Reserch Of Data Transmission Based On GNSS And VANETs

Vehicular Ad Hoc Networks(VANETs), as a special application of the mobile ad hoc network(MANET), has the characteristics of MANET, such as limited transmission bandwidth, short transmission distance, self-organization and self-management. Also it has some special properties different from traditional ad hoc networks, like fast node movement, topology changes frequently, intermittent connectivity and so on. These characteristics make end-to-end data transmission very difficult. However, the nodes’ movement is limited by road topology and has strong dependence on geographical position. Besides, the navigation and positioning equipments have been popularized in vehicles. With the help of global navigation satellite system(GNSS), we can more easily choose the appropriate paths in the network and realize effective transmission. Therefore, VANETs has received the widespread attention at home and abroad.In this thesis, a deep research of vehicles’ movement and data transmission strategy in VANETs is presented based on the precise location information provided by the vehicle’s GNSS equipments. The main work is as follows:1. We collect the real trajectory data of taxis, a basic mobility model is constructed by abstracting the movement of taxis in time and space domain. Then the information entropy of vehicle trajectory is calculated to analysis the regularity of movement and predict vehicle trajectory.2. The vehicle trajectory prediction method based on Markov chains is presented. The method uses positioning system to obtain vehicle’s history trajectory information. Then the state transition matrix is built to predict not only the vehicle’s probable destination but also the continuous trajectory. Then simulation experiments are designed, the presented method is compared with the prediction method based on probability and statistics, some factors that will influence the accuracy of prediction are also analyzed.3. A routing protocol named TPGA is proposed based on greedy algorithm and trajectory prediction is proposed. The trajectory information of the vehicles is used to calculate the packet transmission rate, routing based on the principles of transmission rate. Besides, a valid cache management mechanism is designed to provide real-time and reliable transformation for VANETs. Then the simulation scenario is built to compare TPGA with some typical routing protocols of VANETs and take the result into analysis.4. Based on two typical scenarios of VANETs, urban and suburban, we use the real map of Chengdu to validate the simulate experiments of TPGA. Pile pressure on the protocol in three aspects: simulation time, cache size and number of disconnected nodes to test the reliability and practicability of TPGA under the condition of real scenarios and pressure.