This system is based on digital communication principle, using a wireless identification system constructed by integrated single-chip narrowband ultra-high frequency transceiver. The basic working principle and hardware design ideas of the wireless RF identification system are expounded, and the flow chart of the programming scheme is given. Design from low-power, efficient identification, and utility perspectives. Radio frequency identification tags for vehicles are designed. The test results show that the system can achieve effective identification within 300m in the complicated pavement condition (busy pavement), and 500 m range effective identification can be achieved under the varying conditions.
Internet of Things refers to various information sensor, such as sensors, RFIDs, global positioning systems, infrared sensors, laser scanners, gas sensors, and other devices and technologies, and collect any need to monitor in real time. Connecting, interacting objects or processes, collecting various needs of sound, light, electricity, biological, location, etc., a huge network formed with the Internet. Its purpose is to achieve objects, objects, people, all items and network connections, convenient to identify, manage, and control. This project is based on key issues of data acquisition, transmission and application in vehicle-in-vehicle network, and develops a new generation of vehicle RFIT based on short-range radio frequency communication technology. The system consists of a short-to-line wireless communication vehicle unit (Base Station System, BSS), a point-to-multi-point wireless recognition system (WIS), which can be used to cover within the base station coverage Vehicle identification and intelligent guidance.
1 system hardware design
The wireless RF identification system system is mainly composed of a control section, a radio frequency portion, and an external extension application portion. With low power MCUs, the integrated single-chip narrowband ultra-high frequency transceiver, built-in optimized design antennas. Power supply and high integration short distance wireless identification RF terminal (OBU) with advanced photovoltaic cells. This terminal is small, low power consumption, wide range of appropriate, and establishes an open protocol and standard interface for easy connection to existing systems or other systems.
Wireless RF Identification System System Working is shown in Figure 1.
1.1 control circuit design
The control unit adopts the industry's low power consumption to compare the MSP430 series produced by Ti Company, which is a 16-bit ultra-low-power mixed signal processor (Mired Signal PROESSOR) in Ti1996, which is actually Application requirements integrated many analog circuits, digital circuits, and microprocessors on one chip, providing a "single slice" solution. The working principle in the WIS system is the same, so it focuses on the OBU part design, which controls the part of the schematic shown in Figure 2.
The input voltage of the MSP430F2274 is 1.8 ~ 3.6V. When operating under 1 MHz clock conditions, the power consumption of the chip is about 200 to 400μA, and the minimum power consumption of the clock shutdown mode is only 0.1μA. Due to the different functional modules opened at the system, three different working modes of standby, operation, and dormancy effectively reduce system power consumption.
Wireless RF Identification System System uses two clock systems; basic clock systems and digital oscillator clock systems (DCO), using an external crystal oscillator (32 768 Hz). After the power-on reset, the MCU (MicroProgrammed Control Unit Microprogram) is first started to ensure that the program starts from the correct position to ensure that the crystal oscillator has sufficient starting and stable time. The software can then set the appropriate register control bits to determine the last system clock frequency. If the crystal oscillator is faulty when used as MCU clock MCLK, the DCO will start automatically to ensure the normal operation of the system; if the program runs, it can be reset by the watchdog. This design uses the upper peripheral module watchdog (WDT), analog comparator A, Timer A (Timer_a), Timer B (Timer_B), serial port USART, hardware multiplier, 10-bit / 12-bit ADC, SPI bus, etc. .
1.2 RF circuit
The RF portion employs TI CC1020 as a radio frequency control unit, which is a real single-chip narrow band ultra-high frequency transceiver in the industry. There are three modulation methods of FSK / GFSK / OOK, the minimum channel interval is 50 kHz, which can meet multi-channel Strict requirements of narrowband applications (402 ~ 470 MHz and 804 ~ 94O MHz band), multiple operating bands can freely switch, operating voltage 2.3 ~ 3.6 V, ideal for integration to extend to mobile devices as wireless digital or electronic labels. The chip complies with EN300 220.Arib STD-T67 and FCC CFR47 Part15 specification.
