Method and apparatus for improving the accuracy of relative position estimates in a satellite-based navigation system

• US 6,049,304 A
• Filed: 07/10/1997
• Issued: 04/11/2000
• Est. Priority Date: 07/10/1997
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Rannoch Corporation (General Dynamics Corporation)
• Inventors: Baldwin, Jonathan C., Rudel, Marc-Philippe
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/891,227
• Time in Patent Office: 1,006 Days
• Field of Search: 342/357, 342/455, 342/357.08, 342/357.12, 701/213
• US Class Current: 342/357.34
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]
• CPC Class Codes: G01S 2205/005 for aircraft positioning relative to other aircraft
• CPC Class Codes: G01S 5/0072 Transmission between mobile stations, e.g. anti-collision systems

Abstract

The accuracy of relative position estimates between two vehicles, generated using a satellite-based navigation system, is improved by eliminating at an early stage in the calculation process, errors affecting simultaneously both receivers. The standard absolute navigation equations are modified to solve directly for relative position, while avoiding a final step differentiation, thereby providing increased precision.

Claims

1. A method for determining the relative position between a first receiver and a second receiver using a satellite-based navigation system utilizing a constellation of navigation satellites and a communication link between the first receiver and the second receiver, the method comprising the steps of:

receiving, from a first plurality of satellites of the constellation of navigation satellites, a first plurality of navigation signals at the first receiver;

receiving, from a second plurality of satellites of the constellation of navigation satellites, a second plurality of navigation signals at the second receiver;

computing, at the first receiver, a position estimate of the first receiver;

computing, at the second receiver, a position estimate of the second receiver;

transmitting from the second receiver to the first receiver, through the communication link, the second plurality of navigation signals and the position estimate of the second receiver;

computing, at the first receiver, a plurality of satellite positions of the first and second pluralities of satellites;

computing, at the first receiver, a first plurality of unit vectors between the first receiver and the first plurality of satellites;

computing, at the first receiver, a second plurality of unit vectors between the second receiver and the second plurality of satellites;

extracting, at the first receiver, from the first plurality of navigation signals, a first plurality of raw pseudoranges between the first receiver and each of the first plurality of satellites;

extracting, at the first receiver from the second plurality of navigation signals, a second plurality of raw pseudoranges between the second receiver and each of the second plurality of satellites;

computing, at the first receiver, a first plurality of range equivalents of the clock offsets of each of the first plurality of satellites;

computing, at the first receiver, a second plurality of range equivalents of the clock offsets of each of the second plurality of satellites; and

determining a precise relative position between the first receiver and the second receiver from the plurality of satellite positions of the first and second pluralities of satellites, the first and second pluralities of unit vectors, the first and second pluralities of raw pseudoranges, and the first and second pluralities of range equivalents of the clock offsets of each of the first and second pluralities of satellites, respectively.

2. The method of claim 1, wherein said satellite-based navigation system comprises a plurality of pseudolites.

6. The apparatus of claim 1, wherein said satellite-based navigation system comprises a plurality of pseudolites.

7. The method of claim 1, wherein said step of receiving, from a first plurality of satellites of the constellation of navigation satellites, a first plurality of navigation signals at the first receiver comprises the steps of:

receiving a first group of ephemeris data characterizing predetermined orbits of each of the first plurality of satellites of the constellation of navigation satellites; and

receiving a first group of satellite time signals from each of the first plurality of satellites of the constellation of navigation satellites.

8. The method of claim 7, wherein said step of receiving, from a second plurality of satellites of the constellation of navigation satellites, a second plurality of navigation signals at the second receiver comprises the steps of:

receiving a second group of ephemeris data characterizing predetermined orbits of each of the second plurality of satellites of the constellation of navigation satellites; and

receiving a second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites.

9. The method of claim 8, wherein said step of computing, at the first receiver, a position estimate of the first receiver comprises the step of:

generating a position estimate of the first receiver using an inertial navigation system.

10. The method of claim 9, wherein said step of computing, at the second receiver, a position estimate of the second receiver comprises the step of:

generating a position estimate of the second receiver using an inertial navigation system.

