Adaptive holdover timing error estimation and correction

Patent metadata

Field	Value
Publication number	US-9425652-B2
Application number	US-201414305608-A
Country	US
Kind code	B2
Filing date	Jun 16, 2014
Priority date	Jun 16, 2014
Publication date	Aug 23, 2016
Grant date	Aug 23, 2016

Abstract

Disclosed herein are a variety of various systems and method for adaptive holdover time error estimation. In one embodiment a system may include a local time source configured to generate a local time signal and an external time source interface configured to receive an external time signal. A time source subsystem may be configured to compare the local time signal and the external time signal and to determine a temperature-dependent signal drift rate of the local time signal relative to the external time signal. The time source subsystem may be a time-dependent signal drift rate of the local time signal relative to the external time signal. A holdover subsystem may detect a loss of reception of the external time signal during a holdover period and may estimate a total maximum error based on an estimated maximum time-dependent error and an estimated maximum temperature-dependent error.

First claim

What is claimed:

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.

Assignees

• Schweitzer Engineering Lab Inc

Inventors

• Rippon Daniel B
• Achanta Shankar V

Classifications

• H03L1/02

  against variations of temperature only · CPC title

• H04J3/0688

  Change of the master or reference, e.g. take-over or failure of the master · CPC title

• H04J3/0667

  Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays (arrangements for monitoring round trip delays in packet switching networks H04L43/0864) · CPC title

• H02J13/10

  characterised by displaying of information or by user interaction, e.g. supervisory control and data acquisition [SCADA] systems · CPC title

• H02J13/1337

  involving the use of Internet protocols · CPC title