Radio Frequency Identification (RFID) RFID is a non-contact automatic identification technology. Its basic principle is to use the RF signal and spatial coupling (inductance and electromagnetic coupling) transmission characteristics to achieve automatic identification of the identified object. The RFID system generally consists of two parts. , radio frequency tag (Tag) and radio frequency reader (Reader). In RFID applications, an electronic tag is attached to an identified object. When the identified item with the RF tag enters the readable range of the reader, the reader automatically reads the information agreed upon in the RF tag in a contactless manner. It is taken out to realize the function of automatically identifying items and collecting item mark information.
RFID technology has broad application prospects in the production, retail, logistics and transportation industries. In order to solve the problem of visual dynamic monitoring of logistics materials in the process of requesting, transporting and distributing, RFID technology is widely used in the field of military logistics. The basic usage is to install a radio frequency reader network in warehouses, terminals, stations and important traffic intersections. Nodes, when the military materials with radio frequency tags pass, the relevant material information, transportation information and safety information are automatically collected and uploaded, realizing the visual monitoring of the logistics material supply chain.
1 RF reader function requirements
The RF reader is used to read and write various types of information stored in the RF tag from a long distance. Consider the ability to monitor materials during transportation. The RF reader is required to adapt to the field work environment. Designed with reliable anti-jamming and protection measures
The main performance requirements of the RF reader are as follows:
(1) Omnidirectional radio frequency tag identification and reading and writing functions;
(2) High-speed data processing capabilities:
(3) Diversified data communication interface design:
(4) It can adapt to the rapid reading of radio frequency tags under high-speed motion:
(5) For use in AC/DC power supply, consider the vehicle-based design;
(6) Perfect anti-interference, lightning protection and surge measures;
(7) Software middleware development, configuration, and operation are convenient and fast.
2 reader structure
According to the functional requirements, the design of the RF reader is mainly composed of the control module, the RF transceiver module, the antenna unit, the communication interface module and the power module. As shown in Figure 1. The control module is based on NXP's LPC23 series of high-performance ARM7 embedded microcontrollers (MCUs). Built-in μC/OS-II multitasking operating system. It constitutes a real-time multi-task high-speed data processing platform, and implements functions such as radio frequency control, air protocol, data storage, Ethernet protocol, and serial port communication through peripheral circuits.
The RF reader is located between the RF tag and the software middleware and is the main carrier of the data link layer and the media access layer protocol stack. High-speed, large-capacity data processing capabilities and real-time multitasking control are required. To this end, the reader designed an embedded real-time multitasking platform composed of a 32-bit high-speed MCU+FP-GA+IxC/OS-II multitasking operating system. The platform is reliable, stable, and has a rich peripheral interface and good scalability. It effectively ensures the fast collection, processing and exchange of information. The RF transceiver module completes the carrier generation and air signaling modulation/demodulation functions. The two antennas of the antenna unit are arranged perpendicularly to each other. Connected to the RF transceiver circuit via a small RF cable. It realizes the function of reading and writing the RF signal in the omnidirectional direction of the field. The communication interface module provides three communication interfaces: RS232, RS485 and Ethernet. The power module provides reliable AC and DC power supply protection for the hardware and software system.
