MIMO-OFDM for LTE 최수용. 연세대학교전기전자공학과

Transcription

1 MIMO-OFDM for LTE 최수용 연세대학교전기전자공학과

2 LTE 시스템의특징 : Architecture LTE(Long Term Evolution) (=E-UTRAN) SAE(System Architecture Evolution) (=EPC) EPS(Evolved Packet System) = E-UTRAN + EPC Internet Operator Service etc. 2G Circuit Core Core Network CS Networks EPC (SAE) Core network 3G User mgmt. Operator service E-UTRAN (LTE) LTE Packet Core Radio Access Network Non-3GPP WiFi, WiMAX, CDMA2000/HRPD EPS : Evolved Packet System IP : Internet Protocol CS : Circuit Switching EPC : Evolved Packet Core SAE : System Architecture Evolution IP Networks E-UTRAN : Evolved Universal Terrestrial Radio Access Network WiFi : Wireless Fidelity WiMAX : Worldwide Interoperability for Microwave Access CDMA : Code Division Multiple Access HRPD : High Rate Packet Data 1/44

3 LTE 시스템의특징 : Architecture One RAN node: enb SGSN : Serving GPRS Support Node GPRS : General Packet Radio Services GGSN : Gateway GPRS Support Node RNC : Radio Network Controller MME : Mobility Management Entity ATM : Asynchronous Transfer Mode NAS : Non-Access Stratum RRM : Radio Resource Management PDCP : Packet Data Convergence Protocol RRC : Radio Resource Control RLC : Radio Link Control 2/44

4 이동통신서비스의진화와발전 2G, 3G 3.5G (HSDPA, EVDO) 4G (LTE, WiMAX) Access Scheme CDMA OFDM(A) Modulation Link Adaptation ARQ QPSK Mainly PC ARQ without soft combining Up to 16QAM (64QAM in HSPA+) QPSK, 16QAM, 64QAM Mainly AMC with channel awarescheduler HARQ with soft combining Handover Soft handover Hard handover Duplexing Antenna Technology FDD Rx Antenna Diversity (MIMO in HSPA+) FDD, TDD is emerging Various Antenna Diversity, MIMO, BF CDMA : Code Division Multiple Access OFDMA : Orthogonal Frequency Multiple Access QPSK : Quadrature Phase Shift Keying QAM : Quadrature Amplitude Modulation HSPA : High Speed Packet Access PC : Power Control AMC : Adaptive Modulation and Coding ARQ : Automatic Repeat request HARQ : Hybrid Automatic Repeat request FDD : Frequency Division Duplex TDD : Time Division Duplex MIMO : Multiple Input Multiple Output BF : Beam-Forming 3/44

5 LTE 시스템과기존 3G 시스템의비교 Better Data Rate and Latency Spectrum Flexibility CDMA WCDMA SISO QPSK, 16QAM Fixed bandwidth OFDMA SC-FDMA MIMO 64QAM Flexible bandwidth, Duplex flexibility Latency: 20ms Bandwidth: 5MHz Peak data rate: 42Mbps Spectral eff.: 0.53bps/Hz/cell Latency: 5ms Bandwidth: up to 20MHz Peak data rate: 326.4Mbps Spectral eff.: 2.67bps/Hz/cell Low prices Simple and value added Higher quality Simple Architecture Circuit Core Packet Core EPC Packet Core only Roughly 3~4 times performance improvement than 3G Ubiquity EPC : Evolved Packet Core 4/44

6 LTE 시스템과기존 3G 시스템의비교 HSPA HSPA+ WiMAX wave2 LTE WiMAX m Bandwidth(MHz) 5 5 5, 7, 8.75, , 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/QPSK Turbo Code/HARQ 64QAM/16QAM Turbo Code/HARQ 64QAM/16QAM Turbo Code/HARQ 64QAM/64QAM Turbo Code/HARQ 64QAM/64QAM Turbo Code/HARQ User Plane Latency 25ms 20ms 20ms 5ms 10ms DL Peak Data Rate 14.4Mbps 42Mbps UL Peak Data Rate 5.76Mbps 11.52Mbps 14.4Mbps (10MHz, 2 2 MIMO) (DL:UL=2:1) 13Mbps (10MHz, 1 2 MIMO) (DL:UL=2:1) 172.8Mbps (20MHz, 2 2 MIMO) 326.4Mbps (20MHz, 4 4 MIMO) 86.4Mbps (20MHz, 1 2 MIMO) 172Mbps (20MHz, 2 4 MIMO 160Mbps (20MHz, 2 2 MIMO) 300Mbps (20MHz, 4 4 MIMO) 56Mbps (20MHz, 1 2 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 Switching PS : Packet Switching VoIP : Voice over Internet Protocol 5/44

