GPS receiver having a rapid acquisition of GPS satellite signals

• US 5,594,453 A
• Filed: 11/01/1994
• Issued: 01/14/1997
• Est. Priority Date: 11/01/1994
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Rodal, Eric B., Lau, Chung Y., Farmer, Dominic G.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US08/332,958
• Time in Patent Office: 805 Days
• Field of Search: 342/357, 342/352, 342/386
• US Class Current: 342/357.65
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/34 Power consumption

Abstract

A GPS receiver having a rapid acquisition of a GPS satellite signal when a normal operational mode is entered after a low power standby mode. The GPS receiver includes an RF section for receiving the GPS satellite signal and providing an GPS IF signal, a correlator section for providing a correlation signal for the correlation between the GPS IF signal and a GPS replica signal, and a microprocessor section for receiving the correlation signal and calculating a geographical location of the GPS receiver. The GPS replica signal is based upon a reference frequency from a reference oscillator and a reference time from a timer. In the standby mode, the operation of the RF section, correlator section, and microprocessor section is inhibited while the reference oscillator and time continue to operate. In order to increase acquisition speed upon entering the normal mode, the microprocessor section provides the correlator section with an initial frequency adjustment to correct for drift in the reference frequency during the standby mode. The microprocessor section provides the initial frequency adjustment based upon a learned frequency correction that is based upon the frequency adjustment that results in acquisition of the GPS satellite signal after alternating one or more times between the standby mode and the normal mode. Alternately, the initial frequency adjustment is calculated from a stored frequency/temperature relationship and a temperature for the reference oscillator measured by a temperature sensor.

Claims

1. A GPS receiver having a normal mode to acquire a GPS signal from one or more GPS satellites and to provide a location of the receiver, having a low power standby mode, and having a rapid acquisition of the GPS signal when the receiver enters the normal mode after a time duration in the standby mode, the receiver including:

a means for controlling the mode of the GPS receiver for the normal mode and for the standby mode;

a reference oscillator to generate a continuous reference frequency signal in the normal mode and in the standby mode;

a timer to receive the reference frequency signal and to generate a continuous reference time of arrival (TOA) signal in the normal mode and in the standby mode;

a correlator section to receive the reference frequency signal;

to receive the reference TOA signal;

to generate a replica signal having a replica frequency based upon the reference frequency signal and having a replica TOA based upon the reference TOA signal;

to receive an initial adjustment signal, including an initial frequency adjustment and an initial TOA adjustment when the receiver enters the normal mode after a time duration in the standby mode;

to adjust the replica frequency according to the initial frequency adjustment;

to adjust the replica TOA according to the initial TOA adjustment;

to provide a correlation signal for a correlation of the replica signal to the GPS signal; and

to receive a feedback adjustment signal including a feedback frequency adjustment and a feedback TOA adjustment to drive the replica signal to correlate to the GPS signal, thereby acquiring the GPS signal; and

a microprocessor section, including a memory including a learned frequency correction, to calculate the initial frequency adjustment from the learned frequency correction, to provide the initial adjustment signal and the feedback adjustment signal, to calculate the learned frequency correction based upon a difference between the initial frequency adjustment and the feedback frequency adjustment that correlates the replica signal to the GPS signal, and to store the learned frequency correction in the memory.

2. The GPS receiver in claim 1, wherein:

the microprocessor section is further to calculate the initial frequency adjustment based upon a portion of the learned frequency correction calculated from a portion of a selected time duration in the standby mode that has completed when the standby mode is interrupted before the selected time duration has completed.

3. The GPS receiver in claim 1, wherein:

the memory further includes a learned TOA correction; and

the microprocessor section is further to calculate the initial TOA adjustment based upon the learned TOA correction, to calculate the learned TOA correction based upon a difference between the initial TOA adjustment and the feedback TOA adjustment that correlates the replica signal to the GPS signal, and to store the learned TOA correction in the memory.

