An Adaptive Demodulation Structure for UHF RFID Readers Based on the Phase of Input Signal

In the Radio Frequency Identification (RFID) system, the phase of the tag signal is random in the realistic environment. We present an adaptive demodulation structure based on the phase of the input signal, in which the reader can always choose the channel which has the largest signal to noise ratio (SNR) from I-ch, Q-ch or I&Q-ch according to the phase of the tag signal. For the reason that the tag signal may contain a large DC-offset noise, the estimation accuracy is susceptible when the reader directly uses the amplitude of I-ch and Q-ch signals to obtain the phase of the tag signal. Thus, we propose an estimation method based on the correlation peaks of the I-ch and Q-ch signals and the computational complexity of the proposed method is very low. Theoretical and simulation results show that the SNR of the demodulated signal can be improved up to 3dB and the demodulation performance of the reader is improved effectively.