Impact of General Channel Aging Conditions on the Downlink Performance of Massive MIMO

TL;DR

This paper investigates how channel aging caused by user mobility and phase noise impacts massive MIMO downlink performance, deriving deterministic equivalents for SINRs and comparing precoding schemes.

Contribution

It introduces a joint model for Doppler shift and phase noise effects, providing new insights into their combined impact on massive MIMO systems with different precoding methods.

Findings

User mobility has a more severe impact than phase noise at moderate speeds.

Phase noise significantly affects performance at low mobility.

Deterministic equivalents for SINRs are derived for MRT and RZF precoding.

Abstract

Recent works have identified massive multiple-input-multiple-output (MIMO) as a key technology for achieving substantial gains in spectral and energy efficiency. Additionally, the turn to low-cost transceivers, being prone to hardware impairments is the most effective and attractive way for cost-efficient applications concerning massive MIMO systems. In this context, the impact of channel aging, which severely affects the performance, is investigated herein by considering a generalized model. Specifically, we show that both Doppler shift because of the users' relative movement as well as phase noise due to noisy local oscillators (LOs) contribute to channel aging. To this end, we first propose a joint model, encompassing both effects, in order to investigate the performance of a massive MIMO system based on the inevitable time-varying nature of realistic mobile communications. Then, we derive the deterministic equivalents (DEs) for the signal-to-noise-and-interference ratios (SINRs) with maximum ratio transmission (MRT) and regularized zero-forcing precoding (RZF). Our analysis not only demonstrates a performance comparison between MRT and RZF under these conditions, but most importantly, it reveals interesting properties regarding the effects of user mobility and phase noise. In particular, the large antenna limit behavior depends profoundly on both effects, but the burden due to user mobility is much more detrimental than phase noise even for moderate user velocities ($\approx30$ km/h), while the negative impact of phase noise is noteworthy at lower mobility conditions.