Design And Experimental Studies On Vehicle Navigation Terminal Based On Embedded Technology

China is a country having large population, and the amount of populationaccounts for 1/5 of the world total population. As the social economy develops,the Chinese transportation facilities and its management have been muchimproved, but it can't follow the rising rate of the vehicles. At the end 2005, thecities with population more than 1 million count up to 170, and the number ofautomobiles surpasses 30 million. Because the speed of vehicle has to be slow,the exhaust discharged by the vehicles is increased, making the air quality ofthe city much worse. The traffic jam not only aggravates the environmentalpollution, but also damages people's health, and even influences directly theeconomic development of city and country.The vehicle navigation system is an important application of ITS, and it isan integrative Hi-Tech system of global positioning system GPS, modernwireless communication technology GSM/GPRS and geographical informationsystem GIS. It has the potentiality of giving full use of existing trafficinfrastructure, improving traffic flow and transportation efficiency utilizing theresources of the network, ensuring the traffic safety , relieving the traffic jam,so it is an effective measure to reduce the environmental pollution.The central server navigation system is composed of more than seven parts,including car-serving-platform of GPS, the car-mounted navigation terminal,the GPS positioning system, the mobile serving platform GSM/GPRS, thetraffic control center, the service centre of weather information, and socialsecurity departments such as 110 , 112 , 120 ,etc.The global navigation digital map of central server guidance system islocated on the GIS server in the central sever. The principle of 'navigation whenneeded' is adopted, and in this way the inconvenience brought by the updatingof navigation digital map and the extra payment. The Way planning isperformed on the server central server, and the requirement to hardware ofcar-mounted navigation terminal could be decreased. The cost could bedecreased much.The users inform the serving center of the Destination of their trip and theRoute prearranged through the pronunciation platform of the center. The centergives the users information of their location (longitude and latitude) by wirelesscommunication network GSM/GPRS. In addition, the center will plan for theuser a optimized driving route, with the least time needed, the shortest route, theleast expense. Moreover, the center may collect through the Internetinformation meteorology, the traffic flow, traffic congestion and so on. Thenavigation data planned is downloaded on the navigation terminal on thevehicle through the network GSM/GPRS .The car-mounted navigation terminal is an important of the central serverguidance system. The car-mounted navigation terminal math the navigation dataplanned by the GPS service center and the GPS localization data, and providesway guidance to the users. The car-mounted navigation terminal is mainlycomposed of imbedded hardware system, imbedded operation system,imbedded navigation application software, and having the function of routeguidance, car-carrying telephone, parking assistance,vehicle-carry-entertainments, breakdown diagnosis, urgent rescue and so on.This paper analyzed the system function demand, and then developedembedded hardware system using the Motorola 16 micro controllersMC9S12DP512 as its core, assisted by the GPS localization module, thewireless communication module GSM/GPRS, the pronunciation synthesismodule, the back-draft radar module, and the man-machine connection.The car-mounted navigation terminal has complex functions, and needs thesupport of an operating system. But the existing mature operating systems, suchas WinCE, Linux, VxWorks, are high in the hardware performance demand,occupies massive systems resources, and needs considerable expense. Therefore,a real-time operating system based on the duty dispatch is designed. Theoperating system has duty courses and equipment courses. In order to attainmulti-duties and the multi-equipment parallel processing, the dispatch of patrolscanning courses is used. A course is performed or not is determined by coursesdispatch and information is transformed by stack between two courses.The embedded operating system dispatches in a manner of non-depriving,and there is no timer strictly defined. So, the time piece datum can't beprovided for courses and codes for returning to the scanning dispatch processneed to be added by the programmers in the duty courses and equipmentcourses. Because of this, the time of performing the duty courses is determinedby the programmers, and so is the real-time property of the system. But theparticipates to the design procedure has a large number, and the quality of codesis different, thus real-time property of the whole system turns out to be adifficult problem, and improvement needs further study.The match of maps is the essential technology of vehicle carries guidancesystem. In this system, the map matching has the following constraint:(1) The maps used for navigation is the local navigation digital mapsprovided by the center with planned driving route. The way matched needs tobe known, thus the complexity of the map matching is decreased;(2)The system does not provide the demonstration function of navigationelectron map, only provides the simple chart and the pronunciation outputnavigation of information through the LCD contact interface;(3) The processor used in the system is a 16-bit micro controller, witchmainly faces on the control domain, and its computing ability is limited, so thecomputing capacity of CPU must be in consideration when designed.Under the above three constraints, a simple real-time map matchingalgorithm suit for this system must be designed. In the algorithm, multi-bytescalculations of multiplication, division, root, trigonometrically function, aremostly avoided and real-time property of the system is enhanced.After the algorithm design completes, the MapX tool is used to design asimple test simulation system. Using the driving data gathered by GPSlocalization module in Changchun urban streets, the validity of the algorithm isconfirmed in the simulation system.It can be seen through the simulation experiment that the match algorithmwok quite well when the road section is sparse. When the vehicles are incrowded road sections, because the GPS satellite signal is covered and so thepositioning accuracy decreases, the accuracy of map matching also drops. Oncethe vehicles are in the region receiving no GPS signal, the guidance system thendoesn't work at all. How to position the vehicles with more accuracy is aproblem needs further study in the system...