Network for carrier phase differential GPS corrections

• US 5,477,458 A
• Filed: 01/03/1994
• Issued: 12/19/1995
• Est. Priority Date: 01/03/1994
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Loomis, Peter V. W.
• Primary Examiner(s): Chin, Gary
• Assistant Examiner(s): PHAN, THAI Q
• Application Number:
  US08/177,011
• Time in Patent Office: 715 Days
• Field of Search: 364/449, 364/458, 364/459, 364/444, 364/443, 342/357, 342/352, 342/463
• US Class Current: 701/215
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/071 DGPS corrections
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]

Abstract

Method and apparatus for providing GPS pseudorange correction information over a selected geographic region S with a diameter of up to 3000 km with an associated inaccuracy no greater than 5 cm. N spaced apart GPS fiducial stations (N≧3), whose location coordinates (u_n, v_n, v_n) are fixed and are known with high accuracy, are provided within or adjacent to the region R. Each fiducial station n (n=1, 2, . . . , N) receives GPS signals from at least four common-view GPS satellites, numbered m=1, 2, . . . , M (M≧3), computes its own GPS-determined location coordinates, compares these coordinates with its known location coordinates determines the pseudorange corrections PRC(t;t0;m;n) for its GPS-determined location, and transmits these correction signals to a central station located within or adjacent to the region S. The central station retransmits the pseudorange correction signals throughout the region S. A mobile GPS station within or adjacent to the region S has stored within its coordinates (u'"'"', v'"'"', w'"'"') of the GPS determined last location of that mobile station and the spatial coordinates (u_n(k), v_n(k), w_n(k)) (k=1, 2, . . . , K; K≧3) of K GPS fiducial stations within S that are closest to the last determined location of that mobile station. The mobile station then computes the differential GPS corrections for the GPS- determined present location of that mobile station. Alternatively, the fiducial stations can transmit to the central station unprocessed GPS signals for determination of the pseudorange correction signals at the central station. This approach can be modified it the region S is two-dimensional, where only one coordinate u is needed.

Claims

1. A method of providing GPS pseudorange and carrier phase correction information over a selected geographic region S with a diameter of up to about 3000 km with an associated inaccuracy as low as 5 cm, to provide increased accuracy for a GPS user in moving from a first selected location A to a second selected location B, the method comprising the steps of:

(1) providing N spaced apart GPS fiducial stations, numbered n=1, 2, . . . , N (N≧

3), whose location coordinates (u_n,v_n,w_n) in a selected coordinate system are fixed and known with high accuracy, within the region S;

(2) causing each fiducial station to receive GPS information signals including pseudorange information and carrier phase information from M GPS satellites, numbered m=1, 2, . . . , M (M≧

3), to compute the GPS-determined location of that fiducial station, to compute pseudorange corrections PRC(t;

t0;

m;

n) at a selected time t0, which are valid for times t≧

t0 that are near t0 and which reconcile the GPS-determined location with the known location of fiducial station number n using GPS signals received from satellite number m, to compute cumulative carrier phase correction signals χ

(t;

t0;

m;

n) corresponding to receipt at fiducial station number n of GPS carrier phase information from satellite number m, and to broadcast these pseudorange correction signals and carrier phase correction signals;

(3) providing a GPS user with a mobile GPS station within the region S, which has stored within the station the coordinates (u'"'"',v'"'"',w'"'"') of an estimated present location vector u'"'"' of that mobile station and the spatial coordinates (u_n(k), v_n(k), w_n(k)) (k=1, 2, . . . , K;

K≧

3) of K GPS fiducial stations with corresponding location vectors u_n(k) within S that form a bounding polygon for the estimated present location of that mobile station, where the mobile station receives at least one of (i) a set of pseudorange signals PR(t;

t0;

m;

mobile) and (ii) a set of carrier phase signals Φ

(t;

t0;

m;

mobile) from the GPS satellites and receives at least one of (i) a set of pseudorange correction signals PRC(t;

t0;

m;

n) (m=1, . . . , M) and (ii) a set of carrier phase correction signals χ

(t;

t0;

m;

n) from the fiducial stations number n=n(k) (k=1,2, . . . , K), where the GPS user is to move from a first selected location A to a second selected location B;

(4) selecting coefficients a_k '"'"' that minimizes the norm of the vector difference ##EQU6## under the constraint a₁ '"'"'+a₂ '"'"'+ . . . +a_K '"'"'=1, with -0.5≦

a_k '"'"'≦

1.5, for a selected number p>

0;

(5) determining at least one of (1) a set of pseudorange corrections and for that mobile station at its present location by the relations ##EQU7## and (2) a set of carrier phase correction signals for that mobile station at its present location by the relations ##EQU8## (6) computing at least one of (1) a set of corrected pseudorange signals for this mobile station, using the relations ##EQU9## and (2) a set of corrected carrier phase signals Φ

for this mobile station, using the relations ##EQU10## (7) using at least one of (1) the set of corrected pseudorange signals PR(t;

t0;

m;

mobile;

corr) and (2) the set of corrected carrier phase signals Φ

(t;

t0;

m;

mobile;

corr) to determine a corrected present location of this mobile station and to replace the estimated present location by the corrected present location of this mobile station; and

(8) displaying at least one corrected present location of this mobile station for an estimated mobile station location that is distinct from the locations A and B.

