  Channel reciprocity in time-division duplexing (TDD) massive multiple-input
multiple-output (MIMO) systems can be exploited to reduce the overhead required
for the acquisition of channel state information (CSI). However, perfect
reciprocity is unrealistic in practical systems due to random radio-frequency
(RF) circuit mismatches in uplink and downlink channels. This can result in a
significant degradation in the performance of linear precoding schemes, which
are sensitive to the accuracy of the CSI. In this paper, we model and analyse
the impact of RF mismatches on the performance of linear precoding in a TDD
multi-user massive MIMO system, by taking the channel estimation error into
considerations. We use the truncated Gaussian distribution to model the RF
mismatch, and derive closed-form expressions of the output
signal-to-interference-plus-noise ratio for maximum ratio transmission and zero
forcing precoders. We further investigate the asymptotic performance of the
derived expressions, to provide valuable insights into the practical system
designs, including useful guidelines for the selection of the effective
precoding schemes. Simulation results are presented to demonstrate the validity
and accuracy of the proposed analytical results.
