Joint hybrid RF/baseband transceiver design for multi-user MIMO downlink in millimeter wave communication system

Millimeter wave (mmWave) communication systems employ hybrid RF/baseband transceivers that divide the spatial signal processing into radio frequency and baseband domains in order to reduce the hardware complexity resulting from the use of large number of antennas elements. In this paper, we consider two designs for hybrid multi-user MIMO downlink that minimizes the sum mean square error (SMSE), based on perfect channel knowledge (non-robust design) and transceiver design considering the channel imperfections (robust design). In the robust design, the channel state information (CSI) is assumed to be perturbed by estimation error and follows Gaussian distribution with known error variance. In both the designs, reduced hardware complexity is achieved by analog-digital hybrid processing by using orthogonal matching pursuit (OMP)-based sparse signal processing. We evaluate the performance of both the proposed schemes based on various parameters and also compare it with conventional fully-digital system. We present numerical results over various dictionaries. The comparison results show that robust design is resilient to the presence of CSI errors. Furthermore, we also demonstrate the convergence of both the proposed algorithms to a limit even though global convergence is hard to prove due to non convex nature of overall optimization problem.