Short distance wireless communication in the design of RFID system for automobile applications
source: 21IC time: 2012-05-15
3 RF communication process of
OBU and BSS communication process consists of 3 steps: establishing a link, information exchange and release link, as shown in figure 5.
The first step: to connect the OBU location coordinate information and ID code through the preset parameters stored in the control unit MCU Flash, and long-term preservation. BSS (base station system) using downlink positioning to the OBU circulation broadcast (base station identification frame control) information, determine the frame synchronization information and data link control, into the effective communication within the region of the OBU is activated after the request to establish a connection and to confirm the effectiveness and sends a response message to the corresponding OBU, or no response ;
The second step: information exchange this design uses the method of detecting the RF signal strength to determine whether OBU enters the service area, the detection signal strength is greater than the maximum signal of 1 / 2, sending and receiving wireless handshake, now that OBU has entered into the service area. In this stage, the private link identifies all frame must be with OBU, and implement error control. For the OBU downlink judgment can be the ID to determine whether to belong to the same system, not a system with ID, OBU is automatically deleted from the record. Use of frequency hopping mechanism of OBU reporting information, a fixed channel random selection of the service area of a handshake communication, prevent the occurrence of channel blockage.
The third step: release the connection using the same detection signal intensity is less than the maximum intensity of 1 / 2, the car has left the station that. RSU and OBU to complete all the application, and delete link identifier, a dedicated communication link the release order, by the connection release timer according to application service confirmed that releases the connection.
4 OBU and BSS communication process to develop
A simple protocol structure of three layers of the communication protocol based on open system interconnection system structure of the seven layer model, the physical layer, data link layer and application layer.
1) physical layer physical layer is mainly the communication by the standard, as the current international has not yet formed about 433 MHz short distance wireless communication standard, physical layer standard definitions are not the same, as shown in table 1. Figure 6 is the Manchester coding.
2) data link layer data link layer control between OBU and BSS in the process of information exchange, a connection to a data link establishment and release, the data frame definition and frame synchronization, provides frame data transmission control, fault-tolerant control, data link layer control and link parameter exchange. Transmission of data in the data frame transmission, as shown in figure 7.
3) the user program application layer standards, communication messages between various application definition format, providing information interface open, for other databases or applications call.
5 ending
Radio frequency identification system is designed in this paper uses low power TI series MSP430 microcontroller, TI company specializing in battery powered equipment of low power consumption design. Radio frequency chip for the TI, CC1020, high integration, can realize small size and low power consumption, easy installation, suitable for the construction of vehicles without parking monitoring and control system. Test results show the complex road conditions (busy road) can be realized in the range of 300 m have the effect of recognition, distance can reach recognition in the range of 500 m.
