Hybrid Beamforming With Selection for Multiuser Massive MIMO Systems

Abstract

This work studies a variant of hybrid beamforming, namely, hybrid beamforming\nwith selection (HBwS), as an attractive solution to reduce the hardware cost of\nmulti-user Massive Multiple-Input-Multiple-Output systems, while retaining good\nperformance. Unlike conventional hybrid beamforming, in a transceiver with\nHBwS, the antenna array is fed by an analog beamforming matrix with $\\bar{L}$\ninput ports, where $\\bar{L}$ is larger than the number of up/down-conversion\nchains $\\bar{K}$. A bank of switches connects the instantaneously best\n$\\bar{K}$ out of the $\\bar{L}$ input ports to the up/down-conversion chains.\nThe analog beamformer is designed based on average channel statistics and\ntherefore needs to be updated only infrequently, while the switches operate\nbased on instantaneous channel knowledge. HBwS allows use of simpler hardware\nin the beamformer that only need to adjust to the statistics, while also\nenabling the effective analog beams to adapt to the instantaneous channel\nvariations via switching. This provides better user separability, beamforming\ngain, and/or simpler hardware than some conventional hybrid schemes. In this\nwork, a novel design for the analog beamformer is derived and approaches to\nreduce the hardware and computational cost of a multi-user HBwS system are\nexplored. In addition, we study how $\\bar{L}$, the switch bank architecture,\nthe number of users and the channel estimation overhead impact system\nperformance.\n