Radio tag system and method with improved tag interference avoidance

• US 6,034,603 A
• Filed: 01/24/1997
• Issued: 03/07/2000
• Est. Priority Date: 01/24/1997
• Status: Expired due to Term

• Current Assignee: Axcess International, Inc. (Amphion Innovations PLC)
• Original Assignee: Axcess, Inc.
• Inventors: Steeves, Wayne E.
• Primary Examiner(s): TONG, NINA C
• Application Number:
  US08/789,148
• Time in Patent Office: 1,138 Days
• Field of Search: 340/572, 340/568, 340/571, 340/505, 340/928, 340/502, 340/825.54, 340/825.34, 340/825.35, 342/42, 342/51, 342/40, 342/44, 342/50, 370/448, 370/310, 370/347, 370/445, 370/825.44, 455/31.3, 235/384
• 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 7/10039 interrogator driven, i.e. synchronous
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas

Abstract

A data transmission system includes a reader transceiver and one or more tag transceivers. The reader transmits an activation signal to a tag. The tag selectively transmits a response signal to the reader at a specific time determined by a detected level of communications channel activity. The detector operates in a low-power standby state until the time it receives the activation signal, and then operates in an active state. The invention further incorporates a technique to maintain an extremely low power state to the tag during quiescent mode while retaining full sensitivity to reader activation signals. The reader transceivers are of a modular architecture with each module operating independently, yet in concert with the others. The modules are interconnected in a media independent method and can interact remotely with other modules.

Claims

1. A tag transceiver, comprising:

a receiver module operable to listen for radio frequency activity;

a processor module operable to detect radio frequency activity, to determine an amount of radio frequency activity during a period of time based on detected radio frequency activity during a plurality of sub-periods of the period, and to initiate transmission of a signal based on the amount of radio frequency activity; and

a transmitter module operable to transmit the signal.

2. The tag transceiver of claim 1, wherein the processor module is operable to synchronize with a second tag transceiver and determine the amount of radio frequency activity during a fixed passive period of the second tag transceiver.

3. The tag transceiver of claim 2, wherein:

the fixed passive period of the second tag transceiver follows a fixed number of transmissions from the second tag transceiver; and

the processor module synchronizes with the second tag transceiver by detecting the fixed number of transmissions.

4. The tag transceiver of claim 1, wherein:

the period of time is a plurality of cycles;

the amount of radio frequency traffic relates to a number of the cycles during which the processor module detects radio frequency activity; and

the processor module initiates transmission of the signal if the number of cycles during which the processor module detects radio frequency activity is below a threshold value.

5. The tag transceiver of claim 1, wherein the processor module initiates transmission of the signal by generating a plurality of time slots and determining a specific time for transmitting the signal according to a randomized time slot selection.

6. The tag transceiver of claim 1, wherein the processor module activates from a stand-by state in response to receiving an activation signal at the receiver module.

7. A method for transmitting data from a tag transceiver, the method comprising:

listening for radio frequency activity;

determining an amount of radio frequency activity during a period of time based on detected radio frequency activity during a plurality of sub-periods of the period; and

initiating transmission of a response signal based on the amount of radio frequency activity.

8. The method of claim 7, further comprising:

synchronizing the tag transceiver with a second tag transceiver; and

determining the amount of radio frequency activity during a fixed passive period of the second tag transceiver.

9. The method of claim 8, wherein:

the fixed passive period of the second tag transceiver follows a fixed number of transmissions from the second tag transceiver; and

the tag transceiver synchronizes with the second tag transceiver by detecting the fixed number of transmissions.

10. The method of claim 7, wherein:

the period of time is a plurality of cycles;

the amount of radio frequency traffic relates to a number of the cycles during which the tag transceiver detects radio frequency activity; and

the tag transceiver initiates transmission of the response signal if the number of cycles during which the tag transceiver detects radio frequency activity is below a threshold value.

11. The method of claim 7, wherein initiating transmission of the response signal comprises generating a plurality of time slots and determining a specific time for transmitting the signal according to a randomized time slot selection.

12. The method of claim 7, further comprising:

receiving an activation signal from a reader transceiver; and

changing from a stand-by state to an active state in response to receiving the activation signal.

13. A data transmission system, comprising:

a reader transceiver operable to transmit a request signal; and

a tag transceiver operable to receive the request signal and to transmit a response signal, wherein the tag transceiver listens for radio frequency activity, determines an amount of radio frequency activity during a period of time based on detected radio frequency activity during a plurality of sub-periods of the period, and initiates transmission of the response signal based on the amount of radio frequency activity.

14. The system of claim 13, wherein the tag transceiver is operable to synchronize with a second tag transceiver and to determine the amount of radio frequency activity during a fixed passive period of the second tag transceiver.

15. The system of claim 14, wherein:

the fixed passive period of the second tag transceiver follows a fixed number of transmissions from the second tag transceiver; and

the tag transceiver synchronizes with the second tag transceiver by detecting the fixed number of transmissions.

16. The system of claim 13, wherein:

the period of time is a plurality of cycles;

the amount of radio frequency traffic relates to a number of the cycles during which the tag transceiver detects radio frequency activity; and

the tag transceiver initiates transmission of the signal if the number of cycles during which the tag transceiver detects radio frequency activity is below a threshold value.

17. The system of claim 13, wherein the tag transceiver initiates transmission of the response signal by generating a plurality of time slots and determining a specific time for transmitting the signal according to a randomized time slot selection.

18. The system of claim 13, wherein:

the reader transceiver transmits an activation signal; and

the tag transceiver changes from a stand-by state to an active state in response to receiving the activation signal.

19. The system of claim 13, wherein:

the reader transceiver transmits an acknowledgment signal in response to receiving the response signal from the tag transceiver; and

the tag transceiver re-transmits the response signal if the tag transceiver does not receive the acknowledgment signal.

20. The system of claim 13, wherein:

the response signal includes a reader identification associated with the reader transceiver; and

a second reader transceiver is operable to receive the response signal and communicate the response signal to the reader transceiver based on the reader identification.

21. The system of claim 13, wherein:

the request signal includes a tag identification associated with the tag transceiver;

the tag transceiver is operable to receive a portion of the request signal including the tag identification and to transmit an error signal indicating a failure to receive the complete request signal; and

the reader transceiver is operable to receive the error signal and to re-transmit the request signal.

22. A method for transmitting data from a tag transceiver, comprising;

listening for transmission activity at a radio frequency, the transmission activity including transmissions from other tag transceivers;

determining an amount of transmission activity at the radio frequency during a period of time;

generating a number of time slots based on the amount of transmission activity;

randomly selecting one of the time slots as a transmission time slot; and

transmitting a signal during the transmission time slot.

23. The method of claim 22, wherein the number of time slots is proportional to the amount of transmission activity.

24. The method of claim 22, wherein the transmission time slot is randomly selected from the plurality of time slots.

25. The method of claim 22, further comprising immediately initiating transmission of the signal in response to detecting no transmission activity at the radio frequency during the period of time.

26. The method of claim 22, further comprising:

synchronizing the tag transceiver with a second tag transceiver; and

determining the amount of transmission activity during a fixed passive transmission period of the second tag transceiver.

27. The method of claim 26, wherein:

the fixed passive transmission period of the second tag transceiver follows a fixed number of transmissions from the second tag transceiver; and

a tag transceiver synchronizes with the second tag transceiver by detecting the fixed number of transmissions.

28. The method of claim 27, wherein the period of time is a plurality of transmission cycles of the second tag transceiver and each transmission cycle includes the fixed passive period.