Efficient urban broadcast protocol for V2V communications with Relay Control

In Vehicle-to-Vehicle (V2V) communications, broadcast is expected to disseminate information to other vehicles efficiently. However, due to shadowing of buildings, especially in urban areas, the V2V communications at an intersection is unreliable. Thus it is difficult to disseminate information to all directions at an intersection. Moreover, most of existing protocols which consider intersections in urban area need to use digital map, which is costly and hard to update frequently. Also, they depend on periodic beacons to judge whether or not nodes rebroadcast. They require a lot of control overheads, especially in urban areas, which prejudice efficiency and reliability of message delivery. In this paper, an efficient urban broadcast scheme is proposed for V2V communications in urban environment, which does not rely on the digital map and periodic beacon exchanges. Without digital map, we identify intersection by the difference of a theoretical RSSI (Received Signal Strength Indicator) value and a measured RSSI value. We decide RAD (Random Assessment Delay) by difference of RSSIs as well as a distance between a sender and a receiver to achieve low end-to-end delay. Also we use angle between vectors and vertical distance to get high reception ratio. Both of them are significant for safety critical services of ITS. Simulation results show that proposal scheme achieves higher reception ratio and shorter delivery time than existing broadcast protocols in different loads and vehicle densities.