Downlink Power Control for Massive MIMO Cellular Systems with Optimal User Association

TL;DR

This paper proposes an optimal user association and power control strategy for Massive MIMO downlink systems, reducing power consumption while maintaining spectral efficiency and balancing load among base stations.

Contribution

It derives a novel optimal user association rule and joint power control method for Massive MIMO systems under fixed spectral efficiency constraints.

Findings

Significant power savings compared to small-scale systems.

Effective load balancing among base stations.

Enhanced spectral efficiency with optimized user association.

Abstract

This paper aims to minimize the total transmit power consumption for Massive MIMO (multiple-input multiple-output) downlink cellular systems when each user is served by the optimized subset of the base stations (BSs). We derive a lower bound on the ergodic spectral efficiency (SE) for Rayleigh fading channels and maximum ratio transmission (MRT) when the BSs cooperate using non-coherent joint transmission. We solve the joint user association and downlink transmit power minimization problem optimally under fixed SE constraints. Furthermore, we solve a max-min fairness problem with user specific weights that maximizes the worst SE among the users. The optimal BS-user association rule is derived, which is different from maximum signal-to-noise-ratio (max-SNR) association. Simulation results manifest that the proposed methods can provide good SE for the users using less transmit power than in small-scale systems and that the optimal user association can effectively balance the load between BSs when needed.