2. The method of claim 1, further comprising the steps of;

choosing said integer K to be 3; and

selecting said coefficients a_k '"'"'(k=1, 2,

     3) to satisfy the relations ##EQU11##

3. The method of claim 1, further comprising the step of using a preceding GPS-determined present location of said mobile station as an estimate of the present location of said mobile station.

4. The method of claim 1, further comprising the step of using an uncorrected GPS-determined present location of said mobile station as an estimate of the present location of said mobile station.

5. The method of claim 1, further comprising the step of selecting said spatial coordinates (u_n(k),v_n(k),w_n(k)) (k=1, 2, . . . , K) of said fiducial stations that form said bounding polygon for said mobile station so that said bounding polygon has a diameter no greater than about 200 km.

6. The method of claim 1, further comprising the step of transmitting said pseudorange correction signals and said carrier phase correction signals from each of a selected group of one or more fiducial stations at least once in every time interval of length Δ

t, where Δ

t lies in the range 0.1-15 seconds.

7. The method of claim 1, further comprising the step of transmitting said pseudorange correction signals and said carrier phase correction signals from each of a selected group of one or more fiducial stations at least once in every time interval of length Δ

t, where Δ

t lies in the range 15-900 seconds.

8. The method of claim 1, further comprising the steps of:

applying data compression to said GPS information signals before said signals are transmitted by at least one of said fiducial stations; and

applying data decompression to said GPS information signals received by said mobile station from each fiducial station that transmits these signals in data-compressed format.

9. A method of providing GPS pseudorange correction and carrier phase correction information over a selected geographic region S with a diameter of up to about 200 km with an associated inaccuracy as low as 5 cm, to provide increased accuracy for a GPS user in moving from a first selected location A to a second selected location B, the method comprising the steps of:

(1) providing N spaced apart GPS fiducial stations, numbered n=1, 2, . . . , N (N≧

3), whose location coordinates (u_n,v_n,w_n) in a selected coordinate system are fixed and known with high accuracy, within the region S

(2) causing each fiducial station to receive GPS signals from M GPS satellites, numbered m=1, 2, . . . , M (M≧

3), to resolve carrier phase integer ambiguities associated with that fiducial station, and to transmit GPS information signals, including pseudorange and carrier phase information received from these satellites;

(3) providing a central station, associated with the region S, that receives the GPS information signals transmitted by at least three fiducial stations within the region S, computes the GPS pseudorange corrections PRC(t;

t0;

m;

n) at a selected time t0, which are valid for times t≧

t0 that are near t0 and which reconcile the GPS-determined location with the known location of fiducial station number n using GPS signals received from satellite number m;

(4) providing a GPS user with a mobile GPS station within the region S that has stored within it the coordinates (u'"'"',v'"'"',w'"'"') of an estimated present location of that mobile station, where the mobile station receives GPS signals from the GPS satellites and estimates its present location and receives signals transmitted by the central station, where the GPS user is to move from a first selected location A to a second selected location B;

(5) causing the central station to compute parameters c_hjk (m) that allow determination of total pseudorange corrections TPRC(t;

t0;

m;

u,v,w), that approximate the pseudorange corrections valid at each fiducial station and are given by the relations ##EQU12## for a station whose coordinates are (u,v,w), where the parameters c_hjk (m) are chosen to minimize a selected error associated with use of the total pseudorange corrections and (u0,v0,w0) are selected location coordinates;

(6) causing the central station to broadcast at least one of the parameters c_hjk (m);

(7) causing the mobile station to receive the information on the parameters c_hjk (m) from the central station, and to compute the pseudorange corrections and to compute corrected pseudorange signals applicable to the estimated location of the mobile station;

(8) using the corrected pseudorange signals to compute a corrected present location of this mobile station and to replace the estimated present location of this mobile station by the corrected present location; and

(9) displaying at least one corrected present location of this mobile station for an estimated mobile station location that is distinct from the locations A and B.

10. The method of claim 9, further comprising the step of choosing said total pseudorange corrections to be of the form

11. The method of claim 9, further comprising the step of choosing said total pseudorange corrections to be of the form

12. The method of claim 9, further comprising the step of choosing said selected error to be of the form ##EQU13## where p is a selected positive number.

13. The method of claim 9, further comprising the step of transmitting said pseudorange correction signals and said phase integer signals from each of a selected group of one or more fiducial stations at least once in every time interval of length Δ

t, where Δ

t lies in the range 0.1-15 seconds.

14. The method of claim 9, further comprising the step of transmitting said pseudorange correction signals and said phase integer signals from each of a selected group of one or more fiducial stations at least once in every time interval of length Δ

t, where Δ

t lies in the range 15-900 seconds.

15. The method of claim 9, further comprising the steps of:

applying data compression to said GPS information signals before said signals are transmitted by at least one of said fiducial stations; and

applying data decompression to said GPS information signals received by said central station from each fiducial station that transmits these signals in data-compressed format.

16. The method of claim 9, further comprising the steps of:

applying data compression to said total pseudorange correction information signals before said signals are transmitted by said central station; and

applying data decompression to said total pseudorange correction information signals received by said mobile station from said central station.