Analysis of BD precoding for distributed large-scale MIMO systems with RF mismatches at UEs

To avoid the heavy overhead of the pilots and feedback, the time division duplex (TDD) operation is used due to the channel reciprocity. When multiple antennas are equipped at the user equipments (UEs), the radio access units (RAUs) can use the block diagonalization (BD) precoding to improve the system performance. However, the mismatches of the radio frequency (RF) circuits at both sides of the links make the whole communication channels non-symmetric in practical systems. And it may be not enough to only perform calibration at the RAUs. In this paper, we focus on the RF mismatches at the UEs for the large-scale distributed MIMO systems with BD precoding. According to the theoretical analysis and simulation results, we find that the RF mismatches at the UEs still lead to a negligible performance loss although the partial calibration has been performed at the RAUs. And It is strongly suggested that reciprocity calibration should be performed at both the RAUs and the UEs.