V2X Collective Perception Message Aging Against Time Drift
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Solution Overview
Problem
Current V2X systems face challenges in environmental perception due to limited sensor range and accuracy, particularly in urban areas with building obstructions and remote locations, and time synchronization issues affecting the freshness of collective perception messages.
Innovation Solution
A device and vehicle system that includes a wireless transceiver and processor to calculate and transmit collective perception messages with an object age that accounts for processing and transmission delays, ensuring message freshness and avoiding infinite flooding of old messages by discarding messages older than a default value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the absolute value of the timestamp is used to evaluate message freshness, then the message age can be calculated, but precise time synchronization is required which is difficult to achieve in practice due to time drift
Solution Approach 1:
The patent introduces an intermediary reference timestamp (first timestamp) from a common time source that both transmitting and receiving devices can use. Instead of directly comparing absolute timestamps that drift apart, the system uses this intermediary reference to calculate relative time differences, thereby mediating the time synchronization problem between devices.
Solution Approach 2:
The patent copies the reference timestamp from a common time source to both the transmitting device and receiving device. By having both devices possess the same reference timestamp copy, they can independently calculate message age without requiring continuous synchronization, thus eliminating the time drift problem while maintaining measurement accuracy.
2Quantity of substance
If collective perception messages are broadcast repeatedly through V2X sidelink to expand cognitive range, then the number of cognitive objects increases, but infinite flooding of old messages occurs
Solution Approach 1:
The patent implements a feedback mechanism where the receiving device calculates the message age based on the embedded reference timestamp and compares it against a threshold. This feedback control prevents old messages from being propagated further, thereby controlling the spread of information and preventing infinite flooding while still allowing legitimate messages to propagate.
Solution Approach 2:
The patent changes the parameter used for message evaluation from absolute timestamp to relative message age calculated from a reference timestamp. This parameter transformation allows the system to distinguish between fresh and old messages objectively, enabling selective propagation based on message freshness rather than absolute time values that are subject to drift.
3Measurement precision
If GNSS is used for time synchronization in V2X, then high time accuracy can be achieved, but unstable weather or road conditions severely degrade synchronization accuracy
Solution Approach 1:
The patent applies preliminary action by embedding the reference timestamp in the message at the source before transmission. This allows the receiving device to calculate message age locally without requiring real-time synchronization during message exchange, thus eliminating the need for continuous GNSS synchronization and its associated vulnerabilities to environmental conditions.
Data Source
AI summary
A device, suitable for a V2X (Vehicle-to-everything) system, is disclosed. The device includes a wireless transceiver and a processor. The wireless transceiver is configured to receive a first collective perception message from a transmitting device of the V2X system. The first collective perception message comprises a first object age of a perceived object of the first collective perception message calculated by the transmitting device. The processor is coupled to the wireless transceiver, and the processor is configured to calculate a second object age of the perceived object of a second collective perception message. The second object age comprises a processing delay of the device and the first object age.