3 hardware system design
3.1 MCP860T embedded processor based on PowerPC system
In the hardware system design of the RF reader, the performance of the embedded microprocessor is undoubtedly a key factor affecting the performance of the entire device. According to the function and performance requirements of the system, after comparison, the MCU adopts the 32-bit LPC2387 ARM7 microcontroller of NXP, and the best working frequency reaches 72MHz, which can realize high-speed throughput transmission of data, and the system has strong fast response capability. . The LPC2387 is a peripheral resource-rich controller. Integrated 512KBFlash Rom.98KB SRAM. Hardware can encrypt program code space to maximize the protection of developers' intellectual property and ensure the security of military applications. The controller integrates 8 types of 15 serial communication interfaces. Including 1 10/100Mb/sEthernet. Industrial PHY.1 USB2.0 full speed (12Mb/s) data interface, 2 CAN interfaces, 4 UART controllers (UART1 complies with 16C550 industry standard, UART3 supports IrDA mode), 3-channel high-speed I2C bus, the highest data transmission speed is 400kb/s.1 PS. The 1 channel SPI and 2 buffered SSP bus rich connection VI meet the needs of data communication and peripheral expansion: LPC2387 supports SD/MMC interface, which provides guarantee for the storage of a large amount of configuration information and temporary material information. The temperature is -40~C~+85~C, and the LQFP100 package meets the requirements of wide operating temperature and small size for military applications. In addition, the LPC2387 provides a watchdog timer, four 32-bit timer/counters, and rich GPIO resources.
3.2
Using FPGA to implement complex logic control FPGA adopts LatTIce LFXP3C logic device, which mainly completes 6 functions: realizes interface with CPU, performs system interrupt processing, realizes multi-channel data encoding and decoding, completes control of RF board switch, ADC Control section and LED control section.
Because the FPGA is used to realize the digital circuit codec function, the reliability of the system is greatly improved by comparing the software codec.
3.3 Communication interface and protection measures
RF transceiver communication interfaces are Ethernet, RS-485 and RS-232. In order to ensure reliable data transmission, the equipment adapts to the field environment, and various types of interfaces are designed with protection circuits.
The protection circuit of the Ethernet interface is divided into two levels: the discharge tube and the TVS array chip, which can protect against the impact of lightning strikes and surges on the network isolation transformer. The TVS array chip is mainly used in this circuit because of the TVS diode junction capacitance designed inside the chip. Smaller. Can greatly reduce the impact on high-speed network data
The RS-232 and RS-485 protection circuits are divided into three levels of protection: self-recovery fuses, discharge tubes and TVS diodes to protect against overcurrent, lightning strikes and surges.
3.4 Reliable power supply circuit design
The power module provides power supply for each part of the internal circuit of the reader. The reader has AC and DC power supply modes. The AC power circuit is designed for wide voltage (90~260V) input, and the DC voltage input range is 12~24V. The scope of adaptation is wide. To improve the reliability of the system. The power module uses mature AC/DC and DC/DC.
The power module filters, steps down, and stabilizes the external AC and DC power supply.
Both ac and dc varistors, ceramic gas discharge tubes and mains filters are added. The varistor and the ceramic gas discharge tube mainly play the role of overvoltage protection, and the power filter can filter the high frequency interference signal of the power supply to ensure that the system can still work normally under the harsh power supply environment.
The power processing circuit is also designed with a transient voltage protection circuit to effectively protect the unit circuit of the reader.
3.5 antenna diversity technology design
The design of the low frequency receiver in the RF reader adopts the technique of antenna diversity reception in two mutually perpendicular directions, so that the RF tag can be reliably activated when entering the excitation magnetic field from either direction.
The dual-channel diversity receiving and transmitting technology used by the reader ensures that the reading area has no directionality and no blind zone. These two antenna diversity technologies successfully solve the multipath effect problem of data transmission and reception under high-speed moving state of the tag, effectively improve the accuracy of recognition, and realize high-speed dynamic acquisition of material information.
4 software system features
The software system adopts the open source μC/OS-II embedded operating system as the management platform. It has strong stability and safety and is compact. The software system also takes many security technical measures, including access control for read and write, subsystem with protection, audit trail, core authorization, and so on. Provide users with the necessary security.
The function and interface control function system provided by the RF reader is shown in Figure 2.
5 Conclusion
This paper presents a design scheme of RF reader based on MCU+FPGA. The solution has the characteristics of high data processing speed, rich communication and control interfaces, and simple software development and configuration. The military radio frequency identification reader developed by this has passed the appraisal of relevant departments. And through application practice, the product is stable and reliable.
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