# US 8,542,147 B2 · Precise absolute time transfer from a satellite system

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- Number: US 8,542,147 B2
- Document ID: US8542147B2
- Status: Granted
- Kind: B2
- Application number: 13/267,714
- Filed: 2011-10-06
- Published: 2012-08-30
- Granted: 2013-09-24
- Earliest claimed: 2008-05-30
- Assignees: The Boeing Company
- Applicants: David A. Whelan; Gregory M. Gutt
- Inventors: David A. Whelan; Gregory M. Gutt
- Web page: https://patentgrep.com/patent/US8542147B2

## CPC

- G01S 19/05: providing aiding data
- G01S 19/21: Interference related issues {; Issues related to cross-correlation, spoofing or other methods of denial of service}
- G01S 19/23: Testing, monitoring, correcting or calibrating of receiver elements
- G01S 19/256: {relating to timing, e.g. time of week, code phase, timing offset}
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

Various techniques are provided for obtaining a precise absolute time using a satellite system. In one example, a method of transferring precise absolute time from a satellite to a device includes receiving data from a messaging channel, wherein the data has a frame structure. The method also includes using the data to identify the satellite and a position of the satellite, correcting for signal time of flight using the satellite identity and the position, and using the data as a time reference to align a receiver clock to the frame structure. The method also includes, with the receiver clock aligned to the frame structure, receiving a precision time signal from the satellite, wherein the precision time signal comprises a periodic repeating code. The method also includes determining a timing phase of the code and using the timing phase to determine a precise absolute time.

## Claims

### Claim 1

A method of transferring precise absolute time from a satellite to a device, the method comprising:
receiving data from a messaging channel, wherein the data has a frame structure;
using the data to identify the satellite and a position of the satellite;
correcting for signal time of flight using the satellite identity and the position of the satellite;
using the data as a time reference to align a receiver clock to the frame structure;
with the receiver clock aligned to the frame structure, receiving a precision time signal from the satellite, wherein the precision time signal comprises a periodic repeating code;
determining a timing phase of the code; and
using the timing phase to determine a precise absolute time.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
receiving the data from the messaging channel in response to an acquisition channel being unavailable, wherein the messaging channel is distinct from the acquisition channel.

### Claim 3 (depends on 1)

The method of claim 1, wherein:
the messaging channel is one of a plurality of messaging channels carrying the data.

### Claim 4 (depends on 1)

The method of claim 1, wherein:
the messaging channel is one of a plurality of messaging channels carrying the data and for which a priori acquisition information is possessed by the receiver.

### Claim 5 (depends on 1)

The method of claim 1, wherein:
the messaging channel is one of a plurality of distinct messaging channels carrying the data from the same satellite.

### Claim 6 (depends on 1)

The method of claim 1, wherein:
the messaging channel is one of a plurality of messaging channels carrying the data;
at least one of the messaging channels carries data from a different satellite from the satellite; and
the satellite and the different satellite are in the same satellite constellation.

### Claim 7 (depends on 1)

The method of claim 1, wherein:
the messaging channel is one of a plurality of messaging channels carrying the data;
at least one of the messaging channels carries data from a different satellite from the satellite; and
the satellite and the different satellite are in different satellite constellations.

### Claim 8 (depends on 1)

The method of claim 1, wherein:
the frame structure is an L band frame structure; and
the data includes an L band frame count (LBFC).

### Claim 9 (depends on 1)

The method of claim 1, wherein the data includes at least one of X, Y, and Z coordinates for the position of the satellite or a satellite vehicle identification (SVID) of the satellite.

### Claim 10 (depends on 1)

The method of claim 1, wherein:
the messaging channel is one of a plurality of messaging channels carrying the data; and
the device is programmed with a specific acquisition class according to a priority levels-queuing methodology for receiving data on a back-up frequency of one or more of the plurality of messaging channels.

### Claim 11

A receiver unit adapted for use in attenuated or jammed environments, comprising:
an antenna adapted to receive a signal from a satellite acquisition channel or a messaging channel;
a processor;
a receiver clock; and
a memory for storing a plurality of machine readable instructions which when executed by the processor cause the receiver unit to:
receive data from the acquisition channel or the messaging channel, wherein the data has a frame structure,
use the data to determine an identity of the satellite and a position of the satellite,
correct for signal time of flight using the identity of the satellite and the position of the satellite,
use the data as a time reference to align the receiver clock to the frame structure,
with the receiver clock aligned to the frame structure, receive a precision time signal from the satellite, wherein the precision time signal comprises a periodic repeating code,
determine a timing phase of the code, and
use the timing phase to determine a precise absolute time.

### Claim 12 (depends on 11)

The receiver unit of claim 11, wherein the instructions when executed by the processor further cause the receiver unit to:
receive the data from the messaging channel in response to an acquisition channel being unavailable, wherein the messaging channel is distinct from the acquisition channel.

### Claim 13 (depends on 11)

The receiver unit of claim 11, wherein:
the messaging channel is one of a plurality of messaging channels carrying the data.

### Claim 14 (depends on 11)

The receiver unit of claim 11, wherein:
the messaging channel is one of a plurality of messaging channels carrying the data and for which a priori acquisition information is possessed by the receiver unit.

### Claim 15 (depends on 11)

The receiver unit of claim 11, wherein:
the messaging channel is one of a plurality of distinct messaging channels carrying the data from the same satellite.

### Claim 16 (depends on 11)

The receiver unit of claim 11, wherein:
the messaging channel is one of a plurality of messaging channels carrying the data;
at least one of the messaging channels carries data from a different satellite from the satellite; and
the satellite and the different satellite are in the same satellite constellation.

### Claim 17 (depends on 11)

The receiver unit of claim 11, wherein:
the messaging channel is one of a plurality of messaging channels carrying the data;
at least one of the messaging channels carries data from a different satellite from the satellite; and
the satellite and the different satellite are in different satellite constellations.

### Claim 18 (depends on 11)

The receiver unit of claim 11, wherein:
the frame structure is an L band frame structure; and
the data includes an L band frame count (LBFC).

### Claim 19 (depends on 11)

The receiver unit of claim 11, wherein the data includes a satellite vehicle identification (SVID) of the satellite.