Model, analysis, and improvements for inter-vehicle communication using one-hop periodic broadcasting based on the 802.11p protocol

Many future vehicle safety applications will rely on one-hop Periodic Broadcast Communication (oPBC). The key technology for supporting this communication system is the new standard IEEE 802.11p which employs the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) mechanism to resolve channel access competition. In this work, we first aim at understanding the behavior of such oPBC under varying load conditions by considering three important quality aspects of vehicle safety applications: reliability, fairness, and delay. Second, we investigate possible improvements of these quality aspects. We start with a clear mathematical model which gives the foundation for making an accurate simulation model as well as for defining new appropriate metrics to judge the aforementioned quality aspects. We evaluate oPBC with a strictly periodic broadcasting scheme, i.e., each vehicle broadcasts messages in a strictly periodic manner. The evaluation reveals that the hidden terminal, or Hidden Node (HN), problem is the main cause of various quality degradations especially when the network is unsaturated. To be more specific, the HN problem reduces the message reception ratio (i.e., reliability degradation) and causes unfair message reception ratios for vehicles (i.e., fairness degradation). Moreover, it causes long lasting consecutive message losses (i.e., delay degradation) between vehicles while they are encountering each other, i.e., entering their Communication Ranges (CRs). In some serious cases, a certain vehicle could not successfully deliver any of its messages to a particularly destination vehicle throughout an entire encounter interval of these two vehicles. We propose three simple but effective broadcasting schemes to alleviate the impact of the HN problem. Though these solutions do not affect the message reception ratio (i.e., reliability) of the entire network, they do improve the fairness and delay aspects. These solutions are fully compatible with the IEEE 802.11p standard, i.e., they are application-level solutions and can be easily introduced in practice.