On Reusing Pilots Among Interfering Cells in Massive MIMO

TL;DR

This paper proposes hierarchical pilot reuse schemes in massive MIMO systems to mitigate pilot contamination, demonstrating that less aggressive reuse improves throughput when channel coherence time is sufficiently large.

Contribution

It introduces novel hierarchical pilot reuse methods with a closed-form optimal pilot assignment for maximizing sum-rate in massive MIMO systems.

Findings

Hierarchical pilot reuse effectively reduces pilot contamination.

Less aggressive pilot reuse improves system throughput.

Optimal pilot assignment maximizes sum-rate under certain conditions.

Abstract

Pilot contamination, caused by the reuse of pilots among interfering cells, remains as a significant obstacle that limits the performance of massive multi-input multi-output antenna systems. To handle this problem, less aggressive reuse of pilots involving allocation of additional pilots for interfering users is closely examined in this paper. Hierarchical pilot reuse methods are proposed, which effectively mitigate pilot contamination and increase the net throughput of the system. Among the suggested hierarchical pilot reuse schemes, the optimal way of assigning pilots to different users is obtained in a closed-form solution which maximizes the net sum-rate in a given coherence time. Simulation results confirm that when the ratio of the channel coherence time to the number of users in each cell is sufficiently large, less aggressive reuse of pilots yields significant performance advantage relative to the case where all cells reuse the same pilot set.