Gap coverage for GPS signals

• US 5,587,716 A
• Filed: 09/29/1995
• Issued: 12/24/1996
• Est. Priority Date: 09/29/1995
• Status: Expired due to Term

• 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:
  US08/537,110
• Time in Patent Office: 452 Days
• Field of Search: 342/357, 455/12.1
• US Class Current: 342/357.24
• CPC Class Codes: G01S 19/27 creating, predicting or correcting ephemeris or almanac data within the receiver
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]
• CPC Class Codes: G01S 5/009 Transmission of differential positioning data to mobile

Abstract

A method for compensating for temporary loss of differential GPS correction signals for a satellite, numbered j, during an IODE changeover interval. Differences Δe_i (t;j;n+1,n)=e_i (t;j;n+1)-e_i (t;j;n) (i=1, . . . , I) are formed for I ephemeris parameters used to describe the ephemeris for the satellite (j) during IODE intervals number n+1 and n. These differences are approximated for a DGPS blank-out time interval, given by t(j;n+1)_IODE Δt_rev,mob ≦t<t(j;n+1)_IODE +Δt_ch +Δt_rev,ref, during which a GPS reference station continues to broadcast DGPS correction information based on the old ephemeris data that was valid during the preceding IODE time interval, given by t(j;n)_IODE ≦t<t(j;n+1)_IODE. These ephemeris differences are used by a mobile station that receives DGPS correction information from the GPS reference station to produce corrected GPS information for a blank-out time interval. Ephemeris parameter differences can be replaced by differences of satellite-station ranges ΔR(t;j;n+1,n)=R(t;j;n+1)-R(t;j;n) in an alternative approach.

Claims

1. A method for compensating for temporary loss of differential GPS correction signals for a satellite during an IODE changeover interval, the method comprising the steps of:

receiving ephemeris data for a satellite, numbered j, during two consecutive IODE time intervals, given by t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE, and t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE, when the ephemeris data are available for at least one satellite numbered j=1, . . . , J (J≧

3);

receiving differential GPS correction signals for satellite number j for a time interval t(j;

n)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the IODE time interval t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE for satellite j, where Δ

t_ch is a first selected non-negative temporal length, Δ

t_rev,ref is a second selected positive temporal length;

receiving differential GPS correction signals for satellite j for a time interval t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+2)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the time interval t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE for satellite j;

for two selected times t=t'"'"'₂ and t=t'"'"'₃ satisfying the constraints t(j;

n)_IODE <

t'"'"'₂ ≦

t(j;

n+1)_IODE <

t'"'"'₃, determining the time variation of each of I ephemeris parameters e_i (t;

j;

n) (i=1, . . . , I;

I≧

1) that determine the ephemeris of satellite j during the time interval given by t'"'"'₂ ≦

t<

t'"'"'₃ ;

for two selected times t=t"₂ and t=t"₃ satisfying the constraints t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t"₂ <

t"₃, determining the time variation of each of I ephemeris parameters e_i (t;

j;

n+1) (i=1, . . . , I;

I≧

1) that determine the ephemeris of satellite j during the time interval given by t"₂ ≦

t<

t"₃, where Δ

t_rev,mob is a third selected positive temporal length;

determining an approximation Δ

π

_i (t;

j;

n+1,n) for each of the I ephemeris parameter difference values Δ

e_i (t;

j;

n+1,n)=e_i (t;

j;

n+1)-e_i (t;

j;

n) in a time interval that includes at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ; and

estimating the values of each of the I ephemeris parameters e_i (t;

j;

n) in at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref by the approximation e_i (t;

j;

n)_est =e_i (t;

j;

n+1)-Δ

π

_i (t;

j;

n+1,n).

2. The method of claim 1, further comprising the step of choosing said approximation π

_i (t;

j;

n+1,n) for said ephemeris parameter difference Δ

e_i (t;

j;

n+1,n) from the class of functions consisting of polynomials, ratios of polynomials, trigonometric functions, sums and ratios of exponential functions, and logarithm functions.

3. The method of claim 2, further comprising the step of choosing said approximation π

_i (t;

j;

n+1,n) to be a polynomial of degree M≧

2 in the time variable t.

4. The method of claim 1, further comprising the step of choosing said second temporal length Δ

t_rev,ref to be not less than 18 seconds and not more than 600 seconds.

5. The method of claim 1, further comprising the step of choosing said third temporal length Δ

t_rev,mob to be not less than 18 seconds and not more than 600 seconds.

