Outage Analysis of Downlink URLLC in Massive MIMO systems with Power Allocation

TL;DR

This paper examines the trade-offs in downlink URLLC performance in Massive MIMO systems, focusing on power allocation strategies to optimize reliability and spectral efficiency under channel knowledge constraints.

Contribution

It introduces a comprehensive analysis of power allocation methods for Massive MIMO URLLC, highlighting the impact on reliability and spectral efficiency with different precoding schemes.

Findings

Max-min SINR power allocation yields highest reliability.

Trade-off between reliability and spectral efficiency is evident.

Optimal pilot symbol allocation depends on device multiplexing needs.

Abstract

Massive MIMO is seen as a main enabler for low latency communications, thanks to its high spatial degrees of freedom. The channel hardening and favorable propagation properties of Massive MIMO are particularly important for multiplexing several URLLC devices. However, the actual utility of channel hardening and spatial multiplexing is dependent critically on the accuracy of channel knowledge. When several low latency devices are multiplexed, the cost for acquiring accurate knowledge becomes critical, and it is not evident how many devices can be served with a latency-reliability requirement and how many pilot symbols should be allocated. This paper investigates the trade-off between achieving high spectral efficiency and high reliability in the downlink, by employing various power allocation strategies, for maximum ratio and minimum mean square error precoders. The results show that using max-min SINR power allocation achieves the best reliability, at the expense of lower sum spectral efficiency.