE. The execution result of the soft handover indicates the increase or decrease of the cells in the active set.
Monitor set: The set of cells that are not in the active set but are being observed by the UE based on the neighboring cell information from the UTRAN. The UE measures the cells in the observation set. When the measurement results satisfy certain conditions, the cells may be added to the active set. Therefore, the observation set sometimes is also called the candidate set.
Detected set: The set of cells that have been detected by the UE but do not belong to the active set or the observation set. The UTRAN can request the UE to report the measurement result of the detected set. Since the cells in the detected set are not listed in the neighboring cell list, this set is also called the unlisted set.
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Soft Handover Flow
RNC (SRNC)
AirBridgeAirBridge
AirBridgeAirBridge
AirBridgeAirBridge
Core NetworkCore Network
Node B
It is no handover in this slide, only one radio links is connected with UE.
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Soft Handover Flow
RNC (SRNC)
AirBridgeAirBridge
AirBridgeAirBridge
AirBridgeAirBridge
Merged in NodeB
Core NetworkCore Network
Node B
It is softer handover. During the handover, the cells in active set belong to one NodeB. The NodeB uses the RAKE receiver to combine the data, and the UE also combines the data in RAKE receiver.
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Soft Handover Flow
Merged in RNC
RNC (SRNC)
AirBridgeAirBridge
AirBridgeAirBridge
AirBridgeAirBridge
Core NetworkCore Network
Node B
It is soft handover. During the handover, the cells in active set belong to one RNC, but different NodeBs. So the UE can combine the data in RAKE receiver. But in uplink, the data are combined with selection combination in RNC.
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Soft Handover Flow (SRNC-DRNC)
Merged in SRNC
Node B
AirBridgeAirBridge
AirBridgeAirBridge
AirBridgeAirBridge
Serving RNC
Drift RNC
Core NetworkCore Network
It is soft handover. During the handover, the cells in active set belong to different RNCs. So the UE can combine the data in RAKE receiver. But in uplink, the data are combined with selection combination in SRNC.
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Soft Handover Flow (SRNC Relocation)
Node B
AirBridgeAirBridge
AirBridgeAirBridge
AirBridgeAirBridge
Serving RNC
RNC
Core NetworkCore Network
There is no handover, but the SRNC has been changed.
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Typical Soft Handover Flow (L3 Signaling)
Soft handover is triggered by 1A/1B/1C or 1D event
Measurement Report (1A/1B/1C or 1D)
Measurement Control
RRC Connection Setup Procedure
RNCUE
Active Set Update
Active Set Update Complete
Measurement Control
The soft handover procedure comprises the following steps:
Based on the Measurement Control information from the RNC, the UE measures the intra-frequency neighboring cells, and reports the measurement result to the RNC via Measurement Report.
The RNC compares the reported measurement result with the set threshold to decide the cells to be added and deleted.
(If some cells are to be added, the RNC notifies the Node B to get ready. )
The RNC notifies the UE to add and/or delete cells via the Active Set Updatemessage.
After the UE successfully update the active set, UE will send Active Set UpdateComplete to inform RNC.
(if the cells are deleted, the Node B will be notified to release the corresponding resources. )
After the soft handover, perhaps the measurement control information changes, if it is, RNC will send new Measurement Control to UE.
The original communication is not affected during the soft handover procedure so that smooth handover from a cell to another can be successfully completed.
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Soft Handover Flow (Add Branch in AS)
For adding a cell into Active Set, RNC will notify NodeB to prepare the new RL before sending Active Set Update.
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Soft Handover Flow (Del Branch from AS)
For deleting a cell from Active Set, RNC sends Active Set Update to UE first. After UE deleting the RL successfully, RNC will inform NodeB to delete the RL.
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Hard Handover
Before Handover After Handover
Radio Link can not exist simultaneously
SRNC
NodeBNodeB
SRNC
NodeBNodeB
CNCN
It is hard handover. The UE disconnects the original radio link, then connects to the target cell. It happens in intra-frequency, inter-frequency and inter-RAT.
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Intra-Frequency Hard Handover
Intra-Frequency hard handover is triggered by 1D event
Measurement Control (Intra-freq)
RRC Connection Setup Procedure
RNCUE
Measurement Control (Intra-Freq)
Physical Channel Reconfiguration
Physical Channel Reconfiguration Complete
Decision to setup new RL
Measurement Report (1D)
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Inter-frequency Handover
Measurement Report(2D)
Measurement Control (Intra-freq)
RRC Connection Setup Procedure
RNCUE
Measurement Control (Inter-Freq)
Decision to enter compress mode
Physical Channel Reconfiguration
Physical Channel Reconfiguration Complete
Measurement Report
Decision to setup new RL
Measurement Control (2D & 2F)
Physical Channel Reconfiguration
Physical Channel Reconfiguration Complete
Measurement Control (Intra-freq)
Description:
Step 1 to step 5 is similar with soft handover, the differences are:
The SRNC sends the Physical Channel Reconfiguration message carrying the target cell information to the UE via the downlink DCCH.
After the UE hands over from the source cell to the target cell, the Node B of the source cell detects the radio link communication failure and then sends the Radio Link Failure Indication message to the SRNC, indicating the radio link failure.
After successfully handing over to the target cell, the UE sends the Physical Channel Reconfiguration Complete message to the SRNC via the DCCH, notifying the SRNC that the physical cannel reconfiguration is complete.
The Node B where the source cell is deletes the radio link resources, and then responds to the SRNC with the Radio Link Deletion Response message.
The SRNC adopts the ALCAP protocol to release the Iub interface transport bearer of the SRNC and the Node B where the source cell is.
Page77Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Inter-RAT Handover Flow (UMTS->GSM)
Measurement Report(2D)
Measurement Control (Intra-freq)
RRC Connection Setup Procedure
RNCUE
Measurement Control (Inter-RAT)
Decision to enter compress mode
Physical Channel Reconfiguration
Physical Channel Reconfiguration Complete
Measurement Report (GSM)Decision to
handover to GSM
Measurement Control (2D & 2F)
Relocation Required
3G MSC3G MSC
Prepare Handover
BSC
Handover Request
Handover Request ACKPrepare Handover
ResponseRelocation Command
Inter-System Handover Command
Handover Complete
Handover CompltetSend END
Signal RequestIu Release Command
Iu Release Complete
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Inter-RAT Handover Flow (GSM->UMTS)
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Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA HSDPA Principles
Page1Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Course Learning ObjectivesReview WCDMA and HSDPA evolution and standards
Define HSDPA protocol stack
Describe new channels for HSDPA
Explain the physical channel processing
HSDPA impact on protocol stack
Identify HSDPA UE categories
Define HSDPA protocols of Mac sub-layer
Page2Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
References3GPP Release 6 Specification References
TS 25.308 HSDPA overall description stage2
TS 25.211 Physical channel and mapping of transport channels onto physical channel (FDD)
TS 25.212 Multiplexing and channel coding (FDD)
TS 25.213 Spreading and modulation (FDD)
TS 25.214 Physical layer procedure (FDD)
TS 25.306 UE radio access capabilities
TS 25.321 Medium Access Control (MAC) protocol specification
TS 25.322 Radio Link Control (RLC) protocol specification
TS 25.331 Radio Resource Control (RRC) protocol specification
Page3Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channels
4. HSDPA Physical Layer Processing
5. HSDPA Layer2 Protocol
Page4Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Evolution
14.4Mbps10.0MbpsHSDPA
2.0Mbps384kbpsR99 WCDMA
473kbps120kbpsEDGE
171kbps40kbpsGPRS
9.6kbps9.6kbpsGSM
Downlink Peak Data Rate (Theoretical Maximum)
Downlink Peak Data Rate (Typical Deployment)
GSMGSM GPRSGPRS
EDGEEDGE
WCDMA WCDMA R99R99
HSDPA HSDPA R5R5
HSUPA HSUPA R6R6
WCDMA Evolution
WCDMA evolved from GSM/GPRS, inheriting much of the upper layer functionality directly from those systems. The first commercial deployments of WCDMA are based on a version of the standards called Release 99.
Enhanced Data rates for GSM Evolution (EDGE) is another system in the GSM/GPRS family that some operators have deployed as an intermediate step before deploying WCDMA.
HSDPA was introduced in WCDMA Release 5 to offer higher speed Downlink data services.
Release 6 introduces the Enhanced Uplink (i.e. HSUPA) that will provide faster data services for the Uplink.
Page5Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
High Speed Downlink Packet Access
What are the benefits of HSDPA
Higher Data Rates
Peak data rate up to 14Mbps per user
Higher Capacity
More subscribers and throughput
Further reduces the cost per megabyte
Richer Application
Low latency – improvement for
streaming ,interactive, background
applications
Data Services and High Speed Downlink Packet Access (HSDPA)
Data Services are expected to grow significantly within the next few years. Current 2.5G and 3G operators are already reporting that a significant proportion of usage is now due to data, implying an increasing demand for high-data-rate, content-rich multimedia services. Although current Release 99 WCDMA systems offer a maximum practical data rate of 384 kbps, the 3rd Generation Partnership Project (3GPP) have included in Release 5 of the specifications a new high-speed, low-delay feature referred to as High Speed Downlink Packet Access (HSDPA).
HSDPA provides significant enhancements to the Downlink compared to WCDMA Release 99 in terms of peak data rate, cell throughput, and round trip delay. This is achieved through the implementation of a fast channel control and allocation mechanism that employs such features as Adaptive Modulation and Coding and fast Hybrid Automatic Repeat Request (HARQ). Shorter Physical Layer frames are also employed.
Page6Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
How is Packet Data handled in Release 99 (FDD) ?
DCH ( Dedicated Channel )
Spreading codes assigned per user
Closed loop power control
Soft handover
FACH ( Common Channel )
Common Spreading code
No closed loop power control
No soft handover
Release 99 Packet Data
Node B
Node B
Release 99 Packet Data
There are different techniques defined in the Release 99 specification to enable Downlink packet data. Most commonly, data transmission is supported using either the Dedicated Channel (DCH) or the Forward Access Channel (FACH).
The DCH is the primary means of supporting packet data services. Each user is assigned a unique Orthogonal Variable Spreading Factor (OVSF) code dependent on the required data rate. Fast closed loop Power Control is employed to ensure that a target Signal to Interference Ratio (SIR) is maintained in order to control the block error rate (BLER). Macro Diversity is supported using soft handover.
Data transfer can also be supported on the FACH. This common channel employs a fixed OVSF code. As it needs to be received by all UEs, higher data rates are generally not supported. Macro Diversity is also not supported and the channel operates with a fixed (or slow changing) power allocation. Each data block contains a unique UE identifier that allows a given UE to keep itsown data and discard that belonging to other UEs.
