Re-Evaluation Strategies for 5G NR V2X Communications.

5G NR V2X introduces novel MAC features to support advanced V2X services for connected and automated driving. One of these features is the re-evaluation mechanism designed to detect and avoid packet collisions. The re-evaluation mechanism checks before every transmission if the selected resources are still available. If another vehicle has selected the same resources, the re-evaluation mechanism triggers a reselection of resources. The 3GPP standard defines different strategies for vehicles to decide when to perform a re-evaluation check, and how many times a re-evaluation check should be executed before the transmission of a packet. This study evaluates for the first time the impact of two standard strategies on the operation and performance of NR V2X mode 2. The evaluation demonstrates that the two strategies offer a balance between transmission latency and computational cost. We then propose an alternative re-evaluation check strategy that can simultaneously reduce the transmission latency and computational cost without actually degrading the reliability of NR V2X mode 2 transmissions.