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

摘要

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