Page7Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Release 99 Downlink LimitationDedicated Channel Features ( DCH )
Maximum implemented downlink of 384kbps
OVSF code limitation for high data rate users
Rate change according to burst throughput is slow
Outer loop power control responds slowly to channel
Common Channel Features ( FACH )Good for burst data application
Only low data rates supported
Fixed transmit power
Release 99 Downlink Limitations
1. Although WCDMA Release 99 standard allows for maximum data rates of up to 2.0 Mbps, it has only been widely implemented with a maximum data rate of 384 kbps. This data rate is achieved by allocating a dedicated channel to each user. The use of dedicated resources can be a limitation, especially for data applications with burstycharacteristics. Each dedicated channel uses an OVSF code. Shorter codes are used for higher data rates and longer codes for lower data rates. When an OVSF of a particular length is used, all longer OVSF codes derived from that code become unavailable. This limits the number of simultaneous high speed data users in a given cell. The Release 99 standards provide support for a Secondary Scrambling Code, which eases this limitation, but it has not been widely implemented in commercial systems and will likely be removed from future versions of the specification. The data rate of a dedicated channel can be adjusted to accommodate varying requirements of a data service application, but the procedure for doing so is slow and thus inefficient. Capacity is controlled both by the maximum amount of PA power that is available and by the power requirement of each data service. In dedicated mode, fast power control is used so that a target Eb/No is achieved on the Downlink. However, the required Eb/No set point changes at a much slower rate. This can result in wasted resources whereby a better than required Eb/No is achieved for the required BLER.
Page8Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
High Speed Downlink Packet AccessThe differences between HSDPA and R99
Set of high data rate channel
Channels are shared by multiple users
Each user may be assigned all or part of the resource every 2ms
HSDPA user#1HSDPA user#2HSDPA user#3HSDPA user#4
Node B
a set of HS-PDSCHs
Code multiplexing for HSDPA
2ms
“Big shared pipe”
High Speed Downlink Packet Access (HSDPA)
In HSDPA, the NodeB allocates a set of high speed channels. These channels are assigned to a user using a fast scheduling algorithm that allocates the channels every 2 ms. All or part of the channels may be assigned to a given user during any 2 ms period.
The rapid scheduling of HSDPA is well-suited to the bursty nature of packet data. During periods of high activity, a given user may get a larger percentage of thechannel bandwidth, while it gets little or no bandwidth during periods of low activity.
Page9Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
High Speed Downlink Packet AccessHow will HSDPA figure out the limitations of R99
Adaptive modulation and coding
Fast feedback of Channel condition
QPSK and16QAM
Channel coding rate from 1/3 to 1
Multi-code operation
Multiple codes allocated per user
Fixed spreading factor
NodeB fast Scheduling
Physical Layer HARQ ( Hybrid Automatic Repeat reQuest )
HSDPA Basic Concepts
In HSDPA a common channel with fixed power is employed for data transfer. Users are separated in both the time and code domains. A fixed spreading factor is employed but multi codes operation is possible for increased data rates.
Adaptive Modulation and Coding (AMC) replaces the role of power control so that the modulation and coding rate are changed depending on the channel condition.
This is accomplished by locating the scheduling algorithm for channel allocation at the NodeB instead of the RNC in Release 99.
Page10Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
High Speed Downlink Packet Access
Comparison Summary
HighLowMediumData Rate
GoodGoodPoorSuitability for Bursty
Not SupportedNot SupportedSupportedSoft Handover
Fixed Power with link
adaptationNo
Closed Inner Loop at 1500Hz & Closed Outer
Loop
Power Control
SharedSharedDedicatedChannel TypeHSDPAFACHDCHMode
Comparison Summary
DCH and FACH are the two Release 99 channels typically used for packet switched data in practice. The advantages and disadvantages of each approach are apparent. Whereas DCH is suited for medium high data rates (with a maximum rate of 384 kbps), rate switching is slow, making it unsuitable and inefficient for bursty data such as a Web browsing application. By contrast, FACH provides good support for bursty data but is a common channel without power control or other mechanism to account for channel conditions. This makes it unsuitable for higher data rates. Switching from DCH to FACH is slow and inefficient, due in part to the typical timer values used to detect inactivity
HSDPA is suitable to high date rates for a bursty application, though we will see that the absence of soft handover makes it more suitable for stationary or low-mobility users than for highly mobile users. HSDPA typically operates at a fixed power, but feedback from the UE can instruct the NodeB to use lower power when the UE is in good channel conditions. Link adaptation is used to adjust data rate, coding, and modulation to quickly respond to changing channel conditions.
Page11Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channels
4. HSDPA Physical Layer Processing
5. HSDPA Layer2 Protocol
Page12Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HSDPA Key Techniques
AMC (Adaptive Modulation & Coding)Data rate adapted to radio condition on 2ms
Fast Scheduling based on CQI and fairness
Scheduling of user on 2ms
HARQ(Hybrid ARQ)with Soft combing
Reduce round trip time
16QAM16QAM in complement to QPSK
for higher peak bit rates
SF16, 2ms and CDM/TDMDynamic shared in Time and code domain
3 New Physical Channels
Block 1 Block 2Block 1
Block 1?
Block 1Block 1?
+
Page13Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Adaptive Modulation and CodingAMC ( Adaptive Modulation and Coding ) in accordance with CQI
( Channel Quality Indicator )
Adjust data rate to compensation channel condition
Good channel condition – higher data rate
Bad channel condition – lower data rate
Adjust channel coding rate to compensation channel condition
Good channel condition – channel coding rate is higher e.g. 3/4
Bad channel condition –channel coding rate is higher e.g. 1/3
Adjust the modulation scheme to compensation channel condition
Good channel condition – high order modulation scheme e.g. 16QAM
Bad channel condition – low order modulation scheme e.g. QPSK
Page14Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Adaptive Modulation and CodingAMC ( Adaptive Modulation and Coding ) based on CQI ( Channel Quality Indicator )
CQI ( channel quality indicator )
UE measures the channel quality and reports to NodeB every 2ms or more cycle
NodeB selects modulation scheme ,data block size based on CQI
Bad channel condition→ More power Node B Node B
Power Control Rate Adaptation
Good channel condition
Bad channel condition
Good channel condition→ less power
→ low data rate
→ high data rate
Page15Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
CQI mapping table for UE category 10
Out of rangeOut of rangeN/AN/A00
001616--QAMQAM151525558255583030
001616--QAMQAM151524222242222929
001616--QAMQAM151523370233702828
……………………………………………………
001616--QAMQAM55466446641818
001616--QAMQAM55418941891717
001616--QAMQAM55356535651616
00QPSKQPSK55331933191515
00QPSKQPSK44258325831414
00QPSKQPSK44227922791313
……………………………………………………
00QPSKQPSK1117317322
00QPSKQPSK1113713711
Reference power Reference power
adjustment adjustment ΔΔModulationModulation
Number of Number of
HSHS--PDSCHPDSCHTransport Transport
Block SizeBlock SizeCQI valueCQI value
CQI Mapping Table
The CQI table consists of 30 entries, where each entry indicates a different TFRC. Transport Format Resource Combination (TFRC) points to the combination of number of HS-PDSCH channelization codes, modulation scheme, and the HS-DSCH transport block size. The 5-bit CQI reported by a UE is an index into this table containing all possible TFRC combinations for that UE category. The TFRC combinations are different for UEs with different HS-DSCH UE categories because of the differences in the UE capabilities. Along with TFRC, CQI may also indicate a power offset relative to the current HS-PDSCH power. The CQI table shown in the slide is for UE categories supporting up to 15 HS-PDSCH codes (HSDPA terminal category 10)
Page16Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HSDPA UE Categories
28800363015Category 12
14400363025Category 11
17280027952115Category 10
17280020251115Category 9
13440014411110Category 8
11520014411110Category 7
67200729815Category 6
57600729815Category 5
38400729825Category 4
28800729825Category 3
28800729835Category 2
19200729835Category 1
Total Number of Soft Channel Bits
Maximum Number of Bits of an HS-DSCH Transport
Block Received Within an HS-DSCH TTI
Minimum Inter-TTI Interval
Maximum Number of HS-DSCH Codes
Received
UE Category
HSDPA RF performance depends on UE capability
UE Categories
HSDPA is advertised with data rates up to 14 Mbps. However, the actual HS-DSCH peak data rate depends on the UE’s HS-DSCH category. As shown in the table, only a category 10 UE can achieve the maximum HSDPA throughput of 14 Mbps when using all 15 HS-PDSCHs simultaneously.
Factors that decide the UE’s HS-DSCH category are:
HS-PDSCH codes – Determines the number of simultaneous HS-PDSCH channels that can be decoded by a UE.
Inter-TTI interval – Determines the minimum interval (in terms of HS-DSCH TTI) between two successive HS-PDSCH assignments. The more HARQ processes a UE supports, the shorter the inter-TTI interval. A minimum inter-TTI of 1 requires at least 6 simultaneous HARQ processes.
Transport Block size – Determines the maximum size of transport block that can be sent on HS-DSCH in a TTI. It is dependent on the number of HS-PDSCH codes and the modulation scheme.
IR buffer size – Determines the maximum number of soft bits that can be bufferedby a UE across all simultaneously running HARQ processes.
Page17Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Hybrid Automatic Repeat reQuestConventional ARQ
In a conventional ARQ scheme, received data blocks that can not be correctly decoded are discarded and retransmitted data blocks are separately decoded
Hybrid ARQ ( HARQ )
In case of Hybrid ARQ with soft combining, received data blocks that can not be correctly decoded are not discarded. Instead the corresponding received signal is buffered and soft combined with later received retransmission of information bits. Decoding is then applied to the combined signal
Page18Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Hybrid Automatic Repeat reQuestExample for HARQ
The use of HARQ with soft combining increases the effective received
Eb/Io for each retransmission and thus increases the probability for
correct decoding of retransmissions, compare to conventional ARQ
The maximum retransmission amount of HARQ procedure can be set. (NodeB LMT)
Page19Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Hybrid Automatic Repeat reQuestThere are many different schemes for HARQ with soft combining
These schemes differ in the structure of retransmissions and in the way by which the soft combining is carried out at the receiver
In case of Chase combining ( CC ) each retransmission is an identical copy of the original transmission
In case of Incremental Redundancy ( IR ) each retransmission may add new redundancy
HARQ is a technique that transmitter sends new set of parity bits if the previous transmission failed (NACK) and receiver buffer the failed decodes for soft combining with later retransmission.
