3GPP LTE (Rel. 8) Overview

3GPP R8 LTE Overview

조봉열, Bong Youl (Brian) [email protected]

Intel Corporation

mailto:[email protected]

LTE/MIMO 표준기술 2

ContentsTechnology Evolution

OFDM(A) and SC-FDMA

LTE OverviewLTE Radio Interface ArchitectureLTE Downlink TransmissionLTE Uplink TransmissionLTE Cell Search

Summary

Technology Evolution


Worldwide Mobile UsersNumber Percentage

cdmaOne 2,512,409 0.06% CDMA2000 1X 309,507,900 7.18% CDMA2000 1xEV-DO 121,821,983 2.83% CDMA2000 1xEV-DO Rev. A 13,912,386 0.32% Subtotal for 3GPP2 447,754,678 10.39%

Subtotal for 3GPP 3,837,689,086 89.03%Subtotal for 3GPP except GSM 388,678,183 9.02%

GSM 3,449,010,903 80.02% WCDMA 255,773,412 5.93% WCDMA HSPA 132,079,727 3.06% TD-SCDMA 825,044 0.02%

TDMA 753,411 0.02% PDC 2,752,436 0.06% iDEN 21,361,981 0.50% Total 4,310,311,592

* Data supplied by GSMA Mobile Infolink on Aug/07/2009


3GPP Standards Evolution

GPRSGPRSDL PDR: 50 kbpsDL PDR: 50 kbpsUL PDR: 21 kbpsUL PDR: 21 kbps

EGPRSEGPRSDL PDR: 236 kbpsDL PDR: 236 kbpsUL PDR: 118 kbpsUL PDR: 118 kbps

GERANGERANSAICSAIC

PS HandoverPS Handover

GERANGERANEvolutionEvolution

MSRDMSRDDual CarrierDual Carrier

Ongoing GERAN Evolution

UMTSUMTSWCDMAWCDMA

(5MHz)(5MHz)DL PDR: 384 kbpsDL PDR: 384 kbpsUL PDR: 64 kbpsUL PDR: 64 kbps

R5 HSDPAR5 HSDPA(5MHz)(5MHz)

DL PDR: 14 MbpsDL PDR: 14 MbpsUL PDR: 384 kbpsUL PDR: 384 kbps

R6 HSUPAR6 HSUPA(5 MHz)(5 MHz)

DL PDR: 14 MbpsDL PDR: 14 MbpsUL PDR: 5.7 MbpsUL PDR: 5.7 Mbps

R7 HSPAR7 HSPAEvolutionEvolution

(5 MHz)(5 MHz)DL PDR: 28.8 MbpsDL PDR: 28.8 MbpsUL PDR: 11.5 MbpsUL PDR: 11.5 Mbps

R8 HSPAR8 HSPAEvolutionEvolution

(5 MHz)(5 MHz)DL PDR: 43.2 MbpsDL PDR: 43.2 MbpsUL PDR: 11.5 MbpsUL PDR: 11.5 Mbps

Ongoing HSPA Evolution

R7 LTER7 LTEFeasibilityFeasibility

StudyStudy(1.25(1.25--20MHz)20MHz)

R8R8LTE/SAELTE/SAE(1.4(1.4--20MHz)20MHz)

DL PDR: DL PDR: ≥ 100 MbpsUL PDR: UL PDR: ≥ 50 Mbps

R9 &R9 &LTELTE--Adv Adv (R10)(R10)……

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009+


Technology Evolution Path

802.16m ?(WiMAX R2.0)

LTE-Adv ?

?

2010+

3G Technology Evolution

Broadband Wireless Technology Evolution

2005 2006 2007-2009

3G 3.5G~3.99G IMT-Adv?

Wi-FiOFDM

802.16eOFDMA

802.16eMIMO-OFDMA

(WiMAX R1.0)

WCDMA (R99)

EVDO R.0

HSDPA (R5)HSPA+ (R7/R8)

3GPP LTE (R8)

EVDO R.B3GPP2 UMBEVDO R.A


Advancement For High Data Rate

2G, 3G 3.5G(HSDPA,EVDO)

4G(LTE,WiMAX)

Access Scheme CDMA OFDM(A)

Modulation QPSK Up to 16QAM

Link Adaptation Mainly PC Mainly AMC with channel-aware scheduler

ARQ ARQ without soft combining HARQ with soft combining

Handover SHO HHO

QPSK,16QAM,64QAM

Duplexing FDD FDD, TDD is emerging

Antenna Technology Rx Antenna Diversity Various Antenna

Diversity, MIMO, BF

OFDM(A) and SC-FDMA


ISI Prevents High Data Rate?In general, ISI prevents “HIGH DATA RATE”

Symbol rate increase Ts decrease severe ISI Symbol rate decrease Ts increase less ISI

Multipath profile in the wireless channel (which is already given)

time

s1System#1 s2

Ts

s1 s2 s3 s4 s5 s6 s7 s8 s9 s10 s11 s12 s13 s14 s15System#2 s16

Ts

• System#2 achieves 10x higher data rate by using 10x more spectrum (BW)• However, at the same time, system#2 suffers 10x more severe ISI due to

short symbol duration compared to the multipath profile in the time domain


Multicarrier to “Minimize” ISI EffectWays to “minimize” inter-symbol interference:

Reduce the symbol rate, but data rate goes down tooEqualizers, but equalization is processor intensive & expensive

Solution:Transmit data over multiple carrier frequencies in parallel

Narrow, slower channels are MUCH LESS vulnerable to ISI thanks to long symbol duration compared to the multipath delay in time domainOFDM splits data into parallel, independent, narrowband channels (“subcarriers”)Expensive adaptive equalizers are not required

We are talking about “Broadband Wireless” which requires high data rate


Guard Interval To “Remove” ISI


Cyclic Prefix for Guard Interval


More on CP (Cyclic Prefix)

OFDM guarantee no interference ‘between’ subsequent OFDM symbolsOFDM allows ISI ‘within’ one OFDM symbol

Then, how can we remove ISI ‘within’ each OFDM symbol?


Circular ConvolutionCircular convolution

where is a periodic version of x[n] with period L.

DFT

The duality b/w circular convolution in the time domain and simple multiplication in the frequency domain is a property unique to DFTThe above simple formula describes an ISI-free channel in the frequency domain, where each input symbol X[m] is simply scaled by a complex value H[m]It is trivial to recover the input symbol by simply computing


Frequency Domain Model of OFDM Tx/Rx

One-tap EQ


OFDMA: (1) Better BW UtilizationCell center area: mostly BW-limited regionCell edge area: mostly power-limited region

To better utilize the resource FDM-based access is required on top of TDM-based access

Enhance uplink link budget!

Active subcarriers are divided into subsets called “resource block”When subscriber uses very few resource blocks,

It can concentrate all transmitting power (e.g. 200mW) in the used resource blocksIt will have additional gain on uplink

10*log10(Fs), where Fs is the power concentration factor

200mW

200mW

Total System BW


OFDMA: (2) Freq. Domain SchedulingLoading gain by “frequency selective scheduling”

Localized subcarrier assignment Distributed subcarrier assignment


DL Channel Dependent Scheduling in time and frequency domains


OFDMA: (3) Interference CoordinationFlexible Fractional Frequency Reuse

Cell-A

Cell-B

Cell-C

A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4A5

B5 C5

A1 A2 A3 A4 B3 B4 C1 C2 C3 C4A5 B5 C5

C2 C3 C4 C5

Pow

er

B2

C1

A5A4 B5B4A3A2A1 B3B2B1

good users weak users

good user weak user

weak users good users

B1


A Brief History of OFDM*1966: Chang shows that multicarrier modulation can solve the multipath problem without reducing data rate

R. W. Chang, “Synthesis of band-limited orthogonal signals for multichannel data transmission”, Bell Systems Technical Journal, 45:1775-1796, Dec. 1966

1971: Weinstein and Ebert show that multicarrier modulation can be accomplished using a DFT

