Automobile wireless radio frequency identification system based on short-range wireless communication technology

1.3 System Power Supply

The power supply of the wireless radio frequency identification system is a combination of photovoltaic cells as daily power supply and lithium-ion batteries as backup batteries. Under good light conditions, the energy storage battery is charged by solar energy. A certain amount of light time every day can basically meet the daily work needs of the OBU, greatly extending the service life of the backup battery and the working life of the OBU. It is suitable for vehicles that often run outdoors and can collect sufficient sunlight for the photovoltaic cells to work.

1.4 System Development Environment

The system development environment of the wireless radio frequency identification system is as follows: 1) IAR Embedded Workbench for MSP430 compiler; 2) PADS PCB Design Solutions 2007 Bisi circuit board design tool.

2 System Program Design

The program adopts modular design and is written in C language. It mainly consists of 4 parts: main program module, communication program module, peripheral circuit processing module, interrupt and storage module. The main program mainly completes the initialization of the control unit, the configuration of various parameters, and the configuration and initialization of each peripheral module; the communication program module mainly handles the configuration of the RF chip and the 433 MHz transceiver processing; the peripheral circuit processing module mainly handles the system external LED indication, voltage detection, sound prompts, buttons and other processing; the interrupt and storage module mainly handles system interrupts and record storage. The main program flow is shown in Figure 4.

 

3 RF communication process

The communication process between OBU and BSS is divided into 3 steps: establishing a link, exchanging information and releasing the link, as shown in Figure 5.

 

Step 1: Establishing a connection The coordinate information of the OBU location and its ID code are stored in the Flash of the control unit MCU through preset parameters and are saved for a long time. BSS (base station system) uses the downlink to broadcast positioning (base station identification frame control) information to OBU in a loop, determine frame structure synchronization information and data link control information, etc. After the OBU that enters the effective communication area is activated, it requests to establish a connection and confirm the validity and sends a response message to the corresponding OBU, otherwise it will not respond; [page]

Step 2: Information exchange This design uses the method of detecting the strength of the radio frequency signal to determine whether the OBU has entered the service area. When the detected signal strength is greater than 1/2 of the maximum signal, the sender and receiver implement a wireless handshake, and at this time, the OBU is considered to have entered the service area. In this stage, all frames must carry the private link identification of the OBU and implement error control. For the judgment of the uplink and downlink of the OBU, the ID number can be used to determine whether it belongs to the same system. The OBU with an ID number that is not the same system is automatically deleted from the record. When the OBU reports information, the frequency hopping mechanism is used to randomly select a fixed channel in the service area for handshake communication to prevent channel congestion.

Step 3: Release the connection. When the detection signal strength is less than 1/2 of the maximum strength, it is considered that the car has left the station. After RSU and OBU complete all applications, they delete the link identifier and issue a dedicated communication link release instruction. The connection release timer releases the connection according to the confirmation of the application service.

4 Development of the communication process between OBU and BSS The communication

protocol establishes a simple three-layer protocol structure based on the seven-layer protocol model of the open system interconnection architecture, namely the physical layer, the data link layer and the application layer.

1) Physical layer The physical layer is mainly a communication signal standard. Since there is no unified standard for 433 MHz short-range wireless communication in the world, the physical layer defined by various standards is also different, as shown in Table 1. Figure 6 shows the Manchester encoding method.

 

2) Data link layer The data link layer controls the information exchange process between OBU and BSS, and stipulates the establishment and release of data link connection, the definition and frame synchronization of data frames, the control of frame data transmission, fault tolerance control, data link layer control and the exchange of link connection parameters. Data transmission is carried out by data frame transmission, as shown in Figure 7.

3) Application layer The application layer formulates standard user function programs, defines the format of communication messages between various applications, and provides an open message interface for other databases or applications to call.

5 Conclusion

The RFID system designed in this paper uses the MSP430 microcontroller of TI's low-power series, which is specially designed by TI for low-power battery-powered devices. The RF chip is also TI's CC1020, which has high integration, small size, low power consumption, and easy installation. It is suitable for the construction of vehicle parking-free monitoring and surveillance systems. The test results show that effective recognition can be achieved within a range of 300 m in complex road conditions (busy roads), and within a range of 500 m in line-of-sight conditions.