Convergence Zone

• US 20130021198A1
• Filed: 01/05/2012
• Published: 01/24/2013
• Est. Priority Date: 01/05/2011
• Status: Active Grant

• Current Assignee: Qualcomm technologies international, ltd. (Qualcomm, Inc.)
• Original Assignee: Cambridge Silicon Radio Limited (Qualcomm, Inc.)
• Inventors: Pratt, Anthony Richard, Jarvis, Murray Robert
• Granted Patent: US 9,086,479 B2
• Time in Patent Office: Days
• US Class Current: 342/357.25
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• CPC Class Codes: G01S 19/28 Satellite selection
• CPC Class Codes: G01S 19/42 Determining position

Abstract

Apparatus for calculating the location of a receiver in a satellite navigation system, the apparatus being arranged to calculate a location of the receiver by means of an algorithm that utilises an estimate of receiver location and/or an estimate of absolute time, the apparatus being arranged to perform the calculation in such a way as to extend a convergence zone within which the algorithm is capable of generating the correct location for the receiver despite an error in the estimate(s).

Claims

1. An apparatus for calculating the location of a receiver in a satellite navigation system, the apparatus being arranged to calculate a location of the receiver by means of an algorithm that utilises an estimate of receiver location and/or an estimate of absolute time, the apparatus being arranged to perform the calculation in such a way as to extend a convergence zone within which the algorithm is capable of generating the correct location for the receiver despite an error in the estimate(s).

2. An apparatus as claimed in claim 1, wherein the apparatus is arranged to calculate the location of the receiver in dependence on signalling events received by the receiver from a plurality of satellites, the size of the convergence zone being dependent on which satellites from a constellation of satellites visible to the receiver are used to calculate the location.

3. An apparatus as claimed in claim 2, wherein the apparatus is arranged to extend the convergence zone by using a subset of the satellites visible to the receiver to calculate the location.

4. An apparatus as claimed in claim 3, wherein the apparatus is arranged to select as the subset the predetermined number of satellites associated with the largest convergence zone achievable by a predetermined number of the satellites in the constellation of satellites visible to the receiver.

5. An apparatus as claimed in claim 3, wherein the apparatus is arranged to select the subset in dependence on an error associated with the estimate of receiver location.

6. An apparatus as claimed in claim 3, wherein the apparatus is arranged to select the subset in dependence on an error associated with the estimate of absolute time.

7. An apparatus as claimed in claim 3, wherein the apparatus is arranged to select the subset by:

forming a candidate set comprising satellites that are visible to the receiver;

repeatedly identifying which of the satellites in the candidate set is associated with the smallest convergence zone and eliminating that satellite from the candidate set until the candidate set consists of a predetermined number of satellites; and

selecting the set of satellites to comprise the predetermined number of satellites in the candidate set.

8. An apparatus as claimed in claim 3, wherein the apparatus is arranged to select the set of satellites by:

identifying one or more candidate sets of satellites that could be formed from the constellation of satellites visible to the receiver and used to calculate a location for the receiver;

determining a convergence zone associated with each of the candidate sets; and

selecting as the set of satellites the candidate set associated with the largest convergence zone.

9. An apparatus as claimed in claim 3, wherein the apparatus is arranged to select the subset of satellites to consist of a predetermined number of satellites in the set of visible satellites that have the highest levels of elevation relative to the receiver.

10. An apparatus as claimed in claim 3, wherein the apparatus is arranged to select the set of satellites to consist of a predetermined number of satellites in the set of visible satellites that have the lowest line-of-sight velocities relative to the receiver.

11. An apparatus as claimed in claim 3, wherein the apparatus is arranged to designate one of the subset as a reference satellite.

12. An apparatus as claimed in claim 1, wherein the apparatus is arranged to calculate the location of the receiver in dependence on an indication of a transit time for a signalling event to travel between a satellite and the receiver.

13. An apparatus as claimed in claim 12, wherein the indication of the transit time incorporates an ambiguity, the apparatus being arranged to extend the convergence zone by assuming a first possibility for said ambiguity and calculating a location of the receiver in dependence on that first possibility and, if the location generated by that calculation is not correct, assuming a second possibility for said ambiguity and calculating a location of the receiver in dependence on that second possibility.

14. An apparatus as claimed in claim 13, wherein the apparatus is arranged to:

identify the ambiguity possibilities;

determine a convergence zone associated with each of said possibilities; and

calculate the location of the receiver in dependence on the possibility associated with the largest convergence zone and, if that calculation does not generate a correct location for the receiver, repeat the calculation for the possibilities associated with successively smaller convergence zones until a correct location for the receiver is generated.

15. An apparatus as claimed in claim 12, wherein the signalling event is transmitted at regular intervals by the satellite, the apparatus being arranged to extend the convergence zone by adding and/or subtracting to/from the indication of transit time an indication of a time between the transmission of those signalling events by the satellite and repeat the calculation of the receiver'"'"'s location in dependence on the adjusted indication of transit time.

16. An apparatus as claimed in claim 14, wherein the apparatus is arranged to form a residual representative of a combined error in:

an indication of an expected transit time for a signalling event to travel from a first satellite to the receiver; and

an indication of an expected transit time for a signalling event to travel from a second satellite to the receiver;

by comparing those indications of expected transit time with indications of transit time measured by the receiver;

the apparatus being arranged to form the adjusted indication of transit time by adding and/or subtracting to/from the residual the indication of the time between the transmission of the signalling events by the first or second satellites.

17. A method for calculating the location of a receiver in a satellite navigation system, the method comprising calculating a location of the receiver by means of an algorithm that utilises an estimate of receiver location and/or an estimate of absolute time, the method further comprising performing the calculation in such a way as to extend a convergence zone within which the algorithm is capable of generating the correct location for the receiver despite an error in the estimate(s).

18. A computer-readable medium encoded with instructions, that when executed by an apparatus for calculating the location of a receiver in a satellite navigation system, causes the apparatus to calculate a location of the receiver by means of an algorithm that utilises an estimate of receiver location and/or an estimate of absolute time, and to perform the calculation in such a way as to extend a convergence zone within which the algorithm is capable of generating the correct location for the receiver despite an error in the estimate(s).