Ionospheric correction for single frequency GPS receivers using three satellites

• US 6,169,958 B1
• Filed: 04/09/1999
• Issued: 01/02/2001
• Est. Priority Date: 04/09/1999
• Status: Active Grant

• Current Assignee: Mitsubishi Electric & Electronics USA Incorporated (Mitsubishi Electric Corporation)
• Original Assignee: Vsis, Inc.
• Inventors: Usman, Mohammad, Nagasamy, Vijay, Sun, James
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): ARTHUR JEANGLAUDE, GERTRUDE
• Application Number:
  US09/289,552
• Time in Patent Office: 634 Days
• Field of Search: 701/207, 701/213, 701/214, 701/215, 701/216, 701/221, 701/224, 701/225, 701/226, 701/300, 342/357.01, 342/357.02, 342/357.03, 342/357.06, 342/357.08, 342/357.09
• US Class Current: 701/213
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude
• CPC Class Codes: G01S 19/42 Determining position

Abstract

Systems and methods are disclosed for ionospheric correction in a system employing a single GPS frequency receiver for determining the geographic location of an object on the earth'"'"'s surface. The receiver receives signals transmitted at the GPS L₁ frequency from at least first, second and third GPS satellites, the first, second and third satellites having respective orbital positions relative to the receiver such that the total electron count (TEC) contribution to ionoshperic interference to signals transmitted by the respective satellites and received by the receiver is approximately the same. Respective measured distances of the three satellites to the receiver are determined based on the actual signal transmission times. True distances of the respective satellites are then calculated based on the assumption that the TEC contribution to the interference from each satellite is approximately the same.

Claims

1. A method using satellite signal transmission for determining the geographic location of a receiver on the earth'"'"'s surface, comprising:

receiving a first signal transmitted at a known frequency from a first satellite having a known orbital position;

receiving a second signal transmitted at the same frequency as the first signal from a second satellite having a known orbital position;

receiving a third signal transmitted at the same frequency as the first signal from a third satellite having a known orbital position;

calculating measured distances λ

¹, λ

² and λ

³ of the respective first, second and third satellites from the receiver based at least in part on the transmission time of the respective first, second and third signals; and

calculating actual distances ρ

¹, ρ

² and ρ

³ of the respective first, second and third satellites from the receiver based on the measured distances λ

¹, λ

² and λ

³, according to the relationships $\frac{F_{\mathrm{pp}}^1}{F_{\mathrm{pp}}^2}<br><br>\left({\mathrm{\lambda <br><br>}}^2-{\mathrm{\rho <br><br>}}^2\right)={\mathrm{\lambda <br><br>}}^1-{\mathrm{\rho <br><br>}}^1,<br><br>\frac{F_{\mathrm{pp}}^1}{F_{\mathrm{pp}}^3}<br><br>\left({\mathrm{\lambda <br><br>}}^3-{\mathrm{\rho <br><br>}}^3\right)={\mathrm{\lambda <br><br>}}^1-{\mathrm{\rho <br><br>}}^1,\mathrm{and}$$\frac{F_{\mathrm{pp}}^2}{F_{\mathrm{pp}}^3}<br><br>\left({\mathrm{\lambda <br><br>}}^3-{\mathrm{\rho <br><br>}}^3\right)={\mathrm{\lambda <br><br>}}^2-{\mathrm{\rho <br><br>}}^2,$

where F_pp¹, F_pp², and F_pp³ are obliquity factors for the respective first, second and third satellites based on the respective angles φ

₁, φ

₂ and φ

₃ they form with a plane tangent to the earth'"'"'s surface at the geographic location of the receiver, with $F_{\mathrm{pp}}^1=-{\left[1-{\left(\frac{R_e<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\phi <br><br>}}_1}{R_e+H_r}\right)}^2\right]}^{-\frac{1}{2}},<br><br>F_{\mathrm{pp}}^2=-{\left[1-{\left(\frac{R_e<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\phi <br><br>}}_2}{R_e+H_r}\right)}^2\right]}^{-\frac{1}{2}},\mathrm{and}$$F_{\mathrm{pp}}^3={\left[1-{\left(\frac{R_e<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\phi <br><br>}}_3}{R_e+H_r}\right)}^2\right]}^{-\frac{1}{2}},$

where R_e is the radius of the earth and H_r is the height of maximum electron density in the ionosphere surrounding the earth'"'"'s surface.

2. The method of claim 1, wherein the first second and third satellites are global positioning system (GPS) satellites.

3. The method of claim 2, wherein the first second and third signals are transmitted at the GPS L₁ signal frequency.

4. The method of claim 1, wherein the first, second and third satellites have respective orbital positions relative to the receiver such that the total electron count (TEC) contribution to ionoshperic interference to the transmission of the first, second and third signals is approximately the same.

5. A system for determining the geographic location of objects on the earth'"'"'s surface, comprising:

a receiver configured to receive signals transmitted at a selected frequency from first, second and third satellites having known orbital positions, the receiver further configured to

calculate measured distances λ

¹, λ

² and λ

³ of the respective first, second and third satellites from the receiver based at least in part on the transmission time of the received signals, and

calculate actual distances ρ

¹, ρ

² and ρ

³ of the respective first, second and third satellites from the receiver based on the measured distances λ

