Communication and distance measurement in an addressed wide band RFID system

• US 8,193,913 B2
• Filed: 09/12/2005
• Issued: 06/05/2012
• Est. Priority Date: 09/13/2004
• Status: Active Grant

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Zebra Enterprise Solutions Corp. (Zebra Technologies Corporation)
• Inventors: Raphaeli, Dan, Kaplan, Gideon
• Primary Examiner(s): SYED, NABIL H
• Application Number:
  US11/574,883
• Publication Number:
  US 20080186136A1
• Time in Patent Office: 2,458 Days
• Field of Search: 340/10.1, 340/10.2, 340/10.31, 340/10.3, 340/10.4, 340/572.1, 340/539.26
• US Class Current: 340/10.2
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• 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 7/10059 transponder driven

Abstract

A method for communicating between elements including a reader and tags of a radio frequency identification system. The method includes addressing a wide-band-message signal by including in the signal an identifier of the first tag. The addressed wide-band-message signal is transmitted by the reader. A first tag waits to receive the addressed wide-band-message signal; and upon receiving the addressed wide-band-message signal and recognizing the identifier, the first tag responds to the addressed wide-band-message signal by transmitting an addressed wide-band response signal either back to the reader or to a relaying tag. The tag relays to another element of the system by transferring at least one datum of the query from the addressed wide-band-message signal to the addressed wide-band response signal, where the elements are readers or tags. The system and method allow for many parallel wide band addressed links, and for position determination using at least two tags with known locations.

Claims

1. In a radio frequency identification system of elements including at least one reader and a plurality of tags, including a first tag and a second tag, a method for communicating between the at least one reader and the tags, the method comprising:

addressing a wide-band-message signal by including in said signal a first-tag identifier of the first tag, thereby producing an addressed wide-band-message signal with a destination being the first tag along with other tag identifiers for respective other tags forming a first set of addressed tags;

transmitting said addressed wide-band-message signal by the reader;

determining a probability of collision for the addressed wide-band-message signal transmitted relative to a threshold and not conducting transmission of an additional addressed wide-band-message signal responsive to the probability of collision being below the threshold;

transmitting the additional addressed wide-band-message signal addressed for a second set of addressed tags responsive to the probability of collision exceeding the threshold, the second set of addressed tags being a smaller set of tags than the first set of addressed tags;

waiting to receive by the first tag said addressed wide-band-message signal; and

upon receiving said addressed wide-band message signal and recognizing said identifier, responding to said addressed wide-band-message signal by transmitting by the first tag an addressed wide-band response signal.

2. The method, according to claim 1, wherein said signals include at least one pulse sequence, wherein each pulse sequence includes a short train of pulses.

3. The method, according to claim 1, wherein said responding to said addressed wide band message signal begins during said receiving of said addressed wide band message signals.

4. The method, according to claim 1, wherein prior to said transmitting by the first tag an addressed wide-band response signal, further comprising delaying said transmitting of the wide band response signal by a pseudo-random delay period in order to reduce a probability of a collision.

5. The method, according to claim 1, further comprising, prior to said responding:

addressing by the first tag said addressed wide-band response signal by including in said signal at least one identifier of at least one other element of the system.

6. The method, according to claim 5, further comprising relaying at least a portion of a query from the reader to said at least one other element of the system by transferring at least one datum of the query from said addressed wide-band-message signal to said addressed wide-band response signal.

7. The method, according to claim 1, further comprising determining a distance from the reader to the first tag by measuring a round trip time delay including a time of flight of at least one of said wide-band signals;

determining a distance from at least one other element of the system to the first tag by measuring a round trip time delay including a time of flight of at least one other wide-band signal communicating between the first tag and said at least one other element; and

calculating position information of said first tag based on said distances.

8. The method, according to claim 1, further comprising determining by the reader a probability of a collision between expected wide band response signals and when said probability is greater than a previously determined threshold, transmitting by the reader at least one additional addressed wide band message signal, whereby said at least one additional addressed wide band message signal initiates a new communication session of the system thereby reducing a collision probability.