7 LTE System Performance Peak Data Rate Case Downlink (64QAM, 20MHz) Uplink (20MHz) Peak Data Rate (Mbps) 2x2 MIMO x4 MIMO ) 16QAM QAM ) 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 6/44

8 LTE Key Features Downlink: 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) Making MS as cheap as possible by moving all the burdens from MS to BS User data rates o DL (baseline): MHz BW w/ 2x2 SU-MIMO o UL (baseline): 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) HARQ o Incremental redundancy is used as the soft combining strategy o Retransmission time: 8 ms Modulation o DL/UL data channel = QPSK/16QAM/64QAM Hard handover-based mobility 7/44

9 LTE Key Features cont d MIMO SM (Spatial Multiplexing), Beamforming, Antenna Diversity Min requirement: 2 enb antennas & 2 UE rx antennas o DL: Single-User MIMO up to 4x4 supportable, MU-MIMO o UL: MU-MIMO Resource block o 12 subcarriers with subcarrier BW of 15kHz à 180kHz o 24 subcarriers with subcarrier BW of 7.5kHz (only for MBMS) Subcarrier operation o Frequency selective by localized subcarrier o Frequency diversity by distributed subcarrier & frequency hopping Frequency hopping o Intra-TTI: UL (once per 0.5ms slot), DL (once per 66us symbol) o Inter-TTI: across retransmissions Bearer services o Packet only no circuit switched voice or data services are supported o Voice must use VoIP MBSFN o 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 duration o The signal at MS will appear exactly as a signal transmitted from a single cell site and subject to multi-path o Not only improve the received signal strength but also eliminate inter-cell interference 8/44

10 LTE Modulation Schemes Downlink Downlink channels PBCH (Physical Broadcast Channel) PDCCH (Physical Downlink Control Channel) PDSCH (Physical Downlink Shared Channel) PCFICH (Physical Control Format Indicator Channel) PHICH (Physical Hybrid ARQ Indicator Channel) Physical signals RS (Reference Signal) P-SS (Primary Synchronization Signal) S-SS (Secondary Synchronization Signal) Uplink Physical channels PUCCH (Physical Uplink Control Channel) PUSCH (Physical Uplink Shared Channel) PRACH (Physical Random Access Channel) Physical signals Demodulation RS (Demodulation Reference Signal) Sounding RS (Sounding Reference Signal) Modulation scheme QPSK QPSK QPSK, 16QAM, 64QAM QPSK BPSK modulated I and Q Modulation scheme Complex I+jQ pseudo random sequence One of three Zadoff-Chu sequence Two 31-bit BPSK M-sequence Modulation scheme BPSK, QPSK QPSK, 16QAM, 64QAM u th Zadoff-Chu Modulation scheme Zadoff-Chu Based on Zadoff-Chu 9/44

11 Vertical/Horizontal MIMO Vertical Encoded 2x2 MIMO System = Single CodeWord MIMO (SCW MIMO) 같은 FEC 및 modulation Uplink? Downlink? Horizontal Encoded 2x2 MIMO System = Multiple Codeword MIMO (MCW MIMO) : MU-MIMO Antenna 마다다른 FEC 및 modulation 10/44

12 SFBC STBC (Space Time Block Code) SFBC (Space Frequency Block Code)

13 Cyclic Delay Diversity (CDD) 3GPP Release 8 LTE 표준 Burst frequency selective fading 채널의심한변화 Scattered frequency selective fading 주파수영역에서인터리빙 주파수코딩이득증대 12/44

