FREQUENCY AIDING METHOD AND SYSTEM FOR NAVIGATION SATELLITE RECEIVER WITH CRYSTAL OSCILLATOR FREQUENCY HYSTERESIS

• US 20090278735A1
• Filed: 05/09/2008
• Published: 11/12/2009
• Est. Priority Date: 05/09/2008
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: Blackberry Limited
• Inventors: Jin, Xin, Rosselet, Andrew Jonathan Gilbert, Grant, Christopher James
• Granted Patent: US 7,956,804 B2
• Time in Patent Office: Days
• US Class Current: 342/357.640
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS

Abstract

A method and apparatus for estimating oscillator signal variation due to temperature and for providing an estimated frequency to a GPS receiver in order to assist the GPS receiver to acquire the signals quickly is disclosed. A temperature sensor is closely thermally coupled with the crystal oscillator in the GPS receiver and during GPS tracking mode, when the error in the oscillator signal is known with precision, outer bounds of TCXO frequency at given temperatures are maintained, which may correspond to rising and falling temperature conditions. During acquisition mode, an estimated frequency value is provided to the GPS receiver based on a determined average of these bounds. Optionally, an uncertainty factor associated with the frequency estimated may also be provided. The two bounds take into account the hysteresis effects of the oscillator signal drift due to temperature so that a more accurate initial frequency estimate can be provided to the GPS receiver, thus reducing its average time to first fix.

Claims

1. A navigation satellite receiver, comprising:

a crystal oscillator having an operable temperature range, the crystal oscillator adapted to generate an input clock signal having an actual frequency that drifts from a nominal frequency over the operable temperature range;

a temperature sensor thermally coupled with the crystal oscillator for taking temperature measurements of the crystal oscillator;

a navigation platform for receiving a plurality of signals having a known transmit frequency, the platform being capable of operating;

in an acquisition mode in which the navigation platform attempts to receive, based on the input clock signal, at least one signal from at least one navigation satellite within a search window;

in an operational mode, in which the navigation platform is adapted to receive, based on the input clock signal, a plurality of signals from different navigation satellites to obtain a current positional fix for the receiver; and

a processor for producing first and second sets of frequency information, indicative of a discrepancy between the actual and the nominal frequency of the input clock signal, as a function of oscillator temperature measurements taken by the temperature sensor;

whereby in acquisition mode, the navigation platform determines at least one parameter of the search window for a current oscillator temperature, based on the first and/or second sets of frequency information, to take into account any discrepancy between the actual frequency in relation to the nominal frequency of the input clock signal.

2. A receiver according to claim 1, wherein the frequency information is selected from a group consisting of frequency difference, frequency offset, frequency error, frequency difference uncertainty, frequency offset uncertainty and frequency error uncertainty,

3. A receiver according to claim 1, wherein the navigation platform is Assisted-GPS (A-GPS) compliant.

4. A receiver according to claim 1, wherein the navigation platform forwards the frequency information to the processor periodically.

5. A receiver according to claim 1, wherein the operable temperature range is substantially between approximately −

20°

C. and approximately 80°

C.

6. A receiver according to claim 1, wherein the crystal oscillator is a temperature compensated crystal oscillator (TCXO).

7. A receiver according to claim 1, wherein corresponding values in the first and second sets of frequency information correspond to a rising and falling temperature trend respectively.

8. A receiver according to claim 1, wherein corresponding values in the first and second sets of frequency information correspond to a maximum bound and minimum bound respectively.

9. A receiver according to claim 1, wherein the navigation platform is further capable of operating in a test mode, whereby at least the minimum number of signals from the at least one satellites may be generated and received by the receiver and further frequency information may be determined.

10. A receiver according to claim 1, wherein the receiver is a mobile device.

11. A method for providing frequency aiding information, for an input clock signal generated by a crystal oscillator having an operable temperature range and having an actual frequency that drifts from a nominal frequency across the operable temperature range, to a navigation platform in a navigation satellite receiver comprising a temperature sensor thermally coupled with the crystal oscillator for taking temperature measurements thereof, the navigation platform for receiving a plurality of signals having a known transmit frequency and being capable of operating in an acquisition mode in which the navigation platform attempts to receive, based on the input clock signal, at least one signal from at least one navigation satellite within a search window and in an operational mode, in which the navigation platform is adapted to receive, based on the input clock signal, a plurality of signals from different navigation satellites to obtain a current positional fix for the receiver;

the method comprising the acts of;

a. in the operational mode;

i. obtaining frequency data indicative of a discrepancy between the actual frequency and the nominal frequency of the input clock signal;

ii. taking a contemporaneous temperature measurement of the crystal oscillator; and

iii. associating the frequency data with the temperature measurement and updating first and/or second sets of frequency information therewith; and

b. in the acquisition mode;

i. taking a current temperature measurement of the crystal oscillator; and

ii. determining at least one parameter of the search window for a current crystal oscillator temperature, based on the first and/or second sets of frequency information, to take into account any discrepancy between the actual frequency in relation to the nominal frequency of the input clock signal at the current oscillator temperature.

12. The method according to claim 11, wherein the frequency data and/or frequency information are selected from a group consisting of frequency difference, frequency offset, frequency error, frequency difference uncertainty, frequency offset uncertainty and frequency error uncertainty, frequency offset uncertainty and frequency error uncertainty.

