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GPS receiver utilizing a communication link
| 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 GPS receiver in one embodiment includes an antenna which receives GPS signals at an RF frequency from in view satellites; a downconverter coupled to the antenna for reducing the RF frequency of the received GPS signals to an intermediate frequency (IF); a digitizer coupled to the downconverter and sampling the IF GPS signals at a predetermined rate to produce sampled IF GPS signals; a memory coupled to the digitizer storing the sampled IF GPS signals (a snapshot of GPS signals); and a digital signal processor (DSP) coupled to the memory and operating under stored instructions thereby performing Fast Fourier Transform (FFT) operations on the sampled IF GPS signals to provide pseudorange information. These operations typically also include preprocessing and post processing of the GPS signals. After a snapshot of data is taken, the receiver front end is powered down. The GPS receiver in one embodiment also includes other power management features and includes, in another embodiment the capability to correct for errors in its local oscillator which is used to sample the GPS signals. The calculation speed of pseudoranges, and sensitivity of operation, is enhanced by the transmission of the Doppler frequency shifts of in view satellites to the receiver from an external source, such as a basestation in one embodiment of the invention. |
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DETAILED DESCRIPTION OF THE INVENTION This invention concerns apparatuses and methods for computing the position of a mobile, or remote, object in a manner that results in the remote hardware having very low power dissipation and the ability to operate with very low received signal levels.
That is, power consumption is reduced while receiver sensitivity is increased.
This is made possible by the implementation of the remote receiving functions, as shown in FIG.
1A, as well as the transmission of Doppler information from a separately located basestation 10 to the remote or GPS mobile unit 20.
It should be noted that pseudoranges may be used to compute the remote's geographical position in many different ways.
Three examples are: 1.
Method 1: By re-transmitting the satellite data messages to the remote 20 from the basestation 10, the remote 20 may combine this information with the pseudorange measurements to compute its position.
See, for example, U.
S.
Pat.
No.
5,365,450, which is incorporated herein by reference.
Typically, the remote unit 20 performs the computation of position in the remote 20.
2.
Method 2: The remote 20 may gather the satellite ephemeris data from the reception of GPS signals in the normal manner that is commonly practiced in the art.
This data, which typically is valid for one to two hours, may be combined with pseudorange measurements to complete, typically in the remote unit, the position calculation.
3.
Method 3: The remote 20 may transmit over a communications link 16 the pseudoranges to the basestation 10 which can combine this information with the satellite ephemeris data to complete the position calculation.
See, for example, U.
S.
Pat.
No.
5,225,842, which is incorporated herein by reference.
In approaches (or Methods) 1 and 3, it is assumed that the basestation 10 and remote 20 have a common view of all satellites of interest and are positioned close enough to one another to resolve a time ambiguity associated with the repetition rate of the GPS pseudorandom codes
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Cell Phones 
