Covert timing synchronization

• US 10,405,287 B1
• Filed: 05/17/2017
• Issued: 09/03/2019
• Est. Priority Date: 07/27/2016
• Status: Active Grant

• Current Assignee: Robotic Research OPCO LLC
• Original Assignee: Robotic Research LLC
• Inventors: Lacaze, Alberto Daniel, Murphy, Karl
• Primary Examiner(s): Cho, Un C
• Assistant Examiner(s): Rahman, Shah M
• Application Number:
  US15/597,831
• Time in Patent Office: 839 Days
• CPC Class Codes: H04L 7/0016 correction of synchronization errors
• CPC Class Codes: H04W 56/001 Synchronization between nodes
• CPC Class Codes: H04W 56/003 Arrangements to increase tolerance to errors in transmission or reception timing
• CPC Class Codes: H04W 56/004 compensating for timing error of reception due to propagation delay
• CPC Class Codes: H04W 56/0065 using measurement of signal travel time

Abstract

A signal is emitted by an unrelated, non-cooperating party. The SA scans this spectrum, and selects and filters to a portion of the signal emitted. The SA, using its internal clock, time tags a sequence of peaks of the time domain of the filtered signal. The SA sends (over the internet or other method) the time tagged peaks, frequency and location of the emission to the IN. The IN receives the message from the SA. It compares the peaks with its own data, collected using its local antenna at the specified frequency. The IN uses its location, and the location encoded in the message, to compute the different time of arrival of the signal, and uses the locally found peaks at that frequency to determine a “phase shift.” The phase shift is used to calculate the local clock skew. The SA repeats step 2, selecting a different frequency.

Claims

1. A system designed to synchronize remote clocks composed of:

a. a synchronization authority (SA), permanent or mobile, that has access to a clock, to be considered the master clock;

SA can measure Radio Frequency (RF) emissions;

the SA can get a signal in the RF emissions;

b. an installation (IN), permanent or mobile, that has interest in having its clock synchronized with the SA;

the IN has a clock;

the IN can also measure RF emissions in the same frequencies as the SA;

the IN can get a signal in the RF emissions;

c. a cooperative or uncooperative source of RF emissions that is within range of both SA and IN;

d. a method for sending information packets between the SA and the IN that encode time of the signals in the RF emissions at the SA;

e. a method for comparing signals information received at the IN from the SA with signals in the RF emissions received at the IN locally, a delta in the comparing shows a time skew;

f. the ability of the IN to store either raw signal in RF emissions received and time tagged locally, or the information of time tagged signals from SA;

g. a known location of the source of RF emissions that is sent to, or known by, both the SA and the IN;

h. the known location is used to compute the difference time of flight of signals in the RF emissions, from the source to the SA and the source to the IN, to further increase the synchronization accuracy; and

i. the time of flight from the source to the SA can be subtracted by the SA from the signal time tags, so as to further conceal the location of the SA.

2. The system of claim 1, wherein the method of information exchange between the SA and the IN is converted though cryptology or other means.

3. The system of claim 1, wherein

the IN solves the integer ambiguity problem by collecting enough measurements, provided by the SA to satisfactory filter.

4. The system of claim 1, wherein

in step f, all information is recorded;

or

only information of a particular frequency, known by both SA and IN, spectrum is recorded;

or

only a particular part of the spectrum at a particular time range, or ranges, are recorded.

5. The system of ea claim 1, further comprising

a method for intelligently selecting the frequency spectrum of the emitter by selecting only frequencies above a certain threshold;

only from known emitters;

only from emitters that have been authenticated;

only from emitters for which the location is known;

only for emitters that are known not to have multipath problems;

only for emitters that are from friendly/non-friendly forces;

only for emitters that are known to reach certain set of INs;

only for emitters that are in a particular geolocation; and

only for emitters that emit a particular waveform (FM, AM, etc.), or a combination of them.

6. The system of claim 1, further comprising

randomly or semi-randomly selecting the frequency being used at the SA;

and

sending this frequency limits to the INs.

7. The system of claim 1, further comprising

having multiple SAs and INs.

8. The system of claim 1, further comprising

having a co-located SA-IN that acts as a “

repeater”

to extend the zone of synchronization.

9. The system of claim 8, further comprising

a double check, where each SA-IN checks other SA-INs to detect spoofing.

10. The system of claim 1, further comprising

eliminating synchronizations that do not fit within the error profile of the INs clock as outliers, multi-return signals, and possibly spoofers.

11. The system of claim 1, wherein

the position of the SA and the emitter is known by the INs.

12. The system of claim 1, wherein

signal features used for a correlation are peaks, phases shifts, and quadrature shifts.

13. The system of claim 1, wherein

the SA looks for sequences of emissions that are above a certain entropy or certain level of uniqueness.

14. The system of claim 1, wherein

the information, for which bandwidth and time will be used for correlation, is either known by both SA and IN, or is transmitted, or shared a priori, to minimize storage needs at the IN.

15. A system designed to synchronize remote clocks composed of:

a. a synchronization authority (SA), permanent or mobile, that has access to a clock, to be considered the master clock;

SA can measure Radio Frequency (RF) emissions;

the SA can find areas in the spectrum that may provide get signal strength degraded below a level to be recognized;

b. an installation (IN), permanent or mobile, that has interest in having its clock synchronized with the SA;

the IN has a clock;

the IN can also measure RF emissions in the same frequencies as the SA;

the IN can correlate signals in the RF emissions;

c. a cooperative or uncooperative source of RF emissions that is within range of both SA and IN;

d. a method for sending information packets between the SA and the IN that encode time and signal at the SA;

e. a method for correlating signals information received at the IN from the SA with the signal sensed locally;

a delta in the correlating shows a time skew;

f. the ability of the IN to store either raw signal in RF emissions received and time tagged locally, or the information of time tagged signals from SA;

g. a known location of the source of RF emissions that is sent to, or known by, both the SA and the IN;

h. the known location is used to compute the difference time of flight of signals in the RF emissions from the source, to the SA and to the IN, to further increase the synchronization accuracy; and

i. the time of flight from the source to the SA can be subtracted by the SA from the signal time tags, so as to further conceal the location of the SA.

16. The system of claim 15, wherein

the IN is installed on a vehicle that uses its dead reckoning capabilities to find its location.

17. The system of claim 15, wherein

a vehicle determines its position by using multiple packets received from multiple SAs;

and

the system can solve both for time and position given that enough SAs are present and within RF range.