Autonomous Vehicle Time Source Ranking for Sensor Timestamp Accuracy
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Solution Overview
Problem
Autonomous vehicles face challenges in motion planning and control due to inaccuracies in time synchronization among various sensors and devices, which are often costly and confusing to manage with conventional high-precision crystal oscillators.
Innovation Solution
A time source ranking system that synchronizes local oscillators with GPS pulse signals, generates timestamps with varying granularities, and ranks time sources for accuracy, ensuring precise timekeeping across sensors and devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high precision crystal oscillators are used to generate time, then time accuracy is improved, but cost and device complexity increase
Solution Approach 1:
The patent replaces expensive high-precision crystal oscillators with cheaper, lower-precision oscillators. The system uses multiple inexpensive oscillators from different sensors and devices, ranking them by precision and selecting the best available source dynamically, thereby achieving accurate timekeeping without relying on costly hardware
Solution Approach 2:
The patent introduces a time source ranking system that acts as an intermediary between multiple low-precision oscillators and the time synchronization requirement. This ranking system evaluates and selects the most accurate time source from available sensors and devices, mediating the time generation process without requiring any single component to be highly precise
2Adaptability or versatility
If multiple clock sources from sensors and devices are used to generate time, then availability is improved, but time synchronization accuracy deteriorates due to confusion and imprecision
Solution Approach 1:
The patent segments the time source selection process into distinct evaluation criteria and ranking levels. Each sensor and device's clock source is independently evaluated based on its precision characteristics, and they are ranked hierarchically. This segmentation allows the system to manage multiple sources systematically rather than dealing with them as a confused whole
Solution Approach 2:
The patent implements a feedback mechanism where the system continuously monitors the performance and availability of multiple clock sources, ranks them based on current conditions, and selects the best source dynamically. This feedback loop ensures that the system adapts to changing conditions while maintaining time synchronization accuracy
Data Source
AI summary
In one embodiment, a system receives a number of times from a number of time sources including sensors and real-time clocks (RTCs), wherein the sensors are in communication with an autonomous driving vehicle (ADV) and the sensors include at least a GPS sensor. The system generates a difference histogram based on a time for each of the time sources for a difference between a time of the GPS sensor and a time for each of the other sensors and RTCs. The system ranks the sensors and RTCs based on the difference histogram. The system selects a time source from one of the sensors or RTCs with a least difference in time with respect to the GPS sensor. The system generates a timestamp based on the selected time source to timestamp sensor data for a sensor unit of the ADV.