Effect of array configuration on multiuser diversity with opportunistic beamforming

Abstract

Opportunistic beamforming (OBF) is a multiple- antenna technique which induces large and fast channel fluc- tuations to increase multiuser diversity gains with very limited channel feedback. For this technique, we consider both the uniform and nonuniform linear antenna arrays at a base station, and show that the array configuration plays a very important role on exploiting multiuser diversity. Three Rayleigh fading environments are discussed, including a fixed environment, a mobile environment, and a more practical environment in which users move with a range of speeds so that fading rates are various. Given an environment, the selected array configuration should be a compromise among the three criteria: total throughput, performance fairness, and system complexity. Our results show that the nonuniform array is a good choice to balance these criteria in performing OBF.