Asynchronous communication system for remote monitoring of objects or an environment

• US 20060034348A1
• Filed: 08/10/2004
• Published: 02/16/2006
• Est. Priority Date: 08/10/2004
• Status: Active Grant

• Current Assignee: Mayo Foundation For Medical Education And Research (Mayo Clinic)
• Original Assignee: Mayo Foundation For Medical Education And Research (Mayo Clinic)
• Inventors: Coker, Jonathan Darrel, Holmes, David R. III, Philpott, Rick Allen, Welch, Edward Brian, Schaefer, Timothy Michael
• Granted Patent: US 7,643,536 B2
• Time in Patent Office: Days
• US Class Current: 375/130
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04J 13/16 Code allocation

Abstract

A system provides for remote monitoring using asynchronous code division multiple access (CDMA) communication techniques between a base station and one or more transponders. Each transponder is attached or otherwise associated with an object or an environment to be monitored. Upon receipt of an interrogation signal, a transponder generates and transmits a coded transponder signal containing the monitored data. The coded transponder signal is generated using a spreading code. Each transponder is associated with a unique, mutually exclusive set of spreading codes. Each spreading code is based on a unique transponder address and the monitored data to be sent. A detector asynchronously monitors received signals for any of the available spreading codes. Once the detector detects a particular spreading code, the base station can identify the source transponder and extract the monitored data.

Claims

1. A transponder comprising:

a clock generator that generates a transmit clock based on an interrogation signal;

a code generator that generates a spreading code from a set of spreading codes allocated to the transponder using the transmit clock; and

a signal generator that transmits a transponder signal that includes the spreading code.

2. The transponder of claim 1, wherein the clock generator frequency modulates the interrogation signal to generate the transmit clock.

3. The transponder of claim 1, wherein the clock generator comprises a clock divider.

4. The transponder of claim 3, wherein the clock divider comprises a divide-by-n circuit.

5. The transponder of claim 1, wherein the clock generator comprises a clock multiplier.

6. The transponder of claim 1, wherein the set of spreading codes comprise substantially orthogonal spreading codes.

7. The transponder of claim 1, wherein the set of spreading codes comprise binary spreading codes.

8. The transponder of claim 7, wherein the binary spreading codes comprise one of Gold codes and Kasami codes.

9. The transponder of claim 1, wherein the set of spreading codes comprise multi-level spreading codes.

10. The transponder of claim 1, wherein the code generator generates an n-bit spreading code.

11. The transponder of claim 10, wherein the m-bit spreading code includes address bits and data bits.

12. The transponder of claim 11, wherein the address bits define the set of spreading codes allocated to the transponder.

13. The transponder of claim 1, wherein the code generator includes an upper linear feedback shift register and a lower linear feedback shift register, each of which generates a pseudorandom noise sequence.

14. The transponder of claim 13, wherein the code generator generates an n-bit spreading code, and wherein the pseudorandom noise sequences have a period of 2ⁿ−

1.

15. The transponder of claim 13, wherein the pseudorandom noise sequences generated by the upper and the lower linear feedback shift registers are modulo-2 added together to produce the spreading code.

16. The transponder of claim 1, further comprising a threshold/trigger circuit to detect the interrogation signal and apply power to the transponder in response to the interrogation signal.

17. A system, comprising:

a set of one or more transponders, wherein each transponder comprises;

a clock generator that generates a transmit clock based on an interrogation signal;

a code generator that generates a spreading code from a set of spreading codes allocated to the transponder using the transmit clock; and

a signal generator that transmits a transponder signal that includes the spreading code; and

a detector that acquires received signals and examines the received signals to detect presence of one or more spreading codes.

18. The system of claim 17, wherein the detector identifies which of the transponders transmitted the received signal based on the spreading code.

19. The system of claim 17, wherein the detector identifies data conveyed by the received signal based on the spreading code.

20. The system of claim 19, wherein each of the transponders is associated with one of an object or an environment to be monitored, and wherein the data conveyed by the spreading code is status information concerning the object or the environment to be monitored.

21. The system of claim 17, wherein the set of spreading codes allocated to each of the transponders is a unique set of spreading codes.

22. The system of claim 17, wherein the detector includes a processor that performs a correlation of each received signal with an ideal code correlator for each spreading code in the system.

23. The system of claim 22, wherein the processor compares the correlation to detection criterion to detect presence of any one of the spreading codes in the system.