11. The method of claim 8, wherein said step of transmitting from the second receiver to the first receiver, through the communication link, the second plurality of navigation signals and the position estimate of the second receiver comprises the steps of:

transmitting the second group of ephemeris data characterizing predetermined orbits of each of the second plurality of satellites of the constellation of navigation satellites from the second receiver to the first receiver; and

transmitting the second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites from the second receiver to the first receiver.

12. The method of claim 11, wherein said step of computing, at the first receiver, a plurality of satellite positions of the first and second pluralities of satellites comprises the steps of:

computing positions of the first plurality of satellites from the first group of ephemeris data characterizing predetermined orbits of each of the first plurality of satellites of the constellation of navigation satellites; and

computing positions of the second plurality of satellites from the second group of ephemeris data characterizing predetermined orbits of each of the second plurality of satellites of the constellation of navigation satellites.

13. The method of claim 12, wherein said step of computing, at the first receiver, a first plurality of unit vectors between the first receiver and each of the first plurality of satellites comprises the step of calculating each of the first plurality of unit vectors as:

##EQU16## where A₁ denotes the position of the first receiver, and S₁,i denotes the position of an i^th satellite in the first plurality of satellites.

14. The method of claim 13, wherein said step of computing, at the first receiver, a second plurality of unit vectors between the second receiver and each of the second plurality of satellites comprises the step of calculating each of the second plurality of unit vectors as:

##EQU17## where A₂ denotes the position of the second receiver, and S₂,j denotes the position of a j^th satellite in the second plurality of satellites.

15. The method of claim 14, wherein said step of extracting, at the first receiver, a first plurality of raw pseudoranges between the first receiver and each of the first plurality of satellites from the first plurality of navigation signals comprises the steps of:

measuring differences between a clock signal generated at the first receiver and the first group of satellite time signals from each of the first plurality of satellites of the constellation of navigation satellites to measure a first group of propagation times for the first plurality of navigation signals from each of the first plurality of satellites; and

multiplying each of the first group of propagation times by the speed of light to produce a first group of raw pseudoranges between the first receiver and each of the first group of satellites.

16. The method of claim 15, wherein said step of extracting, at the first receiver, a second plurality of raw pseudoranges between the second receiver and the second plurality of satellites from the second plurality of navigation signals comprises the steps of:

measuring differences between a clock signal generated at the second receiver and the second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites to measure a second group of propagation times for the second plurality of navigation signals from each of the second plurality of satellites; and

multiplying each of the second group of propagation times by the speed of light to produce a second group of raw pseudoranges between the second receiver and each of the second group of satellites.

17. The method of claim 16, wherein said step of computing, at the first receiver, a plurality of satellite positions of the first and second pluralities of satellites comprises the step of calculating a plurality of satellite positions for the first and second pluralities of satellites using the equations:

##EQU18##

space="preserve" listing-type="equation">cos φ

.sub.k =cos ν

.sub.k cos ω

-sin ν

.sub.k sin ω

space="preserve" listing-type="equation">sin φ

.sub.k =sin ν

.sub.k cos ω

+sin ω

cos ν

.sub.k

Where k ε

{1, . . . , 6},

e denotes eccentricity of elliptical orbits,

E_k denotes an eccentric anomaly of orbit,

ω

denotes an argument of perigee,

ν

denotes true anomaly of orbit, and

φ

_k denotes an argument of latitude.

18. The method of claim 17, wherein said step of determining a precise relative position between the first receiver and the second receiver comprises the step of determining the precise relative position between the first receiver and the second receiver from the plurality of satellite positions of the first and second pluralities of satellites, the first and second pluralities of unit vectors, the first and second pluralities of raw pseudoranges, and the first and second pluralities of range equivalents of the clock offsets of each of the first and second pluralities of satellites, respectively by solving the set of equations:

space="preserve" listing-type="equation">(u.sub.1,i +u.sub.2,j )·

A.sub.1 A.sub.2 +(1+u.sub.1,i ·

u.sub.2,j )(e.sub.1 -e.sub.2)=(1+u.sub.1,i ·

u.sub.2,j )

space="preserve" listing-type="equation">(ρ

.sub.1,i -ρ

.sub.2,j -e.sub.1,i +e.sub.2,j)+(u.sub.1,i +u.sub.2,j )·

S.sub.1,i S.sub.2,j

where A₁ denotes the position of the first receiver,

A₂ denotes the position of the second receiver,

S₁,i denotes the position of an i^th satellite in the first plurality of satellites,

