Opportunistic AP Selection in Cell-Free Massive MIMO-OFDM Systems

TL;DR

This paper introduces an opportunistic AP selection scheme in cell-free massive MIMO-OFDM systems that improves power and spectral efficiency by activating only near APs for each user and orthogonally assigning subcarriers.

Contribution

It proposes a novel opportunistic transmission scheme that assigns subcarriers orthogonally and activates only near APs, enhancing efficiency in cell-free massive MIMO-OFDM systems.

Findings

Significant power efficiency improvements.

Enhanced spectral efficiency.

Feasibility of downlink pilots with fewer active APs.

Abstract

Exploiting the degree of freedom in the frequency domain and the near-far effect among different access points (APs), this paper proposes an opportunistic transmission scheme in cell-free massive MIMO-OFDM systems. The key idea is to orthogonally assign subcarriers among different users, so that there is only one user on each subcarrier. Then, a user is only served by its near APs through opportunistic selection, while the far APs are deactivated to avoid wasting power over their channels with severe propagation losses. Moreover, the number of active APs per subcarrier becomes small due to the opportunistic selection, making the use of downlink pilots and coherent detection feasible. As corroborated by numerical results, the proposed scheme can bring a significant performance boost in terms of both power efficiency and spectral efficiency.