Architecture And Road Network Model Of Vehicle Navigation System

Traffic jam and its induced problems such as traffic environment pollution, traffic security and traffic energy consumption have attracted more and more attention. If we can combine the satellite, the general control center on the ground, the detecting equipment on the road, the in-vehicle computer and the control system on the road by network communication techniques, then the driver can at once obtain an optimal driving path simply by telling in-vehicle computer where he is and where he wants to go. This idea motivates the so-called intelligent transportation system (ITS) or named as intelligent vehicle highway system (IVHS).The vehicle navigation system (VNS) is an important part of ITS. Based on the road network digital map constructed by Geographic Information System (GIS ) technique, VNS can position the vehicle by using the GPS, dead reckoning, map-matching techniques. Thus, as long as the traveler tells in-vehicle computer where he is and where he wants to go, the VNS will in real time present the static or dynamic optimal route information according to the information supplied by traffic information center. In addition, the driver can be guided by VNS while driving. Therefore, to study VNS can not only make the travel convenient but also be valuable in the view of economy and society.The VNS is a very complicate system, which is a combination of various theories and techniques. Researchers have performed deeply study on many parts of VNS, including digital map, position system, path planning and communication. At present, there are many kinds of mature navigation equipment, but as a complex system, there still exist many issues need studied. For example, the VNS, which can communicate in both directions, can not only supply the traveler with various services, but also it can collect the trafficinformation that can be used as reference of dynamic assignment of the traffic flow. So far, this kind of advanced traffic information system has been applied in the USA, Japan and Europe, but still there are some techniques and theories need to be improved. Under this background, we study the architecture of the VNS and the road network model, and slso do some research on path planning and voice-guiding system based on the proposed road network model. The main content is as follows:1. From the technique point of view, the VNS can be categorized as autonomous navigation system and central navigation system, while the central navigation system is the direction of the future VNS. The central navigation system is composed of three parts: control center, in-vehicle navigation terminator and public moving communication service platform. It is composed of supervising and control server, communication server, supervising and control terminal, database system and display terminal etc., and the design of the supervising and control server is one of the key techniques of VNS, which is also the main job of this thesie. This thesis emphasizes on the design of central supervising server for the control center of central VNS, categorizes the function modules for the system, and designs some function of the software system utilizing class view.2. Navigation geography database is the base of positioning and path planning. While the road network data is one of the mainly stored data of the navigation geography database, so the organization and impression of the road network data is to some extend decides the rationality, veracity, and celerity of the path planning. Therefore, we study the road network model of the VNS considering the traffic constraints. As the traffic in the city becomes more and more complex, there exist many complicated crossings and road segment, so traditional network organization and impression based on sigle-line model and bi-line model cannot satisfy the requirement of path planning in VNS. We abstract the complex road network as a simple road network, and on the complex nodes, we record the turning constraints rules by turning table. Thus, the traditional shortest path algorithm can be used to perform path planning, and in the route guiding process, the detailed information on the complex crossing and road will be given to the traveler.3. We design the data structure of the stored road network based on constrained road network model. According to the idea of multilevel linked list, we improve the traditional data structure of the adjacency list and realize the turning constraint relationship expressed by three nodes adopting multilevel pointer. When constructing the road network topology, we conquer the obstacle that the traditional data structure cannot store adjacent three nodes by reading the node turning table and storing the father node, the current node and the sub-node to the corresponding position of the adjacency list. The simulation results verify that the constructed road-network-topology data storing method can describe the traffic constraints.4. According to the constrained road network data-storing structure, we design a fast path planning algorithm base on A* algorithm and design the cost function. While designing the cost function, we consider the rank of the road and so the high rank road can be chose when perform the algorithm. Since the situation of high rank road is better, the algorithm can improve the safety and comfort of the driving. The simulation results imply that the algorithm is efficient and the planned path satisfies the requirement of the VNS.5. Based on the path planning results of the constrained road network model we design the voice-based navigation system and give the design scheme of its software and hardware.As a summary, we have done some research on the architecture of the VNS and the road network model. The main content includes the design of the supervising server of the central VNS, the analysis and design of the road network model considering the traffic constraints, the design of the road network storing data structure, the path planning experiment base on constrained road network model and the design of the route guiding system. The experimental results imply that, the supervising server is well designed and the system is stable and the voice-based navigation system is precise, credible and stable. The simulation results verify that the designed road network model can describe the traffic constraints, and the road network storing data structure is simple and reliable.