Note 16 MIMO-OFDM for LTE

MIMO-OFDMfor LTE

MIMO-OFDMfor LTE최수용

csyong@yonsei.ac.kr

http://web.yonsei.ac.kr/sychoi/

연세대학교전기전자공학과

Note 16. MIMO-OFDM for LTE연세대학교 전기전자공학과 최수용

LTE 시스템의특징: ArchitectureLTE(Long Term Evolution) (=E-UTRAN)

SAE(System Architecture Evolution) (=EPC)

EPS(Evolved Packet System) = E-UTRAN + EPC

Circuit Core

User mgmt.Operator

service

Packet Core

CS Networks

IP Networks

Non-3GPPWiFi, WiMAX,

CDMA2000/HRPD

Core Network

Internet

Operator

Service etc.

Internet

Operator

Service etc.

EPC (SAE)Core network

E-UTRAN (LTE)Radio Access

Network

E-UTRAN (LTE)Radio Access

Network

EPS : Evolved Packet SystemIP : Internet ProtocolCS : Circuit SwitchingEPC : Evolved Packet CoreSAE : System Architecture EvolutionE-UTRAN : Evolved Universal Terrestrial Radio Access Network

WiFi : Wireless FidelityWiMAX : Worldwide Interoperability

for Microwave AccessCDMA : Code Division Multiple AccessHRPD : High Rate Packet Data

LTE 시스템의특징: Architecture

One RAN node: eNBOne RAN node: eNB

ATM : Asynchronous Transfer ModeNAS : Non-Access StratumRRM : Radio Resource ManagementPDCP : Packet Data Convergence ProtocolRRC : Radio Resource ControlRLC : Radio Link Control

SGSN : Serving GPRS Support NodeGPRS : General Packet Radio ServicesGGSN : Gateway GPRS Support NodeRNC : Radio Network ControllerMME : Mobility Management Entity

이동통신서비스의진화와발전

2G, 3G3.5G

(HSDPA, EVDO)4G

(LTE, WiMAX)

Access Scheme CDMA OFDM(A)

Modulation QPSKUp to 16QAM

(64QAM in HSPA+)QPSK, 16QAM,

Link Adaptation Mainly PCMainly AMC with channel aware-

scheduler

ARQARQ without soft

combiningHARQ with soft combining

Handover Soft handover Hard handover

Duplexing FDDFDD,

TDD is emerging

Antenna Technology

Rx Antenna Diversity(MIMO in HSPA+)

Various Antenna Diversity, MIMO, BF

CDMA : Code Division Multiple AccessOFDMA : Orthogonal Frequency Multiple AccessQPSK : Quadrature Phase Shift KeyingQAM : Quadrature Amplitude ModulationHSPA : High Speed Packet AccessPC : Power Control

AMC : Adaptive Modulation and CodingARQ : Automatic Repeat reQuestHARQ : Hybrid Automatic Repeat reQuestFDD : Frequency Division DuplexTDD : Time Division DuplexMIMO : Multiple Input Multiple OutputBF : Beam-Forming

LTE 시스템과기존 3G 시스템의비교

CDMAWCDMA

SISOQPSK, 16QAM

CDMAWCDMA

SISOQPSK, 16QAM

OFDMASC-FDMA

MIMO64QAM

OFDMASC-FDMA

MIMO64QAM

Fixed bandwidth

Flexible bandwidth,

Duplex flexibility

Flexible bandwidth,

Duplex flexibility

Circuit Core Packet CoreCircuit Core Packet Core

EPCPacket Core only

BetterData RateandLatency

SpectrumFlexibility

SimpleArchitecture

Latency: 5msBandwidth: up to 20MHz

Peak data rate: 326.4MbpsSpectral eff.:

2.67bps/Hz/cell

Latency: 5msBandwidth: up to 20MHz

Peak data rate: 326.4MbpsSpectral eff.:

2.67bps/Hz/cell

Roughly 3~4 times performance improvement than 3G

Latency: 20msBandwidth: 5MHz

Peak data rate: 42MbpsSpectral eff.:

0.53bps/Hz/cell

Latency: 20msBandwidth: 5MHz

Peak data rate: 42MbpsSpectral eff.:

