A Heterogeneous Massive MIMO Technique for Uniform Service in Cellular Networks

TL;DR

The paper tackles the problem of poor QoS for cell-edge users in cellular MIMO and the high deployment costs of cell-free massive MIMO (CFmMIMO). It introduces heterogeneous massive MIMO (HmMIMO), combining a central base station with a large antenna array and distributed edge APs connected via fronthaul, to deliver uniform QoS with reduced infrastructure. Closed-form UL and DL spectral efficiency expressions are derived under correlated Rayleigh channels and TDD operation, accounting for channel estimation errors and inter-cell interference. Numerical results show that HmMIMO can achieve 95%-likely per-user SE comparable to CFmMIMO while significantly lowering fronthaul and AP-site costs (e.g., with 1/4 antenna aggregation, $\approx$0.65 vs 0.61 bps/Hz; fronthaul reductions around 25-50%). The work provides a practical, cost-effective pathway to uniform service in dense cellular deployments by balancing centralized processing with edge distributed antennas.

Abstract

Traditional cellular networks struggle with poor quality of service (QoS) for cell-edge users, while cell-free (CF) systems offer uniform QoS but incur high roll-out costs due to acquiring numerous access point (AP) sites and deploying a large-scale optical fiber network to connect them. This paper proposes a cost-effective heterogeneous massive MIMO architecture that integrates centralized co-located antennas at a cell-center base station with distributed edge APs. By strategically splitting massive antennas between centralized and distributed nodes, the system maintains high user fairness comparable to CF systems but reduces infrastructure costs substantially, by minimizing the required number of AP sites and fronthaul connections. Numerical results demonstrate its superiority in balancing performance and costs compared to cellular and CF systems.

Figures (3)

• Figure 1: A comparative illustration of cellular, cell-free, and heterogeneous massive MIMO networks.
• Figure 2: The system model of a toy example for the proposed heterogeneous massive MIMO with two adjacent cells.
• Figure 3: Performance comparison of cellular, cell-free, and heterogeneous massive MIMO networks in per-user SE.