13. The method according to claim 11, wherein the first and second sets of frequency information are initialized to a value indicative of an untrained status.

14. The method according to claim 13, wherein step a.iii comprises identifying whether the contemporaneous temperature measurement is indicative of a temperature trend, and if not, updating any untrained value in either or both of the first and second sets of frequency information having a temperature index corresponding to the temperature measurement, with the frequency data.

15. The method according to claim 13, wherein step a.iii comprises identifying whether the contemporaneous temperature measurement is indicative of a temperature trend, and if so, updating an entry, in a selected one of the first and second sets of frequency information corresponding to the identified trend, and having a temperature index corresponding to the contemporaneous temperature measurement, based upon the frequency data.

16. The method according to claim 13, wherein the step of updating a value comprises identifying whether the frequency data lies between a stored value in each of the first and second sets of frequency information having a temperature index corresponding to the contemporaneous temperature measurement, and if so, substituting an updated value which slowly converges to the frequency data, and if not, substituting an updated value which rapidly converges to the frequency data.

17. The method according to claim 16, wherein the step of substituting an updated value which slowly converges to the frequency data and the step of substituting an updated value which rapidly converges to the frequency data each comprise calculating the stored value and a difference between the frequency data and the stored value weighting the difference by a coefficient, adding the stored value thereto to produce a sum and substituting the sum for the stored value.

18. The method according to claim 17, wherein the coefficient in the step of substituting a value which slowly converges to the frequency data is small in relation to the coefficient in the step of substituting a value which rapidly converges to the frequency data.

19. The method according to claim 17, wherein the coefficient is a divisor which is an exponent of 2.

20. The method according to claim 13, wherein step b.ii comprises providing an uncertainty factor indicative of a perceived uncertainty in the estimated frequency information.

21. The method according to claim 13, wherein step b.ii comprises providing a value, corresponding to at least one of the first and second sets of frequency information, that is not untrained, chosen from a group consisting of:

A. at least one value in the at least one of the first and second sets of frequency information, and having a temperature index corresponding to the current temperature measurement;

B. at least one value, interpolated from among values in the at least one of the first and second sets of frequency information, and in proximity to a value of subparagraph A. that is untrained;

C. at least one value in the at least one of the first and second sets of frequency information, and in proximity to a value of subparagraph A. that is untrained; and

D. at least one value in the at least one of the first and second sets of frequency information.

22. The method according to claim 21, wherein the step of providing a value comprises multiplying the value corresponding to the first set of frequency information by a weighting constant in the range of [0,1], multiplying the value corresponding to the second set of frequency information by a difference from 1 of the weighting constant and adding the multiplied values.

23. A processor, in a navigation satellite receiver comprising:

a crystal oscillator having an operable temperature range, the crystal oscillator adapted to generate an input clock signal having an actual frequency that drifts from a nominal frequency over the operable temperature range;

a temperature sensor thermally coupled with the crystal oscillator for taking a temperature measurements of the crystal oscillator;

a navigation platform for receiving a plurality of signals having a known transmit frequency, the platform being capable of operating;

in an acquisition mode in which the navigation platform attempts to receive based on the input clock signal, at least one signal from at least one navigation satellite within a search window;

in an operational mode, in which the navigation platform is adapted to receive, based on the input clock signal, a plurality of signals from different navigation satellites to obtain a current positional fix for the receiver;

the processor for producing first and second sets of frequency information indicative of a discrepancy between the actual and the nominal frequency of the input clock signal as a function of oscillator temperature measurements taken by the temperature sensor;

whereby in acquisition mode, the navigation platform determines at least one parameter of the search window for a current oscillator temperature based on the first and/or second sets of frequency information, to take into account any discrepancy between the actual frequency in relation to the nominal frequency of the input clock signal.

24. A computer-readable medium in a processor, in a navigation satellite receiver comprising:

a crystal oscillator having an operable temperature range, the crystal oscillator adapted to generate an input clock signal having an actual frequency that drifts from a nominal frequency over the operable temperature range;

a temperature sensor thermally coupled with the crystal oscillator for taking a temperature measurements of the crystal oscillator;

a navigation platform for receiving a plurality of signals having a known transmit frequency, the platform being capable of operating;

in an acquisition mode in which the navigation platform attempts to receive based on the input clock signal, at least one signal from at least one navigation satellite within a search window;

in an operational mode, in which the navigation platform is adapted to receive, based on the input clock signal, a plurality of signals from different navigation satellites to obtain a current positional fix for the receiver;

the medium having stored thereon, computer-readable and computer-executable instruction which, when executed by the processor, cause the processor to perform steps comprising;

a. in the operational mode;

i. obtaining frequency data indicative of a discrepancy between the actual frequency and the nominal frequency of the input clock signal;

ii. taking a contemporaneous temperature measurement of the crystal oscillator; and

iii. associating the frequency data with the temperature measurement and updating first and/or second sets of frequency information therewith; and

b. in the acquisition mode;

i. taking a current temperature measurement of the crystal oscillator; and

ii. determining at least one parameter of the search window for a current crystal oscillator temperature based on the first and/or second sets of frequency information, to take into account any discrepancy between the actual frequency in relation to the nominal frequency of the input clock signal at the current oscillator temperature.