Unsourced Random Access with Threshold$-$Based Feedback

In this paper we focus on a feedback mechanism for unsourced random access (URA) communications. We propose an algorithm to construct feedback packets broadcasted to the users by the base station (BS) as well as the feedback packet format that allows the users to estimate their channels and infer positive or negative feedback based on the presented thresholding algorithm. We demonstrate that the proposed feedback imposes a much smaller complexity burden on the users compared to the feedback that positively acknowledges all successful or negatively acknowledges all undecoded users. We also show that the proposed feedback technique can lead to a substantial reduction in the packet error rates and signal-to-noise ratios (SNR)s required to support various numbers of active users in the system.