S. Weinstein and P. Ebert, “Data Transmission by frequency-division multiplexing using the discrete Fourier transform”, IEEE Transactions on Communications, 19(5): 628-634, Oct. 1971

1985: Cimini at Bell Labs identifies many of the key issues in OFDM transmission and does a proof-of-concept design

L. J. Cimini, “Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing”, IEEE Transactions on Communications, 33(7): 665-675, July 1985

1993: DSL adopts OFDM1999: IEEE 802.11 releases the 802.11a standard for OFDM

* Jeffrey Andrews, et al., Fundamentals of WiMAX, Prentice Hall, 2007


OFDM in Communication Systems3GPP LTE3GPP2 UMBIEEE 802.16e Mobile WiMAX

DAB, DVB-T, DVB-HT-DMBMediaFlo

IEEE 802.11a WLAN

xDSLPLCEtc…


SC-FDMA TransmitterSC-FDMA is a new hybrid modulation technique combining the low PAR single carrier methods of current systems with the frequency allocation flexibility and long symbol time of OFDMSC-FDMA is sometimes referred to as Discrete Fourier Transform Spread OFDM = DFT-SOFDM

Signal at each subcarrier is linear combination of all M symbols

Low PAPR

Low PAPR

High PAPR

DFTSub-carrier Mapping

CPinsertion

Size-M

Size-N

Coded symbol rate= R

Msymbols

IFFT

Spreading


CM of OFDMA & SC-FDMA

OFDMA

SC-FDMA 16QAM

SC-FDMA QPSK

SC-FDMA pi/2-BPSK


R8 LTE DL OFDMA


R8 LTE UL SC-FDMA (LFDMA)


Comparing OFDM and SC-FDMA*QPSK example using N=4 subcarriersHow OFDM and SC-FDMA would be used to transmit a sequence of 8 QPSK symbols

* Moray Rumney (Agilent), “Concepts of 3GPP LTE”, Live Webinar, Sep. 20th, 2007.


Comparing OFDM and SC-FDMA


Time Domain Equalizer

In general, the complexity of time-discrete equalizer with linear equalization implementation (as above) grows relatively rapidly with the bandwidth of the signal to be equalized

A more wideband signal is subject to relatively more frequency selectivity or, equivalently, more time dispersion. This implies the equalizer needs to have a larger span.A more wideband signal leads to a correspondingly higher sampling rate for the received signal. Thus, also the receiver-filter processing needs to be carried out with a correspondingly higher rate.


Frequency Domain Equalizer

Frequency domain equalization basically consists ofA size-N DFT/FFTN complex multiplications (the frequency-domain filter)A size-N inverse DFT/FFT

Especially in extensive frequency selective channel, the complexity of the frequency domain equalization can be significantly less than that of time domain equalization

* D. Falconer, et al., “Frequency domain equalization for single-carrier broadband wireless systems,” IEEE Communication Magazine, vol.40, no.4, April 2002

LTE Overview


3GPP SpecificationsLTE Study Phase (Release 7)

TR 25.813, E-UTRA and E-UTRAN: Radio interface protocol aspectsTR 25.814, Physical layer aspects for E-UTRATR 25.912, Feasibility study for E-UTRA and E-UTRANTR 25.913, Requirements for E-UTRA and E-UTRAN

LTE Specifications (Release 8)TS 36.101, E-UTRA: UE radio transmission and receptionTS 36.104, E-UTRA: BS radio transmission and receptionTS 36.201, E-UTRA: LTE Physical Layer - General DescriptionTS 36.211, E-UTRA: Physical channels and modulationTS 36.212, E-UTRA: Multiplexing and channel codingTS 36.213, E-UTRA: Physical layer proceduresTS 36.214, E-UTRA: Physical layer – MeasurementsTS 36.300, E-UTRA and E-UTRAN: Overall description; Stage 2TS 36.302, E-UTRA: Services provided by the physical layerTS 36.306, E-UTRA: UE Radio Access CapabilitiesTS 35.321, E-UTRA: Medium Access Control (MAC) protocol specificationTS 36.323, E-UTRA: Packet Data Convergence Protocol (PDCP) specification TS 36.331, E-UTRA: Radio Resource Control (RRC); Protocol specificationTS 36.401, E-UTRAN: Architecture description TR 36.938, E-UTRAN: Improved network controlled mobility between LTE and 3GPP2/mobile WiMAX radio technologiesTR 36.956, E-UTRA; Repeater planning guidelines and system analysis


3GPP LTELTE focus is on:

enhancement of the Universal Terrestrial Radio Access (UTRA)optimisation of the UTRAN architecture

With HSPA (downlink and uplink), UTRA will remain highly competitive for several yearsLTE project aims to ensure the continued competitiveness of the 3GPP technologies for the future (started at Nov. 2004)Motivations

Need for PS optimized systemEvolve UMTS towards packet only system

Need for higher data ratesCan be achieved with HSDPA/HSUPA and/or new air interface defined by 3GPP LTE

Need for high quality of servicesUse of licensed frequencies to guarantee quality of servicesAlways-on experience (reduce control plane latency significantly)Reduce round trip delay

Need for cheaper infrastructureSimplify architecture, reduce number of network elementsMost data users are less mobile


Detailed Requirements*Peak data rate

Instantaneous downlink peak data rate of 100 Mb/s within a 20 MHz downlink spectrum allocation (5 bps/Hz) Instantaneous uplink peak data rate of 50 Mb/s (2.5 bps/Hz) within a 20MHz uplink spectrum allocation)

Control-plane latency Transition time of less than 100 ms from a camped state, such as Release 6 Idle Mode, to an active state such as Release 6 CELL_DCH Transition time of less than 50 ms between a dormant state such as Release 6 CELL_PCH and an active state such as Release 6 CELL_DCH

Control-plane capacityAt least 200 users per cell should be supported in the active state for spectrum allocations up to 5 MHz

User-plane latency Less than 5 ms in unload condition (ie single user with single data stream) for small IP packet

* 3GPP TR 25.913, Technical Specification Group RAN: Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN), Release 8, Version 8.0.0, Dec. 2008


Detailed RequirementsAverage user throughput

Downlink: average user throughput per MHz, 3 to 4 times Release 6 HSDPAUplink: average user throughput per MHz, 2 to 3 times Release 6 Enhanced Uplink

Cell edge user throughputDownlink: user throughput per MHz at 5% of CDF, 2 to 3 times Release 6 HSDPAUplink: user throughput per MHz at 5% of CDF, 2 to 3 times Release 6 Enhanced Uplink

Spectrum efficiencyDownlink: In a loaded network, target for spectrum efficiency (bits/sec/Hz/site), 3 to 4 times Release 6 HSDPA ) Uplink: In a loaded network, target for spectrum efficiency (bits/sec/Hz/site), 2 to 3 times Release 6 Enhanced Uplink

MobilityE-UTRAN should be optimized for low mobile speed from 0 to 15 km/hHigher mobile speed between 15 and 120 km/h should be supported with high performance Mobility across the cellular network shall be maintained at speeds from 120 km/h to 350 km/h (or even up to 500 km/h depending on the frequency band)

CoverageThroughput, spectrum efficiency and mobility targets above should be met up to 5 km cells, and with a slight degradation up to 30 km cells. Cells range up to 100 km should not be precluded.


