Evolved UTRA and UTRAN Investigation on Multiple Antenna Transmission Techniques in Evolved UTRA Evolved UTRA (E-UTRA) and UTRAN represent long-term evolution (LTE) of technology to maintain continuous growth in mobile communications industry Competitive technology even in G era RAN evolution to enable smooth migration to G H. H. Taoka,, Y. Y. Kishiyama,, A. A. Morimoto,, H. H. Kawai,, T. T. Kawahara,, K. K. Higuchi,, and M. M. Sawahashi Radio Access Network Development Department, NTT NTT DoCoMo, Inc. Inc. Department of of Electrical Engineering, Tokyo University of of Science Department of of Information Network Engineering, Musashi Institute of of Technology Commercial deployment: Accomplished successfully Specifications and system development: Ongoing Evolved UTRA and UTRAN Launch G Mid-term evolution Long-term evolution G G G 98s 99s s s s Features of Evolved UTRA and UTRAN OFDM-Based Radio Access in Downlink Features of Evolved UTRA and UTRAN Scalable bandwidths: Support.,,,,, and MHz Packet-switching (PS) mode only: Including Voice over IP (VoIP) Short latency: Short C-plane latency (connection delay) less than - msec and U-plane latency (transmission delay) less than msec Higher data rate: Peak data rate: Mbps in downlink (DL) and Mbps in uplink (UL) Higher user throughput and spectrum efficiency Cell edge user throughput: - times (DL) and - times (UL) Spectrum efficiency: - times (DL) and - times (UL) High commonality between FDD and TDD Application of essential techniques for packet radio access -domain scheduling, AMC, Hybrid ARQ, etc. High-quality MBMS using single-frequency network (SFN) OFDM-based radio access Robust against multi-path interference (MPI) Flexible accommodation of different spectrum arrangements High quality reception using soft-combining for broadcast/multicast (MBMS) signal Sub-frame Time Resource block (RB) Localized transmission (Different colors represent different users) Distributed transmission
Single-carrier (SC)-FDMA based radio access Low PAPR (Peak-to-average power ratio) feature to achieve large coverage area -domain orthogonalization of multiple access users within the same cell MPI suppression using frequency domain equalizer Insert cyclic prefix to utilize frequency-domain equalizer Coded data symbol SC-FDMA Based Radio Access in Uplink DFT Sub-carrier mapping IFFT Addition of CP Transmit signal Subframe RB scheduling MIMO Transmission Techniques in E-UTRA MIMO multiplexing (to data channel) Baseline«-by- MIMO (Downlink)«-by- SIMO (Uplink) Maximum of antennas. Supports single user-mimo (SDM) and multi user-mimo (SDMA) Introduction of uplink SU-MIMO to be investigated for future release MIMO diversity (transmit diversity) (to data and control channel) Apply appropriate transmit diversity scheme to each downlink / uplink physical channel Adaptive beam-forming (to data channel) Beneficial in increasing cell edge user data rate and coverage DFT-Spread OFDM Time hopping Contiguous RBs are assigned to user equipment (UE) to maintain single-carrier property 6 Objective Present features of MIMO transmission techniques in E-UTRA physical layer and evaluation results of DoCoMo s simulations. - MIMO multiplexing (SU-MIMO and MU-MIMO) - Transmit diversity - Adaptive beamforming Single User (SU)-MIMO 7 8
Downlink SU-MIMO in E-UTRA Features of SU-MIMO in E-UTRA Codebook-based precoding Adaptive precoding (transmit antenna weight) based on codebook Multiple-codeword transmission Link adaptation and automatic repeat request (ARQ) operation per codeword Rank adaptation Adaptive control of spatially multiplexed streams (layers) Support for multiple SU-MIMO modes Closed-loop type: Zero- / small- / large-delaycdd precoding Open-loop type: Large-delay CDD precoding (FFS) Transmit data S/P Codebook-Based Precoding Modulation and channel coding Node B (Base Station) Closed-loop type adaptive precoding User-dependent optimum beams to increase user throughput Fully utilize power amplifier for all antennas Tracking of instantaneous channel variations Codebook-based precoding Feedback of precoding matrix indicator (PMI) from UE Support both frequency selective and non-selective precoding Layer # Layer # UE Adaptive modulation and coding Precoding Feedback of PMI 9 Codebook for precoding Codebook -Tx: Discrete Fourier Transform (DFT) and antenna selection based. 