Analysis And Measurement Of Ultra High Frequency Radio Frequency Identification Systems

In recent years, with the rapid development of internet of things (IOT), radio frequency identification (RFID) as one of the key technologies also achieved a new rapid development. RFID has a comprehensive application in many fields, such as industrial automation, transportation, identification and logistics etc, and expands its application scope continually. Meanwhile, the diversity of RFID standards and the particularity of the application also bring new demands and challenges to the test and the performance evaluation of RFID systems. Based on these, the delta radar cross section (delta RCS), bit error rate (BER), backscattered modulation and performance evaluation model of passive ultra high frequency (UHF) RFID systems are researched in this paper, which applies with electromagnetic fields, microwave and antennas testing and statistical analysis method. The main content and work are as follows:Firstly, this paper describes the basic theory, compositions and relevant standards of RFID systems. From the RFID testing principles, technologies and contents, the test methods and equipment of RFID system are researched. Then a test platform is built based on the virtual instrument technology, software defined radio (SDR) and RF test technologies. This paper introduces the key of the architectural form, the selection of hardware and the design of software, and gives some measuring methods and results for specific parameters. The results show that the platform has ability for test of reliability, compatibility and stability, which can complete the test of protocol and conformance, electrical properties, sniffer, and performance of system and application scenarios. It possesses the function of performance index analysis and visualization of performance evaluations, which supports multi-protocol and user-defined standards. It meets demand of public services such as RFID technology research and test, hardware product certification test, application test.Secondly, based on theory of RFID technology and backscatter, a relationship is derived between BER of backscatter link and the passive tag's delta RCS of state "0" and state "1". Therefore, this paper presents a new method which is adapted to analysis and test for BER of RFID communication link. A measurement system based on virtual instruments is built, and introduces vector subtraction methods to eliminate the errors brought by direct path leakage signal between transmit and receive antennas. Furthermore delta RCS and the BER of backscattered signal under different parameters are measured and analyzed. Experimental results show that the greater the transmitted power, the bigger the BER of backscatter link when the received power meet required sensitivity of readers and tags.Thirdly, optimal conditions for maximizing the effective received power of reader receiver for passive UHF RFID system are analyzed in this paper. The modulation index of tag backscatter link which affectied by mismatched impendence is discussed. Representations based on backscattered modulation index are derived, which are used for calculating normalized effective received power of reader receiver, lower boundary of signal noise ratio (SNR) for demodulated output signal and BER. Modulation index of backscatter link under different parameters is measured in open indoor environment. The measurement results show that the tag can be detected successfully when the modulation index of backscatter link is in 5% to 10%. When the modulation index of backscatter link is greater than 10 percent, the power absorbed by chip of tags is too low to work normally; the modulated signal of backscatter link cannot be demodulated and decoded correctly. When the modulation index is less than 5 percent, the effective power received by the receiver of readers is too low and the BER is too high, so the tags cannot be identified successfully.Finally, an experiment is designed to test the performance of RFID systems based on the theory of design of experiment (DOE). The RFID systems performance evaluation regression model is established with the key influence factors affecting the performance of RFID system which provided by statistical analysis method. The simulated applications scenarios are built to enhance the test efficiency and reduce the cost, which is based on the OPC technology of LabVIEW and real time control technology of PLC. An improved algorithm based on learning vector quantization (LVQ) and genetic algorithm (GA) is introduced in the prediction of the identification rate of RFID systems. The GA-LVQ algorithm takes advantage of the powerful learning, association, simple calculation and classification of LVQ and strong global search function, solving ability and robustness of GA. Meanwhile, a modified learning speed rule is introduced to guarantee the stability of learning algorithm; on the other hand, a dynamic adjustment method of crossover and mutation is introduced to avoid loss of excellent gene and population drab problems, and improve the learning efficiency. Experimental results show that the GA-LVQ algorithm has better precision, learning efficiency and robustness.