24. The system of claim 23, wherein the detection criterion comprises a threshold detection criterion.

25. The system of claim 24, wherein the threshold detection criterion changes as a function of time.

26. The system of claim 22, wherein the detector includes a code allocation lookup table that maps transponders to their allocated spreading codes, and wherein the processor accesses the code allocation lookup table to identify which transponder transmitted the spreading code and to identify data conveyed by the spreading code.

27. The system of claim 17, wherein the transponders and the detector communicate asynchronously.

28. The system of claim 17, wherein the clock generator frequency modulates the interrogation signal to generate the transmit clock.

29. The system of claim 17, wherein the clock generator comprises a clock divider.

30. The system of claim 29, wherein the clock divider generates a transmit clock that is approximately one-half the frequency of the interrogation signal.

31. A method comprising:

sending an interrogation signal sufficient to enable communication with one or more transponders; and

asynchronously examining received signal samples to detect presence of one or more of a plurality of spreading codes sent by the transponders.

32. The method of claim 31, wherein asynchronously examining received signals comprises:

asynchronously acquiring received signal samples;

performing a correlation between the received signal samples and an ideal code correlator for each of the plurality of spreading codes; and

comparing the correlation to detection criterion to detect presence of any one of the spreading codes.

33. The method of claim 32, wherein performing a correlation comprises performing the correlation using Fourier methods.

34. The method of claim 32, wherein performing a correlation comprises performing the correlation using a discrete circular correlation.

35. The method of claim 31, further comprising assigning a unique set of spreading codes from the plurality of spreading codes to each of the transponders.

36. The method of claim 35, wherein assigning a unique set of spreading codes comprises assigning a unique address to each of the transponders.

37. The method of claim 35, further comprising:

generating a transmit clock based on the interrogation signal;

generating a spreading code from the assigned unique sets of spreading codes using the transmit clock; and

transmitting a coded transponder signal that includes the generated spreading code.

38. The method of claim 31, further comprising:

identifying which of the transponders sent the detected spreading code; and

identifying data conveyed by the detected spreading code.

39. The method of claim 38, wherein identifying which of the transponders sent the detected spreading code and identifying data conveyed by the received signal comprise referencing a code allocation look-up table.

40. The method of claim 31, wherein the plurality of spreading codes comprise substantially orthogonal spreading codes.

41. The method of claim 31, wherein the plurality of spreading codes comprise binary spreading codes.

42. The method of claim 41, wherein the binary spreading codes comprise one of Gold codes and Kasami codes.

43. The method of claim 31, wherein the plurality of spreading codes comprise multi-level spreading codes.

44. A system, comprising:

an interrogator that sends an interrogation signal;

a set of one or more transponders, each of which is allocated a unique set of spreading codes from a plurality of spreading codes, and each of which transmits a transponder signal containing one of the allocated spreading codes in response to the interrogation signal; and

a detector that asynchronously examines received signals to detect presence of one or more of the plurality of spreading codes.

45. The system of claim 44, wherein the detector includes a processor that performs a correlation between a sample of the received signals and an ideal code correlator for each of the plurality of spreading codes.

46. The system of claim 45, wherein the processor performs the correlation using discrete Fourier transforms.

47. The system of claim 46, wherein the ideal code correlators are stored as a Fourier representation of an ideal transponder signal.

48. The system of claim 45, wherein the processor performs the correlation using a discrete circular correlation.

49. The system of claim 45, wherein the processor compares the correlation to detection criterion to determine whether the sample of the received signals includes any of the spreading codes.

50. The system of claim 45, wherein the detection criterion comprises a threshold detection criterion.

51. The system of claim 50, wherein a threshold value of the threshold detection criterion adjusts as a function of time.

52. The system of claim 44, further comprising a code allocation lookup table that maps transponders to their allocated spreading codes, and wherein the processor accesses the code allocation lookup table to identify which transponder transmitted the detected spreading code and to identify the data conveyed by the detected spreading code.

53. The system of claim 44, wherein each transponder includes:

a clock generator that generates a transmit clock based on the interrogation signal;

a code generator that generates a spreading code from the set of spreading codes allocated to the transponder using the transmit clock; and

a signal generator that transmits a coded transponder signal that includes the spreading code generated by the code generator.

54. The system of claim 53, wherein the clock generator generates a frequency modulated clock.

55. The system of claim 53, wherein the clock generator comprises a clock divider.