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Method and apparatus for acquiring satellite positioning system signals
| Details |
Inventors: Krasner, Norman F.;
Assignee: SnapTrack, Inc. (San Jose, CA)
Primary Examiner: Blum; Theodore M.
Assistant Examiner:
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor & Zafman
A method and an apparatus which acquire satellite positioning system (SPS) signals in an SPS receiver. Information on time of day, approximate receiver location, and satellite positions are used to reduce the time to search and acquire signals from one or more SPS satellites. In an example of a method of the invention, a first pseudorange to a first SPS satellite is determined, and an approximate location of the SPS receiver is determined. An estimated pseudorange for a second pseudorange to a second SPS satellite is determined from the approximate location and a satellite position of the second SPS satellite. The SPS receiver then searches for SPS signals from the second SPS satellite in a range determined by the estimated pseudorange. Typically, this method reduces the search time to initially acquire SPS signals from the second SPS satellite, and the estimated pseudorange is not based on a previously determined pseudorange for said second SPS satellite. In a particular example of the invention, the approximate location is determined from a cell based information source which correlates an identification of each of various wireless cell sites with an approximate location for objects within a cell of a wireless cell based communication system, such as a cellular (or cell based) telephone system. In other examples of the invention, relatively precise time of day information may be used with information indicating satellite positions and information indicating the approximate location to determine an estimated pseudorange for a first SPS satellite to be acquired. |
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DETAILED DESCRIPTION The present invention provides various methods and apparatuses for reducing the acquisition time of signals from SPS satellites.
In an example of a method of the present invention, an approximate location of the SPS receiver is determined.
An estimated pseudorange for a particular SPS satellite is determined from time of day, the approximate location and satellite position information of the particular SPS satellite.
The SPS receiver then searches for SPS signals from the particular SPS satellite in a range determined by the estimated pseudorange.
Typically, this method reduces the search time to initially acquire SPS signals from the particular SPS satellite.
In one particular example of the present invention, the approximate location is determined from a cell based information source which correlates an identification of each of various wireless cell sites with an approximate location for objects within a cell serviced by a wireless cell site in a wireless cell based communication system, such as a cellular telephone system.
In another particular example of the present invention, a server system assists a mobile SPS receiver by determining the estimated pseudoranges and causing these estimated pseudoranges to be transmitted to a mobile SPS receiver.
The server may be coupled to the mobile SPS receiver through a wireless cell based communication system.
In other examples of the present invention, the time to acquire signals from SPS satellites may be reduced by determining a time of day to an accuracy of better than a framing period of the SPS signals (e.
g.
1 millisecond for U.
S.
GPS system) and obtaining a set of mathematical expressions which specify (for a given approximate location at a given time) the estimated distance (or time of signal travel) from an SPS satellite.
The time of day and the mathematical expressions determine the estimated pseudoranges around which searching may be performed to acquire SPS signals from SPS satellites.
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Cell Phones 
