Analysis And Research Of The Key Test Technologies Of The Ultra-high Frequency Radio Frequency Identification Systems

With the development of information technology, the global Internet of Things (IOT) was emerging during the past decade. The Radio Frequency Identification (RFID) is one of the key technologies to IOT. It’s a kind of non-contact automatic identification technology using radio frequency signals to transfer information. Currently it’s the most influential information identification technology with the exception of the bar code technology. RFID is an important branch of the automatic identification technology, and becomes the hot research field and catches widespread attention. The Ultra-High Frequency(UHF) RFID tags have many prominent characteristics, such as:smaller size antenna, higher identification speed, larger identification range than other type of tags, hense the UHF RFID is obtaining more and more applications in our daily life, such as Electronic Toll Collection (ETC).logistic supply chain management, item tracking, and so on. The various environments affect the identifying performance results of the RFID systems. This requires the RFID systems have better performance. More and more people focus on the RFID performance research and performance measurement. It is one of challenge topic to research and design a simple-operating and well-functioned test instrument.Because of the particular characteristics, the UHF RFID working principles, identification performance, testing theories and measurement methods are analyzed. The key questions such as:the impact of dynamic parameters and material on the performance, radar cross section(RCS)measurement method, anti-collision efficiency test are studied in this paper. A series of ultra-high frequency RFID products performance test principles and methods are proposed.Firstly, the basic theory of RFID, test principles, relevant RFID standards and test apparatus architecture for radio frequency identification are described. According to the current situation of RFID test technology, a well-functioned test platform is built based on the virtual instrument technology and software defined radio (SDR) technology. The platform has following functions:RFID’s reading performance test, air interface conformance test, electrical properties test, sniffer, and so on. It supports multi-protocol and user-defined standards test. The platform has the ability for test of reliability, compatibility and stability and it can provide good guidance and reference for the RFID researchers and clients. Secondly, based on wireless communication theory and the RFID backscattering principles, the impact of RFID system communication parameters changes on system performance is analyzed. With the RFID test platform, a new test method using combination parameters to test RFID performance is presented. It finds that Tari, modulation depth and pulse duty cycle (pulse width. PW) have great impact on the RFID link power by discussion the ISO/IEC18000-6type C protocol. Through a series of combination of parameters tests, the optimized UHF RFID communication parameters combination for optimization performance is gotten. The theory and test results show that, small Tari, approximately50%duty cycle and high modulation index are the optimal combination. Thus the tag antenna will receive the maximum power and system will have the maximum read range.Thirdly, the tag’s power reflection coefficient, power transmission coefficient, match state, antenna gain and chip sensitivity have great influence on the tag’s received power which leads to the read range and read rate changed. RFID system reading performances are measured under a variety of different materials which will affect the tag’s antenna gain and resistance. Through setting the tag with different velocities, different attached locations, different dielectric material and antenna polarization angle to test and research the RFID system’s read performance, we evaluate the tag’s performance under different environment factors. The test results show that the starting point and movement speed of the tag and the transmitting time will cause different reading performance. The distance between the tag and media, which the tag attached to, has a strengthening or weakening influence on the system’s performance. The metal will cause tag antenna detuning. Usually, dipole antenna will be completely unable to work when it is too closed to metals and liquids.Finally, a novel measurement method is proposed to test the RFID system’s anti-collision efficiency. This method adopts the Markov chain model to simulate the RFID anti-collision algorithm process and this can quantify the RFID system identifying performance as system’s read efficiency and recognition speed. RFID anti-collision process is a random process. The adaptive Q-algorithm which based on the dynamic ALOHA algorithm is a general anti-collision algorithm used in the UHF RFID systems. In every frame RFID communication sequence, the process that tag selects the slot is a binomial random process. The combination state (Q, n) is defined, where the parameter Q is the tag’s slot random number and value n is the number of the remaining tags in the reader’s reading range. Because of the combined state (Q. n). the process of derivation indicates that the state transfer is a Markov chain model. Then we used the Markov chain to simulate the combination state to adjust the parameter Q and value n effectively. The state transfer process is realized with virtual instrument platform to achieve anti-collision efficiency. Simulation and test show that the simulation and test results are consistent well when it use the Markov chain model to simulate the anti-collision process.