Systems and methods for acquisition and tracking of low CNR GPS signals

• US 20060071851A1
• Filed: 09/22/2005
• Published: 04/06/2006
• Est. Priority Date: 10/06/2004
• Status: Active Grant

• Current Assignee: Ohio University
• Original Assignee: Ohio University
• Inventors: Gunawardena, Sanjeev, Soloviev, Andrey, Graas, Frank van
• Granted Patent: US 8,013,789 B2
• Time in Patent Office: Days
• US Class Current: 342/357.395
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/246 involving long acquisition integration times, extended snapshots of signals or methods specifically directed towards weak signal acquisition
• CPC Class Codes: G01S 19/26 involving a sensor measurement for aiding acquisition or tracking
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial

Abstract

A receiver for continuous carrier phase tracking of low carrier-to-noise ratio (“CNR”) signals from a plurality of radio navigation satellites while the receiver is mobile. The receiver may have: a radio frequency (RF) front-end that provides satellite data corresponding to signals received from the plurality of radio navigation satellites; an inertial measurement unit (IMU) that provides inertial data; and a processor circuit in circuit communication with the RF front end and the IMU, the processor circuit being capable of using satellite data from the RF front-end and inertial data from the IMU to perform continuous carrier phase tracking of low CNR radio navigation satellite signals having a CNR of about 20 dB-Hz, while the receiver is mobile. The receiver may be a GPS receiver for continuous carrier phase tracking of low-CNR GPS signals.

Claims

1. A receiver for tracking of low carrier-to-noise ratio (“

CNR”

) signals from a plurality of radio navigation satellites while the receiver is mobile, comprising;

(a) a radio frequency (RF) front-end that provides satellite data corresponding to signals received from the plurality of radio navigation satellites; and

(b) an inertial measurement unit (MU) that provides inertial data; and

(c) a processor circuit in circuit communication with the RF front end and the IMU, the processor circuit being capable of using satellite data from the RF front-end and inertial data from the IMU to perform continuous carrier phase tracking of low CNR radio navigation satellite signals having a CNR of about 20 dB-Hz, while the receiver is mobile.

2. The receiver according to claim 1 wherein the processor circuit is capable of using satellite data from the RF front-end and inertial data from the IMU to acquire, and perform continuous carrier phase tracking of, low CNR satellite signals having a CNR of about 20 dB-Hz, while the receiver is mobile.

3. The receiver according to claim 1 wherein the processor circuit is capable of using satellite data from the RF front-end and inertial data from the IMU to perform continuous carrier phase tracking of low CNR satellite signals having a CNR of about 15 dB-Hz, while the receiver is mobile.

4. The receiver according to claim 1 wherein the processor circuit is capable of using satellite data from the RF front-end and inertial data from the IMU to acquire, and perform continuous carrier phase tracking of, low CNR satellite signals having a CNR of about 15 dB-Hz, while the receiver is mobile.

5. The receiver according to claim 1 wherein:

(a) the radio frequency (RF) front-end comprises a GPS front-end that provides GPS data corresponding to signals received from a plurality of GPS radio navigation satellites; and

(b) the processor circuit is in circuit communication with the GPS front end and the IMU and is capable of using GPS data from the GPS front-end and inertial data from the IMU to perform continuous carrier phase tracking of low CNR GPS satellite signals having a CNR of about 20 dB-Hz, while the receiver is mobile.

6. The receiver according to claim 5 wherein the processor is capable of using GPS data from the GPS front-end and inertial data from the IMU to perform continuous carrier phase tracking of low CNR GPS satellite signals having a CNR of about 15 dB-Hz, while the receiver is mobile.

7. The receiver according to any of claims 1-6 wherein the processor processes inertial data from the IMU so that the receiver appears to be stationary during satellite signal integration to increase satellite signal integration time.

8. The receiver according to any of claims 1-6 wherein the processor uses a Kalman filter to process inertial data from the IMU so that the receiver appears to be stationary during satellite signal integration to increase satellite signal integration time.

9. The receiver according to any of claims 1-6 wherein the processor is capable of continuously determining and outputting navigation data determined from the received low CNR satellite signals.

10. The receiver according to any of claims 5-6 wherein the processor is capable of continuously determining and outputting GPS code and carrier phase measurements determined from the received low CNR GPS satellite signals.