6. A method for compensating for temporary loss of differential GPS correction signals for a satellite during an IODE changeover interval, the method comprising the steps of:

receiving ephemeris data for a satellite, numbered j, during two consecutive IODE time intervals, given by t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE, and t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE, when the ephemeris data are available for at least one satellite numbered j=1, . . . , J (J≧

3);

receiving differential GPS correction signals for satellite number j for a time interval t(j;

n)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the IODE time interval t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE for satellite j, where Δ

t_ch is a first selected non-negative temporal length, Δ

t_rev,ref is a second selected positive temporal length;

receiving differential GPS correction signals for satellite j for a time interval t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+2)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the time interval t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE for satellite j;

for two selected times t=t'"'"'₂ and t=t'"'"'₃ satisfying the constraints t(j;

n)_IODE <

t'"'"'₂ ≦

t(j;

n+1)_IODE <

t'"'"'₃, determining the time variation of the range R(t;

j;

n) from satellite j to a selected location from ephemeris data that determine the ephemeris of satellite j during the time interval given by t'"'"'₂ ≦

t<

t'"'"'₃ ;

for two selected times t=t"₂ and t=t"₃ satisfying the constraints t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t"₂ <

t"₃, determining the time variation of the range R(t;

j;

n+1) from satellite j to the selected location from ephemeris data that determine the ephemeris of satellite j during the time interval given by t"₂ ≦

t<

t"₃, where Δ

t_rev,mob is a third selected positive temporal length;

determining an approximation Δ

ρ

(t;

j;

n+1,n) for the range difference values Δ

R(t;

j;

n+1,n)=R(t;

j;

n+1)-R(t;

j;

n) in a time interval that includes at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ; and

estimating the range values R(t;

j;

n) in at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref by the approximation R(t;

j;

n)_est =R(t;

j;

n+1)-Δ

ρ

(t;

j;

n+1,n).

7. The method of claim 6, further comprising the step of choosing said approximation Δ

ρ

(t;

j;

n+1,n) for said range difference Δ

R(t;

j;

n+1,n) from the class of functions consisting of polynomials, ratios of polynomials, trigonometric functions, sums and ratios of exponential functions, and logarithm functions.

8. The method of claim 7, further comprising the step of choosing said approximation Δ

ρ

(t;

j;

n+1,n) to be a polynomial of degree M≧

1 in the time variable t.

9. The method of claim 6, further comprising the step of choosing said second temporal length Δ

t_rev,ref to be not less than 18 seconds and not more than 600 seconds.

10. The method of claim 6, further comprising the step of choosing said third temporal length Δ

t_rev,mob to be not less than 18 seconds and not more than 600 seconds.

11. A method for compensating for temporary loss of differential GPS correction signals for a satellite during an IODE changeover interval, the method comprising the steps of:

receiving ephemeris data for a satellite, numbered j, during two consecutive IODE time intervals, given by t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE, and t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE, when the ephemeris data are available for at least one satellite numbered j=1, . . . , J (J≧

3);

receiving differential GPS correction signals for satellite number j for a time interval t(j;

n)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the IODE time interval t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE for satellite j, where Δ

t_ch is a first selected non-negative temporal length, Δ

t_rev,ref is a second selected positive temporal length;

receiving differential GPS correction signals for satellite j for a time interval t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+2)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the time interval t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE for satellite j;

for two selected times t=t'"'"'₂ and t=t'"'"'₃ satisfying the constraints t(j;

n)_IODE <

t'"'"'₂ ≦

t(j;

n+1)_IODE <

t'"'"'₃, determining the time variation of each of I ephemeris parameters e_i (t;

j;

n) (i=1, . . . , I;

I≧

1) that determine the ephemeris of satellite j during the time interval given by t'"'"'₂ ≦

t<

t'"'"'₃ ;

for two selected times t=t"₂ and t=t"₃ satisfying the constraints t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t"₂ <

t"₃, determining the time variation of each of I ephemeris parameters e_i (t;

j;

n+1) (i=1, . . . , I;

I≧

1) that determine the ephemeris of satellite j during the time interval given by t"₂ ≦

t<

t"₃, where Δ

t_rev,mob is a third selected positive temporal length;

determining an approximation π

_i (t;

j;

n) for each of the I ephemeris parameter values e_i (t;

j;

n) in a time interval that includes at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+2)_IODE +Δ

t_ch +Δ

t_rev,ref ; and

estimating the values of each of the I ephemeris parameters e_i (t;

j;

n) in at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref by the approximation e_i (t;

j;

n)_est =π

_i (t;

j;

n).

