Wireless Ranging Timestamp Disambiguation for Precise Distance Measurement
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Solution Overview
Problem
Existing wireless ranging processes involve significant signaling overhead and complex calculations due to the exchange of numerous null data packets and timestamp ambiguities, which affect the accuracy and efficiency of distance determination between wireless devices.
Innovation Solution
A method to resolve timestamp ambiguities by using exact, ambiguity-free local timestamps to form approximate timestamps for reported timestamps, and combining them to achieve exact, ambiguity-free distance calculations, while excluding devices that are too far to resolve ambiguities, and employing passive ranging to listen to exchanges between other devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If numerous null data packets and timestamp exchanges are used for ranging, then measurement precision is improved, but signaling overhead increases
Solution Approach 1:
The patent extracts and removes the problematic wrap-around ambiguity from the timestamp system by introducing a separate wrap-around counter. This counter specifically tracks the number of times the timestamp has wrapped around, allowing the main timestamp to remain simple while the ambiguity is handled separately. This extraction resolves the contradiction by maintaining measurement precision without requiring numerous redundant packets.
Solution Approach 2:
The patent adds a new dimension to the timestamp system by introducing a wrap-around counter that operates independently from the main timestamp. This dimensional addition allows the system to track time more accurately over extended periods without increasing the complexity of individual timestamp exchanges, thereby reducing signaling overhead while maintaining precision.
2Device complexity
If timestamp wrap-around ambiguity is not resolved, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The wrap-around counter serves as an intermediary element that mediates between the simple timestamp system and the requirement for accurate long-term time tracking. Rather than making the timestamp itself complex, the counter acts as a separate tracking mechanism that resolves ambiguity without increasing the complexity of the primary timestamp processing.
Solution Approach 2:
The time tracking function is segmented into two independent components: the main timestamp that records time within a cycle, and the wrap-around counter that records the number of cycles. This segmentation allows each component to remain simple while together they provide accurate long-term time tracking, resolving the contradiction between simplicity and precision.
3Measurement precision
If all devices are included in ranging calculations, then measurement precision is improved, but device complexity increases due to ambiguity resolution
Solution Approach 1:
Each wireless device independently maintains its own wrap-around counter and uses it to resolve its own timestamp ambiguities. This self-service approach eliminates the need for complex inter-device coordination to resolve ambiguities, allowing all devices to be included in ranging calculations without proportionally increasing system-wide complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces signaling overhead and improves the accuracy and efficiency of wireless ranging by resolving timestamp ambiguities, enabling precise distance measurements between wireless devices.
Implementation Method 1
determining a time-of-flight (ToF) of the RF signals based on the ranging information, and calculating the distance by multiplying the ToF by the speed of light
Data Source
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AI summary
A method of performing ranging, by a first device, with respect to a second device is provided. According to an embodiment, the method includes: receiving, by the first device, a plurality of timestamps including a first timestamp and a second timestamp, and determining, by the first device, a range R with respect to the second device by calculating an average time-of-flight (TOF) of the first wireless signal and the second wireless signal based on the first timestamp and the second timestamp. The first timestamp indicates a time-of-arrival (TOA) of a first wireless signal arriving at the second device, a maximum possible value of the first timestamp being Tmax1. The second timestamp indicates a time-of-departure (TOD) of a second wireless signal departing from the second device, and a maximum possible value of the second timestamp being Tmax2 and greater than Tmax1.