| Nowadays, Campus Smart Card has gradually become a vital vector of information communication in campus, and its applications have increased dramatically ranging from E-wallet to Attendance Systems. In Donghua University, the faculty can take the shuttle bus between the campuses by Campus Smart Card, which helps checking on work attendance。However, it is hard to collect the data from vehicular terminals on the shuttle buses efficiently, because the present acquisition method depends on manual labor, which is time-consuming and easy to fail when the buses shuttle frequently. By setting the wireless base station, wireless access network provides a wireless access solution for Campus Smart Card data acquisition system to realize the automatic transportation of collected data.With the support of the Public Service System Construction Project of "211 project" for Donghua University, the wireless access networkprotocol of Campus Smart Card data acquisition system has beenresearched and designed.Firstly, the state-of-the-art techniques are introduced. With the analysis of alternative solutions in designing global structure, this paper puts forward a feasible solution and describes the function demands, topological structure, modular division and communication principle of the whole system.Secondly, the software and hardware platforms of the wireless communication sub-system are discussed. The system structure of wireless communication sub-system is described from both hardware and software point of view, including embedded microprocessors, radio frequency modules, wireless communication modules and embedded operating systems. Following the seven layer model of OSI, this paper designs a protocol stack structure of wireless communication sub-system.Thirdly, the data link layer protocol of wireless network is studied. Some commonly-used methods of error control are introduced and CRC code is selected as the checked code by comparing the strong point and the weak point of some check codes. By analyzing a few multiple access protocol, 1-persistent CSMA protocol based on random access protocol is proved to be more suitable for the data acquisition system. In addition, this paper designs the link-layer frame format of data link layer protocol and the procedure of error detection and collision avoidance, whose quality is tested through loss tolerant experiment with the discussions on the test results.Fourthly, the transport layer protocol is designed in detail. By analyzing the flow control and error control protocols, the coherent Stop-Wait protocol had been selected to accomplish flow and error control functions for flow and error control. Further more, the transport-layer packet format and the cooperation procedure between sender and receiver protocol is designed, and the protocol performance is discussed from both function and efficiency aspects, followed by a communication reliability test.Finally, the application layer protocol is described according to the demand of application system. Combined with Client/Server structure based on polling protocol, application-layer message type and format are illustrated as well as message communication procedure between processes. The feasibility and capability of the application layer protocol is analyzed and the debug procedure of the whole wireless communication protocol is described at the end of the paper.The innovation of this paper is to introduce wireless access technology to wireless data transmission of Campus Smart Card by designing a special wireless communication protocol used by vehicular terminals and wireless base stations, which not only solves the automation problem of mobile data acquisition cheaply and efficiently, but also explores a new research area of engineering application. |
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