Example for Chase Combining ( CC ) Scheme
Example for Incremental Redundancy ( IR ) Scheme
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Hybrid Automatic Repeat reQuestEach HSDPA assignment is handled by a HARQ process
HARQ processes run in NodeB and UE
The UE HARQ process is responsible for:
Attempting to decode the data
Deciding whether to send ACK or NACK
Soft combining of retransmitted data
The NodeB HARQ process is responsible for:
Selecting the corrected bits to send according to the selected
retransmission scheme and UE capability
Hybrid Automatic Repeat Request (HARQ)
To support consecutive assignments, HSDPA defines a Hybrid Automatic Repeat Request (HARQ) protocol. This protocol is implemented in both the NodeB and the UE, and consists of procedures implemented in both the MAC-hs sublayer and the Physical Layer. When the NodeB assigns an HSDPA subframe to a UE, it also assigns a HARQ process to handle the data transfer. The UE HARQ process is responsible for
Decoding the initial transmission
Sending an ACK or NACK
Soft-combining retransmissions of the data packet until it is successfully decoded or until NodeB aborts the packet
The maximum number of HARQ processes that a UE supports is a function of its HSDPA category. The minimum number of HARQ processes supported by any UE is 2, which corresponds to a UE that uses an inter-TTI interval of 3.
Page22Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Short TTI (2ms) Shorter TTI ( Transmission Time Interval ) is to reduce RTT
( round trip time )
Shorter TTI is necessary to benefit from other functionalities
such as AMC, scheduling algorithm and HARQ
Page23Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
In HSDPA, a new DL transport channel is introduced call HS-
DSCH. The idea is that a part of the total downlink code resource
is dynamically shared between HSDPA and Release 99
Shared Channel Transmission
Shared channel transmission implies that a certain amount of radio resource of a cell (code and power) is seem as a common resource that is dynamically shared between users.
Page24Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
In HSDPA, a new DL transport channel is introduced call HS-
DSCH. The idea is that a part of the total downlink power resource
is dynamically shared between HSDPA and Release 99
Shared Channel Transmission
Time
Allowed power for HSDPA
Total Power
DPCH
Power for CCH
Higher power utility efficiency
TimePower margin for DCH power control
Shared channel transmission implies that a certain amount of radio resource of a cell (code and power) is seem as a common resource that is dynamically shared between users.
The NodeB transmit power allocation algorithm is not specified by the standard, but two possible schemes are likely:
� Static – A fixed amount of power is allocated to HSDPA channels (i.e. the HS-PDSCHsand HS-SCCHs). Remaining power is distributed among common channels and power controlled dedicated channels. The overall transmit power fluctuates as a function of the power controlled channels.
� Dynamic – HSDAP( i.e.HS-PDSCH and HS-SCCH ) power is allocated dynamically as a function of the remaining available power, which fluctuates due to the power controlled dedicated channels. The overall transmit power of the cell remains constant.
The above diagram does not consider the Node B’s power margin, whereby the Node B’s power fluctuates. The Node Bpower doesn’t really remain constant, due to the peak-to-average ratio of transmit power.
Page25Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Shared Channel TransmissionThe codes are assigned to HSDPA user only when they are actually to be used for transmission, which leads to efficient code and power utilization
In HSDPA, the idea is that a part of the total downlink code resource is dynamically shared between a set of HSDPA users
There can be multiple (up to 15) HS-PDSCHs in a serving cell, which enables use of both time division and code division multiple access methods.
Page26Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Higher-Order Modulation SchemeHSDPA modulation scheme
QPSK
16QAM
WCDMA R99 uses QPSK data modulation for downlink transmission. To support higher data rate, higher order data modulation, such as 16QAM can be used.
Compared to QPSK modulation, higher order modulation is more bandwidth efficient i.e. can carry more bits per Hertz
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Fast Scheduling Fast scheduling is about to decided to which terminal the shared
channel transmission should be directed at any given moment
The basic idea of fast scheduling is to transmit at the fading peaks of the channel in order to increase the throughput and to use resource more efficiently. But this might lead to large variations in data rate of the users. The trade-off is between the cell throughput and fairness against users.
There are a number of scheduling algorithms that take into consideration the trade-off between throughput and fairness:
Round Robin (RR): radio resource are allocated to communication links on a sequential basis, not taking into account the instantaneous radio channel conditions experienced by each link.
Max C/I: for maximum cell throughput ,the radio resource should be as much as possible be allocated to communication links with the best instantaneous channel condition.
Proportional Fair (PF): allocates the channel to the user with relatively best channel quality.
Enhanced Proportional Fair (EPF): allocates the channel to the user according to relatively best channel quality, fairness, guarantee bit rate requirement.
Page28Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HSDPA New Physical Channels
Page29Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channels
4. HSDPA Physical Layer Processing
5. HSDPA Layer2 Protocol
Page30Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
R99 Physical Channels
Release 99 Channels
This diagram shows possible mappings of logical, transport, and physical channels in the control and user planes for UMTS Release 99.
Some channels exist only in Physical Layer (CPICH, SCH, DPCCH, AICH, PICH). These channels carry no upper layer signaling or user data.
Transport channels carry the following types of information:
Broadcast Control Channel (BCH) – Broadcast information that defines overall system configuration.
Paging Channel (PCH) – Paging notification messages. A Paging Indicator Channel (PICH) is associated with a PCH to allow a UE to quickly determine whether it needs to read the PCH during its assigned paging occasion.
Forward Access Channel (FACH) – Common Downlink signaling messages. Also carries dedicated Downlink signaling and user information to a UE operating in Cell_FACH state.
Random Access Channel (RACH) – Common Uplink signaling messages. Also carries dedicated Uplink signaling and user information to a UE operating in Cell_FACH state.
Dedicated Channel (DCH) – Dedicated signaling and user information for a UE operating in the Cell_DCH state. DCH is mapped to a Dedicated Physical Data Channel (DPDCH). An associated Dedicated Physical Control Channel (DPCCH) carries Physical Layer control information, such as power control commands.
Page31Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HSDPA Physical Layer ChannelsNew HSDPA Channels
High Speed Downlink shared Channel ( HS-DSCH )
Downlink Transport Channel
High Speed Shared Control Channel ( HS-SCCH )
Downlink Control Channel
High Speed Physical Downlink Shared Channel ( HS-PDSCH )
Downlink Physical Channel
High Speed Dedicated Physical Control Channel ( HS-DPCCH )
Uplink Control Channel
HSDPA introduces three new Downlink channels and one new Uplink channel:
High Speed Downlink Shared Channel (HS-DSCH) – A Downlink transport channel shared by several UEs. The HS-DSCH is associated with one or several Shared Control Channels (HS-SCCH). It operates on a 2 ms Transmission Time Interval (TTI).
High Speed Shared Control Channel (HS-SCCH) – A Downlink physical channel used to carry Downlink control information related to HS-DSCH transmission. The UE monitors this channel continuously to determine when to read its data from the HS-DSCH, and the modulation scheme used on the assigned physical channel.
High Speed Physical Downlink Shared Channel (HS-PDSCH) – A Downlink physical channel shared by several UEs. It supports Quadrature Phase Shift Keying (QPSK) and 16-Quadrature Amplitude Modulation (16-QAM) and multi-code transmission. It is allocated to a user at 2 ms intervals.
High Speed Dedicated Physical Control Channel (HS-DPCCH) – An Uplink physical channel that carries feedback from the UE to assist the Node B’s scheduling algorithm. The feedback includes a Channel Quality Indicator (CQI) and a positive or negative acknowledgement (ACK/NACK) of a previous HS-DSCH transmission.
Page32Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HSDPA Physical Channels
HSDPA Channels (continued)
Only dedicated logical user data channels may be mapped to HS-DSCH. When DTCH is mapped to HS-DSCH, only Unacknowledged Mode (UM) and Acknowledged Mode (AM) channels may be used.
A UE operating in HSDPA mode also has at least one Release 99 dedicated channel (DCH/DPDCH) allocated, to ensure that RRC and NAS signaling can always be sent, even if the UE is not able to receive the high speed channels.
The HS-DPCCH is a Physical Layer control channel. It carries no upper layer information, and therefore has no logical or transport channel mapping.
Page33Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Physical layer Frame DurationFrame Duration
10ms radio frame, 15 slots
2ms HSDPA sub-frame, 3 slots
1 HS-DSCH Transport Time interval (TTI)
Slot Duration
2560chips per slot
7680 chips per HSDPA sub-frame
Symbol Timing
QPSK: 2bits / symbol
16QAM: 4bits / symbol
R99 radio frame
10ms
HSDPA sub-frame
2ms
Time slot
0.67ms
Physical Layer Frame Timing
A basic WCDMA radio frame is 10 ms long and has 15 slots. HSDPA introduces the notion of sub-frames within a WCDMA radio frame. An HSDPA sub-frame is 2 ms (3 slots) long and all the HS-channels use this sub-frame timing. The sub-frame allows fast user switching where the shared channel can potentially be assigned to a different user every sub-frame. As the HSDPA sub-frame is only 2ms long, it alleviates the need for power control. HS-DSCH has a fixed TTI of 2 ms. Each HS-DSCH transport block is mapped to an HS-PDSCH sub-frame. HS-SCCH and HSDPCCH also use the 2ms sub-frame to transmit control and feedback respectively.
Each HSDPA sub-frame has 3 slots and each slot is comprised of symbols. The number of symbols in a slot depends on the spreading factor used for that channel. HS-PDSCH, HS-SCCH,and HS-DPCCH use SF 16, 128, and 256 respectively, giving number of symbols per slot as 160 (HS-PDSCH), 20 (HS-SCCH), and 10 (HS-DPCCH).
A symbol is made up of 1 or more bits and each bit is spread using SF to an equivalent number of chips. A QPSK symbol consists of two consecutive bits, one bit each mapped onto the I and Q branch. A 16-QAM symbol, on the other hand, has four consecutive bits with two bits on each branch.
HSDPA use 2ms TTI. Shorter TTI mechanism can reduce the latency ,and then increase fast schedule times. Shorter TTI mechanism can better trace the variation of wireless environment
Page34Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-PDSCH sub-frame StructureHS-PDSCH sub-frame structure
3 time slots constituted one TTI (2ms) , only one TB will be sent during one TTI
Fixed spreading factor ( SF=16 )
May use QPSK or 16QAM modulation scheme
Up to 15 HS-PDSCH may be assigned simultaneously
UE capability indicated max. number of codes it supports
All HS-PDSCH used to carry user’s data
UE can be assigned multiple OVSF code ( SF=16 ) based on UE Categories
HS-PDSCH
When the UE decodes the HS-SCCH and determines that there is an HS-DSCH assignment in the next TTI, it decodes the assigned HS-PDSCHs. Each HS-PDSCH uses an OVSF of length 16. If multiple HS-PDSCHs are assigned simultaneously to one UE, they must use consecutive OVSF codes. The HS-SCCH indicates the first OVSF code and the number of codes for each assignment.
