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GPS receiver utilizing a communication link
| Details |
Inventors: Krasner, Norman F.;
Assignee: SnapTrack, Inc. (Campbell, CA)
Primary Examiner: Blum; Theodore M.
Assistant Examiner:
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor & Zafman
Methods and apparatuses for deriving an approximate Doppler for a satellite positioning system (SPS) receiver from an approximate location which is obtained from a cellular communication system information source. In one embodiment, an approximate location of the SPS receiver is derived from the information source and this approximation location is used to determine approximate Dopplers to a plurality of SPS satellites at a given time. The approximate Dopplers are then used to reduce processing time in either determining pseudoranges to the SPS satellites or acquiring signals from the SPS satellites. In another aspect of the invention, a reference signal is used to provide a local oscillator signal which is used to acquire SPS signals in an SPS receiver. This reference signal is extracted from a data signal modulated on a carrier frequency. The data signal on the carrier frequency is transmitted from, in one example, a wireless cell site which is communicating with the SPS receiver which has a cellular based communication receiver. |
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DETAILED DESCRIPTION In one aspect of the present invention, a method is described for reducing processing time due to Doppler error in a satellite positioning system (SPS) receiver having a cell based communication receiver.
The method includes determining an approximate location of the SPS receiver from a cell based information source.
This approximate location is determined by using at least one of a location of a cellular service area which includes a cell site which is capable of communicating with the cell based communication receiver or a location of the cell site itself.
The method further includes determining an approximate Doppler for at least one SPS satellite relative to the SPS receiver, where the approximate Doppler is based upon the approximate location.
This approximate Doppler is used in the SPS receiver to reduce processing time in either determining at least one pseudorange to the at least one SPS satellite, or in acquiring signals from the at least one SPS satellite.
An exemplary embodiment of this method is a cellular telephone which includes a GPS receiver.
The cellular telephone operates by communicating with cell sites, each of which are connected to a cellular switching center.
A database, which represents a cellular based information source, may be maintained at the cellular switching center or at the cell site or at a remote processing station, which may be termed a "server," may be used to determine an approximate location of the cellular telephone based upon the cell site (or cellular service area) with which the cellular telephone is communicating.
This approximate location may then be used to derive an approximate Doppler relative to the various SPS satellites which are transmitting SPS signals to the GPS receiver in the cellular telephone.
This approximate Doppler is then transmitted in one embodiment from the cell site to the cellular telephone, and is then used in the GPS receiver in order to reduce processing time due to Doppler induced effects in the GPS receiver
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