Performance Enhancement of C-V2X Mode 4 with Balanced Resource Allocation

Cellular vehicles-to-everything (C-V2X) is an essential technology to enhance road safety, traffic management and smart mobility. C-V2X Mode 4 uses sensing based semi-persistent scheduling (SB-SPS) to mitigate packet collisions, that consists of several mechanisms (i.e., random selection of resources, probabilistic reselection, and monitoring resource utilization pattern). The packet collision probability, however, is still non-negligible, and the CAM (cooperative awareness message) delivery ratio (CDR) is far from target requirements for high reliability and low latency applications. Especially, when the number of vehicles increases beyond 300, the packet collision probability increases in the environment of congested metropolitan area. In this paper, we analyze the performance of C-V2X Mode 4 in congested metropolitan areas, and propose a balanced resource allocation scheme that is providing a remarkable enhanced performance, considering the half-duplex communication mechanism in C-V2X Mode 4. The proposed method allocates resources in distributed manner with balanced usage of subframes, instead of random selection of resources in resource map, to mitigate CAM packet losses by half-duplex communications. From the performance analysis with simulation, we confirmed that the proposed scheme provided 97% of CDR for 500 vehicles, while the existing scheme provided only 87% for the same condition.