GPS receiver using coarse orbital parameters for achieving a fast time to first fix

• US 6,225,945 B1
• Filed: 09/22/1999
• Issued: 05/01/2001
• Est. Priority Date: 09/22/1999
• Status: Active Grant

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Loomis, Peter Van Wyck
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Mull, Fred H
• Application Number:
  US09/401,442
• Time in Patent Office: 587 Days
• Field of Search: 342/357.12, 342/357.14, 342/357.06, 342/357.13, 701/213, 701/216
• US Class Current: 342/357.46
• 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 19/40 Correcting position, velocity or attitude
• CPC Class Codes: G01S 19/52 Determining velocity

Abstract

A GPS receiver having a fast time to first fix by comparing measured range rates for GPS satellites to GPS satellite velocities that are calculated from coarse GPS satellite orbital parameters. The coarse GPS satellite parameters are GPS almanac parameters or GPS ephemeris parameters that are older than the GPS-specified curve fit interval. The GPS receiver includes a satellite velocity calculator and a satellite line-of-sight calculator using the coarse GPS satellite orbital parameters previously stored in memory for calculating GPS satellite velocities and unit vectors to GPS satellites, respectively; a range rate measurer using GPS signal carrier measurements for determining range rates to GPS satellites; a user velocity calculator using the satellite velocities, unit vectors, and range rates for calculating a user velocity; and a user location integrator for integrating the user velocity from the last user location for a first location fix. Optionally, the user velocity calculator provides user direction information that can be used for initializing an inertial navigation device.

Claims

1. A method for a fast time to first fix in a global positioning system (GPS) receiver, comprising steps of:

calculating a satellite velocity for said GPS satellite from coarse orbital parameters, said coarse orbital parameters including at least one of (i) ephemeris data having an age greater than a selected aging time period and (ii) almanac data;

measuring a range rate to said GPS satellite;

calculating a user velocity of said GPS receiver from said satellite velocity and said range rate;

retrieving a last location fix for said GPS receiver; and

calculating a new location fix from said last location fix and said user velocity.

2. The method of claim 1, further comprising steps of:

calculating a unit vector for a satellite direction to said GPS satellite; and

wherein;

the step of calculating said user velocity includes using said unit vector.

3. The method of claim 1, wherein:

the step of measuring said range rate includes steps of making carrier measurements on a GPS signal from said GPS satellite; and

determining said range rate from said carrier measurements.

4. A method for a fast time to first fix in a global positioning system (GPS) receiver, comprising steps of:

calculating a satellite velocity for said GPS satellite from coarse orbital parameters, said coarse orbital parameters including at least one of (i) ephemeris data having an age greater than a selected aging time period and (ii) almanac data;

measuring a range rate to said GPS satellite;

calculating a user velocity of said GPS receiver using said satellite velocity and said range rate; and

determining a user direction from said user velocity.

5. The method of claim 4, further comprising a step of:

initializing an inertial navigation device with said user direction.

6. The method of claim 4, further comprising steps of:

calculating a unit vector for a satellite direction to said GPS satellite; and

wherein;

the step of calculating said user velocity includes using said unit vector.

7. The method of claim 4, wherein:

the step of measuring said range rate includes steps of making carrier measurements on a GPS signal from said GPS satellite; and

determining said range rate from said carrier measurements.

8. A GPS receiver, comprising:

a memory for storing a last user location fix for the GPS receiver and coarse orbital parameters pertaining to a GPS satellite, said coarse orbital parameters including at least one of (i) ephemeris data having an age greater than a selected aging time period and (ii) almanac data;

a satellite velocity calculator for calculating a satellite velocity of said GPS satellite from said coarse orbital parameters;

a range rate measurer for measuring a range rate to said GPS satellite;

a user velocity calculator for calculating a user vector of said GPS receiver from said satellite velocity and said range rate; and

a user location integrator for calculating a new location fix from said last location fix and said user velocity.

9. The GPS receiver of claim 8, further comprising:

a line-of-sight calculator for calculating a unit vector for a satellite direction to said GPS satellite; and

wherein;

the user velocity calculator is further for using said unit vector for calculating said user velocity.

10. The GPS receiver of claim 8, wherein:

the range rate measurer is further for determining said range rate using carrier measurements on a GPS signal from said GPS satellite.

11. A GPS receiver, comprising:

a memory for storing a last user location fix for the GPS receiver and coarse orbital parameters pertaining to a GPS satellite, said coarse orbital parameters including at least one of (i) ephemeris data having an age greater than a selected aging time period and (ii) almanac data;

a satellite velocity calculator for calculating a satellite velocity of said GPS satellite from said coarse orbital parameters;

a range rate measurer for measuring a range rate to said GPS satellite; and

a user velocity calculator for calculating a user vector of said GPS receiver from said satellite velocity and said range rate, determining a user direction from said user velocity, and providing information for said user direction.

12. The GPS receiver of claim 11, wherein:

said user direction is for use for initializing an inertial navigation device.

13. The GPS receiver of claim 11, further comprising:

a line-of-sight calculator for calculating a unit vector for a satellite direction to said GPS satellite; and

wherein;

the user velocity calculator is further for using said unit vector for calculating said user velocity.

14. The GPS receiver of claim 11, wherein:

the range rate measurer is further for determining said range rate using carrier measurements on a GPS signal from said GPS satellite.