  5G NR Sidelink (SL) has demonstrated the promising capability for
infrastructure-less cellular coverage. Understanding the fundamentals of the NR
SL channel access mechanism, Semi-Persistent Scheduling (SPS), which is
specified by the 3rd Generation Partnership Project (3GPP), is a necessity to
enhance the NR SL Packet Reception Ratio (PRR). However, most existing works
fail to account for the new SPS features introduced in NR SL, which might be
out-of-date for comprehensively describing the NR SL PRR. The existing models
ignore the relationships between SPS parameters and therefore do not provide
sufficient insights into the PRR of SPS. This work proposes a novel SPS PRR
model incorporating MAC collisions based on new features in NR SL. We extend
our model by loosening several simplifying assumptions made in our initial
modeling. The extended models illustrate how the PRR is affected by various SPS
parameters. The computed results are validated via simulations using the
network simulator (ns-3), which provides important guidelines for future NR SL
enhancement work.
