Asynchronous Cell-Free Massive MIMO-OFDM: Mixed Coherent and Non-Coherent Transmissions

TL;DR

This paper analyzes a mixed coherent and non-coherent transmission approach in cell-free MIMO-OFDM systems, providing performance metrics and clustering algorithms to enhance sum-rate under asynchronous reception.

Contribution

It introduces a novel mixed transmission scheme with a closed-form sum-rate expression and an efficient clustering algorithm for asynchronous CF mMIMO-OFDM systems.

Findings

Mixed transmissions improve sum-rate performance.

Closed-form sum-rate expression derived for maximum ratio precoding.

Clustering algorithm effectively groups access points for phase shift management.

Abstract

In this letter, we analyze the performance of mixed coherent and non-coherent transmissions approach, which can improve the performance of cell-free multiple-input multiple-output orthogonal frequency division multiplexing (CF mMIMO-OFDM) systems under asynchronous reception. To this end, we first obtain the achievable downlink sum-rate for the mixed coherent and non-coherent transmissions, and then provide a closed-form expression for the case with the maximum ratio precoding. Subsequently, an efficient clustering algorithm is proposed to group access points into different clusters with the same quantized phase shift in each cluster. Numerical results demonstrate that the mixed coherent and non-coherent transmissions can effectively improve the sum-rate of CF mMIMO-OFDM systems under asynchronous reception.