Slave Clock Synchronization Using Kalman Filter Drift Estimation
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Solution Overview
Problem
Existing clock synchronization methods fail to accurately account for drift and skew between slave and master clocks, leading to synchronization issues due to oscillator aging and environmental factors, especially in applications where high-quality oscillators are not feasible.
Innovation Solution
A method and system that estimate the offset, skew, and drift of a slave clock relative to a master clock by exchanging timing messages and using Kalman filtering to record and analyze the times of message sending and receiving, allowing for continuous synchronization and holdover mechanisms when the reference source is unavailable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-quality ovenized quartz crystal oscillators are used to reduce aging and drift, then clock accuracy is improved, but cost increases significantly
Solution Approach 1:
The patent uses inexpensive quartz oscillators instead of expensive high-quality oscillators, accepting that they will drift and age faster. The system compensates for this by frequently synchronizing with the reference clock, effectively treating the oscillator as a short-lived component that is continuously corrected rather than relying on its inherent long-term stability.
Solution Approach 2:
The patent implements a feedback mechanism where the slave clock continuously monitors its drift relative to the master clock through timestamped messages. The system calculates offset, skew, and drift parameters and uses this feedback to adjust timing, compensating for the limitations of inexpensive oscillators without requiring expensive hardware.
2Device complexity
If quartz oscillators are used instead of cesium or rubidium-based oscillators to reduce cost, then device complexity is reduced, but synchronization frequency must increase
Solution Approach 1:
The patent implements dynamic synchronization where the system adapts its synchronization behavior based on observed drift rates. Rather than using fixed high-frequency synchronization, the system calculates actual drift parameters and adjusts accordingly, allowing less frequent synchronization when drift is slow while maintaining accuracy when drift increases.
Solution Approach 2:
The patent changes the approach from hardware-based accuracy (using stable oscillators) to parameter-based compensation (measuring and correcting offset, skew, and drift). By introducing drift as a measurable parameter and compensating for it through calculation rather than hardware stability, the system can use inexpensive oscillators without requiring excessively frequent synchronization.
3Measurement precision
If environmental factors are minimized through careful oscillator design and placement, then aging is reduced, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent introduces timestamped synchronization messages as an intermediary mechanism. Rather than trying to protect the oscillator from environmental factors through complex design, the system uses external reference messages to measure and compensate for environmental effects on the oscillator, transferring the protection function from hardware design to software-based correction.
Data Source
AI summary
This invention relates to methods and systems for estimating offset, skew and drift. Embodiments of the invention relate to methods and systems which allow these relationships between a slave clock and a master clock to be estimated based on the exchange of timestamped messages between the master and the slave. Further embodiments of the invention set out uses of these estimates to synchronize a local clock in a slave to a master and to steer the slave clock to stay aligned to the master clock when the master clock is temporarily unavailable or the communication path between slave and master is temporarily unavailable.