Disciplined time scale generator for primary reference clocks

• US 5,666,330 A
• Filed: 07/21/1994
• Issued: 09/09/1997
• Est. Priority Date: 07/21/1994
• Status: Expired due to Term

• Current Assignee: Microsemi Frequency And Time Corporation
• Original Assignee: Telecom Solutions Incorporated
• Inventors: Zampetti, George Philip
• Primary Examiner(s): Roskoski, Bernard
• Application Number:
  US08/278,423
• Time in Patent Office: 1,146 Days
• Field of Search: 368/47-57
• US Class Current: 368/47
• CPC Class Codes: G04G 7/02 by radio
• CPC Class Codes: H04J 3/0688 Change of the master or reference, e.g. take-over or failure of the master

Abstract

Methods and apparati are disclosed for providing disciplined clock signals at a plurality of nodes located throughout a network. In the preferred embodiments, a plurality of clocks are ensembled to provide ensemble time base information. A universal clock signal such as from a global positioning satellite (GPS) or Loran receiver is also provided and the ensembled time information is disciplined to the frequency or the phase of the universal clock signal to provide syntonization or synchronization throughout the network.

Claims

1. A method of attaining syntonisation between a local clock and a universal time source, wherein the universal time is transmitted via a signal over a medium that is subject to adding linear and non-linear noise effects to the signal, the method comprising:

providing a plurality of constituent time clocks, each time clock providing a clock signal at the output;

ensembling the outputs of the time clocks to provide ensembled time clock information, wherein the ensembled time clock information is more stable than any of the constituent time clocks;

receiving the universal time clock signal

repeatedly determining the difference in frequency between the universal disciplining clock signal and the ensembled time clock information; and

generating from a plurality of said frequency differences and at least one of the constituent time clocks and the ensembled time, a clock signal at the same frequency as the universal time clock signal.

2. The method of claim 1, wherein the method further comprises providing a receiver adapted to receive a global positioning satellite timing signal to provide the universal time clock signal.

3. The method of claim 1, wherein the method further comprises providing a receiver adapted to receive a Loran timing signal to provide the universal time clock signal.

4. The method of claim 1, wherein the method further comprises:

providing a time measuring device having two inputs to provide information representative of the phase difference between the two input signals

repetitively selecting different constituent clocks as a first input to the time measuring device and providing the information representative of the phase difference between the output clock signal and the selected one of the constituent clock signals; and

producing a data matrix based upon the information from the representative phase differences for use in ensembling the clock signals.

5. The method of claim 4, wherein the matrix comprises a pairwise matrix.

6. The method of claim 4, wherein the matrix comprises an incremental pairwise matrix.

7. A time scale generator having:

a plurality of local clocks, each local clock producing timing information, the timing information having a level of reliability and stability;

an ensembler responsive to the plurality of local clocks to produce time scale information, the time scale information having a level of reliability and stability greater than the levels of stability and reliability of the timing information of each of the local clocks;

a receiver adapted to receive from a communications channel that is subject to adding linear and non-linear noise to a universal disciplining signal having timing information therein;

a universal disciplining clock signal generator producing universal disciplining clock information having timing parameter information in response to the received signal; and

a means for disciplining the ensembled time base information to the timing parameter information of the universal disciplining clock information to provide a disciplined output signal.

8. The time scale generator of claim 7, wherein the universal time clock information is a universal time clock signal and the ensembled time information is an ensembled clock signal and the generator further comprises:

a time measuring device to provide information related to at least one of the frequency and the phase difference between the ensembled time clock signal and the universal disciplining clock signal;

a controllable oscillator responsive to the ensembled time clock signal and control information to produce a clock signal based upon the ensembled time clock signal and the control information; and

a controller responsive to the output of the time measuring device to produce the control information for the controllable oscillator such that the output of the oscillator is frequency disciplined.

9. The time scale generator of claim 8, wherein the controller averages the information from the time measuring device over a lengthy period of time.

10. The time scale generator of claim 7, wherein the generator includes a processor that performs the programmatic steps of:

producing pairwise data for each local clock and the universal disciplining clock signal;

producing data representative of the ensemble state based upon the pairwise data for each local clock;

determining the difference between the ensemble state and the universal time clock signal at various points in time to obtain an average difference; and

outputting a clock signal based upon the difference between the ensemble state and having the long-term frequency of the universal clock signal based upon the average difference.

