RFID joint acquisition of time sync and timebase

• US 7,419,096 B2
• Filed: 05/24/2005
• Issued: 09/02/2008
• Est. Priority Date: 06/04/2004
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Colleran, William T., Cooper, Scott Anthony, Esterberg, Aanand
• Primary Examiner(s): WALSH, DANIEL I
• Application Number:
  US11/136,948
• Publication Number:
  US 20050269408A1
• Time in Patent Office: 1,197 Days
• Field of Search: 340/572.1, 340/572.2, 340/10.1, 235/435, 235/451, 235/487, 235/492, 235/493
• US Class Current: 235/451
• 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

Systems and methods to determine timebase and timing (i.e., time sync) of received signals in RFID systems. Multiple matched filters corresponding to multiple timebases are used to receive the preambles of signals received from RFID tags. The multiple matched filters define a range of expected timebases of the received signals. The matched filter with the maximum output signal peak is used to derive the timebase and timing of the received signal. Viterbi techniques can be used in determining the timebase and timing to incorporate a portion of the data signal in addition to the preamble. Reconfigurable matched filters can be used so that after a preliminary timebase is determined as described above, the matched filters can be reconfigured to define a new smaller range centered about the preliminary timebase. This allows the timebase to be determined with finer resolution when another preamble portion is received.

Claims

1. A method for using a Radio Frequency Identification (RFID) reader comprising:

receiving a RFID tag signal at the RFID reader, wherein the RFID tag signal has a preamble portion;

filtering the signal using a plurality of preamble matched filters corresponding to a first plurality of timebases, to form a first plurality of output signals; and

determining a first timebase of the signal using the first plurality of output signals.

2. The method of claim 1, further comprising receiving a data portion of the signal using a data matched filter, wherein the data matched filter corresponds to the first timebase.

3. The method of claim 1, wherein determining the first timebase further comprises determining the first timebase in response to a determination of which output signal of the plurality of first output signals had a maximum peak magnitude, wherein the first timebase is derived from the corresponding timebase of the matched filter that outputted the output signal with the maximum peak magnitude.

4. The method of claim 1 further comprising synchronizing a receiver with the signal in response to detection of a maximum peak of the first plurality of output signals.

5. The method of claim 1 further comprising:

configuring the plurality of preamble matched filters to correspond to a second plurality of timebases;

filtering a second preamble portion using the configured plurality of preamble matched filters to form a second plurality of output signals;

determining a second timebase of the received data signal from the second plurality of output signals; and

receiving a data portion of the data signal using a data matched filter, wherein the data matched filter corresponds to the second timebase.

6. The method of claim 1, further comprising filtering a data portion of the signal using a plurality of data matched filters corresponding to the first plurality of timebases to form a third plurality of output signals;

wherein the first timebase is determined using the first and third plurality of output signals.

7. The method of claim 6, wherein a Viterbi-based process is used to determine the first timebase.

8. The method of claim 1, wherein the signal comprises a backscatter signal from a RFID tag.

9. A RFID reader for determining a timebase of a signal received from an RFID tag, comprising:

means for filtering the received signal having a preamble portion by a plurality of preamble matched filters;

means for forming a first plurality of output signals corresponding to a first plurality of timebases; and

means for determining a first timebase of the received signal using the first plurality of output signals.

10. The system of claim 9, wherein the first timebase is from determination of a matched filter that outputted an output signal of the first plurality of output signals with a maximum peak magnitude.

11. The system of claim 9 further comprising means for synchronizing a receiver with the received signal in response to detection of a maximum peak of the plurality of output signals.

12. The system of claim 9 farther comprising means for configuring the means for filtering to form a second plurality of output signals corresponding to a second plurality of timebases.

13. The system of claim 9 farther comprising means for filtering a data portion of the signal to form a third plurality of output signals corresponding to the first plurality of timebases;

wherein the first timebase is determined using the first and third plurality of output signals.

14. A RFID reader system for determining a timebase of a received RFID Tag signal, the system comprising:

a first plurality of preamble matched filters, corresponding to a first plurality of timebases, to receive a preamble portion of a signal from a radio frequency identification (RFID) tag; and

a timebase unit to determine a timebase of the signal from a first plurality of output signals of the first plurality of preamble matched filters.

15. The system of claim 14, wherein the timebase unit is to determine which output signal of the first plurality of output signals had a maximum peak magnitude, wherein the first timebase is derived from the corresponding timebase of the matched filter that outputted the output signal with the maximum peak magnitude.

16. The system of claim 14, wherein the timebase unit is further to synchronize a receiver with the signal in response to a detection of a maximum peak of the first plurality of output signals.

17. The system of claim 14, wherein the timebase unit is further to configure the first plurality of matched filters to form a second plurality of output signals corresponding to a second plurality of timebases.

18. The system of claim 14, wherein the timebase unit further comprises a second plurality of matched filters to filter a data portion of the signal to form a third plurality of output signals corresponding to the first plurality of timebases;

wherein the timebase unit determines the first timebase using the first and third plurality of output signals.

19. The system of claim 18, wherein the timebase unit uses a Viterbi-based process to determine the first timebase.

20. A computer-readable medium having stored thereon a design of a circuit according to claim 14