Ethernet Sensor Synchronization With Trigger Timestamps
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Controlling sensors over Ethernet networks with high time accuracy is challenging due to variable latency, especially when using Energy-Efficient Ethernet (EEE), where propagation times can vary by several tens of microseconds, while time accuracy requirements are often in the order of less than one microsecond.
Innovation Solution
The implementation of a system that includes a transceiver and a processor configured to generate packets with trigger timestamps, transport timestamps, and presentation timestamps, allowing for precise control and synchronization of sensor data delivery and presentation, exceeding network latency and optimizing power usage through scheduled link activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Energy-Efficient Ethernet (EEE) protocols are used to reduce power consumption, then energy efficiency is improved, but time accuracy deteriorates due to variable propagation times
Solution Approach 1:
The system performs preliminary actions by generating transport timestamps that predict future wake-up times and trigger timestamps that specify exact delivery times before the actual data transmission occurs. This allows the receiving device to prepare in advance, buffer data at the correct time, and maintain time accuracy despite EEE-induced variable latency.
Solution Approach 2:
Timestamps serve as intermediaries between the transmitting and receiving devices. The transport timestamp mediates the scheduling of data transmission during wake windows, while the trigger timestamp mediates the precise delivery timing to the application, decoupling the actual transmission time from the required delivery time.
2Measurement precision
If timestamps are used to ensure precise timing, then time accuracy is improved, but device complexity increases due to buffering and timestamp management
Solution Approach 1:
The timing mechanism is segmented into two distinct timestamp types: transport timestamps for network transmission scheduling and trigger timestamps for application-level delivery timing. This segmentation allows each timestamp to handle a specific aspect of timing, simplifying the overall system architecture while maintaining high time accuracy.
Solution Approach 2:
The system uses periodic wake-up windows in EEE mode, where data transmission occurs at regular intervals. By aligning timestamp generation with these periodic wake windows, the system maintains deterministic timing behavior despite the intermittent nature of EEE operation, reducing the need for complex continuous timing mechanisms.
3Measurement precision
If data is buffered to exceed maximal latency, then time accuracy is improved, but loss of time increases due to waiting
Solution Approach 1:
The transmitting device performs preliminary action by calculating the trigger timestamp to account for maximal network latency in advance. This allows the receiving device to buffer data for the exact duration needed to compensate for latency without excessive waiting, as the buffer duration is precisely determined by the latency calculation rather than being arbitrary or overly conservative.
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
An apparatus for controlling a sensor over a network includes a transceiver and a processor. The transceiver is configured to communicate over a network. The processor is configured to receive or generate control data for controlling a sensor connected to the network, to generate a packet including (i) the control data and (ii) a trigger timestamp indicative of a future time at which the control data is to be provided to the sensor, and to transmit the packet using the transceiver over the network.