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

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.