Tag-Side Frequency Division Multiplexing RFID System with Harmonic Suppression

With the increasing applications of ultra-high frequency (UHF) radio-frequency identification (RFID) in various fields that require rapid identification of a large number of tags, improving the throughput of RFID systems has become the research focus currently. By modulating tag signals to different Miller-subcarrier frequencies, the frequency division multiple access (FDMA) RFID system with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$M$</tex>-values of 2 and 6 has been proposed. Furthermore, after analyzing the spectrum of the Miller-coded signal, the tag harmonic signal suppression algorithm, based on the Costas loop, has been proposed, which reconstructs the harmonic interference signal of the first channel and subtracts the interference in the second channel. The suppression performance of the algorithm can reach 14 dB and 11 dB through simulation and experiment. The reader that supports simultaneous query for tags has been designed and developed utilizing the Xilinx XC7Z020 chip and can successfully receive the tag signals in two channels.