Accurate timing distribution by high-frequency radio

Patent metadata

Field	Value
Publication number	US-10148345-B2
Application number	US-201414341093-A
Country	US
Kind code	B2
Filing date	Jul 25, 2014
Priority date	Jul 26, 2013
Publication date	Dec 4, 2018
Grant date	Dec 4, 2018

Abstract

A method of obtaining an absolute time reference for a high-frequency (HF) sounding signal includes transmitting a reference signal at a first location and transmitting a sounding signal in close proximity to the transmitting of the reference signal at the first location. The method additionally includes receiving the reference signal at a second location and receiving the sounding signal at the second location. The method further includes determining a relative delay at the second location of the sounding signal in relation to the reference signal. The method also includes determining a propagation mode based upon the relative delay. The method additionally includes determining an absolute time reference based upon the propagation mode being observed. Additional methods and associated systems for implementing the methods are also provided.

First claim

What is claimed is:

1. A receiver for simultaneously receiving one or more input signals of a plurality of frequencies, the receiver comprising:
an antenna having an antenna port;
an input conditioning circuit having an input coupled to the antenna port;
a comb filter having an input coupled to an output of the input conditioning circuit;
a decimator including a low-pass filter, the decimator having an input coupled to an output of the comb filter;
a digital signal processor configured to:
receive a decimated signal from an output of the decimator and in response thereto generate an extracted sounder signal;
extract selected time and frequency information from the decimated signal to produce an extracted time and frequency signal; and determine a propagation model of the input signals based upon the extracted sounder signal, and a time offset based upon the propagation model;

a local time reference circuit to generate a local time reference value; and a correction circuit configured to receive the time offset, the extracted time and frequency signal and the local time reference value at respective inputs, and in response thereto correct the local time reference value.

2. The receiver of claim 1 , wherein the plurality of frequencies comprise one or more WWV frequencies.

3. The receiver of claim 1 , wherein the input signals include narrow-band sounding signals.

4. The receiver of claim 1 , wherein the input conditioning circuit is coupled to a swept narrow-band receiver for processing swept sounder signals.

5. The receiver of claim 4 , wherein the swept narrow-band receiver is implemented in analog signal processing.

6. The receiver of claim 4 , wherein the swept narrow-band receiver is implemented digitally in a software defined radio.

7. The receiver of claim 4 , wherein the swept narrow-band receiver is implemented with a combination of analog and digital processing elements.

8. The receiver of claim 1 , wherein the input conditioning circuit is configured to receive the input signals from the antenna port, and configured to filter timing signals of the input signals from other signals of the input signals.

9. The receiver of claim 8 , wherein the input conditioning circuit is further configured to amplify the timing signals sufficiently for demodulation and decoding thereof.

10. The receiver of claim 9 , wherein the comb filter is configured to receive a filtered and amplified signal from the input conditioning circuit at the comb filter input, and in response thereto generate a combed signal with a magnitude response having a comb-like shape of substantially uniform weighting at the comb filter output.

11. The receiver of claim 10 , wherein the decimator is configured to receive the combed signal from the comb filter at the decimator input, and in response thereto generate the decimated signal, wherein the combed signal has a first sampling rate and the decimated signal has a second sampling rate that is substantially less than the first sampling rate.

12. The receiver of claim 1 , wherein the input signals include: sounding signals, and time and frequency reference signals, and wherein the extracted sounder signal is based upon sounding signal portions of the decimated signal.

13. The receiver of claim 12 , wherein the time offset corresponds to an offset between the sounding signals and the time and frequency signals.

14. The receiver of claim 1 , wherein the correction circuit is further configured to generate an absolute time reference at an output of the correction circuit in response to correcting the local time reference value.

15. The receiver of claim 1 , wherein the antenna is a loop antenna, a dipole antenna, or a multi-resonant ferrite antenna.

16. The receiver of claim 1 , wherein the antenna is a polarimetric antenna.

17. A method, comprising:
simultaneously receiving one or more input signals of a plurality of frequencies at an antenna of a receiver;
filtering timing signals of the input signals from other signals of the input signals, and amplifying the timing signals, using an input conditioning circuit of the receiver to generate a filtered and amplified signal;
filtering the filtered and amplified signal with a comb filter of the receiver to produce a combed signal;
generating a decimated signal with a decimator of the receiver in response to the combed signal, the decimator including a low-pass filter;
generating an extracted sounder signal using a digital signal processor of the receiver in response to the decimated signal, wherein the extracted sounder signal is based upon sounding signal portions of the decimated signal;
extracting selected time and frequency information using the digital signal processor from the decimated signal to produce an extracted time and frequency signal;
determining a propagation model of the input signals using the digital signal processor based upon the extracted sounder signal;
determining a time offset of the input signals using the digital signal processor based upon the propagation model;
generating a local time reference value with a local time reference circuit of the receiver;
receiving the time offset, the extracted time and frequency signal and the local time reference value at respective inputs of a correction circuit of the receiver; and
correcting the local time reference value with the correction circuit based upon the time offset and the extracted time and frequency signal.

18. The method of claim 17 , further comprising:
generating an absolute time reference at an output of the correction circuit in response to correcting the local time reference value.

19. The method of claim 17 , wherein filtering the filtered and amplified signal with a comb filter comprises: filtering the filtered and amplified signal with a comb filter of the receiver to produce a combed signal with a magnitude response having a comb-like shape of substantially uniform weighting.

20. The method of claim 17 , wherein generating a decimated signal further comprises: generating the decimated signal such that the combed signal has a first sampling rate and the decimated signal has a second sampling rate that is substantially less than the first sampling rate.

Assignees

• Massachusetts Inst Technology

Inventors

• Robey Frank C

Classifications

• G01S11/02

  using radio waves (G01S19/00 takes precedence) · CPC title

• H04B7/22 Primary

  Scatter propagation systems {, e.g. ionospheric, tropospheric or meteor scatter} · CPC title

• G01S13/0218

  Very long range radars, e.g. surface wave radar, over-the-horizon or ionospheric propagation systems (for meteorological use G01S13/95) · CPC title