GNSS receiver using signals of opportunity and assistance information to reduce the time to first fix

• US 8,558,738 B2
• Filed: 05/22/2009
• Issued: 10/15/2013
• Est. Priority Date: 05/22/2008
• Status: Active Grant

• Current Assignee: Novatel Incorporated (Hexagon AB)
• Original Assignee: Novatel Incorporated (Hexagon AB)
• Inventors: Ladd, Jonathan, Fenton, Patrick C.
• Primary Examiner(s): GALT, CASSI J
• Application Number:
  US12/471,046
• Publication Number:
  US 20090322601A1
• Time in Patent Office: 1,607 Days
• Field of Search: 342/347.42, 342/357.49, 342/357.62, 342/357.63, 342/357.64, 342/357.65, 342/345.68, 342/357.71, 342/357.73
• US Class Current: 342/357.62
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/26 involving a sensor measurement for aiding acquisition or tracking
• CPC Class Codes: G01S 19/27 creating, predicting or correcting ephemeris or almanac data within the receiver

Abstract

A GNSS receiver reduces the time to first fix by utilizing the properties of existing radiated signals of opportunity, such as AM or FM radio signals, television signals and so forth, to reduce the uncertainties associated with oscillator frequency and phase, and further utilizing an Almanac and battery backed-up date and time to determine the satellites in view and reduce the uncertainties associated with Doppler. The receiver may use multiple signals of opportunity to determine the city or local area in which the receiver is located based on the set of frequencies of the signals, and also to reduce search uncertainties for oscillator frequency by estimating an offset based on the differences between the frequencies of the respective signals of opportunity at the receiver and the nominal broadcast frequencies of the signals.

Claims

1. A GNSS receiver including:

a radio frequency front end for receiving GNSS satellite signals and signals of opportunity, which contain random content, the radio frequency front end including one ore more configurable front end filters that scan broadcast signals to tune to signals of opportunity;

an oscillator used for acquiring and tracking the GNSS satellite signals; and

one or more processors configured to

process selected signals of opportunity and estimate a frequency offset for the oscillator based on a difference between the frequencies of one or more of the selected signals of opportunity as determined by the front end and nominal broadcast frequencies of the one or more selected signals of opportunity, and

use the estimated oscillator frequency offset to reduce a search window for acquiring the GNSS satellite signals.

2. The GNSS receiver of claim 1 wherein the one or more processors further determine an estimated location of the receiver based on the broadcast frequencies of multiple signals of opportunity and signal of opportunity transmitter location information.

3. The GNSS receiver of claim 1 further including

a real time clock that maintains current time and date,

a memory for storing an Almanac, and

the one or more processors determine satellites in view and estimate Doppler offsets associated with signals from the satellites in view based on an estimated location of the receiver, the stored Almanac and the current time and date and utilize the estimated Doppler offsets to further reduce the search window.

4. The GNSS receiver of claim 3 wherein the one or more processors determine the estimated location of the receiver based on the broadcast frequencies of multiple signals of opportunity and signal of opportunity transmitter location information.

5. The GNSS receiver of claim 4 further including a connection to a communications network, the network providing the signal of opportunity transmitter location information to the receiver over the connection.

6. The GNSS receiver of claim 5 wherein the receiver selects the signals of opportunity from a list of usable signals of opportunity.

7. The GNSS receiver of claim 5 wherein the network connection provides access to the internet.

8. The GNSS receiver of claim 1 wherein the one or more processors phase lock the oscillator used for signal acquisition and tracking to one of the signals of opportunity to provide narrow band tracking of the GNSS signals.

9. The GNSS receiver of claim 1 further including

a real time clock that maintains current time and date;

and

the one or more processors are further configured to determine time to within several microseconds of GNSS time based on the maintained current time and a timing property of the signals of opportunity, and preposition code searching based on known times of code chip transmissions from GNSS satellites.

22. The GNSS receiver of claim 1 wherein the one or more processors select the signals of opportunity based on one or more of field strength of the signals at the receiver and stability of the carrier frequency.

23. The GNSS receiver of claim 1 wherein the one or more configurable front end filters are one or more of charged capacitor filters and digital FIR filters.

10. A GNSS receiver including:

a radio frequency front end for receiving GNSS satellite signals and signals of opportunity, which contain random content, the radio frequency front end including one or more configurable front end filters that scan broadcast signals to tune to signals of opportunity;

an oscillator for use in acquiring and tracking the GNSS satellite signals; and

one or more processors configured to

select one or more signals of opportunity, process the selected signals of opportunity and phase lock the oscillator to one of the selected signals of opportunity, and

use a narrowed band to track the GNSS satellite signals.

11. A system for reducing the time to first fix position, the system including:

a base GNSS receiver for acquiring and tracking GNSS satellite signals and providing assistance information;

a remote GNSS receiver with

a radio frequency front end for receiving GNSS satellite signals and signals of opportunity, which contain random content, the radio frequency front end including one or more configurable front end filters that scan broadcast signals to tune to signals of opportunity;

a network connection to receive assistance information from the base GNSS receiver;

an oscillator for use in acquiring and tracking the GNSS signals; and

one or more processors configured to

select one or more signals of opportunity, process the selected signals of opportunity and estimate a frequency offset for the oscillator based on a difference between the frequencies of one or more of the selected signals of opportunity as determined by the front end and broadcast frequencies of the one or more signals of opportunity, and

use the estimated oscillator frequency offset to reduce a search window for acquiring the GNSS satellite signals.

12. The system of claim 11 wherein the assistance information is the broadcast frequencies of the signals of opportunity.

13. The system of claim 12 wherein broadcast frequencies are determined by the base GNSS receiver when the base GNSS receiver is phase locked to a GNSS frequency.

14. The system of claim 12 wherein the broadcast frequencies are the nominal broadcast frequencies of the signals of opportunity.

15. The system of claim 11 wherein

the assistance information is the location of signal of opportunity transmitters, and

the one or more processors determine the estimated location of the receiver based on the broadcast frequencies of multiple signals of opportunity and signal of opportunity transmitter location information.

16. The system of claim 11 wherein

the assistance information is navigation messages and message bit timing, and

the one or more processors wipe the navigation messages from received GNSS satellite signals and use correlation intervals that span multiple message bits to acquire the GNSS satellite signals.

17. The system of claim 11 wherein

the assistance information includes one or more of a list of GNSS satellites in view, associated Doppler offsets, ephemeris information, and

the remote receiver uses the assistance information to reduce the search to satellites in view and further reduce the search window based on the Doppler offsets.

18. The system of claim 11 wherein the remote receiver further includes

a real time clock for maintaining current time and date;

and

the one or more processors are further configured to determine time to within several microseconds of GNSS time based on the maintained current time and a timing property of the signals of opportunity, and preposition code searching based upon known times of code chip transmissions from GNSS satellites.

19. The system of claim 11 wherein

the assistance information includes current time and date, estimated city or area location information and an Almanac, and

the one or more processors determine satellites in view and associated estimated Doppler offsets using the assistance information and utilize the estimated offsets to reduce further reduce the search window.

20. The system of claim 16 wherein the one or more processors

phase lock an oscillator used in acquiring and tracking the GNSS signals to one of the signals of opportunity, and

narrow a band used to track the GNSS satellite signals.

21. The system of claim 11 wherein the network connection is wireless, wired or both.