Self adjustment of a frequency offset in a GPS receiver

• US 6,697,016 B1
• Filed: 09/30/2002
• Issued: 02/24/2004
• Est. Priority Date: 09/30/2002
• Status: Active Grant

• Current Assignee: Motorola Mobility LLC (Lenovo Group Ltd.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Voor, Thomas E., Deck, Ronald H.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US10/260,940
• Time in Patent Office: 512 Days
• Field of Search: 342/357.15, 342/357.06, 342/357.12, 701/213
• US Class Current: 342/357.62
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: H03J 2200/05 Alignment of transmitter with a receiver, after fabrication

Abstract

A global positioning system (GPS) receiver (102) has a reference oscillator (114) for use in synthesizing signals for use in receiving and acquiring GPS satellite signals by a GPS downconverter (110). Upon manufacture of the receiver (204), the receiver is tested and a factory frequency offset of the oscillator is determined (206). It has been found that the heat used in reflowing the solder used to attach receiver components causes the operating frequency of oscillator devices, such as crystals, to shift considerably. In addition, during a brief period after manufacture of the receiver, the frequency of the oscillator shifts back towards its original operating frequency, and so much so that the narrow search window used to search for a GPS carrier is inadequate, and it is likely that the receiver would not locate the desired carrier signal. The invention takes advantage of the time period after manufacture, when the frequency of the oscillator settles, and the first time unit is turned on, the receiver is used proactively with a wide search window (212) to determine an operating frequency offset. Then, for subsequent location determination operations, a narrow search window is used (222).

Claims

1. A method of performing self adjustment of a frequency offset in a global positioning system (GPS) receiver to correct frequency error of a reference oscillator of the GPS receiver, comprising:

determining a factory frequency offset of the reference oscillator of the GPS receiver upon manufacture of the GPS receiver;

after determining the factory frequency offset, searching for a GPS satellite signal using the factory frequency offset and a wide frequency range search window;

after commencing searching for the GPS signal, acquiring a GPS satellite signal;

upon acquiring the GPS signal, determining an operating frequency offset of the reference oscillator of the GPS receiver from a frequency of the GPS satellite signal; and

upon determining the operating frequency offset, thereafter using a narrow frequency range search window for subsequently acquiring GPS satellite signals.

2. A method of performing self adjustment of a frequency offset in a GPS receiver as defined in claim 1, wherein determining the operating frequency offset is performed with the wide frequency range search window set wider than a specified frequency tolerance over temperature of the reference oscillator.

3. A method of performing self adjustment of a frequency offset in a GPS receiver as defined in claim 1, wherein determining the frequency offset is performed by determining the factory frequency offset and determining the operating frequency offset are preformed by determining the frequency offset of a reference crystal oscillator.

4. A method of performing self adjustment of a frequency offset in a GPS receiver as defined in claim 3, wherein determining the frequency offset is performed by determining the factory frequency offset and determining the operating frequency offset are preformed by determining the frequency offset of a temperature compensated reference crystal oscillator.

5. A method of performing self adjustment of a frequency offset in a GPS receiver as defined in claim 1, wherein, upon determining the operating frequency offset, thereafter using a frequency range search window substantially equal to a frequency tolerance over temperature of the reference oscillator for subsequently acquiring GPS satellite signals.

6. A method of performing self adjustment of a frequency offset in a GPS receiver as defined in claim 1, wherein upon commencing searching for the GPS signal, displaying a message on a display of the GPS receiver instructing a user of the GPS receiver to move the GPS receiver to an unobstructed location.

7. A method of performing self adjustment of a frequency offset in a GPS receiver as defined in claim 6, wherein displaying the message is performed after searching of the GPS satellite signal and not finding the GPS satellite signal after a period of time.

8. A method of performing self adjustment of a frequency offset in a mobile communication device having a global positioning system (GPS) receiver to correct frequency error of a reference oscillator of the GPS receiver, comprising:

determining a factory frequency offset of the reference oscillator of the GPS receiver upon manufacture of the GPS receiver;

after determining the factory frequency offset, searching for a GPS satellite signal using the factory frequency offset and a wide frequency range search window;

after commencing searching for the GPS signal, acquiring a GPS satellite signal;

upon acquiring the GPS signal, determining an operating frequency offset of the reference oscillator of the GPS receiver from a frequency of the GPS satellite signal; and

upon determining the operating frequency offset, thereafter using a narrow frequency range search window and aiding information received from a source outside of the mobile communication device for subsequently acquiring GPS satellite signals.

9. A method of performing self adjustment of a frequency offset in a mobile communication device having a GPS receiver as defined in claim 8, wherein determining the operating frequency offset is performed with the wide frequency window range search window set wider than a specified frequency tolerance over temperature of the reference oscillator.

10. A method of performing self adjustment of a frequency offset in a mobile communication device having a GPS receiver as defined in claim 8, wherein determining the frequency offset is performed by determining the factory frequency offset and determining the operating frequency offset are preformed by determining the frequency offset of a reference crystal oscillator.

11. A method of performing self adjustment of a frequency offset in a mobile communication device having a GPS receiver as defined in claim 10, wherein determining the frequency offset is performed by determining the factory frequency offset and determining the operating frequency offset are preformed by determining the frequency offset of a temperature compensated reference crystal oscillator.

12. A method of performing self adjustment of a frequency offset in a mobile communication device having a GPS receiver as defined in claim 8, wherein, upon determining the operating frequency offset, thereafter using a frequency range search window substantially equal to a frequency tolerance over temperature of the reference oscillator for subsequently acquiring GPS satellite signals.

13. A method of performing self adjustment of a frequency offset in a mobile communication device having a GPS receiver as defined in claim 8, wherein upon commencing searching for the GPS signal, displaying a message on a display of the GPS receiver instructing a user of the GPS receiver to move the GPS receiver to an outdoor location.

14. A method of performing self adjustment of a frequency offset in a mobile communication device having a GPS receiver as defined in claim 13, wherein displaying the message is performed after searching of the GPS satellite signal and not finding the GPS satellite signal after a period of time.

15. A method of performing self adjustment of a frequency offset in a mobile communication device as defined in claim 8, wherein upon commencing searching for the GPS signal, displaying a message on a display of the GPS receiver instructing a user of the GPS receiver to move the GPS receiver to an unobstructed location.

16. A method of performing self adjustment of a frequency offset in a global positioning system (GPS) receiver to correct frequency error of a reference oscillator of the GPS receiver, comprising:

searching for a GPS satellite signal using a wide frequency range search window;

after commencing searching for the GPS signal, acquiring a GPS satellite signal;

upon acquiring the GPS signal, determining an operating frequency offset of the reference oscillator of the GPS receiver from a frequency of the GPS satellite signal; and

upon determining the operating frequency offset, thereafter using a narrow frequency range search window for subsequently acquiring GPS satellite signals.