Adaptive holdover timing error estimation and correction

1. A system for adaptive holdover time error estimation, comprising:

a local time source configured to generate a local time signal;

an external time source interface configured to receive an external time signal;

a temperature determination subsystem configured to determine a plurality of temperature measurements in proximity to the local time source at a corresponding plurality of times;

a temperature-dependent model subsystem configured to develop a temperature-dependent model based on the plurality of temperature measurements and comparison of the local time signal to the external time signal at a corresponding plurality of times;

a time-dependent model subsystem configured to develop a time-dependent model based on a plurality of comparisons of the local time signal to the external time signal at a corresponding plurality of times;

a holdover subsystem configured to:

detect a loss of reception of the external time signal during a holdover period;

estimate a maximum time-dependent error based on the time-dependent model and a duration of the holdover period;

estimate a maximum temperature-dependent error based on the temperature-dependent model;

determine an estimated total maximum error based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error; and

a communication system configured to transmit the local time signal and the estimated total maximum error to at least one receiving device.

2. A method of adaptive holdover duration time error estimation, the method comprising:

generating a local time signal using a local time source;

receiving an external time signal;

losing reception of the external time signal during a holdover period;

estimating a maximum time-dependent error based on a duration of the holdover period;

estimating a maximum temperature-dependent error based on a current temperature;

determining an estimated total maximum error based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error; and

transmitting the local time signal and the estimated total maximum error to a receiving device.

3. The method of claim 2 , further comprising:

generating a temperature-dependent model of the local time source based on a plurality of temperature measurements and comparison of the local time signal to the external time signal at a corresponding plurality of times; and

wherein the temperature-dependent model is used in estimating the maximum temperature-dependent error.

4. The method of claim 3 , further comprising:

determining an average of the plurality of temperature measurements; and

using the average of the plurality of temperature measurements to estimate the maximum temperature-dependent error.

5. The method of claim 2 , further comprising:

generating a time-dependent model of the local time source based on a comparison of the local time signal to the external time signal over a temporal period; and

wherein the time-dependent model is used in determining the maximum time-dependent error.

6. The system of claim 2 , wherein the local time source comprises one of a voltage-controlled temperature compensated crystal oscillator, a phase locked loop oscillator, a time locked loop oscillator, a rubidium oscillator, a cesium oscillator, a microelectromechanical oscillator, an oven controlled crystal oscillator, and temperature compensated crystal oscillator.

7. The method of claim 2 , wherein the external time signal comprises at least one of a Global Navigation Satellite System and a National Institute of Science and Technology radio broadcast.

8. The method of claim 2 , wherein transmitting the local time signal and the estimated total maximum error to the receiving device comprises transmitting the local time signal according to a protocol chosen from one of the group consisting of an Inter-Range Instrumentation Group protocol, an IEEE 1588 protocol, a Network Time Protocol, a Simple Network Time Protocol, and a synchronous transport protocol.

9. The method of claim 2 , wherein the estimated total maximum error is transmitted in a clock accuracy enumeration field.

10. The method of claim 2 , further comprising:

the receiving device receiving the local time signal and the estimated total maximum error;

determining that the estimated total maximum error exceeds an accuracy requirement; and

disregarding the local time signal.

11. The method of claim 2 , further comprising:

determining a temperature-dependent signal drift rate of the local time signal relative to the external time signal; and

determining a time-dependent signal drift rate of the local time signal relative to the external time signal;

wherein estimating the maximum time-dependent error is further based on the temperature-dependent signal drift rate and estimating the maximum temperature-dependent error is further based on the time-dependent signal drift rate.

12. The method of claim 2 , further comprising:

determining that the current temperature falls outside of a bounded range; and

applying an adjustment to the maximum temperature-dependent error.

13. The method of claim 2 , further comprising correcting the local time signal based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error.

14. A system configured for adaptive holdover time error estimation, comprising:

a local time source configured to generate a local time signal;

an external time source interface configured to receive an external time signal;

a holdover subsystem configured to:

detect a loss of reception of the external time signal during a holdover period;

estimate a maximum time-dependent error based on a duration of the holdover period;

estimate a maximum temperature-dependent error based on a current temperature;

determine an estimated total maximum error based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error;

a communication system configured to transmit the local time signal and the estimated total maximum error to at least one receiving device.

15. The system of claim 14 , wherein the external time source interface comprises a Global Navigation Satellite System input; and

wherein the external time signal is received via the Global Navigation Satellite System interface.

16. The system of claim 14 , wherein the external time source interface comprises an Inter-Range Instrumentation Group (IRIG) input; and

wherein the external time signal is received via the IRIG input.

17. The system of claim 14 , wherein the communication system comprises:

a network communication port configured to distribute the local time signal and the estimated total maximum error to the at least one receiving device.

18. The system of claim 14 , wherein the local time signal and the estimated total maximum error are distributed to the at least one receiving device using a protocol selected from the group consisting of an Inter-Range Instrumentation Group protocol, an IEEE 1588 protocol, a Network Time Protocol, a Simple Network Time Protocol, and a synchronous transport protocol.

19. The system of claim 14 , wherein the local time source comprises one of a voltage-controlled temperature compensated crystal oscillator, a phase locked loop oscillator, a time locked loop oscillator, a rubidium oscillator, a cesium oscillator, a microelectromechanical oscillator, an oven controlled crystal oscillator, and temperature compensated crystal oscillator.

20. The system of claim 14 , wherein the holdover subsystem is further configured to determine whether the current temperature falls outside of a bounded range and to apply an adjustment to the maximum temperature-dependent error when the current temperature falls outside of the bounded range.

21. The system of claim 14 , wherein the time source subsystem is further configured to correct the local time signal based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error.

22. The system of claim 14 , further comprising:

a time source subsystem configured to compare the local time signal and the external time signal and determine:

a temperature-dependent signal drift rate of the local time signal relative to the external time signal; a time-dependent signal drift rate of the local time signal relative to the external time signal; and

wherein the holdover subsystem is further configured to estimate the maximum time-dependent error is further based on the temperature-dependent signal drift rate and estimating the maximum temperature-dependent error is further based on the time-dependent signal drift rate.

23. The system of claim 22 , further comprising:

a temperature determination subsystem configured to determine a plurality of temperature measurements in proximity to the local time source at a corresponding plurality of times;

wherein the time source subsystem is configured to utilize the plurality of temperature measurements to determine the temperature-dependent signal drift rate.

24. The system of claim 22 , further comprising:

a temperature-dependent model subsystem configured to develop a temperature-dependent model based on a plurality of temperature measurements and comparison of the local time signal to the external time signal at a corresponding plurality of times; and

wherein the time source subsystem uses the temperature-dependent model to determine the maximum temperature-dependent error.

25. The system of claim 22 , further comprising:

a time-dependent model subsystem configured to develop a time-dependent model based on a plurality of comparisons of the local time signal to the external time signal at a corresponding plurality of times; and

wherein the time source subsystem uses the time-dependent model to determine the maximum time-dependent error.