Fault-Tolerant Clock Synchronization in Wireless Time-Triggered Networks
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Solution Overview
Problem
Existing wireless data transmission protocols, such as WiFi, result in unpredictable message delays due to shared frequency bands, making it difficult to establish an accurate global time in distributed real-time systems.
Innovation Solution
Implementing a method with Global Navigation System signal generators (GNSSGs) using a wired timed communication system to establish a precise global time, and utilizing two different wireless communication systems: one for unidirectional synchronization messages and another for bidirectional data messages, with the latter being time-stamped and transmitted according to a scheduled trigger derived from the global time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wireless data transmission protocols (e.g., WiFi) are used for communication, then device compatibility and ease of operation are improved, but message delay predictability deteriorates
Solution Approach 1:
The communication system is segmented into two separate wireless communication systems: one dedicated to synchronization message transmission and another to data message transmission. This segmentation prevents interference between synchronization and data traffic, ensuring predictable timing for time-controlled applications while maintaining ease of operation through standardized protocols.
Solution Approach 2:
A wired timed communication system acts as an intermediary to establish a reference time that is then distributed wirelessly to node computers. This intermediary layer provides a stable time reference that compensates for the inherent unpredictability of wireless transmission delays, enabling accurate clock synchronization.
2Device complexity
If a single wireless communication system is used for both synchronization and data transmission, then device complexity is reduced, but time synchronization precision deteriorates
Solution Approach 1:
The communication infrastructure is divided into specialized channels: one wireless system for synchronization messages and another for data messages. This functional segmentation ensures that synchronization traffic is not interfered with by data traffic, achieving sub-100-nanosecond time synchronization precision while keeping each individual communication system relatively simple.
3Productivity
If multiple node computers transmit data messages simultaneously on shared wireless channels, then communication efficiency is improved, but message delay predictability deteriorates
Solution Approach 1:
Node computers receive and store pre-calculated transmission schedules that specify exact time slots for data message transmission. These schedules are determined in advance based on the global reference time, allowing nodes to transmit efficiently in designated slots without collision while maintaining predictable delays for time-controlled messaging.
Solution Approach 2:
The system implements periodic time slots for data transmission based on the global reference time. Node computers transmit data messages at predetermined periodic intervals assigned to them, ensuring efficient channel utilization while maintaining deterministic timing characteristics required for real-time applications.
4Adaptability or versatility
If wireless communication is used instead of wired communication for all messages, then system flexibility and mobility are improved, but time synchronization precision deteriorates
Solution Approach 1:
A wired timed communication system serves as a stable intermediary for establishing the reference time, while wireless communication is used for distributing this reference time to mobile node computers. This hybrid approach combines the precision of wired communication for time establishment with the flexibility of wireless communication for broad distribution, achieving both high precision and system adaptability.
Data Source
Figure 1~2
AI summary
The invention relates to a method for the wireless fault-tolerant synchronization of clocks of node computers in a distributed real-time system, which distributed real-time system comprises a number of arenas, wherein a multiplicity of node computers communicate with base stations in each arena using time-controlled wireless data messages, wherein one or more base stations are arranged in each arena, and wherein at least one Global Navigation System Signal Generator (GNSSG) is present in each arena, wherein all GNSSGs communicate with one another via a wired time-controlled communication system (ZKS) using time-controlled messages, and wherein each GNSSG transmits at least one GNS message exactly at the beginning of each full and half minute of the global ZKS time provided by the time-controlled communication system, and wherein a node computer disciplines the oscillator of the clock thereof using at least one received GNS message and therefore participates in the global ZKS time, and wherein trigger signals for transmitting time-controlled data messages between the node computers and the base stations on one or preferably more wireless bidirectional data channels are derived from the progression of the global ZKS time according to a schedule individually created a priori for each node computer and each base station.