On the Advantages of Asynchrony in the Unsourced MAC
Abstract
In this work we demonstrate how a lack of synchronization can in fact be advantageous in the problem of random access. Specifically, we consider a multiple-access problem over a frame-asynchronous 2-user binary-input adder channel in the unsourced setup (2-UBAC). Previous work has shown that under perfect synchronization the per-user rates achievable with linear codes over the 2-UBAC are limited by 0.5 bit per channel use (compared to the capacity of 0.75). In this paper, we first demonstrate that arbitrary small (even single-bit) shift between the user's frames enables (random) linear codes to attain full capacity of 0.75 bit/user. Furthermore, we derive density evolution equations for irregular LDPC codes, and prove (via concentration arguments) that they correctly track the asymptotic bit-error rate of a BP decoder. Optimizing the degree distributions we construct LDPC codes achieving per-user rates of 0.73 bit per channel use.
Keywords
Cite
@article{arxiv.2305.06985,
title = {On the Advantages of Asynchrony in the Unsourced MAC},
author = {Alexander Fengler and Alejandro Lancho and Krishna Narayanan and Yury Polyanskiy},
journal= {arXiv preprint arXiv:2305.06985},
year = {2023}
}
Comments
Accepted for presentation at IEEE ISIT 2023