Short Range Wireless Communication Applied In Its Electronic Toll Collection System

1. IntroductionWith the need of the road transportation and the development of modern high technology, Intelligent Transportation System (ITS) is developed, and it is a new road and traffic system. ITS integrates advanced information technology, navigation technology, data transferring technology, automatic control technology, image analysis technology, computer network and information processing technology, and applies to traffic management system, and establishes an effective, real-time, all-directions transportation management system.The research of the intelligence transportation system must make out the layer, lay particular emphasis on, and carry on diversified development. According to the actual circumstance of our country, we should synthesize to consider various transport methods, such as city transportation, highway, railroad, sea mail andaviation...etc, draw up the stage target and have the leading field.In regard to currently, the research of the Chinese ITS should be divided into two parts:Build up ETC, adopt the short distance wireless communication technique, combine the existing Internet technique, will bring huge social and economic performance.Its social and economic performances have:1. Increasing the grade of service to highway transportation.2. Relieve the traffic jam, make the road transportation more safety.3. Increasing the efficiency of running, saving time and do good to the environmental protection.4. Easy to carry on the supervision to the whole circumstance of the highway's transportation.2 .Overall Scheme Of SystemThe object of this system is to make ETC reality for management of the highway system. The practical system is made of three units: On-vehicle Wireless Transmitting Unit, Road-aside Transmitting Unit, Center Station andInternet Managing Unit.The chief mission of the system is the design of On-vehicle Wireless Transmitting Unit and Road-aside Transmitting Unit. The process of concrete works are as followed: Whenever a car enters the toll station, the sensor fixed on orbit can feel the arrival of it and transmits the information to the center station. And then, the center station starts up the transmitting device of road-side to inform the on-vehicle machine to receive the data. When the on-vehicle machine receives them it will transmit a piece of affirming information and be ready for transmitting information. Afterwards, the on-vehicle machine transmits data information, address numbers and checkout information. When the center station receives them, the database managing system found the originalcar's information and wrote them into the relevant database according to the source address. Once the information interchanged successfully, the circuitry will be removed. When another car entered the toll station, the whole process will be repeated.The system was classified as the design of hardware and software.3. Realization Of The System's Hardware And SoftwareThe whole hardware system is made of three units.. The Center Station Network Management unit mainly includes local-area nerwork and center station database management unit. The Center Station Network Managing Unit mainly lies in the design of the software.lt is not the keystone of the system's design.However, the keystone is Wireless Transmitting Unit .It is classified as hardware design and software design.The hardware is the short range wireless data transmitting module whose type is nRF905. nRF905 is a single-chip radio transceiver for the 433/868/915 MHz ISM band. Power supply ranges froml.9 to 3.6V. The transceiver consists of a fully integrated frequency synthesiser, receiver chain with demodulator, a power amplifier, a crystal oscillator and a modulator. The ShockBurst feature automatically handles preamble and CRC. Configuration is easily programmable by using the SPI interface. Current consumption is very low, in transmit only 11mA at an output power of -lOdBm, and in receive mode 12.5mA. Built in power down modes makes power saving easily realizable.Integrated chip, MC1488 and MC1489, also can realize interchanging between TTL and RS-232.But, when using those chips they need two kinds of electrical source of 12V except for the +5V, which is not convenient, so it is a good idea to select the single power supplied and low power RS-232 chip and MAX3232.They have the character of low power, high corresponding velocity, various packaging formats, single power supplied and less periphery appliances.The MCU adopted a single-chip of AT89LV51 which is a low-voltage, high-performance CMOS 8-bit microcomputer. By combing a versatile 8-bit CPU with Flash on a monolithic chip, the AT89LV51 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications.For software, C51 language is chosen. The design of data frame, namely the design of communication protocol is the point of software. In addition, designing and improving error control arithmetic is included. Only after considering these factors well, the center station can receive exactly these information that sent by the bus sender. For data frame, something format like HDLC protocol is designed. With this kind of format, communication is carried by the means of information bag that has the stable format. Data frame is consist of control frame and information frame. The function of control frame is to be finished the control of link layer and guaranteed the system can work normally.An adaptive error control scheme with combination of FEC and ARQ is presented for error control. This kind of control scheme is displayed the advantage of different correct codes and it is efficient for system dependability, validity and error probability.4.ConclusionsThis paper discusses primarily the combination of short range wireless communication technology and intelligent transportation system. These have extensive application. In this paper, it's applied mostly in electronic toll collection system, which is realized by the development of data communication module.