Systems and methods for resolving GPS pseudo-range ambiguity

• US 6,408,178 B1
• Filed: 03/29/1999
• Issued: 06/18/2002
• Est. Priority Date: 03/29/1999
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Wickstrom, Daniel, Solve, Torbjorn, Jolley, Edward V.
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): Tran, Congvan
• Application Number:
  US09/280,318
• Time in Patent Office: 1,177 Days
• Field of Search: 455/18.1, 455/403, 455/422, 455/424, 455/427, 455/458, 342/352, 342/355, 342/357.01, 342/357.06, 342/357.08, 342/357.12, 701/213, 701/214, 701/215
• US Class Current: 455/427
• CPC Class Codes: G01S 19/09 providing processing capability normally carried out by the receiver
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/252 Employing an initial estimate of location in generating assistance data
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 19/46 the supplementary measurement being of a radio-wave signal type

Abstract

Methods and systems are provided for determining a position of a mobile terminal that includes a satellite radiotelephone and a global positioning system (GPS) receiver based on knowledge of the position of the communication satellite spot-beam in which the mobile terminal is located. Using knowledge of the location of the communication satellite spot-beam, the present invention can resolve the one-millisecond ambiguity, that typically arises from the code repeat length where relative code phase may be determined but absolute code phase (i.e. one millisecond increments) could be off by one or more code periods. The spot-beam identifier is obtained from the satellite communication system and used to determine the geographic location of the spot-beam. Trial positions, i.e., candidate mobile terminal positions, are then selected to cover the spot-beam area, with spacing between trial positions provided to account for the one-millisecond ambiguity. Pseudo-range measurements are generated for each trial position and used to generate position fixes. The best position fix, for example a fix selection based on a self-consistency check, is then selected as the mobile terminal'"'"'s position. In an additional aspect of the present invention, the number of trial positions is reduced by selecting an arc of positions within the spot-beam as trial positions based on timing delay information from the satellite communication system.

Claims

1. A method for determining a position of a mobile terminal comprising the steps of:

obtaining an identification of a spot-beam in which the mobile terminal is located from a satellite radiotelephone system communication;

generating a plurality of trial positions within the spot-beam;

determining candidate position fixes for the mobile terminal for at least two of the plurality of trial positions based on GPS signals received by the mobile terminal from a plurality of global positioning system (GPS) satellites;

selecting one of the determined candidate position fixes as the position of the mobile terminal; and

wherein the determining step further comprises the steps of;

calculating a plurality of initial pseudo-range estimates corresponding to the plurality of GPS satellites for one of the plurality of trial positions based on the GPS signals received by the mobile terminal, the GPS signals having a code length, including determining fractional code periods from the received GPS signals;

adjusting the initial pseudo-range estimates to produce a plurality of candidate pseudo-range estimates for the mobile terminal for the one of the plurality of trial positions;

generating the candidate position fix for the mobile terminal for the one of the plurality of trial positions based on the plurality of candidate pseudo-range estimates, and

repeating the calculating, adjusting and generating steps for a second one of the plurality of trial positions.

2. A method according to claim 1 wherein the adjusting step includes the steps of:

truncating each of the initial pseudo-range estimates to produce a corresponding plurality of integer code length distances for the one of the plurality of trial positions;

adding distances corresponding to the fractional code periods derived from the received GPS signals to the plurality of integer code length distances to provide a corresponding plurality of candidate pseudo-range estimates for the mobile terminal.

3. A method according to claim 1 wherein the adjusting step includes the step of:

modifying the plurality of initial pseudo-range estimates to account for relative differences between the fractional code periods derived from the received GPS signals to provide a corresponding plurality of candidate pseudo-range estimates for the mobile terminal.

4. A method according to claim 1 wherein the repeating step comprises the step of executing the calculating, adjusting and generating steps for each of the plurality of trial positions to provide candidate position fixes for the mobile terminal for each of the plurality of trial positions.

5. A method according to claim 4 wherein the step of repeating the determining step is preceded by the step of selecting the plurality of GPS satellites from visible GPS satellites based on the elevation of the visible GPS satellites relative to one of the plurality of trial positions.

6. A method according to claim 4 wherein the position fixes are least squares position fixes, wherein said step of repeating the determining step comprises the step of repeating the determining step for at least four GPS satellites and wherein the selecting step further comprises the step of selecting one of the candidate position fixes as the position of the mobile terminal based on a self-consistency check.

7. A method according to claim 6 wherein the selecting step comprises the step of selecting one of the determined candidate position fixes using an overdetermined set of equations.

8. A method according to claim 7 wherein the selecting step includes the steps of:

Q-R decomposing a direction cosine matrix determined from the candidate position fixes; and

multiplying non-constrained dimensions of a transpose of a Q matrix from the decomposing step by delta pseudo-range values from the candidate position fixes.

9. A method according to claim 1 wherein the step of generating a plurality of trial positions comprises the step of generating the plurality of trial positions wherein each of the trial positions is located no more than approximately 150 kilometers of another of the plurality of trial positions.

