Global position system (GPS) user receiver and geometric surface processing for all-in-view coherent GPS signal PRN codes acquisition and navigation solution

• US 7,688,261 B2
• Filed: 08/09/2006
• Issued: 03/30/2010
• Est. Priority Date: 03/15/2006
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: DiEsposti, Raymond S.
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US11/501,556
• Publication Number:
  US 20090171583A1
• Time in Patent Office: 1,329 Days
• Field of Search: 342/357.02, 342/357.06, 342/357.12, 342/357.15, 701/207, 701/213, 701/215
• US Class Current: 342/357.64
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• CPC Class Codes: G01S 19/252 Employing an initial estimate of location in generating assistance data
• CPC Class Codes: G01S 19/393 Trajectory determination or predictive tracking, e.g. Kalman filtering
• CPC Class Codes: G01S 19/51 Relative positioning

Abstract

A method and system for enabling a more robust detection, acquisition and positioning solution capability for a GPS device. The system and method uses GPS satellite ranging signals based on a simultaneous, all-in-view coherent PRN code signal processing scheme, rather than acquisition of GPS signals one at a time, in order to predict a location of a GPS user receiver. Additionally, image processing techniques, ultra-tight coupling processing techniques, or a combination thereof, are used to further enhance accuracy in determining the location of the user receiver. Signal processing techniques are used to determine the location of the GPS user receiver when no GPS satellite ranging signals can be individually detected, or when only one or two strong GPS satellite ranging signals can be individually detected in weak signal environments, jamming conditions, and a combination thereof.

Claims

1. A method of rapidly determining a location of a global positioning system (GPS) receiver, the method comprising:

using a base station having a known location to receive ranging signals ranging data from a plurality of satellites within view of the user receiver;

receiving, at the user receiver, from the base station, a set of initialization data, base-station location data, time aiding data and boundary data, prior to using said user receiver in attempting to determine a pseudorange of a first one of said satellites;

using the user receiver to receive a time synch function from the base station to synchronize a user receiver clock and ranging signals ranging data as received at the base station at an epoch time;

using the user receiver to search within a Earth-reference search space region and a predefined search space boundary having a plurality of grid point locations based on the base-station-location data;

acquiring simultaneously least two of the satellite ranging signals from each of the plurality of satellites in view of the user receiver;

searching over carrier phase angle combinations for received ranging signals at each of the plurality of grid points;

combining power outputs of the received ranging signals at each of the plurality of grid point locations, and determining therefrom a probable location of the user receiver; and

assessing reliability of the probable location.

2. The method of claim 1, wherein combining power outputs further comprises determining the probable location when a maximum coherently combined power output is detected.

3. The method of claim 2, further comprising:

analyzing a smoothed geometric surface model of combined power output surface data over the search space region to locate the maximum power output.

4. The method of claim 3, wherein analyzing the smoothed geometric surface model of the combined power output surface data further comprises:

adjusting a user receiver time offset to maximize each of the combined power outputs corresponding to a particular grid point location;

predicting an image pattern for the combined power outputs over the resulting search space region based on predicted geometry and signal characteristics of each said received satellite ranging signal;

applying algorithms and image processing techniques to analyze the smoothed geometric surface model relative to residual noise to enhance detection of the maximum power output;

generating discrimination parameters from the smoothed geometric surface model associated with slopes, peaks and ridges in the smoothed geometric surface model; and

validating the probable location solution by analyzing the discrimination parameters to confirm that the probable location corresponds to a maximum peak in the smoothed geometric surface model and that the ridges in the smoothed geometric surface model triangulate to the probable location.

5. The method of claim 4, wherein applying the image processing techniques further comprises applying the image processing techniques to smooth the noise relative to the image pattern, by fitting a smoothed predicted geometric surface model to the combined power output surface data;

and thus locking onto underlying signal surface characteristics to determine the maximum power output.

6. The method of claim 4, further comprising:

perturbing a converged ultra-tight coupling (UTC) GPS/INS solution;

processing the received ranging signals in order to coherently combine the power outputs at a converged UTC solution grid point;

processing the received ranging signals in order to attempt to coherently combine the power outputs of the received ranging signals at each of the plurality of grid point locations in a vicinity of the converged UTC GPS/INS coupling solution to determine a second probable location;

fitting a geometric surface model to the power outputs associated with the converged UTC GPS/INS solution grid point and the power outputs associated with nearby fit points;

determining the reliability of the converged UTC GPS/INS solution by;

analyzing the geometric surface model to determine if the converged UTC GPS/INS solution grid point corresponds to the maximum power output, indicating the processing is tracking actual GPS signals; and

analyzing the geometric surface model to determine if the converged solution may not be associated with a maximum power output peak, indicating the processing may not be tracking the actual GPS signals.

7. The method of claim 5, further comprising:

processing multiple snap shots of the geometric surface model over a predetermined period of time in order to determine the probable location.

8. The method of claim 7, wherein processing the multiple snap shots of the geometric surface model over time further comprises:

evolving the smoothed geometric surface model in a predictable fashion based on known geometry and use of motion models to predict dynamics of its geometric surface;

filtering the combined power outputs of the geometric surface over time to produce smooth combined power outputs;

interpolating the smoothed combined power outputs geometric surface model to locate the maximum combined power output at a particular grid point location and time epoch that corresponds to the probable location of the user receiver;

generating discrimination parameters associated with slopes, peaks and ridges in the smoothed power surface model; and

analyzing the discrimination parameters to confirm that the probable location corresponds to a maximum peak in the geometric surface and that the ridges in the geometric surface triangulate to the probable location.