The High Speed Physical Downlink Shared Channel (HS- PDSCH) is used to carry the High Speed Downlink Shared Channel (HS-DSCH).
An HS-PDSCH may use QPSK, 16QAM or 64QAM modulation symbols. In above figure, M is the number of bits per modulation symbols i.e. M=2 for QPSK, M=4 for 16QAM and M=6 for 64QAM.
A UE is a member of one of 12 categories, as a function of its hardware capabilities. Each category represents different values of the following parameters:
Number of simultaneous HS-PDSCH codes (5, 10, or 15)
Maximum transport block size
Inter-TTI interval – minimum time between consecutive assignments.
Incremental redundancy buffer size – used to soft-combine symbols from retransmissions.
Page35Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-SCCH sub-frame StructureHS-SCCH sub- frame structure
3 time slots constitutes one TTI ( 2ms )
HS-SCCH SF=128, QPSK only, Fixed rate of 60kbps
HS-SCCH carries the following control messages: Xue, Xccs, Xms, Xrv, Xtbs, Xhap and Xnd
UE demodulates HS-SCCH sub-frame and find out the received data addressed to the UE with Xue. Then UE demodulates HS-PDSCH sub-frame with Xccs, Xms, Xrv, Xhap, Xtbs and Xnd are used for HARQ Process
UE may need to simultaneous monitor up to four HS-SCCHs
Xue [16bits]:UE identity, Multiple UEs may be monitoring the same set of HS-SCCHs. Each UE has an assigned identity called the H-RNTI.
Xccs [7bits]:channelization code set, The HS-SCCH indicates which of the OVSF codes allocated to the HS-PDSCHs will be used. HS-PDSCH uses multi-code transmission, which means that multiple OVSF codes may be assigned to one UE at the same time
Xms [1bit]:modulation scheme, HS-PDSCH uses either QPSK or 16-QAM modulation. This can change from one assignment to the next, and HS-SCCH indicates which method will be used.
Xrv[3bits]:redundancy version, The HARQ protocol supports retransmissions and incremental redundancy. These parameters allow the UE to differentiate new transmissions from retransmissions.
Xtbs [6bits]:transport block size, The HS-SCCH indicates how much data will be sent during the next assignment
Xhap [3bits]:HARQ process number
Xnd [1bit]:new data indicator
Page36Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-DPCCH sub-frame StructureHS-DPCCH sub-frame structure
TTI=2ms ( 3 time slots ), SF=256, Fixed rate of 15kbps, carry 2 types of HSDPA uplink physical layer control message, including ACK/NACK CQI
ACK and NACK notifies NodeB that UE has received correct downlink data or not. The field defines like this: 1-NACK, 0-ACK
CQI reflects physical channel quality indicator based on CPICH strength, and reported by period range from 0 to 160ms ( 0 means no transmission ). Usually the period is 2ms ( one TTI )
ACK/NACK and CQI having different function may be controlled independently by different parameters.
HS-DPCCH
Whenever the UE is operating in HSDPA mode, it uses the HS-DPCCH to give feedback to the serving Node B. This feedback consist of two parts:
ACK/NACK – The UE sends a positive or negative acknowledgement for each HS-DSCH assignment. UTRAN may configure the UE to repeat the ACK/NACK, up to a maximum of 4 transmissions. The first ACK/NACK for a given HS-DSCH assignment is sent 5 ms (7.5 slots) after the end of the HS-DSCH transmission.
Channel Quality Indicator (CQI) – The UE measures the channel quality of the Downlink CPICH and computes a CQI value. The value is an index into a table, and corresponds to the maximum data rate that the UE can decode with an error rate of less than 10%, assuming the channel conditions don’t change. UTRAN may configure the UE to repeat the CQI, up to a maximum of 4 transmissions. UTRAN may also configure the periodicity of CQI reporting, ranging from 2 ms to 160 ms.
Page37Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Uplink HS-DPCCH preamble and postamble
Transmit Preamble and Postamble on HS-DPCCH around ACK / NACK
Eases the decoding, which allows HS-DPCCH to operate at lower power
The general rule of when N_acknack_transmit > 1
In R5, whether the data is received by UE is judged based on ACK/NACK. Pre/Postamble is introduced since R6. Position is the 1st slot in HS-DPCCH sub-frame, same as ACK/NACK.
Advantage of Pre/PostambleMore coding gain is introduced, since Node B could judge whether the data is received by UE on the basis of more correlative slots If ensuring the same demodulation performance of ACK/NACK, PO (ACK/NACK) could be reduced. Accordingly, UL interference to be reduced
Problem of Pre/PostambleMore decoding complexity is introduced More power is consumed by UE to send Pre/Postamble
Page39Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Associated physical channel –A -DPCH
﹡Besides 3 physical channels on top. There is another physical channel named DPCH, which is a dedicated channel . DPCH is also called associated
channel used for signalling transmission and power control
﹡ DPCH does not carry service generally, sometimes carry real time (RT) service such as AMR service
UE
HSDPA Serving Cell
HS_DPCCHHS_PDSCH
HS_SCCH Downlink DPDCH&DPCCH (i.e.
associated DPCH)
Uplink DPDCH&DPCCH (i.e. associated DPCH)
When a DL RAB is mapped onto the HS-DSCH, UL DCH is set up regardless of the existence of UL data. UL DCH transmits the UL signaling, UL RLC acknowledgement message and possible UL service data. DL DCH is set up to transmit the DL signaling. These DCHs are called associated DCHs.
When the UE is in soft handover or softer handover, the HS-DSCH data can be transmitted only in the HSDPA serving cell while the DCH data can be transmitted in all the cells in the active set.
﹡ F-DPCH ( Fractional Dedicated Physical Channel ) is a new downlink physical channel in release 6. Release 6 supports mapping the SRB to the HS channels on both the Downlink and the Uplink (provided that HS channels are activated). This results in faster signaling and, for PS-only calls, the DCH (i.e. associated DCHs) is not reserved for signaling. To maintain closed loop power control functionality without the DCH (i.e. associated DCH), a new physical channel is introduced: the F-DPCH (Fractional DPCH).
Page40Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Fractional Dedicated Physical Channel (F-DPCH)
The F-DPCH is a new physical channel in Release 6
Purpose of F-DPCH introduction is to keep the closed loop power control working for HSDPA users without an assigned DPCH (A-DPCH)
The difference of HSDPA physical channels between Release5 and Release6
The Downlink A-DPCH occupies one code per user in the cell
The F-DPCH is a shared physical channel. It has only TPC bits information
The F-DPCH is a new physical channel in release 6. Huawei RAN10 product support this physical channel
The F-DPCH is a special case of the Downlink DPCCH. It has only TPC bits information; no Pilot or data fields are carried. It multiplexes the TCP bits for a maximum of 10 UEswith different frame offsets. The TPC bits forwarded on the F-DPCH are needed to control the power of the HS-DPCCH (Uplink channel)
Page41Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Fractional Dedicated Physical Channel (F-DPCH)
The F-DPCH carries control information generated at layer 1 (TPC commands). It is a special case of downlink DPCCH
Following figure shows the frame structure of the F-DPCH
Each frame of length 10ms is split into 15 slots, each of length Tslot = 2560 chips, corresponding to one power-control period, SF=256
Each user occupy one Symbol in one slot to bear TPC command, Pilot and TFCI is not needed
Up to 10 users can be multiplexed on one F-DPCH(Tx OFF) NOFF2 bits
Slot #0 Slot #1 Slot #i Slot #14
Tslot = 2560 chips
1 radio frame: Tf = 10 ms
TPC NTPC bits
(Tx OFF) NOFF1 bits
10 users can be multiplexed on one F-DPCH
Advantage of F-DPCH introduction
Code utilization efficiency is improved up to 90%, especially used for large number
of VoIP users
Problem of F-DPCH introduction
Code utilization efficiency could be downgraded in SHO due to the timing restrictions
on when TPC bits can be transmitted to UE’s in SHO zones
TPC
TPC
TPC
TPC
TPC
TPC
TPC
TPC
TPC
TPC
TPC
TPC
TPC
UE1
UE2
UE3
UE4
UE5
UE6
UE7
UE8
UE9
UE10
P-CCPCH frameoffset(256chip)
0
1
2
3
4
5
6
7
8
9
Page42Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HSDPA Physical Channels TimingStart of HS-SCCH is aligned with the start of PCCPCH
HS-PDSCH, subframe is transmitted two slots after the associated HS-SCCH subframe
H S-SC C H
H S-PD SC H
3 slo ts = 2 m s
D PC H
τD PC H
R adio fram e w ith (SFN m odulo 2) = 0 P -C C PC H
2 slo ts
3 slo ts = 2 m s
S lo t S lot S lot S lo t S lo t S lot S lot S lo t Slot S lot S lot S lo t Slot S lot S lo t
15 slo ts = 10 m s
Subfram e #0 Subfram e #1 Subfram e #2 Subfram e #3 Subfram e #4
R adio fram e w ith (SFN m odulo 2)=1 10 m s
Subfram e #0 Subfram e #1 Subfram e #2 Subfram e #3 Subfram e #4
H S-D PC C H 3 slo ts = 2 m s
~7.5 slo ts
HSPDA Channel Timing
HSDPA channel timing is based on a time interval of 2 ms, or 3 slots
1. The UE measures the Downlink channel quality and sends a CQI report on the HS-DPCCH. An ACK or NACK from a previously received block may also be included in this transmission
2. If the NodeB decides to send data to the UE, it will send information on the HS-SCCH to assign the physical channel and give the UE information about how the data was encoded. The earliest that this assignment can be made is in the sub-frame following the end of CQI report.
