Vector backscattered signal analysis of piggyback modulation for passive UHF RFID tags

Summary form only given, as follows. We describe a “piggyback modulation” technique to integrate sensing functions with existing standard passive UHF RFID tags through electromagnetic coupling. The vector analysis and measurement for backscattered signals with piggyback modulation is presented. Measuring both amplitude and phase of the backscattered wave makes advanced demodulations possible. Quasi-4-QAM demodulation is proposed to reduce the interferences between two independent data streams and improve the bit error rate.