6 and precoding matrices for rank and rank, respectively. -Tx: House Holder based. 6 precoding matrices for ranks,,, and. Features of specified codebook Unitary matrices Constant modulus: Constant amplitude for each antenna component in precoding weight matrices Nested structure: Precoding matrices for lower rank are part of precoding columns for higher rank Codebook index Number of layers Codebook for Precoding Codebook for -Tx antennas j j j j Codeword-Based Link Adaptation and Rank Adaptation Codeword-based link adaptation Link adaptation (AMC) and Hybrid ARQ operation per codeword Maximum of two codewords Rank adaptation Control number of transmitted layers (rank) according to spatial channel condition, e.g., received SINR and fading correlation between antennas. UE# Adaptive control of transmission rank Rank = Low received SINR High spatial correlation Node B Rank = UE# High received SINR Low spatial correlation
SU-MIMO Transmission Mode in E-UTRA SU-MIMO transmission modes supported in E-UTRA Closed-loop type Spatial multiplexing using channel-dependent adaptive precoding. Zero-delay cyclic delay diversity (CDD) precoding No CDD operation in combination with adaptive precoding. Small-delay CDD precoding CDD operation with cyclic delay shift of 6 to nsec ( MHz) Obtain additional multi-user diversity gain in combination with frequency scheduling in low frequency selective channel, e.g., line-of-sight (LOS) condition. Large-delay CDD precoding CDD operation with cyclic delay shift of 6 to μsec. Reduce performance degradation using frequency diversity of CDD under medium mobility conditions, i.e., precoding cannot track instantaneous channel variation. Open-loop type Spatial multiplexing using channel-independent fixed precoding Large-delay CDD precoding (FFS) Throughput (Mbps) 8 7 6 Throughput Performance Using Zero-Delay CDD Precoding selective precoding non-selective precoding SVD precoding Without precoding TU channel model f D =. Hz Subband size = 9 khz Throughput (Mbps) selective precoding non-selective precoding Subband size = 9 khz - 8 6 8 6 Average received SNR (db) Average received SNR (db) -by- MIMO -by- MIMO Throughput performance with precoding is increased compared to that w/o precoding especially when rank is lower than number of antennas selective precoding can obtains additional throughput gain compared to that for frequency non-selective precoding 8 7 6 SVD precoding Without precoding TU channel model f D =. Hz CDF.8.6.. User Throughput Performance Using Zero-Delay CDD Precoding in Multiple Cells HSDPA (MHz) E-UTRA (MHz) -by- SIMO -by- MIMO -by- MIMO E-UTRA HSDPA (-by- SIMO)... Normalized user throughput (Mbps/MHz) 9 cells, -sectors per cell Inter-site distance: m UEs / sector TU channel model Full buffer traffic Proportional fairness (PF) f D =. Hz (v = km/h) With rank adaptation -by- and -by- MIMO obtain approximately (9)% average user throughput gain compared to that for -by- SIMO. Multi User (MU)-MIMO 6
