Insights on the Uplink Operation of a 1-bit Radio-Over-Fiber Architecture in Multi-User D-MIMO Communication

TL;DR

This paper explores a 1-bit radio-over-fiber D-MIMO architecture for uplink communication, demonstrating its feasibility and identifying key challenges like dynamic range limitations, with potential solutions such as UE power control.

Contribution

It provides an experimental and simulation-based analysis of a 1-bit fronthaul D-MIMO system, highlighting its performance and practical issues in uplink transmission.

Findings

Achieves 3GPP NR error-vector magnitude standards across scenarios.

Identifies uplink bottleneck due to automatic gain control limitations.

Suggests UE power control as a mitigation strategy.

Abstract

We consider a distributed multiple-input multiple-output (D-MIMO) testbed in which, to enable coherent-phase transmission without over-the-air synchronization, the remote radio heads (RRHs) are connected to a central unit via a 1-bit radio-over-fiber fronthaul. Specifically, 1-bit samples of the radio-frequency signal are exchanged over the fronthaul. We investigate via both measurements and simulations based on an accurate model of the testbed hardware, the capability of the proposed architecture to provide uniform quality of services over the coverage area--one of the promises of D-MIMO. Our results are encouraging: for the case in which two user equipments (UEs) communicate over the same 75MHz signal bandwidth, the measured error-vector magnitude meets the 3GPP New Radio specification of 12.5\% for 16QAM across all tested DMIMO scenarios. We also determine that uplink transmission is a potential bottleneck, due to the limited dynamic range of the automatic gain controller, which prevents the 1-bit quantizer to benefit from dithering. We show that this issue can be mitigated via UE power control.