A Random Access Protocol for Pilot Allocation in Crowded Massive MIMO Systems

TL;DR

This paper introduces the SUCRe protocol, a novel random access method for Massive MIMO systems that efficiently resolves pilot collisions among many UEs, enabling scalable and reliable network access in crowded environments.

Contribution

The paper presents the SUCRe protocol, leveraging Massive MIMO's properties to enable distributed collision detection and resolution, improving access efficiency in dense networks.

Findings

SUCRe resolves most pilot collisions in crowded scenarios.

The protocol maintains high network admission rates.

It enables efficient access in overloaded networks.

Abstract

The Massive MIMO (multiple-input multiple-output) technology has great potential to manage the rapid growth of wireless data traffic. Massive MIMO achieves tremendous spectral efficiency by spatial multiplexing of many tens of user equipments (UEs). These gains are only achieved in practice if many more UEs can connect efficiently to the network than today. As the number of UEs increases, while each UE intermittently accesses the network, the random access functionality becomes essential to share the limited number of pilots among the UEs. In this paper, we revisit the random access problem in the Massive MIMO context and develop a reengineered protocol, termed strongest-user collision resolution (SUCRe). An accessing UE asks for a dedicated pilot by sending an uncoordinated random access pilot, with a risk that other UEs send the same pilot. The favorable propagation of Massive MIMO channels is utilized to enable distributed collision detection at each UE, thereby determining the strength of the contenders' signals and deciding to repeat the pilot if the UE judges that its signal at the receiver is the strongest. The SUCRe protocol resolves the vast majority of all pilot collisions in crowded urban scenarios and continues to admit UEs efficiently in overloaded networks.