MU-MIMO in E-UTRA Downlink MU-MIMO (SDMA) in E-UTRA Semi-static switching between SU-MIMO and MU-MIMO mode. MU-MIMO scheme focusing on high correlated antenna elements, e.g., array antennas. Only one layer per UE. Reuse (a part of) precoding vector codebook for SU-MIMO. Uplink MU-MIMO in E-UTRA Uplink MU-MIMO can be applied in E-UTRA. Detailed MU-MIMO scheme is outside the scope of standard. Node B j Transmit Diversity j 7 8 Downlink Transmit Diversity Schemes Tx diversity for Synchronization Channel (SCH) Precoding vector switching (PVS) Switching of set of fixed precoding vectors in time domain. PVS does not require a priori knowledge of number of transmitter antennas. Tx diversity for MBMS channel Cyclic Delay Diversity (CDD) Sufficient diversity gain obtained by soft-combining in SFN CDD can be applied for additional diversity gain without need for orthogonal reference signal (pilot channel) per antenna Tx diversity for other common/shared control channels and shared data channels Space Block Coding (SFBC) (-Tx antennas) Combination of SFBC and Switched Transmit Diversity (SFBC+FSTD) (-Tx antennas) Alamouti s rate- block coding is applied in SFBC. Transmit antenna switching sub-carrier by subcarrier in FSTD. Largest Tx diversity gain is obtained using SFBC-based scheme. 9 Average PER - - - Average PER Performance of Two-Antenna Transmit Diversity Schemes QPSK Symbol repetition factor = CDD SFBC FSTD PVS R = / -by- MIMO TU channel f D =. Hz ρ =. R = / - 6 8 Average received SNR (db) SFBC achieves better performance compared to other schemes especially for high coding rate case. Required average received SNR using SFBC is decreased by approximately..7 db compared to that for CDD.
Uplink Transmit Diversity Schemes Tx diversity for Random Access Channel (RACH) and L/L control channel Time Switched Transmit Diversity (TSTD). Transmit antenna switching in the time domain. Tx diversity for shared data channel Closed-Loop Antenna Selection Transmit Diversity (CL-ASTD) Adaptive antenna selection based on channel quality measurement UE alternately transmits sounding reference signals (RSs) for channel quality measurement from each transmitter antenna. Transmission bandwidth for frequency-domain scheduling Time From Tx Ant. # Ant. # sub-frame (=. msec) Sounding RS Shared data channel CDF - - - Throughput Performance Using CL-ASTD f D =. Hz UEs / sector Closed loop-astd -antenna..... User throughput (Mbps) -MHz system bandwidth 9 cells, -sectors per cell Inter-site distance: 7 m TU channel model With fractional TPC Full buffer traffic Proportional fairness (PF) User throughput at % CDF is improved by approximately % compared to that for - antenna transmission CL-ASTD is beneficial in enhancing the cell edge user throughput. Adaptive Beamforming Adaptive Beamforming Adaptive beamforming (BF) with narrow antenna separation Beneficial in increasing the cell edge user data rate and coverage for UEs under low to high mobility conditions. BF schemes in E-UTRA downlink Codebook-based BF (same as precoding) Direction of arrival (DOA) estimation-based BF Weight generation Common RS Dedicated RS Codebook-based BF Based on antenna weight information feedback from UE Requires Common RS for respective antenna Not necessary DOA estimation-based BF Based on DOA estimation in uplink Can be constant irrespective of number of transmitter antennas Necessary Dedicated RS is specified for demodulation of beamformed shared data channel especially for more than four antennas in E-UTRA
Sector throughput (Mbps) Throughput Performance Using Adaptive Beamforming -MHz system bandwidth 6-ray TU channel ISD = 7 m f D =. Hz users / sector Sector throughput % CDF user throughput... Codebook-based BF DOA-based BF 6 8 Number of antennas % CDF user throughput (Mbps) Improvement in DOAbased BF compared to codebook-based BF is remarkable when the number of transmit antenna exceeds DOA-based BF with 8 antennas increases sector throughput and % CDF user throughput by approximately % and 7% compared to -antenna BF. Conclusion Presented features of transmission techniques related to MIMO in E-UTRA along with DoCoMo s evaluations E-UTRA downlink SU-MIMO (SDM) and MU-MIMO (SDMA) Transmit diversity Adaptive beamforming E-UTRA uplink MU-MIMO Transmit diversity Clarified further performance improvement using MIMO transmission based on E-UTRA air interface 6