0.53bps/Hz/cell

Low prices

Simple andvalue added

Higher quality

Ubiquity

EPC : Evolved Packet Core

LTE 시스템과기존 3G 시스템의비교HSPA HSPA+ WiMAX wave2 LTE WiMAX 802.16m

Bandwidth(MHz) 5 5 5, 7, 8.75, 10 1.4, 3, 5, 10, 15, 20 5, 7, 8.75, 10 ,20 ,40

Multiple Access CDMA CDMA OFDMA OFDMA/SC-FDMA OFDMA

Duplex FDD FDD TDD FDD, TDD FDD, TDD

MIMO - MIMO(2×2, 4×4) MIMO(2×2, 4×4) MIMO(2×2, 4×4) MIMO(2×2, 4×4, 8×8)

Peak Modulation(UL/DL) & Coding

16QAM/QPSKTurbo Code/HARQ

64QAM/16QAMTurbo Code/HARQ

64QAM/64QAMTurbo Code/HARQ

User Plane Latency 25ms 20ms 20ms 5ms 10ms

DL Peak Data Rate 14.4Mbps 42Mbps14.4Mbps

(10MHz, 2×2 MIMO)(DL:UL=2:1)

§ 172.8Mbps(20MHz, 2×2 MIMO)

§ 326.4Mbps(20MHz, 4×4 MIMO)

§ 160Mbps(20MHz, 2×2 MIMO)

UL Peak Data Rate 5.76Mbps 11.52Mbps13Mbps

(10MHz, 1×2 MIMO)(DL:UL=2:1)

§ 86.4Mbps(20MHz, 1×2 MIMO)

§ 172Mbps(20MHz, 2×4 MIMO

§ 135Mbps(20MHz, 2×4 MIMO

Service CS & PS CS & PS PS & Voice(VoIP) PS & Voice(VoIP) PS & Voice(VoIP)

Mobility Up to 350Km Up to 350Km Up to 120Km Up to 350Km Up to 350Km

CS : Circuit SwitchingPS : Packet SwitchingVoIP : Voice over Internet Protocol

LTE System PerformancePeak Data Rate

1) ~14% reference signal overhead (4 Tx antennas in DL)~10% common channel overhead (1 UE/subframe)~7% waveform overhead (CP)~10% guard band~ (1/1) code rate

2) ~14% reference signal overhead (1 Tx antenna in UL)~0.6% random access overhead~7% waveform overhead (CP)~10% guard band~ (1/1) code rate

Case Peak Data Rate (Mbps)Downlink(64QAM, 20MHz)

2x2 MIMO 150.84x4 MIMO 302.8 1)

Uplink(20MHz)

16QAM 51.064QAM 75.4 2)

LTE Key FeaturesDownlink: OFDMA (Orthogonal Frequency Division Multiple Access)o Less critical AMP efficiency in BS side

o Concerns on high RX complexity in terminal side

Uplink: SC-FDMA (Single Carrier-FDMA)o Less critical RX complexity in BS side

o Critical 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)

User data rateso DL (baseline): 150.8 Mbps @ 20 MHz BW w/ 2x2 SU-MIMO

o UL (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 ms

TTI (transmit time interval): 1 ms (= 1 sub-frame)

HARQo Incremental redundancy is used as the soft combining strategy

o Retransmission time: 8 ms

Modulationo DL/UL data channel = QPSK/16QAM/64QAM

Hard handover-based mobility

Making MS as cheap 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 antennaso DL: Single-User MIMO up to 4x4 supportable, MU-MIMOo UL: MU-MIMO

Resource blocko 12 subcarriers with subcarrier BW of 15kHz à “180kHz”o 24 subcarriers with subcarrier BW of 7.5kHz (only for MBMS)

Subcarrier operationo Frequency selective by localized subcarriero Frequency diversity by distributed subcarrier & frequency hopping

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

Bearer serviceso Packet only – no circuit switched voice or data services are supportedo Voice must use VoIP

MBSFNo Multicast/Broadcast over a Single Frequency Network o To support a Multimedia Broadcast and Multicast System (MBMS)o Time-synchronized common waveform is transmitted from multiple cells for a given durationo The signal at MS will appear exactly as a signal transmitted from a single cell site and subject to multi-patho Not only “improve the received signal strength” but also “eliminate inter-cell interference”

