Pilot-Based Unsourced Random Access With a Massive MIMO Receiver, Interference Cancellation, and Power Control

We consider the unsourced random access problem on a Rayleigh block-fading AWGN channel with multiple receive antennas. Specifically, we treat slow fading scenario where coherence blocklength is large compared to number of active users and message can be transmitted in single block. Unsourced refers form grant-free are constrained use same codebook therefore priori indistinguishable. The receiver must recover list messages up permutations. In this paper, propose an approach based splitting user into two parts. First, small block bits selects relatively short codeword from common “pilot” codebook. Then remaining encoded by standard code for Gaussian channel. makes measurement vector approximate passing (MMV-AMP) algorithm estimate channels part, then uses estimated perform coherent maximum ratio combining (MRC) decode second part. provide accurate closed-form approximated analysis proposed scheme. Furthermore, analyze MRC decoding when successive interference cancellation performed over groups users, striking attractive tradeoff between complexity performance. Finally, investigate impact power control policies, taking account unique nature massive access. As byproduct, also present extension MMV-AMP which allows pathloss coefficients treated as deterministic unknowns performing likelihood estimation each step algorithm.