Precise absolute time transfer from a satellite system

• US 8,035,558 B2
• Filed: 05/30/2008
• Issued: 10/11/2011
• Est. Priority Date: 05/30/2008
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Ferrell, Barton G., Cohen, Clark E., Gutt, Gregory M., Whelan, David A., Brumley, Robert W.
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US12/130,893
• Publication Number:
  US 20090315764A1
• Time in Patent Office: 1,229 Days
• Field of Search: 342/357.22, 342/357.39, 342/357.42, 342/357.64, 701/207, 701/213
• US Class Current: 342/357.64
• CPC Class Codes: G01S 19/05 providing aiding data
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/256 relating to timing, e.g. time of week, code phase, timing offset

Abstract

Systems and methods according to one or more embodiments are provided for obtaining a precise absolute time using a satellite system. The precise absolute time may be used, for example, as an aid for positioning systems including navigation in attenuated or jammed environments. A method of obtaining precise absolute time transfer from a satellite according to an embodiment comprises: receiving a precision time signal from a satellite, wherein the precision time signal comprises a periodic repeating code; determining a timing phase of the code; receiving additional aiding information; and using the timing phase and the additional aiding information to determine a precise absolute time.

Claims

1. A method of obtaining precise absolute time transfer from a satellite, the method comprising:

receiving a precision time signal from a satellite, wherein the precision time signal comprises a periodic repeating code;

determining a timing phase of the code;

receiving aiding information through a network, wherein the network is provided by ground based infrastructure; and

using the timing phase and the aiding information to determine a precise absolute time.

2. The method of claim 1, wherein the network is a cellular network, a WiFi network, or an Internet network.

3. The method of claim 1, wherein the code alternates between a coarse timing code and a pseudorandom code.

4. The method of claim 1, wherein the satellite is a first satellite, the method further comprising:

using the precise absolute time to align positioning correlators of a receiver unit to determine a positioning signal from a second satellite in an attenuated or jammed environment.

5. The method of claim 4, wherein the second satellite is a Global Positioning System (GPS) satellite.

6. The method of claim 1, wherein the satellite is a Low Earth Orbit (LEO) satellite.

7. The method of claim 6, wherein the LEO satellite is an Iridium satellite or a Globalstar satellite.

8. The method of claim 1, wherein the aiding information is orbit information associated with the satellite, an approximate time within about 5 seconds, an approximate range between the satellite and a receiver unit within about 3000 meters, or clock offset information associated with a clock of the satellite.

9. The method of claim 1, further comprising determining the aiding information from a Doppler profile of the satellite.

10. A receiver unit adapted for use in attenuated or jammed environments comprising:

an antenna adapted to receive a precision time signal from a satellite and receive aiding information through a network, wherein the network is provided by ground based infrastructure, wherein the precision time signal comprises a periodic repeating code;

a processor; and

a memory adapted to store a plurality of computer readable instructions which when executed by the processor are adapted to cause the receiver unit to;

determine a timing phase of the code, and

use the timing phase and the aiding information to determine a precise absolute time.

11. The receiver unit of claim 10, wherein the satellite is a first satellite, the receiver unit further comprising:

system correlators adapted to be aligned based on the precise absolute time to perform navigation based on a positioning signal received from a second satellite.

12. The receiver unit of claim 11, wherein the system correlators are implemented by the processor.

13. The receiver unit of claim 10, wherein the satellite is a Low Earth Orbit (LEO) satellite.

14. The receiver unit of claim 13, wherein the LEO satellite is an Iridium satellite or a Globalstar satellite.

15. The receiver unit of claim 10, wherein the network is a cellular network, a WiFi network, or an Internet network.

16. The receiver unit of claim 10, wherein the code alternates between a coarse timing code and a pseudorandom code.

17. The receiver unit of claim 10, wherein the receiver unit is a cellular telephone, a handheld navigation device, a vehicle-based navigation device, or an aircraft-based navigation device.

18. The receiver unit of claim 10, wherein the precision time signal further comprises data and wherein the determining the timing phase of the code further comprises:

receiving the data over a frequency band of the satellite;

downconverting and sampling the received data;

capturing and storing the sampled data in appropriate blocks;

performing a coarse acquisition search of the sampled data;

screening for peaks in the sampled data;

performing a fine acquisition search at a location of a screened peak determined from the coarse acquisition search so that a best peak is determined; and

determining the timing phase of the code based on an identified message that generated the best peak and relative time.

19. The receiver unit of claim 18, wherein the performing the coarse acquisition search of the sampled data further comprises:

selecting a portion of the sampled data for detailed processing;

estimating Doppler of the portion of the sampled data using a known orbit model and estimated time;

digitally demodulating the portion of the sampled data with sine and cosine functions based on a known frequency sub band;

decimating the portion of the sampled data;

applying a Fast Fourier Transform to the decimated portion of the sampled data so that a highest peak and associated frequency are determined; and

continuing to a next portion of the sampled data and repeating the detailed processing.