Massive MIMO Systems With IQ Imbalance: Channel Estimation and Sum Rate Limits
Abstract: In this paper, we study the impact of in in-phase and quadrature imbalance (IQI) on single-cell cell multiuser multiple multiple-input multiple-output output systems with large antenna arrays. Moreover, we consider a time time-division division duplex system, where we assume uplink/downlink channel reciprocity in the downlink precoding design. First, we investigate the effect of transceiver IQI on the uplink channel estimation by deriving the linear minimum minimum-mean-square-error error estimator for the IQ-impaired IQ model and prove that only the receiver IQI at the base station (BS) limits the estimation accuracy. Then, hen, we study the impact of uplink/downlink channel mismatch on the downlink rate caused by different IQI at the BS and user equipments (UEs). We prove that the achievable downlink rate of each UE is limited either by the receiver IQI at the UEs or jointly by the transmit and receive IQI at the BS, when there is mismatch between the uplink and downlink channels.