S₂,j denotes the position of a j^th satellite in the second plurality of satellites,

3. A method for computing the relative position between a first receiver and a second receiver using a satellite-based navigation system having a constellation of navigation satellites and a communication link between the first receiver and the second receiver, the method comprising the steps of:

receiving, at the first receiver, from a first plurality of satellites of the constellation of navigation satellites, a first plurality of navigation signals;

receiving, at the second receiver, from a second plurality of satellites of the constellation of navigation satellites, a second plurality of navigation signals;

computing, at the first receiver, a first plurality of unit vectors between the first receiver and the first plurality of satellites;

computing, at the second receiver, a second plurality of unit vectors between the second receiver and the second plurality of satellites;

computing, at the first receiver, a plurality of satellite positions of the first and second pluralities of satellites;

extracting, at the first receiver, from the first plurality of navigation signals, a first plurality of raw pseudoranges between the first receiver and each of the first plurality of satellites;

extracting, at the second receiver, from the second plurality of navigation signals, a second plurality of raw pseudoranges between the second receiver and each of the second plurality of satellites;

computing, at the first receiver, a first plurality of range equivalents of the clock offsets of each of the first plurality of satellites;

computing, at the second receiver, a second plurality of range equivalents of the clock offsets of each of the second plurality of satellites; and

transmitting from the second receiver to the first receiver, through the communication link, the second plurality of unit vectors, the second plurality of raw pseudoranges, and the second plurality of range equivalents of the clock offsets of each of the second plurality of satellites;

determining a precise relative position between the first receiver and the second receiver from the plurality of satellite positions of the first and second pluralities of satellites, the first and second pluralities of unit vectors, the first and second pluralities of raw pseudoranges, and the first and second pluralities of range equivalents of the clock offsets of each of the first and second plurality of satellites, respectively.

4. The method of claim 3, wherein said satellite-based navigation system comprises a plurality of pseudolites.

20. The method of claim 3, wherein said step of receiving, from a first plurality of satellites of the constellation of navigation satellites, a first plurality of navigation signals at the first receiver comprises the steps of:

receiving a first group of ephemeris data characterizing predetermined orbits of each of the first plurality of satellites of the constellation of navigation satellites; and

receiving a first group of satellite time signals from each of the first plurality of satellites of the constellation of navigation satellites.

22. The method of claim 20, wherein said step of computing, at the first receiver, a first plurality of unit vectors between the first receiver and each of the first plurality of satellites comprises the step of calculating each of the first plurality of unit vectors as:

##EQU19## where A₁ denotes the position of the first receiver, and S₁,i denotes the position of an i^th satellite in the first plurality of satellites.

24. The method of claim 22, wherein said step of extracting, at the first receiver, a first plurality of raw pseudoranges between the first receiver and each of the first plurality of satellites from the first plurality of navigation signals comprises the steps of:

measuring differences between a clock signal generated at the first receiver and the first group of satellite time signals from each of the first plurality of satellites of the constellation of navigation satellites to measure a first group of propagation times for the first plurality of navigation signals from each of the first plurality of satellites; and

multiplying each of the first group of propagation times by the speed of light to produce a first group of raw pseudoranges between the first receiver and each of the first group of satellites.

26. The method of claim 24, wherein said step of computing, at the first receiver, a plurality of satellite positions of the first and second pluralities of satellites comprises the step of calculating a plurality of satellite positions of the first and second pluralities of satellites using the equations:

##EQU21##

space="preserve" listing-type="equation">cos φ

.sub.k =cos ν

.sub.k cos ω

-sin ν

.sub.k sin ω

space="preserve" listing-type="equation">sin φ

.sub.k =sin ν

.sub.k cos ω

+sin ω

cos ν

.sub.k

Where k ε

{1, . . . , 6},

e denotes eccentricity of elliptical orbits,

E_k denotes an eccentric anomaly of orbit,

ω

denotes an argument of perigee,

ν

denotes true anomaly of orbit, and

φ

_k denotes an argument of latitude.

