Ultra-high Frequency Rfid Baseband Signal Processing And Phase Estimation

In recent years, location technology is developing toward the direction of short-range and high-precision, the application environment is extended from outdoor to indoor, with the emergence of many effective indoor positioning technology. RFID location technology won much widespread attention with its features such as non-contact, automatic identification and so on. Passive UHF RFID also has the far recognition distance, low power, low cost and other significant advantages, with good development prospects.Currently, a lot of research work has already been done on the Passive UHF RFID location technology, mainly in location models and localization algorithms. The positioning is based on two kinds of parameters, attenuation and propagation delay. However in practice, because of the impact of multi-path fading effect, these two methods are especially vulnerable to interference and the data to be measured made very high demands for the receiver as the received signal is so weak that can hardly be detected in engineering.Our group proposed a new solution to measure distance based on phase difference estimation of subcarrier in UHF RFID, which measures the distance between reader and tag by measuring the phase difference of the received signal and the transmitted signal. With regard to the special application environment, this paper analyzed the characteristics of passive RFID system in detail, investigated the effect of all processing nodes to the signal waveform and the additional phase shift. In the light of the different measuring parameters, compared the principles and performances of various positioning methods, meanwhile focused on the key issues of the positioning technology based on phase measurement, put forward the phase difference estimation scheme suited for this solution, did some simulationvwork and obtained a lot of useful data. In order to expand the dynamic range of distance measurement, this paper presents a mode involving variable dual wave, one is longer and the other is shorter, to ensure the accuracy of the short distance measurement in particular.