Method and system for all-in-view coherent GPS signal PRN codes acquisition and navigation solution determination

• US 20070216575A1
• Filed: 03/15/2006
• Published: 09/20/2007
• Est. Priority Date: 03/15/2006
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: DiEsposti, Raymond
• Granted Patent: US 7,579,986 B2
• Time in Patent Office: Days
• US Class Current: 342/357.640
• CPC Class Codes: G01S 19/252 Employing an initial estimate of location in generating assistance data

Abstract

A method and system of the present disclosure allow for a more robust detection of 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. Additionally, the method and system may enable 10 dB or more improvement in signal-to-ratio (SNR) acquisition performance of the combined signals when compared to conventional acquisition approaches of acquiring GPS PRN code signals one at a time. The method and system also automatically enables removal of ranging errors common to both the user and base station and minimizes the introduction of multi-path errors into code phase measurements.

Claims

1. A method for rapidly acquiring and using a plurality of satellite ranging signals having satellite codes to rapidly determine a real time position of a user receiver, the method comprising:

using a wireless assist link to transmit to the user receiver, from a base station, a set of initialization data and base-station-location data to limit a search space grid, in which the user receiver is located, to predetermined geographic dimensions;

using the base station to transmit to the user receiver a time synch function to enable the user receiver to synchronize a user receiver clock, and satellite ranging data as received at the base station at an epoch time;

using the user receiver to search within the search space grid based on the base-station-location data and acquire simultaneously at least one of the satellite codes from a plurality of satellites in view of the user receiver; and

using the user receiver to combine coherently received satellite codes and to detect therefrom a probable location of the user receiver.

2. The method of claim 1, further comprising:

using the user receiver to detect a grid point location within the predetermined geographic dimensions at which the received satellite codes will be coherently combined.

3. The method of claim 1, wherein the set of initialization data and the time synch function are used to predict at least one satellite code phase for each of the plurality of satellites in the search grid point.

4. The method of claim 3, wherein each satellite code signal phase at a grid point is predicted using geometric relationships relative to the base station.

5. The method of claim 4, wherein each satellite predicted code phases at the grid point is used to acquire simultaneously a plurality of satellite ranging signal code phases as received by the user receiver.

6. The method of claim 1, wherein the operation of combining coherently the received satellite codes comprises:

analyzing a power output produced by each of the received satellite codes at each of a plurality of grid point locations in geographic dimensions;

summing coherently all of the power outputs for each of the plurality of grid point locations; and

determining when a summed power output indicates a maximum power value for the plurality of grid point locations within the geographic dimensions to identify the probable location of the user receiver.

7. The method of claim 1, further comprising:

providing time aiding to reduce error time of the user receiver and aid acquisition of the satellite codes;

providing frequency aiding to reduce or eliminate the frequency search space; and

adjusting a code phase for any change in satellite motion since the epoch time.

8. The method of claim 1, wherein the geographic dimensions comprises a two-dimensional grid or a three-dimensional grid of Earth coordinates.

9. The method of claim 8, wherein the two-dimensional grid comprises no greater than about 10 km×

10 km square.

10. The method of claim 1, wherein the set of initialization data comprises at least one of:

almanac data;

satellite ephemeris data;

clock data; and

size or boundary data, and base station ranging measurements for the search space grid.

11. A method for determining a position of a user receiver using satellite ranging signals, comprising:

transmitting to a user receiver, from a base station via a wireless assist link, initialization data and base-station-location data to limit a search by the user receiver for a plurality of satellite ranging signals to a predetermined geographic area circumscribing a present location of the user terminal;

using the user receiver to search within the predetermined geographic area having a plurality of gird point locations for each of the plurality of satellite ranging signals from each spaced-based GPS satellite that is within view of the user receiver;

using the user receiver to combine, coherently, a power output of all received ones of said ranging signals at each of the plurality of grid point locations within the predetermined geographic area, to determine a maximum power output value; and

having the user receiver use the maximum power output value to extrapolate a probable location of the user terminal.

12. The method of claim 11, further comprising:

searching over at least one carrier phase combination within the geographic area to detect and acquire simultaneously all of the GPS satellite ranging signals sent by the satellites in view of the user receiver;

providing time aiding to reduce time error of the user receiver and aid the search;

providing frequency aiding to reduce or eliminate frequency search space; and

estimating the probable location for the user receiver relative to the base station based on selecting a combined signal power that corresponds to a maximum combined power over the geographic area.

13. The method of claim 12, wherein the maximum power output value is indicative of a highest summed power output of all said satellite ranging signals present for each of the grid point locations, that identifies the probable location of the user receiver.

14. The method of claim 11, further comprising:

reducing the geographic area based on the probable location;

searching over at least one carrier phase combination within a reduced search area grid to detect and acquire simultaneously a second set of GPS satellite ranging signals;

detecting a grid point location within the reduced search space grid;

adjusting a code phase for any change in satellite motion since epoch time;

combining coherently each satellite code of the second set of GPS satellite ranging signals at the grid point location to produce a second combined power output;

determining whether the second combined power output indicates a refined location for the user receiver; and

estimating the refined location of the user receiver relative to the base station within the reduced search area grid.

15. The method of claim 11, wherein the geographic area further comprises a two-dimensional group of Earth coordinates of no larger than about a 10 km×

10 km square.

16. The method of claim 11, wherein the geographic area further comprises a three dimensional group of Earth coordinates.

17. The method of claim 11, wherein the initial data comprises almanac or satellite ephemeris and clock data, satellite PRN ranging data including satellite ranging measuring data as received at the base station at an epoch time, and size and boundary data to limit the search space grid, in which the user receiver is located.

19. The system of claim 17, wherein the user receiver is further configured to refine the probable location by searching over at least one carrier phase combination within a reduced search area grid and to estimate a refined location of the user receiver relative to the base station.

20. The system of claim 17, wherein the user receiver is further configured to detect a plurality of grid point locations within the search space grid and coherently sum the power outputs of each of the ranging signals at each of the plurality of grid point locations to determine a maximum power output.

21. The system of claim 19, wherein the maximum power output corresponds to a highest power output of the plurality of grid point locations found within the search space grid, such that the maximum power identifies the probable location.

18. A global positioning system (GPS) for rapidly determining a position of a user receiver from satellite ranging signals from a plurality of satellites in view of the user receiver, comprising:

a plurality of GPS satellites configured to produce a plurality of GPS satellite ranging signals having a pseudo random code;

a base station configured to generate a set of initialization data, time synch function, and base-station-location data to limit a search space grid to predetermined geographic dimensions, the base station is further configured to receive the plurality of GPS satellite ranging signals to produce time aiding data to synchronize a user receiver clock to reduce time error for the search space grid and aid acquisition of the plurality of GPS ranging signals and to transmit the time aiding data and the set of initialization data; and

a user receiver in wireless communication with the base station and is configured to receive the set of initialization data and the time aiding data, the user receiver is further configured to receive the time synch function to synchronize a user receiver clock and ranging signals ranging data as received at the base station at an epoch time, the user receiver is operable to search within the search space grid based on the base-station-location data and acquire simultaneously at least one of the ranging signals from the plurality of satellites in view of the user receiver, and the user receiver being further configured to combine coherently power outputs of received ranging signals, and to detect therefrom a probable location of the user receiver.