Low power radio controlled clock incorporating independent timing corrections

• US 8,533,516 B2
• Filed: 09/22/2011
• Issued: 09/10/2013
• Est. Priority Date: 09/22/2010
• Status: Expired due to Fees

• Current Assignee: Grindstone Capital LLC
• Original Assignee: XW LLC
• Inventors: Eliezer, Oren E., Awasthi, Aditya
• Primary Examiner(s): KNOLL, CLIFFORD H
• Application Number:
  US13/240,615
• Publication Number:
  US 20120082008A1
• Time in Patent Office: 719 Days
• Field of Search: 713400-401, 375/238, 368 46- 47
• US Class Current: 713/400
• CPC Class Codes: G04R 20/12 Decoding time data; Circuits therefor
• CPC Class Codes: G04R 40/06 by computing the time value implied by the radio signal
• CPC Class Codes: H04W 56/0035 detecting errors in frequency or phase
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A timekeeping device that tracks the time provided by a digital broadcast and the protocol of that broadcast, defined by its data frame structure and modulation scheme, are adapted to allow for superior performance of the timekeeping devices in terms of range of operation, immunity to interference, ability to operate with lower cost antennas due to enhanced link robustness, and reduced energy consumption. The timekeeping device operates with infrequent receptions of the broadcast by relying on independent self-compensation. This alleviates the need for frequent receptions to ensure timing accuracy while reducing energy consumption. The mean and variability of successive measurements of timing drift are evaluated and an estimated upper bound for the drift-estimation error is set. Based on this bound, the device employs a reception strategy that relies on less frequent receptions, corresponding to the error in estimating the drift rather than to the magnitude of the drift itself.

Claims

1. A method of timing correction and drift compensation (compensation for drift) for use in a timekeeping device, said method comprising:

recording and tracking over time a plurality of timing drift adjustments of said timekeeping device that are made based on a known synchronization sequence received as part of a broadcast frame assumed to represent accurate timing;

calculating a timing drift rate estimate corresponding to a frequency error in accordance with the plurality of timing drift adjustments performed and the instances at which they were performed; and

applying timing adjustments to said timekeeping device in accordance with said calculated timing drift rate estimate.

2. The method according to claim 1, wherein said plurality of timing adjustments, made in conjunction with the reception of said known synchronization sequence in a received signal, are performed at instances substantially equally distanced from one another, representing a substantially constant rate of reception.

3. The method according to claim 1, wherein said plurality of timing drift adjustments, made in conjunction with the reception of a known synchronization sequence in a received signal, are performed at instances substantially unequally distanced from one another so as to provide a variable rate of reception based timing drift adjustments.

4. The method according to claim 1, wherein an initial timing rate drift estimate is calculated initially at the time of manufacture.

5. The method according to claim 1, wherein said timing drift estimate is calculated as a function of one or more factors selected from the group consisting of mean, variance, maximum and time derivative trend of the plurality of timing drift rate estimates.

6. The method according to claim 1, wherein said calculated timing drift rate estimate is applied in self-compensation in accordance with a schedule determined so as to yield a reduction in energy consumption.

7. The method according to claim 1, further comprising determining a schedule for reception based on said calculated timing drift rate estimate.

8. The method according to claim 7, further comprising considering one or more factors in determining the schedule for reception.

9. The method according to claim 7, wherein said schedule for reception is based on instances selected to satisfy conditions of maximal allowable drift.

10. The method according to claim 7, further comprising measuring and correcting at each reception instance the actual timing drift established for that instance and revising said timing drift rate estimate based thereon.

11. The method according to claim 10, further comprising reducing the period for reception if the actual timing drift measured exceeds an allowable range.

12. The method according to claim 10, further comprising increasing the period for reception if the actual timing drift measured is below an allowable range, thereby providing a further reduction in energy consumption.

13. The method according to claim 1, wherein timing drift adjustments to said timekeeping device are made using said calculated timing drift rate estimate for a time period determined based on the error in estimating its own timing drift rather than on the magnitude of the drift rate itself, wherein said time period permits less frequent reception than would otherwise be required.

14. The method according to claim 1, further comprising providing an indication when the measured timing drift exceeds a threshold.

15. A method of timing correction for use in a timekeeping device, said method comprising:

determining an estimated timing drift rate experienced by said timekeeping device by recording and tracking over time a plurality of timing adjustments performed by said timekeeping device based on a synchronization sequence received as part of a broadcast frame;

performing independent self-compensation of timing drift using said estimated timing drift rate in accordance with a drift compensation schedule; and

performing receptions in accordance with a reception schedule whereby reception instances occur infrequently at a rate based on an estimate of the error in calculating said estimated timing drift rate and not on the magnitude of the timing drift rate itself.

