Semi-Persistent Scheduling with Single Shot Transmissions for Aperiodic Traffic

The cellular Vehicle-to-Everything (C-V2X) standard from 3GPP specifies semi-persistent scheduling (SPS) for medium access control (MAC). While SPS was originally designed with regular status updates in mind, experimental studies have shown some variability in the generation of V2X messages. As a result, packets might arrive that cannot be transferred via SPS reservations within a predefined delay budget. This triggers new reservations, which has a negative effect on MAC operation and performance. With this in mind, we propose a modification to the SPS protocol that uses single-shot transfers while maintaining the current SPS reservations. We evaluate the performance of the modified SPS scheme using both analytical and numerical simulations for Poisson traffic. Specifically, we derive a closed solution for throughput as a function of the delay budget and the resource reservation interval. We provide a performance comparison with SPS for periodic traffic and quantify the performance loss due to the aperiodic traffic.