Spectrum and Energy Efficiencies for Multiuser Pairs Massive MIMO Systems With Full-Duplex Amplify-and-Forward Relay

To achieve insights about the impact of amplified loop interference, we consider a dual-hop fullduplex (FD) massive multiple-input multiple-output (MIMO) amplify-and-forward (AF) relaying system in terms of achievable ergodic rates for each user pair as well as spectrum and energy efficiencies. It is assumed that the base station (or relay) is equipped with MRx receive antennas and MTxtransmit antennas, while all sources and destinations have a single antenna. For such FD massive MIMO AF relaying systems, the closedform expressions of the lower bounds of achievable ergodic rates are derived first with a finite number of receive and transmit antennas at base station. Then, the asymptotic performance analysis is performed by considering three different power-scaling schemes: 1) P_S = E_S/M_Rx and P_R = E_R; 2) P_S = E_S and P_R = E_R/M_Tx; and 3) P_S = E_S/M_Rx and P_R = E_R/M_Tx, where E_S and E_R are fixed, and P_S and P_R denote the transmit powers of each source and relay, respectively. Our results show that only when the power-scaling 2) is utilized, do the FD massive MIMO AF relay systems have the ability to restrict the loop interference, so that the system performance is free of loop interference when the number of antennas at the relay is large enough. On the contrary, with the power-scaling cases 1) and 3), the systems have no ability to cancel the loop interference even if M_Rx or M_Tx (or both) goes to infinity. The insight is different from the results in the FD massive MIMO decode-and-forward relaying systems where the loop interference can be entirely eliminated for the three power-scaling cases.