An Multi-hop Broadcast Protocol Of Emergency Safety Message In Vehicular Network

With the increasing of the number of motor vehicles, more and more traffic accidents threaten the development of social economy and life safety. How to reduce the number of traffic accidents is an urgent problem in vehicular application. Vehicular safety application requires high real-time and high reliability. Multi-hop broadcast communication protocol is an efficient mean to achieve high real-time and high reliability.Scholars have done lots of related work at home and abroad, but there are the following problems. Previous intersectional broadcast protocols have not taken traffic lights and traffic phase information into consideration. This will increase the hop count and broadcasting delay from one intersection to next one. Additionally they have not initialized a broadcast in each branch road segment. This will cut down the reliability of transmitting safety message. The existing broadcast protocols based on MAC layer ignore the influence of the transmission rate and transmission power. This may result in that the relaying node is not competent.In order to solve the problems, we propose the directional broadcast protocols in straight roads and intersectional broadcast protocols based on traffic phase. First, Adding the transmission power and transmission rate into selection criteria will result in the improving of forwarding ability of relaying nodes. Secondly, we set up the traffic phase matrix based on the traffic phase information, which can be used to get the condition of valid area. Only the relaying nodes in valid areas can participate in the competition for relaying nodes. This way guarantees that the emergency message is delivered at less hop number and in less time. Thirdly, the three roads successively select a node for replying a BCTS frame. This way improves the transmitting reliability of safety message. Lastly, we get the simulation result by simulating the two multi-hop broadcast protocols at the platform of VISSIM5.30and NS-3. Compared with the conventional protocols, the number of collision, the average time of selecting relaying-nodes and the end-to-end delay of our protocol decrease by2.42%,2.40%and5.63%respectively. The branching reliability has increased. When the density reaches20veh/km, the reception success rate stays the same. The reception success rate satisfies the safety application’s requirement.