Uplink Sounding Reference Signal Coordination to Combat Pilot Contamination in 5G Massive MIMO

TL;DR

This paper evaluates uplink sounding reference signal strategies in 5G massive MIMO, introducing a novel neighbor-aware fractional reuse scheme that improves cell throughput by balancing resource sharing and contamination mitigation.

Contribution

It proposes a new neighbor-aware fractional reuse scheme for UL SRS in 5G massive MIMO, enhancing pilot contamination management and network throughput.

Findings

FR-NA outperforms fixed reuse and existing schemes in simulations.

The scheme effectively balances resource sharing and interference protection.

Cell throughput is significantly improved with FR-NA.

Abstract

To guarantee the success of massive multiple-input multiple-output (MIMO), one of the main challenges to solve is the efficient management of pilot contamination. Allocation of fully orthogonal pilot sequences across the network would provide a solution to the problem, but the associated overhead would make this approach infeasible in practical systems. Ongoing fifth-generation (5G) standardisation activities are debating the amount of resources to be dedicated to the transmission of pilot sequences, focussing on uplink sounding reference signals (UL SRSs) design. In this paper, we extensively evaluate the performance of various UL SRS allocation strategies in practical deployments, shedding light on their strengths and weaknesses. Furthermore, we introduce a novel UL SRS fractional reuse (FR) scheme, denoted neighbour-aware FR (FR-NA). The proposed FR-NA generalizes the fixed reuse paradigm, and entails a tradeoff between i) aggressively sharing some UL SRS resources, and ii) protecting other UL SRS resources with the aim of relieving neighbouring BSs from pilot contamination. Said features result in a cell throughput improvement over both fixed reuse and state-of-the-art FR based on a cell-centric perspective.