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

Abstract

In this work we treat the unsourced random access problem on a Rayleigh\nblock-fading AWGN channel with multiple receive antennas. Specifically, we\nconsider the slowly fading scenario where the coherence block-length is large\ncompared to the number of active users and the message can be transmitted in\none coherence block. Unsourced random access refers to a form of grant-free\nrandom access where users are considered to be a-priori indistinguishable and\nthe receiver recovers a list of transmitted messages up to permutation. In this\nwork we show that, when the coherence block length is large enough, a\nconventional approach based on the transmission of non-orthogonal pilot\nsequences with subsequent channel estimation and Maximum-Ratio-Combining (MRC)\nprovides a simple energy-efficient solution whose performance can be well\napproximated in closed form. For the finite block-length simulations we use a\nrandomly sub-sampled DFT matrix as pilot matrix, a low-complexity approximate\nmessage passing algorithm for activity detection and a state-of-the-art polar\ncode as single-user error correction code with a successive-cancellation-list\ndecoder. These simulations prove the scalability of the presented approach and\nthe quality of the analysis.\n