Multi-User Hybrid Precoding for Millimeter-Wave Communications Based on a Linear Successive Allocation Method

Hybrid analog and digital precoding is one possibility for making the communication in the underutilized millimeter-wave frequency bands viable for future cellular networks. This paper proposes new algorithms for the design of hybrid precoders in the downlink of a multi-user scenario. The algorithms are based on the Linear Successive Allocation (LISA) method developed for the traditional fully digital precoding. It successively allocates data streams to users and suppresses the inter-stream interference in two steps. By a simple approximation, the two steps are mapped to the analog and digital domain to obtain the new multi-user hybrid precoding algorithm Hybrid LISA (H-LISA). Furthermore, a low-complexity version is developed by exploiting the typical structure of mmWave channels. We also present modifications of H-LISA for hybrid analog and digital processing at the users and for the case that the phase shifts of practical phase shifters implementing the analog part of the hybrid processing are quantized. The good performance of the proposed methods is demonstrated by simulation results. In addition, we discuss the impact of channel estimation errors on the achievable sum rate.