Age of Information for V2X: Irregular Repetition Slotted ALOHA and Semi-Persistent Scheduling

Abstract

In the context of Vehicle-to-Everything (V2X) networks, semantic metrics such as the Age of Information (AoI) have emerged as alternatives to conventional performance metrics. This has prompted a re-evaluation of well-established channel access protocols such as Semi-Persistent Scheduling (SPS) and Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) from the perspective of these newly-introduced metrics. In parallel to this trend, new protocols such as Irregular Repetition Slotted ALOHA (IRSA) are proposed for application in V2X communication. In this paper, we investigate the AoI performance of IRSA in the context of V2X communication, by using SPS as a benchmark. The provided comparison indicates that, while SPS can achieve higher throughput than IRSA, IRSA results in a notably lower mean AoI and reduced age violation probability in certain operation regimes. These observations are of particular relevance to safety-related applications for autonomous driving, where the channel access protocols are required to support the broadcast of Cooperative Awareness Messages (CAMs) carrying time-sensitive status updates.