WCDMA Principle 20110930 B V1.0

8/22/2019 WCDMA Principle 20110930 B V1.0

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WCDMA RAN Fundamental

Confidential Information of Huawei. No Spreading Without Permission

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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 mostimportant 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


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Put forward in 1985 by the ITU (International Telecommunication Union), the

3G mobile communication system was called the FPLMTS (Future Public LandMobile 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 applicationof 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 airinterface 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.


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ITU has allocated 230 MHz frequency for the 3G mobile communication

system IMT-2000: 1885 ~ 2025MHz in the uplink and 2110~ 2200 MHz in thedownlink. 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.


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The WCDMA system uses the following frequency spectrum (bands other than

those specified by 3GPP may also be used): Uplink 1920 MHz ~ 1980 MHz anddownlink 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.


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Compatible with abundant services and applications of 2G, 3G system has an

open integrated service platform to provide a wide prospect for various 3Gservices.

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.


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Formulated by the European standardization organization 3GPP, the core

network evolves on the basis of GSM/GPRS and can thus be compatible withthe 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.


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In mobile communication systems, GSM adopts TDMA; WCDMA, cdma2000

and TD-SCDMA adopt CDMA.


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Frequency Division Multiple Access means dividing the whole available

spectrum into many single radio channels (transmit/receive carrier pair). Eachchannel 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.


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In third generation mobile communication systems, WCDMA and cdma2000

adopt frequency division duplex (FDD), TD-SCDMA adopts time divisionduplex (TDD).


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WCDMA including the RAN (Radio Access Network) and the CN (Core

Network). The RAN is used to process all the radio-related functions, whilethe 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 isused 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.


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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 PacketAccess) 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.


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The layer 1 supports all functions required for the transmission of bit

streams on the physical medium. It is also in charge of measurementsfunction consisting in indicating to higher layers, for example, Frame

Error Rate (FER), Signal to Interference Ratio (SIR), interference power

and transmit power.

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.


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Protocol structures in UTRAN terrestrial interfaces are designed

according to the same general protocol model. This model is shown inabove 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

Si nalin Bearer for the A lication Protocol ma or ma not be


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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


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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


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The Iub interface is the terrestrial interface between NodeB and RNC.

The Radio Network Layer defines procedures related to the operationof 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-Cprocedure 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.


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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.


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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


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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. Thatexchange has to be done as fast as possible in order to better follow the

evolution of the channels quality.


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Scrambling can make transmission in security.


signals.

Bit, Symbol, Chip





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During the transmission, there are many interferences and fading. To

guarantee reliable transmission, system should overcome these influencethrough 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 transportblocks 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.


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UTRAN employs two FEC schemes: convolutional codes and turbo codes. The

idea is to add redundancy to the transmitted bit stream, sO that occasional biterrors 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 Shannons 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. Theidea 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.


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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 fastmoving 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.


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signals.

Bit, Symbol, Chip





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Correlation is used to measure similarity of any two arbitrary signals. It is

computed by multiplying the two signals and then summing (integrating) theresult 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.


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By spreading, each symbol is multiplied with all the chips in the orthogonal

sequence assigned to the user. The resulting sequence is processed and isthen 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.


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The receiver dispreads the chips by using the same code used in the

transmitter. Notice that under no-noise conditions, the symbols or digits arecompletely recovered without 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.


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Traditional radio communication systems transmit data using the minimum

bandwidth required to carry it as a narrowband signal. CDMA system mixtheir 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.


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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 is384kbps(R99). After the spreading, the chip rate of different service all

become 3.84Mcps.


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Spreading means increasing the bandwidth of the signal beyond the

bandwidth normally required to accommodate the information. The spreadingprocess 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). Channelization codes 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.


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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 factorof the code, and k is the sequence of code, 0kSF-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.


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The channelization codes are Orthogonal Variable Spreading Factor(OVSF)

codes. They are used to preserve orthogonality between different physicalchannels. They also increase the clock rate to 3.84 Mcps. The OVSF codesare 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 users bit. Because the chip rate isconstant, the different lengths of codes enable to have different user datarates. Low SFs are reserved for high rate services while high SFs are for lowrate services.

