A Markov Perspective on C-V2X Mode 4

This paper proposes a multi-dimensional Markov model to evaluate the medium access control (MAC) layer performance of 3GPP cellular vehicle to everything (V2X) Mode 4. The Mode 4 specifications enable quality of service guarantees in a decentralized manner, without the connectivity of a cellular base station, and therefore, ideal for V2X messaging in intelligent transportation systems (ITS). To this end, periodic cooperative aware messages (CAMs) and event triggered decentralized environmental notification messages (DENMs) are considered in the paper. The discrete time Markov model consists of a node model, a queue model, and traffic generators for CAM and DENM packets that are dependent and solved in closed form and iteratively. The model is applied to a highway scenario to provide insights on the average delay, the collision probability, and the channel utilization in Mode 4. The results show that Mode 4 has been partially over-specified for ITS applications and able to serve CAMs and DENMs conveniently. However, there exists locally optimal combinations of CAM and DENM intervals that can lead to lower average delay.