Self-monitoring satellite system

• US 6,667,713 B2
• Filed: 08/24/2001
• Issued: 12/23/2003
• Est. Priority Date: 08/24/2001
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Spectrum Astro
• Inventors: Pullen, Samuel P., Green, Gaylord B.
• Primary Examiner(s): ISSING, GREGORY C
• Application Number:
  US09/938,983
• Publication Number:
  US 20030040852A1
• Time in Patent Office: 851 Days
• Field of Search: 342/352, 342/357.02, 342/368, 342/372, 342/377, 342/173, 342/174, 342/358, 701/29, 701/31, 701/13, 455/9, 455/67.4, 455/67.5, 455/67.7, 455/115.1, 340/539, 714/49, 714/18
• US Class Current: 342/357.31
• CPC Class Codes: G01S 19/02 Details of the space or ground control segments
• CPC Class Codes: G01S 19/08 providing integrity information, e.g. health of satellites or quality of ephemeris data
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment

Abstract

A self-monitoring satellite system is disclosed to more quickly and accurately convey satellite signal information and verification of its reliability to users of the signal. In a first aspect, the satellite includes one or more receivers on the satellite to monitor the reliability of signals transmitted from the satellite. In a second aspect, a warning signal is generated and transmitted substantially simultaneous with an unreliable satellite signal and at the same frequency as the satellite signal. Exemplary embodiments to implement the various aspects of the self-monitoring satellite system invention are configured as global positioning system (GPS) satellites, signals, and receivers.

Claims

1. A self-monitoring satellite comprising:

a transmitter mounted on the satellite;

a receiver mounted on the satellite and configured to receive a signal transmitted from the satellite; and

a processor associated with the receiver and configured to interpret the received signal to determine position information, velocity information and time information included in the received signal, and to monitor the reliability of the determined information.

2. The self-monitoring satellite of claim 1, wherein the processor is configured to monitor at least one of pseudo-random code distortion, clock drift, signal power level, code-carrier divergence, data parity, code structure, clock rate, clock acceleration, signal deformation, and broadcast ephemeris and clock navigation data.

3. The self-monitoring satellite of claim 1, wherein the satellite is configured as a GPS satellite.

4. The self-monitoring satellite of claim 1, wherein the processor is further configured to generate a warning signal if the information is unreliable.

5. The self-monitoring satellite of claim 1, wherein the transmitter is configured to transmit the signal from the satellite at each of at least two frequencies.

6. The self-monitoring satellite of claim 5, wherein the at least two frequencies include a frequency of approximately 1575.42 MHz, a frequency of approximately 1227.60 MHz, and a frequency of approximately 1176 MHz.

7. The self-monitoring satellite of claim 4, wherein the transmitter is configured to transmit the warning signal at a frequency equal to a frequency of a transmitted signal to which the warning signal pertains.

8. A method of monitoring the reliability of a signal transmitted from a satellite, the method comprising:

receiving the signal on the satellite from which the signal was transmitted, the transmitted signal including position information, velocity information and time information; and

monitoring the information included in the received signal on the satellite for reliability.

9. The method of claim 8, wherein monitoring the information comprises monitoring at least one of pseudo-random code distortion, clock drift, signal power level, code-carrier divergence, data parity, code structure, clock rate, clock acceleration, signal deformation, and broadcast ephemeris and clock navigation data.

10. The method of claim 8, further comprising generating a warning signal regarding reliability of monitored information.

11. The method of claim 10, further comprising transmitting the warning signal substantially simultaneous with the satellite signal to which the warning data applies.

12. The method of claim 11, wherein transmitting the warning signal substantially simultaneous with the satellite signal comprises transmitting the warning signal less than 2 seconds after the satellite signal to which the warning signal applies is transmitted.

13. The method of claim 10, further comprising transmitting the warning signal at a frequency equal to a frequency at which the satellite signal to which the warning signal pertains was transmitted.

14. A method of warning a satellite signal user of an unreliable signal, the method comprising:

transmitting a satellite signal including satellite data to a receiver;

evaluating a characteristic of the transmitted satellite signal for reliability at the satellite;

transmitting a warning signal to the receiver, the warning signal including warning data relating to the reliability of the evaluated characteristic of the satellite signal;

receiving both the warning signal and the satellite signal at the receiver; and

determining whether to rely upon the satellite signal in response to the warning signal.

15. The method of claim 14, wherein evaluating the signal characteristic comprises evaluating at least one of pseudo-random code distortion, clock drift, signal power level, code-carrier divergence, data parity, code structure, clock rate, clock acceleration, signal deformation and broadcast ephemeris and clock navigation data.