5. An apparatus for determining the relative position between a first receiver and a second receiver using signals from a satellite-based navigation system utilizing a constellation of navigation satellites, the apparatus comprising:

a first receiver for receiving a first plurality of navigation signals from the constellation of navigation satellites;

a second receiver for receiving a second plurality of navigation signals from the constellation of navigation satellites;

means, coupled to said first receiver and the second receiver, for computing, based upon said first plurality of navigation signals and said second plurality of navigation signals, a first matrix comprising weighted coefficients, a second matrix comprising observable parameters and solving for the relative navigation equation position using said first matrix and said second matrix,

where said first matrix of weighted coefficients comprises;

where;

##EQU14## where unit vectors are calculated as;

##EQU15## where i and j vary between 1 and n, and 1 and p, respectively, where n represents a number of the first plurality of satellites,

where p represents a number of the second plurality of satellites,

A₁ denotes the position of the first receiver,

A₂ denotes the position of the second receiver,

S₁,i denotes the position of an i^th satellite in the first plurality of satellites, and

S₂,j denotes the position of a j^th satellite in the second plurality of satellites.

54. The apparatus of claim 5 where said second matrix of observable parameters comprises:

##EQU26## where;

space="preserve" listing-type="equation">o.sub.ij =(1+u.sub.1,i ·

u.sub.2,j )(ρ

.sub.1,i -ρ

.sub.2,j -e.sub.1,i +e.sub.2,j)+(u.sub.1,i +u.sub.2,j ) ·

S.sub.1,i S.sub.2,j

where unit vectors are calculated as;

##EQU27## where i and j vary between 1 and n, and 1 and p, respectively, where n represents a number of the first plurality of ##EQU28## satellites, where p represents a number of the second plurality of satellites,

A₁ denotes the position of the first receiver,

A₂ denotes the position of the second receiver,

S₁,i denotes the position of an i^th satellite in the first plurality of satellites,

S₂,j denotes the position of a j^th satellite in the second plurality of satellites,

ρ

₁,i denotes a pseudorange between the first receiver and an i^th satellite in the first plurality of satellites,

ρ

₂,j denotes a pseudorange between the second receiver and a j^th satellite in the second plurality of satellites,

e₁,i denotes a range equivalent of a clock offset of an i^th satellite of first plurality of satellites, and

e₂,j denotes a range equivalent of a clock offset of an j^th satellite of second plurality of satellites.

19. ρ

₁. i denotes a pseudorange between the first receiver and an i^th satellite in the first plurality of satellites,

ρ

₂,j denotes a pseudorange between the second receiver and a j^th satellite in the second plurality of satellites,

e₁ denotes a range equivalent for a first receiver clock offset, and

e₂ denotes a range equivalent for a second receiver clock offset,

e₁,i denotes a range equivalent of a clock offset of an i^th satellite of first plurality of satellites,

e₂,j denotes a range equivalent of a clock offset of an j^th satellite of second plurality of satellites, and

where i and j vary between 1 and n, and 1 and p, respectively,

where n represents a number of the first plurality of satellites, and

where p represents a number of the second plurality of satellites.

21. The method of claim 19, wherein said step of receiving, from a second plurality of satellites of the constellation of navigation satellites, a second plurality of navigation signals at the second receiver comprises the steps of:

receiving a second group of ephemeris data characterizing predetermined orbits of each of the second plurality of satellites of the constellation of navigation satellites; and

receiving a second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites.

23. The method of claim 21, wherein said step of computing, at the second receiver, a second plurality of unit vectors between the second receiver and each of the second plurality of satellites comprises the step of calculating each of the second plurality of unit vectors as:

##EQU20## where A₂ denotes the position of the second receiver, and S₂,j denotes the position of a j^th satellite in the second plurality of satellites.

