Downlink Multi-User Hybrid Beamforming Systems With Receiver IQ Imbalance: Pre-Compensation and Performance Analysis

We consider the downlink (DL) of a multi-user hybrid beamforming system having receiver IQ imbalance (Rx-IQI). For a generic channel model and any IQI unaware hybrid precoder, we derive a generalized expression of the DL signal-to-interference-and-noise-ratio (SINR) using which we show that the corresponding DL sum-rate is limited by the Rx-IQI parameters. Therefore, we propose a novel Rx-IQI pre-compensation algorithm and we derive a generalized DL SINR expression for the Rx-IQI pre-compensation scenario. Using the derived SINR expressions, we provide closed-form sum-rate expressions of the zero-forcing hybrid precoder for uncorrelated Rayleigh fading and sparse mm-wave channels. Through analysis and numerical simulations, we show that the proposed algorithm almost achieves the performance of an IQI-free system.