Broadband and Fast Carrier Cancellation for Backscattered RFID Communications

Ultrahigh frequency radio frequency identification (UHF RFID) uses backscattered electromagnetic (EM) modulation techniques to communicate between readers and tags. The suppression of the carrier signal leaked from the transmission channel to the receiving channel is the key factor that determines the reader's sensitivity. In this letter, a broadband, fast carrier cancellation technique is proposed. The reader system uses two transmission ports: one is for the transmission of the interrogating signal and carrier waves (CWs) and the other port can dynamically sample the leakage signal in the receiving channel and generate a cancellation signal with the same amplitude but opposite phase of the leakage. This technique is implemented using an AD9361 transceiver chip as RF front end and a field-programmable gate array (FPGA) board as the protocol and cancellation controller. Experiments demonstrate that a suppression of around 92 to 106 dB can be achieved within 0.5 ms in a UHF RFID system. The cancellation technique is also broadband; with a matched antenna, the experiment shows that cancellation can work effectively from 0.3 to 6 GHz.