The selection of the load frequency frequency is 430 MHz as the operating frequency. This band is the ISM band, which is in line with the national wireless management committee standard without requiring frequency points. With the modulation method of FSK, it has a higher anti-interference ability and low error rate. The forward error correction channel coding technology is used, and the ability of data anti-sudden interference and random interference, and the channel bit error rate is 10-2. When the actual bit error rate is 10-5 ~ 10-6. At an open-wide grounding condition, the baud rate is 2A KBS, the large suction cup antenna (length 2m, gain 7.8 dB distance ground height 2m) is 800 m. The RF chip standard configuration provides 8 channels to meet a variety of communication portfolios. The communication stability and anti-interference resistance are enhanced due to narrowband communication technology.
1.3 system power supply
The radio frequency identification system power supply portion is combined as a spare battery as a spare battery as a spare battery by a photovoltaic battery. The energy storage battery is charged by solar energy under the conditions of light, and a certain illumination time must be substantially satisfied with the daily operation of OBU, which greatly prolongs the service life of the spare battery while prolonging OBU's work life. Suitable for vehicles that are often run outdoors, you can collect enough sunlight supply-to-light battery work.
1.4 system development environment
The wireless RF identification system system development environment is as follows: 1) IAR Embedded Workbench for MSP430 compiler; 2) PADS PCB Design Solutions 2007 B. Circuit Board Design Tools.
2 system program design
The program uses modular design and writes in C language. Mainly consisting 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 and initialization of various parameters, etc., and the communication program module mainly processes the configuration of the RF chip and 433 MHz transmission and reception processing; the peripheral circuit processing module mainly indicates the external LED of the system. Voltage detection, sound prompts in button and other processing; interrupt and storage modules primarily handle system interrupts and record storage.
3 RF communication process
OBU and BSS communication process are divided into 3 steps: establish links, information exchange, and release links.
Step 1: Establish the coordinate information of the location of the OBU and its ID code stored in the FLASH of the control unit MCU by preset parameters, and saved for a long time. BSS (base station system) utilizes a downlink to the OBU loop broadcast transmission positioning (base station identification frame control) information, determines information such as frame structure synchronization information, and data link control, and enters the OBU within the effective communication area to be activated to establish a connection And perform validity confirmation and send response information to the corresponding OBU, otherwise it will not respond;
Step 2: Information exchange This design uses methods to detect RF signal intensity sizes to determine if the OBU enters the service area. When the detection signal strength is greater than 1/2 of the maximum signal, the transmit and receive the wireless handshake. At this time, it is considered that the OBU has entered the service. Region. In this stage, all frames must have an OBU's private link identifier and perform errors control. The determination of the downstream of the OBU can determine if it belongs to the same system, not the OBU of the ID number of the same system, is automatically deleted from the record. When the OBU is reported, the frequency hopping mechanism is used, randomly selects a fixed channel of the service area to hand over, preventing the channel blockage.
Step 3: The release connection also uses the detection signal intensity less than 1/2 of the maximum strength, it is considered that the car has been away from the station. After all applications, RSUs are completed, delete and link identification, issue a dedicated communication link release instruction, and the connection release timer is released according to the application service to release this connection.
4 OBU and BSS communication process development
The communication protocol establishes three simple protocol structures, namely the physical layer, data link layer, and application layer based on the open system interconnected architecture.
1) The physical layer physics layer is mainly standard, and because the standards that have not yet formed a unified 433 MHz short-range wireless communication unified, the physical layers of various standards are not the same, as shown in Table 1. Figure 6 is a Manchester coding method.
2) The data link layer data link layer controls the information exchange process between the OBU and BSS, the establishment and release of the data link connection, the definition of the data frame and the frame synchronization, the control, fault tolerance control, data of the frame data transmission, data The parameter exchange of link layer control and link connection is specified. Data transfer is performed in data frame transmission.
3) Application layer Application layer Develop standard user function programs, defines the format of communication messages between various applications, providing open message interfaces for other databases or applications.
5 Conclusion
The RF Identification System designed in this paper employs the TI low-power series of MSP430 microcontrollers, which is designed for low power consumption for battery-powered equipment. The RF chip is also TI company CC1020, high integration, small size, low power consumption, easy to install, suitable for construction vehicles free parking monitoring and monitoring system. Test results show that there is an effect identification in a 300 m range (busy pavement), and the sight of 500 m is recognized within 500 m.
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