SYSTEMS AND METHODS FOR COLLISION AVOIDANCE IN A MULTIPLE RFID INTERROGATOR ENVIRONMENT

• US 20090015382A1
• Filed: 06/27/2008
• Published: 01/15/2009
• Est. Priority Date: 06/29/2007
• Status: Active Grant

• Current Assignee: Smartrac Technology Fletcher, Inc. (Avery Dennison Corporation)
• Original Assignee: Neology Incorporated (OEP Technologie BV)
• Inventors: Greefkes, Kirk
• Granted Patent: US 9,035,748 B2
• Time in Patent Office: Days
• US Class Current: 340/10.200
• 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 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: H04W 74/085 collision avoidance

Abstract

A method for collision avoidance in a multi-reader environment comprising a plurality of Radio Frequency Identification (RFID) interrogators, the method comprises each of the plurality of interrogators entering a quiet state during which none of the interrogators transmits, each of the plurality of interrogators selecting a transmit time after the quiet period during which each of the interrogator will attempt to transmit, each of the plurality of interrogators monitoring their associated receive path, an interrogator of the plurality of interrogators transmitting an instruction during its selected transmit time indicating the beginning of a session when the interrogator does not detect data on its receive path prior to its select transmit time, the interrogator comparing its receive path to its transmit path when it transmits the instruction, the interrogator returning to the quiet state when the receive path does not match the transmit path, and the interrogator completing the session when the receive path matches the transmit path.

Claims

1. A method for collision avoidance in a multi-reader environment comprising a plurality of Radio Frequency Identification (RFID) interrogators, the method comprising;

each of the plurality of interrogators entering a quiet state during which none of the interrogators transmits;

each of the plurality of interrogators selecting a transmit time after the quiet period during which each of the interrogator will attempt to transmit;

each of the plurality of interrogators monitoring their associated receive path;

an interrogator of the plurality of interrogators transmitting an instruction during its selected transmit time indicting the beginning of a session when the interrogator does not detect data on its receive path prior to its select transmit time;

the interrogator comparing its receive path to its transmit path when it transmits the instruction;

the interrogator returning to the quiet state when the receive path does not match the transmit path; and

the interrogator completing the session when the receive path matches the transmit path.

2. The method of claim 1, further comprising an interrogator of the plurality of interrogators returning to the quiet state when the interrogator detects data on its receive path prior to its selected transmit time.

3. The method of claim 1, further comprising, after the first instruction is transmitted;

the interrogator monitoring its associated receive path;

the interrogator transmitting a second instruction during its selected transmit time when the interrogator does not detect data on its receive path prior to its select transmit time; and

the interrogator returning to the quiet state when the interrogator detects data on its receive path prior to its selected transmit time.

4. The method of claim 3, further comprising:

the interrogator comparing its receive path to its transmit path when it transmits the second instruction;

the interrogator returning to the quiet state when the receive path does not match the transmit path; and

the interrogator completing the session when the receive path matches the transmit path.

5. The method of claim 1, further comprising the interrogator completing the session and returning the quiet state after completion of the session, during which the interrogator waits for a predetermined time plus a time equal to an arbitration time before attempting to begin a session again.

6. The method of claim 1, wherein each of the plurality of interrogators is configured to randomly select a transmit time.

7. The method of claim 6, wherein randomly selected transmit time is one of a plurality of defined transmit slots.

8. The method of claim 7, wherein the transmit slots are defined according to a slotted-Aloha scheme.

10. The method of claim 7, wherein the length of the plurality of transmit slots is defined by the minimum number of bits per slot.

11. The method of claim 7, wherein the length of the plurality of transmit slots is defined by the arbitration tolerance.

12. The method of claim 7, wherein the length of the plurality of transmit slots is defined by the number of interrogators included in the plurality of interrogators.

13. The method of claim 1, wherein certain of the plurality of interrogators have priority over the rest of the plurality of interrogators when selecting a transmission time.

9. The method of 7, wherein the length of the plurality of transmit slots is defined by the lowest bit rate being used by the plurality of interrogators.

14. An RFID interrogator, comprising;

a transmit circuit configured to generate transmit data;

a receive circuit configured to decode receive data;

a collision detection circuit configured to compare the transmit data with the receive data;

a processor coupled with the transmit circuit and the receive circuit, the processor configured to execute instructions; and

a memory coupled with the processor, the memory configured to store instructions, the instructions configured to cause the processor to;

enter a quiet state during which the processor prevent the transmit circuit from generating transmit data,

select a transmit time after the quiet period during which the interrogator will attempt to transmit data via the transmit circuit,

cause an instruction to be transmit an instruction during the selected transmit time indicating the beginning of a session when the receiver does not detect data on its receive path prior to the select transmit time,

return to the quiet state when the collision detection circuit detects that the receive path does not match the transmit path after the instruction is transmitted, and

allow the interrogator to complete the session when the collision detection circuit determines that the receive path matches the transmit path after the instruction is transmitted.

15. The RFID interrogator of claim 14, wherein the instructions are further configured to cause the processor to return to the quiet state when the receiver detects data on its receive path prior to its selected transmit time.

16. The RFID interrogator of claim 14, wherein the instructions are further configured to cause the processor to:

cause a second instruction to be transmitted via the transmit circuit during the selected transmit time when the receiver does not detect data on its receive path after the first instruction has been transmitted and prior to its select transmit time; and

return to the quiet state when the receiver detects data on its receive path after the first instruction has been transmitted and prior to its selected transmit time.

17. The RFID interrogator of claim 16, wherein the instructions are further configured to cause the processor to:

return to the quiet state when the collision detection circuit determines that the receive path does not match the transmit path; and

allow the interrogator to complete the session when the collision detection circuit determines that the receive path matches the transmit path.

18. The RFID interrogator of claim 14, wherein the instructions are further configured to cause the processor to allow the interrogator to complete the session and return to the quiet state after completion of the session, during which the interrogator waits for a predetermined time plus a time equal to an arbitration time before attempting to begin a session again.

19. The RFID interrogator of claim 14, wherein the instructions are further configured to cause the processor to randomly select a transmit time.

20. The RFID interrogator of claim 19, wherein randomly selected transmit time is one of a plurality of defined transmit slots.

21. The RFID interrogator of claim 20, wherein the transmit slots are defined according to a slotted-Aloha scheme.

23. The RFID interrogator of claim 20, wherein the length of the plurality of transmit slots is defined by the minimum number of bits per slot.

24. The RFID interrogator of claim 20, wherein the length of the plurality of transmit slots is defined by the arbitration tolerance.

25. The RFID interrogator of claim 20, wherein the length of the plurality of transmit slots is defined by the number of interrogators included in a plurality of interrogators that includes the interrogator.

22. The RFID interrogator of 20, wherein the length of the plurality of transmit slots is defined by the lowest bit rate being used by a plurality of interrogators that includes the interrogator.