Systems, Methods, Devices And Subassemblies For Rapid-Acquisition Access To High-Precision Positioning, Navigation And/Or Timing Solutions
Position, navigation and/or timing (PNT) solutions may be provided with levels of precision that have previously and conventionally been associated with carrier phase differential GPS (CDGPS) techniques that employ a fixed terrestrial reference station or with GPS PPP techniques that employ fixed terrestrial stations and corrections distribution networks of generally limited terrestrial coverage. Using techniques described herein, high-precision PNT solutions may be provided without resort to a generally proximate, terrestrial ground station having a fixed and precisely known position. Instead, techniques described herein utilize a carrier phase model and measurements from plural satellites (typically 4 or more) wherein at least one is a low earth orbiting (LEO) satellite. For an Iridium LEO solution, particular techniques are described that allow extraction of an Iridium carrier phase observables, notwithstanding TDMA gaps and random phase rotations and biases inherent in the transmitted signals.
Latest Apple Patents:
This application is a continuation of U.S. Pat. No. 13/935,885, filed Jul. 5, 2013, which claims priority to U.S. provisional applications 61/668,984, filed Jul. 6, 2012, and 61/691,661, filed Aug. 21, 2012, each entitled “Systems, Methods, Devices and Subassemblies for Rapid-Acquisition Access to High-Precision Positioning, Navigation and/or Timing Solutions.” The entirety of each of the foregoing applications in incorporated by reference herein.
BACKGROUND1. Field of the Invention
The present invention relates to high-precision position, navigation and/or timing (PNT) solutions based on signals received from overhead assets such as satellites and, in particular, to techniques suitable for providing rapid acquisition access to such PNT solutions without resort to a generally proximate, terrestrial ground station with fixed and precisely known position. This disclosure relates generally to location-based services.
2. Description of the Related Art
Traditional precision satellite navigation techniques such as real time kinematic (RTK) and differential GPS (DGPS) techniques commonly used in surveying and high accuracy timing applications, depend on a terrestrial reference station in close proximity to the receiver to provide the receiver with measurements from satellites within view of both the terrestrial reference station and the receiver itself. The receiver commonly differences these reference station measurements (typically carrier phase measurements) with its own, and extracts extremely accurate and precise positioning and timing information from the differenced measurements. GPS-based precise point positioning (PPP) techniques employ a network of terrestrial reference stations to observe satellite orbits and, based thereon, broadcast corrections to receiver equipment via geosynchronous (GEO) satellites or a terrestrial communications network. In each case, centimeter-level in positioning solutions may be achieved. Unfortunately, RTK, DGPS and PPP techniques all require warm-up (convergence) times of about thirty (30) minutes to achieve high accuracy and/or integrity solutions. In addition, requirements for fixed terrestrial reference stations and/or coverage patterns of terrestrially-based, or geosynchronous overhead, correction distribution infrastructure can limit availability of conventional high-precision navigation techniques.
Improved techniques are desired.
SUMMARYIt has been discovered that position, navigation and/or timing (PNT) solutions may be provided with levels of precision that have previously and conventionally been associated with carrier phase differential GPS (CDGPS) techniques that employ a fixed terrestrial reference station or with GPS PPP techniques that employ fixed terrestrial stations and corrections distribution networks of generally limited terrestrial coverage. Using techniques described herein, high-precision PNT solutions may be provided without resort to a generally proximate, terrestrial ground station having a fixed and precisely known position. Instead, techniques described herein utilize a carrier phase model and measurements from plural satellites (typically 4 or more) wherein at least one is a low earth orbiting (LEO) satellite. For an Iridium LEO solution, particular techniques are described that allow extraction of an Iridium carrier phase observables, notwithstanding TDMA gaps and random phase rotations and biases inherent in the transmitted signals.
Receiver solution quality (at least for high precision solutions) can depend strongly on angular motion of a satellite across the sky, which for typically GNSS constellations such as the mid-Earth orbit (MEO) typical of GPS, GLONASS, Galileo and Compass (BeiDou-2) constellations, is quite slow. High quality solutions may require many tens of minutes. However, by including (e.g., modeling and measuring carrier phase for signals received from) at least one LEO satellite, high-quality, reference stationless solutions may be provided in a fraction of the time. Extraction of Iridium carrier phase observables presents particular challenges that can be addressed using techniques described herein. In addition, by eliminating the necessity of a fixed terrestrial reference station employed by conventional RTK or CDGPS systems and/or by untethering from GPS PPP correction distribution infrastructure of generally limited terrestrial coverage, the developed techniques can allow greater deployment flexibility.
Using the developed techniques, a receiver uses un-differenced carrier phase measurements directly to eliminate the need for a fixed terrestrial reference station. Instead, the receiver leans on the satellite as a space-based “reference station”, effectively transferring the quality of the satellite's clock and knowledge of the satellite's orbit into its own solution. In typical MEO- and geosynchronous (GEO)-based satellite navigation, though, this technique would yield the undesirable property that the ambiguities in the satellite measurements could not be resolved in a practical amount of time to be useful, since the geometrical relationship between the receiver and the visible MEO/GEO satellites changes slowly over the course of several hours. However, by employing at least one low Earth orbit (LEO) satellite, rapid movement across the sky provides useful geometrical variation that allows ambiguities for all satellites (including any available MEO/GEO satellites) to be resolved with greatly reduced startup (convergence) time. For an exemplary LEO constellation of interest, namely the Iridium constellation, signal structure complexities have been addressed which allow extraction of useful carrier phase observables.
