Research On Data Transmission Technologies In Vehicular Ad Hoc Networks

Vehicular Ad Hoc Networks(VANETs) are the important parts of intelligent transport systems and catch lots of attentions from researchers all over the world. A VANET consists of a collection of vehicles communicating with each other or with roadside infrastructures by wireless techniques. In VANETs, all the vehicle information is collected, reorganized and shared, by which way users can get various services and the probabilities of traffic jams and accidents decrease, with the efficiency of travelling increasing.In VANETs, data transmissions among nodes are affected by node mobility, communication environment, and forwarding policies. When the density of nodes is high, channel collisions happen frequently. Besides, the channel quality is affected by complicated city environment, with the result that data links are unstable and data transmissions are usually broken. Additionally, there is not a proper forwarding policy in some special application case. Thus, the problem of data transmission in VANETs is studied and some related protocols are compared to design new protocols. The work in this dissertation is detailed as follows.First, many protocols of data transmission are carefully studied. The dissertation analyzes the related protocols of data transmission, including MAC protocols, routing protocols and some other protocols. All of them are compared in terms of their advantages and disadvantages, which is the fundamental knowledge of the future work.Second, an S-disjunct code-based beacon dissemination protocol is proposed. As contention-based MAC protocols cannot afford enough link resource to all the nodes in networks at high node density, the dissertation proposes an S-disjunct code-based beacon dissemination protocol. It utilizes S-disjunct code to distribute accessing slots to nodes and uses a transmission range control algorithm to tune the signal coverage range to avoid collisions. The simulation results show the delivery rate can achieve as high as 95%, with a low collision rate.Third, a spread utility-based advertisement dissemination protocol and a node utility-based advertisement dissemination protocol are proposed. Because of the low delivery rate of advertisement dissemination, this dissertation provides a spread utility-based advertisement dissemination protocol. In addition, this dissertation improves the performance by considering probabilities of nodes visiting a shop and proposes a node utility-based advertisement dissemination protocol. The simulation results show that the spread utility-based protocol can achieve a higher delivery rate than current protocols and the node utility-based protocol can get a trade-off between the delivery rate and visiting probability and achieve a relatively best performance.At last, two link state-based file scheduling algorithms in sending queue are proposed. In VANETs where multiple types of data coexist, the successful delivery rate of large files is low. Therefore, a scheduling problem of files in sending queues of nodes is proposed and it is proved to be an NP-COMPLETE problem. Then the dissertation proposes a transmission time-based distributed scheduling algorithm and a link duration time-based distributed scheduling algorithm to maximize the successful delivery rate and network throughput. According to the simulation results, they perform better than the current practices.