Multi-node point-to-point satellite communication system employing multiple geo satellites

• US 6,990,314 B1
• Filed: 05/22/2000
• Issued: 01/24/2006
• Est. Priority Date: 03/18/1999
• Status: Expired due to Fees

• Current Assignee: Hughes Electronics Corporation (AT&T, Inc.)
• Original Assignee: The DIRECTV Group, Inc. (AT&T, Inc.)
• Inventors: Chang, Donald C. D., Yung, Kar W., Hagen, Frank A., Flammang, Richard
• Primary Examiner(s): Corsaro, Nick
• Assistant Examiner(s): Dean, Raymond S
• Application Number:
  US09/576,652
• Time in Patent Office: 2,073 Days
• Field of Search: 342/388, 342/418, 342/357, 398/125, 455/427, 455/429, 455/430, 455/426, 455/12.1, 455/13.1, 370/95, 370/320, 370/325, 375/1, 244/158.R, 244/159
• US Class Current: 455/13.1
• CPC Class Codes: H04B 7/18534 for enhancing link reliablility, e.g. satellites diversity

Abstract

A wireless communication system includes a satellite constellation consisting of a plurality of satellites. Each of the plurality of satellites is in an orbit whose eccentricity and inclination are perturbed relative to the same geosynchronous orbit. Each of the satellites in the constellation is capable of relaying signals in either direction between a central ground hub and a plurality of mobile user terminals. The plurality of satellites are configured such that the period of their geosynchronous orbit remains substantially constant at one sidereal day.

Claims

1. A method for transmitting communications signals to a plurality of mobile terminals, comprising:

processing a received signal at a ground hub;

radiating a first portion of said signal and a second portion of said signal through multiple paths to at least two satellites;

re-radiating said signal from said at least two satellites to an intended mobile terminal;

combining the first portion of the signal and the second portion of the signal at the mobile terminal to reform the signal;

whereby an orbit of said satellite is being perturbed in inclination and eccentricity relative to a common geosynchronous reference orbit;

whereby apparent satellite motion of said at least two satellites about the geosynchronous reference orbit remain substantially uniform.

2. The method of claim 1, further comprising:

radiating a signal from said intended mobile terminal to said at least two perturbed satellites;

re-radiating said signal from said at least two perturbed satellites to said ground hub.

3. The method of claim 2, further comprising:

determining a relationship between said inclination and said eccentricity of said satellites such that they appear to move at a constant speed along circular paths whose centers are located at the position of a hypothetical reference satellite in an unperturbed geosynchronous orbit.

4. The method of claim 3, further comprising:

maintaining the geometry of said cluster of at least two satellites such that the distances between any two of said satellites is relatively constant.

5. The method of claim 4, further comprising:

adding additional satellites to said at least two satellites to augment the satellite constellation.

6. The method of claim 4, wherein the conditions for circular apparent motion of the perturbed satellite relative to said satellite constellation center is approximated by the following:

sini=2ε

t_o=±

1/4t_GEO.

7. A mobile wireless communication system, comprising:

a satellite constellation consisting of a plurality of satellites, each of the plurality of satellites in an orbit that is a perturbed geosynchronous orbit centered about a geosynchronous reference orbit position;

each of said plurality of satellites being capable of relaying signals between the ground hub and the plurality of user terminals in either direction;

whereby as said satellite constellation appears to rotate at a uniform rate above the geosynchronous reference orbit as viewed by a single user so that the apparent inter-satellite spatial relationships are maintained.

8. The mobile wireless communication system of claim 7, wherein each of said plurality of satellites has its inclination and eccentricity perturbed relative to a common geosynchronous reference orbit.

9. The mobile wireless communication system of claim 7, wherein the respective distances among the said plurality of satellites is substantially constant.

10. The mobile wireless communication system of claim 8, wherein the orbit of each of said plurality of satellites is perturbed such that it appears to move at a constant speed along a circular path as viewed by a single user. $\sin$

 

⁢

i=2⁢

 

⁢

ɛ

$t_o=\pm <br><br>\frac{1}{4}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{GEO}}.$

.

11. The mobile wireless communication system of claim 7, wherein in order for coherent reception of signals by their intended user, said intended user'"'"'s location must be determined to within a specified tolerance ε

_x, which is determined according to the following equation;

${\mathrm{\varepsilon <br><br>}}_x<br><br><<br><br><<br><br>\frac{{\mathrm{\varepsilon <br><br>}}_{\mathrm{tol}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\lambda <br><br>}}_{\min }<br><br>\text{\hspace{1em}<br><br>}<br><br>r_{\min }}{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>D_{x<br><br>\text{\hspace{1em}<br><br>}<br><br>\max }}.$

.

12. The mobile wireless communication system of claim 7, wherein in order for incoherent reception of signals from interfering (non-intended) users, said interfering users must be displaced at least a distance $\Delta$

⁢

 

⁢

xmin≥

crmax2⁢

wN⁢

 

⁢

δ

⁢

 

⁢

Δ

⁢

 

⁢

Dx⁢

 

⁢

min

from the user receiving the signal.

13. The mobile wireless communication system of claim 10, wherein the apparent motions of said plurality of satellites in said satellite constellation can be arranged to appear circular as perceived from any one point in the coverage area.

14. A method for establishing a link between a ground hub and a plurality of mobile terminals, comprising:

preprocessing a received signal at said ground hub;

transmitting a first portion and a second portion of said signal through different paths to a plurality of satellites in a satellite constellation to an intended one of the mobile terminals;

combining the first portion of the signal and the second portion of the signal at the mobile terminal to reform the signal;

perturbing the inclination and eccentricity of said plurality of satellites relative to a common geosynchronous reference orbit; and

determining a relationship between said inclination and said eccentricity of said plurality of satellites such that they appear to move at a constant speed along circular paths where centers are located at a position defined by a hypothetical reference satellite in an unperturbed geosynchronous orbit.

15. The method of claim 14, further comprising:

maintaining the periods of geosynchronous orbit of said plurality of satellites substantially constant.

16. The method of claim 14, further comprising:

maintaining the apparent inter-satellite spatial relationships between said plurality of satellites as they appear to rotate.

17. The method of claim 14, wherein said relationship is approximated by the following:

$\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>i=2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\varepsilon <br><br>}$$t_o=\pm <br><br>\frac{1}{4}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_{\mathrm{GEO}}.$

.

18. The method of claim 14 wherein in order for incoherent reception of signals from interfering (non-intended) users, said interfering users must be displaced at least a distance $\Delta$

⁢

 

⁢

Xmin≥

CrMAX2⁢

WN⁢

 

⁢

δ

⁢

 

⁢

Δ

⁢

 

⁢

Dx⁢

 

⁢

MIN

from the user receiving the signal.

19. The method of claim 14, wherein in order for coherent reception of signals by their intended user, said intended user'"'"'s location must be determined to within a specified tolerance ε

_x, which is determined according to the following equation;

${\mathrm{\varepsilon <br><br>}}_x<br><br><<br><br><<br><br>\frac{{\mathrm{\varepsilon <br><br>}}_{\mathrm{tol}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\tau <br><br>}}_{\min }<br><br>\text{\hspace{1em}<br><br>}<br><br>r_{\min }}{{\mathrm{\Delta <br><br>}}_{x<br><br>\text{\hspace{1em}<br><br>}<br><br>\min }}.$

.