Two-Stage Space-Time Receiver Structure for Multi-User Hybrid mmW Massive MIMO Systems

This paper considers a hybrid two-stage space-time receiver structure for uplink millimeter wave (mmW) based systems, where the user terminals (UTs) and the base station (BS) are equipped with a large antenna array and the number of radio frequency (RF) chains is lower than the number of antennas. In the first stage the analog transmit and receive beamformers/precoders are computed for each UT BS pair considering multi-user interference free links, to maximize the desired signal power for each UT. In the second one, an iterative block space-time equalizer is designed to explicitly remove the multiuser interference. The designed space-time equalizer is optimized by using as a metric the mean square error (MSE) between the transmitted data vector and its estimate after the digital equalizer. Our performance results have shown that the proposed iterative space-time equalizer outperforms the linear MMSE based receivers for hybrid mmW massive MIMO architectures.