INS Time Synchronization Using Backup Clocks During GNSS Outages
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Solution Overview
Problem
Autonomous driving vehicles face challenges in localization when Global Navigation Satellite System (GNSS) data is unavailable, as inertial measurement unit (IMU) data cannot be synchronized without a timestamp, leading to an inability to perform localization and navigate effectively.
Innovation Solution
An inertial navigation system (INS) incorporates an alternative source of time information, such as a real-time clock (RTC) or Network Time Protocol (NTP), to timestamp sensor data, allowing synchronization and localization even without GNSS data, by identifying and utilizing alternative time sources to synchronize IMU data and additional sensor data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GNSS data is used for time synchronization in INS, then localization accuracy is improved, but system reliability deteriorates when GNSS data is unavailable
Solution Approach 1:
The patent introduces an intermediary time synchronization mechanism that operates independently of GNSS. The INS system uses alternative time sources (such as vehicle clock or sensor data timestamps) to synchronize IMU data when GNSS is unavailable, allowing the system to maintain localization functionality without relying solely on GNSS for time synchronization.
Solution Approach 2:
The system performs preliminary time synchronization using available time sources before GNSS data becomes unavailable. By establishing time synchronization in advance through alternative sources and maintaining the ability to switch between time sources, the system prepares for potential GNSS outages and ensures continuous operation.
2Reliability
If alternative time sources are used to synchronize sensor data, then system reliability is improved during GNSS outages, but time synchronization precision deteriorates
Solution Approach 1:
The patent applies partial action by using alternative time sources only when necessary (during GNSS outages) rather than continuously. The system uses the least intrusive time synchronization method needed to maintain functionality, switching to alternative sources only when GNSS is unavailable, thus minimizing the impact on overall time synchronization precision while ensuring reliability during outages.
3Duration of action of stationary object
If IMU data is timestamped without GNSS, then navigation continuity is improved, but data synchronization capability deteriorates
Solution Approach 1:
The patent extracts the time synchronization function from its dependency on GNSS data. By separating time stamping capability from GNSS reliance, the system can continue timestamping IMU data and maintaining navigation using alternative time sources, while the loss of GNSS-based synchronization is compensated by this extracted functionality implemented through other means.
Data Source
AI summary
In one embodiment, a method for synchronizing sensor data of an autonomous driving vehicle includes determining, by a processing device of an inertial navigation system (INS), that global navigation satellite system (GNSS) data is unavailable and identifying an alternative source of time information. The method further includes retrieving time information from the alternative source and synchronizing sensor data with the time information from the alternative source of time information.