Methods for Recovering RFID Data Based Upon Probability Using an RFID Receiver

Abstract

RFID data signals from RFID tags may be recovered by determining the probabilities of transitions between data states between a series of a pairs of signal samples using a set of predetermined probabilities related to data, timing, baud rate and/or phase variables affecting the received signal and processing those determined probabilities to determine the sequence of such transitions that has the highest probability of occurrence. A second set of predetermined probabilities related to transitions in the opposite direction may be used to sequence in a reverse direction. The determination of the sequence representing the RFID tag data may be iterated in both directions until further iterations do not change the determined probabilities.

What is claimed: 
     
         1 . A method for operating an RFID receiver, comprising:
 sampling a received signal including RFID data signals from at least one interrogated RFID tag;   providing a set of predetermined probabilities of a received signal sample making a specific transition between data states, each predetermined probability related to data, timing and baud rate variables affecting the received signal;   applying the set of predetermined probabilities to each of a plurality of pairs of signal samples to determine probabilities of the received signal having made the specific transitions between each of the signal samples in that pair; and   processing the determined probabilities to recover RFID data signals by determining a sequence of transitions in the received signal having the highest probability of occurrence.   
     
     
         2 . The method of  claim 1  wherein each of the predetermined probabilities is also related to a phase variable affecting the received signal. 
     
     
         3 . The method of  claim 2  wherein the applying the set of predetermined probabilities, and the processing the determined probabilities, are iterated to recover the RFID data signals. 
     
     
         4 . The method of  claim 3  wherein the set of predetermined probabilities are related to transitions in a first direction and a second opposite direction, the method further comprising:
 providing a first set of predetermined probabilities related to transitions in a first direction; 
 applying the first set of predetermined probabilities to each of a plurality of pairs of signal samples to determine first probabilities of the received signal making the specific transitions between each of the signal samples in that pair in the first direction;
 providing a second set of predetermined probabilities related to transitions in the second opposite direction; and 
 applying the second set of predetermined probabilities to each of the plurality of pairs of signal samples to determine second probabilities of the received signal making the specific transitions between each of the signal samples in that pair in the second opposite direction; and 
 processing the first and second determined probabilities to recover the RFID signals. 
 
 
     
     
         5 . The method of  claim 4  wherein applying the first and second set of predetermined probabilities, and the processing the first and second determined probabilities, are iterated to recover the RFID data signals. 
     
     
         6 . The method of  claim 5  wherein the applying and processing are iterated until further iterations do not further change the first or second determined probabilities.