Decoding with memory in RFID system

• US 7,510,117 B2
• Filed: 06/04/2004
• Issued: 03/31/2009
• Est. Priority Date: 06/04/2004
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Esterberg, Aanand
• Primary Examiner(s): WALSH, DANIEL I
• Application Number:
  US10/861,073
• Publication Number:
  US 20050270185A1
• Time in Patent Office: 1,761 Days
• Field of Search: 434/317, 235/449, 235/435, 235/43, 235/487, 235/492, 235/444, 235/451, 235/493, 340/572.1, 340/10.1, 340/572.4, 340/10.3, 340/825.58, 340/825.64, 341/50, 375/641, 375/316
• US Class Current: 235/435
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Abstract

RFID readers, RFID tags, software, and methods decode a signal received in an RFID system. From received data, a decoder determines a number of possible test series for the output. In one embodiment, the decoder uses a memory of a previous sample to derive a subsequent sample in the test series, so as to ensure that all the test series are valid. A metric is then computed for how well each test series fits the received data. The metrics are compared to select for output the test series with the best fit. In a further embodiment, at least one of the metrics is further used to determine if a collision were present.

Claims

1. A radio frequency identification (RFID) reader comprising:

an antenna to receive a wireless signal;

a matched filter to derive a sequence of analog signal data from the wireless signal; and

a decoder that compares at least two test series of successive samples that correspond to the analog data, and to select one of the test series for outputting.

2. The RFID reader of claim 1, wherein

the series meet preset validity criteria.

3. The RFID reader of claim 1, wherein

the selected series is the one with the best fit with the sequence of analog data.

4. The RFID reader of claim 1, wherein

a first one of the samples has a value that depends on a value of a second one of the samples that occurs before the first sample in the same series.

5. The RFID reader of claim 1, wherein the decoder is adapted to

compute a distance metric for each of the series with respect to the sequence,

select one of the metrics, and

select for outputting the series corresponding to the selected metric.

6. The RFID reader of claim 5, wherein

the distance metric is computed from a sum aggregated from individual differences of values of the samples from the corresponding analog data.

7. The REID reader of claim 6, wherein

the sum is of the absolute values of the differences.

8. The RFID reader of claim 6, wherein

the sum is of the squared values of the differences.

9. The REID reader of claim 6, wherein

the selected metric is the one corresponding to the smallest sum.

10. The REID reader of claim 5, further comprising:

a first module to compute a Received Signal Strength Indicator (RSSI) from the received analog data sequence; and

a second module to output a detected collision if the computed RSSI exceeds a preset RSSI threshold and the selected metric exceeds a preset metric threshold.

11. The REID reader of claim 10, wherein the second module includes:

a first comparator to compare the computed RSSI to the RSSI threshold; and

a second comparator to compare the selected metric to the metric threshold.

12. An REID reading device comprising:

means for receiving a sequence of analog data;

means for deriving from the sequence at least two test series of successive samples that correspond to the analog data;

means for computing a distance metric for each of the test series with respect to the sequence;

means for selecting one of the metrics; and

means for outputting the test series corresponding to the selected metric.

13. The device of claim 12, wherein

the series meet preset validity criteria.

14. The device of claim 12, wherein

the output series is the one with the best fit with the sequence of analog data.

15. The device of claim 12, wherein

a first one of the samples has a value that depends on a value of a second one of the samples that occurs before the first sample in the same series.

16. The device of claim 12, wherein

the distance metric is computed from a sum aggregated from individual differences of values of the samples from the corresponding analog data.

17. The device of claim 16, wherein

the sum is of the absolute values of the differences.

18. The device of claim 16, wherein

the sum is of the squared values of the differences.

19. The device of claim 16, wherein

the selected metric is the one corresponding to the smallest sum.

20. The device of claim 12, further comprising:

means for computing a Received Signal Strength Indicator (RSSI) from the received analog data sequence; and

means for outputting a detected collision if the computed RSSI exceeds a preset RSSI threshold and if the selected metric exceeds a preset metric threshold.

21. The device of claim 20, further comprising:

means for comparing the computed RSSI to the RSSI threshold.

22. The device of claim 20, further comprising:

means for comparing the selected metric to the metric threshold.

23. A method of using an REID reader comprising:

receiving a sequence of analog data;

deriving from the sequence at least two test series of successive samples that correspond to the analog data;

computing a distance metric for each of the test series with respect to the sequence;

selecting one of the metrics; and

outputting the test series corresponding to the selected metric.

24. The method of claim 23, wherein

the series meet preset validity criteria.

25. The method of claim 23, wherein

the output series is the one with the best fit with the sequence of analog data.

26. The method of claim 23, wherein

a first one of the samples has a value that depends on a value of a second one of the samples that occurs before the first sample in the same series.

27. The method of claim 23, wherein

the distance metric is computed from a sum aggregated from individual differences of values of the samples from the corresponding analog data.

28. The method of claim 27, wherein

the sum is of the absolute values of the differences.

29. The method of claim 27, wherein

the sum is of the squared values of the differences.

30. The method of claim 27, wherein

the selected metric is the one corresponding to the smallest sum.

31. The method of claim 23, further comprising:

computing a Received Signal Strength Indicator (RSSI) from the received analog data sequence; and

outputting a detected collision if the computed RSSI exceeds a preset RSSI threshold and if the selected metric exceeds a preset metric threshold.

32. The method of claim 31, further comprising:

comparing the computed RSSI to the RSSI threshold.

33. The method of claim 31, further comprising:

comparing the selected metric to the metric threshold.