Improved bounds for the many-user MAC

TL;DR

This paper introduces new, computationally feasible bounds for the energy efficiency of many-user MACs in 5G scenarios, surpassing previous bounds at higher payloads using spatially coupled codes and AMP algorithms.

Contribution

It provides novel achievability bounds for many-user MACs that are computationally feasible up to 100 bits, improving upon prior bounds at higher payloads.

Findings

Bounds are computable up to 100 bits payload.

New bounds outperform previous ones at higher payloads.

Applicable to AWGN and Rayleigh fading MACs.

Abstract

Many-user MAC is an important model for understanding energy efficiency of massive random access in 5G and beyond. Introduced in Polyanskiy'2017 for the AWGN channel, subsequent works have provided improved bounds on the asymptotic minimum energy-per-bit required to achieve a target per-user error at a given user density and payload, going beyond the AWGN setting. The best known rigorous bounds use spatially coupled codes along with the optimal AMP algorithm. But these bounds are infeasible to compute beyond a few (around 10) bits of payload. In this paper, we provide new achievability bounds for the many-user AWGN and quasi-static Rayleigh fading MACs using the spatially coupled codebook design along with a scalar AMP algorithm. The obtained bounds are computable even up to 100 bits and outperform the previous ones at this payload.