Closed-form analysis of channel non-reciprocity due to transceiver and antenna coupling mismatches in multi-user massive MIMO network

In this paper, we analyze the impact of channel non-reciprocity due to two implementation imperfections, namely, transceiver frequency-response and antenna mutual coupling mismatches at the base-station side in multi-user massive MIMO system context Signal models are first developed to characterize the joint effects of these two imperfections in precoded multi-user downlink transmission, covering both zero-forcing (ZF) and maximum ratio transmission (MRT) based transmitter processing. Then closed-form expressions for evaluating the resulting performance degradation are derived in terms of effective SENR at terminal receiver input as well as lower bound of maximum achievable sum-rate in the system. Based on the derived results, it is also possible to directly evaluate non-reciprocity calibration requirements at the BS with given performance targets, e.g., desired effective SENR for each user or the overall system throughput, at given SNR level. The analysis also shows that the ZF precoding can be sensitive to the channel non-reciprocity problem even in the case that large amounts of antennas are deployed while the impact of implementation imperfections on MRT precoded system is less severe.