1 Introduction Since the 1960s, many countries have begun to study navigation and positioning technology. The vehicle navigation system measures and solves the instantaneous motion state and position of the vehicle, and provides it to the driver or autopilot to realize the correct operation or control of the vehicle. The development of vehicle navigation systems began in the early 1970s. The US Highway Administration proposed an Electronic Route Guidance System (ERGS) in the early 1970s. This system is a navigation system with wireless route guidance capabilities, which points at a short distance. The standard network as its basic technical starting point forms the central dynamic path guidance function of the navigation system; however, due to limited funds, this system was ultimately not implemented. In the 1990s, the GPS-based navigation system was continuously improved, and it has entered the practical stage at home and abroad. The PATHFINDER system developed in the United States and the VICS system in Japan. In China, GPS positioning and navigation technology has also developed tremendously in recent years, such as the WP2000 system developed by Xi'an 504, which is mainly used for navigation and alarm. 2. GPS overview 2.1 Introduction to GPS system The global positioning system, or GPS for short, is a constellation of 24 navigation satellites orbiting the earth. The GPS receiver uses the precise time and location information sent by these satellites to locate. The system can provide three-dimensional coordinates of all points on the earth. The Pentagon in the United States uses navigation data provided by GPS to deal with difficult terrain and various emergencies, and it also controls this system. Although GPS is mainly used for military purposes, its value in the civilian and commercial fields is constantly being recognized. GPS satellites therefore send two types of codes: an encrypted code PPS (also known as P code) for military use only, and a standard DPS code (C / A code) for civilian use. The US government announced at the beginning of the 21st century that since the night of May 1, 2000, the SA policy was cancelled, which greatly improved the positioning accuracy of civilian C / A codes. The GPS system is mainly composed of three parts: (1) GPS satellite (space part), (2) ground monitoring system, (3) GPS receiver (user part). 2.2 Basic principles of GPS positioning The basic principle of GPS positioning is to determine the position of the point to be measured based on the instantaneous position of the satellite moving at high speed as the known starting data, and adopting the method of spatial distance resection. GPS positioning is based on the distance (or distance difference) between the GPS satellite and the user receiver antenna, and the point corresponding to the user receiver is determined according to the known satellite instantaneous coordinates, that is, the three-dimensional coordinates of the point (X, y, z), the key is to determine the distance between the user's receiver antenna and the GPS satellite. There are two main GPS positioning methods: absolute positioning and relative positioning. 3. The application of GPS in vehicle positioning and navigation The research on vehicle positioning and navigation started abroad in the 1970s and is currently called AVLN (AutomaTIc Vehicle LocaTION and NavigaTIon). AVLN is the basic link of Intelligent Transportation System (ITS) or Intelligent Vehicle / Highway System (IVHS). The GPS vehicle positioning and navigation system has achieved rapid development in China since 1995 due to the easy realization of precise positioning, the relative low cost, and the relative independence of design and installation. The GPS laboratory of the University of Science and Technology of China has also made pioneering work in it. 3.1 Development of GPS vehicle navigation system As a high-tech, GPS global positioning technology was mainly used in the field of railway, air transportation and maritime transportation in the past. As the GPS global positioning system technology matures, the technology begins to turn to the field of road transportation. At present, GPS vehicle positioning systems are mainly used in public transportation, rental, passenger transportation and other industries. The phenomenon of highway traffic congestion can be solved well by GPS positioning technology. GPS vehicle positioning system is a system that provides positioning information for motor vehicles by means of GPS global positioning system. The GPS system can provide global coverage, all-weather, free high-precision standard time / navigation and positioning services. The GPS receiver can obtain latitude and longitude information in real time to determine the latitude and longitude position and speed, time and other information. The vehicle positioning system will obtain a series of information. Process to determine the specific location of the vehicle. Japan, Toyota, Toshiba, Sony, etc. are in the world's leading position in the research of car navigation systems. In 1991, Toshiba ’s car navigation system used an operable TV GPS receiver to display information such as restaurants, hotels, and shops along the way. In 1994, Sony introduced a car navigation system with electronic maps, which combined an 8-channel GPS receiver with a CD-ROM format map and information database, and was able to receive traffic flow information sent by FM radio broadcasts. Major companies such as Mercedes-Benz, Toyota and Honda are actively developing their own navigation information systems to expand the navigation information service market. In the United States, Chrysler has developed a GPS-based vehicle navigation system. After the satellite signal is lost, the system can work with a compass and a log to keep the vehicle continuing to navigate. Westinghouse was the first bus in Paris to use vehicle scheduling and navigation systems. 3.2 GPS and vehicle navigation system The application of GPS in ITS is mainly reflected in vehicle navigation. Among the various applications of GPS, the application of vehicle positioning and navigation has developed fastest, and has achieved huge economic and social benefits. Vehicle applications have leapt to the top of GPS applications. Although cars are part of people's daily lives, owning a car does not necessarily make our lives more convenient. Public transportation runs on fixed traffic routes. Unlike this, car and truck drivers need to know the route to their destination and where to park. If the road network is intricate, drivers will easily get lost. This situation is both anxious and wastes precious time. The vehicle navigation system is like a confident navigator sitting in the co-pilot position of the car, guiding the driver to reach the destination on time without any effort. Even with a navigation system, if the driver's ability to distinguish the direction is too poor, it is easy to get lost. If you mark your current location and destination on the display, then things will be easier. The arrow on