Least Squares Equalization for RFID

The continuously increasing number of applications for contactless smartcard systems also led to an increase of the amount of data that is transmitted from RFID tags to reader devices. This also requires high transmission speeds beyond one Mbit/s. Recently a prototype transmitting at 6.78Mbits/s was proposed. When transmitting data from an RFID tag to an RFID reader at such high transmission speeds the transmission suffers from inter-symbol interference. Contrary to standard communication scenarios this inter-symbol interference (ISI) is not caused by linear time invariant systems. Instead the transmission by load modulation can be interpreted as transmission through a non-linear system. For counteracting the intersymbol interference we propose a least squares (LS) equalization method. This method does not rely on the assumption that ISI is caused by a linear system but only constructs a linear system to correct ISI. We discuss the application of LS equalization for tag to reader communication by load modulation. We show how an LS equalizer can be incorporated in a RFID receiver and show by simulation that least squares equalization represents a feasible method for counteracting ISI in RFID systems. In addition simulation results concerning the effect of the training sequence length on the equalizer's performance are shown.