Detailed RequirementsSpectrum flexibility

E-UTRA shall operate in spectrum allocations of different sizes, including 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz in both the uplink and downlink. Operation in paired and unpaired spectrum shall be supported

Co-existence and Inter-working with 3GPP RAT (UTRAN, GERAN)Architecture and migration

Single E-UTRAN architecture The E-UTRAN architecture shall be packet based, although provision should be made to support systems supporting real-time and conversational class traffic E-UTRAN architecture shall support an end-to-end QoSBackhaul communication protocols should be optimized

Radio Resource Management requirementsEnhanced support for end to end QoSSupport of load sharing and policy management across different Radio Access Technologies

Complexity Minimize the number of options No redundant mandatory features


LTE System PerformancePeak Data Rate

baseline

baseline150.8

302.8

51.0

75.4


LTE System Performance – cont’dDownlink Spectral Efficiency

Uplink Spectral Efficiency

LTE Key Features


Downlink: OFDMA (Orthogonal Frequency Division Multiple Access)Less critical AMP efficiency in BS sideConcerns on high RX complexity in terminal side

Uplink: SC-FDMA (Single Carrier-FDMA)Less critical RX complexity in BS sideCritical AMP complexity in terminal side (Cost, power Consumption, UL coverage)

Single node RAN (eNB)Support FDD (frame type 1) & TDD (frame type 2 for TD-SCDMA) <cf> H-FDD MSUser data rates

DL (baseline): 150.8 Mbps @ 20 MHz BW w/ 2x2 SU-MIMOUL (baseline): 75.4 Mbps @ 20 MHz BW w/ non-MIMO or 1x2 MU-MIMO

Radio frame: 10 ms (= 20 slots)Sub-frame: 1 ms (= 2 slots)Slot: 0.5 msTTI: 1 msHARQ

Incremental redundancy is used as the soft combining strategyRetransmission time: 8 ms

ModulationDL/UL data channel = QPSK/16QAM/64QAM

Making MS cheap as much as possible by

moving all the burdens from MS to BS


LTE Key Features – cont’dMIMO SM (Spatial Multiplexing), Beamforming, Antenna DiversityMin requirement: 2 eNB antennas & 2 UE rx antennas

DL: Single-User MIMO up to 4x4 supportableUL: 1x2 MU-MIMO, Optional 2x2 SU-MIMO

Resource block12 subcarriers with subcarrier BW of 15kHz “180kHz”24 subcarriers with subcarrier BW of 7.5kHz (only for MBMS)

Subcarrier operationFrequency selective by localized subcarrierFrequency diversity by distributed subcarrier & frequency hopping

Frequency hoppingIntra-TTI: UL (once per 0.5ms slot), DL (once per 66us symbol)Inter-TTI: across retransmissions

Bearer servicesPacket only – no circuit switched voice or data services are supportedVoice must use VoIP

MBSFNMulticast/Broadcast over a Single Frequency Network To support a Multimedia Broadcast and Multicast System (MBMS)Time-synchronized common waveform is transmitted from multiple cells for a given duration

The signal at MS will appear exactly as a signal transmitted from a single cell site and subject to multi-pathNot only “improve the received signal strength” but also “eliminate inter-cell interference”


E-UTRAN Architecture*

* 3GPP TS 36.300, E-UTRA and E-UTRAN; Overall description; Stage 2, Release 9, V9.0.0, June 2009


Functional Split b/w E-UTRAN and EPC*



3GPP Architecture EvolutionTowards Flat Architecture


E-UTRA Frequency Band*

Japan, Korea?

Korea?

EuropeKorea?

US

US

China?

* 3GPP TS 36.101, E-UTRA: UE radio transmission and reception, Release 9, V9.0.0, June 2009


E-UTRA Channel Bandwidth*1RB = 180kHz 6RBs = 1.08MHz, 100RBs = 18MHz6RBs (72 subcarriers) with 128 FFT, 100RBs (1200 subcarriers) with 2048 FFT

* 3GPP TS 36.101, E-UTRA: UE radio transmission and reception, Release 9, V9.0.0, June 2009


TS 36.101 for UE, 36.104 for eNBTransmitter characteristics

Transmit powerOutput power dynamicsTransmit signal qualityOutput RF spectrum emissionsTransmit intermodulation

Receiver characteristicsReference sensitivity power levelMaximum input levelAdjacent Channel Selectivity (ACS)Blocking characteristicsIntermodulation characteristicsSpurious emissions

Performance requirement (below is examples for UE)Dual-antenna receiver capabilitySimultaneous unicast and MBMS operationsDemodulation of PDSCH (Cell-Specific Reference Symbols)Minimum Requirement QPSK/16QAM/64QAMTransmit diversity performanceOpen-loop spatial multiplexing performanceClosed-loop spatial multiplexing performanceMU-MIMO


Conformance TestTS 36.141 Evolved Universal Terrestrial Radio Access (E-UTRA); Base Station (BS) conformance testing TS 36.143 Evolved Universal Terrestrial Radio Access (E-UTRA); FDD repeater conformance testing

TS 36.508 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Packet Core (EPC); Common test environments for User Equipment (UE) conformance testing TS 36.509 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Packet Core (EPC); Special conformance testing functions for User Equipment (UE)

TS 36.521-1 Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) conformance specification; Radio transmission and reception; Part 1: Conformance testing TS 36.521-2 Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) conformance specification; Radio transmission and reception; Part 2: Implementation Conformance Statement (ICS) TS 36.521-3 Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) conformance specification; Radio transmission and reception; Part 3: Radio Resource Management (RRM) conformance testing TS 36.523-1 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Packet Core (EPC); User Equipment (UE) conformance specification; Part 1: Protocol conformance specificationTS 36.523-2 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Packet Core (EPC); User Equipment (UE) conformance specification; Part 2: ICS TS 36.523-3 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Packet Core (EPC); User Equipment (UE) conformance specification; Part 3: Test suites

LTE Radio Interface Architecture


LTE Protocol Architecture (DL)


Logical Channels: “type of information it carries”

Control ChannelsBroadcast Control Channel (BCCH)used for transmission of system information from the network to all UEs in a cellPaging Control Channel (PCCH)used for paging of UEs whose location on cell level is not known to the networkCommon Control Channel (CCCH)used for transmission of control information in conjunction with random access, i.e., used for UEs having no RRC connectionDedicated Control Channel (DCCH)used for transmission of control information to/from a UE, i.e., used for UEs having RRC connection (e.g. handover messages)Multicast Control Channel (MCCH)used for transmission of control information required for reception of MTCH

Traffic ChannelsDedicated Traffic Channel (DTCH)used for transmission of user data to/from a UEMulticast Traffic Channel (MTCH)used for transmission of MBMS services



Transport Channels: “how”, “with what characteristics”

DownlinkBroadcast Channel (BCH)

A fixed TFUsed for transmission of parts of BCCH, so called MIB

Paging Channel (PCH) Used for transmission of paging information from PCCHSupports discontinuous reception (DRX)

Downlink Shared Channel (DL-SCH) Main transport channel used for transmission of downlink data in LTEUsed also for transmission of parts of BCCH, so called SIBSupports discontinuous reception (DRX)

Multicast Channel (MCH)Used to support MBMS

UplinkUplink Shared Channel (UL-SCH)

Uplink counterpart to the DL-SCHRandom Access Channel(s) (RACH)

Transport channel which doesn’t carry transport blocksCollision risk



DL Physical ChannelsPhysical Downlink Shared Channel (PDSCH)

실제 downlink user data를 전송하기 위한 transport channel인 DL-SCH와 paging 정보를 전송하기 위한 transport channel인 PCH가 매핑

동적 방송 정보인 SI (System Information) 값들도 RRC 메시지 형태로 DL-SCH를 통해 전송되므로 이 역시 PDSCH로 매핑

이 경우는 전체 셀 영역으로 도달될 수 있는 능력이 요구되기도 함

Physical Broadcast Channel (PBCH)UE가 cell search과정을 마친 후에 최초로 검출하는 채널로서, 다른 물리 계층 채널들을 수신하기 위하여 반드시 필요한 기본적인 시스템 정보들인 MIB (Master Information Block)를 전송하기 위한 transport channel인 BCH가 매핑

Physical Multicast Channel (PMCH)방송형 데이터를 전송하기 위한 transport channel 인 MCH가 매핑

Physical Control Format Indicator Channel (PCFICH)매 subframe마다 전송, only one PCFICH in each cellInforms UE about CFI which indicates the number of OFDM symbols used for PDCCHstransmission

Physical Downlink Control Channel (PDCCH)Informs UE about resource allocation of PCH and DL-SCHHARQ information related to DL-SCHUL scheduling grant

Physical HARQ Indicator Channel (PHICH)Carries HARQ ACK/NACKs in response to UL transmission


UL Physical ChannelsPhysical Uplink Shared Channel (PUSCH)