the display indicates your current location and suggests which direction you should travel to reach your destination. Some navigation systems have voice navigation prompts, such as turning right in front, or you are halfway away from your destination. Therefore, the driver does not need to look at the display frequently. Another attractive feature of the navigation system is the data information software library, which brings together local road information such as restaurants, golf courses, and other entertainment venues. The so-called GPS vehicle navigation system is a system that uses received GPS signals to monitor and locate the maneuvering target, and optimizes and guides its movement according to the track situation. The use of vehicle navigation systems can bring many benefits such as shortening driving time, reaching the destination quickly, reducing energy consumption, and ensuring driving safety. The normal operation of the vehicle's GPS positioning and navigation system requires at least ancillary facilities such as a global GPS satellite system, a lightweight and reliable GPS receiver, a fast and powerful computing system, a wide-ranging and detailed electronic map, and a wireless communication network. 3.2.1 Vehicle positioning technology Vehicle positioning technology is the basis of the entire vehicle navigation system, and almost all functions in the system are premised on the accuracy of vehicle positioning. The accuracy and real-time nature of vehicle positioning are directly related to the practical value and overall performance of an intelligent transportation system. Due to the special and important role of vehicle positioning technology in vehicle navigation systems, vehicle positioning technology has always been a key topic for various vehicle navigation system research and development organizations. GPS Global Positioning System is a huge cosmic and aerospace project proposed and implemented by the United States. Its original purpose was to serve the U.S. military, but with the civilization of GPS technology in recent years, it has gradually become a global tool. In terms of mobile information systems on land, GPS is gradually being applied to the fields of security and vehicle navigation. GPS has high positioning accuracy and good real-time performance, and can basically meet the accuracy requirements of the vehicle navigation system in the future ITS. Therefore, the development and application of GPS-based vehicle automatic positioning / navigation and management systems are increasingly being highly valued by various departments at home and abroad, and will show huge economic and social benefits. 3.2.2 GPS vehicle positioning system hardware design The specific working environment of vehicle-mounted equipment requires that the size of the GPS vehicle positioning system be as small as possible and the reliability as high as possible. Therefore, the core part of the system hardware is suitable for selecting an embedded computer. With the rapid development of computer technology, embedding microcomputers as controllers in products has begun to be seen everywhere. Due to the widespread popularity of PC architectures, PC-compatible software, hardware, peripherals, and development tools are richer and cheaper than other architectures. Using PC architectures for embedded applications means that development can be significantly reduced Cost, reduce risk and shorten development cycle, and reduce many headache system maintenance and technical support. The PC / 104 computer can meet the above requirements. It is small in size and highly integrated. It provides full compatibility with the PC bus in architecture, hardware and software, and the compact structure of the stacking module is very suitable for the unique requirements of embedded control applications. . Due to the use of CMOS devices, the PC / 104 module has low power consumption, no heat dissipation problems, and a wide operating temperature range (0-700 ° C); the structure is compact and very compact, occupying an area of ​​only 90mm & TImes; 96mm, and the ultra-small size makes installation It is easy to carry and carry; it reduces the number of product parts; the system composed of modules is directly stacked without the need for a chassis and a bottom plate; it has good shock resistance and shock resistance. The existing PC / 104 module provides a wide variety of components for the construction of embedded systems. Its highly integrated and modular structure is suitable for a variety of applications. 3.2.3 Electronic map based on GPS navigation technology The electronic map is an important part of the GPS navigation system. It is the interface between the navigation system and the user. It combines the received navigation and positioning signals with the geographic characteristics of the maneuvering target ’s driving range. It dynamically and intuitively manages the movement of the target and Guidance, so that the user can use the navigation system conveniently and concisely without understanding the meaning of the received data. The electronic map is still an extension of the performance of the navigation system. Since the electronic map is composed of corresponding software, it can easily realize various functions and maximize the potential of the navigation system to be convenient, accurate and fast, without the need for hardware. Adjustment. 3.2.4 Map matching technology The driving path of the vehicle displayed on the electronic map is measured by positioning technology. However, no matter what kind of positioning technology has its insurmountable limitations. Radio navigation technology depends on external equipment, and its positioning accuracy is limited by the coverage area of ​​the wireless network (such as Sign PoST) or affected by the accuracy of positioning signals (such as GPS); the accuracy of the navigation technology is speculated by the direction detector and vehicle speed The accuracy of the pulse equipment is limited, and it has accumulated errors, that is, as the distance traveled by the vehicle increases, the error becomes larger and larger. Due to these errors, the position of the vehicle is deviated. Map matching is a technology to determine the position of a vehicle on a map, and its error correction technology precisely avoids the limitations that the positioning technology cannot overcome. Map matching refers to that the GPS receiver measures the current position information of its carrier, and then obtains the relevant information from the electronic map database, and then obtains the deviation information such as the carrier position through the matching algorithm, and corrects it in real time to accurately display the vehicle s position. It can be said that the effect of map matching algorithm is directly related to the accuracy of vehicle positioning. Map matching technology is the key technology that determines the final performance of navigation products. A more ideal way of navigation. 　　
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