Clock Offset and Skew Estimation Using Kalman Filter

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Solution Overview

Problem

Existing clock synchronization methods, particularly those using IEEE 1588 Precision Time Protocol (PTP), assume clocks differ only by an offset, neglecting the inherent skew, which leads to inaccurate synchronization, especially in critical applications requiring stringent accuracy.

Innovation Solution

A method employing a Kalman filter for recursive estimation of both clock offset and skew using timestamps from Sync and Delay_Req messages, accounting for measurement noise and process noise to accurately synchronize local clocks with a remote master clock.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If only clock offset estimation is performed using IEEE 1588 PTP, then the synchronization method is simple, but the synchronization accuracy deteriorates because clock skew is neglected

Engineering Contradiction:

Improvesynchronization method complexityVSAvoidsynchronization accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent extends the traditional offset-only model to a more comprehensive model that includes both offset and skew parameters. By changing the parameter set from single offset to offset-plus-skew, the system achieves more accurate synchronization while maintaining reasonable complexity through structured estimation procedures.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent adds another dimension to the synchronization problem by incorporating skew estimation alongside offset estimation. This dimensional expansion allows the system to account for frequency differences between clocks, transforming a one-dimensional offset correction into a two-dimensional offset-and-skew correction framework.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If both offset and skew are estimated simultaneously using advanced algorithms, then synchronization accuracy improves, but computational complexity increases

Engineering Contradiction:

Improvesynchronization accuracyVSAvoidcomputational complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the estimation process into distinct phases: timestamp collection, delay calculation, and parameter estimation. By dividing the complex simultaneous estimation into manageable steps, the system reduces computational burden while maintaining accuracy through structured processing of offset and skew parameters separately but cooperatively.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent performs preliminary actions by collecting timestamps and calculating delays before performing the actual offset and skew estimation. This preparation step organizes the data in advance, making the subsequent estimation process more efficient and reducing real-time computational complexity while preserving synchronization accuracy.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS8959381B2Method and system for clock offset and skew estimation

Publication Date: 2015.02.17 BRITISH TELECOM PLC

AI summary

This invention relates to methods and devices for clock offset and skew estimation. The invention has particular application in the alignment of slave clocks to a master clock. In embodiments of the invention, the slave clock employs an independent free running clock and a recursive estimation technique to estimate the clock offset and clock skew between the slave and master clocks. The slave can then use the offset and skew to correct the free running clock to reflect an accurate image of the master clock.