Clock Synchronization Using Validity Time for Railway Systems
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Solution Overview
Problem
Distributed systems in railway installations, such as those using CBTC, face challenges in ensuring security while maintaining the fastest possible response time, particularly in synchronizing platform facades and vehicle circulation.
Innovation Solution
Implementing a synchronization method that synchronizes local clocks within the controller's processing chains to a global clock, reducing asynchronism and optimizing response times by using redundancy and dedicated synchronization signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If local clocks in processing chains are used for autonomous operation, then system autonomy and flexibility are improved, but asynchronism between processing chains increases causing security issues
Solution Approach 1:
The system divides the clock function into two segments: a global clock providing time reference and a local clock providing timing autonomy. Each processing chain has its own local clock that can operate autonomously but is calibrated against the global clock, allowing segmentation of functions while maintaining overall synchronization.
Solution Approach 2:
The global clock acts as an intermediary between processing chains to establish a common time reference. Instead of directly synchronizing all local clocks to each other, they all reference the global clock as an intermediary, simplifying the synchronization architecture while maintaining security.
2Reliability
If global clock synchronization is implemented, then asynchronism is reduced improving security, but response time increases due to synchronization latency
Solution Approach 1:
The system performs preliminary synchronization by having processing chains periodically align their local clocks with the global clock before critical operations. This preliminary action ensures synchronization is already in place when needed, reducing the need for real-time synchronization delays.
Solution Approach 2:
Clock synchronization occurs periodically rather than continuously, with processing chains updating their local clocks at regular intervals against the global clock. This periodic action maintains synchronization security while minimizing the time overhead compared to continuous synchronization.
3Reliability
If validity time is assigned to output signals, then security margin is optimized, but system complexity increases due to additional timing management
Solution Approach 1:
The system changes the parameter of output signals by adding a validity time attribute. Each output signal carries information about its temporal validity window, allowing receiving processing chains to automatically determine whether the signal is still valid without complex external validation logic.
Solution Approach 2:
The timing information is copied along with the data signal itself. The validity time is embedded in the signal packet, creating a self-contained unit that carries both data and its temporal context, eliminating the need for separate timing management systems.
Data Source
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AI summary
The present invention relates to a method for synchronizing a system comprising a plurality of input modules (22), the method comprising associating a local input date with the input signal by the input module (22) that produced the signal, transmitting each input signal from an input module (22) to the computer (24), generating output signals for one or more output modules (26), calculating an end-of-validity time for the output signal by using a second function, transmitting each output signal from the computer (24) to the output module (26), and for each end-of-validity time for the output signal, a time base change operation performed by the output module (26).