| At the era of information technology, people pay more attention to the accuracy and real-time of the information than before. Under this circumstances, Jilin University is commissioned by the Science and Technology Department of Jilin Province, do the platforms research of ProbCar Dynamic Navigation of the Central-based Vehicle Navigation System。The research and development platform include service center, vehicle(with GPS),communication units,ProbCar and so on. The position information of the vehicle is transmit to service center by communication units. According to the information provided by the vehicle, we make a path planning and update the database of customer. The commands of service center and the section sequences after path planning (the information is commands of the vehicle movement and the service information of path planning) are transmit to vehicle by communication units.Service centre includes service terminals, the destination database, matching units of maps, path planning units. According to road conditions and dynamic information and task requirements provided by the vehicle, the information will get integrated treatments. As a part of the research and development platform, the emphasis of this paper is the research of protocols that make every unit can have a real-time communication of the service centre in Vehicle Navigation System. Under the research background of the project that"A Research Based on ProbCar Dynamic Path Navigation Methods"of the Science and Technology Department of Jilin Province, the paper combines the actual system requirements with the research conditions of our own. On VC++ platform, the communication problem of the service centre are solved in the low-cost vehicle navigation system. The main research work is:(1)According to the actual situation of the service centre,the characteristics of the system is determined and, the assumption of fake token bus system is presented. On VC++ platform, the ideas of fake token bus are achieved simply with the help of socket technology and multicate technology and soon.This paper is based on the ideas of standard token bus. Given the complexity of standard token bus protocol and the difficulty to achieve, the operational principle of algorithm of the standard token bus are revised and achieved easily.Since our site is PC, in order to meet the real-time requirement of system, the structure of the frames is modified and adopted.In the site-accessing algorithm, initiative ideas are adopted. When the sites want to be accessed the ring will be applied. In the token passing algorithm,is adopted. This can make sure that the tokens can not be lost and it is useful for the maintenance of tokens. In the whole process of protocols running, the lists of ring members are introduced. Its presence will be beneficial to the maintenance of the rings.At the same time, I hope that this system can be applied to practical application.(2) According to the characteristic of actual system, the real-time and feasibility of communication are analyzed in this system.The real-time of system includes real-time communication and real-time task scheduling, so the design ideas must ensure the principle of real-time. Based on the analysis of real-time communication, we found the key to improve the real-time of system----queuing delay and MAC protocol problems. We made further analysis for queuing model is made and combined it with the characteristics of system, the performance analysis of m/m/1/n/n model is given, and it is the guarantee for the real-time and feasibility. We also analyze that the change of parameters also has an impact on system performance. Finally better methods that can improve the real-time of system is founded, and the parameterμ(service ratio) has great impact on system performance. In order to improve it, the approach is that we must improve the algorithms of the application software in addition to hardware improvement.Because the service objects of the service centre include not only the general public vehicles but also the police and administrative staff vehicles.This paper presents queue model with priority. The high-priority with low-priority information is compared to illuminate that this system will provide high-priority information with convenience.For these characteristics, we all have done simulation experiments.(3) Based on actual system, the task scheduling is analyzed in order to ensure real-time of the system.There are the scheduling problems for our system, and the obvious phenomenon is in the service terminals and there are sequence problems between tasks. In order to ensure the effective work of service terminals, the task scheduling problems are analyzed on the basis of this system.Based on the deep study in scheduling theory, we understand that the tasks served by service terminals have the characteristics of prior bind in this system, and the tasks have the non-cyclical characteristics, so C-EDF Aalgorithm is chosen. The real-time task scheduling of the system with it is analyzed, too. By the analysis of many examples, this task scheduling algorithm is very effective and reasonable in the node with N tasks. The results show that our system can achieve good task scheduling in the real-time instance. Proof of the C-EDF algorithm than EDF algorithm can more effectively ensure that the priority constraints task scheduling.(4) The performance of fake token protocol is analyzed.After the establishment of system, if you want to actual application is be wanted, what most concerned about is its performance. Through the general analysis of performance and theoretical research, the analytic theory that matches this system is presented, and give some parameter values of fake token bus are given.The analysis of this system is general and it conforms to the actual situation.Through the amendment of protocols and the realization of the program and the analysis of performance, as we know, it is the most important that theory and practice are combined together.
|
PDF Full Text Request