11. The receiver according to any of claims 1-6 wherein the processor is capable of continuously determining and outputting navigation data determined from the received low CNR satellite signals in the presence of broadband radio frequency interference at about 30 dB/MHz above the received satellite signal strength.

12. The receiver according to any of claims 5-6 wherein the processor is capable of continuously determining and outputting GPS code and carrier phase measurements determined from the received low CNR GPS satellite signals in the presence of broadband radio frequency interference at about 30 dB/MHz above the received GPS satellite signal strength.

13. The receiver according to claim 1 wherein the processor is capable of tracking and/or acquiring low CNR satellite signals having a CNR of about 15 dB-Hz, without using the actual values of navigation data bits broadcast by the radio navigation satellites.

14. The receiver according to claim 1 wherein the processor is capable of tracking and/or acquiring low CNR satellite signals having a CNR of about 15 dB-Hz, including using an energy-based bit estimation algorithm to determine values of navigation data bits broadcast by the radio navigation satellites, the estimation algorithm searching for a navigation data bit combination that maximizes signal energy over a tracking integration interval, without using the actual values of navigation data bits broadcast by the radio navigation satellites.

15. The receiver according to any of claims 1-6 wherein the processor is capable of decoding navigation data bits broadcast by the radio navigation satellites using the energy-based bit estimation, beat repeatability over frames, and compensating for sign reversals.

16. The receiver according to any of claims 1-6 further comprising a data sample interleaver to interleave received satellite data with inertial data from the IMU to permit association of the inertial data to the received satellite data without requiring the inertial data to be time-tagged to GPS time.

17. The receiver according to any of claims 1-6 further comprising a data sample interleaver to interleave received satellite data with other data received from at least one other source to permit association of the other data to the received satellite data without requiring the other data to be time-tagged to GPS time.

18. The receiver according to any of claims 1-6 wherein the low CNR radio navigation satellite signals are received with an antenna and there is a lever arm between the antenna and the IMU and further wherein the processor compensates for the lever arm between the antenna and the IMU.

19. The receiver according to any of claims 1-6 wherein the processor uses integrated velocity to calibrate the IMU.

20. The receiver according to any of claims 1-6 wherein the processor is capable of using carrier phase of low CNR radio navigation satellite signals to calibrate the IMU without resolving the integer ambiguities.

21. The receiver according to any of claims 1-6 wherein the processor comprises a split sum correlator permitting numerically controlled oscillators corresponding to satellites being tracked to be updated at a receiver epoch rather than a satellite signal epoch.

22. The receiver according to any of claims 1-6 wherein the processor comprises a split sum correlator permitting numerically controlled oscillators corresponding to all satellites being tracked to be updated at common receiver time epochs rather than non-common satellite time epochs, thereby simplifying the measurement computation process by eliminating the need to convert measurements that would otherwise have been made at satellite time epochs into a common receiver time epoch.

23. The receiver according to any of claims 1-6 wherein the processor comprises a split sum correlator that breaks the correlation result into two parts, corresponding to partial correlations about satellite time epochs, with respect to the receiver time epochs, thereby preventing destructive correlation due to navigation data bit sign changes.

24. The receiver according to claim 23 wherein the processor sends both parts of the correlation result to baseband processing software in unmodified form, where the baseband processing software compensates for the destructive energy correlation due to navigation bit sign changes.

25. The receiver according to claim 23 wherein the satellite time epochs are obtained from a G1 register of a C/A code generator.

26. The receiver according to any of claims 1-6 wherein the processor uses a frequency domain-based circular correlation operation and further uses a code Doppler compensation method in the frequency domain-based circular correlation operation.

27. The receiver according to any of claims 1-6 wherein the processor is capable of using satellite data from the RF front-end and inertial data from the IMM without using differential satellite signals based on data from a stationary receiver site to perform said continuous carrier phase tracking of low CNR radio navigation satellite signals while the receiver is mobile.

28. The receiver according to any of claims 1-6 wherein the processor compensates for motion of a correlation peak by:

(a) performing fine motion compensation to correct for sub-bin energy fading of the correlation peak by matching a conjugated FFT of a local C/A code (CAF) vector in a corresponding block engine to a corresponding code offset of an incoming satellite signal; and

(b) performing coarse motion compensation to correct for the bin-to-bin hopping of the fine motion compensated correlation peak by reading-in an associated input memory array in a translated order that compensates for a peak hop.