3. During the next 2ms HS-DSCH transmission time, one or more HS-PDSCHs carry the UE’s data. The HS-SCCH transmission overlaps the HS-PDSCH transmission
4. After the UE decodes the data, it sends an ACK or NACK on the HS-DPCCH. The UE must send the ACK or NACK 5ms(i.e. 7.5 slots) after the end of the HS-DSCH transmission. If the UE sends a NACK, the NodeBmay send the data again during a later time slot, or may choose not to retransmit the data. A CQI report may also be included in this transmission
Page43Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Theoretical HSDPA Maximum Data Rate
Theoretical HSDPA Maximum data rate is 14.4Mbps
How do we get to 14.4Mbps ?Multi-code transmission
NodeB must allocate all 15 OVSF codes ( SF =16 ) to one UE
Consecutive assignments using multiple HARQ processNodeB must allocate all time slots to one UE
UE must decode all transmission correctly on the first transmission
Low channel coding gainEffective code rate = 1
Requires very good channel conditions to decode
16QAMRequires very good channel condition
Theoretical HSDPA Maximum Data Rate
The theoretical maximum data rate is 14.4 Mbps. The following techniques are used to achieve this data rate:
Multi-code transmission – Up to 15 HS-PDSCH channels may be assigned to a single UE during one 2 ms TTI.
Consecutive assignments – The HARQ procedure allows the NodeB to send back-to-back assignments at 2 ms intervals.
Lower Coding Gain –Higher data rates can be achieved by puncturing more bits for a higher effective code rate (and thus lower coding gain).
16-QAM – This modulation scheme increases the data rate over QPSK by a factor of 2.
Page44Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
More Data Rate Factors More factors that affect HSDPA data rate
Inter- TTI interval
Retransmission
ACK / NACK Repetition
Assuming
5 OVSF code for HS-PDSCH
Consecutive assignment
QPSK
Turbo code rate =1/3
Retransmission
75% of data block decoded on first transmission
25% of data block decoded on second transmission
Other factors that influence the maximum data rate are:
Inter-TTI Interval – The interval between consecutive assignments is called the inter-TTI interval. If the UE supports an inter-TTI interval of 1, then it is capable of receiving a new HSDPA assignment every 2 ms. Allowed values of the inter-TTI interval are 1, 2, and 3
Retransmissions – If the UE NACKs a transmission, the NodeB may retransmit that data in a subsequent assignment. The retransmission may consist of identical symbols that were sent previously, or may be a different redundancy version of the turbo coded output symbols
ACK/NACK Repetition – The NodeB may configure the UE to send the ACK/NACK transmission up to four times
Page45Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
More Data Rate Factors 5 OVSF code for HS-PDSCH
14.4Mbps / 3 = 4.8Mbps
QPSK
4.8Mbps / 2 = 2.4Mbps
Turbo code rate =1/3
2.4Mbps / 3 = 0.8Mbps
Retransmission
0.8Mbps × 0.8 = 640 kbps
54321
Decoded on 1st transmit Decoded on 2nd transmit
Page46Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channels
4. HSDPA Physical Layer Processing
5. HSDPA Layer2 Protocol
Page47Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HSDPA Physical Layer Model-Downlink
NodeB PHY UE PHY
HS-PDSCH – carries actual information payload from HS-DSCH
HS-SCCH – carries Physical Layer control information including HARQ
parameters, OVSF codes, and UE ID
HSDPA Physical Layer Model – Downlink
In 3GPP Release 5, two new Downlink physical channels have been introduced to enable HSDPA. In addition, the existing R99 channels are also required for HSDPA operation.
HS-PDSCH – Transmitted by NodeB to send HS-DSCH data to UEs in the HSDPA serving cell. Unlike a dedicated channel, this shared channel is assigned to a user for a 2ms period and may be assigned to another user in the next 2ms period. This fast scheduling rate is well suited for the bursty packet data and helps increase the capacity of a cell. There can be multiple (up to 15) HS-PDSCHs in a serving cell, which enables use of both time division and code
division multiple access methods. HS-PDSCH carries user data and has a transport channel HSDSCH mapped on it.
HS-SCCH – Transmitted by NodeB to signal control information to the users in the HSDPA serving cell. This channel is shared by multiple users and the control information sent on it is masked with a UE ID. The mask allows a UE to identify if there is HS-DSCH data for it in the upcoming HS-PDSCH sub-frame and the control information tells how to decode that data. HS-SCCH does not have a transport channel mapped on it.
Page48Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HSDPA Physical Layer Model-Uplink
NodeB PHY UE PHY
HS-DPCCH – carries feedback signaling consisting of HARQ acknowledgement and channel quality indicator (CQI)
HSDPA Physical Layer Model – Uplink
In 3GPP Release 5, there is one new Uplink physical channel. The existing R99 channels are required for the HSDPA operation.
HS-DPCCH – Transmitted by the UE to signal feedback information to Node B. The feedback information consists of:
1. acknowledgement of data received by the UE on HS-PDSCH
2. Downlink channel quality indicator (CQI)
NodeB uses this feedback information to send retransmissions and to schedule HS-PDSCH transmissions to UEs. HS-DPCCH doesn’t carry any higher layer control or traffic and doesn’t have a transport channel mapped on it.
Page49Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Downlink HS-PDSCHHigh Speed Physical Downlink Shared Channel (HS-
PDSCH)
Fixed SF 16 with 3 slots format
Uo to 15 HS-PDSCH under one cell
May use QPSK or 16QAM modulation scheme
DL HS-PDSCH – High Speed Physical Downlink Shared Channel
An HS-PDSCH channel carries the actual user payload to the UE. One HS-PDSCH subframe contains one TTI (2 ms) of HS-DSCH transport channel payload. There is no transport channel multiplexing in HSDPA so the information contained in HS-PDSCH subframe is from a single
HS-DSCH transport channel.
An HS-DSCH serving cell can have as many as 15 channelization codes assigned to HS-PDCH. The HS-PDSCH channels are shared among different users by using time division, code division or a combination of the two multiple access methods. The number of HS-PDSCHs that can be simultaneously decoded by a UE depends on the HS-DSCH UE Category.
The phase reference used for demodulating HS-PDSCH is the same as for the associated DL DPCH. By default, P-CPICH is used as the phase reference.
Page50Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Downlink HS-PDSCHHS-DSCH Processing chain
New Physical Layer Procedures in
Release 5
Bit Scrambling
Physical Layer HARQ functionality
HS-DSCH interleaving
Constellation re-arrangement for 16QAM
The HS-DSCH channel coding involves a number of other functions performed by the NodeB’s Physical Layer. The main reason for this additional processing is the dynamic size of the transport block transmitted in an HS-DSCH TTI. Other reasons include large HS-DSCH payload size and the possible use of 16-QAM modulation for HS-PDSCH. Comparing the coding chain for the Release 99 channel with the Release 5 HS-DSCH channel, some blocks have been removed and some new blocks have been added.
HS-DSCH coding chain does not require:
1. Concatenation, because there is always only one transport block per HS-DSCH TTI. The transport block size, however, varies from 137 bits to 27952 bits. In case of retransmission, the transport block size remains the same as of the original transmission.
2. First DTX insertion, because HS-DSCH doesn’t support fixed position transport channel and thus Blind Transport Format Detection (BTFD).
3. Second DTX insertion, because there is just one transport channel mapped on to HS-PDSCH.
4. Radio frame segmentation, because HS-DSCH has a fixed TTI of 2 ms, which is equal to the HS-PDSCH sub-frame duration.
5. Transport channel multiplexing, because there is just one transport channel mapped on to HS-PDSCH.
Page51Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-DSCH Channel CodingMac delivers one HS-DSCH TB per TTI to Physical Layer
CRC Attachment
24 bits CRC added per TB
Bit Scrambling
Facilitates uniform distribution of 16- QAM symbols at receiver
Code Block Segmentation
Turbo encoder has a fixed max. code block size of 5114 bits
If bit scrambled data is more than 5114 bits, need to segment into equal code blocks
HS-DSCH Channel Coding
NodeB’s MAC-hs delivers the HS-DSCH transport channel data to the Physical Layer in NodeB. The Physical Layer then performs a number of functions on the HS-DSCH TTI data before the data is finally mapped to one or more HS-PDSCH physical channels.
CRC Attachment – A fixed 24-bit Cyclic Redundancy Check (CRC) is attached to HS-DSCH TTI data. There is only one transport block per HS-DSCH TTI.
Bit Scrambling – Done to avoid non-uniform symbol distribution over 16-QAM constellation at the receiver. A uniform symbol distribution helps the UE efficiently decode the received HS-DSCH bits. Typically, the received symbols are uniformly distributed over the entire constellation. However, certain degenerate HS-DSCH bit sequences (e.g., the all-ones or all-zeroes sequences) could violate this condition, leading to an asymmetric HS-DSCH bit distribution (over {0,1}) and hence a non-uniform 16-QAM symbol distribution at the receiver input. This is true regardless of the use of turbo-encoding on the HS-DSCH, due to the possibility of transmitting turbo-codewords comprised predominantly of systematic bits. The estimated performance loss due to the non-uniform distribution in such very unlikely cases is between
Code Block Segmentation – It is done if the number of bits output from the bit scrambler is more than the maximum input code block size of the FEC encoder. The maximum encoder code block size in case of HS-DSCH is 5114 bits. If segmentation is performed, all the resulting segments are of equal size and may require adding some filler bits to the beginning of 1st code block. The filler bits are all 0s and are transmitted along with data.
Page52Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-DSCH Channel CodingChannel Coding
Rate 1/3 Turbo coder used for Channel coding
Effective code rate changes after HARQ
HS-DSCH Channel Coding (continued)
FEC Coding – Rate 1/3 turbo coder is used for encoding HS-DSCH bits. FEC coding is done on one or more code blocks, where code blocks are formed by segmenting bit scrambled HS-DSCH data (if more than 5114 bits). The output from turbo coder consists of Systematic bits (original input data bits) and Parity bits. For each input bit, there is 1 Systematic bit and 2 Parity bits.
Twelve tail bits are added per block after encoding for the trellis termination. The encoded blocks, when more than one, are serially concatenated and fed to the HARQ block. The code rate after turbo encoding is 1/3 but the effective coder rate after HARQ rate matching may be different. An effective code rate of close to 1 is required to achieve peak throughput of 14.4 kbps.
Systematicbits
Parity 1bits
Parity2bits
RM_P1_1
RM_P2_1
RM_P1_2
RM_P2_2
RM_S
First Rate Matching Second Rate MatchingVirtual IR Buffer
Nsys
Np1
Np2
Nt,sys
Nt,p1
Nt,p2
bitseparation
NTTIbit
collection
NdataC W
Page53Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-DSCH Channel CodingHybrid ARQ (HARQ)
Combines ARQ with adaptive channel
coding
NodeB sends new set of parity bits if
previous transmission failed (NACK)
UE buffers the failed decodes for soft
combining with future retransmission
Soft Combining is done before each
channel decoding attempt
HS-DSCH Channel Coding (continued)
Hybrid ARQ (HARQ) – HARQ is a technique combining FEC and ARQ methods that save information from previous failed decode attempts to be used in the future decoding. There are two different HARQ schemes, Chase Combine and IR, depending on which bits are chosen to be sent over the air to UE. The redundancy version (RV) parameters, r and s, indicate to the UE the HARQ scheme used for the current transmission.
