Fully Asynchronous Unsourced Random Access over Fading Channels

TL;DR

This paper introduces a fully asynchronous unsourced random access scheme over fading channels, combining pilot sequences and polar codes with a double sliding-window decoder to improve practical applicability with minimal performance loss.

Contribution

It proposes a novel asynchronous access scheme using a combined pilot-polar code structure and a double sliding-window decoding method, advancing the state of unsourced random access.

Findings

Performance close to synchronous benchmarks

Effective joint timing and channel estimation

Robust interference cancellation

Abstract

We examine unsourced random access in a fully asynchronous setup, where active users transmit their data without restriction on the start time over a fading channel. In the proposed scheme, the transmitted signal consists of a pilot sequence and a polar codeword, with the polar codeword distributed across the data part of the packet in an on-off pattern. The receiver uses a double sliding-window decoder, where the inner window employs iterative decoding with joint timing and pilot detection, channel estimation, single-user decoding, and successive interference cancellation to recover the message bits, while the outer window enhances interference cancellation. The numerical results indicate that the proposed scheme exhibits only a slight performance loss compared to the synchronous benchmark while being more applicable in practice.