9. The method, according to claim 1, wherein said waiting includes scanning in the time domain.

10. The method, according to claim 1, when said first tag is active solely a portion of the time and thereby conserves power, further comprising deactivating said first tag into a sleep mode;

and activating said first tag periodically with a predefined duty cycle.

11. The method, according to claim 1, wherein said waiting includes scanning in the frequency domain by sweeping a center frequency in predefined steps such as to cover a desired frequency range until said addressed wide band message signal is detected.

12. The method, according to claim 1, further comprising addressing a second wide-band-message signal by including in said signal a second-tag identifier of the second tag, thereby producing a second addressed wide-band-message signal;

transmitting said second addressed wide-band-message signal;

waiting to receive by the second tag said second addressed wide-band-message signal; and

upon receiving said second addressed wide-band-message signal and recognizing said second-tag identifier, responding to said second addressed wide-band-message signal by transmitting by the second tag a second wide band addressed response signal.

13. The method, according to claim 12, wherein said addressed wide-band-response signal and said second addressed wide-band-response signal are addressed to a third tag of the system by including in said addressed wide-band-response signals a third-tag identifier of said third tag.

14. The method, according to claim 13, further comprising determining distances respectively from said third tag to said first and second tags by measuring a round trip time delay including respective time of flights of said addressed wide-band-response signals transmitted to said third tag;

and calculating position information of said third tag based on said distances.

15. The method, according to claim 12, wherein said wide band addressed response signals are received by the reader and include overlapping wide band response signals, the method further comprising distinguishing said overlapping wide band response signals by demodulating said overlapping wide band response signals.

16. The method, according to claim 12, wherein the reader does not receive an expected wide band response signal to at least one of said addressed wide-band-message signals, the method further comprising waiting for a random period of time;

and retransmitting said at least one addressed wide-band-message signal.

17. In a radio frequency identification system of elements including at least one reader and a plurality of tags, wherein at least one of said elements includes a wide-band wireless transceiver comprising:

an addressing mechanism which addresses a wide-band message signal by including in said message signal an identifier of at least one element of the system, and thereby produces an addressed wide-band message signal along with other tag identifiers for respective other elements forming a first set of addressed tags, and

a transmitter which transmits said addressed wide-band message signal for which a probability of collision is determined relative to a threshold such that transmission of an additional addressed wide-band-message signal is not conducted responsive to the probability of collision being below the threshold, and such that transmission of the additional addressed wide-band-message signal that is addressed for a second set of addressed tags is conducted responsive to the probability of collision exceeding the threshold, the second set of addressed tags being a smaller set of tags than the first set of addressed tags.

18. The wide-band wireless transceiver, according to claim 17, further comprising:

a receiver which receives said addressed wide-band message signal, and a processor which reads said addressed wide-band message signal and recognizes said identifier.

19. The wide-band wireless transceiver, according to claim 18, wherein said addressed wide-band signal undergoes a plurality of multi-path reflections and wherein said receiver includes a multi-path compensation mechanism which compensates at least in part for said multi-path reflections.

20. The wide-band wireless transceiver, according to claim 19, wherein said compensation mechanism includes reviewing a list of source identifiers associated with said addressed wide-band signal and upon finding a plurality of identical source identifiers in said list within a previously defined period of time, removing at least one said identical identifier from said list.

21. The wide-band wireless transceiver, according to claim 18, further comprising:

a time measurement mechanism which measures round trip delay between transmitting said addressed wide band message signal and receiving a response to said addressed wide band message signal from at least one of the elements of the system.

22. The wide-band wireless transceiver, according to claim 18, further comprising:

a radio frequency detection mechanism attached to said receiver which detects presence of radio frequency activity in a time window and solely in the absence of said activity responds to said addressed wide-band message signal during said time window and in the presence of said radio frequency activity during said time window detects again for RF activity during a new time window.

23. The wide-band wireless transceiver, according to claim 18, wherein said processor relays at least a portion of said addressed wide band message signal to another element of the system.