The Research On Key Technologies Of Data Dissemination For Urban Vehicular Ad Hoc Networks

As one of the important components of Intelligent Transportation System(ITS), Vehicular Ad Hoc Network(VANET) has caused worldwide automobile industry’s high attention and widely research in academic communities. By Vehicle-to-Vehicle(V2V)and Vehicle-to-Infrastructure(V2I) communication, VANET could support drivers getting beyond-line-of-sight information about other vehicles and real-time traffic, which plays an important role in accident warning, protecting traffic safety, optimizing traffic flow and providing a variety of services for the occupants, etc. As the foundation of applications in VANET, data dissemination plays an important role for promoting the development of VANET.Nowadays, urban VANET could provide various services, and each vehicle participates in more and more network applications. The demand of non-safety applications becomes more and more obvious. High coverage ratio, satisfying spatio-temporal relevance and low load have become three of the most important objects in non-safety data dissemination. However, the complicated mobility and communication environments in urban VANET cause highly dynamic topology and unstable links between V2 V and V2 I,which brings severe challenges to data distribution. For non-safety data dissemination in urban VANET, this thesis conducts research from two aspects of data placement and local data dissemination. The main contents and contributions of this thesis are summarized as follows.First, a macroscopic flow model for urban traffic named TLECTM is built, and a greed algorithm name MFPGA for data placement is designed. It could effectively improve data coverage by predicting the traffic flow in urban scenarios. In urban road networks, there are some input flows and output flows in intersections, many kinds of traffic light assignments. Moreover, there is a variety of abnormal traffic changes. For characterizing the urban traffic flow, a Traffic Light Extension to Cell Transmission Model(TLECTM) is built. Based on this model, a Macroscopic Flow Prediction based Greed Algorithm for Data Placement(MFPGA) is proposed for maximizing data coverage.Second, a probabilistic model for intersection traffic is proposed, and several algorithms for data placement are designed. It is the premise for covering a vehicle to place the data on the route of the vehicle. However, it is difficult and even infeasible to get the detailed trajectories of each vehicle. Aiming at this problem, a probabilistic model for intersection traffic is proposed, which is based on the OD matrix and the topology of road network, and utilizes random route selection for obtaining the probability of vehicles through the intersection and routes superposition among different vehicles. An optimal algorithm and two greed algorithms based on this model are proposed for maximizing data coverage.Third, a lifetime model for local data dissemination in urban VANET is proposed.Due to the mobility of vehicles, the local topology of VANET changes rapidly. It could not guarantee the data exists in this local region for a long time. The lifetime of data is a basic problem. Based on probability theory, the spatial relevance and contacts among vehicles are analyzed, and the influence of arrival rate, velocity, region size and communication range on the lifetime is characterized. Lifetime Model for two-way highway are improved,and a new model for urban intersection is proposed, which supports the design of data dissemination protocol.Finally, a lightweight local data dissemination protocol(LDDP) is proposed. In urban VANET, the vehicles pass through the region quickly, and the communication in the region is temporary. According to this character, LPPD determines the spatio and temporal parameters in order to limit the range of data diffusion and insure the local property of data dissemination. Moreover, LDDP utilizes the mechanism of store and forward,and deletes the replica as soon as possible by dynamic deletion mechanism. LDDP could effectively reduce storage cost without any loss of lifetime and coverage.