Both HARQ combining schemes soft combine bits from the previous failed decodes with the currently received retransmission. Soft combining helps minimize the number of retransmissions. For a retransmission, HARQ uses the same transport block size and consequently the same number of HS-DSCH bits that were used in the initial transmission.
Page54Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-DSCH Channel Coding – Physical Layer HARQ Functionality
Physical Layer HARQ consists of two rate matching stages and a
virtual buffer
1st stage: matches number of input bits to the virtual IR buffer size
IR buffer size is determined by UE’s soft memory capability
Puncturing is done if inputs bits exceed the virtual IR buffer size
2nd stage: matches numbers of bits to the number of HS-PDSCH bits
in the given TTI
Redundancy Version (RV) parameters control the output from 2nd stage
Repetition or puncturing is done to perform 2nd stage rate matching
First Transmission
Always self-decodable, RV parameters s = 1
Chase Combining
Each retransmission is self decodable, RV parameter s = 1, Systematic bits are prioritized
Same coded data packet may be sent in each retransmission, Using the same RV parameter r in each retransmission
Retransmission with a different r value implies different set of punctured bits
Receiver attempts to decode by soft combining multiple copies
Incremental Redundancy (IR)
Retransmissions are not self decodable, RV parameter s = 0, Parity bits are prioritized
Redundant information is incrementally transmitted if initial decoding fails
Each retransmission provides additional redundant bits to the receiver
RV parameter r is different for different set of redundancy bits
Receiver attempts to decode based on accumulated bits
Systematicbits
Parity 1bits
Parity2bits
RM_P1_1
RM_P2_1
RM_P1_2
RM_P2_2
RM_S
First Rate Matching Second Rate MatchingVirtual IR Buffer
Nsys
Np1
Np2
Nt,sys
Nt,p1
Nt,p2
bitseparation
NTTIbit
collection
NdataC W
HS-DSCH Channel Coding – HARQ Combining Schemes
HARQ combining refers to the combining of the HS-DSCH soft bits in the receiver (UE). If an HS-DSCH sub-frame transmission is not correctly decoded (CRC failure) by the UE’s Physical Layer the soft bits from this failed decode are buffered in the IR buffer to be combined with the future retransmissions. This type of combining changes the effective received code rate with each retransmission and helps in minimizing the number of retransmissions. There are different types of HARQ combining schemes:
� Chase combining requires each retransmission to be self-decodable. The transmitter may retransmit the same coded data packet in which case the decoder at the receiver combines multiple copies of the same transmitted packet weighted by the received SNR. Time diversity gain is thus obtained. Using a different redundancy version parameter r, a different set of puncture bits can be used in each retransmission.
� Incremental Redundancy (IR) is another implementation of the HARQ technique where retransmissions are not self decodable, i.e., they may have a very low proportion (or none) of the systematic bits. Additional redundant information, prioritizing the parity bits, is incrementally transmitted if the decoding fails on the prior attempt. Retransmitted sub-frames are soft combined with the buffered soft bits to achieve additional coding gain, which helps the UE to successfully decode the sub-frame.
The RV parameter signaled to the UE indicates the HARQ scheme used, allowing the UE to use the same scheme for HARQ combining.
RV parameters mapping list (3GPP TS25.212)
Page56Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-DSCH Channel Coding –Segmentation and interleaving
Physical Channel SegmentationSegments data equally into P segments
P is number of HS-PDSCHs allocated to UEUp to 15
Total HS-PDSCH bits per TTI:
P * ( Number of bits per HS-PDSCH channel )
HS-DSCH interleavingBlock interleaving using 32*30 matrix
Write in rows, read out columns
Done separately on each HS-PDSCH
Page57Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-DSCH Channel Coding-16QAM Constellation Re-arrangement
Bit Reliability
change with bit position within a symbol
is different for 0 and 1 in case of i2 and q2
HS-DSCH Channel Coding – 16-QAM Constellation Rearrangement
An optional 16-QAM modulation scheme has been introduced for HS-PDSCH to achieve high data rates. Constellation rearrangement is required in the case of 16-QAM modulation because two of the four bits in a 16-QAM symbol have a higher probability of error than the other two bits. The rearrangement occurs during retransmission and disperses the error probability equally among all the bits when averaged over retransmissions.
The reliabilities of the bits mapped to the 16-QAM symbols vary from the most significant bits (i1, q1) to the least significant bits (i2, q2). These variations reduce the performance of the turbo decoder with respect to having equal bit reliabilities. By rearranging the signal constellation during retransmissions, the same bit gets placed at different positions within a symbol across different retransmissions and the bit reliabilities are averaged out over the retransmissions. For both Chase combining and IR, the decoder performance increases with the constellation rearrangement due to a more homogeneous input of log-likelihood values to the turbo decoder.
The bits output from the HS-DSCH interleaver are taken in groups of four consecutive bits (i1q1i2q2) and then rearranged based on the value of constellation version parameter b. NodeB signals this parameter to the UE on HS-SCCH channel so that the UE can undo this bit rearrangement. In case of QPSK modulation, the constellation rearrangement block is transparent.
Constellation re-arrangement for 16QAM [TS25.212]
Swapping MSBs with LSBs and inversion of logical values of LSBs3
Inversion of the logical values of LSBs2
Swapping MSBs with LSBs1
None 0
OperationOutput bit sequence constellation
version parameter b
3,2,1,, +++ kpkpkpkp vvvv
1,,3,2, +++ kpkpkpkp vvvv
3,2,1,, +++ kpkpkpkp vvvv
1,,3,2, +++ kpkpkpkp vvvv
Page59Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-DSCH Physical Channel Mapping
Bits are mapped to one or more HS-PDSCH
Same number of bits/sub-frame on each HS-PDSCH
HS-DSCH Physical Channel Mapping
After constellation rearrangement (only for 16-QAM) or HS-DSCH interleaving (for QPSK), the HS-DSCH bits are finally mapped to one or more HS-PDSCH channels. This is called Physical Channel Mapping. A UE may be assigned one or more HS-PDSCH codes depending on the UE capability, QoS requirement, and the NodeB’s radio resource availability. In case of more than one HS-PDSCH channel assigned to a UE, the number of bits in the given sub-frame on each
assigned HS-PDSCH channel is the same.
Page60Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Physical Layer Process Case for HS-DSCH
Page61Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Downlink HS-SCCHHigh Speed Shared Control Channel (HS-SCCH)
Fixed rate 60kbps (SF 128) channel with one slot format
UE may need to simultaneously monitor up to four HS-SCCHs
More than four HS-SCCHs possible under one cell
QPSK only
DL HS-SCCH – High Speed Shared Control Channel
The NodeB transmits control information required for detecting and decoding HS-PDSCH sub-frames to UEs on HS-SCCH channel. UEs are signaled to monitor a set of HS-SCCH channels containing up to a maximum of four HS-SCCHs. At any time, only one of the four HS-SCCHs contains information for a given UE. There may be more than four active HS-SCCHs under a cell. Multiple users are assigned to the same HS-SCCH (or set of HS-SCCHs) and thus a
UE can successfully decode the information on this channel only when the information is intended for that UE. The HS-SCCH information is scrambled with the UE ID, which enables the desired UE to successfully decode HS-SCCH. The reason for having multiple HS-SCCHs is to enable NodeB to address multiple UEs in the same sub-frame.
Page62Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Downlink HS-SCCHHS-SCCH Processing chain
HS-SCCH Channel Coding
Convolutional coding and CRC coding are used as the main channel coding schemes by NodeBforthe HS-SCCH channel. Part 1 and Part 2 of an HS-SCCH sub-frame are individually coded and mapped to the allocated slots in a sub-frame. Both Part 1 and Part 2 are scrambled with the UE ID. The UE ID used for scrambling HS-SCCH is a 16-bit HS-DSCH Radio Network Temporary Identity (H-RNTI).
Part 1 consists of the following information:
Channelization Code Set – Contains the number of in-sequence HS-PDSCH codes assigned to a UE and the offset of the first code.
Modulation Scheme – HS-PDSCH modulation scheme where 0 = QPSK and 1 = 16-QAM.
Part 2 consists of the following information:
Transport Block Size – The transport block size used for the corresponding HS-PDSCH sub-frame is signaled as a 6-bit Transport Format Resource Indicator (TFRI). The actual transport block size in bits is derived from TFRI and depends on the modulation scheme and the number of HS-PDSCH channelization codes signaled on HS-SCCH.
HARQ Process ID – Contains the HARQ process ID for the corresponding HS-PDSCH sub-frame. There may be one to eight simultaneous HARQ processes running in a UE.
Redundancy & Constellation Version – Contains RV parameters r and s that are used by the Physical Layer HARQ functionality. If 16-QAM modulation is used, this field also contains the constellation version parameter b that indicates the rearranged version of 16-QAM constellation used for the corresponding HS-PDSCH sub-frame transmission.
New Data Indicator – Contains 1-bit indicator that toggles every time the NodeB sends new HS-DSCH data. The indicator is not toggled in case of retransmissions.
Page63Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
HS-PDSCH and HS-SCCH Spreading and Modulation
HS-PDSCH is spread with SF 16, scrambled with Primary Scramble Code
HS-SCCH is spread with SF 128, scrambled with same code as HS-PDSCH
The Downlink physical channels (except SCH) are spread to the chip rate with individual channelization codes and then scrambled with the same scrambling code. All such channels use QPSK modulation except HS-PDSCH, which can use either QPSK or 16-QAM.
The Downlink physical channels HS-SCCH and HS-PDSCH consist of a sequence of binary symbols. In the case of QPSK modulation, each pair of two consecutive symbols is first serial-to-parallel converted and then mapped to the I and Q branches. The QPSK modulation mapper maps the even and odd numbered symbols to the I and Q branch respectively. In the case of 16-QAM modulation, a set of four consecutive binary symbols nk, nk+1, nk+2, nk+3 (with k mod 4 = 0) is serial-to-parallel converted to two consecutive binary symbols (i1= nk, i2= nk+2) on the I branch and two consecutive binary symbols (q1= nk+1, q2= nk+3) on the Q branch and then mapped to 16-QAM constellation by the modulation mapper. The modulation mapper converts the binary symbols into the real-valued symbols.