LTE Modulation SchemesDownlinkDownlink channels Modulation scheme

PBCH (Physical Broadcast Channel) QPSK

PDCCH (Physical Downlink Control Channel) QPSK

PDSCH (Physical Downlink Shared Channel) QPSK, 16QAM, 64QAM

PCFICH (Physical Control Format Indicator Channel) QPSK

PHICH (Physical Hybrid ARQ Indicator Channel) BPSK modulated I and Q

Physical signals Modulation scheme

RS (Reference Signal) Complex I+jQ pseudo random sequence

P-SS (Primary Synchronization Signal) One of three Zadoff-Chu sequence

S-SS (Secondary Synchronization Signal) Two 31-bit BPSK M-sequence

UplinkPhysical channels Modulation scheme

PUCCH (Physical Uplink Control Channel) BPSK, QPSK

PUSCH (Physical Uplink Shared Channel) QPSK, 16QAM, 64QAM

PRACH (Physical Random Access Channel) uth Zadoff-Chu

Physical signals Modulation scheme

Demodulation RS (Demodulation Reference Signal) Zadoff-Chu

Sounding RS (Sounding Reference Signal) Based on Zadoff-Chu

Vertical/Horizontal MIMO

Antenna 마다 다른 FEC 및 modulation

Vertical Encoded 2x2 MIMO System = Single CodeWord MIMO (SCW MIMO)

Horizontal Encoded 2x2 MIMO System = Multiple Codeword MIMO (MCW MIMO) : MU-MIMO

같은 FEC 및 modulation

Uplink? Downlink?

SFBC STBC (Space Time Block Code)

SFBC (Space Frequency Block Code)

Cyclic Delay Diversity (CDD)3GPP Release 8 LTE 표준

채널의심한변화

Scattered frequency selective fading주파수영역에서인터리빙

주파수코딩이득증대Burst frequency selective fading

AMS (Adaptive MIMO Switching)

§ CQI (Channel Quality Index) : AMC§ PMI (Precoding Mapping Index) : Precoder§ RI (Rank Index) : Number of stream

MIMO 기법Open/closed loop MIMO

Multicell MIMO, COMP(cooperative multi-point Tx & Rx) – LTE-A

R8 LTE MIMO Design PrinciplesAnti-fading: TD(Transmit diversity) (and SM)

Enhance spectral efficiency: SM (TD and BF)

Enhance SNR: BF (and codebook-based precoding)

Channel adaptive: CL precoding, Rank adaptation

R8 LTE MIMO Summary

(Frequency switched transmit diversity)

(Precoding vector switching)(Time switched transmit diversity)

(Demodulation)16/44

LTE 물리채널별 MIMO 기술Physical channel Usage Tx Diversity SM-MIMO CDD

Reference Signal X X XPrimary, & Secondary Synch Signal X X X

Physical Broadcasting Channel

System information (Master information Block)

Physical Control Format Indication Channel

Control FormatIndicator( Subframe마다전송, OFDM symbol 수)

Physical Downlink Control Channel

자원할당, HARQ 및scheduling 정보 O X X

Physical Multicast Channel

방송형 data O O X

Physical Downlink Shared Channel

Downlink user data O O O

LTE PHY - DL

Contents

o Frame and Slot Structure

o Physical Channel Processing

o Physical Signals

o Physical Channels

LTE DL 기술의개요Multiple Accesso DL : OFDMA

Bandwidth : Scalable bandwidth up to 20Mhz : 1.4M, 3M, 5M, 10M, 20M

FDD와 TDD의동시지원 (FDD가대부분)o TDD 방식은중국의 TD-SCDMA에서 LTE로의진화를정의

Modulation for DL/UL : QPSK, 16QAM, 64QAM

10ms PHY frame, 1ms TTI

Resource Block (RB)o 180khz(15khz Subcarrier × 12개) : 일반 resource block

o 180khz(7.5khz Subcarrier × 24개) : MBMS resource block

다양한안테나기술

o 2 ×2, 4 ×4 MIMO for DL

o Rx diversity

E-UTRA Channel Bandwidth*

1RB (15KHz/carriers, 12 carriers) = 180kHz

à 6RBs = 1.08MHz, à 100RBs = 18MHz

6RBs (72 subcarriers) with 128 FFT, 100RBs (1200 subcarriers) with 2048 FFT

Table 5.6-1 Transmission bandwidth configuration NRB in E-UTRA channel bandwidths

Figure 5.6-1 Definition of Channel Bandwidth and Transmission Bandwidth Configuration for one E UTRA carrier

