Power and Spectral Efficiency of Multi-Pair Massive Antenna Relaying Systems With Zero-Forcing Relay Beamforming

We consider a multi-pair multi-antenna relay system, delivering data from multi-sources to their destinations simultaneously with the help of a massive antenna relay. We analyze the spectral efficiency and power scaling laws under perfect and imperfect channel state information (CSI) for zero-forcing relay beamforming. The analysis shows that the transmit power can be scaled down by 1/M^α at the users and by 1/M^β at the relay as the number M of relay antennas increases, where (α,β) = (t,1) or (1,t) for 0 ≤ t ≤ 1 in the case of perfect CSI and (α,β) = (t,1 -t) or (1/2,t) for 0 ≤ t ≤ 1/2 in the case of imperfect CSI.