Downlink and Uplink Transmissions in Distributed Large-Scale MIMO Systems for BD Precoding with Partial Calibration

Abstract

When both access points (APs) and user equipments (UEs) have multiple antennas, the block diagonalization (BD) precoding is preferred for the distributed large-scale multiple-input multiple-output (MIMO) systems. In time division duplexing (TDD) operation, the APs can exploit the estimated uplink channel for downlink joint precoding transmission to simultaneously serve multiple UEs, due to the principle of channel reciprocity. However, the non-symmetric hardware radio frequency (RF) circuits at both sides of the link disable the channel reciprocity and result in a system performance loss. Based on a low complex BD precoding method, this paper designs a scheme for both the downlink and the uplink transmissions with the partial calibration. Theoretical analysis and simulation results show that the inter-stream interference (ISI) can be canceled out at the UEs through the minimum mean square error (MMSE) receiver in the downlink transmission. While in the uplink transmission, the APs can distinguish each data stream of every UE via the maximal ratio combining (MRC) receiver. Besides, the interference suppression precoding matrix at the APs can be used for both the downlink and uplink transmissions, which need to be calculated only once.