Mode Switching Strategies in Cellular-V2X

Cellular-V2X facilitates a direct communication among vehicles and with the roadside traffic infrastructure. It addresses use cases for safety and traffic efficiency, where data are disseminated in a vehicle's vicinity with short-latency constraints. Cellular-V2X provides two modes: when the vehicle is located in the coverage of the cellular network, the corresponding base station manages the transmission resources for the direct message exchange. In the out-of-coverage mode, the vehicle does not require cellular coverage and allocates its resources autonomously. Though the in-coverage mode is the preferred mode of operation, it is not always available. Due to the vehicle mobility and other reasons, a vehicle may need to dynamically switch between the two modes. Mode switching affects the communication quality since the vehicle cannot send and receive messages during the execution of the switching procedure. We propose three decision strategies for mode switching: forced, signal strength-based and load-based mode switching. We describe the mode switching decision by a cost function and derive individual functions for each of the proposed strategies. Decomposing the overall mode switching procedure into subsequent phases, we understand the different types of latencies incurred at every stage of mode switching.