  Grant-free access schemes are candidates to support future massive multiple
access applications owing to their capability to reduce control signaling and
latency. As a promising class of grant-free schemes, coded random access
schemes can achieve high reliabilities also with uncoordinated transmissions
and therefore in presence packet collisions. In this paper, an analysis tool
for coded random access, based on density evolution, is proposed and exploited
for system design and optimization. In sharp contrast with the existing
literature, where such tools have been developed under simplified channel
assumptions, the proposed tool captures not only MAC layer features, but also
the physical wireless fading channel and a realistic physical layer signal
processing based on multiple antennas and randomly-chosen orthogonal pilots.
Theoretical results are validated by comparison with symbol-level Monte Carlo
simulations.
