Time Source Recovery for Autonomous Driving Vehicles
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Solution Overview
Problem
Autonomous driving vehicles face challenges in accurately synchronizing time sources from various sensors and devices, particularly when a GPS time source is unavailable, leading to potential inaccuracies in motion planning and control.
Innovation Solution
A method and apparatus for recovering a time source in autonomous driving vehicles by determining the difference between local and GPS time sources, and smoothly converging the local time source to the GPS time source within a predetermined interval when the GPS becomes available, ensuring accurate timestamping of sensor data for perception and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If GPS time source is unavailable, then autonomous vehicle can operate independently, but time synchronization accuracy deteriorates
Solution Approach 1:
The system pre-establishes a local time source and continuously monitors GPS signal availability. When GPS becomes unavailable, the system has already prepared the local time source to take over, ensuring seamless transition without losing time synchronization capability. This preliminary preparation resolves the contradiction by having backup timing infrastructure ready before GPS failure occurs.
Solution Approach 2:
The local time source acts as an intermediary between the vehicle's internal timing needs and the external GPS time source. When GPS is unavailable, the local time source mediates by providing alternative timing reference, allowing the vehicle to maintain operational independence while preserving time synchronization accuracy through the intermediary local clock.
2Reliability
If multiple clock sources are used, then time redundancy is improved, but time synchronization complexity increases
Solution Approach 1:
The system dynamically adjusts the role of different time sources based on GPS availability. When GPS is available, it serves as the primary time source; when unavailable, the local time source becomes primary. This dynamic switching mechanism maintains time redundancy while managing complexity through automated role assignment rather than requiring complex simultaneous coordination of multiple independent clocks.
Solution Approach 2:
The system continuously monitors GPS signal status and uses this feedback to automatically switch between time sources. When GPS signal is lost, the feedback mechanism triggers activation of the local time source. This feedback-driven approach simplifies the management of multiple clock sources by using automatic detection and response rather than complex manual coordination, resolving the contradiction between redundancy and complexity.
3Adaptability or versatility
If local time source is used when GPS is unavailable, then operational independence is improved, but time accuracy deteriorates
Solution Approach 1:
The system pre-synchronizes the local time source with GPS time while GPS is available, creating a time reference that is already aligned with the standard. When GPS becomes unavailable, this pre-synchronized local time source continues from its last known accurate state, cushioning against accuracy deterioration by maintaining the previously established time reference rather than allowing immediate drift.
Data Source
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AI summary
In one embodiment, a system determines a difference in time between a local time source and a time of a GPS sensor. The system determines a max limit in difference and a max recovery increment or max recovery time interval for a smooth time source recovery. The system determines that the difference between the local time source and a time of the GPS sensor to be less than the max limit. The system plans a smooth recovery of the time source to converge the local time source to a time of the GPS sensor within the max recovery time interval. The system generates a timestamp based on the recovered time source to timestamp sensor data for a sensor unit of the ADV.