10. A method according to claim 9 wherein the step of generating a plurality of trial positions comprises the step of generating the plurality of trial positions on a grid covering the spot-beam.

11. A method according to claim 1 wherein the step of obtaining comprises the steps of:

receiving a spot-beam identifier from the satellite radiotelephone system communication; and

calculating a geographic location of the spot-beam based on the received spot-beam identifier.

12. A method according to claim 11 wherein the calculating step comprises the step of calculating the geographic location of the spot-beam based on satellite ephemeris data obtained from the satellite radiotelephone system communication and antenna direction coordinates.

13. A method according to claim 11 wherein the calculating step comprises the step of calculating the geographic location of the spot-beam based on boundary points for the spot-beam stored in the mobile terminal.

14. A method according to claim 1 further comprising the steps of:

obtaining satellite communication timing information from the satellite radiotelephone system communication; and

wherein the generating step comprises the step of generating a plurality of trial positions based on the obtained timing information.

15. A method according to claim 14 wherein the timing information is timing delay information and wherein the generating step comprises the step of selecting the plurality of trial positions along an arc of positions substantially equidistant from a satellite transmitting the satellite radiotelephone system communication based on the timing delay information.

17. A method according to claim 14 wherein the obtaining step comprises the steps of:

requesting the satellite communication timing information from a satellite radiotelephone system satellite on a high margin random access channel; and

receiving the satellite communication timing information from the satellite radiotelephone system satellite on a high margin paging channel.

18. A method according to claim 17 wherein the satellite communication timing information is timing delay information and wherein the requesting step comprises the step of transmitting a request including a timing update request having a request number identifier and wherein the step of receiving comprises the step of receiving a timing update having an associated identifier corresponding to the request number identifier.

19. A method according to claim 1 wherein the repeating, calculating, adjusting and generating steps are performed by the mobile terminal.

20. A method according to claim 4 wherein the calculating step includes the steps of:

receiving a GPS signal at the mobile terminal from each of the plurality of GPS satellites;

determining a code phase for each of the plurality of GPS satellites from the received GPS signals at the mobile terminal; and

providing the determined code phases with time-stamps to a remote GPS station from the mobile terminal; and

wherein the repeating, calculating, adjusting and generating steps are performed by the GPS station.

16. A method for determining a position of a mobile terminal comprising the steps of:

obtaining an identification of a spot-beam in which the mobile terminal is located from a satellite radiotelephone system communication;

obtaining satellite communication timing information from the satellite radiotelephone system communication;

generating a plurality of trial positions within the spot-beam based on the obtained timing information;

determining candidate position fixes for the mobile terminal for at least two of the plurality of trial positions based on GPS signals received by the mobile terminal from a plurality of global positioning system (GPS) satellites;

selecting one of the determined candidate position fixes as the position of the mobile terminal; and

wherein the timing information is timing delay information and wherein the generating step comprises the step of selecting the plurality of trial positions along at least one arc of positions substantially equidistant from a satellite transmitting the satellite radiotelephone system communication based on the timing delay information wherein each of the trial positions is located no more than approximately 150 kilometers of another of the plurality of trial positions.

21. A position computation system for a mobile terminal, comprising:

means for obtaining an identification of a spot-beam in which the mobile terminal is located from a satellite radiotelephone system communication;

means for generating a plurality of trial positions within the spot-beam;

means for determining candidate position fixes for the mobile terminal for at least two of the plurality of trial positions based on global positioning system (GPS) signals received by the mobile terminal from a plurality of GPS satellites;

means for selecting one of the determined candidate position fixes as the position of the mobile terminal; and

wherein the means for determining further comprises;

means for calculating a plurality of initial pseudo-range estimates corresponding to the plurality of GPS satellites for one of the plurality of trial positions based on the GPS signals received by the mobile terminal, the GPS signals having a code length, including determining fractional code periods from the received GPS signals;

means for adjusting the initial pseudo-range estimates to produce a plurality of candidate pseudo-range estimates for the mobile terminal for the one of the plurality of trial positions; and

means for generating the candidate position fix for the mobile terminal for the one of the plurality of trial positions based on the plurality of candidate pseudo-range estimates.

22. A system according to claim 21 wherein the means for adjusting further comprises:

means for truncating each of the initial pseudo-range estimates to produce a corresponding plurality of integer code length distances for the one of the plurality of trial positions; and

means for adding distances corresponding to the fractional code periods derived from the received GPS signals to the plurality of integer code length distances to provide a corresponding plurality of candidate pseudo-range estimates for the mobile terminal.

23. A system according to claim 21 wherein the means for adjusting further comprises:

means for modifying the plurality of initial pseudo-range estimates to account for relative differences between the fractional code periods derived from the received GPS signals to provide a corresponding plurality of candidate pseudo-range estimates for the mobile terminal.

24. A system according to claim 21 further comprising means for selecting a plurality of GPS satellites from visible GPS satellites based on the elevation of the visible GPS satellites relative to one of the plurality of trial positions.

