Secured data transmission and error recovery mechanism in cordless telephones

• US 5,073,932 A
• Filed: 08/31/1990
• Issued: 12/17/1991
• Est. Priority Date: 08/31/1990
• Status: Expired due to Term

• Current Assignee: TronTech Licensing Incorporated
• Original Assignee: Phonemate, Inc.
• Inventors: Brown, Sanford M. III, Yossifor, Oded
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US07/575,587
• Time in Patent Office: 473 Days
• Field of Search: 379/62, 371/36, 371/41l49.2, 371/65, 380/48, 380/2, 380/23
• US Class Current: 380/270
• CPC Class Codes: H04L 1/004 by using forward error control H04L1/0618 takes precedence; coding, decoding or code conversion, for error detection or correction H03M13/00
• CPC Class Codes: H04M 1/727 Identification code transfer arrangements

Abstract

A novel method is disclosed that facilitates secured transmission of data between the transmitting and receiving ends of a cordless telephone by encapsulating the desired command in a message code. This message code includes synchronization, security, and error detection codes as well as the encapsulated command. Both the process that generates the security code and the process that enables recovery from errors during data transmission efficiently utilize the limited memory and processing capabilities available on the cordless telephones.

Claims

1. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data comprising:

transmission of a security code to ensure that random or unauthorized data is not accepted by the receiving unit;

transmission of a message bit sequence to ensure that data is not misinterpreted;

transmission of a command sequence comprising data sent by the transmitting unit; and

transmission of an error detection code to ensure that errors arising within said message bit sequence and said command sequence are detected.

2. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 1 wherein the method includes transmission of a synchronization code that prepares the receiving unit for an incoming message.

3. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 1, wherein said security code, said message bit sequence, said command sequence, and said error detection code are incorporated within a message code that is sent as a whole from the transmitting unit to the receiving unit.

4. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 3 wherein the method includes transmission of a synchronization code that prepares the receiving unit for an incoming message.

5. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless telephone while maintaining integrity of the transmitted data as set forth in claim 3, wherein said data integrity is maintained by both analyzing said message code for errors after said message code is received as well as receiving said message code in a manner that reduces the introduction of error into a transmitted message code during reception.

6. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 5, wherein said analyzing said message code for errors comprises parity checking and said manner of reception that reduces the introduction of error comprises a Majority Vote method.

7. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 3, wherein errors in transmitted data are recovered by retransmission of said message code by the transmitting unit to the receiving unit.

8. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 4, wherein said synchronization code comprises a predetermined bit sequence of bits of alternating values.

9. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 1, wherein said security code is randomly generated.

10. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 9, wherein said security code is generated by the base portion of a cordless phone system and transferred to the handset portion of said cordless phone system before the handset portion is separated from the base portion.

11. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 9, wherein said security code is generated by a free running counter.

12. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 9, wherein said security code is filtered to ensure that excessively contiguous bit sequences are removed or altered.

13. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 9, wherein:

said security code is 12 bits long;

a first 4 bit sequence of said 12 bit security code is compared to second and third 4 bit sequences of said 12 bit security code and if said three 4 bit sequences are equal, then said second 4 bit sequence is incremented by one; and

if 5 contiguous bits of said 12 bit security code are the same, then a fifth bit of said 5 bit sequence is complemented.

14. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 1, wherein said message bit sequence comprises a sequence that alternates with each message code.

15. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 14, wherein said message code is retransmitted by the transmitting unit to the receiving unit if said error detection code is not appropriate for said parity of said message bit sequence and said command code sequence.

16. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 1, wherein said message bit sequence comprises a single bit.

17. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data as set forth in claim 1, wherein said command sequence is of sufficient length to convey a command from the transmitter to the receiver and said command sequence does not contain excessively contiguous bit sequences of the same value.

