Vehicle Timestamp Generation Without GNSS Signal
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Solution Overview
Problem
Vehicles participating in vehicle ad-hoc networks, such as Car2X, face challenges in synchronizing time references for event messages, as they require a global time base for accurate evaluation and processing, which is unavailable when GNSS signals are insufficient, rendering messages useless.
Innovation Solution
A method using a global time base derived from GNSS signals, with a fallback to a local time base if GNSS is unavailable, allowing vehicles to participate and send analyzable messages by updating time before system start or querying from external sources like vehicle clocks or other network participants, ensuring time synchronization within tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a global time base from GNSS signals is used for timestamp generation, then time synchronization accuracy is improved, but the system becomes inoperable when GNSS signals are unavailable
Solution Approach 1:
The system stores timestamp data and vehicle state information in memory before GNSS signal loss occurs. This preliminary storage of reference data enables the vehicle to continue participating in the ad-hoc network using locally stored timestamps even when global time synchronization is unavailable, thus maintaining operational availability while preserving the ability to achieve high synchronization accuracy when signals are available
Solution Approach 2:
The system introduces an intermediary local time base that bridges the gap between the global GNSS time base and the vehicle's internal clock. When GNSS signals are unavailable, the local time base derived from stored timestamp data serves as a mediator, allowing the vehicle to generate meaningful timestamps and maintain network participation without direct GNSS connection
2Measurement precision
If the vehicle system remains active to update time continuously, then time synchronization is maintained, but power consumption increases
Solution Approach 1:
Instead of continuous time updates, the system performs time synchronization periodically when GNSS signals are available. The timestamp data and vehicle state information are stored in memory during these periodic synchronization events, allowing the system to maintain accurate time references without continuous power consumption from active signal processing
Solution Approach 2:
The system uses its own stored timestamp data and state information to maintain time synchronization autonomously when GNSS signals are unavailable. By serving itself with previously stored reference data, the vehicle avoids the need for continuous external signal reception and processing, significantly reducing power consumption while maintaining synchronization capability
Data Source
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AI summary
The invention relates to a method for generating a time stamp in a vehicle (4) which participates in a vehicle ad-hoc network, said method associating, by giving out the time stamp, an event (16), which is transmitted in a message (28), with a clock time (32). Said clock time is generated by updating a global time base (38) that can be derived from a global satellite navigation signal (20) called GNSS signal (20). The method according to the invention comprises the following steps: - checking whether a GNSS signal (12) can be received, and - generating the clock time (32) based on a local time base (50) if an insufficient number of global satellite navigation signals (12) for deriving the global time base (38) is available.