Research On Efficient Routing Protocol In Vehicular Ad Hoc Networks

As an important part of the Intelligent Transportation Systems(ITS),vehicular ad hoc networks(VANETs)have received extensive attention from academics and in-dustry due to its broad prospects in increasing road traffic safety and improving traffic efficiency.In the research of VANETs,efficient routing protocols play an important role in realizing the communication and interconnection between nodes in the network.However,the rapid change of network topology,the limitation of the movement tra-jectory of the vehicle nodes and the instability of the wireless link in VANETs bring great challenges to the analysis and design of routing protocols.How to deal with these challenges and design efficient routing protocols are urgent problems to be solved in the current research of VANETs.To solve this problem,the design of efficient broadcast,geocast and unicast routing protocols in VANETs is deeply studied in this thesis to provide core support for safety applications such as traffic safety,danger warning,etc.,and non-safety applications like information collection,advertising push,etc.The main contents of this thesis are as follows:1.In the broadcast protocols proposed for VANETs,only one vehicle is allowed to send information at a certain time in the broadcast direction,otherwise conflicts will happen.To solve the problem,a time synchronization scheme for concur-rent transmission is proposed in this thesis.Based on the time synchronization scheme,a broadcast protocol based on concurrent transmission is presented.In the protocol,multiple vehicles is allowed to forward the same information at the same time in the broadccast direction.Even if some forwarders fail to forward information,other forwarders that receive information can still forward informa-tion,reducing the waiting time in the broadcast delay and increasing the reliability of the broadcast.The experimental results show that the proposed protocol can effectively reduce the delay and increase the reliability.2.In the traditional abiding geocast protocols,the fixed broadcast cycle in the pe-riodic broadcast strategy cannot adapt to the change of the network topology,which may induce excessive redundant transmission.To solve the problem,an abiding geocast protocol based on carrier sets is proposed in this thesis.Carrier sets consist of information carrier nodes set-up and maintained based on Stability Estimation Index in each street Uncovered vehicles passing by destination area can get abiding messages through one-hop broadcast from vehicles in carrier sets when they need the messages,which not only avoids significant overhead pro-duced by multi-hop broadcast but also enhances the receiving probability.The experimental results verify the efficiency and reliability of the proposed protocol.3.In millimeter wave(mmWave)vehicular communication,beam scanning is usu-ally used for beam alignment.However,beam scanning takes a long time,which makes it unsuitable for the mmWave vehicular communications with high-speed nodes.Moreover,the existing research about mmWave vehicular communication is usually based on one-hop transmission.However,due to the limited transmis-sion range of millimeter waves,in many cases,multi-hop transmission is required to transmit information from the source node to the destination node.To solve these problems,an opportunistic routing protocol based on position information for beam alignment in mmWave vehicular communication is proposed in this the-sis.Beam alignment is performed based on the location information of neighbor nodes instead of beam scanning,which avoids the increase of network load and delay caused by beam scanning.Moreover,when the opportunity routing is used,even if one candidate forwarder fails to forward the packet,the other candidate forwarders that receive the packet can still forward,decreasing the network load and unicast delay caused by a large number of retransmissions.The experimen-tal results show that the proposed protocol can effectively reduce the end-to-end delay and improve the packet delivery ratio and network yield.