| With the continuous development of automobile industry and the rapid increase of automobile ownership,the following problems,such as road traffic safety,traffic congestion and air pollution,have become increasingly prominent.As an important part of the Internet of things,the VANET is considered as a key technology to build a future intelligent transportation system and improve the level of road traffic safety,which has attracted extensive attention from the academic and industrial sectors of the world.In the research of vehicular networking technology,the fast and reliable transmission of safety emergency information is the most important task,which plays a key role in improving vehicle safety and reducing traffic congestion.In VANETs,vehicle nodes move at high speed,network topology changes rapidly with time,and network continuous connectivity is poor,which bring great challenges to the design of fast and reliable transmission mechanism of emergency information.Multi-hop broadcast protocol is the best choice to solve this problem because of its wide coverage and high transmission efficiency.The network transmission of probability-based multi-hop broadcast protocol is real-time,but the reliability of data transmission is poor due to the uncertain choice of relay nodes.Therefore,how to improve network transmission reliability and reduce network delay as much as possible has become an urgent problem for probability-based multi-hop broadcast protocols.Based on this topic,this paper studies the probability-based multi-hop broadcast protocol for the fast and reliable transmission of emergency messages.Firstly,an optimization method of network transmission reliability based on the success forwarding probability is proposed,so that the multi-hop broadcast protocol based on the success forwarding probability can meet the real-time and reliability requirements of the network for urgent message transmission.In order to further improve the adaptability of multi-hop broadcast protocol to vehicle density,a multi-hop broadcast protocol based on the relative position number probability is proposed,which controls the number of candidate forwarding nodes participating in competitive forwarding by pre-dynamic clustering.In the case of actual traffic flow,the position distribution of vehicles is uncertain.The forwarding probability distribution mechanism based on the relative position can ensure that the candidate forwarding node furthest from the relative source node has sufficient and maximum forwarding probability and improve the reliability and efficiency of network transmission.A probabilistic multi-hop broadcast protocol based on link quality is proposed to solve the problem of instability of vehicle-network communication link.The utility value calculation method of link is based on the relative velocity of inter-vehicle spacing,which reflects the validity of communication link between source node and candidate forwarding node.Combined with link quality,the forwarding probability distribution mechanism based on link utility value is designed,which reduces the failure probability and data redundancy of network transmission.In summary,the main contributions and innovations of this paper include:1.In order to improve the reliability of the probability-based multi-hop broadcast protocol,a multi-hop broadcast protocol based on the success forwarding probability is proposed by adding the influence factor of successful forwarding probability on the basis of the negative exponential forwarding probability function.The optimal success forwarding probability can be obtained in an optimized influence factor of success forwarding probability.In the process of forwarding node selection,the higher successful forwarding probability means less competition times,which reduces network delay of multi-hop broadcast protocol.2.In order to further improve the adaptability of multi-hop broadcast protocol to vehicle density and avoid broadcasting storm and data redundancy in high-density vehicle environment,the pre-dynamic clustering algorithm is adopted to select the appropriate number of candidate forwarding nodes.The clustering algorithm takes the balance of the number of cluster heads and the degree of aggregation within the cluster as the optimization objective.Through the selection of the weighting factors,all cluster member nodes have the highest concentration degree as far as possible under the premise of ensuring the number of cluster heads.3.Based on the pre-dynamic clustering algorithm,a multi-hop broadcast protocol based on the relative position number probability is proposed.By using the neighbor node information number table generated in the stable process of clustering,the vehicle node number based on relative position is taken as the relevant variable of forwarding probability distribution function,and in the case of actual vehicle location distribution,the candidate forwarding node farthest from the source node has the highest forwarding probability.Based on the one-dimensional markov model,the average one-hop delay of network transmission is calculated.Simulation results show that compared with the existing probability-based multi-hop broadcast scheme,the protocol improves the performance in three aspects: the successful forwarding probability,the average number of copies and the average one-hop delay.4.A probabilistic multi-hop broadcast protocol based on link quality is proposed to solve the problem of poor connectivity stability of VANET.Due to the high-speed movement of vehicles,the communication link between vehicle nodes is in the state of frequent connection and interruption.According to the distance between vehicles and the relative velocity,a calculation method of link utility value is proposed,which reflects the effectiveness of the communication link between source node and candidate forwarding node.The forwarding probability function is designed according to the link utility value,and the effect of link quality on the selection of relay node is fully considered,so that the remote candidate forwarding node with the most reliable communication link has the highest forwarding probability,which improves the reliability and efficiency of network transmission. |
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