25. The method of claim 23, wherein said step of extracting, at the second receiver, a second plurality of raw pseudoranges between the second receiver and each of the second plurality of satellites from the second plurality of navigation signals comprises the steps of:

measuring differences between a clock signal generated at the second receiver and the second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites to measure a second group of propagation times for the second plurality of navigation signals from each of the second plurality of satellites; and

multiplying each of the second group of propagation times by the speed of light to produce a second group of raw pseudoranges between the second receiver and each of the second group of satellites.

27. The method of claim 25, wherein said step of determining a precise relative position between the first receiver and the second receiver from the plurality of satellite positions of the first and second pluralities of satellites, the first and second pluralities of unit vectors, the first and second pluralities of raw pseudoranges, and the first and second pluralities of range equivalents of the clock offsets of each of the first and second pluralities of satellites, respectively, by solving the set of equations:

space="preserve" listing-type="equation">(u.sub.1,i +u.sub.2,j )·

A.sub.1 A.sub.2 +(1+u.sub.1,i ·

u.sub.2,j )(e.sub.1 -e.sub.2)=(1+u.sub.1,i ·

2j)

space="preserve" listing-type="equation">(ρ

.sub.1,i -ρ

.sub.2,j -e.sub.1,i +e.sub.2,j)+(u.sub.1,i +u.sub.2,j )·

S.sub.1,i S.sub.2,j

where A₁ denotes the position of the first receiver,

A₂ denotes the position of the second receiver,

S₁,i denotes the position of an i^th satellite in the first plurality of satellites,

S₂,j denotes the position of a j^th satellite in the second plurality of satellites,

30. The apparatus of claim 27, wherein said means for receiving, from a first plurality of satellites of the constellation of navigation satellites, a first plurality of navigation signals at the first receiver comprises:

means for receiving a first group of ephemeris data characterizing predetermined orbits of each of the first plurality of satellites of the constellation of navigation satellites; and

means for receiving a first group of satellite time signals from each of the first plurality of satellites of the constellation of navigation satellites.

33. The apparatus of claim 30, wherein said means for computing a position estimate of the second receiver comprises:

means for generating a position estimate of the second receiver using an inertial navigation system.

36. The apparatus of claim 33, wherein said means for computing a first plurality of unit vectors between the first receiver and each of the first plurality of satellites comprises means for calculating each of the first plurality of unit vectors as:

##EQU22## where A₁ denotes the position of the first receiver, and S₁,i denotes the position of an i^th satellite in the first plurality of satellites.

39. The apparatus of claim 36, wherein said means for extracting from the second plurality of navigation signals, a second plurality of raw pseudoranges between the second receiver and the second plurality of satellites comprises:

means for measuring differences between a clock signal generated at the second receiver and the second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites to measure a second group of propagation times for the second plurality of navigation signals from each of the second plurality of satellites; and

means for multiplying each of the second group of propagation times by the speed of light to produce a second group of raw pseudoranges between the second receiver and each of the second group of satellites.

42. The apparatus of claim 39, wherein said means for determining a precise relative position between the first receiver and the second receiver comprises means for determining the precise relative position between the first receiver and the second receiver from the plurality of satellite positions of the first and second pluralities of satellites, the first and second pluralities of unit vectors, the first and second pluralities of raw pseudoranges, and the first and second pluralities of range equivalents of the clock offsets of each of the first and second pluralities of satellites, respectively by solving the set of equations:

space="preserve" listing-type="equation">(u.sub.1,i +u.sub.2,j )·

A.sub.1 A.sub.2 +(1+u.sub.1,i ·

u.sub.2,j )(e.sub.1 e.sub.2)=1+u.sub.1,i ·

u.sub.2,j )

space="preserve" listing-type="equation">(ρ

.sub.1,i -ρ

.sub.2,j -e.sub.1,i +e.sub.2,j) +(u.sub.1,i +u.sub.2,j )·

S.sub.1,i S.sub.2,j

where A₁ denotes the position of the first receiver,

A₂ denotes the position of the second receiver,

S₁,i denotes the position of an i^th satellite in the first plurality of satellites,

S₂,j denotes the position of a j^th satellite in the second plurality of satellites,

ρ

₁,i denotes a pseudorange between the first receiver and an i^th satellite in the first plurality of satellites,

ρ

₂,j denotes a pseudorange between the second receiver and a j^th satellite in the second plurality of satellites,

e₁ denotes a range equivalent for a first receiver clock offset, and

e₂ denotes a range equivalent for a second receiver clock offset,

e₁,i denotes a range equivalent of a clock offset of an i^th satellite of first plurality of satellites,

e₂,j denotes a range equivalent of a clock offset of an j^th satellite of second plurality of satellites, and

where i and j vary between 1 and n, and 1 and p, respectively,

where n represents a number of the first plurality of satellites, and

where p represents a number of the second plurality of satellites.