Uplink counterpart of PDSCHCarries UL-SCH

Physical Uplink Control Channel (PUCCH)Carries HARQ ACK/NAKs in response to DL transmissionCarries Scheduling Request (SR)Carries channel status reports such as CQI, PMI and RIAt most one PUCCH per UE

Physical Random Access Channel (PRACH)Carries the random access preamble


LTE Channel Mapping

Downlink

Uplink


Terminal States

RRC_CONNECTEDActive state where UE is connected to a specific cellOne or several IP addresses as well as an identity of the terminal, Cell Radio-Network Temporary Identifier (C-RNTI), used for signaling purposes b/w UE and network, have been assignedTwo substates: IN_SYNC & OUT_OF_SYNC whether or not uplink is synchronized to the network

RRC_IDLELow activity state where US sleeps most of the time to reduce battery consumptionUplink synchronization is not maintained and hence only uplink transmission that may take place is random accessIn downlink, US can periodically wake up to be paged for incoming callsUE keeps its IP address(es) and other internal info to rapidly move to RRC_CONNECTED


Example of LTE Data Flow

LTE Downlink Transmission


Frame Structure: Type 1 for FDD

where, Ts = 1/(15000 x 2048) seconds “the smallest time unit in LTE”Tf = 307200 x Ts = 10 ms

#0 #1 #2 #3 #19

One slot, Tslot = 15360×Ts = 0.5 ms

One radio frame, Tf = 307200×Ts=10 ms

#18

One subframe


Frame Structure: Type 2 for TDD


Frame Structure: FDD/TDD


DL Slot Structure: Downlink bandwidth configuration,

expressed in units of

: Resource block size in the frequency domain, expressed as a number of subcarriers

: Number of OFDM symbols in an downlink slot

RBscN

RBscN

DLRBN

DLsymbN

DLsymbN

slotT

0=l 1DLsymb −= Nl

RB

scD

LR

BN

N×

RB

scN

RBsc

DLsymb NN ×

),( lk

0=k

1RBsc

DLRB −= NNk

The minimum RB the eNB uses for LTE scheduling is “1ms (1subframe) x 180kHz (12subcarriers @ 15kHz spacing)”


DefinitionsResource Grid

Defined as subcarriers in frequency domain and OFDM symbols in time domain

The quantity depends on the DL transmission BW configured in the cell and shall fulfill

The set of allowed values for is given by TS 36.101, TS 36.104

Resource Block (1 RB = 180 kHz)Defined as “consecutive” subcarriers in frequency domain and “consecutive” OFDM symbols in time domain

Corresponding to one slot in the time domain and 180 kHz in the frequency domain

Resource ElementUniquely defined by the index pair in a slot where and are the indices in the frequency and time domain, respectively

1106 DLRB ≤≤ N

RBsc

DLRB NN DL

symbN

RBscN

( )lk,

DLRBN

DLRBN

DLsymbN

1,...,0 DLsymb −= Nl1,...,0 RB

scDLRB −= NNk


Normal CP & Extended CP


PRB and VRB (LVRB, DVRB)Physical resource blocks are numbered from 0 to in the frequency domain.

The relation between the physical resource block number in the frequency domain and resource elements in a slot is given by

A virtual resource block is of the same size as a physical resource block. Two types of virtual resource blocks are defined: LVRB and DVRB

Virtual resource blocks of localized type are mapped directly to PRBs such that virtual resource block corresponds to physical resource block . Virtual resource blocks are numbered from 0 to , where .

1DLRB −N

PRBn),( lk

⎥⎥⎦

⎥

⎢⎢⎣

⎢= RB

scPRB N

kn

VRBn VRBPRB nn =

1DLVRB −N DL

RBDLVRB NN =


DVRBVirtual resource blocks of distributed type are mapped to PRBs as follows

Consecutive VRBs are not mapped to PRBs that are consecutive in the frequency domain

Even a single VRB pair is distributed in the frequency domain

The exact size of the frequency gap depends on the overall downlink cell BW

Resource-element groups (REG)


Basic unit for mapping of PCFICH, PHICH, and PDCCHResource-element groups are used for defining the mapping of control channels to resource elements. Mapping of a symbol-quadruplet

onto a resource-element group is defined such that elements are mapped to resource elements of the resource-element group not used for cell-specific reference signals in increasing order of l and k

)3(),2(),1(),( +++ iziziziz

)(iz),( lk

n+0

n+1

n+2

n+3

n+4

n+5

n+6

n+7

n+0

n+1

n+2

n+3

n+4

n+5

n+6


DL Physical Channel Processing

OFDM signal generation

Layer Mapper

Scrambling

Precoding

Modulation Mapper

Modulation Mapper

Resourceelement mapper

OFDM signal generationScrambling

code words layers antenna ports

Resourceelement mapper

scrambling of coded bits in each of the code words to be transmitted on a physical channelmodulation of scrambled bits to generate complex-valued modulation symbolsmapping of the complex-valued modulation symbols onto one or several transmission layersprecoding of the complex-valued modulation symbols on each layer for transmission on the antenna portsmapping of complex-valued modulation symbols for each antenna port to resource elementsgeneration of complex-valued time-domain OFDM signal for each antenna port


Channel Coding

Turbo codePCCC (exactly the same as in WCDMA/HSPA)QPP (quadratic polynomial permutation) interleaver

Modulation


DL Layer Mapping and Precoding


Explained in MIMO session


DL OFDM Signal GenerationOFDM Parameters

N = 2048 for ∆f=15kHzN = 4096 for ∆f=7.5kHz

Check with resource block parameters(160+2048) x Ts = 71.88us(144+2048) x Ts = 71.35us71.88us + 71.35us x 6 = 0.5ms

Normal Cyclic Prefix = 160 Ts = 5.2 usNormal Cyclic Prefix = 144 Ts = 4.7 us Extended Cyclic Prefix = 512 Ts = 16.7 usExtended Cyclic Prefix for MBMS = 1024 Ts = 33.3 us

( ) s,CP0 TNNt l ×+<≤


DL Physical Channels & SignalsPhysical channels

Physical Downlink Shared Channel (PDSCH)Physical Broadcast Channel (PBCH)Physical Multicast Channel (PMCH)Physical Control Format Indicator Channel (PCFICH)Physical Downlink Control Channel (PDCCH)Physical HARQ Indicator Channel (PHICH)

Physical signalsReference Signals

Cell-specific RS, associated with non-MBSFN transmissionAid coherent detection (pilot)Reference channel for CQI from UE to eNB

MBSFN RS, associated with MBSFN transmissionUE-specific RS

Synchronization SignalsCarries frequency and symbol timing synchronizationPSS (Primary SS) and SSS (Secondary SS)


DL Reference SignalsCell-specific reference signals

Are transmitted in every downlink subframe, and span entire cell BWCan be used for coherent demodulation of any downlink transmission “except” when so-called non-codebook-based beamforming is usedUsing antenna ports {0, 1, 2, 3}

MBSFN reference signalsAre used for channel estimation for coherent demodulation of signals being transmitted by means of MBSFNUsing antenna port 4

UE-specific reference signals Is specifically intended for channel estimation for coherent demodulation of DL-SCH when non-codebook-based beamforming is used.Are transmitted only within the RB assigned for DL-SCH to that specific UEUsing antenna port 5

Cell-Specific Reference Signals


When estimating the channel for a certain RB, UE may not only use the reference symbols within that RB but also, in frequency domain, neighbor RBs, as well as reference symbols of previously received slots/subframes

Pseudo-random sequence generation

is the slot number within a radio frame.is the OFDM symbol number within the slot.

The pseudo-random sequence c(i) is a length-31 Gold sequence.

