Unsourced Random Massive Access with Beam-Space Tree Decoding

TL;DR

This paper introduces a beam-space tree decoding scheme for unsourced random access in mmWave massive MIMO systems, leveraging beam division properties to improve decoding performance and reduce complexity.

Contribution

It proposes two novel beam-space tree decoders that exploit beam division in mmWave MIMO for unsourced random access, enhancing accuracy and efficiency.

Findings

The proposed decoders outperform conventional schemes in error probability.

The hard decision decoder reduces search space and complexity.

The soft decision decoder improves packet recovery through list decoding.

Abstract

The core requirement of massive Machine-Type Communication (mMTC) is to support reliable and fast access for an enormous number of machine-type devices (MTDs). In many practical applications, the base station (BS) only concerns the list of received messages instead of the source information, introducing the emerging concept of unsourced random access (URA). Although some massive multiple-input multiple-output (MIMO) URA schemes have been proposed recently, the unique propagation properties of millimeter-wave (mmWave) massive MIMO systems are not fully exploited in conventional URA schemes. In grant-free random access, the BS cannot perform receive beamforming independently as the identities of active users are unknown to the BS. Therefore, only the intrinsic beam division property can be exploited to improve the decoding performance. In this paper, a URA scheme based on beam-space tree decoding is proposed for mmWave massive MIMO system. Specifically, two beam-space tree decoders are designed based on hard decision and soft decision, respectively, to utilize the beam division property. They both leverage the beam division property to assist in discriminating the sub-blocks transmitted from different users. Besides, the first decoder can reduce the searching space, enjoying a low complexity. The second decoder exploits the advantage of list decoding to recover the miss-detected packets. Simulation results verify the superiority of the proposed URA schemes compared to the conventional URA schemes in terms of error probability.