Broadcasting Of Security Message And Congestion Control In Vehicular Networks

With the rapid development of world economy and auto industry, the vehicle plays more and more important role in daily life. However, the problems emerged at the same time can not be negligible. The situation of frequent accidents and serious traffic congestion all over the world bring huge loss to social economic and the safety of people's lives and property. With the development of wireless communication technology, to solve the traffic safety problem, Vehicular Ad Hoc Network (VANET) turns up based on the researches of Mobile Ad Hoc Network (MANET). VANET is formed by the communication between V2V (Vehicle to Vehicle) and V2I (Vehicle to Infrastructure). VANET is used to transmit real-time information, such as vehicle safety warning message and driving assistance message, and provides entertainment services, such as vehicle entertainment, real-time navigation and so on, making the transportation network more secure, efficient.The research in MANET is well developed nowadays. However, because of the characteristics of VANET such as more easily attacked by malicious behavior, the rapidly dynamical topology, the unstable wireless channel condition and the easily congested channel, it is clear that the main points of VANET are different from MANET.This thesis summarizes the characteristics and the existing work of VANET. According to the characteristics of VANET, this thesis mainly considers about how to guarantee the security of vehicular communications, how to adapt to the rapidly changed network topology and how to improve the channel congestion status. This thesis presents the significance and researches about secure messages broadcasting and the congestion control mechanism. Then, it analyzes and proposes several algorithms for secure messages broadcasting and the congestion control mechanism, respectively. Followed by the analysis, corresponding algorithm is proposed. Firstly, to efficiently broadcast the security messages, according to the problem of network easily attacked by illegitimate nodes, we analyze the difficulties in certificate revocation list distribution and propose the movement-assisted certificate revocation list distribution mechanism MCRLD. Then the AAVP and PAVP algorithms are proposed for different applications to assist roadside unites (RSUs) in distributing certificate revocation list (CRL). The simulation result shows their efficiency, such as the percentage of vehicles that receive the CRL is increased and the time delay of vehicles that receive the CRL is decreased. So, the approach obviously improves the performance of evicting illegitimate nodes and security messages broadcasting.Secondly, for controlling the channel congestion, we adopt transmission power control approach. We propose the Steepest Descent Power Control algorithm (SDPC) and the power control algorithm based on channel busy time algorithm (PCCBT) which adapt to the rapidly dynamical network topology and the wireless channel instability.SDPC is based on the steepest descent theory and the efficiency of SDPC in terms of the number of iterations for computing the transmission power values decreases and converging speed increases. As a result, the transmission power to transmit their status information can be quickly adaptive to the vehicle dynamic and surroundings situations. Therefore, channel congestion can be effectively under control and the security of vehicular networks can also be improved.According to the channel instability situation in VANET, especially the channel can be easily affected by some factors, such as the building block and the interference of wireless signal. We choose the channel busy time to estimate the network congestion situation and propose PCCBT algorithm. Whenever monitoring the congestion, the vehicles would adjust the transmission power to improve the channel status, i.e., we adopt the feedback regulatory mechanism to get the power value according to the practical situation. The simulation result shows that PCCBT algorithm can improve the ability of packet reception, thereby enhancing the transmission reliability and the driving security.Finally, the thesis concludes presented work of VANET, and highlights some future work.