PTP Time Synchronization Validation Over Unreliable Ethernet
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Solution Overview
Problem
Inaccuracies in environment models for autonomous vehicles due to differences in local time stamps from different environment sensors, leading to impaired autonomous driving performance, even with redundant sensors and diverse fusion algorithms, especially when synchronized over unreliable communication networks.
Innovation Solution
A method involving forward and reverse time-synchronization using the Precision Time Protocol (PTP) over Ethernet networks, with a validator having a high integrity level (ASIL D) to ensure synchronization accuracy, utilizing a master clock, slave clocks, and validator clocks, and employing different EtherTypes for message prioritization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If time-synchronization is performed over an unreliable communication network (e.g., Ethernet with switches), then the system can achieve wide coverage and connectivity, but the synchronization accuracy and integrity level deteriorate due to network uncertainties
Solution Approach 1:
The patent introduces a validator as an intermediary component that mediates between the communication network and the time-synchronization process. The validator receives synchronized time values from multiple slave clocks, validates their consistency, and determines whether synchronization succeeded or failed. This intermediary layer protects the system from network-induced synchronization errors while maintaining wide network coverage.
Solution Approach 2:
The patent implements a feedback mechanism where synchronized time values are sent back to the validator for verification. The validator compares time values from multiple slave clocks and provides feedback on synchronization quality. This feedback loop enables the system to detect and respond to synchronization failures caused by network unreliability, maintaining high integrity levels despite using standard Ethernet infrastructure.
2Extent of automation
If multiple slave clocks are synchronized via a fusion unit over the communication network, then time-synchronization can be achieved across distributed sensors, but synchronization accuracy deteriorates due to network-induced timing errors
Solution Approach 1:
The patent performs preliminary validation of time synchronization before the synchronized time values are used for sensor data fusion. The validator checks whether slave clocks are properly synchronized with the master clock before allowing their time stamps to be used in environment model determination. This preliminary action prevents inaccurate time stamps from degrading measurement precision in automated sensor fusion applications.
Solution Approach 2:
The patent prepares for potential synchronization failures by implementing a validator that can detect and flag timing errors before they affect sensor fusion. The system cushions against network-induced timing errors by validating time values in advance and determining synchronization status, preventing inaccurate time stamps from compromising measurement precision in autonomous driving applications.
3Ease of manufacture
If standard PTP protocol is used for time-synchronization over Ethernet, then implementation simplicity is improved, but synchronization reliability deteriorates due to lack of integrity assurance
Solution Approach 1:
The patent introduces a validator as an intermediary layer between the standard PTP protocol and the application layer. The validator receives time synchronization data from PTP, validates its consistency across multiple slave clocks, and determines synchronization success or failure. This intermediary maintains implementation simplicity by building upon standard PTP while adding reliability through validation logic.
Solution Approach 2:
The patent adds a feedback validation layer that monitors PTP synchronization outcomes. The validator receives feedback from multiple slave clocks about their synchronized time values and determines whether synchronization met required integrity levels. This feedback mechanism maintains ease of implementation by using standard PTP infrastructure while improving reliability through additional validation and status reporting.
Data Source
Figure 1a~2a
Figure 2b~3
AI summary
The present document describes a method for performing time-synchronization between a master clock and a plurality of slave clocks. The method comprises performing a forward time-synchronization from the master clock to the plurality of slave clocks. Furthermore, the method comprises performing a reverse time-synchronization from the plurality of slave clocks to a corresponding plurality of validator clocks. In addition, the method comprises validating the time- synchronization between the plurality of slave clocks, notably between the master clock and the plurality of slave clocks, based on the plurality of validator clocks.