* 3GPP TS 36.101, E-UTRA: UE radio transmission and reception, Release 9

Channel Bandwidth (MHz) 1.4 3 5 10 15 20

Number of Occupied Subcarrier including DC (Nsc)

73(12*6+1)

181(12*15+1)

301(12*15+1)

601(12*50+1) 901 1201

FFT Size (N) 128 256 512 1024 1536 2048

Sampling Rate (MHz) 1.92 3.84 7.68 15.36 23.04 30.72

Number of Resource Blocks (NRB) (12 carriers/RB) 6 15 25 50 75 100

Flexible Frequency Channel of LTELTE 에서는공통제어신호를전송하는 1.4Mhz를포함하는다양한채널대역폭할당가능

채널 BW에따른 RB수및전송 BW채널 BW 1.4Mhz 3Mhz 5Mhz 10Mhz 20Mhz

RB수/tone 수 6/72 15/180 25/300 50/600 100/1200

전송 BW 10.8Mhz 2.7Mhz 4.5Mhz 9Mhz 18Mhz

DL Physical Channel Processing

Scrambling of coded bits in each of the code words to be transmitted on a physical channel

Modulation of scrambled bits to generate complex-valued modulation symbols

Mapping of the complex-valued modulation symbols onto one or several transmission layers

Precoding of the complex-valued modulation symbols on each layer for transmission on the antenna ports

Mapping of complex-valued modulation symbols for each antenna port to resource elements

Generation of complex-valued time domain OFDM signal for each antenna port

Modulation

Physical channel Modulation schemesPDSCH QPSK, 16QAM, 64QAMPMCH QPSK, 16QAM, 64QAM

Physical channel Modulation schemesPBCH QPSK

Physical channel Modulation schemesPCFICH QPSK

Physical channel Modulation schemesPDCCH QPSK

Physical channel Modulation schemesPHICH BPSK

Physical signalso A set of resource elements not carrying

information§ Reference signal

§ Synchronization signal

Physical channelso A set of resource elements carrying

information§ Physical Downlink Shared Channel, PDSCH

§ Physical Broadcast Channels, PBCH

§ Physical Multicast Channel, PMCH

§ Physical Control Format Indicator Channel, PCFICH

§ Physical Downlink Control Channel, PDCCH

§ Physical Hybrid ARQ Indicator Channel, PHICH

Layer mapping and Precoding

Layer Mapping

PrecodingThe precoder takes as input a block of vectors

and generates a block of vectors

to be mapped onto resources on each of the antenna port where

represents the signal for antenna port p.

( ) ( ) ( ) ( ) ( )0 1 layersymb, 0,1, , 1

Tvx i x i x i i M-é ù= = -ë ûL L

( ) ( ) ( ) apsymb, 0,1, , 1

Tpy i y i i Mé ù= = -ë ûL L L

( )( )iy p

Precoding without CDD Precoding for large-delay CDD

( )( )

( )( )( )

( )( )

( )( )úúú

êêê

=úúú

êêê

( )( )

( )( )( ) ( )

( )( )

( )( )úúú

êêê

=úúú

êêê

ixUiDiW

Precoding

Codebook for Precoding – 2 portsThe precoding matrix W(i) shall be selected from below table

Codebook for Precoding – 4 portsdenotes the matrix defined by the columns given by the set {s}

22 nHnnn uuuIW -=

{ }snW

Open loop Spatial MultiplexingTwo antenna ports caseo Large delay CDD along with a fixed precoder matrix is used

Four antenna ports caso Precoder cycling is used

Transmit Diversity SchemesSpace Frequency Block Codes (SFBC)o SFBC is a frequency domain version of the STBC (Alamouti codes)

o Transmit diversity streams are orthogonal and achieve the optimal SNR with a linear receiver

Frequency Switched Transmit Diversity (FSTD) Combining with SFBC

Transmit Diversity SchemesThe transmit matrix for the balanced SFBC-FSTD scheme is given as

The equivalent channel matrix for the balanced SFBC-FSTD scheme is

assuming a matched filter receiver, the resulting channel gains matrix is

(0) (1)(0) (0) (0) (0)

(2) (3)(1) (1) (1) (1)

((2) (2) (2) (2)

(3) (3) (3) (3)

( ) ( ) 0 0(4 ) (4 1) (4 2) (4 3)0 0 ( ) ( )(4 ) (4 1) (4 2) (4 3)