18. A method for securing transmission of data between transmitting and receiving units of handset and base portions of a cordless telephone while maintaining integrity of the transmitted data as set forth in claim 1, wherein said error detection code comprises:

a series of bits of length equal to that of the length of said message bit sequence and said command sequence;

of same value as said message bit sequence and said command sequence if parity of said message bit sequence and said command sequence is even;

or

of complemented value of said message bit sequence and said command sequence if parity of said message bit sequence and said command sequence is odd.

19. A method to secure transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data by transmitting a message code comprising:

a synchronization code of alternating values 4 bits long, said synchronization code preparing said receiving unit for an incoming message code;

a randomly generated security code generated by a free running counter, said security code transferred from the base portion of a cordless phone to the handset portion of said cordless phone before the handset is removed from the base portion, said security code being evaluable in first, second, and third equal length segments, said second segment being incremented by one if all three said segments have the same value, and said security code having all excessively contiguous sequences of equal valued bits being altered so that said excessively contiguous sequences are no longer excessively contiguous;

a message bit that alternates value with each message code;

a command sequence comprising data transmitted from a transmitting unit for reception by a receiving unit, said command sequence containing no excessively contiguous sequences of equal valued bits; and

an error detection code of length same as length of said message bit and said command sequence, said error detection code being the same as said message bit and said command sequence if parity of said message bit and said command sequence is even, but said error detection code being complement to said message bit and said command sequence if parity of said message bit and said command sequence is odd.

20. A method to secure transmission of data between transmitting and receiving units of handset and base portions of a cordless phone while maintaining integrity of the transmitted data by transmitting a message code as set forth in claim 19, wherein said security code is 12 bits long.

21. Circuitry means for generation, verification, and validation of a message code transmitted and received by handset and base portions of a cordless telephone, wherein said circuitry means comprises:

a free running counter for the generation of a security code within said message code;

memory registers for the storage of said security code within both handset and base portions of said cordless telephone;

at least one decision comparator within receiving portions of both handset and base portions of said cordless telephone that samples an incoming bit stream at a rate significantly greater than transmitting portions of both handset and base portions of said cordless telephone;

at least one majority vote comparator that compares consecutive samples of an incoming bit stream by a Majority Vote method;

at least one majority vote shift register for the storage of values generated by said majority vote comparators;

a comparison register that stores two middle bits of four bit values of said majority vote shift register; and

a code comparator that compares said two middle bits stored in said comparison register to each other and a corresponding bit of a known, predetermined code.

22. The circuitry means for generation, verification, and validation of a message code transmitted and received by handset and base portions of a cordless telephone as set forth in claim 21, wherein said known, predetermined code comprises said security code.

23. The circuitry means for generation, verification, and validation of a message code transmitted and received by handset and base portions of a cordless telephone as set forth in claim 21, wherein said known, predetermined code comprises a command.

24. The circuitry means for generation, verification, an validation of a message code transmitted and received by a handset and base portions of a cordless telephone as set forth in claim 21, wherein said circuitry means further comprises a message code assembler that generates said message code by storing said security code, a message bit sequence to ensure proper message code interpretation, a command, and an error detection code said assembler making said message code available for transmission by an associated transmitter.

25. The circuitry means for generation, verification, an validation of a message code transmitted and received by a handset and base portions of a cordless telephone as set forth in claim 24, wherein said message code stores a synchronization code that prepares a receiver for an incoming message.

26. The circuitry means for generation, verification, and validation of a message code transmitted and received by handset and base portions of a cordless telephone as set forth in claim 21, wherein said code comparator signals a parity checker when values stored in said comparison register are equal to corresponding values of a security code, said parity checker then checking an error detection code incorporated within an immediately incoming command code, allowing execution of said command code if said error detection code is valid and denying execution of said command code if said error detection code is invalid.

27. The circuitry means for generation, verification, and validation of a message code transmitted and received by handset and base portions of a cordless telephone as set forth in claim 21, wherein a transmitting unit of said cordless telephone retransmits said message code when a transmitted message code is received containing errors.