Method of obtaining a position fix in a GPS receiver and a GPS receiver for the same

• US 6,775,615 B2
• Filed: 12/13/2002
• Issued: 08/10/2004
• Est. Priority Date: 12/19/2001
• Status: Expired due to Term

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Yule, Andrew T.
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): To, Tuan C
• Application Number:
  US10/319,872
• Publication Number:
  US 20030114982A1
• Time in Patent Office: 606 Days
• Field of Search: 701/213, 701/214, 701/207, 342/357.02, 342/357.04, 342/357.06, 342/357.05, 342/357.09, 342/357.12, 342/357.03, 342/357.01, 342/352, 455/12.1, 455/457, 455/456, 455/405, 345/357.02
• US Class Current: 701/213
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 19/50 whereby the position solution is constrained to lie upon a particular curve or surface, e.g. for locomotives on railway tracks
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

A method of obtaining a position fix in a GPS receiver is disclosed together with a GPS receiver for the same. The method comprising the steps of (i) providing an estimate of clock offset between the GPS receiver and the GPS satellites; (ii) measuring a set of pseudoranges from the GPS receiver to GPS satellites; and (iii) either (a) resolving the set of pseudoranges obtained in step (ii) to obtain a position fix, or (b) providing an estimate of the position of the GPS receiver, resolving the set of pseudoranges obtained in step (ii) to obtain a position fix correction, and obtaining a position fix using the estimate of the position of the GPS receiver and the position fix correction, wherein resolving the pseudoranges in step (iii)(a) or step (iii)(b) does not involve resolving the pseudoranges for either a new clock offset or clock offset correction.

Claims

1. A method of obtaining a position fix in a GPS receiver comprising the steps of:

(i) providing an estimate of clock offset between the GPS receiver and the GPS satellites;

(ii) measuring a set of pseudoranges from the GPS receiver to GPS satellites; and

(iii) either;

(a) resolving the set of pseudoranges obtained in step (ii) to obtain a position fix, or

(b) providing an estimate of the position of the GPS receiver, resolving the set of pseudoranges obtained in step (ii) to obtain a position fix correction, and obtaining a position fix using the estimate of the position of the GPS receiver and the position fix correction

wherein resolving the pseudoranges in step (iii)(a) or step (iii)(b) does not involve resolving the pseudoranges for either a new clock offset or clock offset correction.

2. A method according to claim 1 further comprising the step of (iv) using the position fix obtained in step (iii) to update the estimate of the clock offset in step (i), wherein the steps (i) to (iv) are cyclically repeated.

3. A method according to claim 1 or step 2 wherein step (iii) involves calculated the direction cosines matrix H:

$H=\left(\begin{array}{ccc}\frac{x-s_x^1}{r_1}& \frac{y-s_y^1}{r_1}& \frac{z-s_z^1}{r_1}\\ \frac{x-s_x^2}{r_2}& \frac{y-s_y^2}{r_2}& \frac{z-s_z^2}{r_2}\\ \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}\\ \frac{x-s_x^n}{r_n}& \frac{y-s_y^n}{r_n}& \frac{z-s_z^n}{r_n}\end{array}\right)$

where n is the number of satellites and r_i is the distance from an estimate of the position of the GPS receiver to the i^th satellite, calculated in the following manner;

4. A GPS receiver configured to obtain a position fix by a method according to claim 1.