Integrity monitoring of location and velocity coordinates from differential satellite positioning systems signals

• US 5,831,576 A
• Filed: 06/25/1997
• Issued: 11/03/1998
• Est. Priority Date: 06/02/1994
• Status: Expired due to Fees

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Sheynblat, Len
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US08/883,249
• Time in Patent Office: 496 Days
• Field of Search: 342/357, 701/215
• US Class Current: 342/357.64
• CPC Class Codes: G01S 19/071 DGPS corrections
• CPC Class Codes: G01S 19/08 providing integrity information, e.g. health of satellites or quality of ephemeris data
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]

Abstract

Methods for determining integrity of pseudorange and pseudorange rate signals received from a plurality of M Satellite Positioning System satellites (including GPS and GLONASS), numbered j=j1, j2, . . . , jM, at a reference SATPS station (RS), using pseudorange or pseudorange rate signals received from the same satellites at a nearby signal integrity monitoring (SIM) station. Pseudorange correction values or, alternatively, pseudorange rate correction values, for SATPS signals received at an RS station and at the corresponding SIM station are computed, and difference values between the RS and SIM values are computed for each satellite. If the magnitude of each difference is less than a selected threshold difference, pseudorange corrections or pseudorange rate corrections for that reference station can be used by a nearby mobile station to differentially correct the mobile station location fix coordinates or velocity fix coordinates. If N acceptable pairs of difference values are found for the pseudorange or pseudorange rate corrections, for particular satellites: clock bias or frequency offset can be corrected if N≧1; accuracy of the clock bias or frequency offset coordinate can be monitored if N≧2; and location fix coordinates or velocity fix coordinates can be corrected if N≧3. If magnitudes of differences between measured and known location coordinates or velocity coordinates for the SIM station are less than threshold differences, pseudorange corrections or pseudorange rate corrections for that reference station can be used by a nearby mobile station to differentially correct the mobile station location fix coordinates or velocity fix coordinates.

Claims

1. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting a set of K velocity fix coordinates (I≦

K≦

4) of a mobile SATPS station, the method comprising the steps of;

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location, from M satellites (M≧

K);

determining pseudorange rate correction values for the RS station and for the SIM station for SATPS signals received from at least one common satellite (number j);

forming a magnitude of a difference between the pseudorange rate correction values for the RS station and for the SIM station for substantially the same observation time for the at least one common satellite; and

when the magnitude of the difference is greater than a selected threshold rate, transmitting a signal indicating that SATPS signals received from the at least one common satellite cannot be used to correct K velocity fix coordinates for a mobile SATPS station using DSATPS signals received from the RS station.

2. The method of claim 1, further comprising the step of:

when said magnitude of said difference is not greater than said selected threshold rate, transmitting a signal indicating that SATPS signals received from said at least one common satellite can be used to correct K velocity fix coordinates for a mobile SATPS station using DSATPS signals received from said RS station.

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

measuring a carrier phase value, designated Φ

(t;

i;

j), from an SATPS signal received at said RS station number i at time t from said at least one common satellite, for at least one RS station; and

determining said pseudorange rate values, PRR(t;

i;

j), for at least one of said RS station and said SIM station by the relations

space="preserve" listing-type="equation">PRR(t;

i;

j)= Φ

(t;

i;

j)-Φ

(t-Δ

t;

i;

j)!/Δ

t,

where Δ

t is a selected nonzero time increment.

4. The method of claim 1, further comprising the step of determining said pseudorange rate values, PRR(t;

i;

j), for said RS station number i and said at least one common satellite by the steps of;

measuring a carrier phase value, designated Φ

(D(t;

i;

j), for an SATPS signal received at said RS station number i at time t from said at least one common satellite, for at least one RS station;

approximating a variable y(t) representing the carrier phase value Φ

(t;

i;

j) in a time interval t_n-1 ≦

t≦

t_n+1 as a polynomial of degree at most two,

space="preserve" listing-type="equation">y(t)=y.sub.n +a.sub.n (t-t.sub.n)+b.sub.n (t-t.sub.n).sup.2,

using known values of the variable y(t) at three selected times t=t_n-1, t=t_n and t=t_n+1, with t_n-1 ≦

t_n ≦

t_n+1 ; and

determining said pseudorange rate value, designated PRR(t;

i;

j)_RS, determined for said reference station i at the time t=t_n and said at least one common satellite by the relation

space="preserve" listing-type="equation">PRR(t.sub.n ;

i;

j).sub.RS =y(t.sub.n)=a.sub.n ={(t.sub.n -t.sub.n-1).sup.2 y(t.sub.n+1)-y(t.sub.n)!+(t.sub.n+1 -t.sub.n).sup.2 y(t.sub.n-1)-y(t.sub.n) !}/(t.sub.n+1 -t.sub.n)(t.sub.n+1 -t.sub.n-1)(t.sub.n+1 -t.sub.n-1).