11. The time scale generator of claim 10, wherein the pairwise data is incremental pairwise data.

12. A telecommunication network having a plurality of switching offices having a plurality of local clocks having a frequency with a stability and reliability, wherein the telecommunications network exists in an area that receives a signal over a medium that is subject to adding errors to the signal containing universal disciplining clock timing information having a frequency, wherein the improvement comprises at a plurality of at least some of the switching offices:

a means for ensembling the plurality of local clocks for that office to provide ensembled time base information having a frequency and the ensembled time base information having a reliability and stability greater than each of local clocks for the office;

a means for determining repeatedly the frequency difference between the ensembled time base information and the universal time base clock information; and

a means for providing a local time base signal for use by the local office having a frequency based upon the average frequency difference between the ensembled time and the universal time clock information, whereby the local time base signals at said each of the plurality of switching offices are in syntonisation with each other.

13. The telecommunication network of claim 12, wherein each of the local time base signals is a four kilohertz clock signal.

14. The telecommunications network of claim 12, wherein each of said plurality of switching offices has a receiver coupled to provide the universal time scale information to the determining means.

15. The telecommunications network of claim 12, wherein the means for determining at least a plurality of comprises a stop/start counter.

16. The telecommunications network of claim 12, wherein the means for determining at least some of the plurality of comprises a phase detector producing a signal dependent upon the frequency difference.

17. The telecommunications network of claim 12, wherein the signal containing the universal time clock information is a GPS signal and each of said plurality of has a GPS receiver providing the universal time clock information to the determining means.

18. The telecommunications network of claim 12, wherein a clock source from a first is also used by the means for ensembling to provide the ensembled time base information.

19. A method of providing in a network comprised of a plurality of nodes transmitting units of information between each other, wherein the network being located in an area where a signal including universal time clock information is receivable through a medium that is subject to adding errors to the universal time clock information, syntonisation between a plurality of the nodes, the method comprising:

generating local clock information at each of the plurality of nodes;

receiving the universal time clock information at each of the plurality of nodes;

determining at each of the plurality of nodes from time to time the frequency difference between the local clock information and the universal time clock information;

generating based upon a plurality of the determinations said syntonised clock signal at each of the plurality of nodes having the same frequency.

20. The method of claim 19, wherein the network comprises a telephone network.

21. The method of claim 19, wherein the network comprises a data local area network.

22. The method of claim 19, wherein a plurality of the nodes in the network comprises a telephone switching office.

23. The method of claim 19, wherein the local clock information comprises a plurality of local clocks at each node in the network.

24. The method of claim 23, wherein the method comprises:

determining at each of the plurality of nodes the frequency difference between at least some of the local clocks repeatedly;

producing based upon the frequency differences of the local clocks ensemble time information for each of the plurality of nodes;

generating repeatedly second frequency difference information between the ensemble time information for each of the plurality of nodes and the universal clock information;

generating based upon the second frequency difference information at each of the nodes a clock signal syntonised to a clock signal at each of the other plurality of nodes.

25. The method of claim 24, wherein the ensemble time information for at least some of the plurality of nodes is based in part upon a local clock located at another node.

26. A method for disciplining an ensembled group of clock signals to a universal time source signal provided over a channel having both linear and nonlinear noise effects, the method comprising:

using a time scale algorithm on information relating to the group of clocks and the universal time source signal to provide state estimates of the difference between an ensemble time and each of the group of clocks and to provide an ensemble time state with no weight being given to the universal time source signal in the ensemble time state;

disciplining the ensemble time state to the universal time source signal through a low pass filtering algorithm to provide a disciplined time state;

end

generating a clock signal based upon the disciplined time state.

27. An apparatus for disciplining a collection of clock sources to a universal time scale received over a noisy channel, the apparatus comprising:

a controllable oscillator providing as an output a clock signal disciplined to the universal time scale; and

a processor responsive to each of the clock sources and the universal time scale to provide an ensemble time scale giving the universal time scale zero weight and using the difference between the ensemble time scale and the universal time scale to control the oscillator.