On the Fundamental Limits of MIMO Massive Multiple Access Channels

TL;DR

This paper characterizes the capacity limits of massive MIMO multiple access channels, revealing that the sum rate dominates and individual user rates are unaffected by the number of antennas, with implications for large-scale wireless networks.

Contribution

It introduces an information-theoretic approach based on Gallager's error exponent to analyze the finite dimension region of MIMO mMAC, extending previous results to massive access scenarios.

Findings

Finite dimension region dominated by sum rate constraint

Individual user rate independent of transmit antennas asymptotically

Channel hardening enables near-statistical knowledge performance

Abstract

In this paper, we study the multiple-antenna wireless communication networks, where a large number of devices simultaneously communicate with an access point. The capacity region of multiple-input multiple-output massive multiple access channels (MIMO mMAC) is investigated. While joint typicality decoding is utilized to establish the achievability of capacity region for conventional MAC with fixed number of users, the technique is not directly applicable for MIMO mMAC. Instead, an information-theoretic approach based on Gallager's error exponent analysis is exploited to characterize the \textcolor[rgb]{0,0,0}{finite dimension region} of MIMO mMAC. Theoretical results reveal that the finite dimension region of MIMO mMAC is dominated by sum rate constraint only, and the individual user rate is determined by a specific factor that corresponds to the allocation of sum rate. The rate in conventional MAC is not achievable with massive multiple access, which is due to the fact that successive interference cancellation cannot guarantee an arbitrary small error decoding probability for MIMO mMAC. The results further imply that, asymptotically, the individual user rate is independent of the number of transmit antennas, and channel hardening makes the individual user rate close to that when only statistic knowledge of channel is available at receiver. The finite dimension region of MIMO mMAC is a generalization of the symmetric rate in Chen \emph{et al.} (2017).