The Research On Extraction Method Of RFID Signals Based On Smart Antenna

RFID (radio frequency identification) is an auto identification technology based on wireless communication. RFID system in UHF and microwave band has merits of fast read-write speed, large memory capacity, long recognition distance and multi-tags identification. It has wide application prospect.Firstly, the characteristics of wave propagation in RFID system communication are researched and several RFID signals propagation models are derived, such as indoor propagation model, outdoor propagation model and small scale multipath propagation model. Bit error rate models and formulas for bit error rate are presented by analyzing different modulation models of RFID signals.By adapting spatial spectrum estimation and digital beamforming based on smart antenna technique, a novel extraction and identification method of radio frequency identification (RFID) signals in UHF and microwave band is presented, in order to resolve the difficulty of RFID signals extraction and identification in the noise interference, coherent multi-path and multiple-tags environments. Based on uniform linear array, by applying spatial spectrum estimation algorithm, such as multiple signal classification (MUSIC) algorithm, direction-of-arrivals (DOAs) of RFID signals are estimated properly in the noise interference and multiple-tags environments. By adopting forward-backward spatial smoothing or weighted spatial smoothing technique and taking advantage of the correlation information of subarray output, the direction-of-arrivals (DOAs) of RFID signals are estimated in coherent multi-path environment.At last, by adapting digital beamforming technique and applying the DOAs, weights are adjusted using linear constrained minimum variance (LCMV) criterion or eigenspace-based (ESB) algorithm. Followed by optimal weight vector of digital beamformer, adaptive directional beam is formed to identify RFID signals. The approach can form deep dulls in the directions of interferers and get better performance of DOAs of RFID signals estimation. After reducing the error caused by multipath, RFID signals can be identified and extracted successfully. Simulation results demonstrate that the identification and extraction method possesses a lower SNR threshold as well as a better signals identification and anti-collision capability.