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Successful exchanges of cooperative awareness messages (CAMs) among neighboring vehicles are essential in the intelligent transportation system (ITS) to ensure safe autonomous driving. Especially in cellular vehicle-to-everything (C-V2X) mode-4, where the resource allocation process in the vehicles is autonomous without centralized control, efficient resource selection to minimize collisions is necessary to enhance the CAM delivery ratio (CDR). In this paper, we propose an enhanced operation of LTE C-V2X mode-4 by using virtual cells (VCs) with orthogonal resource allocation, extended master information block (EMIB) with a resource usage bitmap (RuBMP), and smart roaming in the virtual cell boundary. We propose a virtual cell manager (VCM) that monitors resource usage via CAM broadcasts from vehicles, configures the RuBMP to show the overall resource block usage, includes it in EMIB messages, and broadcasts the EMIB every 10ms. The periodic broadcast of the EMIB with the RuBMP enables vehicles to avoid selection of resources currently used by other vehicles, and minimizes collisions during CAM broadcasts. Smart roaming enables seamless, successful CAM broadcasts even at the boundary of virtual cells where resources (subchannels and subframes) must be re-selected based on the state of the next virtual cell. The analytical model of the proposed scheme (including successful CDR) is provided, and the performances are analyzed with NS-3 simulations for overlapped virtual cells in metropolitan areas with high densities of vehicles. The proposed scheme shows a 99.2% (or more) successful CAM delivery ratio for overlapped cells with up to 400 vehicles per virtual cell using four LTE sidelink subchannels.

Enhanced C-V2X Mode-4 with Virtual Cell, Resource Usage Bitmap, and Smart Roaming