14 AMS (Adaptive MIMO Switching) CQI (Channel Quality Index) : AMC PMI (Precoding Mapping Index) : Precoder RI (Rank Index) : Number of stream 13/44

15 MIMO 기법 Open/closed loop MIMO Multicell MIMO, COMP(cooperative multi-point Tx & Rx) LTE-A 14/44

16 R8 LTE MIMO Design Principles Anti-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 15/44

17 R8 LTE MIMO Summary (Precoding vector switching) (Time switched transmit diversity) (Frequency switched transmit diversity) (Demodulation) 16/44

18 LTE 물리채널별 MIMO 기술 Physical channel Usage Tx Diversity SM-MIMO CDD Reference Signal X X X Primary, & Secondary Synch Signal Physical Broadcasting Channel Physical Control Format Indication Channel Physical Downlink Control Channel Physical Multicast Channel Physical Downlink Shared Channel System information (Master information Block) Control Format Indicator( Subframe 마다전송, OFDM symbol 수 ) 자원할당, HARQ 및 scheduling 정보 방송형 data Downlink user data X X X O X X O X X O X X O O X O O O 17/44

19 LTE PHY - DL Contents o Frame and Slot Structure o Physical Channel Processing o Physical Signals o Physical Channels 18/44

20 LTE DL 기술의개요 Multiple Access o DL : OFDMA Bandwidth : Scalable bandwidth up to 20Mhz : 1.4M, 3M, 5M, 10M, 20M FDD와 TDD의동시지원 (FDD가대부분 ) o TDD 방식은중국의 TD-SCDMA 에서 LTE 로의진화를정의 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 19/44

21 E-UTRA Channel Bandwidth* * 3GPP TS , E-UTRA: UE radio transmission and reception, Release 9 Table Transmission bandwidth configuration N RB in E-UTRA channel bandwidths Channel Bandwidth (MHz) Number of Occupied Subcarrier including DC (N sc ) 73 (12*6+1) 181 (12*15+1) 301 (12*15+1) 601 (12*50+1) FFT Size (N) Sampling Rate (MHz) Number of Resource Blocks (N RB ) (12 carriers/rb) RB (15KHz/carriers, 12 carriers) = 180kHz à 6RBs = 1.08MHz, à 100RBs = 18MHz 6RBs (72 subcarriers) with 128 FFT, 100RBs (1200 subcarriers) with 2048 FFT Figure Definition of Channel Bandwidth and Transmission Bandwidth Configuration for one E UTRA carrier 20/44

22 Flexible Frequency Channel of LTE LTE 에서는공통제어신호를전송하는 1.4Mhz 를포함하는다양한채널대역폭할당가능 채널 BW 에따른 RB 수및전송 BW 채널 BW 1.4Mhz 3Mhz 5Mhz 10Mhz 20Mhz RB수 /tone 수 6/72 15/180 25/300 50/ /1200 전송 BW 10.8Mhz 2.7Mhz 4.5Mhz 9Mhz 18Mhz 21/44

23 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 22/44

24 Modulation Physical signals o A set of resource elements not carrying information Reference signal Synchronization signal Physical channels o 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 Physical channel PDSCH PMCH Physical channel PBCH Physical channel PCFICH Physical channel PDCCH Physical channel PHICH Modulation schemes QPSK, 16QAM, 64QAM QPSK, 16QAM, 64QAM Modulation schemes QPSK Modulation schemes QPSK Modulation schemes QPSK Modulation schemes BPSK 23/44

25 Layer mapping and Precoding 24/44

26 Layer Mapping 25/44

27 Precoding The precoder takes as input a block of vectors ( ) ( ) ( ) and generates a block of vectors ( ) T 0 v-1 layer L ( ) ù L symb x i = é ë x i x i û, i = 0,1,, M -1 ( ) T ( p ) ap ( ) y i = é y i ù ë L L û, i = 0,1, L, M symb -1 ( to be mapped onto resources on each of the antenna port where y p ) ( i) represents the signal for antenna port p. Precoding without CDD é y ê ê ê ëy ( 0 ) ( i) M ( -1 ) ( i) ù ú ú = W ú û ( i) ( 0 ) ( i) é x ù ê ê M ê ( ) ( )ú úú v- ëx i û P 1 é y ê ê ê ëy Precoding for large-delay CDD ( 0 ) ( i) M ( -1 ) ( i) ù ú ú = W ú û ( i) D( i) ( 0 ) ( i) é x ù ê U ê M ê ( ) ( )ú úú v- ëx i û P 1 26/44

