RF transponder system having error detection and correction

• US 5,742,618 A
• Filed: 09/04/1996
• Issued: 04/21/1998
• Est. Priority Date: 09/04/1996
• Status: Expired due to Term

• Current Assignee: Assa Abloy AB
• Original Assignee: Palomar Technologies Incorporated
• Inventors: Lowe, Peter R.
• Primary Examiner(s): Chung, Phung M.
• Application Number:
  US08/707,740
• Time in Patent Office: 594 Days
• Field of Search: 371/36, 371/67.1, 371/48, 340/825.54, 340/825
• US Class Current: 714/797
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence

Abstract

An RF transponder system is provided that is capable of detecting and correcting data transmission errors. The RF transponder system includes an exciter that generates an RF excitation signal and a transponder that receives the RF excitation signal and is powered thereby. The transponder generates and transmits a RF response signal including a plurality of data sets each containing a common message. At least one of the data sets is encoded in a manner different from the remaining data sets. The RF response signal is received by a reader that decodes the encoded data sets. Corresponding bits of each of the data sets are compared for purposes of error detection. If a majority of corresponding bits from each of the data sets match, a valid bit is defined thereby. Bits that are not in the majority are discarded. An invalid bit is defined where less than a majority of corresponding bits match a selected bit of a selected data set.

Claims

1. A method for detecting data transmission errors in an RF transponder system comprising:

generating an RF excitation signal with an exciter;

powering a transponder with said RF excitation signal;

generating an RF response signal, including a plurality of data sets, each of said data sets comprising a plurality of bits and each of said data sets containing a common message, wherein at least one of said data sets is encoded in a manner different from the remaining data sets, and transmitting said RF response signal to a reader;

receiving said RF response signal at said reader;

decoding said at least one of said encoded data sets with said reader to provide at least one decoded data set;

comparing corresponding bits of each of said at least one decoded data set and said remaining data sets; and

defining a selected bit of a selected decoded or remaining data set as a valid bit, if said selected bit matches a majority of said corresponding bits.

2. The method recited in claim 1 further comprising discarding said selected bit, if said selected bit does not match said majority.

3. The method recited in claim 1 further comprising defining said selected bit as an invalid bit, if said selected bit does not match said majority.

4. The method recited in claim 1 wherein said common message includes an identification code.

5. The method recited in claim 1 further comprising granting access to a restricted area if said common message matches a stored message at said reader.

6. The method recited in claim 1 further comprising encoding said at least one of said data sets by reversing a bit pattern of said at least one of said data sets.

7. The method recited in claim 1 further comprising the step of integrating said exciter and said reader into a single circuit.

8. An RF transponder system comprising:

an exciter circuit for generating an RF excitation signal;

a transponder powered by said RF excitation signal for generating an RF response signal, including a plurality of data sets, each of said data sets comprising a plurality of bits and each of said data sets containing a common message, for encoding at least one of said data sets in a manner different from the remaining data sets, and for transmitting said RF response signal;

a reader circuit including a decoder for decoding said at least one of said encoded data sets to provide at least one decoded data set, a comparing circuit for comparing corresponding bits of each of said at least one decoded data set and said remaining data sets; and

a voting circuit for defining a selected bit of a selected decoded or remaining data set as a valid bit, if said selected bit matches a majority of said corresponding bits.

9. The RF transponder system recited in claim 8 wherein said reader circuit discards said selected bit, if said selected bit does not match said majority.

10. The RF transponder system recited in claim 8 wherein said reader circuit defines said selected bit as an invalid bit, if said selected bit does not match said majority.

11. The RF transponder system recited in claim 8 wherein said common message is an identification code.

12. The RF transponder system recited in claim 8 further comprising means for granting access to a restricted area if said common message matches a stored message.

13. The RF transponder system recited in claim 8 wherein said at least one of said encoded data sets has a reversed bit pattern.

14. The RF transponder system recited in claim 8 wherein said exciter circuit and said reader circuit are integrated into a single circuit.

15. A method for detecting data transmission errors in an RF transponder system comprising:

generating an RF excitation signal with an exciter;

powering a transponder with said RF excitation signal;

generating an RF response signal, including at least one data set comprising a first plurality of bits defining a message or an identification code, said RF response signal further including a validation field comprising a second plurality of bits produced by applying an algorithm to said first plurality of bits;

transmitting said RF response signal to a reader and receiving said RF response signal including said data set at said reader;

applying said algorithm to said data set received at said reader to produce a third plurality of bits;

comparing said third plurality of bits to said second plurality of bits;

defining said data set as valid, if said third plurality of bits matches said second plurality of bits.

16. The method recited in claim 15 wherein said validation field has 8 bits or 16 bits.

17. The method recited in claim 15 wherein said validation field has fewer bits than said data set.

18. The method recited in claim 15 wherein said algorithm is stored in a memory of said transponder.

19. The method recited in claim 15 wherein said algorithm is stored in a memory of said reader.

20. The method recited in claim 15 wherein said algorithm is created by a remote computer further creating an original programming code for said transponder.