9. The method of claim 1, wherein accessing the reliability of the probable location further comprises:

computing residual noise jitter of the combined power output data over the search space region relative to the smoothed geometric surface model; and

comparing the smoothed geometric surface model at the probable location to the residual noise jitter to predict reliability of the probable location.

10. The method of claim 1, wherein combining power outputs of the received satellite ranging signals further comprises:

determining when the combined power output data over the search space region or the smoothed geometric surface model indicates that no clear maximum power peak exists, thus indicating that the probable location cannot be reliably determined;

using algorithms which make use of a priori or received information to preferentially modify and control the processing for at least one of;

preferential use of a subset of the satellites in view of the user receiver associated with the strongest power levels,

preferential use of a type of PRN code signals,

preferentially processing signals from frequency bands with lower interference or higher predicted carrier-to-noise power ratio to enhance performance;

modifying signal combining weights; and

predicting the probable location of the user receiver.

11. The method of claim 1, wherein acquiring simultaneously at least one satellite ranging signal from the plurality of satellites in view further comprises:

determining when received ones of the satellite ranging signals include strong signals and weak signals;

determining when a number of the strong signals equal less than a predetermined number of strong signals needed to determine the probable location based on processing measured pseudoranges;

constraining the carrier phase angle combinations to measured quantities of the strong signals;

searching through the weak signals using a constrained search space region based on code and carrier phase measurement data related to the strong signals; and

determining the probable location where the search is performed only over the carrier phase angle offsets of the weak signals.

12. The method of claim 1, further comprising:

using ultra-tight coupling techniques to predict an optimal coherent integration time for processing each said satellite ranging signal and computing weights for combining each said power output of the satellite ranging signals.

13. A method for rapidly determining a position of a user receiver in a global positioning system, the method comprising:

using a base station remote from the receiver, and having a known location, to receive ranging signals ranging data from a plurality of satellites within view of the receiver;

using the receiver to receive, from the remote base station, a set of initialization data, base-station location data and time aiding data, prior to the receiver attempting to acquire satellite codes from a first one of the plurality of satellites in view of the receiver;

receiving from the remote base station, at the receiver, a time synch function to synchronize a user receiver clock and ranging data including code and carrier phase ranging data, as received at the remote base station, at an epoch time;

using the receiver to predict PRN code signal carrier phase angles relative to each one of a plurality of grid point locations within an Earth reference search space region;

using the receiver to search within the search space region at a plurality of grid point locations based on the base-station-location data, ranging data received from the remote station, and predicted PRN code phase and carrier phase angles;

acquiring simultaneously at least one of the ranging signals from each of the plurality of satellites in view of the user receiver; and

combining power outputs of the received ranging signals at each of the plurality of grid point locations, and determining therefrom a probable location of the receiver with the search space region.

14. The method of claim 13, wherein combining power outputs further comprises:

receiving carrier phase measurements from the base station at the epoch time in addition to the PRN code phase measurements;

using a finer resolution grid over the search space region in which spacing for the grid point locations are a fraction of a carrier cycle,

predicting the code phase measurements and the carrier phase measurements as received at each said grid point location;

at each said grid point location, adjusting the user receiver clock offset to maximize the combined power outputs; and

determining therefrom a probable location, wherein the grid point location associated with a maximum coherently combined power output indicates the probable location of the receiver.

15. A global positioning system (GPS) user receiver for rapidly determining a position of the user receiver in a global positioning system, the GPS user receiver comprising:

a user interface adapted to generate a request signal and receive an indication of a location of the user receiver;

a base-station-receiving portion for wirelessly receiving initialization data, ranging data as received by the base station at an epoch time, and base-station-location data to limit dimensions of a search space to a predetermined geographic area circumscribing a present location of the user receiver, in which the predetermined geographic area has a plurality of grid point locations, and to output a search signal in response and a time synch function in response thereto to synchronize a user receiver clock at an epoch time, prior to the user receiver attempting to acquire satellite ranging signals;

a navigation system configured to receive the initialization data and the base-station location data and to search within the predetermined geographic area for at least one of said satellite ranging signals from a plurality of GPS satellites that are within view of the user receiver, the navigation system operating to combine power outputs of all received ones of said ranging signals at each of the grid point locations within the predetermined geographic area to produce a maximum coherently combined power output value; and

a control processing unit in communication with the navigation system and configured to receive the maximum power output and to determine the location of the user receiver, and to output a location signal in response thereto.

16. The GPS receiver of claim 15, wherein the navigation system coherently combines the power outputs to determine the location of the user receiver when a maximum power output is detected.

17. The GPS receiver of claim 16, wherein the control processing unit operates to generate and analyze a smoothed geometric surface model fit to the combined power outputs over the search space region to locate the maximum coherently combined power output.

18. The GPS receiver of claim 17, wherein the control processing unit analyzes the smoothed geometric surface model of combined power outputs, and wherein the control processing unit uses smart algorithms and imaging processing techniques to analyze the combined power outputs and to determine the maximum power output based on peaks and ridges of the smoothed geometric surface model, and to assess the reliability of the probable user location solution by analyzing discrimination parameters extracted from the smoothed geometric surface model.

19. The GPS receiver of claim 15, wherein the control processing unit implements ultra-tight coupling to aide in determining the location of the user receiver during jamming conditions or weak signal environments.

20. The GPS receiver of claim 15, wherein the navigation system comprises at least one network bank of slaved correlators configured to combine power outputs of all received ranging signals at each of the plurality of grid point locations to thus provide the maximum coherently combined power output value at a probable user receiver location.