Reseach On The Key Technology Of The MIMO UHF RFID System

Ultra high frequency radio frequency identification(UHF RFID) is a kind of technology for data acquisition, which is widely used in national life.With its non-contact, long reading distance, high data rate and large information storage, The technology has become the new frontier of development. The reliability of UHF radio frequency identification system is controlled by multipath channel, and considering the use of multiple input multiple output(MIMO) in mobile communication technology to solve the problem of multipath fading, therefore, the application of MIMO technology in RFID system is considered as the solution for solving multipath problem in UHF RFID system. In the UHF RFID system using multiple antennas, both tag and reader use multiple antennas.So MIMO channel is formed between the reader and tag,and this is called MIMO UHF RFID system. The MIMO channel and RFID channel system has its own characteristics,so the combination of two technologies will lead the new channel model and the channel characteristic to be unknown. Therefore, the research of MIMO-RFID system channel has become a direction of scientific study.Taking this opportunity as the basis, this paper firstly described the structure and working principle of UHF RFID system. Then, it analyzes the multipath interference of UHF RFID system, and explore the possibility to solve the multipath problem with diversity techniques in MIMO.Furthermore, a MIMO UHF RFID system based on space-polarization diversity is analyzed, the analysis proved that the performance of MIMO UHF RFID system is superior to the traditional RFID system.Additionly, based on the MIMO channel in the space-time coding technology, the performance of MIMO UHF RFID system is analyzed.The article deduced the mathematical expressions of PEP and MIMO diversity gain in MIMO UHF RFID system, and the following conclusions is obtained from the research of PEP and the diversity gain:the maximum diversity gain of MIMO UHF RFID system is determined by the number of tag antenna.On the basis of OSTBC, this paper proposes an iterative orthogonal STBC type(IOSTBC). After theoretical analysis, the coding rate of IOSTBC is higher than the OSTBC at the price of the diversity gain..Finally, the QPSK simulation of OSTBC is carried out in MIMO UHF RFID by MATLAB software. Through the simulation, the theoretical results are confirmed. In addition, from the analysis of the simulation results, we can know how the number of receiving antennas N affects MIMO UHF RFID system. In the low SNR environment, the diversity gain of MIMO UHF RFID system increases with the N. When the number of tag antenna is the same, SNR threshold decreases with the increase of N. In this paper, the simulation of IOSTBC and OSTBC is carried out, and the error performance of IOSTBC is higher than that of OSTBC on the condition of 4 tag antennas.