Distributed Resource Allocation Optimization for User-Centric Cell-Free MIMO Networks

TL;DR

This paper proposes two distributed algorithms for resource allocation in user-centric cell-free MIMO networks, optimizing system throughput and fairness without requiring inter-DU communication, and compares their performance and trade-offs.

Contribution

It introduces novel distributed resource allocation algorithms for cell-free MIMO networks that operate with minimal information exchange and demonstrate significant throughput improvements.

Findings

CU-distributed system achieves 1.3- to 1.8-fold throughput increase.

Algorithms perform user scheduling, beamforming, and power control with channel estimation errors.

The proposed methods outperform local zero-forcing benchmarks.

Abstract

We develop two distributed downlink resource allocation algorithms for user-centric, cell-free, spatially-distributed, multiple-input multiple-output (MIMO) networks. In such networks, each user is served by a subset of nearby transmitters that we call distributed units or DUs. The operation of the DUs in a region is controlled by a central unit (CU). Our first scheme is implemented at the DUs, while the second is implemented at the CUs controlling these DUs. We define a hybrid quality of service metric that enables distributed optimization of system resources in a proportional fair manner. Specifically, each of our algorithms performs user scheduling, beamforming, and power control while accounting for channel estimation errors. Importantly, our algorithm does not require information exchange amongst DUs (CUs) for the DU-distributed (CU-distributed) system, while also smoothly converging. Our results show that our CU-distributed system provides 1.3- to 1.8-fold network throughput compared to the DU-distributed system, with minor increases in complexity and front-haul load - and substantial gains over benchmark schemes like local zero-forcing. We also analyze the trade-offs provided by the CU-distributed system, hence highlighting the significance of deploying multiple CUs in user-centric cell-free networks.