4. A GPS receiver having a normal mode to track a GPS signal from one or more GPS satellites and to provide a location of the receiver, having a low power standby mode, and having a rapid acquisition of the GPS signal when the receiver enters the normal mode after a time duration in the standby mode, the receiver including:

a means for controlling the mode of the receiver for the normal mode and for the standby mode;

a reference oscillator to generate a continuous reference frequency signal in the normal mode and in the standby mode;

a correlator section to receive the reference frequency signal;

to generate a replica signal having a replica frequency based upon the reference frequency signal;

to receive an initial adjustment signal, including an initial frequency adjustment when the receiver enters the normal mode after a time duration in the standby mode;

to adjust the replica frequency according to the initial frequency adjustment;

to provide a correlation signal for a correlation of the replica signal to the GPS signal; and

to receive a feedback adjustment signal including a feedback frequency adjustment to drive the replica signal to correlate to the GPS signal, thereby acquiring the GPS signal; and

a microprocessor section, including a memory including a learned frequency correction, to calculate the initial frequency adjustment from the learned frequency correction, to provide the initial adjustment signal and the feedback adjustment signal, to calculate the learned frequency correction based upon a difference between the initial frequency adjustment and the feedback frequency adjustment that correlates the replica signal to the GPS signal, and to store the learned frequency correction in the memory.

5. The GPS receiver in claim 4, wherein:

the microprocessor section is further to calculate the initial frequency adjustment based upon a portion of the learned frequency correction calculated from a portion of a selected time duration in the standby mode that has completed when the standby mode is interrupted before the selected time duration has completed.

6. A method for rapidly acquiring a GPS signal from one or more GPS satellites in a GPS receiver when the receiver enters a normal mode after a time duration in a low power standby mode, the method including steps of:

providing a reference frequency oscillator to generate a reference frequency signal continuously during the standby mode and during the normal mode and to issue the reference frequency signal to a timer and to a correlator section;

providing a timer using the reference frequency signal to generate a reference TOA signal continuously during the standby mode and during the normal mode and to issue the reference TOA signal to the correlator section;

controlling the GPS receiver to enter the normal mode after the time duration in the standby mode by a means for controlling the mode;

calculating an initial frequency adjustment based upon a learned frequency correction retrieved from a memory in a microprocessor section;

providing an initial adjustment signal from the microprocessor section to the correlator section, the initial adjustment signal including the initial frequency adjustment and an initial TOA adjustment;

generating a replica signal in the correlator section, the replica signal including a replica frequency based upon the reference frequency signal and upon the initial frequency adjustment and including a replica TOA based upon the reference TOA signal and upon the initial TOA adjustment;

providing a correlation signal for a correlation between the replica signal and the GPS signal and issuing the correlation signal to the microprocessor section;

acquiring the GPS signal by correlating the replica signal to the GPS signal by providing a feedback adjustment signal from the microprocessor section to the correlator section, the feedback adjustment signal including a feedback frequency adjustment and a feedback TOA adjustment;

calculating the learned frequency correction from a difference between the initial frequency adjustment and the feedback frequency adjustment that correlates to the GPS signal; and

storing the learned frequency correction in the memory.

7. The GPS receiver in claim 6, wherein;

the step of providing an initial adjustment signal further includes steps of providing a selected time duration for the standby mode and calculating the initial frequency adjustment from a portion of the learned frequency correction calculated from a portion of the selected time duration in the standby mode that has completed when the standby mode is interrupted before the selected time duration has completed.

8. The method of claim 6, wherein:

the step of providing an initial adjustment signal further includes of retrieving a learned TOA correction from the memory and calculating the initial TOA adjustment based upon the learned TOA correction; and

the step of acquiring the GPS signal further includes steps of calculating the learned TOA correction based upon a difference between the initial TOA adjustment and the feedback TOA adjustment that correlates to the GPS signal and storing the learned TOA correction in the memory.

