Automated Vehicle Time Synchronization Under Degraded GNSS
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Solution Overview
Problem
Existing systems face challenges in synchronizing the time between automated vehicles and central servers accurately, particularly in environments where external time synchronization signals like GNSS may degrade, leading to potential interference or delays in marshalling operations.
Innovation Solution
A multi-layered approach is employed to monitor, estimate, and adjust timestamps and time confidence using inputs from various sources, including GNSS, NTP/PTP, and marshalling messages, with models like CMST to calculate time offsets and drift, ensuring accurate time synchronization across automated vehicles and central servers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external time synchronization signals like GNSS are used, then time synchronization between automated vehicles and central servers is achieved, but the system becomes vulnerable to signal degradation and interference
Solution Approach 1:
The patent introduces intermediary time synchronization messages exchanged between the automated vehicle and central server through defined communication layers (application, transport, security, radio link). These messages act as mediators that transfer time synchronization information without direct dependence on external GNSS signals, thereby resolving the vulnerability to signal degradation while maintaining synchronization reliability
Solution Approach 2:
The time synchronization process is segmented into multiple independent layers (application layer, transport layer, security layer, radio link layer), each handling specific aspects of time synchronization. This segmentation allows the system to maintain synchronization through multiple independent pathways, reducing the impact of signal degradation in any single channel
2Measurement precision
If multiple time synchronization layers are implemented, then time synchronization accuracy is improved, but system complexity increases
Solution Approach 1:
The synchronization system is divided into distinct layers (application, transport, security, radio link), each with specific functions and time offset calculations. This segmentation improves measurement precision by addressing time synchronization at each communication stage independently, while the modular structure manages complexity through clear layer boundaries and standardized interfaces
3Measurement precision
If time offsets are calculated at multiple communication layers, then time drift estimation accuracy is improved, but computational requirements increase
Solution Approach 1:
Time offsets are calculated preliminarily at each communication layer before final time synchronization is established. By performing these calculations in advance at distributed points (application layer, transport layer, security layer, radio link layer), the system accumulates precise time drift estimates without requiring intensive real-time computation, thus improving accuracy while managing energy consumption
Data Source
AI summary
A method for synchronizing time between a central server and an automated vehicle (AV) includes exchanging a series of time synchronization (TS) messages and generating a set of time offsets between a pair of TS messages among the series of TS messages. The method further includes changing a system time of the AV using a time drift estimate defined by a set of time assessment models being a function of at least one of a plurality of time inputs or the set of layer time offset values, and controlling the AV using the system time and one or more marshalling instructions providing drive commands from the central server.