16. The method according to claim 15, further comprising measuring and correcting at each reception instance the actual instantaneous timing drift and revising said timing drift estimate based thereon.

17. The method according to claim 15, further comprising reducing the period for reception in said reception schedule if the actual timing drift measured exceeds an allowable range.

18. The method according to claim 15, further comprising increasing the period for reception in said reception schedule if the actual timing drift measured is below an allowable range, thereby providing a further reduction in energy consumption.

19. A timekeeping device, comprising:

a timekeeper circuit operative to keep track of time based on pulses received from a source that may experience a frequency error with respect to its nominal frequency;

a receiver operative to receive a phase modulated synchronization sequence that is part of a broadcast frame spanning multiple seconds in duration; and

a processor operative to perform timing adjustments based on said phase modulated synchronization sequence to reduce the required rate of reception instances thereby reducing energy consumption of said timekeeping device.

20. The device according to claim 19, wherein said timekeeping device comprises a watch.

21. The device according to claim 19, wherein said timekeeping device comprises an alarm clock.

22. The device according to claim 19, wherein said timekeeping device comprises a wall mountable clock.

23. The device according to claim 19, wherein said timekeeping device comprises a utility meter.

24. The device according to claim 19, wherein said processor is operative to acquire an initial timing based on the reception of said phase-modulated data frame where coding is employed to allow for the detection and correction of errors.

25. The method according to claim 19, further comprising measuring and correcting at each reception instance the actual timing drift accumulated up to that instance and revising an estimated timing drift rate based thereon.

26. The method according to claim 19, further comprising reducing the period for reception if the actual timing drift measured exceeds an allowable range.

27. The method according to claim 19, further comprising increasing the period for reception if the actual timing drift measured is below an allowable range, thereby providing a further reduction in energy consumption.

30. The timekeeping device according to claim 20, wherein the retrieval of information from the broadcast is based on demodulating carrier phase for portions of the transmitted bits.

28. A timekeeping device, comprising:

a timekeeper circuit operative to keep track of time based on pulses received from a clock source;

a receiver operative to receive a phase modulated synchronization sequence that is part of a broadcast frame spanning multiple seconds in duration; and

a processor operative to;

perform self-compensation for timing drifts based on one or more measurements of timing errors against timing information obtained from said phase modulated synchronization sequence; and

perform relatively infrequent reception operations thereby providing reduced energy consumption and increased robustness when reception success is not guaranteed.

29. The timekeeping device according to claim 28, wherein accurate timing information is initially obtained through an external resource.

31. The timekeeping device according to claim 28, further comprising a user interface operative to present a user with an estimated bound for error in displayed time.

32. The timekeeping device according to claim 28, further comprising a user interface operative to receive input from a user indicating an upper bound for allowable error in displayed time.

33. A method for performing self-compensation of a timekeeping device, said method comprising:

determining an estimate of the timing drift experienced by said timekeeping device during a period of time, corresponding to a drift rate or frequency error; and

periodically compensating for the amount of drift experienced during said period by adjusting the time maintained by said timekeeping device by an amount in accordance with said timing drift estimate.

34. The method according to claim 33, wherein the timekeeping device compensates for the timing drift estimated to have been experienced during a certain period of time by appropriately adding or subtracting a corresponding portion of said timing drift estimate at fractional points of said period of time thereby smoothening the correction and avoiding it from being noticed by a human user.

35. The method according to claim 33, wherein the period for periodic receptions, performed for the purpose of establishing and compensating for the timing drift of the timekeeping device, is determined based on the magnitude of the timing drift ε

, estimated based on one or more measurements that rely on the reception of an accurate broadcast signal.

36. The method according to claim 33, wherein the periodicity at which receptions are performed is established based on the estimated error in timing drift measurement and estimation, and on the mean and variability amongst multiple measurements.

37. The method according to claim 33, wherein the periodicity at which receptions are performed is determined based on an upper bound (worst case) error in drift measurements established based on worst case drift measured with additional margin.

38. The method according to claim 33, wherein the periodicity at which receptions are performed take into account one or more factors.

39. The method according to claim 33, further comprising tracking successful reception times during the day and maintaining a sorted confidence list containing the best time to receive the broadcast.

40. The method according to claim 33, further comprising tracking both the absolute value of the time drift and its trend thus allowing for extrapolation of the timing drift trajectory.

41. The method according to claim 33, wherein enhanced reliability in configuring the right time in said timekeeping device is achieved through the use of a time-computing procedure that considers information extracted from a received broadcast frame as well as the time currently maintained in the timekeeping device.

42. The method according to claim 33, further comprising an averaging operation wherein a noisy result of the correlation operation with the received synchronization sequence, based on which the timing extraction may be inaccurate, is weighted against the locally maintained time in the timekeeping device such that the timing adjustment considers them both instead of being determined based only on the received signal.