Performance Evaluation of Contention-based Channel Access for mmWave Sidelink Communications

One of the main challenges of future automotive networks is the need to make vehicles aware of their surroundings. Each car will be required to collect data about the environment through dedicated sensors, and share it with its neighbors. Communicating in the millimeter wave spectrum could provide a solution for addressing such requirements. The huge amount of bandwidth available at millimeter wave frequencies, along with an optimized use of the physical resources, could provide massive data rates and low latency capabilities and enable the dissemination of real-time information. In this paper, we focus on platoons of vehicles that share LiDAR pointclouds with their platoon leader, and we use MilliCar, the ns-3 module based on the 3GPP NR V2X specifications, to provide an end-to-end performance evaluation. In particular, we study the trade-offs between using a semi-persistent resource allocation of time slots, with respect to a contention-based approach. By comparing different scheduling alternatives and different clear channel assessment thresholds, we show that coordination among different platoons can mitigate the inter-platoon interference and increase the reliability, whereas a contention-based approach achieves lower transmission delay.