5.

5. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting a set of K location fix coordinates (1≦

K≦

4) of a mobile SATPS station, the method comprising the steps of;

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location, from M selected SATPS satellites (M≧

K);

determining pseudorange correction values for the RS station and for the SIM station for SATPS signals received from at least one common SATPS satellite;

forming a magnitude of a difference between the pseudorange correction values for the RS station and for the SIM station for substantially the same observation time for the at least one common satellite; and

when the magnitude of the difference is greater than a selected threshold value, transmitting a signal indicating that SATPS signals received from the at least one common satellite cannot be used to correct K location fix coordinates for a mobile SATPS station using DSATPS signals received from the RS station.

6. The method of claim 5, further comprising the step of:

when said magnitude of said difference is not greater than said selected threshold rate, transmitting a signal indicating that SATPS signals received from said at least one common satellite can be used to correct K location fix coordinates for a mobile SATPS station using DSATPS signals received from said RS station.

7. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for monitoring a set of K velocity fix coordinates (1≦

K≦

4) of a mobile SATPS station, the method comprising the steps of;

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location, from M selected SATPS satellites (M≧

K+1);

determining pseudorange rate correction values for the RS station and for the SIM station for SATPS signals received from at least one common SATPS satellite (number j);

forming a magnitude of a difference between the pseudorange rate correction values for the RS station and for the SIM station for substantially the same observation time for the at least one common satellite and

when the magnitude of the difference is greater than a selected threshold rate, transmitting a signal indicating that SATPS signals received from the at least one common satellite cannot be used to monitor K velocity fix coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.

8. The method of claim 7, further comprising the step of:

when said magnitude of said difference is not greater than said selected threshold rate, transmitting a signal indicating that SATPS signals received from said at least one common satellite can be used to monitor K velocity fix coordinates for a mobile SATPS station using DSATPS signals received from said RS station.

9. The method of claim 7, further comprising the steps of:

measuring a carrier phase value, designated Φ

(t;

i;

j), from an SATPS signal received at said RS station number i at time t from said at least one common satellite, for at least one RS station; and

determining said pseudorange rate values, PRR(t;

i;

j), for at least one of said RS station and said SIM station by the relations

space="preserve" listing-type="equation">PRR(t;

i;

j)= Φ

(t;

i;

j)-Φ

(t-Δ

t;

i;

j)!/Δ

t,

where Δ

t is a selected nonzero time increment.

10. The method of claim 7, further comprising the step of determining said pseudorange rate values, PRR(t;

i;

j), for said RS station number i and said at least one common satellite by the steps of;

measuring a carrier phase value, designated Φ

(t;

i;

j), for an SATPS signal received at said RS station number i at time t from said at least one common satellite, for at least one RS station;

approximating a variable y(t) representing the carrier phase value Φ

(t;

i;

j) in a time interval t_n-1 ≦

t≦

t_n+1 as a polynomial of degree at most two,

space="preserve" listing-type="equation">y(t)=y.sub.n +a.sub.n (t-t.sub.n)+b.sub.n (t-t.sub.n).sup.2,

using known values of the variable y(t) at three selected times t=t_n-1, t=t_n and t=t_n+1, with t_n-1 ≦

t_n ≦

t_n+1 ; and

determining said pseudorange rate value, designated PRR(t;

i;

j)_RS, determined for said reference station i at the time t=t_n and said at least one common satellite by the relation

space="preserve" listing-type="equation">PRR(t.sub.n ;

i;

j).sub.RS =y(t.sub.n)=a.sub.n ={(t.sub.n -t.sub.n-1).sup.2 y(t.sub.n+1)-y(t.sub.n)!+(t.sub.n+1 -t.sub.n).sup.2 y(t.sub.n-1)-y(t.sub.n) !}/(t.sub.n+1 -t.sub.n)(t.sub.n+1 -t.sub.n-1)(t.sub.n+1 -t.sub.n-1).

11.

11. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for monitoring a set of K location fix coordinates (1≦

K≦

4) of a mobile SATPS station, the method comprising the steps of;

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location, from M selected SATPS satellites (M≧

K+1);

determining pseudorange correction values for the RS station and for the SIM station for SATPS signals received from at least one common satellite;

forming a magnitude of a difference between the pseudorange correction values for the RS station and for the SIM station for substantially the same observation time for the at least one common satellite; and

when the magnitude of the difference is greater than a selected threshold value, transmitting a signal indicating that SATPS signals received from the at least one common satellite cannot be used to monitor K location fix coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.

