Adaptive Pilot Clustering in Heterogeneous Massive MIMO Networks

TL;DR

This paper introduces a distributed coalition formation approach using game theory to optimize pilot reuse in massive MIMO networks, significantly improving spectral efficiency in asymmetric deployments.

Contribution

It proposes a novel low-complexity, distributed coalition formation algorithm for adaptive pilot clustering based on individual stability in heterogeneous massive MIMO networks.

Findings

Fast convergence of the coalition formation algorithm

Substantial spectral efficiency gains over baseline schemes

Effective control of message exchange overhead

Abstract

We consider the uplink of a cellular massive MIMO network. Acquiring channel state information at the base stations (BSs) requires uplink pilot signaling. Since the number of orthogonal pilot sequences is limited by the channel coherence, pilot reuse across cells is necessary to achieve high spectral efficiency. However, finding efficient pilot reuse patterns is non-trivial especially in practical asymmetric BS deployments. We approach this problem using coalitional game theory. Each BS has a few unique pilots and can form coalitions with other BSs to gain access to more pilots. The BSs in a coalition thus benefit from serving more users in their cells, at the expense of higher pilot contamination and interference. Given that a cell's average spectral efficiency depends on the overall pilot reuse pattern, the suitable coalitional game model is in partition form. We develop a low-complexity distributed coalition formation based on individual stability. By incorporating a base station intercommunication budget constraint, we are able to control the overhead in message exchange between the base stations and ensure the algorithm's convergence to a solution of the game called individually stable coalition structure. Simulation results reveal fast algorithmic convergence and substantial performance gains over the baseline schemes with no pilot reuse, full pilot reuse, or random pilot reuse pattern.