Energy-Saving Cell-Free Massive MIMO Precoders with a Per-AP Wideband Kronecker Channel Model

TL;DR

This paper proposes a new power-efficient precoding method for cell-free massive MIMO systems that leverages second-order channel statistics to significantly reduce power consumption while maintaining user rate constraints.

Contribution

It introduces an asymptotic approximation for antenna power based on second-order channel statistics, enabling power savings up to 9 times in low-load scenarios.

Findings

Asymptotic approximation accurately predicts antenna power usage.

Turning off a subset of access points reduces power consumption.

Power savings up to 9x achieved in low-load conditions.

Abstract

We study cell-free massive multiple-input multiple-output precoders that minimize the power consumed by the power amplifiers subject to per-user per-subcarrier rate constraints. The power at each antenna is generally retrieved by solving a fixed-point equation that depends on the instantaneous channel coefficients. Using random matrix theory, we retrieve each antenna power as the solution to a fixed-point equation that depends only on the second-order statistics of the channel. Numerical simulations prove the accuracy of our asymptotic approximation and show how a subset of access points should be turned off to save power consumption, while all the antennas of the active access points are utilized with uniform power across them. This mechanism allows to save consumed power up to a factor of 9$\times$ in low-load scenarios.