Differential system and method for a satellite based navigation

• US 5,490,073 A
• Filed: 04/05/1993
• Issued: 02/06/1996
• Est. Priority Date: 04/05/1993
• Status: Expired due to Term

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Kyrtsos, Christos T.
• Primary Examiner(s): Chin, Gary
• Application Number:
  US08/042,627
• Time in Patent Office: 1,037 Days
• Field of Search: 364/443, 364/444, 364/449, 364/459, 73/178 R, 342/357, 342/358, 342/450, 342/451, 342/457, 340/988
• US Class Current: 701/207
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]
• CPC Class Codes: G05D 1/0278 using satellite positioning signals, e.g. GPS
• CPC Class Codes: G05D 1/0282 generated in a local control room

Abstract

A differential system and method for computing the position of a mobile receiver at or near the surface of the Earth using a base receiver having a known position and using a satellite-based navigation system including a constellation of navigation satellites is disclosed. The method includes the following steps. A base position estimate is computed for the base receiver using a pseudorange from a first satellite and ranges from two other satellites. A first vector difference between the base position estimate and the known position of the base receiver is computed. An initial position estimate is computed for the mobile receiver. A refined position estimate is computed for the mobile receiver using a pseudorange from the first satellite and ranges from two other satellites. A second vector difference between the initial position estimate and the refined position estimate of the mobile receiver is computed. Finally, a third vector difference between the first vector difference and the second vector difference is computed. The position of the first receiver is precisely computed by adding the third vector difference to the initial position estimate for the mobile receiver.

Claims

1. A method for computing the position of a mobile receiver at or near the surface of the Earth using a base receiver having a known position and using a satellite-based navigation system including a constellation of navigation satellites, the method comprising the steps of:

(a) receiving at the base receiver and at the mobile receiver, a navigation signal from a first navigation satellite;

(b) receiving at the base receiver and at the mobile receiver, navigation signals from at least two other navigation satellite;

(c) computing for the base receiver, a first pseudorange based on said navigation signal received from said first navigation satellite, and first and second ranges based on said navigation signals;

received from said at least two other navigation satellites;

(d) computing a base position estimate for the base receiver using said first pseudorange and said first and second range;

(e) computing a first vector difference between the base position estimate and the known position of the base receiver;

(f) computing an initial position estimate for the mobile receiver;

(g) computing for the mobile receiver, a second pseudorange based on said navigation signal received from said first navigation satellite, and third and fourth ranges based on the navigation signals received from at least two other navigation satellites;

(h) computing a refined position estimate for the mobile receiver using said second pseudorange and said third and fourth ranges;

(i) computing a second vector difference between the initial position estimate and the refined position estimate of the mobile receiver;

(j) computing a third vector difference between said first vector difference and said second vector difference; and

(k) adding said third vector difference to said initial position estimate for the mobile receiver to produce a final position estimate for the mobile receiver.

2. The method of claim 1, wherein said initial position estimate is computed using a triangulation technique and pseudoranges and satellite positions from at least four satellites.

3. The method of claim 1, wherein said initial position estimate is computed using a differential technique.

4. The method of claim 3, wherein said at least two other satellites of step (c) are the same as said at least two other satellites of step (g).

5. A method for computing the position of a first receiver at or near the surface of the Earth using a second receiver having a known position and using a satellite-based navigation system including a constellation of navigation satellites, the method comprising the steps of:

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

(b) computing, from said first plurality of navigation signals, a position estimate for the first receiver;

(c) receiving, from the plurality of navigation satellites, a second plurality of navigation signals at the second receiver, said first and second pluralities of satellites including a first satellite common to both;

(d) computing, from each navigation signal, a satellite position;

(e) computing, from the navigation signal from said first satellite, a first pseudorange between said second receiver and said first satellite;

(f) computing, from the position of a second satellite and the known position of the second receiver, a first range between said second satellite and the second receiver;

(g) computing, from the position of a third satellite and the known position of the second receiver, a second range between said third satellite and the second receiver;

(h) computing, from said first pseudorange, said first range, said second range and said positions for said first, second and third satellites, an estimated position of said second receiver;

(i) computing a difference between said estimated and said known positions of said second receiver to determine a first error vector;

(j) computing, from said first plurality of navigation signals, a position estimate for the first receiver;

(k) computing, from the navigation signal from said first satellite, a second pseudorange between said first receiver and said first satellite;

(l) computing, from the position of a second satellite and said estimated position of the first receiver, a third range between said second satellite and the first receiver;

(m) computing, from the position of a third satellite and said estimated position of the first receiver, a fourth range between said third satellite and the first receiver;

(n) computing, from said second pseudorange, said third range, said fourth range and said positions for said first, second and third satellites, a refined estimated position of said first receiver;

(o) computing a difference between said refined estimated position and said estimated position of said first receiver to determine a second error vector;

(p) computing a difference between said first and second error vectors to determine a third error vector for the first receiver; and

(q) using said third error vector to correct the estimated position of the first receiver.

6. The method of claim 5, wherein said position estimate of step (j) is computed using a differential technique.

7. An apparatus for computing the position of a mobile receiver at or near the surface of the Earth using a base receiver having a known position and using a satellite-based navigation system including a constellation of navigation satellites, the apparatus comprising:

(a) means for receiving at the base receiver and at the mobile receiver, a navigation signal from a first navigation satellite;

(b) means for receiving at the base receiver and at the mobile receiver, navigation signals from at least two other navigation satellites;

(c) means for computing for the base receiver, a first pseudorange based on said navigation signal from said first navigation satellite, and first and second ranges based on said navigation signals received from said at least two other navigation satellites;

(d) means, coupled to said base receiver, for computing a base position estimate for the base receiver using said first pseudorange and said first and second ranges and for computing a first vector difference between the base position estimate and the known position of the base receiver;

(e) means for computing an initial position estimate for the mobile receiver;

(f) means for computing for the mobile receiver, a second pseudorange based on said navigation signal received from said first navigation satellite, and third and fourth ranges based on the navigation signals received from at least two other navigation satellites;

(g) means, coupled to the mobile receiver, for computing a refined position estimate for the mobile receiver using said second pseudorange and said third and fourth ranges and for computing a second vector difference between the initial position estimate and the refined position estimate of the mobile receiver; and

(h) means for computing a third vector difference between said first vector difference and said second vector difference and for adding said third vector difference to said initial position estimate for the mobile receiver to produce a final position estimate for the mobile receiver.