System and method for communication with radio frequency identification tags using tow message DFM protocol

• US 6,452,504 B1
• Filed: 09/24/1999
• Issued: 09/17/2002
• Est. Priority Date: 09/24/1999
• Status: Expired due to Fees

• Current Assignee: GE Interlogix Incorporated (General Electric Company)
• Original Assignee: GE Interlogix Incorporated (General Electric Company)
• Inventors: Seal, James
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): BANGACHON, WILLIAM L
• Application Number:
  US09/405,358
• Time in Patent Office: 1,089 Days
• Field of Search: 340/825.49, 340/10.33, 340/10.34, 340/572.4, 340/572.7, 340/572.8, 340/10.4, 340/652, 340/572.1, 340/572.2, 342/42, 342/43, 343/742, 343/867
• US Class Current: 340/572.2
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308

Abstract

The system comprises a plurality of stationary sensors located in an array within certain physical areas. Each sensor comprises a plurality of antenna coils arranged in unique physical orientations and capable of transmitting radio frequency signals of differing phase. The RFID transponder includes an antenna which receives the signals generated by the antenna coils, and compares the phase of at least two of the signals to determined the relative position of the transponder. The antenna coils may emit two direction finding mode (DFM) signals in succession; the first signal with all antenna coils turned on, the second with a subset of the coils turned off. The spatial relationship of the transponder antenna and individual antenna coils precludes all of the signals in each sensor from being rejected by the transponder during emission of both the first and second DFM signal.

Claims

1. A method of maintaining continuous communication between a transceiver and a radio frequency identification (RFID) transponder having an antenna coil, said transceiver having a plurality of antenna coils oriented in a first spatial relationship to each other, the method comprising:

positioning said transponder in relative proximity to said transceiver, said transponder being oriented in a second spatial relationship with respect to said plurality of antenna coils of said transceiver;

concurrently transmitting a first signal according to a first protocol from each of said plurality of antenna coils of said transceiver; and

concurrently transmitting a second signal according to said first protocol from a subset of said plurality of antenna coils of said transceiver;

wherein said first and second spatial relationships are such that either or both of said first signal and said second signal are at least partially coupled to said antenna coil of said transponder.

2. The method of claim 1, wherein the acts of transmitting a first signal and transmitting a second signal are temporally sequential.

3. The method of claim 1, wherein the act of transmitting said first and second signals includes transmitting at least one cyclic redundancy code (CRC).

4. The method of claim 1, wherein the act of transmitting said signals from each of said antenna coils of a given transceiver further comprises shifting said signals in electrical phase with respect to the signals transmitted by the other antenna coils associated with that same transceiver.

5. The method of claim 4, wherein said transceiver comprises three antenna coils, and the act of shifting comprises shifting each signal in electrical phase by 120 degrees.

6. The method of claim 5, wherein said three antenna coils of said given transceiver are orthogonal to each other.

7. A method of determining the position of a radio frequency identification (RFID) transponder with respect to a transceiver, said transponder having an antenna coil configured to receive a radio frequency signal, said transceiver having a first sensor and a second sensor in different locations, said first and second sensors further including a plurality of antenna coils oriented in a first spatial relationship to each other, the method comprising:

positioning said transponder in a second spatial relationship with respect to said first and second sensors;

concurrently transmitting a first signal from each of said plurality of antenna coils of said first and second sensors;

concurrently transmitting a second signal from a subset of said plurality of antenna coils of said first and second sensors; and

determining the position of said transponder relative to said first and second sensors based on said first and second signals received by said antenna coil of said transponder.

8. The method of claim 7, wherein the act of transmitting said first and second signals from each of said antenna coils of said sensors further comprises shifting each of said signals in electrical phase from the others within each sensor.

9. The method of claim 7, wherein a one of the sensors is located nearer the transponder than the other sensor.

10. The method of claim 7, wherein the act of transmitting from a sensor comprises transmitting from three antenna coils, each of which are spatially orthogonal to one another.

11. The method of claim 10, wherein the act of transmitting said second signal comprises transmitting signals from two of the antenna coils of said sensors.

12. The method defined in claim 7, wherein the act of determining the position of the transponder comprises comparing the relative field strengths of said first and second sensors.

13. A radio frequency communication system, comprising:

a first transceiver capable of transmitting a radio frequency signal, said first transceiver having a plurality of antenna coils disposed in different spatial orientations each of which may transmit the radio frequency signal; and

a second transceiver having a directional antenna coil;

wherein said first transceiver is operated so as to selectively concurrently transmit from either all or a subset of said plurality of antenna coils in order to at least partly couple to said directional antenna coil regardless of said directional antenna coil'"'"'s orientation with respect to said transceiver.