Research Of Geographic Routing Protocol Of VANETs In City Environments

Vehicular Ad Hoc Networks(VANETs) is a very valuable research area in Mobile Ad Hoc Networks, and it is also an important part of Intelligent Transportation System. Nodes in VANETs can communicate each other in a one-hop or multi-hop manner. Meanwhile they can exchange information with each other, such as speed, location and so on. Thus they can form an Ad Hoc network spontaneously. With the help of GPS, vehicle sensor and other equipment, VANETs can obtain various kinds of information of the nodes and the roads conveniently. VANETs can also provide many services for drivers, such as road guidance, road warning, network access and so on. It not only improves driving safety, but also increases the driving comfort. In urban road environment, frequent changes in network topology, node movement by road layout constraints, the transmission of the wireless signal by obstruction and other issues, make the design of routing protocol in VANETs more complex. Therefore, it is difficult to design a kind of routing protocol to adapt to the characteristics of VANETs under the city environment.Considering the characteristics of VANETs, this paper proposes an intersection routing protocol based on segment length in VANETs. Neighbor nodes are divided into common neighbor nodes and intersection neighbor nodes. The general idea of the protocol is that intersection neighbor nodes of the current node acquire the connectivity information of its adjacent segments; we chose the intersection neighbor node nearest to the destination node, whose adjacent segments are connected, as the next hop; if none of adjacent segments of the intersection neighbor nodes is connected, the neighbor node of current node nearest to the destination node is as the next hop; relay nodes repeat the above process until reaching the destination node or meeting the local optimum problem, which refers to none of the neighbor nodes of the current node is nearer to destination node than itself. The protocol use different methods to judge the segment connectivity for two cases respectively, which are the segment length is less than the wireless signal communication radius and the segment length is greater than the wireless signal communication radius. When the segment length is less than the wireless signal communication radius, we can judge the segment connectivity by whether there are neighbor nodes of intersection neighbor node in the adjacent segments or extended segments. When the segment length is greater than the wireless signal communication radius, we can use the distributed real time method to obtain the segment connectivity.Considering the problem of frequent network disconnection caused by the building block in an urban environment, this paper proposes a Artificial Spider-Web-based Geographic Routing. The source node use GPS navigation device to obtain the current node and the destination node’s geographical location, speed and other information. It also can acquire the city topology and geographic position information of intersections by spiders searching the electronic map. Firstly, according to the acquired information, the source node searches for the feasible path to the destination node from the electronic map. Then according to the connectivity, delay and hop count information of each section, the source node calculate the sum of the weight of each feasible path and select the optimal path from all feasible paths. At last, the source node forwards packets along the optimal path. If suffered the local optimum problem or forwarding fails, the optimal path will be recalculated.