Optimization of C-V2X Mode 4 Resource Scheduling Protocol Based on CAM Generation Frequency

In the cellular Internet of Vehicles (C-V2X) system, the most important message type in vehicle-vehicle communication (V2V) is cooperative aware message (CAM). When transmitting CAM messages, the existing S-SPS resource scheduling protocols use a fixed range of resource re-selection counters (RC) to take the value, which leads to uneven spectrum resource scheduling, resulting in resource waste. Therefore, this paper proposes an improved S-SPS resource scheduling protocol for CAM data streams, which optimizes the value of RC according to the generation frequency of CAM data streams and vehicle density, so as to improve the utilization rate of system resources and reduce the collision probability. In order to study the performance of the improved protocol, this paper establishes a discrete-time Markov chain model to obtain the system average delay, collision probability, channel utilization and other performance indicators. Numerical simulation results show that compared with the classical protocol, the improved protocol reduces the average delay by 31.59%, the average collision probability by 15.03%, and the channel utilization rate by 15.74% in single-stream transmission. Therefore, the effectiveness of the improved protocol is verified.