Approximate sum rate for massive multiple‐input multiple‐output two‐way relay with Ricean fading

Abstract

This study considers a multi-pair massive multiple-input multiple-output two-way relay network where the M-antenna relay simultaneously serves K pairs of single-antenna users in the same time–frequency resource. For a more general case of Ricean fading channel, the authors propose a fixed-gain maximum ratio combing/maximum ratio transmission relay scheme. The approximate expressions on the ergodic sum rate with such scheme are derived in two cases: (i) M, which is much larger than the users’ Ricean factors, is large enough; and (ii) if M is large enough but bounded, the Ricean factors of all the users go to infinity. Simulation results show that the approximate results are very tight. Based on the result for the first case, they further discuss the power-scaling laws, which reveal that despite the Ricean fading channel and the interference at the relay, the achievable sum rate can still remain unchanged if the transmitted power at each user or at the relay is or both are made inversely proportional to M.