The complex values of reference symbols will vary b/w different reference-symbol position and also b/w different cells. Thus, RS of a cell can be seen as a cell-specific two-dimensional sequence with the period of one frame.Regardless of cell BW, the reference signal sequence is defined assuming the maximum possible LTE cell BW corresponding to 110 RBs in frequency domain

( ) ( ) 12,...,1,0 ,)12(212

1)2(212

1)( DLmax,RB, s

−=+⋅−+⋅−= Nmmcjmcmr nl

Relationship with Cell Identity


504 unique Cell ID:168(N1) Cell ID groups, 3 (N2) Cell ID within each group

Cell ID = 3xN1+N2 = 0 ~ 503 index

504 pseudo-random sequences

One to one mapping between the Cell ID and Pseudo-random sequences

Cell-specific Frequency Shift (N1 mod 6)1 RE shift from current RS position in case of next Cell ID index

Each shift corresponds to 84 different cell identities, that is 6 shifts jointly cover all 504 cell identities.

Effective with RS boosting to enhance reference signal SIR by avoiding the collision of boosted RSs from neighboring cells (assuming time synchronization)


Cell-Specific RS Mapping

0=l0R

0R

0R

0R

6=l 0=l0R

0R

0R

0R

6=l

One

ant

enna

por

tTw

o an

tenn

a po

rts

Resource element (k,l)

Not used for transmission on this antenan port

Reference symbols on this antenna port

0=l0R

0R

0R

0R

6=l 0=l0R

0R

0R

0R

6=l 0=l

1R

1R

1R

1R

6=l 0=l

1R

1R

1R

1R

6=l

0=l0R

0R

0R

0R

6=l 0=l0R

0R

0R

0R

6=l 0=l

1R

1R

1R

1R

6=l 0=l

1R

1R

1R

1R

6=l

Four

ant

enna

por

ts

0=l 6=l 0=l

2R

6=l 0=l 6=l 0=l 6=l2R

2R

2R

3R 3R

3R 3R

even-numbered slots odd-numbered slots

Antenna port 0


Antenna port 1


Antenna port 2


Antenna port 3


MBSFN RS Mapping


MBSFN RS Mapping


UE-specific RS on top of Cell-specific RSUE-specific RS (antenna port 5)

12 symbols per RB pairDL CQI estimation is always based on cell-specific RS (common RS)

PCFICH


The number of OFDM symbols used for control channel can be varying per TTICFI (Control Format Indication)

Information about the number of OFDM symbols (1~4) used for transmission of PDCCHs in a subframe

PCFICH carries CFI

2 bits 32 bits (block coding) 32 bits (cell specific scrambling) 16 symbols (QPSK)Mapping to resource elements: 4 REG (16 RE excluding RS) in the 1st OFDM symbol

Spread over the whole system bandwidthTo avoid the collisions in neighboring cells, the location depends on cell identity

Transmit diversity is applied which is identical to the scheme applied to BCH


PCFICH REG Mapping Cell ID

RBscN

DLRBN

Example for 5 MHz BW LTE= 25 (number of REGs = 50)

= 12

REG


PCFICH Processing

PHICH


HARQ ACK/NAK in response to UL transmission

HI codewords with length of 12 REs = 4 (Walsh spreading) x 3 (repetition)3 groups of 4 contiguous REs (not used for RS and PCFICH)

BPSK modulation with I/Q multiplexing

SF4 x 2 (I/Q) = 8 PHICHs in normal CP

Cell-specific scrambling

Tx diversity, the same antenna ports as PBCH

Typically, PHICH is transmitted in the first OFDM symbol only

For FDD, an uplink transport block received in subframe n should be acknowledged on the PHICH in subframe n+4


PHICH REG Mapping

DLRBN

Cell ID

⎣ ⎦( )⎣ ⎦ ⎣ ⎦( )⎣ ⎦ ⎣ ⎦( )⎪

⎪

⎩

⎪⎪

⎨

⎧

=++⋅

=++⋅

=+⋅

=

′′′

′′′

′′

2mod32'

1mod3'

0mod'

1cellID

1cellID

1cellID

innmnnN

innmnnN

inmnnN

n

iii

iii

ii

lll

lll

ll

i

Example for 5 MHz BW LTE= 25 (number of REGs = 50)

= 12RBscN

DLRBN

REG


PHICH Processing


symbol

Subcarrier

PCFICH/PHICH RE MappingExample for 5 MHz BW LTE

PDCCH DCI Format


PDCCH is used to carry DCI where DCI includes;Downlink scheduling assignments, including PDSCH resource indication, transport format, HARQ-related information, and control information related to SM (if applicable).Uplink scheduling grants, including PUSCH resource indication, transport format, and HARQ-related information. Uplink power control commands

DCI Formats Usage Details

0 UL grant

DL assignment

Power control

For scheduling of PUSCH1 For scheduling of one PDSCH codeword (SIMO, TxD)

1A For compact scheduling of one PDSCH codeword (SIMO, TxD) and random access procedureinitiated by a PDCCH order

1B For compact scheduling of one PDSCH codeword with precoding information (CL single-rank)

1C For very compact scheduling of one PDSCH codeword (paging, RACH response and dynamic BCCH scheduling)

1D For compact scheduling of one PDSCH codeword with precoding & power offset information2 For scheduling PDSCH to UEs configured in CL SM

2A For scheduling PDSCH to UEs configured in OL SM3 For transmission of TPC commands for PUCCH/PUSCH with 2-bit power adjustment

3A For transmission of TPC commands for PUCCH/PUSCH with single bit power adjustment

Downlink Assignment


Major contents of different DCI formats: not exhaustiveDCI format 0/1A indication [1 bit]Distributed transmission flag [1 bit]Resource-block allocation [variable]For the first (or only) transport block

MCS [5 bit]New-data indicator [1 bit]Redundancy version [2 bit]

For the second transport block (present in DCI format 2 only)MCS [5 bit]New-data indicator [1 bit]Redundancy version [2 bit]

HARQ process number [3 bit for FDD]Information related to SM (present in DCI format 2 only)

Pre-coding information [3 bit for 2 antennas, 6 bit for 4 antennas in CL-SM]Number of transmission layerHARQ swap flag [1 bit]

Transmit power control (TPC) for PUCCH [2 bit]Identity (RNTI) of the terminal for which the PDCCH transmission is intended [16 bit]

Uplink Grants


Major contents of DCI format 0 for UL grants: not exhaustiveDCI format 0/1A indication [1 bit]Hopping flag [1 bit]Resource-block allocation [variable]MCS [5 bit]New-data indicator [1 bit]Phase rotation of UL demodulation reference signal [3 bit]Channel-status request flag [1 bit]Transmit power control (TPC) for PUSCH [2 bit]Identity (RNTI) of the terminal for which the PDCCH transmission is intended [16 bit]

The time b/w reception of an UL scheduling grant on a PDCCH and the corresponding transmission on UL-SCH are fixed

For FDD, the time relation is the same as for PHICHUplink grant received in downlink subframe n applies to uplink subframe n+4

PDCCH Processing


First n OFDM symbols< 10RB: 2~4 OFDMA symbols> 10RB: 1~3 OFDMA symbols 1/14~3/14 (10~20%) overhead

PDCCH format based on # of CCE (Control Channel Element, = 9 REGs)Depending on the payload size of control information (DCI payload) & coding rateNumber of CCEs for each of PDCCH may vary and is not signaled, so UE has to blindly determine this

search space: a set of candidate control channels formed by CCEs on a given aggregation level {1, 2, 4, 8}, which UE is supposed to attempt to decode

User identification is based on “UE specific CRC (normal CRC with UE ID masking)”Cell-specific scrambling, QPSK with tail-biting Conv. CodeTx diversity, the same antenna ports as PBCHMapped to REG not assigned to PCFICH or PHICH


PDCCH Processing

System Information


Master information block (MIB) includes the following information:Downlink cell bandwidth [4 bit]PHICH duration [1 bit]PHICH resource [2 bit]System Frame Number (SFN) except two LBSsEtc…