45. The apparatus of claim 42, wherein said means for receiving, from a second plurality of satellites of the constellation of navigation satellites, a second plurality of navigation signals comprises:

means for receiving a second group of ephemeris data characterizing predetermined orbits of each of the second plurality of satellites of the constellation of navigation satellites; and

means for receiving a second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites.

48. The apparatus of claim 45, wherein said means for extracting from the first plurality of navigation signals, a first plurality of raw pseudoranges between the first receiver and each of the first plurality of satellites comprises:

means for measuring differences between a clock signal generated at the first receiver and the first group of satellite time signals from each of the first plurality of satellites of the constellation of navigation satellites to measure a first group of propagation times for the first plurality of navigation signals from each of the first plurality of satellites; and

means for multiplying each of the first group of propagation times by the speed of light to produce a first group of raw pseudoranges between the first receiver and each of the first group of satellites.

51. The apparatus of claim 48, wherein said second receiver further comprises:

means for computing a second plurality of range equivalents of the clock offsets of each of the second plurality of satellites.

55. The apparatus of claim 51, where said means for computing solves the relative navigation equation system using said first matrix and said second matrix using the equation:

space="preserve" listing-type="equation">X=Ψ

O

Where

space="preserve" listing-type="equation">Ψ

=(.sup.t W W).sup.-1 t W.

28. ρ

₁. i denotes a pseudorange between the first receiver and an i^th satellite in the first plurality of satellites,

ρ

₂,j denotes a pseudorange between the second receiver and a j^th satellite in the second plurality of satellites,

e₁ denotes a range equivalent for a first receiver clock offset, and

e₂ denotes a range equivalent for a second receiver clock offset,

e₁,i denotes a range equivalent of a clock offset of an i^th satellite of first plurality of satellites,

e₂,j denotes a range equivalent of a clock offset of an j^th satellite of second plurality of satellites, and

where i and j vary between 1 and n, and 1 and p, respectively,

where n represents a number of the first plurality of satellites, and

where p represents a number of the second plurality of satellites.

31. The apparatus of claim 28, wherein said means for receiving, from a second plurality of satellites of the constellation of navigation satellites, a second plurality of navigation signals at the second receiver comprises:

means for receiving a second group of ephemeris data characterizing predetermined orbits of each of the second plurality of satellites of the constellation of navigation satellites; and

means for receiving a second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites.

34. The apparatus of claim 31, wherein said means for transmitting from the first receiver to the second receiver, through the communication link, the second plurality of navigation signals and the position estimate of the second receiver comprises:

means for transmitting the second group of ephemeris data characterizing predetermined orbits of each of the second plurality of satellites of the constellation of navigation satellites from the second receiver to the first receiver; and

means for transmitting the second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites from the second receiver to the first receiver.

37. The apparatus of claim 34, wherein said means for computing a second plurality of unit vectors between the second receiver and each of the second plurality of satellites comprises calculating each of the second plurality of unit vectors as:

##EQU23## where A₂ denotes the position of the second receiver, and S₂,j denotes the position of a j^th satellite in the second plurality of satellites.

40. The apparatus of claim 37, wherein the first receiver further comprises:

means for computing a first plurality of range equivalents of the clock offsets of each of the first plurality of satellites.

