Method and system for tuning an RFID interrogator

• US 8,120,469 B2
• Filed: 11/08/2006
• Issued: 02/21/2012
• Est. Priority Date: 11/08/2006
• Status: Active Grant

• Current Assignee: NCR Voyix Corporation
• Original Assignee: NCR Corporation
• Inventors: Crooks, John F., Adamee, Andrew J.
• Primary Examiner(s): Nguyen, Nam V
• Application Number:
  US11/557,524
• Publication Number:
  US 20080106380A1
• Time in Patent Office: 1,931 Days
• Field of Search: 340 101- 105, 375/259, 375/227, 370/329, 370/342, 455/63.1, 455/522, 455/67.11
• US Class Current: 340/10.2
• 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
• CPC Class Codes: G06K 7/10019 resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. collision between the communication channels used by wireless communication devices, where the solution is not particularly adapted for RFIDs or the like, H04W74/08
• CPC Class Codes: G06K 7/10217 parameter settings controlling the transmission power of the interrogator

Abstract

A method, apparatus, and system for periodically measuring the level of ambient noise found on a radio frequency channel used by a radio frequency identification interrogator to read radio frequency identification tags. The measured level of ambient noise is then used to dynamically adjust a threshold value used to predict collisions on the channel.

Claims

1. A method for use in optimizing a radio frequency identification interrogator, the method comprising:

receiving a first signal within a radio frequency channel including an instantaneous ambient noise signal;

performing spectral analysis on the first signal to obtain a magnitude of the instantaneous ambient noise signal;

setting a decision threshold value for the interrogator based on a statistical analysis that uses the magnitude of the instantaneous ambient noise signal;

receiving a second signal within the radio frequency channel;

determining that a magnitude of the second signal is greater than the decision threshold value indicative of a collision occurring between a third signal from a first radio frequency identification tag and a fourth signal from a second radio frequency identification tag; and

increasing a number of time slots available for the first and second radio frequency identification tags to send the third and fourth signals.

2. The method of claim 1, wherein the spectral analysis comprises a Fourier analysis of the first signal.

3. The method of claim 1, wherein the magnitude of the instantaneous ambient noise signal is stored in a circular buffer assigned to the radio frequency channel.

4. The method of claim 3, wherein the statistical analysis includes using a Gaussian distribution model on data stored in the circular buffer.

5. The method of claim 4, wherein the decision threshold is set to the mean plus three standard deviations.

6. The method of claim 5, wherein the decision threshold is associated with the radio frequency channel.

7. A radio frequency identification interrogator comprising:

a radio frequency receiver adapted to receive signals on a radio frequency channel;

a processing unit in communication with the receiver; and

a memory unit electrically coupled to the processing unit, wherein the memory unit has stored therein a plurality of instructions which, when executed by the processing unit, cause the processing unit to;

(i) receive a first signal from the receiver including an instantaneous ambient noise signal;

(ii) perform a spectral analysis on the first signal to obtain a magnitude of the instantaneous ambient noise signal;

(iii) set a decision threshold value for the interrogator based on a statistical analysis that uses the magnitude of the instantaneous ambient noise signal;

(iv) receive a second signal within the radio frequency channel;

(v) determine that a magnitude of the second signal is greater than the decision threshold value indicative of a collision occurring between a third signal from a first radio frequency identification tag and a fourth signal from a second radio frequency identification tag; and

(vi) increase a number of time slots available for the first and second radio frequency identification tags to send the third and fourth signals.

8. The interrogator of claim 7, wherein the spectral analysis comprises a Fourier analysis of the first signal.

9. The interrogator of claim 7, wherein the magnitude of the instantaneous ambient noise signal is stored in a circular buffer assigned to the radio frequency channel.

10. The interrogator of claim 9, wherein the statistical analysis includes using a Gaussian distribution model on data stored in the circular buffer.

11. The interrogator of claim 10, wherein the decision threshold is set to the mean plus three standard deviations.

12. The interrogator of claim 11, wherein the decision threshold is associated with the radio frequency channel.