LTE defines different SIBs:SIB1 includes info mainly related to whether an UE is allowed to camp on the cell. This includes info about the operator(s) and about the cell (e.g. PLMN identity list, tracking area code, cell identity, minimum required Rx level in the cell, etc), DL-UL subframe configuration in TDD case, and the scheduling of the remaining SIBs. SIB1 is transmitted every 80ms.SIB2 includes info that UEs need in order to be able to access the cell. This includes info about the UL cell BW, random access parameters, and UL power control parameters. SIBs also includes radio resource configuration of common channels (RACH, BCCH, PCCH, PRACH, PDSCH, PUSCH, PUCCH, and SRS).SIB3 mainly includes info related to cell-reselection.SIB4-8 include neighbor-cell-related info. (E-UTRAN, UTRAN, GERAN, cdma2000)SIB9 contains a home eNB identifierSIB10/11 contains ETWS (Earthquake and Tsunami Warning System) notificationMore to be added

MIB mapped to PBCHOther SIBs mapped to PDSCH

BCH on PBCH


To broadcast a certain set of cell and/or system-specific informationRequirement to be broadcast in the entire coverage area of the cellBCH transmission

The coded BCH transport block is mapped to four subframes (slot #1 in subframe #0) within a 40ms interval40ms timing is blindly detected (no explicit signaling indicating 40ms timing)Each subframe is assumed to be self-decodable, i.e. the BCH can be decoded from a single reception, assuming sufficiently good channel conditions

BCH on PBCH – cont’d


Single (fixed-size) transport block per TTI (40 ms)No HARQCell-specific scrambling, BPSK with ½ tail-biting Conv. Code, Tx diversity(1,2,4)

BCH mapped to 4 OFDM symbols within a subframe in time-domain at 6 RBs(72 subcarriers) excluding DC in freq-domainPBCH is mapped into RE assuming RS from 4 antennas are used at eNB, irrespective of the actual number of TX antennaDifferent transmit diversity schemes per # of antennas

# of ant=2: SFBC# of ant=4: SFBC + FSTD (Frequency Switching Transmit Diversity)

No explicit bits in the PBCH to signal the number of TX antennas at eNBPBCH encoding chain includes CRC masking dependent on the number of configured TX antennas at eNBBlind detection of the number of TX antenna using CRC masking by UE


PBCH Processing


PDSCH Processing

1) RS2) PSS & SSS

and BCH3) PCFICH4) PHICH5) PDCCH6) PDSCH


DL constellation & frame summary

LTE Uplink Transmission


LTE Uplink Key FeaturesSC-FDMA 사용

단말의 PAPR을 낮추어 커버리지를 증가시키기에 적합함

DFT size is limited to products of the integers 2, 3, and 5(e.g. DFT sizes of 60, 72, and 96 are allowed but a DFT size of 84 is not allowed.)

No unused DC-subcarrier is defined

CAZAC (Constant Amplitude Zero Autocorrelation) sequence 사용

Reference signal 및 제어 정보 채널 전송 시 각 단말들의 신호를 구분하기 위하여 CDM을 수행하는 경우 CAZAC sequence를 주로 사용

CAZAC sequence는 시간/주파수 차원에서 일정한 amplitude를 유지하는 특성을 가지

므로 단말의 PAPR을 낮추어 커버리지를 증가시키기에 적합함

MU-MIMO 지원

QPSK/16QAM/64QAM modulation 지원


UL Slot Structure: Uplink bandwidth configuration,

expressed in units of

: Resource block size in the

frequency domain, expressed as a

number of subcarriers

: Number of SC-FDMA symbols in

an uplink slot

RBscN

RBscN

ULRBN

ULsymbN

ULsymbN

slotT

0=l 1ULsymb −= Nl

RB

scU

LR

BN

N×

RB

scN

RBsc

ULsymb NN ×

),( lk

0=k

1RBsc

ULRB −= NNk


DefinitionsResource Grid

Defined as subcarriers in frequency domain and SC-FDMA symbols in time domain

The quantity depends on the UL transmission BW configured in the cell and shall fulfill

The set of allowed values for is given by TS 36.101, TS 36.104

Resource Block

Defined as “consecutive” subcarriers in frequency domain and “consecutive” SC-FDMA symbols in time domain

Corresponding to one slot in the time domain and 180 kHz in the frequency domain

Resource Element

Uniquely defined by the index pair in a slot where and are the indices in the frequency and time domain, respectively

1106 ULRB ≤≤ N

RBsc

ULRB NN UL

symbN

RBscN

( )lk,

ULRBN

ULRBN

ULsymbN

1,...,0 ULsymb −= Nl1,...,0 RB

scULRB −= NNk


UL Physical Channels & SignalsUL physical channels

Physical Uplink Shared Channel (PUSCH)Physical Uplink Control Channel (PUCCH)Physical Random Access Channel (PRACH)

UL physical signalsAn uplink physical signal is used by the physical layer but does not carry information originating from higher layersTwo types of reference signals

UL demodulation reference signal (DRS) for PUSCH, PUCCHUL sounding reference signal (SRS) not associated with PUSCH, PUCCH transmission


UL Reference SignalsUL RS should preferably have the following properties:

Favorable auto- and cross-correlation propertiesLimited power variation in freq-domain to allow for similar channel-estimation quality for all frequenciesLimited power variation in time-domain (low cubic metric) for high PA efficiencySufficiently many RS sequences of the same length to avoid an unreasonable planning effort

Zadoff-Chu SequenceAppeared in IEEE Trans. Inform. Theory in 1972Poly-phase sequenceConstant amplitude zero auto correlation (CAZAC) sequence의 일종

Cyclic autocorrelations are zero for all non-zero lags, Non-zero cross-correlationsConstant power in both the frequency and the time domain

No restriction on code length N

- Sequence number p is relatively prime to N- Sequence length: N- Number of sequences: N-1

,,

)()1(2

2 2

⎪⎩

⎪⎨⎧

=+−

−

npnN

j

pnN

j

p

e

eng π

πwhen N is even

when N is odd


DRSDRS is made from Z-C sequence*, and the DRS sequence length is the same with the number of subcarriers in an assigned RBsDRS is defined with the following parameters

Sequence group (30 options): cell specific parameterSequence (2 options for sequence lengths of 6PRBs or longer): cell specific parameterCyclic shift (12 options): both terminal and cell specific componentsSequence length: given by the UL allocation

Typically,Cyclic shifts are used to multiplex RSs from different UEs within a cell.Different sequence groups are used in neighboring cells.


DRS Location within a SubframeDM RS for PUSCH

Normal CP 적용 시 PUSCH RS는 한 슬롯 당 중앙의 SC-FDMA 심볼에 위치Extended CP 적용 시 PUSCH RS는 한 슬롯 당 3번째 SC-FDMA 심볼에 위치

DM RS for PUCCHFormat 1x

Format 2x


SRS기지국이 각 단말의 상향링크 채널 정보를 추정할 수 있도록 단말이 전송하는 RSReference for channel quality information

CQ measurement for frequency/time aware schedulingCQ measurement for link adaptationCQ measurement for power controlCQ measurement for MIMOTiming measurement

Reference signal sequence is defined by a cyclic shift of a base sequence (ZC)

SRS 전송주기/대역폭은 각 단말마다 고유하게 할당

From as often as once in every 2ms to as infrequently as once in every 160ms (320ms)At least 4 RBs

SRS는 서브프레임의 마지막 SC-FDMA 심볼로 전송

SRS multiplexing byTime, Frequency, Cyclic shifts, and transmission comb (2 combs distributed SC-FDMA)

To avoid the collision b/w SRS and PUSCH transmission from other UEs, SRS transmissions should not extend into the frequency band reserved for PUCCH.