In some embodiments in accordance with the present invention, a method includes receiving at a navigation radio, signals transmitted from a first low earth orbit (LEO) satellite and computing therefrom first carrier phase measurements spanning first and second time epochs during a single overhead pass of the first LEO satellite; receiving at the navigation radio, signals transmitted from at least three additional satellites and computing therefrom respective carrier phase measurements including at least respective second, third and fourth carrier phase measurements; and computationally estimating parameters, including at least receiver position and time parameters, of a system of equations that model carrier phase for signals transmitted from the first LEO satellite at the first and second successive time epochs and for the least three additional satellites. The computing of carrier phase measurements spanning first and second time epochs during a single overhead pass of the first LEO satellite includes using motion constraints to patch temporal gaps in the received signals transmitted from the first LEO satellite and statistically estimating to substantially eliminate from the computed carrier phase measurements otherwise random phase rotations in the received signals transmitted from the first LEO satellite.
In some embodiments, none of the first, second, third or fourth carrier phase measurements used in the estimation or receiver position and time parameters is differenced from carrier phase measured at a fixed terrestrial reference station. In some embodiments, time elapsed between the first and second time epochs provides, from perspective of the receiver, at least about twenty degrees (20°) of angular travel by the first LEO satellite along the single overhead pass. In some embodiments, the at least three additional satellites are part of a medium earth orbit (MEO) constellation.
DESCRIPTION OF THE DRAWINGSThe present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. Further details are provided in Appendix A, which forms an integral portion of the present disclosure.
In the illustrated embodiment, GPS and Iridium RF data are received via combined RF front end. Although the exemplary embodiment of
Claims
1. A method comprising:
- receiving, by an augmentation subsystem, radio frequency (RF) data from a global navigation satellite system (GNSS) receiver;
- receiving, by the augmentation subsystem and from the GNSS receiver, a first position, navigation and timing (PNT) solution;
- receiving, by the augmentation subsystem and from the GNSS receiver, a query for low Earth orbit (LEO) satellite data;
- computing, by the augmentation subsystem, LEO satellite carrier phase observables from the RF data;
- computing, by the augmentation subsystem, a response to the query, wherein computing the response comprises eliminating random phase rotations from the computed LEO carrier phase observables based on the first PNT solution; and
- providing, by the augmentation subsystem, the response to the GNSS receiver for estimating a second PNT solution.
2. The method of claim 1, wherein the RF data is received by a frontend of the GNSS receiver and shared with the augmentation subsystem by the GNSS receiver.
3. The method of claim 1, wherein eliminating the random phase rotations is further based on measurements from an inertial measurement unit (IMU) of the augmentation subsystem.
4. The method of the claim 1, wherein the augmentation subsystem is implemented as an add-on card of the GNSS receiver.
5. The method of claim 1, wherein the augmentation subsystem is implemented as a built-in component the GNSS receiver.
6. A location system comprising:
- an augmentation subsystem including an inertial measurement unit (IMU); and
- a global navigation satellite system (GNSS) receiver, wherein the augmentation subsystem is configured to perform operations comprising: receiving radio frequency (RF) data from the GNSS; receiving, from the GNSS receiver, a first position, navigation and timing (PNT) solution; receiving, from the GNSS receiver, a query for low Earth orbit (LEO) satellite data; computing LEO satellite carrier phase observables from the RF data; computing a response to the query, wherein computing the response comprises eliminating random phase rotations from the computed LEO carrier phase observables based on the first PNT solution; and providing the response to the GNSS receiver for estimating a second PNT solution.
7. The system of claim 6, wherein the RF data is received by a frontend of the GNSS receiver and shared with the augmentation subsystem by the GNSS receiver.
8. The system of claim 6, wherein eliminating the random phase rotations is further based on measurements from an inertial measurement unit (IMU) of the augmentation subsystem.
9. The system of the claim 6, wherein the augmentation subsystem is implemented as an add-on card of the GNSS receiver.
10. The system of claim 6, wherein the augmentation subsystem is implemented as a built-in component the GNSS receiver.
11. A non-transitory computer-readable medium storing instructions operable to cause an augmentation subsystem including an inertial measurement unit (IMU) to perform operations comprising:
- receiving radio frequency (RF) data from a global navigation satellite system (GNSS) receiver;
- receiving, from the GNSS receiver, a first position, navigation and timing (PNT) solution;
- receiving, from the GNSS receiver, a query for low Earth orbit (LEO) satellite data;
- computing LEO satellite carrier phase observables from the RF data;
- computing a response to the query, wherein computing the response comprises eliminating random phase rotations from the computed LEO carrier phase observables based on the first PNT solution; and
- providing the response to the GNSS receiver for estimating a second PNT solution.
12. The non-transitory computer-readable medium of claim 11, comprising a field-programmable gate array (FPGA).
13. The non-transitory computer-readable medium of claim 11, wherein the RF data is received by a frontend of the GNSS receiver and shared with the augmentation subsystem by the GNSS receiver.
14. The non-transitory computer-readable medium of claim 11, wherein eliminating the random phase rotations is further based on measurements from an inertial measurement unit (IMU) of the augmentation subsystem.
15. The non-transitory computer-readable medium of the claim 11, wherein the augmentation subsystem is implemented as an add-on card of the GNSS receiver.
16. The non-transitory computer-readable medium of claim 11, wherein the augmentation subsystem is implemented as a built-in component the GNSS receiver.
Type: Application
Filed: Jun 6, 2016
Publication Date: Oct 27, 2016
Applicant: Apple Inc. (Cupertino, CA)
Inventors: Isaac T. Miller (El Granada, CA), Clark E. Cohen (Washington, DC), Robert W. Brumley (San Mateo, CA), William J. Bencze (Half Moon Bay, CA), Brent M. Ledvina (San Francisco, CA), Thomas J. Holmes (Palo Alto, CA), Mark L. Psiaki (Brooktondale, NY)
Application Number: 15/174,957