A Novel Calibration Error Aware Precoding for Massive MIMO Systems with Imperfect CSI

Massive multiple-input multiple-output (MIMO) is a key technology in deployment of the fifth generation (5G) of wireless communication networks. The performance of such systems strongly relies on the accuracy of the estimated channel state information (CSI) obtained in the training phase. Exploiting channel reciprocity, the downlink CSI is obtained based on the uplink CSI estimated in time division duplex (TDD) mode. However, in a practical scenario, due to hardware impairments, the overall link between transceivers are non-reciprocal. Hence, in order to avoid the estimation error, a calibration process is required. This paper investigates the problem of reciprocity calibration in a massive MIMO system in which it is attempted to design precoders that compensate for non-reciprocal links as well as estimation error in the uplink training phase. Moreover, closed-form expressions are extracted for optimum precoders for both cases of perfect uplink CSI and imperfect uplink CSI. Numerical results demonstrate the out-performance of the proposed precoders compared to the conventional precoders in terms of coping with multi user interference in presence of estimation error.