Broadcast MAC protocol using relative distance for periodic safety messages in vehicular networks

Abstract

Vehicles broadcast basic safety message (BSM) every 100 ms as an essential service in vehicular networks. However, it is difficult to meet the reliability requirement without efficient broadcast protocols. Some of the state-of-the-art protocols are based on TDMA which provides a constant transmission slot to each vehicle in every TDMA frame. It can guarantee collision-free transmissions when every vehicle has a unique transmission slot. In this paper, we propose a TDMA-based sequential broadcast MAC, where each vehicle chooses its transmission slot by calculating the relative distance among vehicles based on receiving power, which roughly makes the order of their transmission slot match with the order among vehicles on the road. The proposed scheme implements a neighbor notification to handle the collision resolution of broadcast messages under non-ideal channel condition. The simulation results show that our protocol can achieve a packet delivery ratio of 97% while decreasing merging collisions.