In modern life, electronic technology is increasingly used to complete information inquiry. The common technologies are mainly bar code technology and RFID (radio frequency idenTIficaTIon) technology. Barcode technology is widely used, but the limitations are also very prominent. For example, the contents of the barcode label cannot be modified. The barcode label must be clean and wear-free. The reader should maintain an appropriate angle when reading/writing the barcode. The reader and the barcode must be visible. RFID is the abbreviation of radio frequency identification. It is a non-contact automatic identification technology. It uses radio technology to establish communication between the reader and the electronic tag, realizes contactless information transmission, and achieves the identification purpose through the transmitted information. . Now RFID technology has been widely used in data collection and processing in production, logistics, transportation, medical, tracking and other applications. The advantages of RFID technology are more prominent. For example, the tag information can be modified, and it can be read at a long distance in a harsh environment, and multiple tags can be processed at the same time.
Depending on the implementation, RFID technology can be divided into passive RFID technology and active RFlD technology. The research and application of passive RFlD technology are relatively mature. All the power supplies required for the operation of electronic tags in the system are obtained by converting the electromagnetic waves transmitted by the received readers. The transmit power of the reader is generally large. The electronic tag in the active RFID technology system has a battery, which can provide power for all devices to work; the reader has lower transmission power requirements, and the effective reading distance is also increased, which is very important when tracking and identifying high-value goods. it works.
l Design of active RFID system1.1 System Structure
The active RFID system consists of an active electronic tag (tag), a reader and a computer. The active electronic tag consists of a coupling element and a chip. Each tag has a unique electronic code (EPC) and is stored with The electronic data of the agreed format; the device for reading the electronic tag information by the reader/writer can be designed as a handheld or fixed type; the computer (host computer) is used for data management and data processing, and its system structure is shown in FIG.
In practical applications, the reader/writer sends a radio frequency signal of a certain frequency, and the electronic tag attached to the surface of the object to be identified receives the radio frequency signal, and then performs corresponding actions. Usually, the reader is connected to the computer, and the information sent back by the electronic tag is read and decoded by the reader and sent to the computer for further processing, thereby achieving the purpose of automatically identifying the body.
1.2 Hardware Design
RFID systems can be divided into different types according to different standards. According to the operating frequency used by the RFID system, it can be divided into four categories: low frequency (LF, 30 ~ 300 kHz), high frequency (HF, 3 ~ 30 MHz), ultra high frequency (UHF, 300 ~ 968 MHz) and microwave (UWF, 2.4 to 5.8 GHz). According to the literature and the analysis and comparison of the advantages and disadvantages of RFID systems in different frequency bands, combined with the requirements of the subject, the tags can be automatically monitored within 50 m, and the data can be read and written. The RFID system with a frequency band of 2.4 GHz is selected. research. The 2.4 GHz frequency has less attenuation and a long transmission distance. It has the characteristics of fast data transmission, high data throughput and strong multi-target capability. At the same time, the 2.4 GHz ISM band is over 83 MHz wide and has 125 channels, which can meet the needs of multi-frequency and frequency hopping, and increase the anti-interference ability of wireless communication.
The main chip for active electronic tags and readers is selected from Texas Instruments' CC2510. The device includes a high performance, low power 8051 microcontroller (MCU) and UHF RF transceiver with integrated 32 KB in system programmable FLASH and embedded 4 KB SRAM with power amplifier (PA), low noise Amplifier (LNA), modem (MODEM) and other functions, QLP package, small size (6 mm & TImes; 6 mm), support popular frequency hopping technology, program control data transmission rate, the fastest data transmission rate of 500 Kb /s. The CC2510 is used in the system, which has the advantages of low power consumption, low cost, and simple and reliable peripheral circuits. In addition, the CC2510 can be configured with frequency hopping communication methods, transmit power and stored procedures for frequency change, read/write distance control and multiple security protocols for multiple security levels.
The active electronic tag consists of the CC2510 wireless transceiver and control module and antenna. Data exchange with the reader by electromagnetic waves. The reader is composed of CC2510 wireless transceiver and control module, antenna, USB interface conversion module and interface circuit. The reader is connected to the host computer through a USB interface and is used to receive data transmitted by the active electronic tag.
1.3 Software Design
The software plays a controlling role in the entire active RFID system and is the soul of coordinating the various parts of the hardware. Mainly related to PC man-machine interface and RFID system software design, PC and reader communication software design, reader RF and active electronic tag RF communication software design.
PC machine software mainly manages the RFID system database, using C "compilation, the database uses SQL Setver 2005. The PC operates the reader through the interface circuit. This part is compiled with VB. The data between the reader and the tag Communication is compiled by standard C language and assembly. In the single-chip computer, the design of communication software similar to PC and MCU is described in many cases, so I won't go into details here. This paper focuses on the design of reliable communication between readers and active electronic tags.
2 Reliable communication researchIn active RFID systems, reliable communication is the most important part, and it almost affects the performance of the entire system. Here, data reliable communication is studied from four aspects: frame identification replacement algorithm, data frame structure, anti-collision processing and retransmission mechanism.
2.1 Frame ID Replacement Algorithm
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