Optimizing user selection schemes in vector broadcast channels

TL;DR

This paper analyzes and optimizes user selection schemes in vector broadcast channels to maximize ergodic downlink sum-rate, considering fairness, multi-user diversity, and beamforming methods.

Contribution

It introduces analytical expressions for ergodic sum-rate for different user selection schemes and optimally sets key parameters to enhance performance.

Findings

Optimal parameter settings improve sum-rate performance.

Greedy schemes exploit multi-user diversity more effectively.

Fairness can be balanced with sum-rate through parameter tuning.

Abstract

In this paper, we focus on the ergodic downlink sum-rate performance of a system consisting of a set of heterogeneous users. We study three user selection schemes to group near-orthogonal users for simultaneous transmission. The first scheme is a random selection policy that achieves fairness, but does not exploit multi-user diversity. The second scheme is a greedy selection policy that fully exploits multi-user diversity, but does not achieve fairness, and the third scheme achieves fairness while partially exploiting multi-user diversity. We also consider two beamforming methods for data transmission, namely, maximum-ratio transmission and zero-forcing beamforming. In all scheduling schemes studied in the paper, there is a key parameter that controls the degrees of orthogonality of channel directions between co-scheduled users. We focus on optimally setting this parameter for each scheduling scheme such that the ergodic downlink sum-rate is maximized. To this end, we derive analytical expressions for the ergodic downlink sum-rate considering each scheduling scheme. Numerical results are also presented to provide further insights.