29. An apparatus for determining the relative position between two points, comprising:

a first receiver located at a first point, for receiving signals from a first plurality of satellites of a satellite-based navigation system having a constellation of navigation satellites;

a second receiver located at a second point, for receiving signals from a second plurality of satellites of the satellite-based navigation system having a constellation of navigation satellites;

a communication link between the first receiver and the second receiver,

wherein the first receiver further includes;

means for receiving, from a first plurality of satellites of the constellation of navigation satellites, a first plurality of navigation signals at the first receiver;

means for computing a position estimate of the first receiver;

means for computing a plurality of satellite positions of the first and second pluralities of satellites;

means for transmitting from the first receiver to the second receiver, through the communication link, the first plurality of navigation signals and the position estimate of the first receiver, and

wherein the second receiver further includes;

means for receiving, from a second plurality of satellites of the constellation of navigation satellites, a second plurality of navigation signals at the second receiver;

means for computing a position estimate of the second receiver;

means for computing a first plurality of unit vectors between the first receiver and each of the first plurality of satellites;

means for computing a second plurality of unit vectors between the second receiver and each of the second plurality of satellites;

means for extracting from the first plurality of navigation signals, a first plurality of raw pseudoranges between the first receiver and each of the first plurality of satellites;

means for extracting from the second plurality of navigation signals, a second plurality of raw pseudoranges between the second receiver and each of the second plurality of satellites;

means for computing a first plurality of range equivalents of the clock offsets of each of the first plurality of satellites;

means for computing a second plurality of range equivalents of the clock offsets of each of the second plurality of satellites; and

means for determining a precise relative position between the first receiver and the second receiver from the pluralities of satellites, the first and second pluralities of unit vectors, the first and second pluralities of raw pseudoranges, and the first and second pluralities of range equivalents of the clock offsets of each of the first and second pluralities of satellites, respectively.

32. The apparatus of claim 29, wherein said means for computing a position estimate of the first receiver comprises:

means for generating a position estimate of the first receiver using an inertial navigation system.

35. The apparatus of claim 32, wherein said means for computing a plurality of satellite positions of the first and second pluralities of satellites comprises:

means for computing positions of the first plurality of satellites from the first group of ephemeris data characterizing predetermined orbits of each of the first plurality of satellites of the constellation of navigation satellites; and

means for computing position of the second plurality of satellites from the second group of ephemeris data characterizing predetermined orbits of each of the second plurality of satellites of the constellation of navigation satellites.

38. The apparatus of claim 35, wherein said means for extracting from the first plurality of navigation signals, a first plurality of raw pseudoranges between the first receiver and each of the first plurality of satellites comprises:

means for measuring differences between a clock signal generated at the first receiver and the first group of satellite time signals from each of the first plurality of satellites of the constellation of navigation satellites to measure a first group of propagation times for the first plurality of navigation signals from each of the first plurality of satellites; and

means for multiplying each of the first group of propagation times by the speed of light to produce a first group of raw pseudoranges between the first receiver and each of the first group of satellites.

41. The apparatus of claim 38, wherein the second receiver further comprises:

means for computing a second plurality of range equivalents of the clock offsets of each of the second plurality of satellites.

44. The apparatus of claim 41, wherein said means for receiving, from a first plurality of satellites of the constellation of navigation satellites, a first plurality of navigation signals comprises:

means for receiving a first group of ephemeris data characterizing predetermined orbits of each of the first plurality of satellites of the constellation of navigation satellites; and

means for receiving a first group of satellite time signals from each of the first plurality of satellites of the constellation of navigation satellites.

47. The apparatus of claim 44, wherein said means for computing a second plurality of unit vectors between the second receiver and each of the second plurality of satellites comprises means for calculating each of the second plurality of unit vectors as:

##EQU25## where A₂ denotes the position of the second receiver, and where S₂,j denotes the position of a j^th satellite in the second plurality of satellites.

50. The apparatus of claim 47, wherein said first receiver further comprises:

means for computing a first plurality of range equivalents of the clock offsets of each of the first plurality of satellites.