9. A method for rapidly acquiring a GPS signal from one or more GPS satellites in a GPS receiver when the receiver enters a normal mode to acquire the GPS signal after a time duration in a low power standby mode, the method including steps of:

providing a reference frequency oscillator to generate a reference frequency signal continuously during the standby mode and during the normal mode and to issue the reference frequency signal to a correlator section;

controlling the GPS receiver to enter the normal mode after the time duration in the standby mode;

calculating an initial frequency adjustment based upon a learned frequency correction retrieved from a memory in a microprocessor section;

providing an initial adjustment signal from a microprocessor section to the correlator section, the initial adjustment signal including the initial frequency adjustment;

generating a replica signal in the correlator section, the replica signal including a replica frequency based upon the reference frequency signal and upon the initial frequency adjustment;

providing a correlation signal for a correlation between the replica signal and the GPS signal to the microprocessor section;

acquiring the GPS signal by correlating the replica signal to the GPS signal by providing a feedback adjustment signal from the microprocessor section to the correlator section, the feedback adjustment signal including a feedback frequency adjustment;

calculating the learned frequency correction from a difference between the initial frequency adjustment and the feedback frequency adjustment that correlates to the GPS signal; and

storing the learned frequency correction in the memory.

10. The GPS receiver in claim 9, wherein;

the step of providing an initial adjustment signal further includes steps of providing a selected time duration for the standby mode and calculating the initial frequency adjustment from a portion of the learned frequency correction calculated from a portion of the selected time duration in the standby mode that has completed when the standby mode is interrupted before the selected time duration has completed.

11. A GPS receiver having a normal mode to acquire a GPS signal from one or more GPS satellites and to provide a location of the receiver and a low power standby mode, and having a rapid acquisition of said GPS signal when the GPS receiver enters said normal mode after a time duration in said standby mode, comprising:

a reference oscillator for generating a continuous reference signal having a reference frequency during said normal mode and during said standby mode;

correlator means, coupled to the reference oscillator for receiving said reference signal, for receiving said GPS signal, for receiving an adjustment signal, and for providing a correlation signal in response to said reference signal, said adjustment signal, and said GPS signal; and

microprocessor means, coupled to the correlator means for receiving said correlation signal and providing said adjustment signal including an initial frequency adjustment when the GPS receiver enters said normal mode, and including a memory including an executable program for calculating said initial frequency adjustment to correct for drift in said reference frequency during said standby mode.

12. The GPS receiver of claim 11, wherein:

said memory further includes a learned frequency correction and said executable program is further for calculating said initial frequency adjustment from said learned frequency correction.

13. The GPS receiver of claim 12, wherein:

said executable program is further for calculating said learned frequency correction based upon a comparison of said adjustment signal including said initial frequency adjustment and said adjustment signal causing a correlation between said reference signal and said GPS signal.

14. The GPS receiver of claim 11, further including:

a temperature sensor, coupled to the reference oscillator for measuring a temperature of the reference oscillator and providing said temperature to the microprocessor means; and

wherein;

said memory further includes a frequency/temperature relationship representative of said reference frequency for said temperature; and

said executable program is further for calculating said initial frequency adjustment based upon said temperature/frequency relationship and said temperature.

15. A method for rapidly acquiring a GPS signal from one or more GPS satellites in a GPS receiver when said receiver enters a normal mode alter a time duration in a low power standby mode, the method including steps of:

generating a continuous reference frequency;

receiving said GPS signal with said GPS receiver when said receiver enters said normal mode from said standby mode;

generating an initial frequency adjustment for correcting for a drift in said reference frequency during said standby mode; and

providing a correlation signal for a correlation of said GPS signal with said reference frequency and said initial frequency adjustment.

16. The method of claim 15, wherein:

the step of generating an initial frequency adjustment includes steps of calculating said initial frequency adjustment from said correlation signal when said normal mode is entered, storing information for said initial frequency adjustment in a memory, and retrieving said information when said normal mode is re-entered after a time in said standby mode.

17. The method of claim 15, wherein:

the step of generating an initial frequency adjustment includes steps of providing a temperature/frequency relationship for said reference frequency for a range of temperatures, measuring a first temperature within said range when exiting said normal mode to enter said standby mode, measuring a second temperature within said range when re-entering said normal mode after said standby mode, and calculating said initial frequency adjustment based upon said first temperature, said second temperature, and said temperature/frequency relationship.