Heterogeneous System Design for Cell-Free Massive MIMO in Wideband Communications

TL;DR

This paper introduces a heterogeneous CFmMIMO system that combines a base station and distributed access points, improving capacity and reducing costs by selectively activating APs for far users.

Contribution

It proposes a novel heterogeneous system architecture that enhances performance and efficiency over traditional homogeneous CFmMIMO setups.

Findings

Outperforms homogeneous CFmMIMO in sum capacity.

Reduces AP installation costs and signaling overhead.

Enables downlink pilots for far users by activating only the closest AP.

Abstract

Cell-free massive multi-input multi-output (CFmMIMO) offers uniform service quality through distributed access points (APs), yet unresolved issues remain. This paper proposes a heterogeneous system design that goes beyond the original CFmMIMO architecture by exploiting the synergy of a base station (BS) and distributed APs. Users are categorized as near users (NUs) and far users (FUs) depending on their proximity to the BS. The BS serves the NUs, while the APs cater to the FUs. Through activating only the closest AP of each FU, the use of downlink pilots is enabled, thereby enhancing performance. This heterogeneous design outperforms other homogeneous massive MIMO configurations, demonstrating superior sum capacity while maintaining comparable user-experienced rates. Moreover, it lowers the costs associated with AP installations and reduces signaling overhead for the fronthaul network.