Achieving Near-Capacity at Low SNR on a Multiple-Antenna Multiple-User Channel

TL;DR

This paper demonstrates that serving fewer users in a multi-antenna multi-user system at low SNR can achieve near-capacity with significantly reduced power and complexity, providing practical guidelines for system design.

Contribution

It analytically shows the power efficiency of serving user subsets at low SNR and offers guidelines for near-capacity performance with fewer users.

Findings

Serving fewer users at low SNR requires minimal extra power.

Serving subsets reduces complexity and channel information needs.

In an 8-user system, serving 4 users achieves near-capacity at low SNR.

Abstract

We analyze the sensitivity of the capacity of a multi-antenna multi-user system to the number of users being served. We show analytically that, for a given desired sum-rate, the extra power needed to serve a subset of the users at low SNR (signal-to-noise ratio) can be very small, and is generally much smaller than the extra power needed to serve the same subset at high SNR. The advantages of serving only subsets of the users are many: multi-user algorithms have lower complexity, reduced channel-state information requirements, and, often, better performance. We provide guidelines on how many users to serve to get near-capacity performance with low complexity. For example, we show how in an eight-antenna eight-user system we can serve only four users and still be approximately 2 dB from capacity at very low SNR.