¹, λ

² and λ

³, according to the relationships $\frac{F_{\mathrm{pp}}^1}{F_{\mathrm{pp}}^2}<br><br>\left({\mathrm{\lambda <br><br>}}^2-{\mathrm{\rho <br><br>}}^2\right)={\mathrm{\lambda <br><br>}}^1-{\mathrm{\rho <br><br>}}^1,<br><br>\frac{F_{\mathrm{pp}}^1}{F_{\mathrm{pp}}^3}<br><br>\left({\mathrm{\lambda <br><br>}}^3-{\mathrm{\rho <br><br>}}^3\right)={\mathrm{\lambda <br><br>}}^1-{\mathrm{\rho <br><br>}}^1,\mathrm{and}$$\frac{F_{\mathrm{pp}}^2}{F_{\mathrm{pp}}^3}<br><br>\left({\mathrm{\lambda <br><br>}}^3-{\mathrm{\rho <br><br>}}^3\right)={\mathrm{\lambda <br><br>}}^2-{\mathrm{\rho <br><br>}}^2,$

where F_pp¹, F_pp², and F_pp³ are obliquity factors for the respective first, second and third satellites based on the respective angles φ

₁, φ

₂ and φ

₃ they form with a plane tangent to the earth'"'"'s surface at the geographic location of the receiver, with $F_{\mathrm{pp}}^1=-{\left[1-{\left(\frac{R_e<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\phi <br><br>}}_1}{R_e+H_r}\right)}^2\right]}^{-\frac{1}{2}},<br><br>F_{\mathrm{pp}}^2=-{\left[1-{\left(\frac{R_e<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\phi <br><br>}}_2}{R_e+H_r}\right)}^2\right]}^{-\frac{1}{2}},\mathrm{and}$$F_{\mathrm{pp}}^3={\left[1-{\left(\frac{R_e<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\phi <br><br>}}_3}{R_e+H_r}\right)}^2\right]}^{-\frac{1}{2}},$

where R_e is the radius of the earth and H_r is the height of maximum electron density in the ionosphere surrounding the earth'"'"'s surface.

6. The system of claim 5, wherein the first second and third satellites are global positioning system (GPS) satellites.

7. The system of claim 6, wherein the first second and third signals are transmitted at the GPS L₁ signal frequency.

8. The system of claim 5, wherein the first, second and third satellites have respective orbital positions relative to the receiver such that the total electron count (TEC) contribution to ionoshperic interference to the transmission of the first, second and third signals is approximately the same.

9. A system for determining the geographic location of objects on the earth'"'"'s surface, comprising:

a single frequency global positioning system (GPS) receiver configured to receive signals transmitted at the GPS L₁ frequency from first, second and third GPS satellites, the respective receiver and satellites having synchronized clocks, the first, second and third satellites having respective orbital positions relative to the receiver such that the total electron count (TEC) contribution to ionoshperic interference to signals transmitted by the respective satellites and received by the receiver is approximately the same, the receiver further configured to calculate measured distances λ

¹, λ

² and λ

³ of the respective first, second and third satellites from the receiver based at least in part on the transmission time of the received signals, and

calculate actual distances ρ

^GPS1, ρ

^GPS2 and ρ

^GPS3 of the respective first, second and third satellites from the receiver based on the measured distances λ

_L1^GPS1, λ

_L1^GPS2 and λ

_L1^GPS3 according to the relationships $\frac{F_{\mathrm{pp}}^{\mathrm{GPS1}}}{F_{\mathrm{pp}}^{\mathrm{GPS2}}}<br><br>\left({\mathrm{\lambda <br><br>}}_{L_1}^{\mathrm{GPS2}}-{\mathrm{\rho <br><br>}}^{\mathrm{GPS2}}\right)={\mathrm{\lambda <br><br>}}_{L_1}^{\mathrm{GPS1}}-{\mathrm{\rho <br><br>}}^{\mathrm{GPS1}},<br><br>\frac{F_{\mathrm{pp}}^{\mathrm{GPS1}}}{F_{\mathrm{pp}}^{\mathrm{GPS3}}}<br><br>\left({\mathrm{\lambda <br><br>}}_{L_1}^{\mathrm{GPS3}}-{\mathrm{\rho <br><br>}}^{\mathrm{GPS3}}\right)={\mathrm{\lambda <br><br>}}_{L_1}^{\mathrm{GPS1}}-{\mathrm{\rho <br><br>}}^{\mathrm{GPS1}},\mathrm{and}$$\frac{F_{\mathrm{pp}}^{\mathrm{GPS2}}}{F_{\mathrm{pp}}^{\mathrm{GPS3}}}<br><br>\left({\mathrm{\lambda <br><br>}}_{L_1}^{\mathrm{GPS3}}-{\mathrm{\rho <br><br>}}^{\mathrm{GPS3}}\right)={\mathrm{\lambda <br><br>}}_{L_1}^{\mathrm{GPS2}}-{\mathrm{\rho <br><br>}}^{\mathrm{GPS2}},$

where F_pp^GPS1, F_pp^GPS2, and F_pp^GPS3 are obliquity factors for the respective first, second and third satellites based on the respective angles φ

₁, φ

₂ and φ

₃ they form with a plane tangent to the earth'"'"'s surface at the geographic location of the receiver, with $F_{\mathrm{pp}}^{\mathrm{GPS1}}=-{\left[1-{\left(\frac{R_e<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\phi <br><br>}}_1}{R_e+H_r}\right)}^2\right]}^{-\frac{1}{2}},<br><br>F_{\mathrm{pp}}^{\mathrm{GPS2}}=-{\left[1-{\left(\frac{R_e<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\phi <br><br>}}_2}{R_e+H_r}\right)}^2\right]}^{-\frac{1}{2}},\mathrm{and}$$F_{\mathrm{pp}}^{\mathrm{GPS3}}={\left[1-{\left(\frac{R_e<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\phi <br><br>}}_3}{R_e+H_r}\right)}^2\right]}^{-\frac{1}{2}},$

where R_e is the radius of the earth and H_r is the height of maximum electron density in the ionosphere surrounding the earth'"'"'s surface.