Mode Switching Performance in Cellular-V2X

Cellular-V2X aims at supporting road safety and traffic management applications and introduces sidelink (PC5) as a new interface. These applications primarily rely on periodic broadcast of small-sized periodic messages and event-triggered notification messages. A key requirement of the applications is to facilitate uninterrupted exchange of messages among the vehicles irrespective of whether the vehicles are inside a base station coverage or not. In Cellular-V2X standardization, two resource allocation modes have been specified: when a vehicle is located inside the coverage of the cellular network, the corresponding base station manages the transmission resources for the direct message exchange. When a vehicle is outside of cellular coverage, it allocates its resources autonomously. The modes are also referred to as “managed” and “unmanaged” mode, or mode 3 and mode 4, respectively. In situations with imperfect cellular coverage by base stations, a vehicle needs to perform mode switching. The present work aims to understand the different phases of the mode switching procedure and to study the latency involved in each phase for both switching scenarios, mode 3 to 4 and vice versa. Considering a realistic road traffic scenario with a highway tunnel, we assess the impact of mode switch latency on the data transmission for a selected mode switch strategy.