Impact and Calibration of Nonlinear Reciprocity Mismatch in Massive MIMO Systems

Time-division-duplexing massive multiple-input multiple-output (MIMO) systems estimate the channel state information (CSI) by leveraging uplink-downlink reciprocity, which is no longer valid when mismatch arises from asymmetric uplink and downlink radio frequency (RF) chains. Existing works treat reciprocity as constant for simplicity. However, practical RF chain consists of nonlinear components, leads to mismatch. In this work, we examine impact calibration approach in MIMO systems. To evaluate mismatch, first derive closed-form expression ergodic achievable rate. Then, analyze performance loss caused show that at base station (BS) side much larger than user equipment side. Therefore, propose a method BS. During calibration, polynomial function applied approximate factor, over-the-air training employed coefficients. After that, coefficients are computed maximizing Simulation results presented verify analytical proposed approach.