29. The receiver according to claim 28 wherein the processor:

(a) expresses the receiver'"'"'s time-of-transmission estimate in units of sub-bin-code-offset to switch (or index) a CAF memory bank that contains an appropriate CAF vector for performing fine peak motion compensation; and

(b) expresses the receiver'"'"'s time-of-transmission estimate in units of whole-bin-code-offset to translate a partial block correlation result vector to while performing block addition to increase the satellite signal integration time of the received signal.

30. The receiver according to any of claims 1-6 wherein the processor:

(a) expresses the receiver'"'"'s time-of-transmission estimate in units of sub-bin-code-offset to switch (or index) a CAF memory bank that contains an appropriate CAF vector for performing fine peak motion compensation; and

(b) expresses the receiver'"'"'s time-of-transmission estimate in units of whole-bin-code-offset to translate a partial block correlation result vector to while performing block addition to increase the satellite signal integration time of the received signal.

31. The receiver according to any of claims 1-6:

(a) further comprising a data sample interleaver to interleave received satellite data with inertial data from the IMU to permit association of the inertial data to the received satellite data without requiring the inertial data to be time-tagged to GPS time; and

(b) wherein the processor processes inertial data from the IMU so that the receiver appears to be stationary during satellite signal integration to increase satellite signal integration time;

(c) wherein the processor is capable of continuously determining and outputting navigation data determined from the received low CNR satellite signals;

(d) wherein the low CNR radio navigation satellite signals are received with an antenna and there is a lever arm between the antenna and the IMU; and

further wherein the processor compensates for the lever arm between the antenna and the IMU;

(e) wherein the processor uses integrated velocity to calibrate the IMU;

(f) wherein the processor comprises a split sum correlator permitting numerically controlled oscillators corresponding to satellites being tracked to be updated at a receiver epoch rather than a satellite signal epoch;

(g) wherein the processor uses a frequency domain-based circular correlation operation; and

(h) wherein the processor is capable of using satellite data from the RF front-end and inertial data from the IMU without using differential satellite signals based on data from a stationary receiver site to perform said continuous carrier phase tracking of low CNR radio navigation satellite signals while the receiver is mobile.

32. The receiver according to any of claims 1-6:

(a) further comprising a data sample interleaver to interleave received satellite data with inertial data from the IMU to permit association of the inertial data to the received satellite data without requiring the inertial data to be time-tagged to GPS time; and

(b) wherein the processor uses a Kalman filter to process inertial data from the IMU so that the receiver appears to be stationary during satellite signal integration to increase satellite signal integration time;

(c) wherein the processor uses an energy-based bit estimation algorithm to determine values of navigation data bits broadcast by the radio navigation satellites, the estimation algorithm searching for a navigation data bit combination that maximizes signal energy over a tracking integration interval, without using the actual values of navigation data bits broadcast by the radio navigation satellites;

(d) wherein the processor is capable of using carrier phase of low CNR radio navigation satellite signals to calibrate the IMU without resolving the integer ambiguities;

(e) wherein the low CNR radio navigation satellite signals are received with an antenna and there is a lever arm between the antenna and the IMM; and

further wherein the processor compensates for the lever arm between the antenna and the EMU;

(f) wherein the processor comprises a split sum correlator permitting numerically controlled oscillators corresponding to all satellites being tracked to be updated at common receiver time epochs rather than non-common satellite time epochs, thereby simplifying the measurement computation process by eliminating the need to convert measurements that would otherwise have been made at satellite time epochs into a common receiver time epoch;

(g) wherein the processor uses a frequency domain-based circular correlation operation and further uses a code Doppler compensation method in the frequency domain-based circular correlation operation; and

(h) wherein the processor is capable of using satellite data from the RF front-end and inertial data from the IMU without using differential satellite signals based on data from a stationary receiver site to perform said continuous carrier phase tracking of low CNR radio navigation satellite signals while the receiver is mobile.

33. The receiver according to claim 31 wherein the processor is capable of decoding navigation data bits broadcast by the radio navigation satellites using the energy-based bit estimation, beat repeatability over frames, and compensating for sign reversals.