The length of an OVSF code is an even number of chips and the number ofcodes (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 orthogonalcodes. Furthermore, any two codes of different layers are orthogonal exceptwhen one of the two codes is a mother code of the other. For example C4,3 isnot orthogonal with C1,0 and C2,1, but is orthogonal with C2,0.

SF in uplink is from 4 to 256.

SF in downlink is from 4 to 512.


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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.


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In addition to spreading, part of the process in the transmitter is the

scrambling operation. This is needed to separate terminals or base stationsfrom each other.


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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.


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There are totally 512 primary scrambling codes defined by 3GPP. They are

further divided into 64 primary scrambling code groups. There are 8 primaryscrambling codes in every group. Each cell is allocated with only one primary

scrambling code.


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signals.

Bit, Symbol, Chip





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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 tomodulate 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 cellular

systems. There are many variants in this family, and only a few of them are

mentioned here.


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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 radians.

NRZ means none return zero.


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The quadrature phase shift keying (QPSK) modulation has four phases: 0, /2,

, and 3/2 radians. Two data bits are transformed into one complex datasymbol; A symbol is any change (keying) of the carrier.


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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.


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signals.

Bit, Symbol, Chip





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A mobile communication channel is a multi-path fading channel and any

transmitted signal reaches a receive end by means of multiple transmissionpaths, such as direct transmission, reflection, scatter, etc.


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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.


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Diversity technology means that after receiving two or more input signals

with mutually uncorrelated fading at the same time, the system demodulatesthese signals and adds them up. Thus, the system can receive more useful

signals and overcome fading.


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Diversity technology is an effective way to overcome overlaid fading. Because

it can be selected in terms of frequency, time and space, diversity technologyincludes 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


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The RAKE receiver is a technique which uses several baseband correlators to

individually process multipath signal components. The outputs from thedifferent 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.


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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.


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N-66

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.


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N-67


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N-68

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 dividedinto 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.


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N-69

As in GSM, UMTS uses the concept of logical channels.

A logical channel is characterized by the type of information that istransferred.

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.


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N-71

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 or downlink.


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N-72

Now we will begin to discuss the physical channel. Physical channel is

the most important and complex channel, and a physical channel isdefined 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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N-73

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 carrycommon control information such as the scrambling code usedin DL (there is a primary CCPCH and additional secondaryCCPCH).

Common Pilot Channels (P-CPICH and S-CPICH): used forcoherent detection of common channels. They indicate thephase reference.

Dedicated Physical Data Channel (DPDCH): used to carrydedicated data coming from layer 2 and above (coming fromDCH).

Dedicated Physical Control Channel (DPCCH): used to carrydedicated control information generated in layer 1 (such aspilot, TPC and TFCI bits).

Page Indicator Channel (PICH): carries indication to inform theUE that paging information is available on the S-CCPCH.

Acquisition Indicator Channel (AICH): it is used to inform a UEthat the network has received its access request.

High Speed Physical Downlink Shared Channel (HS-PDSCH): it isused to carry subscribers BE service data (mapping on HSDPA)coming from layer 2.

High Speed Shared Control Channel (HS-SCCH): it is used to carrycontrol message to HS-PDSCH such as modulation scheme, UEID etc.


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N-74

The different physical channels are:

Dedicated Physical Data Channel (DPDCH): used to carrydedicated 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): itis used to carry feedback message to HS-PDSCH such

CQI,ACK/NACK.


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N-75


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N-76

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 primaryscrambling 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 themobiles 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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N-77

The S-SCH also consists of a code, the Secondary Synchronization Code

(SSC) that indicates which of the 64 scrambling code groups the cellsdownlink 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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N-78

The Common Pilot Channel (CPICH) is a pure physical control channel

broadcasted over the entire cell. It is not linked to any transportchannel. It consists of a sequence of known bits that are transmittedin parallel with the primary and secondary CCPCH.

The PCPICH is used by the mobile to determine which of the 8 possibleprimary scrambling codes is used by the cell, and to provide the phasereference for common channels.

Finding the primary scrambling code is done during the cell searchprocedure through a symbol-by-symbol correlation with all the codeswithin the code group. After the primary scrambling code has beenidentified, the UE can decode system information on the P-CCPCH.

The P-CPICH is the phase reference for the SCH, P-CCPCH, AICH andPICH. It is broadcasted over the entire cell. The channelization codeused 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 theprimary scrambling code of the cell.