Page64Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Uplink HS-DPCCHHigh Speed Dedicated Physical Control Channel (HS-DPCCH)
3 slots format, SF 256, OVSF code – Cch,256,64
Fixed power offset ( ΔACK, ΔNACK, ΔCQI ) relative to Uplink associated DPCCH
CQI measurement reference period is 3 slots, ending 1 slots before CQI is sent
UL HS-DPCCH – High Speed Dedicated Physical Control Channel
Each UE operating in the HSDPA mode has an active Uplink HS-DPCCH along with the dedicated UL DPCCH. The UE uses UL DPCCH as reference for adjusting the HS-DPCCH channel power. UE transmits HS-DPCCH at a fixed power offset relative to UL DPCCH but the offset is different for ACK, NACK, and CQI fields. These power offsets are signaled to UE by UTRAN and are used by UE’s Physical Layer to calculate the HS-DPCCH gain factor (βhs). As the HS-DPCCH power is adjusted relative to UL DPCCH, the Uplink power control is indirectly
adjusting the HS-DPCCH power.
Each subframe (2 ms) of HS-DPCCH has one slot for HARQ ACK/NACK and two slots for Channel Quality Indicator (CQI) field. UTRAN may configure the UE to repeat each ACK/NACK and/or CQI report up to three more times in the consecutive subframes. If there is nothing to acknowledge, i.e., no data received on HS-PDSCH or CRC error on HS-SCCH, then DTX bits are sent in the ACK/NACK field.
UTRAN configures CQI reporting by signaling CQI feedback cycle parameter to UE. Based on the feedback cycle parameter, UE may be asked to not send CQI at all or send CQI at periodic intervals ranging from 2 ms to 160 ms. For example, if the CQI feedback cycle is 4 ms, the UE reports CQI in every other subframe. Those subframes not scheduled to report CQI have DTX bits in place of CQI.
CQI value reflect wireless environment quality of previous sub-frame (i.e reference period in above figure)
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HS-DPCCH Channel Coding1 bit ACK/NACK is coded as 10 bits
5 bits CQI is coded as 20 bits
Sub-frame repetition of ACK/NACK and CQI add more reliability
HS-DPCCH Channel Coding
Channel coding is done by UE’s Physical Layer to add redundant bits to the HS-DPCCH information. In general, there are different methods of doing channel coding such as repetition, convolutional coding, turbo coding, Reed-Muller (RM) coding, etc., but the basic strategy is to add some redundant bits to the original bit(s). This redundancy helps the receiver correctly decode the original bits which may have been impaired due to bad RF channel conditions. The
1-bit ACK/NACK information is coded into 10 bits by repeating the original bit. The 5-bit CQI information is coded into 20 bits by using RM coding.
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HS-DPCCH Spreading and Modulation
Unique OVSF code Cch,256,64
Gain factor βhs is derived from power offsets (ΔACK , ΔNACK , ΔCQI)
Multiplexed on Q branch
Same scrambling code as on UL DPCH
QPSK modulation
HS-DPCCH Spreading and Modulation
The HS-DPCCH channel is I/Q code multiplexed with UL DPCH. Depending on whether the number of active UL DPDCHs is even or odd, HS-DPCCH is mapped on to I or Q branch, respectively. The SF used for HS-DPCCH is 256 with OVSF code number Cch, 256, 64 when there is only one active UL DPDCH. The power offsets ΔACK , ΔNACK , and ΔCQI are signaled to UE by UTRAN through higher layer signaling.
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Contents1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channels
4. HSDPA Physical Layer Processing
5. HSDPA Layer2 Protocol
Page68Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
UMTS Protocol Stack
UMTS Protocol Stack
The UMTS signaling protocol stack is divided into Access Stratum (AS) and Non-Access Stratum (NAS). The Non-Access Stratum architecture evolved from the GSM/GPRS upper layers and is divided into Circuit Switched (CS) and Packet Switched (PS) protocols.
The Access Stratum consists of three layers:
1. Layer 3 – The Radio Resource Control (RRC) layer handles establishment, release, and configuration of radio resources.
2. Layer 2 – Consists of two sub-layers. The Radio Link Control (RLC) sub-layer provides segmentation, re-assembly and other traditional Layer 2 functions. The Medium Access Control (MAC) sub-layer multiplexes data and signaling onto the appropriate channels and controls access to the Physical Layer.
3. Layer 1 – The Physical Layer transfers data over the radio link.
UTRAN protocol structure to be found in 25.301
L3
cont
rol
cont
rol
cont
rol
cont
rol
LogicalChannels
TransportChannels
C-plane signalling U-plane information
PHY
L2/MAC
L1
RLC
DCNtGC
L2/RLC
MAC
RLCRLC
RLCRLC
RLCRLC
RLC
Duplication avoidance
UuS boundary
BMC L2/BMC
control
PDCPPDCP L2/PDCP
DCNtGC
RadioBearers
RRC
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HSDPA Protocol Stack
1. HSDPA Protocol Stack
1. In a Release 99 PS network, the NAS layer protocols are terminated at the SGSN. RRC, RLC,and MAC protocols are terminated at the RNC. The Physical Layer protocol is terminated at the Node B.
2. The Release 5 specifications define a new sublayer of MAC called MAC-hs, which implements the MAC protocols and procedures for HSDPA. This sublayer operates at the NodeBand the UE.
3. UTRAN MAC-hs is responsible for fast scheduling of the HS-PDSCHs. The scheduler determines:
1. To which UEs the channels are assigned.
2. How much data to send.
3. Which modulation scheme to use.
4. Whether to send new data or retransmitted data.
5. Which redundancy version to send.
4. UE MAC-hs is responsible for:
1. Sending ACK or NACK after decoding a block.
2. Re-ordering data blocks before submitting to upper layers, if retransmissions caused data to be received out of order.
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UTRAN Mac Architecture
1. UTRAN MAC Architecture
1. The UTRAN MAC protocol consists of three entities:
2. MAC-hs – Responsible for the high speed HSDPA channels and the only entity of MAC that resides in the Node B. When a UE operates in HSDPA mode, MAC-hs maps user data and signaling from DCCH and DTCH onto the sharedHS-DSCH transport channels.
3. MAC-c/sh – Responsible for common and shared logical (PCCH, BCCH, CCCH, and CTCH) and transport (PCH, BCH, RACH, FACH) channels. MAC-c/shresides in the RNC, and there is one MAC-c/sh entity per RNC. When a UE operates in Cell_FACH state, MAC-c/sh maps user data and signaling from its DCCH and DTCH onto the common FACH and RACH transport channels.
4. MAC-d – Responsible for mapping data from dedicated logical channels (DCCH and DTCH) onto dedicated transport channels (DCH). MAC-d resides in the RNC, and there is one MAC-d entity for each UE to which dedicated logical channels have been assigned.
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UTRAN MAC-hs Architecture
1. UTRAN MAC-hs Architecture
2. Data enters the UTRAN MAC-hs from a set of MAC-d flows. The data is routed to a set of priority queues with the following properties:
1. Up to 8 priority queues and 8 MAC-d flows are allowed per UE.
2. The queue distribution entity maps each MAC-d flow onto one or more priority queues.The mapping is configured when the HSDPA operation begins.
3. Each priority queue is mapped to only one MAC-d flow.
3. When data is removed from a priority queue for transmission, it is assigned to a HARQ process.
4. There are a minimum of 6 and a maximum of 8 HARQ processes per UE. The HARQ process tracks the ACK/NACK signaling for the data block and determines when retransmission is necessary.
5. In response to CQI and ACK/NACK signaling on HS-DPCCH, the scheduler decides:
1. To which UEs the HSDPA channels will be assigned.
2. For each scheduled UE, whether to send new data from a priority queue or a retransmission from a HARQ process.
6. Signaling on HS-SCCH indicates the scheduling decision to the UEs operating in HSDPA mode.
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Mac-hs functionsFlow Control
The flow control entity controls the HSDPA data flow between
RNC and NodeB
Purpose: to reduce the transmission time of HSDPA data on
the UTRAN side and to reduce the data discarded and
retransmitted when the Iub interface or Uu interface is
congested
The transmission capabilities of the Uu interface and Iub
interface are taken into account in a dynamic manner in the
flow control
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Mac-hs functionsScheduling
The scheduling entity handles the priority of the queues and
schedules the priority queues or NACK HARQ processes of the
HS-DSCH UEs in a cell to be transmitted on the HS-DSCH
related physical channels in each TTI
Purpose: to achieve considerable cell throughput capability and
to satisfy user experience
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Mac-hs functionsHARQ
The HARQ entity handles the HARQ protocol for each HS-
DSCH UE
Each HS-DSCH UE has one HARQ entity on the MAC-hs of
the UTRAN side to handle the HARQ functionality
One HARQ entity can support multiple instances (i.e.HARQ
processes) of stop and wait HARQ protocols
Based on the status reports from HS-DPCCH, a new
transmission or retransmission is determined
The round trip time at the physical layer is 12 ms. Therefore, it is necessary for one UE to have multiple parallel instances (HARQ processes) of the stop and wait HARQ protocol to increase the Uu interface throughput
One problem in the receiver caused by multiple HARQ processes is that, in a specific time window, the TBs may arrive out of sequence. Therefore, it is necessary to have reordering functionality on the receiver side
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Mac-hs functionsTFRC selection
The TFRC selection entity selects an appropriate transport
format and resource for the data to be transmitted on HS-
DSCH
The transport format includes the transport block size and
modulation scheme. The resource includes the power resource
and code resource of HS-PDSCH
Transport Format and Resource Combination (TFRC) for each
UE is channel quality based, where AMC is the key technique
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UE MAC-hs Architecture
1. UE MAC-hs Architecture
1. When the UE Physical Layer decodes a data block addressed to it, the associated HARQ process determines whether to ACK or NACK the block. If an ACK is sent, the data block is passed to the assigned re-ordering queue.
2. Re-ordering of MAC-hs PDUs is necessary because up to 8 HARQ processes can be operating on sequentially transmitted data. MAC-hs PDUs can be received out of order when a HARQ process sends a NACK.
3. The re-ordering queue passes the block up to the disassembly entity when it receives consecutive data blocks. The disassembly entity takes apart the MAC-hs PDU into its constituent MAC-d PDUs and passes them up to the appropriate MAC-d flow for processing by the MAC-d layer.
Page78Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Data Flow ExampleData Flow
Transmitter (NodeB)
RNC RLC PDU to NodeB priority queue
NodeB Mac-hs PDU assembly
NodeB HARQ Process
Receiver (UE)
UE HARQ process
UE re-ordering queue
UE Mac-hs PDU disassembly
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Data Flow Example RNC Mac-d PDU to NodeB Priority Queue
Data Flow Example – RNC MAC-d PDU to NodeBPriority Queue
In this example, two logical channels, DTCH 1 and DTCH 2, are mapped to one MAC-d flow.
