Performance Characteristics of Sensing-based SPS of PC5-based C-V2X Mode 4 in Crash Warning Application under Congestion

This paper presents the performance characteristics (notably, the adverse effects on communication quality) of Sensing-based Semi-Persistent Scheduling (Sensing-based SPS) of PC5-based Cellular-V2X mode 4 in crash warning application under congested environments. Sensing-based SPS is a new Cellular-V2X standard. This scheduling protocol has two interference estimation mechanisms to select a transmission slot considered as low interference from a history of slot usages. As the mode 4's channel becomes severely congested, frequent collision errors become to cause missing slot information and, the estimated interference becomes to differ from the actual one. Hence, the two mechanisms become to select a slot with higher interference. Our simulation results revealed that Sensing-based SPS was of 9% lower communication quality than that of a method with no estimation mechanisms in a congested situation. Our behavior analysis and computer simulations pointed out new disadvantages of Sensing-based SPS and presented a necessity to improve the algorithm of Sensing-based SPS.