Performance Enhancements of C-V2X Mode 4 with Virtual Cell and Resource Usage Bitmap

Successful exchange of cooperative awareness messages(CAMs) among vehicles is essential in improving transportation safety for intelligent transportation systems (ITS). This paper presents performance enhancements of C-V2X CAM delivery with i) overlapped virtual cells with orthogonal sub-channel allocations, ii) extended MIB (master information block) with resource usage bitmap, and iii) smart roaming across overlapped virtual cells. In the proposed scheme, virtual cells are configured with 3 ~ 4 orthogonal sub-channels for up to 400 vehicles. The virtual cell manager (VCM) continuously monitors the usages of resources (sub-channels and sub-frames) for CAM broadcasting by vehicles, configures an extended MIB with resource usage bitmap, and periodically broadcasts the extended MIB with a bitmap. By checking the extended MIB with the resource usage bitmap, each vehicle can easily avoid collisions by selecting unused resource. The smart roaming among overlapped virtual cells guarantees seamless CAM deliveries even in the boundaries of virtual cells. The performance of the proposed scheme has been analyzed with NS-3 simulation, and measured results of CAM delivery rates are more than 99 percent in highly congested metropolitan areas.