US 9,813,107 B2
Adaptive echo cancellation for RFID systems
Alastair Malarky, Petersburg (CA)
Assigned to Kapsch TrafficCom AG, Vienna (AT)
Filed by Kapsch TrafficCom AG, Vienna (AT)
Filed on May 28, 2014, as Appl. No. 14/288,851.
Prior Publication US 2014/0357202 A1, Dec. 4, 2014
Int. Cl. H04W 4/00 (2009.01); H04B 1/62 (2006.01); G06K 7/10 (2006.01); H04B 1/525 (2015.01)
CPC H04B 1/62 (2013.01) [G06K 7/10009 (2013.01); G06K 7/10346 (2013.01); H04W 4/008 (2013.01); H04B 1/525 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A method for echo cancellation in a reader for a passive RFID system, comprising:
transmitting a carrier signal and receiving a backscatter-modulated signal;
combining a cancel signal from an echo canceller with the backscatter-modulated signal to obtain a corrected signal;
downconverting the corrected signal to a baseband signal using the carrier signal;
after downconverting, feeding the baseband signal to a demodulator and to the echo canceller;
demodulating, by the demodulator, the baseband signal to obtain transponder information;
low-pass filtering, by the echo canceller, the baseband signal to remove modulated transponder information and produce an error signal; and
updating, by the echo canceller, the cancel signal, wherein the cancel signal is based upon the error signal, the carrier signal, and an estimated complex-valued transfer function, and wherein the cancel signal is proportional to an integral of the error signal over time divided by the estimated complex-valued transfer function or proportional to a cumulative sum of the error signal over a window of samples, divided by the estimated complex-valued transfer function.