43. A apparatus for computing the relative position between two points, comprising:

a first receiver located at a first point, for receiving signals from a satellite-based navigation system having a constellation of navigation satellites;

a second receiver located at a second point, for receiving signals from a satellite-based navigation system having a constellation of navigation satellites; and

a communication link between the first receiver and the second receiver,

wherein the first receiver includes;

means for receiving, from a first plurality of satellites of the constellation of navigation satellites, a first plurality of navigation signals;

means for computing a first plurality of unit vectors between the first receiver and each of the first plurality of satellites;

means for computing a plurality of satellite positions of the first and second pluralities of satellites;

means for extracting from the first plurality of navigation signals, a first plurality of raw pseudoranges between the first receiver and each of the first plurality of satellites;

means for computing a first plurality of range equivalents of the clock offsets of each of the first plurality of satellites;

means for transmitting from the first receiver to the second receiver, through the communication link, the first plurality of unit vectors, the first plurality of raw pseudoranges, and the first plurality of range equivalents of the clock offsets of each of the first plurality of satellites, and

wherein the second receiver includes;

means for receiving, from a second plurality of satellites of the constellation of navigation satellites, a second plurality of navigation signals;

means for computing a second plurality of unit vectors between the second receiver and each of the second plurality of satellites;

.

means for extracting from the second plurality of navigation signals, a second plurality of raw pseudoranges between the first receiver and each of the second plurality of satellites;

means for computing a second plurality of range equivalents of the clock offsets of each of the second plurality of satellites; and

means for determining a precise relative position between the first receiver and the second receiver from the plurality of satellite positions of the first and second pluralities of satellites, the first and second pluralities of unit vectors, the first and second pluralities of raw pseudoranges, and the first and second pluralities of range equivalents of the clock offsets of each of the first and second pluralities of satellites, respectively.

46. The apparatus of claim 43, wherein said means for computing a first plurality of unit vectors between the first receiver and each of the first plurality of satellites comprises means for calculating each of the first plurality of unit vectors as:

##EQU24## where A₁ denotes the position of the first receiver, and S₁,i denotes the position of an i^th satellite in the first plurality of satellites.

49. The apparatus of claim 46, wherein said means for extracting from the second plurality of navigation signals, a second plurality of raw pseudoranges between the second receiver and each of the second plurality of satellites comprises:

means for measuring differences between a clock signal generated at the second receiver and the second group of satellite time signals from each of the second plurality of satellites of the constellation of navigation satellites to measure a second group of propagation times for the second plurality of navigation signals from each of the second plurality of satellites; and

means for multiplying each of the second group of propagation times by the speed of light to produce a second group of raw pseudoranges between the second receiver and each of the second group of satellites.

52. The apparatus of claim 49, wherein said means for determining a precise relative position between the first receiver and the second receiver from the plurality of satellite positions of the first and second pluralities of satellites, the first and second pluralities of unit vectors, the first and second pluralities of raw pseudoranges, and the first and second pluralities of range equivalents of the clock offsets of each of the first and second pluralities of satellites, respectively by solving the set of equations:

space="preserve" listing-type="equation">(u.sub.1,i +u.sub.2,j )·

A.sub.1 A.sub.2 +(1+u.sub.1,i ·

u.sub.2,j )(e.sub.1 e.sub.2)=(1+u.sub.1,i ·

u.sub.2,j )

space="preserve" listing-type="equation">(ρ

.sub.1,i -ρ

.sub.2,j -e.sub.1,i +e.sub.2,j) +(u.sub.1,i +u.sub.2,j )·

S.sub.1,i S.sub.2,j

where A₁ denotes the position of the first receiver,

A₂ denotes the position of the second receiver,

S₁,i denotes the position of an i^th satellite in the first plurality of satellites,

S₂,j denotes the position of a j^th satellite in the second plurality of satellites,

ρ

₁,i denotes a pseudorange between the first receiver and an i^th satellite in the first plurality of satellites,

53. ρ

₂. j denotes a pseudorange between the second receiver and a j^th satellite in the second plurality of satellites,

e₁ denotes a range equivalent for a first receiver clock offset, and

e₂ denotes a range equivalent for a second receiver clock offset,

e₁,i denotes a range equivalent of a clock offset of an i^th satellite of first plurality of satellites,

e₂,j denotes a range equivalent of a clock offset of an j^th satellite of second plurality of satellites, and

where i and j vary between 1 and n, and 1 and p, respectively,

where n represents a number of the first plurality of satellites, and

where p represents a number of the second plurality of satellites.