The Research On VANETs-based Transmission Mechanisms Of Safety-related Information On Highway

Recently, VANETs (Vehicular Ad hoc NETworks) have shown great potentialand application value in safety related scenarios on the highway. VANETs havebecome important parts of ITS (Intelligent Transportation System) and the system ofIoT (Internet of Things), and got widely attentions by the academic and industrialcircles. On the highway, the communications of V2V (Vehicle-to-vehicle) and V2I(Vehicle-to-infrastructure) are two important ways to transmit safety-relatedinformation. The RSU (Road Side Unit) is one of the highway infrastructures. It cancollect traffic and environmental information through V2V and V2I communications.The information gathered by the RSU will be centrally prcessed and reported to thedrivers. For one thing, the information can be used for real-time monitoring ofvehicle’s moving state. If the RSU tests the unusual activities in the traffic throughdata mining, it can provide warning services to the drivers and prevent large scaletraffic accidents. For another, if there has already been an accident in a fixed place,the RSU can put forward the corresponding countermeasures as soon as possible tosave valuable time for the accident rescue and normal traffic recovery. Therefore, theresearch on the information transmission mechanism in highway safety-relatedscenario has great scientific values and practical values. This dissertation focuses onthe research on important technologies of VANETs in highway situations. It willdiscuss the efficiency and performance of the information transmission betweenvehicles and the RSU, which includes the following contributions:First, based on the fact that the speed of each vehicle on the highway followsnormal distribution, this dissertation uses mathematical models and analysis toobtain the probabilities of stable communication between two consecutive CHs(cluster heads) and between CHs in one-dimensional and multi-hop CH chain. Theanalytical results will become theoretical basis of our protocols in followingchapters.Second, we propose an RSU-assisted CH selection protocol in this dissertation using analytical results in Chapter2. In that protocol, the RSU is the initiator andoperator of the CH selection process. It will choose the vehicle with the speedclosest to the average speed on the highway as a CH within CH selection range oneby one to form a one-dimensional and multi-hop CH chain to collect traffic andenvironmental information. The simulation results show that our protocol can makethe RSU’s reception rate of the probing packet has at most19.00%improvement,and make the RSU’s information collection range has900meters extension.Third, in order to improve the stability of one-dimensional and multi-hop CHchain and enlarge the RSU’s information collection range, we propose a backupprotocol in this dissertation. The CH who detects the interruption between itself andits previous CH will launch the backup process, and choose the vehicle with thespeed closest to the average speed on the highway as a new backup CH withinreasonable range. In our simulation, the protocol can achieve2800meters extensionof the RSU’s information collection range with proper configuration. The error rateis low accordingly.Forth, we propose a self-adaptive retransmission protocol to improve the RSU’sreception rate of the probing packets. The protocol can automatically change theretransmission probability of the probing packet in each CH according to thevariation of wireless conditions. When the backup waiting time Tbackupis2s, thesimulation results show that our protocol can improve the RSU’s reception rate ofthe probing packet with7.11%on average and22.53%at most.Fifth, we analyze important information to be obtained by the RSU on thehighway and sort the information into four kinds according to its nature and way ofprocessing. Then we propose a priority based transmission protocol and aprobability bandwidth reserve method based on the information types and theirimportance to reduce the transmission delay of urgent probing packets and thebandwidth consumption. The simulation results show that, the priority basedtransmission protocol can effectively lower the transmission delay of the urgentprobing packet. When an accident happens at4000m in front of the RSU, theaccident information can be obtained within0.18s on average. At the same time, wealso propose a probability bandwidth reserve method to reduce the total number of the urgent probing packet without data aggregation. Under the condition ofmaintaining the RSU’s reception rate, the simulation results show that the totalnumber of the redundant urgent probing packet can be lower at72.73%corresponding to the result not using the method.