RFID reader systems detecting pilot tone

• US 8,350,665 B1
• Filed: 02/28/2012
• Issued: 01/08/2013
• Est. Priority Date: 05/24/2005
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Sundstrom, Kurt E., Cooper, Scott A., Sarajedini, Amir, Esterberg, Aanand, Humes, Todd E., Diorio, Christopher J.
• Primary Examiner(s): Mehmood, Jennifer
• Assistant Examiner(s): Mahase, Pameshanand
• Application Number:
  US13/407,742
• Time in Patent Office: 315 Days
• Field of Search: None
• US Class Current: 340/3.2
• 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 tags are commanded to generate a pilot tone in their backscatter. When the backscattered pilot tone is received in the reader, the pilot tone is used to estimate the tag period/frequency. Then, the estimate is used to seed and lock a symbol timing recovery loop, which provides a detected signal to one or more correlators for detecting the tag preamble. A delayed version of the received tag signal is compared against a baseline signal threshold established from the received signal to detect the pilot tone.

Claims

1. A method for a Radio Frequency Identification (RFID) reader to detect a pilot tone in a signal backscattered from an RFID tag, comprising:

generating a threshold from an ambient noise;

receiving the backscattered signal;

generating a baseline version by scaling the backscattered signal;

generating a delayed version by delaying the backscattered signal; and

detecting the pilot tone when the delayed version exceeds both the threshold and the baseline version.

2. The method of claim 1, in which the tag includes the pilot tone in its backscattered signal responsive to a command from the reader.

3. The method of claim 1, in which the baseline version has a waveform that rises to a cusp and then maintains substantially the cusp value, and the delaying is sufficiently long so that the pilot tone is detected after the cusp.

4. The method of claim 1, in which the pilot tone is detected only if both the delayed version and the baseline version exceed the threshold.

5. The method of claim 1, in which

the backscattered signal is received responsive to a command from the reader,

the command causes the tag to be silent during a silent period, and

the ambient noise is measured during the silent period.

6. The method of claim 1, further comprising using the detected pilot tone to estimate at least one of a frequency of the backscattered signal, a phase of the backscattered signal, and a symbol timing of the backscattered signal.

7. The method of claim 6, further comprising using the at least one estimate to detect at least one of a preamble and data in the backscattered signal.

8. A method for a Radio Frequency Identification (RFID) reader to detect a pilot tone in a signal backscattered from an RFID tag, comprising:

receiving the backscattered signal;

generating a baseline version by scaling the backscattered signal;

generating a delayed version by delaying the backscattered signal; and

detecting the pilot tone when the delayed version exceeds the baseline version.

9. The method of claim 8, further comprising generating a threshold from an ambient noise and in which the pilot tone is detected only if both the delayed version and the baseline version exceed the threshold.

10. The method of claim 8, in which the tag includes the pilot tone in its backscattered signal responsive to a command from the reader.

11. The method of claim 8, in which the baseline version has a waveform that rises to a cusp and then maintains substantially the cusp value, and the delaying is sufficiently long so that the pilot tone is detected after the cusp.

12. The method of claim 9, in which

the backscattered signal is received responsive to a command from the reader,

the command causes the tag to be silent during a silent period, and

the ambient noise is measured during the silent period.

13. The method of claim 8, further comprising using the detected pilot tone to estimate at least one of a frequency of the backscattered signal, a phase of the backscattered signal, and a symbol timing of the backscattered signal.

14. The method of claim 8, further comprising using the at least one estimate to detect at least one of a preamble and data in the backscattered signal.

15. A Radio Frequency Identification (RFID) reader configured to detect a pilot tone in a signal backscattered from an RFID tag, the reader comprising:

a memory; and

a signal-processing module configured to;

receive the backscattered signal;

generate a baseline version by scaling the backscattered signal;

generate a delayed version by delaying the backscattered signal; and

detect the pilot tone when the delayed version exceeds the baseline version.

16. The reader of claim 15, wherein the signal-processing module is further configured to generate a threshold from an ambient noise, and in which the pilot tone is detected only if both the delayed version and the baseline version exceed the threshold.

17. The reader of claim 15, in which the reader transmits a command to the tag at least instructing the tag to include the pilot tone in its backscattered signal.

18. The reader of claim 15, in which the baseline version has a waveform that rises to a cusp and then maintains substantially the cusp value, and the delay is sufficiently long so that the pilot tone is detected after the cusp.

19. The reader of claim 16, in which

the backscattered signal is received responsive to a command from the reader,

the command causes the tag to be silent during a silent period, and

the ambient noise is measured during the silent period.

20. The reader of claim 15, wherein the signal-processing module is further configured to use the detected pilot tone to estimate at least one of a frequency of the backscattered signal, a phase of the backscattered signal, and a symbol timing of the backscattered signal.

21. The reader of claim 20, wherein the signal-processing module is further configured to use the at least one estimate to detect at least one of a preamble and data in the backscattered signal.