Capacity and Multiplexing Architectures potx

1 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath 8. MIMO II: Capacity and Multiplexing Architectures 2 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Outline • Transceiver architectures for fast fading (V-BLAST family) • Transceiver architecture for slow fading (D-BLAST) • Multiple antennas in networks: SDMA 3 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Transmitter and Receiver CSI • Can decompose the MIMO channel into a bunch of orthogonal sub-channels. • Can allocate power and rate to each sub-channel according to waterfilling 4 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Analogy with OFDM Major difference: In MIMO, the U and V matrices depend on the channel H. In OFDM, the IDFT and DFT matrices do not. 5 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Receiver CSI Only The channel matrix H and its singular values λ i 2 's are random and unknown to the transmitter. Has to fix a Q and a power allocation independent of H. Q=I and uniform power allocation is optimal in many cases. It is not trivial to come up with capacity-achieving architectures. 6 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Capacity Can write: Slow fading: Fast fading: 7 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Fast Fading Capacity for I.I.D. Rayleigh Fading 8 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath d.o.f. determines the high SNR slope. 9 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Fast Fading Capacity: Low SNR n r – fold power gain at low SNR 10 8: MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Nature of Performance Gain • At high SNR (d.o.f. limited): min(n t ,n r )-fold d.o.f. gain. MIMO is crucial. • At low SNR (power limited): n r -fold power gain. Only need multiple receive antennas. • At all SNR, min(n t ,n r )-fold gain due to a combination of both effects. [...]... MIMO II: Capacity and Multiplexing Architectures Interference Nulling Focusing on Tx antenna 1: Simple strategy: null out the interference from other antennas Fundamentals of Wireless Communication, Tse&Viswanath 13 8: MIMO II: Capacity and Multiplexing Architectures Receiver Architecture I: Bank of Decorrelators Fundamentals of Wireless Communication, Tse&Viswanath 14 8: MIMO II: Capacity and Multiplexing. .. nulling and match filtering It whitens the interference first and then match filter This is the linear MMSE filter Fundamentals of Wireless Communication, Tse&Viswanath 18 8: MIMO II: Capacity and Multiplexing Architectures MMSE Filter High SNR: MMSE ¼ decorrelator Low SNR: MMSE ¼ matched filter Fundamentals of Wireless Communication, Tse&Viswanath 19 8: MIMO II: Capacity and Multiplexing Architectures. .. Communication, Tse&Viswanath 20 8: MIMO II: Capacity and Multiplexing Architectures Gap at High SNR • MMSE improves the performance of decorrelator at moderate and low SNR • Does not remove the gap in performance at high SNR • To remove that gap we have to go to non-linear receivers Fundamentals of Wireless Communication, Tse&Viswanath 21 8: MIMO II: Capacity and Multiplexing Architectures Successive Interference... Architectures Successive Interference Cancellation Fundamentals of Wireless Communication, Tse&Viswanath 22 8: MIMO II: Capacity and Multiplexing Architectures MMSE-SIC Achieves MIMO Capacity Fundamentals of Wireless Communication, Tse&Viswanath 23 8: MIMO II: Capacity and Multiplexing Architectures Optimality of MMSE-SIC Given a fixed channel H, Why is MMSE-SIC optimal? MMSE is information lossless at... Communication, Tse&Viswanath 16 8: MIMO II: Capacity and Multiplexing Architectures Interference Nulling vs Match Filtering Interference nulling: remove all interference at the expense of reducing the SNR Match filtering: projecting onto h1 to maximize the SNR but SINR may be bad Fundamentals of Wireless Communication, Tse&Viswanath 17 8: MIMO II: Capacity and Multiplexing Architectures Optimal Linear Filter:MMSE... becomes important • Challenge is to combine this with SIC Fundamentals of Wireless Communication, Tse&Viswanath 25 8: MIMO II: Capacity and Multiplexing Architectures D-BLAST MMSE Fundamentals of Wireless Communication, Tse&Viswanath 26 8: MIMO II: Capacity and Multiplexing Architectures Parallel Channel Conversion • D-BLAST converts the MIMO channel into a parallel channel • Any good time-diversity... Communication, Tse&Viswanath 30 8: MIMO II: Capacity and Multiplexing Architectures Uplink-Downlink Reciprocity The total power to achieve given SINR requirements is the same in the two links Can use MMSE filters in the “virtual” uplink for downlink transmit beamforming Fundamentals of Wireless Communication, Tse&Viswanath 31 8: MIMO II: Capacity and Multiplexing Architectures Downlink Transmit Beamforming... downlink • They can also be used to suppress out-of-cell interference and provide diversity Fundamentals of Wireless Communication, Tse&Viswanath 11 8: MIMO II: Capacity and Multiplexing Architectures Transceiver Architecture: V-BLAST • Can get the performance gain by sending independent coded streams at each of the Tx antennas and joint ML decoding • Is this surprising? • Question: – How to get the... Communication, Tse&Viswanath 28 8: MIMO II: Capacity and Multiplexing Architectures SDMA vs Orthogonal MA • Many wireless systems use orthogonal multiple access • How does SDMA compared to just using the receive antenna array to provide a power gain for each user? • At high SINR, the system is d.o.f limited and SDMA provides significant gain • At low SINR, system is power-limited and SDMA provides limited gain... Capacity and Multiplexing Architectures Bank of Decorrelators: Performance i.i.d Rayleigh Fundamentals of Wireless Communication, Tse&Viswanath 15 8: MIMO II: Capacity and Multiplexing Architectures Performance Gap of Decorrelator Achieves the full d.o.f min(nt,nr) of the MIMO channel (Same SNR slope.) But: There is still a substantial constant gap at high SNR At moderate and low SNR, performance sucks . MIMO II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath 8. MIMO II: Capacity and Multiplexing Architectures 2 8: MIMO II: Capacity and Multiplexing. II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Fast Fading Capacity for I.I.D. Rayleigh Fading 8 8: MIMO II: Capacity and Multiplexing Architectures . II: Capacity and Multiplexing Architectures Fundamentals of Wireless Communication, Tse&Viswanath Receiver Architecture I: Bank of Decorrelators 15 8: MIMO II: Capacity and Multiplexing Architectures