Uplink Performance Analysis of Cell-Free mMIMO Systems under Channel Aging

TL;DR

This paper analyzes how channel aging affects uplink performance in cell-free massive MIMO systems, deriving deterministic SINR expressions and comparing performance with cellular and small-cell networks under various mobility scenarios.

Contribution

It introduces a new model for channel aging at different APs and derives deterministic equivalents of SINR, providing insights into system performance under mobility.

Findings

CF-mMIMO outperforms cellular and small-cell networks at low user velocities.

High user velocities increase the impact of channel aging on CF-mMIMO.

Differential aging rates at APs can mitigate aging effects, especially with larger frame durations.

Abstract

In this paper, we investigate the impact of channel aging on the uplink performance of a cell-free~(CF) massive multiple-input multiple-output (mMIMO) system with a minimum mean squared error (MMSE) receiver. To this end, we present a new model for the temporal evolution of the channel, which allows the channel to age at different rates at different access points (APs). Under this setting, we derive the deterministic equivalent of the per-user achievable signal-to-interference-plus-noise ratio (SINR). In addition to validating the theoretical expressions, our simulation results reveal that, {at low user mobilities,} the SINR of CF-mMIMO is nearly 5 dB higher than its cellular counterpart with the same number of antennas, and about 8 dB higher than that of an equivalent small-cell network with the same number of APs. {On the other hand, at very high user velocities, and when the channel between the UEs the different APs age at same rate, the relative impact of aging is higher for CF-mMIMO compared to cellular mMIMO. However, when the channel ages at the different APs with different rates, the effect of aging on CF-mMIMO is marginally mitigated, especially for larger frame durations.