12. A method for compensating for temporary loss of differential GPS correction signals for a satellite during an IODE changeover interval, the method comprising the steps of:

receiving ephemeris data for a satellite, numbered j, during two consecutive IODE time intervals, given by t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE, and t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE, when the ephemeris data are available for at least one satellite numbered j=1, . . . , J (J≧

3);

receiving differential GPS correction signals for satellite number j for a time interval t(j;

n)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the IODE time interval t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE for satellite j, where Δ

t_ch is a first selected non-negative temporal length, Δ

t_rev,ref is a second selected positive temporal length;

receiving differential GPS correction signals for satellite j for a time interval t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+2)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the time interval t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE for satellite j;

for two selected times t=t'"'"'₂ and t=t'"'"'₃ satisfying the constraints t(j;

n)_IODE <

t'"'"'₂ ≦

t(j;

n+1)_IODE <

t'"'"'₃, determining the time variation of the range R(t;

j;

n) from satellite j to a selected location from ephemeris data that determine the ephemeris of satellite j during the time interval given by t'"'"'₂ ≦

t<

t'"'"'₃ ;

for two selected times t=t"₂ and t=t"₃ satisfying the constraints t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t"₂ <

t"₃, determining the time variation of the range R(t;

j;

n+1) from satellite j to the selected location from ephemeris data that determine the ephemeris of satellite j during the time interval given by t"₂ ≦

t<

t"₃, where Δ

t_rev,mob is a third selected positive temporal length;

determining an approximation ρ

(t;

j;

n) for the range values R(t;

j;

n) in a time interval that includes at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ; and

estimating the range values R(t;

j;

n) in at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref by the approximation R(t;

j;

n)_est =ρ

(t;

j;

n).

13. A method for compensating for temporary loss of differential GPS correction signals for a satellite during an IODE changeover interval, the method comprising the steps of:

receiving ephemeris data for a satellite, numbered j, during two consecutive IODE time intervals, given by t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE, and t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE, when the ephemeris data are available for at least one satellite numbered j=1, . . . , J (J≧

3);

receiving differential GPS correction signals for satellite number j for a time interval t(j;

n)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the IODE time interval t(j;

n)_IODE ≦

t<

t(j;

n+1)_IODE for satellite j, where Δ

t_ch is a first selected non-negative temporal length, Δ

t_rev,ref is a second selected positive temporal length;

receiving differential GPS correction signals for satellite j for a time interval t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ≦

t<

t(j;

n+2)_IODE +Δ

t_ch +Δ

t_rev,ref, based upon ephemeris data that are applicable for the time interval t(j;

n+1)_IODE ≦

t<

t(j;

n+2)_IODE for satellite j;

for two selected times t=t'"'"'₂ and t=t'"'"'₃ satisfying the constraints t(j;

n)_IODE <

t'"'"'₂ ≦

t(j;

n+1)_IODE <

t'"'"'₃, determining the time variation of the range R(t;

j;

n) from satellite j to a selected location from ephemeris data that determine the ephemeris of satellite j during the time interval given by t'"'"'₂ ≦

t<

t'"'"'₃ ;

for two selected times t=t"₂ and t=t"₃ satisfying the constraints t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t"₂ <

t"₃, determining the time variation of the range R(t;

j;

n+1) from satellite j to the selected location from ephemeris data that determine the ephemeris of satellite j during the time interval given by t"₂ ≦

t<

t"₃, where Δ

t_rev,mob is a third selected positive temporal length;

determining a first approximation ρ

'"'"'(t;

j;

n+1) for the range values R(t;

j;

n+1) in a time interval that includes at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ;

determining a second approximation Δ

ρ

"(t;

j;

n+1,n) for the range difference values Δ

R(t;

j;

n+1,n)=R(t;

j;

n+1)-R(t;

j;

n) in a time interval that includes at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref ; and

estimating the range values R(t;

j;

n) in at least a portion of the time interval t(j;

n+1)_IODE +Δ

t_rev,mob ≦

t<

t(j;

n+1)_IODE +Δ

t_ch +Δ

t_rev,ref by the approximation R(t;

j;

n)_est =ρ

'"'"'(t;

j;

n+1)-Δ

ρ

"(t;

j;

n+1,n).