On The Uplink Throughput of Zero-Forcing in Cell-Free Massive MIMO with Coarse Quantization

TL;DR

This paper analyzes the uplink throughput of Zero-Forcing in Cell-Free massive MIMO systems with coarse quantization, focusing on CSI transfer strategies under fronthaul capacity constraints.

Contribution

It compares estimate-and-quantize and quantize-and-estimate strategies for CSI acquisition using Bussgang decomposition, highlighting the effectiveness of quantize-and-estimate with low-resolution quantization.

Findings

Quantize-and-estimate performs similarly or better than estimate-and-quantize.

Zero-Forcing achieves measurable uplink rates under coarse quantization.

1-bit resolution quantization is effective with the proposed strategies.

Abstract

The recently proposed Cell-Free massive MIMO architecture is studied for the uplink. In contrast to most previous works, joint detection is performed using global CSI. Therefore, we study strategies for transferring CSI to the CPU taking into account the fronthaul capacity which limits CSI quantization. Two strategies for pilot-based CSI acquisition are considered: estimate-and-quantize and quantize-and-estimate. These are analysed using the Bussgang decomposition. For a given quantization constraint for the data and CSI the achievable rate per user with Zero-Forcing is determined. Numerical results show that quantize-and-estimate (the simpler strategy) is similar to or better than estimate-and-quantize, especially for 1-bit resolution.