Evolution of the 5G New Radio Two-Step Random Access towards 6G Unsourced MAC

TL;DR

This paper analyzes the evolution of 5G New Radio's two-step random access protocol towards 6G, using information-theoretic benchmarks to identify potential improvements for supporting massive IoT deployments.

Contribution

It maps 5G's 2SRA protocol to the unsourced MAC framework, proposing modifications that significantly enhance energy and spectral efficiency for large-scale IoT support.

Findings

Existing 2SRA may not be energy-efficient for large user populations.

Proposed protocol modifications achieve substantial gains in efficiency.

Benchmarking against information-theoretic bounds highlights potential improvements.

Abstract

This report summarizes some considerations on possible evolutions of grant-free random access in the next generation of the 3GPP wireless cellular standard. The analysis is carried out by mapping the problem to the recently-introduced unsourced multiple access channel (UMAC) setup. By doing so, the performance of existing solutions can be benchmarked with information-theoretic bounds, assessing the potential gains that can be achieved over legacy 3GPP schemes. The study focuses on the two-step random access (2SRA) protocol introduced by Release 16 of the 5G New Radio standard, investigating its applicability to support large MTC / IoT terminal populations in a grant-free fashion. The analysis shows that the existing 2SRA scheme may not succeed in providing energy-efficient support to large user populations. Modifications to the protocol are proposed that enable remarkable gains in both energy and spectral efficiency while retaining a strong resemblance to the legacy protocol.