25. A system according to claim 21 wherein the position fixes are least squares position fixes and wherein the means for selecting comprises means for selecting one of the candidate position fixes as the position of the mobile terminal based on a self-consistency check.

26. A system according to claim 21 further comprising:

means for obtaining satellite communication timing information from the satellite radiotelephone system communication; and

wherein the means for generating comprises means for generating a plurality of trial positions based on the obtained timing information.

28. A system according to claim 26 wherein the means for obtaining comprises:

means for requesting the satellite communication timing information from a satellite radiotelephone system satellite on a high margin random access channel; and

means for receiving the satellite communication timing information from the satellite radiotelephone system satellite on a high margin paging channel.

30. A system according to claim 21 wherein the means for calculating comprises:

means for receiving a GPS signal at the mobile terminal from each of the plurality of GPS satellites;

means for determining a code phase for each of the plurality of GPS satellites from the received GPS signals at the mobile terminal; and

means for providing the determined code phases with time-stamps to a remote GPS station from the mobile terminal for determination of the candidate position fixes and selection of one of the determined candidate position fixes as the position of the mobile terminal at the GPS station.

27. A position computation system for a mobile terminal, comprising:

means for obtaining an identification of a spot-beam in which the mobile terminal is located from a satellite radiotelephone system communication;

means for obtaining satellite communication timing information from the satellite radiotelephone system communication;

means for generating a plurality of trial positions within the spot-beam based on the obtained timing information;

means for determining candidate position fixes for the mobile terminal for at least two of the plurality of trial positions based on global positioning system (GPS) signals received by the mobile terminal from a plurality of GPS satellites;

means for selecting one of the determined candidate position fixes as the position of the mobile terminal; and

wherein the timing information is timing delay information and wherein the means for generating comprises means for selecting the plurality of trial positions along at least one arc of positions substantially equidistant from a satellite transmitting the satellite radiotelephone system communication based on the timing delay information wherein each of the trial positions is located no more than approximately 150 kilometers of another of the plurality of trial positions.

29. A position computation system for a mobile terminal, comprising:

means for obtaining an identification of a spot-beam in which the mobile terminal is located from a satellite radiotelephone system communication;

means for requesting satellite communication timing information from a satellite radiotelephone system satellite on a high margin random access channel;

means for receiving the satellite communication timing information from the satellite radiotelephone system satellite on a high margin paging channel;

means for generating a plurality of trial positions within the spot-beam based on the obtained timing information;

means for determining candidate position fixes for the mobile terminal for at least two of the plurality of trial positions based on global positioning system (GPS) signals received by the mobile terminal from a plurality of GPS satellites;

means for selecting one of the determined candidate position fixes as the position of the mobile terminal; and

wherein the satellite communication timing information is timing delay information and wherein the means for requesting comprises means for transmitting a request including a timing update request having a request number identifier and wherein the means for receiving comprises means for receiving a timing update having an associated identifier corresponding to the request number identifier.

31. A method for determining a position of a mobile terminal comprising the steps of:

obtaining an identification of a geographic area in which the mobile terminal is located from a wireless communication system;

generating a plurality of trial positions within the identified geographic area;

determining candidate position fixes for the mobile terminal for at least two of the plurality of trial positions based on GPS signals received by the mobile terminal from a plurality of global positioning system (GPS) satellites;

selecting one of the determined candidate position fixes as the position of the mobile terminal; and

wherein the determining step further comprises the steps of;

calculating a plurality of initial pseudo-range estimates corresponding to the plurality of GPS satellites for one of the plurality of trial positions based on the GPS signals received by the mobile terminal, the GPS signals having a code length, including determining fractional code periods from the received GPS signals;

adjusting the initial pseudo-range estimates to produce a plurality of candidate pseudo-range estimates for the mobile terminal for the one of the plurality of trial positions;

generating the candidate position fix for the mobile terminal for the one of the plurality of trial positions based on the plurality of candidate pseudo-range estimates, and

repeating the calculating, adjusting and generating steps for a second one of the plurality of trial positions.

32. A position computation system for a mobile terminal, comprising:

means for obtaining an identification of a geographic area in which the mobile terminal is located from a wireless communication system;

means for generating a plurality of trial positions within the identified geographic area;

means for determining candidate position fixes for the mobile terminal for at least two of the plurality of trial positions based on GPS signals received by the mobile terminal from a plurality of global positioning system (GPS) satellites;

means for selecting one of the determined candidate position fixes as the position of the mobile terminal; and

wherein the means for determining further comprises;

means for calculating a plurality of initial pseudo-range estimates corresponding to the plurality of GPS satellites for one of the plurality of trial positions based on the GPS signals received by the mobile terminal, the GPS signals having a code length, including determining fractional code periods from the received GPS signals;

means for adjusting the initial pseudo-range estimates to produce a plurality of candidate pseudo-range estimates for the mobile terminal for the one of the plurality of trial positions; and

means for generating the candidate position fix for the mobile terminal for the one of the plurality of trial positions based on the plurality of candidate pseudo-range estimates.