28 Precoding 27/44

29 Codebook for Precoding 2 ports The precoding matrix W(i) shall be selected from below table 28/44

30 Codebook for Precoding 4 ports { s} W n denotes the matrix defined by the columns given by the set {s} W = I - n H 2 2unun un 29/44

31 Open loop Spatial Multiplexing Two antenna ports case o Large delay CDD along with a fixed precoder matrix is used Four antenna ports cas o Precoder cycling is used 30/44

32 Transmit Diversity Schemes Space 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 31/44

33 Transmit Diversity Schemes The transmit matrix for the balanced SFBC-FSTD scheme is given as (0) (0) (0) (0) é é y (4 i) y (4i + 1) y (4i + 2) y (4i + 3) ù ê ê (1) (1) (1) (1) ú y (4 i) y (4i + 1) y (4i + 2) y (4i + 3) ê ê ú (2) (2) (2) (2) = ê ê y (4 i) y (4i + 1) y (4i + 2) y (4i + 3) ú ê - ê (3) (3) (3) (3) ú ë y (4 i) y (4i + 1) y (4i + 2) y (4i + 3) ê û êë (0) (1) x i x i ( ) ( ) 0 0 (2) (3) 0 0 x ( i) x ( i) ( 1) * (0) * ( x ( i) ) ( x ( i) ) 0 0 (3) (2) ( x i ) ( x i ) * * ( ) - ( ) The equivalent channel matrix for the balanced SFBC-FSTD scheme is H éh 0 0 * 0 2 ê * 1 h2 h SFBC-FSTD = ê * 4 ê 0 0 h1 -h3 ê * ê 0 0 h3 h1 ë assuming a matched filter receiver, the resulting channel gains matrix is -h 2 2 é( h0 + h2 ) ù ê ú ê 2 ú 2 2 ê ( h0 + h2 ) ú ê ú = ê ú 2 2 ê ( h1 + h3 ) ú ê ú ê ú 2 2 ê ( h1 + h3 ) ú êë 2 úû ù ú ú ú ú úû ù ú ú ú ú ú úû 32/44

34 Physical signals and channels Physical signals o A set of resource elements not carrying information Reference signal Synchronization signal Physical channels o 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 33/44

35 DL Physical Signals Reference 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 MBSFN Using antenna ports 4 o UE-specific RS Specifically intended for channel estimation for coherent demodulation of DL-SCH when noncodebook-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) 34/44

36 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% 35/44

37 UE-specific RS on top of Cell-specific RS UE-specific RS (antenna port 5) o 12 symbols per RB pair DL CQI estimation is always based on cell-specific RS (common RS) 36/44

38 LTE Cell Search 37/44

39 LTE Cell Search 38/44

40 PDSCH 39/44

41 7 Tx modes in PDSCH Mode 1 : Single-antenna port; port 0 o DL transmissions using a single Tx antenna at enb Mode 2 : Transmit diversity o DL transmission using Alamouti-like transmit diversity schemes o The number of layers is equal to the number of antenna ports 40/44

42 7 Tx modes in PDSCH Mode 3 : Open loop spatial multiplexing 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 no PMI feedback o Exploits CDD in DL transmissions o Up to 4 layers and 4 antennas 41/44

43 7 Tx modes in PDSCH Mode 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 42/44

44 7 Tx modes in PDSCH Mode 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 43/44

45 7 Tx modes in PDSCH Mode 6 : Closed loop Rank=1 precoding o Same as Mode 4 with Rank restriction 1 o No Rank reports are required Mode 7 : Single antenna port; port 5 o Same as Mode 1 using UE-specific Reference Signals instead of Cell-specific Reference Signals (with the help of sounding reference signal) 44/44