( ) ( )nrnr vu)(

,SRS α= RS

sc,)(

, 0),()( Mnnrenr vunj

vu <≤= αα


SRS – cont’dNon-frequency-hopping (wideband) SRS and frequency-hopping SRS

Multiplexing of SRS transmissions from different UEs


Uplink L1/L2 Control SignalingUplink L1/L2 control signaling consists of:

HARQ acknowledgements for received DL-SCH transport blocksUE reports downlink channel conditions including CQI, PMI, and RIScheduling requests

Two different methods for transmission of UL L1/L2 control signalingNo simultaneous transmission of UL-SCH

UE doesn’t have a valid scheduling grant, that is, no resources have been assigned for UL-SCH in the current subframePUCCH is used for transmission of UL L1/L2 control signaling

Simultaneous transmission of UL-SCHUE has a valid scheduling grant, that is, resources have been assigned for UL-SCH in the current subframeUL L1/L2 control signaling is time multiplexed with the coded UL-SCH onto PUSCH prior to SC-FDMA modulationOnly HARQ acknowledgement and channel-status reports are transmittedNo need to request a SR. Instead, in-band buffer status reports are sent in MAC headersThe basis for channel-status reports on PUSCH is aperiodic reportsIf a periodic report is configured to be transmitted on PUCCH in a frame when US is scheduled to transmit PUSCH, then the periodic report is rerouted to PUSCH resources


Periodic/Aperiodic Channel Info Feedback

Periodic reporting Aperiodic reporting

When to send Periodically every 2-160 ms When requested by eNB

Where to send Normally on PUCCH, PUSCH used when multiplexed with data Always on PUSCH

Payload size of the reports 4-11 bits Up to 64 bits

Channel coding Linear block codes RM coding or tail-biting CC

CRC protection No Yes, 8 bit CRC

RI Sent in separate subframes at lower periodicity

Sent separately encoded in the same subframe

Freq. selectivity of CQI Only very limited amount of frequency info

Detailed frequency selective reports are possible

Freq. selectivity of PMI Only wideband PMI Frequency selective PMI reports are possible


UL L1/L2 control signaling on PUCCHThe reasons for locating PUCCH resources at the edges of the spectrum

To maximize frequency diversityTo retain single-carrier property

Multiple UEs can share the same PUCCH resource blockFormat 1: length-12 orthogonal phase rotation sequence + length-4 orthogonal coverFormat 2: length-12 orthogonal phase rotation sequence

PUCCH is never transmitted simultaneously with PUSCH from the same UE2 consecutive PUCCH slots in Time-Frequency Hopping at the slot boundary


Changing UL System BW Via PUCCH Config


PUCCH Formats

PUCCH format

Modulation scheme

Number of bits per subframe Usage

Multiplexing capacity (UE/RB)

1 N/A N/A SRACK/NACKACK/NACK

CQICQI + ACK/NACKCQI + ACK/NACK

1a BPSK 136, 18*, 1236, 18*, 1236, 18*, 12

12, 6*, 412, 6*, 4

1b QPSK 22 QPSK 202a QPSK+BPSK 212b QPSK+QPSK 22 12, 6*, 4

* Typical value with 6 different rotations (choosing every second cyclic shift)

PUCCH Format 2/2a/2b is located at the outermost RBs of system BWACK/NACK for persistently scheduled PDSCH and SRI are located nextACK/NACK for dynamically scheduled PDSCH are located innermost RBs


PUCCH Resource MappingFormat 1

4 symbols are modulated by BPSK/QPSKBPSK/QPSK symbol is multiplied by a length-4 orthogonal cover sequence (a length-3 orthogonal cover when there is SRS), and then it modulates the rotated length-12 sequence.

Reference signals also employ one orthogonal cover sequencePUCCH capacity: up to 3 x 12 = 36 different UEs per each cell-specific sequence(assuming all 12 rotations being available Practically, only 6 rotations.)

Format 2

5 symbols are modulated by QPSK after being multiplied by a phase rotated length-12 cell specific sequence.Resource consumption of one channel-status report is 3x of HARQ acknowledgement


More on PUCCH Multiplexing

CDM and FDMTwo ways for CDM

CDM by means of cyclic shifts of a CAZAC sequenceCDM by means of block-wise spreading with the orthogonal cover sequences

Two main issues with CDMChannel delay spread limits the orthogonality between cyclically shifted CAZAC sequencesChannel Doppler spread limits the orthogonality between block-wise spread sequences


PUCCH Format1 Processing


PUCCH Format2 Processing


UL L1/L2 control signaling on PUSCH


More on Control Signalling on PUSCHCQI/PMI transmitted on PUSCH uses the same modulation scheme as data.ACK/NACK and RI are transmitted so that the coding/scrambling/ modulation maximize the Euclidean distance at the symbol level.The outermost constellation points are used to signal these for 16QAM and 64QAM.Different channel coding

1-bit ACK/NACK: repetition coding2-bit ACK/NACK/RI: simplex codingCQI/PMI < 11bits: (32,N) Reed-Muller codingCQI/PMI > 11bits: tail-biting CC (1/3)

How to keep the performance of control signaling on PUSCH?Different power offset? No! Because SC properties are partially destroyed.Variable coding rate? Yes! The size of physical resources for control is scaled.


PUSCH Processing (1)

UL SC-FDMA Signal Generation


This section applies to all uplink physical signals and physical channels except the physical random access channel

SC-FDMA parameters

where N = 2048

Check with numbers in Table 5.2.3-1.{(160+2048) x Ts} + 6 x {(144+2048) x Ts} = 0.5 ms

6 x {(512+2048) x Ts} = 0.5 ms

( ) s,CP0 TNNt l ×+<≤


PUSCH Frequency HoppingPUSCH transmission

Localized transmission w/o frequency hoppingFrequency Selective Scheduling Gain

Localized transmission with “frequency hopping”

Frequency Diversity Gain, Inter-cell Interference Randomization

Two types of PUSCH frequency hoppingSubband-based hopping according to cell-specific hopping patternsHopping based on explicit hopping information in the scheduling grant


Hopping based on cell-specific patternsSubbands are defined

In 10 MHz BW case, the overall UL BW corresponds to 50 RBs and there are a total of 4 subbands, each consisting of 11 RBs. The remaining 6 RBs are used for PUCCH transmission.

The resource defined by a scheduling grant (VRBs) is not the actual set of RBs for transmission.The resource to use for transmission (PRBs) is the resource provided in the scheduling grant “shifted” a number of subbands according to a cell-specific hopping pattern.


More on hopping w/ cell-specific patternsExample for predefined hopping for PUSCH with 20 RBs and M=4 (subband hopping + mirroring)


Hopping based on explicit informationExplicit hopping information provided in the scheduling grant is about the “offset” of the resource in the second slot, relative to the resource in the first slotSelection b/w hopping based on cell-specific hopping patterns or hopping based on explicit information can be done dynamically.

Cell BW less than 50 RBs1 bit in scheduling grant indicating to specify which scheme is to be usedWhen hopping based on explicit information is selected, the offset is always half of BW

Cell BS equal or larger than 50 RBs2 bits in scheduling grantOne of the combinations indicate that hopping should be based on cell-specific hopping patternsThree remaining combinations indicate hopping of 1/2, +1/4, and -1/4 of BW


PRACHPRACH는 RA 과정에서 단말이 기지국으로 전송하는 preamble이다

6RB를 차지하며 부반송파 간격은 1.25kHz (format #4는 7.5kHz)64 preamble sequences for each cell 64 random access opportunities per PRACH resourceSequence부분은 길이 839의 Z-C sequence로 구성 (format #4는 길이 139)

Phase modulation: Due to the ideal auto-correlation property, there is no intra-cell interference from multiple random access attempt using preambles derived from the same Z-C root sequence.