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N-79

The Primary Common Control Physical Channel (P-CCPCH) is a fixed

rate (SF=256) downlink physical channel used to carry the BCHtransport 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 has one 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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N-80

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 oneradio 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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N-81

The Secondary Common Control Physical Channel (S-CCPCH) is used to

carry the FACH and PCH transport channels. Unlike the P-CCPCH, it isnot 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 thecommunication. 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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N-82

The Physical Random Access Channel (PRACH) is used by the UE to

access the network and to carry small data packets. It carries the RACHtransport 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 doesnt 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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N-83

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 thecontrol 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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N-84

The PRACH transmission is based on the access frame structure. Theaccess frame is access of 15 access slots and lasts 20 ms (2 radioframes).

To avoid too many collisions and to limit interference, a UE must waitat least 3 or 4 access slots between two consecutive preambles.

The PRACH resources (access slots and preamble signatures) can bedivided between different Access Service Classes (ASC) in order toprovide different priorities of RACH usage. The ASC number rangesfrom 0 (highest priority) to 7 (lowest priority).


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N-85

The Acquisition Indicator Channel (AICH) is a common downlink

channel used to control the uplink random accesses. It carries theAcquisition 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, andlasts 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 is

given by a predefined table. There are 16 sequences , 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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N-86

There are two kinds of uplink dedicated physical channels, the

Dedicated Physical Data Channel (DPDCH) and the Dedicated PhysicalControl 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, TFCIFBITPC

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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N-87

On the figure above, we can see the DPDCH and DPCCH time slot

constitution. The parameter k determines the number of symbols perslot. 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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N-88

The uplink DPDCH and DPCCH are I/Q code multiplexed. But the

downlink DPDCH and DPCCH is time multiplexed. This is maindifference.

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 doesnt change.


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N-89

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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N-90

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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N-91

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 ofHS-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.


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N-92

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.


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N-93

This page indicates how the mapping can be done between logical,

transport and physical channels. Not all physical channels arerepresented 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.


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N-94


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N-95

The purpose of the Cell Search Procedureis to give the UE the

possibility of finding a cell and of determining the downlink scramblingcode and frame synchronization of that cell. This is typically performedin 3 steps:

PSCH(Slot synchronization): The UE uses the SCHs primarysynchronization code to acquire slot synchronization to a cell.The primary synchronization code is used by the UE to detectthe existence of a cell and to synchronize the mobile on the TSboundaries.This is typically done with a single filter (or anysimilar device) matched to the primary synchronization codewhich 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 informationrequired to find the frame boundaries and the group number.Each group number corresponds to a unique set of 8 primaryscrambling codes. The frame boundary and the group numberare provided indirectly by selecting a suite of 15 secondarycodes. 16 secondary codes have been defined C1, C2, .C16. 64possible suites have been defined, each suite corresponds to oneof the 64 groups. Each suite of secondary codes is composed of15 secondary codes (chosen in the set of 16), each of which willbe transmitted in one time slot. When the received codesmatches one of the possible suites, the UE has both determinedthe frame boundary and the group number.

PCPICH (Scrambling-code identification): The UE determines theexact primary scrambling code used by the found cell. Theprimary scrambling code is typically identified through symbol-by-symbol correlation over the PCPICH with all the codes within


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N-96

Physical random access procedure

1. Derive the available uplink access slots, in the next full access slot set, forthe 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 RACHsub-channels within the given ASC;

B: select a signature;

C: Increase the Commanded Preamble Power;

D: Decrease the Preamble Retransmission Counter by one. If thePreamble 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


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N-97

Transmitter-antenna diversity can be used to generate multi-path

diversity in places where it would not otherwise exist. Multi-pathdiversity 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


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N-98

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 receivingUE to extract the phase information for both antennas.

The STTD encoding is optional in the UTRAN, but its support is

mandatory for the UEs receiver.


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N-99

Time-switched transmit diversity (TSTD) can be applied to the SCH. Just

like STTD, the support of TSTD is optional in the UTRAN, butmandatory 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).


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N-100

The closed-loop-mode transmit diversity can only be applied to the

downlink channel if there is an associated uplink channel. Thus thismode 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 stations

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 UEs 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.


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WCDMA RAN Fundamental N-101

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