34. The receiver according to claim 32 wherein the processor is capable of decoding navigation data bits broadcast by the radio navigation satellites using the energy-based bit estimation, beat repeatability over frames, and compensating for sign reversals.

35. The receiver according to claim 31 wherein the processor compensates for motion of a correlation peak by:

(a) performing fine motion compensation to correct for sub-bin energy fading of the correlation peak by matching a conjugated FFT of a local C/A code (CAF) vector in a corresponding block engine to a corresponding code offset of an incoming satellite signal; and

(b) performing coarse motion compensation to correct for the bin-to-bin hopping of the fine motion compensated correlation peak by reading-in an associated input memory array in a translated order that compensates for a peak hop.

36. The receiver according to claim 32 wherein the processor compensates for motion of a correlation peak by:

(a) performing fine motion compensation to correct for sub-bin energy fading of the correlation peak by matching a conjugated FFT of a local C/A code (CAF) vector in a corresponding block engine to a corresponding code offset of an incoming satellite signal; and

(b) performing coarse motion compensation to correct for the bin-to-bin hopping of the fine motion compensated correlation peak by reading-in an associated input memory array in a translated order that compensates for a peak hop.

37. The receiver according to claim 32 wherein the processor comprises a split sum correlator that breaks the correlation result into two parts, corresponding to partial correlations about satellite time epochs, with respect to the receiver time epochs, thereby preventing destructive correlation due to navigation data bit sign changes.

38. The receiver according to claim 37 wherein the processor sends both parts of the correlation result to baseband processing software in unmodified form, where the baseband processing software compensates for the destructive energy correlation due to navigation bit sign changes.

39. A method of tracking of low carrier-to-noise ratio (“

CNR”

) signals from a plurality of radio navigation satellites while the receiver is mobile, comprising the steps of;

(a) receiving signals from the plurality of radio navigation satellites;

(b) providing satellite data corresponding to the signals received from the plurality of radio navigation satellites;

(c) providing inertial data from an inertial measurement unit (IMU); and

(d) using the satellite data and the inertial date to perform continuous carrier phase tracking of low CNR radio navigation satellite signals having a CNR of about 20 dB-Hz, while the receiver is mobile.

40. A receiver for tracking of low carrier-to-noise ratio (“

CNR”

) signals from a plurality of radio navigation satellites while the receiver is stationary (dynamic motion of less than 2 cm/s), comprising;

(a) a radio frequency (RF) front-end that provides satellite data corresponding to signals received from the plurality of radio navigation satellites; and

(b) a processor circuit in circuit communication with the RF front end, the processor circuit being capable of using satellite data from the RF front-end to perform continuous carrier phase tracking of low CNR radio navigation satellite signals having a CNR of about 20 dB-Hz, while the receiver is stationary.

41. The receiver according to claim 40 wherein the processor circuit is capable of using satellite data from the RF front-end to acquire, and perform continuous carrier phase tracking of, low CNR satellite signals having a CNR of about 20 dB-Hz, while the receiver is stationary.

42. The receiver according to claim 40 wherein the processor circuit is capable of using satellite data from the RF front-end to perform continuous carrier phase tracking of low CNR satellite signals having a CNR of about 15 dB-Hz, while the receiver is stationary.

43. The receiver according to claim 40 wherein the processor circuit is capable of using satellite data from the RF front-end to acquire, and perform continuous carrier phase tracking of, low CNR satellite signals having a CNR of about 15 dB-Hz, while the receiver is stationary.

44. The receiver according to claim 40 wherein:

(a) the radio frequency (RF) front-end comprises a GPS front-end that provides GPS data corresponding to signals received from a plurality of GPS radio navigation satellites; and

(b) the processor circuit is in circuit communication with the GPS front end and is capable of using GPS data from the GPS front-end to perform continuous carrier phase tracking of low CNR GPS satellite signals having a CNR of about 20 dB-Hz, while the receiver is stationary.

45. The receiver according to claim 44 wherein the processor is capable of using GPS data from the GPS front-end to perform continuous carrier phase tracking of low CNR GPS satellite signals having a CNR of about 15 dB-Hz, while the receiver is stationary.