Five types of preamble formats to accommodate a wide range of scenariosHigher layers control the preamble format

넓은 반경의 셀 환경과 같이 시간 지연이 긴 경우

SINR이 낮은 상황을 고려하여 sequence repetitionSINR이 낮은 상황을 고려하여 sequence repetitionTDD 모드용


Different Preamble Formats


PRACH Location


UL 16QAM SC-FDMA

LTE Cell Search


Synchronization Signals504 unique physical-layer cell identities

168 unique physical-layer cell-identity groups (0~167)3 physical-layer identity within physical-layer cell-identity group (0~2)

SS is using single antenna portHowever, SS can be with UE-transparent transmit antenna scheme (e.g. PVS, TSTD, CDD)Primary SS (PSS) and Secondary SS (SSS)


Primary Synchronization SignalThe sequence used for the primary synchronization signal is generated from a frequency-domain Zadoff-Chu sequence (Length-62)

For frame structure type 1, PSS is mapped to the last OFDM symbol in slots 0 and 10No need to know CP length

The sequence is mapped to REs (6 RBs) according to

Cell ID detection within a cell ID group (3 hypotheses) Half-frame timing detection (Repeat the same sequence twice)

⎪⎩

⎪⎨

⎧

=

== ++−

+−

61,...,32,31

30,...,1,0)(63

)2)(1(

63)1(

ne

nend nnuj

nunj

u π

π

( ) 61,...,0 ,1 ,2

31 , DLsymb

RBsc

DLRB

, =−=+−== nNlNN

nknda lk


Secondary Synchronization SignalThe sequence used for the second synchronization signal is an interleaved concatenation of two length-31 binary sequences (X and Y)The concatenated sequence is scrambled with a scrambling sequence given by PSSThe combination of two length-31 sequences defining SSS differs between slot 0 (SSS1) and slot 10 (SSS2) according to

whereBlind detection of CP-length (2 FFT operations are needed)The same antenna port as for the primary sync signalMapped to 6 RBs

( )( )( ) ( )( ) ( )⎪⎩

⎪⎨⎧

=+

⎪⎩

⎪⎨⎧

=

5 subframein )(0 subframein )()12(

5 subframein )(0 subframein )()2(

)(11

)(0

)(11

)(1

0)(

1

0)(

0

10

01

1

0

nzncnsnzncnsnd

ncnsncnsnd

mm

mm

m

m

300 ≤≤ n


Structure of SSS


Synchronization Signals – cont’dCell ID group detection (the set of valid combination of X and Y for SSS are 168)Frame boundary detection (the m-sequences X and Y are swapped b/w SSS1 and SSS2)


LTE Cell SearchPrimary SSSymbol timing acquisitionFrequency synchronizationCell ID detection within a cell group ID (3 hypotheses)Half-frame boundary detection

Secondary SSCell group ID detection (168 hypotheses)Frame boundary detection (2 hypotheses)CP-length detection (2 hypotheses)

BCH40ms BCH period timing detectioneNB # of tx antenna detectionMIB acquisition(Operation BW, SFN, etc…)

PDCCH reception

SIB acquisition within PDSCH

Check Cell ID with cell-specific RS


(cf) WCDMA Cell Search ProcedureTerminal power on

Detect strongest PSCH

Get slot synch from P-SCH

Get PICH code group info from S-SCH

8 PN codes per group.64 code groups have512 PN codes in total. Get PN code info by evaluating

all 8 PN codes in code group

Get system info from PCCPCH

Wait while monitoring SCCPCH


LTE Cell Search – cont’d*

PSS/SSS, BCHPSS/SSS, BCH

1.4

3

Summary


LTE Frame & Slot Structure

* 윤상보 (삼성), “3GPP LTE & LTE-Advanced System”, 제5차 차세대이동통신 단기강좌, Aug. 2008


DL Frame Structure Type 1*


UL Frame Structure Type 1*

1 RB


E-UTRA UE Capabilities*

* 3GPP TS 36.306, E-UTRA; UE Radio Access Capabilities, Release 8, V8.4.0, June 2009


LTE with Voice?Long-term

Maybe through IMSNear-term

CS FallbackNTT DoCoMo pushed the industry to include CS Fallback as part of the 3GPP standard.With CS Fallback the operator accepts the notion that its brand new LTE network won’t support voice and SMS services. Instead, a control signal is sent to the LTE device indicating an incoming voice call/SMS message at which point the device falls back to the legacy 2G/3G network to receive the call/message.Largely comparable to 1xEV-DO/1XWon’t work for 3GPP2 operators (e.g. Verizon, KDDI, and LGT)

VoLGALeverage the operator’s existing circuit switched CN to carry voice calls and SMS messages over the LTE air interface. In many respects VoLGA is comparable to GAN/UMA, which is how operators like Orange UK and T-Mobile USA leverage Wi-Fi access points to offload voice traffic from their macro cellular networks. In other words VoLGA = GAN/UMA – Wi-Fi.Has been ruled out as from Release 8 or Release 9 of 3GPP

The driver for LTE is the rapid acceleration of mobile data traffic, thus it would be counter productive to use LTE for voice services.What about SR-VCC (Single Radio Voice Call Continuity) to GSM/WCDMA/CDMA?What about coverage?


CS FallbackMobile terminated call

Mobile originated call


Evolution Beyond Release 8LTE MBMSSON enhancementsFurther improvements for enhanced VoIP support in LTEThe requirements for the multi-bandwidth and multi-radio access technology base stationEnhanced mobility support for LTEEnhanced positioning support for LTEDual layer beam forming for Rel.9Enhanced DL transmission for LTE Home-(e)NB

And… LTE-Advanced with Release 10


LTE and WiMAXWhat is 4G (through LTE and WiMAX)?

New Technology: OFDM + MIMONew Biz Model: Mobile Broadband

LTE is justifying WiMAX and WiMAX is justifying LTEThey are using the same fundamental technologiesThey are targeting the same market

Convergence??In technical area: 3GPP LTE-Adv & IEEE 802.16m are getting more and more similarIn biz area: Ecosystem??


Final Message* * Signals Ahead


References[1] 3GPP homepage: www.3gpp.org[2] Hannes Ekström, Anders Furuskär, Jonas Karlsson, Michael Meyer, Stefan Parkvall, Johan Torsner, and Mattias

Wahlqvist (Ericsson), “Technical Solutions for the 3G Long-Term Evolution”, IEEE Communications Magazine, March 2006

[3] Erik Dahlman, Hannes Ekstrom, Anders Furuskar, Ylva Jading, Jonas Karlsson, Magnus Lundevall, and Stefan Parkvall (Ericsson), “The 3G Long-Term Evolution - Radio Interface Concepts and Performance Evaluation”, IEEE VTC 2006

[4] Leonard J. Cimini Jr. and Ye (Geoffrey) Li, “Orthogonal frequency division multiplexing for wireless channels”, AT&T Labs – Research

[5] Richard van Nee and Ramjee Prasad, OFDM for Wireless Multimedia Communications, Artech House Publishers [6] D. Falconer, et al., “Frequency domain equialization for single-carrier broadband wireless systems,” IEEE

Communication Magazine, vol.40, no.4, April 2002[7] Hyung G. Myung, Junsung Lim, and David J. Goodman, “Single Carrier FDMA for Uplink Wireless Transmission”,

IEEE Vehicular Technology Magazine, Sep. 2006[8] 오민석 (LGE), “3GPP LTE”, KRnet 2007, June 29 2007[9] 김학성 (LGE), “3GPP LTE PHY Layer Specification and Technology”, 제4차 차세대이동통신 단기강좌, Feb. 2008[10] Moray Rumney (Agilent), “Concepts of 3GPP LTE”, Live Webinar, Sep. 2007[11] 이상근, 조봉열, 여운영, 쉽게 설명한 3G/4G 이동통신 시스템 (2nd edition), 홍릉과학출판사, 2009[12] Erik Dahlman, et al, 3G Evolution: HSPA and LTE for Mobile Broadband (2nd edition), Academic Press, 2008[13] Harri Holma and Antti Toskala, LTE for UMTS: OFDMA and SC-FDMA Based Radio Access, Wiley, 2009[14] Stefania Sesia, Issam Toufik, and Matthew Baker, LTE, The UMTS Long Term Evolution: From Theory to

Practice, Wiley, 2009[15] David Astély, et al, “LTE: The Evolution of Mobile Broadband,” IEEE Commun. Mag. April 2009[16] Anna Larmo, et al, “The LTE Link-Layer Design,” IEEE Commun. Mag. April 2009[17] LSTI, “Latest Results from the LSTI,” Feb. 2009;

http://www.lstiforum.com/file/news/Latest_LSTI_Results_Feb09_v1.pdf

http://www.3gpp.org/

http://www.lstiforum.com/file/news/Latest_LSTI_Results_Feb09_v1.pdf

Documents

3GPP LTE (Rel. 8) Overview