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-alpha at the users and by 1/M-beta at the relay as the number M of relay antennas increases, where (alpha, beta) = (t, 1) or (1, t) for 0 <= t <= 1 in the case of perfect CSI and (alpha, beta) = (t, 1-t) or (1/2, t) for 0 <= t <= 1/2 in the case of imperfect CSI.