16. The method of claim 14, further comprising transmitting the warning signal to the receiver substantially simultaneous with the satellite signal to which the warning signal applies.

17. The method of claim 16, wherein transmitting the warning signal substantially simultaneous with the satellite signal comprises transmitting the warning signal less than 2 seconds after the satellite signal to which the warning signal applies is transmitted.

18. The method of claim 16, further comprising transmitting the warning signal at a frequency equal to a frequency at which the satellite signal to which the warning signal pertains was transmitted.

19. The method of claim 14, wherein transmitting the satellite signal including satellite data comprises transmitting the satellite data on each of at least two different carrier frequencies.

20. A satellite signal system comprising a processor configured to determine the reliability of a satellite signal, generate a reliability indicator in response to the reliability determination at the satellite, and substantially simultaneously transmit the satellite signal and the reliability indicator to a receiver.

21. The satellite signal system of claim 20, wherein the satellite signal and the reliability indicator are substantially simultaneously transmitted from a satellite on which the satellite signal originated.

22. The satellite signal system of claim 20, wherein the satellite signal is relayed to the receiver by a ground based augmentation system substantially simultaneously with the ground based augmentation system transmitting the reliability indicator to the receiver.

23. The satellite signal system of claim 20, wherein the processor is further configured to transmit the satellite signal at each of at least two different frequencies.

24. The satellite signal system of claim 23, wherein the receiver is configured to receive the satellite signal at each of the two or more frequencies, evaluate each of the received frequencies separately, and compensate for any signal interference between the processor and the receiver.

25. A GPS satellite system comprising:

a plurality of satellites each transmitting a GPS satellite signal;

a first GPS satellite among the plurality of satellites transmitting a GPS satellite signal, the first GPS satellite comprising;

a first satellite receiver configured to monitor the GPS satellite signal transmitted from the first satellite; and

a processor associated with the receiver and configured to evaluate a characteristic of the monitored GPS satellite signal transmitted from the satellite and to transmit a warning signal approximately simultaneous with the transmitted GPS satellite signal if the GPS satellite signal is deemed unreliable; and

a receiver on earth configured to receive one or more transmitted GPS satellite signals and determine therefrom at least one of a position, a velocity and a time reference for the ground receiver.

26. The GPS satellite system of claim 25, the first satellite further comprising a transmitter configured to transmit each GPS satellite signal at each of two or more different frequencies.

27. The GPS satellite system of claim 26, wherein the frequencies comprise a frequency of approximately 1575.42 MHz, a frequency of approximately 1227.60 MHz, and a frequency of approximately 1176 MHz.

28. The GPS satellite system of claim 26, wherein the receiver on earth is configured to evaluate each of the two or more different frequencies separately and compensate for signal interference and ionospheric delay between the first GPS satellite and the receiver on earth in response to the evaluation of the different frequencies.

29. The GPS satellite system of claim 25, wherein the processor of the first GPS satellite is further configured to generate a warning signal if the monitored characteristic makes the GPS satellite signal transmitted from the first GPS satellite unreliable.

30. The GPS satellite system of claim 29, wherein the warning signal comprises warning data including information regarding at least one of which characteristic of the signal is unreliable, how long the signal has been unreliable, and to what extent the characteristic or signal is unreliable.

31. The GPS satellite system of claim 29, wherein the warning signal is transmitted substantially simultaneous with the satellite signal to which the warning signal corresponds.

32. The GPS satellite system of claim 31, wherein the warning signal is transmitted less than 2 seconds after the satellite signal to which the warning signal corresponds.

33. The GPS satellite system of claim 31, wherein the warning signal is transmitted at a frequency equal to a frequency at which the satellite signal to which the warning signal pertains was transmitted.

34. A method of bounding the inaccuracy of a GPS satellite signal at a receiver, the method comprising:

receiving a transmitted GPS satellite signal at a satellite from which the signal was transmitted;

monitoring at least one characteristic of the received signal for reliability; and

transmitting a warning signal approximately simultaneous with the transmitted GPS satellite signal if the signal is deemed unreliable.

35. The method of claim 34, wherein monitoring the characteristic comprises monitoring at least one of pseudo-random code distortion, clock drift, signal power level, code carrier divergence, data parity, code structure, clock rate, clock acceleration, signal deformation and broadcast ephemeris and navigation data.

36. The method of claim 34, further comprising transmitting the warning signal substantially simultaneous with satellite signal to which the warning signal applies.

37. The method of claim 36, wherein transmitting the warning signal substantially simultaneous with the satellite signal comprises transmitting the warning signal less than 2 seconds after the satellite signal to which the warning signal applies is transmitted.