Pilot-Based Unsourced Random Access with a Massive MIMO Receiver in the Quasi-Static Fading Regime

TL;DR

This paper proposes a simple, energy-efficient pilot-based method for unsourced random access in massive MIMO systems under quasi-static fading, demonstrating its effectiveness through analysis and simulations.

Contribution

It introduces a pilot-based approach with MRC for unsourced random access in massive MIMO, providing closed-form performance approximation and validating scalability via simulations.

Findings

Performance well approximated in closed form

Method scalable with system size

Simulation results confirm effectiveness

Abstract

In this work we treat the unsourced random access problem on a Rayleigh block-fading AWGN channel with multiple receive antennas. Specifically, we consider the slowly fading scenario where the coherence block-length is large compared to the number of active users and the message can be transmitted in one coherence block. Unsourced random access refers to a form of grant-free random access where users are considered to be a-priori indistinguishable and the receiver recovers a list of transmitted messages up to permutation. In this work we show that, when the coherence block length is large enough, a conventional approach based on the transmission of non-orthogonal pilot sequences with subsequent channel estimation and Maximum-Ratio-Combining (MRC) provides a simple energy-efficient solution whose performance can be well approximated in closed form. For the finite block-length simulations we use a randomly sub-sampled DFT matrix as pilot matrix, a low-complexity approximate message passing algorithm for activity detection and a state-of-the-art polar code as single-user error correction code with a successive-cancellation-list decoder. These simulations prove the scalability of the presented approach and the quality of the analysis.