RFID receiver
First Claim
1. A method for detecting a data sequence from a sequence of symbols backscattered by an RFID tag, comprising:
- receiving the sequence of backscattered symbols at a receiving antenna, where each backscattered symbol has a random symbol duration, and a random phase resulting from random variations introduced by instability in the RFID backscatter process;
using a receiver to;
over sample the received symbols;
estimate the symbol duration, phase, and data value of each backscattered symbol that are most likely to have occurred using the samples the estimation comprising;
applying a set of matched filters to each sample, where each matched filter sums a different number of recent samples relative to the sample to which the matched filters are applied to obtain a set of matched filter outputs for each sample; and
estimating symbol duration, phase, and data value for each backscattered symbol that are most likely to have occurred using the set of matched filter outputs for each sample; and
determine a sequence of bits based upon the estimated data values of the backscattered symbols; and
outputting the sequence of bits from the receiver as the detected data sequence;
wherein estimating the symbol duration, phase, and the data value for each backscattered symbol comprises estimating the duration and phase of each symbol in the sequence of symbols to account for the random variations introduced by the instability in the RFID backscatter process.
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Accused Products
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 don'"'"'t change the determined probabilities.
58 Citations
23 Claims
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1. A method for detecting a data sequence from a sequence of symbols backscattered by an RFID tag, comprising:
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receiving the sequence of backscattered symbols at a receiving antenna, where each backscattered symbol has a random symbol duration, and a random phase resulting from random variations introduced by instability in the RFID backscatter process; using a receiver to; over sample the received symbols; estimate the symbol duration, phase, and data value of each backscattered symbol that are most likely to have occurred using the samples the estimation comprising; applying a set of matched filters to each sample, where each matched filter sums a different number of recent samples relative to the sample to which the matched filters are applied to obtain a set of matched filter outputs for each sample; and estimating symbol duration, phase, and data value for each backscattered symbol that are most likely to have occurred using the set of matched filter outputs for each sample; and determine a sequence of bits based upon the estimated data values of the backscattered symbols; and outputting the sequence of bits from the receiver as the detected data sequence; wherein estimating the symbol duration, phase, and the data value for each backscattered symbol comprises estimating the duration and phase of each symbol in the sequence of symbols to account for the random variations introduced by the instability in the RFID backscatter process. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for detecting a data sequence from a sequence of symbols backscattered by an RFID tag, comprising:
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receiving the sequence of backscattered symbols at a receiving antenna, where each backscattered symbol has a random symbol duration, and a random phase resulting from random variations introduced by instability in the RFID backscatter process; using a receiver to; over sample the received symbols to produce a set of samples; estimate data values for short sequences of consecutive symbols that are most likely to have occurred based upon the set of samples by applying a set of matched filters to the set of samples, where each matched filter sums a different number of recent samples, and estimating the data value and symbol duration for the backscattered symbols in the short sequences of consecutive symbols that are most likely to have occurred using the set of matched filter outputs, where the duration of each symbol and the phase of each symbol are assumed fixed during each short sequence and are assumed randomly varying between the short sequences due to the instability in the RFID backscatter process; and determine a sequence of bits by combining the estimates of short sequences of data values for consecutive symbols; and outputting the sequence of bits from the receiver as the detected data sequence. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. A method for detecting a data sequence from a sequence of symbols received from a transmitter, comprising:
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receiving the sequence of symbols at a receiving antenna, where each symbol has a random symbol duration, and a random phase resulting from random variations inherent to spectrally impure transmitter reference oscillators; using a receiver to; over sample the received symbols; estimate the symbol duration, phase, and data value of each symbol that are most likely to have occurred using the samples, the estimation comprising; applying a set of matched filters to each sample, where each matched filter sums a different number of recent samples relative to the sample to which the matched filters are applied to obtain a set of matched filter outputs for each sample; and estimating the symbol duration, phase, and data values of each symbol that are most likely to have occurred using the set of matched filter outputs for each sample; and determine a sequence of bits based upon the estimated data values of the symbol sequence; and outputting the sequence of bits from the receiver as the detected data sequence; wherein estimating symbol duration, phase, and the data value for each symbol comprises estimating the duration of each symbol in the sequence of symbols to account for the random variations introduced by spectrally impure transmitter reference oscillators. - View Dependent Claims (23)
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Specification