Systems and methods for collision avoidance in a multiple RFID interrogator environment

• US 9,846,794 B2
• Filed: 05/05/2015
• Issued: 12/19/2017
• 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
• Primary Examiner(s): TUN, NAY L
• Application Number:
  US14/704,727
• Publication Number:
  US 20150235062A1
• Time in Patent Office: 959 Days
• 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 radio frequency identification (RFID) interrogator, comprising;

a transmit (Tx) circuit configured to encode data and transmit the encoded data on a Tx path;

a receive (Rx) circuit configured to receive data from an Rx path and decode the received data;

a collision detection circuit configured to;

monitor the Tx path and the Rx path; and

detect a collision based on data on at least one of the Tx path and the Rx path;

a processor coupled with the Tx circuit and the Rx circuit, the processor configured to execute instructions; and

a memory coupled with the processor, the memory configured to store instructions for causing the processor to perform operations comprising;

causing the RFID interrogator to enter a quiet state for a time period during which the Tx circuit is prevented from transmitting encoded data on the Tx path;

after an expiration of the time period, selecting a first time at which the Tx circuit starts transmitting a first of a plurality of messages on the Tx path;

causing the RFID interrogator to return to the quiet state when the collision detection circuit detects a collision prior to or at the first time;

causing the Tx circuit to start transmitting the first message at the first time when the collision detection circuit does not detect a collision prior to or at the first time;

after the Tx circuit transmits the first message, selecting a second time at which the Tx circuit begins transmitting a second of the plurality of messages on the Tx path;

causing the RFID interrogator to return to the quiet state when the collision detection circuit detects a collision prior to or at the second time;

causing the Tx circuit to transmit the second message at the second time when the collision detection circuit does not detect a collision prior to or at the second time; and

causing the Tx circuit to transmit a remainder of the plurality of messages when the collision detection circuit does not detect a collision prior to or at the second time.

2. The RFID interrogator of claim 1, wherein the instructions causes the processor to perform operations further comprising:

after the Tx circuit transmits the remainder of the plurality of messages, causing the RFID interrogator to return to the quiet state.

3. The RFID interrogator of claim 2, wherein the RFID interrogator remains in the quiet state for a length of time determined based at least in part on an arbitration time.

4. The RFID interrogator of claim 1, wherein the first time comprises a start of a first of a plurality of timeslots.

5. The RFID interrogator of claim 4, wherein the first timeslot is randomly selected from the plurality of timeslots.

6. The RFID interrogator of claim 4, wherein the first timeslot is selected based on a slotted-Aloha scheme.

7. The RFID interrogator of claim 4, wherein the second time comprises a start of a second of the plurality of timeslots.

8. The RFID interrogator of claim 7, wherein the second timeslot is randomly selected from the plurality of timeslots.

9. The RFID interrogator of claim 8, wherein the second timeslot is selected based on a slotted-Aloha scheme.

10. The RFID interrogator of claim 4, wherein a size of each of the plurality of timeslots is determined based on at least one of the following:

a bit rate of one or more interrogators in a multiple or dense interrogator environment, a number of interrogators in a multiple or dense interrogator environment, a minimum number of data bits per timeslot, and an arbitration tolerance.

11. The RFID interrogator of claim 1, further comprising:

an antenna that is shared between the Tx circuit and the Rx circuit; and

a circulator coupling the Tx circuit and the Rx circuit to the antenna, the circulator configured to separate the Tx path and the Rx path to the antenna.

12. The RFID interrogator of claim 11, wherein the collision detection circuit is configured to detect a collision when the data on the Tx path is not equal to the data on the Rx path.

13. The RFID interrogator of claim 1, further comprising:

a Tx antenna that is coupled to the Tx circuit; and

an Rx antenna that is coupled to the Rx circuit.

14. The RFID interrogator of claim 13, wherein the collision detection circuit is configured to detect a collision when data is detected on the Rx path.

15. A method, comprising:

causing an RFID interrogator to enter a quiet state for a time period during which a transmit (Tx) circuit comprising the RFID interrogator is, prevented from transmitting encoded data on a Tx path;

after an expiration of the time period, selecting a first time at which the Tx circuit starts transmitting a first of a plurality of messages on the Tx path;

causing the RFID interrogator to return to the quiet state when a collision detection circuit comprising the RFID interrogator detects a collision prior to or at the first time;

causing the Tx circuit to start transmitting the first message at the first time when the collision detection circuit does not detect a collision prior to or at the first time;

after the Tx circuit transmits the first message, selecting a second time at which the Tx circuit begins transmitting a second of the plurality of messages on the Tx path;

causing the RFID interrogator to return to the quiet state when the collision detection circuit detects a collision prior to or at the second time;

causing the Tx circuit to transmit the second message at the second time when the collision detection circuit does not detect a collision prior to or at the second time; and

causing the Tx circuit to transmit a remainder of the plurality of messages when the collision detection circuit does not detect a collision prior to or at the second time.

16. The method of claim 15, further comprising:

after the Tx circuit transmits the remainder of the plurality of messages, causing the RFID interrogator to return to the quiet state.

17. The method of claim 16, wherein the RFID interrogator remains in the quiet state for a length of time determined based at least in part on an arbitration time.

18. The method of claim 15, wherein the first time comprises a start of a first of a plurality of timeslots.

19. The method of claim 18, wherein the first timeslot is randomly selected from the plurality of timeslots.

20. The method of claim 18, wherein the first timeslot is selected based on a slotted-Aloha scheme.

21. The method of claim 18, wherein the second time comprises a start of a second of the plurality of timeslots.

22. The method of claim 21, wherein the second timeslot is randomly selected from the plurality of timeslots.

23. The method of claim 21, wherein the second timeslot is selected based on a slotted-Aloha scheme.

24. The method of claim 18, wherein a size of each of the plurality of timeslots is determined based on at least one of the following:

a bit rate of one or more interrogators in a multiple or dense interrogator environment, a number of interrogators in a multiple or dense interrogator environment, a minimum number of data bits per timeslot, and an arbitration tolerance.

25. The method of claim 15, wherein the RFID interrogator further comprises:

an antenna that is shared between the Tx circuit and an Rx circuit; and

a circulator coupling the Tx circuit and an Rx circuit to the antenna, the circulator configured to separate the Tx path and an Rx path to the antenna.

26. The method of claim 25, wherein the collision detection circuit is configured to detect a collision when the data on the Tx path is not equal to the data on the Rx path.

27. The method of claim 15, wherein the RFID interrogator further comprises:

a Tx antenna that is coupled to the Tx circuit; and

an Rx antenna that is coupled to an Rx, circuit.

28. The method of claim 27, wherein the collision detection circuit is configured to detect a collision when data is detected on the Rx path.