12. The method of claim 11, further comprising the step of:

when said magnitude of said difference is not greater than said selected threshold value, transmitting a signal indicating that SATPS signals received from said at least one common satellite can be used to monitor K location fix coordinates for a mobile SATPS station using DSATPS signals received from said RS station.

13. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting the frequency offset for a mobile SATPS station, the method comprising the steps of:

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location, from M selected SATPS satellites (M≧

1);

determining pseudorange rate correction values for the RS station and for the SIM station for SATPS signals received from at least one common satellite (number j);

forming a magnitude of a difference between the pseudorange rate correction values for the RS station and for the SIM station for substantially the same observation time for the at least one common satellite; and

when the magnitude of the difference is greater than a selected threshold rate, transmitting a signal indicating that SATPS signals received from the at least one common satellite cannot be used for correcting the frequency offset of a mobile SATPS station using DSATPS signals received from the RS station number i.

14. The method of claim 13, further comprising the step of:

when said magnitude of said difference is not greater than said selected threshold rate, transmitting a signal indicating that SATPS signals received from said at least one common satellite can be used for correcting the frequency offset of a mobile SATPS station using DSATPS signals received from said RS station.

15. The method of claim 13, further comprising the steps of:

measuring a carrier phase value, designated Φ

(t;

i;

j), from an SATPS signal received at said RS station number i at time t from said at least one common satellite, for at least one RS station; and

determining said pseudorange rate values, PRR(t;

i;

j), for at least one of said RS station and said SIM station by the relations

space="preserve" listing-type="equation">PRR(t;

i;

j)= Φ

(t;

i;

j)-Φ

(t-Δ

t;

i;

j)!/Δ

t,

where Δ

t is a selected nonzero time increment.

16. The method of claim 13, further comprising the step of determining said pseudorange rate values, PRR(t;

i;

j), for said RS station number i and said at least one common satellite by the steps of;

measuring a carrier phase value, designated Φ

(t;

i;

j), for an SATPS signal received at said RS station number i at time t from said at least one common satellite, for at least one RS station;

approximating a variable y(t) representing the carrier phase value Φ

(t;

i;

j) in a time interval t_n-1 ≦

t≦

t_n+1 as a polynomial of degree at most two,

space="preserve" listing-type="equation">y(t)=y.sub.n +a.sub.n (t-t.sub.n)+b.sub.n (t-t.sub.n).sup.2,

using known values of the variable y(t) at three selected times t=t_n-1, t=t_n and t=t_n+1, with t_n-1 ≦

t_n+1 ; and

determining said pseudorange rate value, designated PRR(t;

i;

j)_RS, determined for said reference station i at the time t=t_n and at least one common satellite by the relation

space="preserve" listing-type="equation">PRR(t.sub.n ;

i;

j).sub.RS =y(t.sub.n)=a.sub.n ={(t.sub.n -t.sub.n-1).sup.2 y(t.sub.n+1)-y(t.sub.n)!+(t.sub.n+1 -t.sub.n).sup.2 y(t.sub.n-1)-y(t.sub.n) !}/(t.sub.n+1 -t.sub.n)(t.sub.n+1 -t.sub.n-1)(t.sub.n+1 -t.sub.n-1).

17.

17. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting the clock bias for a mobile SATPS station, the method comprising the steps of:

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location, from M selected SATPS satellites (M≧

1);

determining pseudorange correction values for the RS station and for the SIM station for SATPS signals received from at least one common satellite;

forming a magnitude of a difference between the pseudorange correction values for the RS station and for the SIM station for substantially the same observation time for the at least one common satellite; and

when the magnitude of the difference is greater than a selected threshold value, transmitting a signal indicating that SATPS signals received from the at least one common satellite cannot be used for correcting a clock bias of a mobile SATPS station using DSATPS signals received from the RS station number i.

18. The method of claim 17, further comprising the step of:

when said magnitude of said difference is not greater than said selected threshold value, transmitting a signal indicating that SATPS signals received from said at least one common satellite can be used for correcting a clock bias of a mobile SATPS station using DSATPS signals received from said RS station.

19. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for monitoring the frequency offset for a mobile SATPS station, the method comprising the steps of:

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location, from M selected SATPS satellites (M≧

2);

determining pseudorange rate correction values for the RS station and for the SIM station for SATPS signals received from at least one common satellite (number j);

forming a magnitude of a difference between the pseudorange rate correction values for the RS station and for the SIM station for substantially the same observation time for the at least one common satellite; and

when the magnitude of the difference is greater than a selected threshold rate, transmitting a signal indicating that SATPS signals received from the at least one common satellite cannot be used for monitoring the frequency offset of a mobile SATPS station using DSATPS signals received from the RS station number i.

20. The method of claim 19, further comprising the step of:

when said magnitude of said difference is not greater than said selected threshold rate, transmitting a signal indicating that SATPS signals received from said at least one common satellite can be used for monitoring the frequency offset of a mobile SATPS station using DSATPS signals received from said RS station.

21. The method of claim 19, further comprising the steps of:

measuring a carrier phase value, designated Φ

(t;

i;

j), from an SATPS signal received at said RS station number i at time t from said at least one common satellite, for at least one RS station; and

determining said pseudorange rate values, PRR(t;

i;

j), for at least one of said RS station and said SIM station by the relations

space="preserve" listing-type="equation">PRR(t;

i;

j)= Φ

(t;

i;

j)-Φ

(t-Δ

t;

i;

j)!/Δ

t

where Δ

t is a selected nonzero time increment.

22. The method of claim 19, further comprising the step of determining said pseudorange rate values, PRR(t;

i;

j), for said RS station number i and said at least one common satellite by the steps of;

measuring a carrier phase value, designated Φ

(t;

i;

j), for an SATPS signal received at said RS station number i at time t from said at least one common satellite, for at least one RS station;

approximating a variable y(t) representing the carrier phase value Φ

(t;

i;

j) in a time interval t_n-1 ≦

t≦

t_n+1 as a polynomial of degree at most two,

space="preserve" listing-type="equation">y(t)=y.sub.n +a.sub.n (t-t.sub.n)+b.sub.n (t-t.sub.n).sup.2,

using known values of the variable y(t) at three selected times t=t_n-1, t=t_n and t=t_n+1, with t_n-1 ≦

t_n ≦

t_n+1 ; and

determining said pseudorange rate value, designated PRR(t;

i;

j)_RS, determined for said reference station i at the time t=t_n and said at least one common satellite by the relation

space="preserve" listing-type="equation">PRR(t.sub.n ;

i;

j).sub.RS =y(t.sub.n)=a.sub.n ={(t.sub.n -t.sub.n-1).sup.2 y(t.sub.n+1)-y(t.sub.n)!+(t.sub.n+1 -t.sub.n).sup.2 y(t.sub.n-1)-y(t.sub.n)!}/(t.sub.n+1 -t.sub.n)(t.sub.n+1 -t.sub.n-1)(t.sub.n+1 -t.sub.n-1).

23.

23. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for monitoring the clock bias for a mobile SATPS station, the method comprising the steps of:

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location, from M selected SATPS satellites (M≧

2);

determining pseudorange correction values for the RS station and for the SIM station for SATPS signals received from at least one common satellite;

forming a magnitude of a difference between the pseudorange correction values for the RS station and for the SIM station for substantially the same observation time for the at least one common satellite; and

when the magnitude of the difference is greater than a selected threshold value, transmitting a signal indicating that SATPS signals received from the at least one common satellite cannot be used for monitoring a clock bias of a mobile SATPS station using DSATPS signals received from the RS station number i.

24. The method of claim 23, further comprising the step of:

when said magnitude of said difference is not greater than said selected threshold value, transmitting a signal indicating that SATPS signals received from said at least one common satellite can be used for monitoring a clock bias of a mobile SATPS station using DSATPS signals received from said RS station.

25. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting at least one of a set of K velocity coordinates (1≦

K≦

3) of a mobile SATPS station, the method comprising the steps of;

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location and known velocity coordinates, from M selected SATPS satellites (M≧

K);

determining velocity coordinates for the SIM station for SATPS signals received from the satellites;

forming a magnitude of at least one velocity difference between each known velocity coordinate and the corresponding determined velocity coordinate for the SIM station for substantially the same observation time for at least one common satellite; and

when the magnitude of the at least one velocity difference is greater than a selected threshold velocity difference, transmitting a signal indicating that SATPS signals received from the M satellites cannot be used to correct K velocity coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.

26. The method of claim 25, further comprising the step of:

when the magnitude of each said velocity difference is no greater than said selected threshold velocity difference, transmitting a signal indicating that SATPS signals received from the M satellites can be used to correct K velocity coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.

27. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting at least one of a set of K location coordinates (1≦

K≦

3) of a mobile SATPS station, the method comprising the steps of;

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having known location coordinates, from M selected SATPS satellites (M≧

K);

determining location coordinates for the SIM station for SATPS signals received from the satellites;

forming a magnitude of at least one location difference between each known location coordinate and the corresponding determined location coordinate for the SIM station for substantially the same observation time for at least one common satellite; and

when the magnitude of the at least one location difference is greater than a selected threshold velocity difference, transmitting a signal indicating that SATPS signals received from the M satellites cannot be used to correct K location coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.

28. The method of claim 27, further comprising the step of:

when the magnitude of each said location difference is no greater than said selected threshold location difference, transmitting a signal indicating that SATPS signals received from the M satellites can be used to correct K location coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.

29. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting the frequency offset for a mobile SATPS station, the method comprising the steps of:

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location and known velocity coordinates, from M SATPS satellites (M≧

1);

determining velocity coordinates for the SIM station for SATPS signals received from the satellites;

forming a magnitude of at least one velocity difference between each known velocity coordinate and the corresponding determined velocity coordinate for the SIM station for substantially the same observation time for at least one common satellite; and

when the magnitude of the at least one velocity difference is greater than a selected threshold velocity difference, transmitting a signal indicating that SATPS signals received from the M satellites cannot be used to correct frequency offset for a mobile SATPS station using DSATPS signals received from the RS station number i.

30. The method of claim 29, further comprising the step of:

when the magnitude of each said velocity difference is no greater than said selected threshold velocity difference, transmitting a signal indicating that SATPS signals received from the M satellites can be used to correct frequency offset for a mobile SATPS station using DSATPS signals received from the RS station number i.

31. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting the clock bias for a mobile SATPS station, the method comprising the steps of:

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having known location coordinates, from M selected SATPS satellites (M≧

1);

determining location coordinates for the SIM station for SATPS signals received from the M satellites;

forming at least one magnitude of a location difference between each known location coordinate and the corresponding determined location coordinate for the SIM station for substantially the same observation time for at least one common satellite; and

when the magnitude of the at least one location difference is greater than a selected threshold velocity difference, transmitting a signal indicating that SATPS signals received from the M satellites cannot be used to clock bias for a mobile SATPS station using DSATPS signals received from the RS station number i.

32. The method of claim 31, further comprising the step of:

when the magnitude of each said location difference is no greater than said selected threshold location difference, transmitting a signal indicating that SATPS signals received from the M satellites can be used to correct clock bias for a mobile SATPS station using DSATPS signals received from the RS station number i.

33. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting at least one of a set of K velocity coordinates (1≦

K≦

3) of a mobile SATPS station, the method comprising the steps of;

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having a known location and known velocity coordinates, from M selected SATPS satellites (M≧

K);

determining velocity coordinates for the SIM station for SATPS signals received from the satellites;

forming a velocity difference between each known velocity coordinate and the corresponding determined velocity coordinate for the SIM station for substantially the same observation time for the M satellites; and

when a sum of squares of the velocity differences is greater than a selected threshold velocity difference squared, transmitting a signal indicating that SATPS signals received from the M satellites cannot be used to correct K velocity fix coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.

34. The method of claim 33, further comprising the step of:

when a sum of squares of the velocity differences is no greater than said selected threshold velocity difference squared, transmitting a signal indicating that SATPS signals received from the M satellites can be used to correct K velocity fix coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.

35. A method of determining the integrity of differential Satellite Positioning System (DSATPS) signals developed at a Satellite Positioning System (SATPS) reference station and used for correcting at least one of a set of K location coordinates (1≦

K≦

3) of a mobile SATPS station, the method comprising the steps of;

receiving SATPS signals at an SATPS reference station (RS), numbered i and having a known location, and at an SATPS signal integrity monitoring station (SIM), numbered i and having known location coordinates, from M selected SATPS satellites (M≧

K);

determining location coordinates for the SIM station for SATPS signals received from the satellites;

forming a location difference between each known location coordinate and the corresponding determined location coordinate for the SIM station for substantially the same observation time for the M satellites; and

when a sum of squares of the location differences is greater than a selected threshold location difference squared, transmitting a signal indicating that SATPS signals received from the M satellites cannot be used to correct K location fix coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.

36. The method of claim 35, further comprising the step of:

when a sum of squares of the location differences is no greater than said selected threshold location difference squared, transmitting a signal indicating that SATPS signals received from the M satellites can be used to correct K location fix coordinates for a mobile SATPS station using DSATPS signals received from the RS station number i.