Transparent Clocks for Time Transfer with Packet Delay Variation Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The IEEE 1588 PTP standard faces challenges in achieving precise clock synchronization due to packet delay variation (PDV), which introduces noise and degrades synchronization accuracy, especially when timing messages pass through transparent clocks that do not accurately account for residence times.
Innovation Solution
The method involves using end-to-end transparent clocks to measure and update residence times, which are then used to estimate skew and offset in slave clocks, potentially improving synchronization accuracy to levels comparable to GPS by compensating for message delivery variability across the network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If packet-based time transfer is used to avoid GPS costs and accessibility issues, then deployment flexibility and cost are improved, but packet delay variation degrades synchronization accuracy
Solution Approach 1:
The patent segments the end-to-end delay measurement into individual residence time measurements at each transparent clock node. Each transparent clock measures and reports its own residence time separately, allowing the slave clock to compensate for delay variation at each segment rather than treating the entire path as a single unknown variable.
Solution Approach 2:
Transparent clocks act as intermediaries that measure and report residence times. These intermediary devices provide delay information that would otherwise be unavailable, enabling the slave clock to compensate for network delays without requiring direct master-slave interaction for each measurement.
2Measurement precision
If transparent clocks are used to measure residence times, then synchronization accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes transparent clocks multi-functional by enabling them to perform both their traditional packet forwarding function and the additional function of measuring and reporting residence times. This universal approach allows existing network infrastructure to provide synchronization support without requiring dedicated timing devices at each node.
Solution Approach 2:
Each transparent clock autonomously measures its own residence time and includes this information in PTP messages. The devices serve themselves by generating the timing data they need, eliminating the requirement for external measurement equipment or complex centralized control systems.
3Measurement precision
If residence times are accurately measured and compensated, then clock synchronization precision is improved, but calculation complexity increases
Solution Approach 1:
The patent performs preliminary measurement of residence times at each transparent clock node and includes this information in PTP messages before the slave clock needs to perform its synchronization calculation. By preparing the delay data in advance, the slave clock receives pre-processed information that simplifies its offset and skew estimation calculations.
Solution Approach 2:
The system implements feedback by having transparent clocks report their measured residence times back to the slave clock through PTP messages. This feedback loop provides the slave with accurate delay information that it uses to compensate for network variations and improve synchronization precision.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
This invention relates to methods and devices for time transfer. The invention has particular application in the alignment of slave clocks to a master clock and dealing with packet delay variations. In embodiments of the invention, the slave clock uses the residence times measured by end-to-end transparent clocks to compensate for clock synchronization errors that arise due to variability in message transfer delays. Embodiments provide a simple linear approximation technique and a Kalman filter-based technique for estimating offset and skew of the slave clock.