摘 要
无线数据传输技术的快速发展给相关产业和领域的发展带来了极大的机遇，其中受益最大的当属在数据采集与传输系统方面的应用。无线传输技术大大扩展了数据采集与传输系统的应用范围，降低了制造和维护成本，提高了系统的设计与运行效率。本课题所研究的VPS（The vehicle positioning system，车载定位系统)即属于这种系统的一种具体应用。
车载定位系统是ITS（the Intelligent Transportation System ，智能交通系统）中车辆部分的应用,是智能交通系统的一个关键子系统，其内部的无线传输模块是智能交通系统移动终端与信息服务中心进行数据交换的通信平台，因此关系到整个系统的稳定性、安全性、实时性与运作成本。迅速发展的移动数据通信业务为车载定位系统的构建提供了理想的平台。在移动数据通信业务中，基于GSM（Global System for Mobile Communications，全球移动通讯系统）的SMS（Short Message Service，短消息服务）和GPRS（General Packet Radio Service，通用分组无线服务）分别具有各自的优缺点，适用于不同的具体应用。应用SMS构建的无线传输平台具有简单易用的特点，可以用在数据传输要求不高的情况中。GPRS技术则在实时性、安全性、传输速度和能力等方面有更大的优势，适用于更广范围的应用。
在课题研究中，采用了西门子公司生产的MC35i无线模块，通过它进行车载定位系统中无线传输部分的设计。MC35i模块是新一代的双频GSM/GPRS引擎，可以利用它比较方便地进行基于短消息或GPRS的移动数据传输。基于课题的现实要求，采用了比较简易的短消息传输模式，实验证明在成本极低的AT89S52单片机的控制下，样机中的无线传输模块可以稳定工作并进行短消息的收发。具体的硬件电路设计为项目升级提供了充分的余地，可以通过简单的改动实现基于GPRS通信的功能，继而进一步扩展整个系统的功能。
关键词： GSM；短消息；MC35i；模块
ABSTRACT
The development of wireless data transmission technology greatly stimulates the development of relative industries. One of the most beneficial fields is the system of data acquisition and transmission. The wireless data transmission technology expands the application of the system. The building and maintaining cost is reduced, designing and running efficiency is raised. The vehicle positioning system (VPS) discussed in this paper is one of the applications.
The vehicle positioning system, as a key sub-system, is the terminal application in the Intelligent Transportation System (ITS). The wireless transmission module in VPS serves as the communication link between terminals and service center of ITS. So the stability, security and cost are largely influenced by the wireless transmission module. The mobile communication technology offers an ideal environment for the construction of this module. Among the data transmission services in the mobile communication system, SMS (Short Message Service) and GPRS (General Packet Radio Service) has their own advantages and disadvantages. The two services suit different applications. The research and design based on SMS is simple and can be used in applications without high requirement on data transmission. GPRS is better in security, transmission rate and functionality so is adaptive to more extensive applications.
The MC35i wireless module by SIMENS is introduced in the design of wireless data transmission module in the vehicle positioning system. The MC35i is the new generation dual modes GSM/GPRS engine, which enables data transmission over both SMS and GPRS. According to the current requirement by the project, the SMS mode is adopted. The experiment shows that under the control of AT89S52 MCU(MicroController Unit), the module can implement the sending and receiving of short messages with stability. The specific hardware design offers great possibilities for system upgrades. With slightly modification, the GPRS transmission can be achieved so that the function of the whole system can be extended.
