  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.