The MAC-d entity in the RNC constructs MAC-d PDUs by prepending a header to each RLC PDU. The MAC-d header contains a C/T field that identifies the DTCH from which the data came. The priority DTCH 1 is higher than DTCH 2, so MAC-d selects all the PDUs from DTCH1, and then all the PDUs from DTCH 2.
The MAC-d flow is mapped to a MAC-hs priority queue. The RNC transfers the data across the Iub interface to the Node B, where the MAC-hs entity stores the MAC-d PDUs in the priority queue, preserving the order of the PDUs as sent across the Iubinterface.
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Data Flow Example NodeB Mac-hs PDU Assembly
Mac-hs PDU structure
Data Flow Example – NodeBMAC-hs PDU Assembly
When the scheduler in the NodeB MAC-hs decides to send data from a given priority queue, it constructs a MAC-hs PDU. The scheduler determines the size of the MAC-hsPDU as a function of the UE’s CQI report, number of HS-PDSCHs, available transmit power, and other proprietary parameters.
MAC-d PDUs are packed into the MAC-hs PDU sequentially. The MAC-hs PDU is then sent to the Physical Layer as the HS-DSCH transport block. The MAC-hs PDU header consists of the
following fields:
Version Flag (VF) – Always set to 0 for this release.
Queue Identifier (QID) – Identifies the priority queue in the NodeB from which the data came, and the re-ordering queue in the UE to which the data is being sent.
Transmission Sequence Number (TSN) – Used by the re-ordering protocol to ensure inorder delivery of MAC-d PDUs when retransmissions occur.
Size Index Identifier (SID) – When HSDPA operations begin, the RNC sends a signaling message to the UE that maps valid MAC-d PDU sizes to a set of up to 7 SIDs.
Number (N) – Indicates the number of consecutive MAC-d PDUs of the size given by the previous SID. The maximum number of MAC-d PDUs in a MAC-hs PDU is 70.
Flag (F) – One-bit flag field to indicate the end of the MAC-hs header.
Padding – MAC-hs adds padding as needed to fill the MAC-hs PDU size (transport block size) chosen by the scheduler.
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Data Flow Example NodeB HARQ Process
Data Flow Example – NodeB HARQ Process
The scheduler chooses a HARQ process from which to send the PDU. The NodeB supports up to 8 HARQ processes for each UE.
The NodeB transmits the HARQ process ID in the second part of the HS-SCCH. A one-bit indicator, the New Data Indicator (NDI), in the second part of HS-SCCH is toggled whenever a new PDU is transmitted.
The Physical Layer uses the UE’s H-RNTI to scramble the HS-SCCH. When the UE monitors the HS-SCCH, it looks for subframes scrambled with its H-RNTI, ignoring those that don’t match and processing those that do.
The NodeB sends the MAC-hs PDU to the Physical Layer on the HS-DSCH transport channel. The Physical Layer processes the data and maps it onto one or more HS-PDSCHs.
The HARQ protocol supports the following features:
� Soft combining – If the UE NACKs a data block, the NodeB may retransmit the data. The Physical Layer performs soft combining of the retransmitted symbols with those previously received.
� Stop and Wait (SAW) – Each HARQ process, up to a maximum of 8, operates independently on one data block until that block is correctly decoded or transmission is aborted by the NodeB.
� Synchronous ACK/NACK – The UE transmits an ACK or NACK for a given block at a fixed time following reception of the data.
� Asynchronous retransmission – The NodeB sends a retransmission any time after an NACK is received. The earliest this can occur is 10 ms after the previous transmission. A more typical value is expected to be 12 ms, due to internal delays in the Node B scheduling algorithm. A retransmission could occur later than 12 ms depending on channel quality reported by the UE and other internal scheduling decisions.
HARQ Protocol signaling on HS-SCCH
HARQ Protocol HS-SCCH Information
The Node B sends control Information for the HARQ protocol on the HS-SCCH. The first slot of the HS-SCCH is scrambled with the UE’s H-RNTI, which identifies the UE to which this HSDPA assignment belongs. A 16-bit CRC masked with the UE’s H-RNTI is computed over both parts.
The information on HS-SCCH includes:
� Channelization Code Set – Which HS-PDSCH codes to use, and how many channels.
� Modulation Scheme – QPSK or 16-QAM
� HARQ Process ID – Which HARQ process should decode the next HSDPA assignment.
� Transport Format Resource Indicator (TFRI) – A 6-bit value that maps to the Transport Block size of the data.
� Redundancy and Constellation Version – The redundancy version indicates to the Turbo decoder which combination of systematic and parity bits will be sent. For 16-QAM, the constellation version indicates how the symbols were mapped to the constellation.
� New Data Indicator (NDI) – A 1-bit value that is toggled whenever new data is sent to a given HARQ process, to allow it to distinguish a retransmission from a new transmission.
Page83Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Data Flow Example UE HARQ Process
Data Flow Example – UE HARQ Process
Each UE HARQ process performs operations within the Physical Layer and within the MAC-hs layer.
Physical Layer HARQ Process Operations
When the UE decodes its H-RNTI on the HS-SCCH, it prepares to decode the next HS-DSCH TTI. The HS-SCCH includes a HARQ process ID. In the Physical Layer, the HARQ process decodes the associated HS-PDSCHs. If the data is decoded correctly, the data is routed to the MAC-hs part of the HARQ process.
MAC-hs Layer HARQ Process Operations
The MAC-hs HARQ process generates either an ACK or a NACK to be sent in the subframe numbered 5 in the diagram above. If the UE sends an ACK and the NodeB decodes the ACK correctly, the earliest that HARQ process 1 can be used for a new data block is the subframe numbered 8 above. If other data blocks are sent to the UE during the intervening subframes, they must be assigned to other HARQ processes.
UE HARQ Process flowchart
UE HARQ Process Flowchart
The control flow for a HARQ process in the UE is as follows:
1. When a data block is received, compare the New Data Indicator (NDI) bit with the value
received in the previous block.
If NDI is different, flush data in the buffer and store new data
If NDI is the same and the buffer is empty, this data has already been decoded correctly, so discard it and send an ACK. This can happen if the Node B interprets an ACK as a NACK, and retransmits the data block.
If NDI is the same and the buffer is not empty, soft combine the new data with data already in the buffer.
2. Attempt to decode the data in the buffer.
If correctly decoded, deliver the data to the re-ordering queue, flush the buffer, and send an ACK.
If incorrectly decoded, keep the data in the buffer and send a NACK.
HARQ Protocol Errors
Errors can occur in the HARQ protocol if the Node B misinterprets the UE’sACK/NACK.
If the Node B receives nothing in the HS-DPCCH slot in which it expects an ACK or NACK, it treats it as a NACK
If the Node B interprets an ACK as a NACK, a packet may be retransmitted when it was not necessary to do
The UE HARQ process detects this condition by the fact that the New Data Indicator bit is the same value as the previous transmission, so it discards the data and sends another ACK
Another type of protocol error occurs if the Node B misinterprets a NACK as an ACK. In this case, the Node B assumes the UE correctly decoded the data, so it sends a new data block to the same HARQ process
The HARQ process in UE side must discard the previous transmission and attempt to decode the new block, sending the ACK or NACK accordingly.
This is a worse error than mistaking an ACK, because data is lost and must be recovered by higher layer protocols (i.e., RLC)
Page86Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Data Flow ExampleUE re-ordering Queue
Data Flow Example – UE Re-ordering Queue
When the UE’s HARQ process ACKs the data block, it routes the MAC-hs PDU to a re-ordering queue, according to the QID given in the MAC-hs header. The re-ordering queue uses the TSN in the MAC-hs header to put the PDUs in the correct order. The re-ordering queue routes consecutively received PDUs to the disassembly entity.
If a HARQ process sends a NACK, this can create a hole in the re-ordering queue. The re-ordering queue buffers subsequent PDUs until either the missing PDU is successfully received, or the reordering protocol stops waiting for that PDU. Two mechanisms, timer-based and window-based, are used for stall avoidance. These are examined in detail in later slides.
This example illustrates a simple case in which consecutive assignments originate from the same NodeB priority queue and thus are all routed to the same re-ordering queue. In a more complicated example, data from multiple priority queues can be interleaved according to the NodeB MAC-hs scheduling decisions.
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Data Flow ExampleUE Mac-hs PDU Disassembly
Data Flow Example – UE MAC-hs PDU Disassembly
The UE MAC-hs entity disassembles the MAC-hs PDU, using the information in the MAC-hs header to separate the PDUs. It passes the MAC-d PDUs to the MAC-d entity, which then delivers the PDUs to the DTCH logical channels, using the C/T field to differentiate channels.
Page88Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Re-ordering ProtocolFeatures of the MAC-hs Re-ordering Protocol
Each reordering queue operates independently
Control information in MAC-hs headerQueue ID (QID), 3 bits
Transmission Sequence Number (TSN), 6 bits
In-sequence delivery of MAC-d PDUs to RLCHARQ protocol may deliver data out of sequence
RLC requires in-sequence delivery
Re-ordering Protocol – MAC-hs Header
The MAC-hs PDU header consists of the following fields:
� Version Flag (VF) – Always set to 0 for this release.
� Queue Identifier (QID) – Identifies the priority queue in the Node B from which the data came, and the re-ordering queue in the UE to which the data is being sent.
� Transmission Sequence Number (TSN) – Used by the re-ordering protocol to ensure in-order delivery of MAC-d PDUs when retransmissions occur.
� Size Index Identifier (SID) – When HSDPA operations begin, the RNC sends a signaling message to the UE that maps valid MAC-d PDU sizes to a set of up to 7 SIDs.
� Number (N) – Indicates the number of consecutive MAC-d PDUs of the size given by the previous SID. The maximum number of MAC-d PDUs in a MAC-hs PDU is 70.
� Flag (F) – One-bit flag field to indicate the end of the MAC-hs header.
� Padding – Padding as needed to fill the scheduled MAC-hs size.
Page89Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Re-ordering ProtocolIn-sequence Delivery of Mac-hs PDUs
Re-ordering Protocol – In-sequence Delivery of MAC-hs PDUs
When a HARQ process sends a NACK, a hole is created in the re-ordering queue for which that PDU was intended. As subsequent PDUs are received, the re-ordering queue buffers those PDUs to prevent them from being delivered out of order to the RLC layer above MAC-hs.
When the missing PDU is received correctly, the re-ordering queue inserts it into the correct position in the buffer and delivers it and all subsequent consecutive PDUs that are awaiting delivery.
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