(4 ) (4 1) (4 2) (4 3)(4 ) (4 1) (4 2) (4 3)

x i x iy i y i y i y ix i x iy i y i y i y i

xy i y i y i y iy i y i y i y i

é ù+ + +ê ú+ + +ê ú = -ê ú+ + +ê ú

+ + +ë û

( ) ( )( ) ( )

* *1) (0)

* *(3) (2)

( ) ( ) 0 0

0 0 ( ) ( )

x i x i

é ùê úê úê úê úê ú

- -ê úë û

4 *1 3

0 00 01

0 040 0

SFBC FSTD

h hh h

Hh hh h

é ù-ê úê ú=ê ú-ê úê úë û

2 20 2

2 21 3

( ) 0 0 02

( )0 0 02

é ù+ê úê ú

+ê úê ú

= ê ú+ê ú

ê úê ú

+ê úê úë û

Physical signals and channelsPhysical signalso A set of resource elements not carrying information

§ Reference signal

§ Synchronization signal

Physical channelso A set of resource elements carrying information

§ Physical Downlink Shared Channel, PDSCH

§ Physical Broadcast Channels, PBCH

§ Physical Multicast Channel, PMCH

§ Physical Control Format Indicator Channel, PCFICH

§ Physical Downlink Control Channel, PDCCH

§ Physical Hybrid ARQ Indicator Channel, PHICH

DL Physical SignalsReference signals (RS)o Cell-specific RS: associated with non-MBSFN transmission (unicast RS)

§ Transmitted in every downlink subframe, and span entire cell BW

§ Used for initial cell search

§ Used for downlink signal strength measurements for scheduling and handover

§ Using antenna ports {0, 1, 2, 3}

o MBSFN RS: associated with MBSFN transmission§ Used for channel estimation for coherent demodulations of signals being transmitted by means of

§ Using antenna ports 4

o UE-specific RS§ Specifically intended for channel estimation for coherent demodulation of DL-SCH when non-

codebook-based beamforming is used

§ Using antenna port 5

Synchronization Signals (SS)o Carries frequency and symbol timing synchronization

o PSS (Primary SS) and SSS (Secondary SS)

Cell-Specific RS mapping

Normal CP

Extended CP

1 Tx ant 4.76% 5.56%

2 Tx ant 9.52% 11.11%

4 Tx ant 14.29% 15.87%

UE-specific RS on top of Cell-specific RSUE-specific RS (antenna port 5)o 12 symbols per RB pair

DL CQI estimation is always based on cell-specific RS (common RS)

LTE Cell Search

7 Tx modes in PDSCHMode 1 : Single-antenna port; port 0o DL transmissions using a single Tx antenna at eNB

Mode 2 : Transmit diversityo DL transmission using Alamouti-like transmit diversity schemes

o The number of layers is equal to the number of antenna ports

7 Tx modes in PDSCHMode 3 : Open loop spatial multiplexingo Transmit different streams of data simultaneously on the same RB(s) by exploiting the

spatial dimension of the radio channel. These data streams belong to the same user

o Up to 2 codewords transmissions with “no PMI feedback”

o Exploits CDD in DL transmissions

o Up to 4 layers and 4 antennas

7 Tx modes in PDSCHMode 4 : Closed loop spatial multiplexing (SU-MIMO)o Transmit different streams of data simultaneously on the same RB(s) by exploiting the

spatial dimension of the radio channel. These data streams belong to the same user

o Up to 2 codewords transmissions with “RI and PMI feedback”

o Exploits CDD in DL transmissions

o Up to 4 layers and 4 antennas

7 Tx modes in PDSCHMode 5 : Multi-user MIMO (MU-MIMO)o Transmit different streams of data simultaneously on the same RB(s) by exploiting the

spatial dimension of the radio channel. These data streams belong to different users

o Also known as downlink SDMA

o Single codewords and single Layer per user (UE reports only PMI, no RI is reported)

o Up to 4 Tx antennas at eNB

o Different users can use the same time/freq resources in different location within a cell

7 Tx modes in PDSCHMode 6 : Closed loop Rank=1 precodingo Same as Mode 4 with Rank restriction 1

o No Rank reports are required

Mode 7 : Single antenna port; port 5o Same as Mode 1 using UE-specific Reference Signals instead of Cell-specific

Reference Signals (with the help of sounding reference signal)

Note 16 MIMO-OFDM for LTE

Documents

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