Power Allocation Schemes for Multicell Massive MIMO Systems

TL;DR

This paper explores power allocation strategies in multicell massive MIMO systems, deriving rate expressions, proposing a low-complexity scheduling mechanism, and analyzing the conditions under which these strategies significantly improve sum rates.

Contribution

It introduces a practical scheduling-based power allocation scheme for multicell massive MIMO, with analytical insights into its performance and when it provides notable gains.

Findings

Power allocation schemes significantly improve sum rate with practical antenna setups.

Gains diminish as the number of antennas M approaches infinity with fixed users N.

When both M and N grow large together, rate improvements depend on the M/N ratio.

Abstract

This paper investigates the sum-rate gains brought by power allocation strategies in multicell massive multipleinput multiple-output systems, assuming time-division duplex transmission. For both uplink and downlink, we derive tractable expressions for the achievable rate with zero-forcing receivers and precoders respectively. To avoid high complexity joint optimization across the network, we propose a scheduling mechanism for power allocation, where in a single time slot, only cells that do not interfere with each other adjust their transmit powers. Based on this, corresponding transmit power allocation strategies are derived, aimed at maximizing the sum rate per-cell. These schemes are shown to bring considerable gains over equal power allocation for practical antenna configurations (e.g., up to a few hundred). However, with fixed number of users (N), these gains diminish as M turns to infinity, and equal power allocation becomes optimal. A different conclusion is drawn for the case where both M and N grow large together, in which case: (i) improved rates are achieved as M grows with fixed M/N ratio, and (ii) the relative gains over the equal power allocation diminish as M/N grows. Moreover, we also provide applicable values of M/N under an acceptable power allocation gain threshold, which can be used as to determine when the proposed power allocation schemes yield appreciable gains, and when they do not. From the network point of view, the proposed scheduling approach can achieve almost the same performance as the joint power allocation after one scheduling round, with much reduced complexity.