Wireless Distance Detection via Clock Drift Prediction
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Solution Overview
Problem
The existing FTM protocol in IEEE 802.11 is insensitive to small changes in distance between wireless devices due to limited precision, requiring multiple exchanges and consuming energy, making it difficult to detect small changes in distance accurately.
Innovation Solution
A method that determines variations in a parameter over time based on timing signals between wireless devices, utilizing periodic step transitions due to relative clock drift, to predict when a periodic step transition is expected to occur and compare measured values with expected values to detect changes in distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple FTM exchanges are used to measure distance more accurately, then measurement precision is improved, but energy consumption increases and time is lost
Solution Approach 1:
The patent performs preliminary analysis of clock drift patterns and predicts future step transition times. By predicting when step transitions will occur, the system can schedule distance measurements at these specific moments, achieving high precision with fewer measurements and thus lower energy consumption
Solution Approach 2:
The patent replaces the traditional mechanical approach of repeatedly performing full FTM exchange sequences with a signal processing approach. By analyzing parameter variations and predicting step transitions in the timing data, the system achieves accurate distance measurement without requiring multiple complete FTM protocol exchanges, thereby reducing energy consumption
2Measurement precision
If multiple FTM exchanges are used to measure distance more accurately, then measurement precision is improved, but time consumption increases
Solution Approach 1:
The system performs preliminary characterization of the clock drift behavior and predicts step transition times in advance. This allows the system to know exactly when to perform measurements, eliminating the need for multiple trial measurements and reducing overall time consumption while maintaining high precision
Solution Approach 2:
The patent exploits the periodic nature of step transitions caused by clock drift. By identifying the periodic pattern and predicting future transitions, the system can perform measurements at optimal intervals rather than continuously or through multiple complete FTM sequences, thereby reducing time consumption while maintaining measurement precision
3Measurement precision
If FTM protocol is used for distance measurement, then distance can be determined, but small changes in distance cannot be detected due to sampling interval limitations
Solution Approach 1:
The patent replaces direct distance measurement through multiple FTM exchanges with an indirect measurement approach. By analyzing variations in timing parameters and predicting step transitions caused by clock drift, the system can detect subtle changes in distance that would be imperceptible in raw FTM measurements, effectively overcoming the sampling interval limitation
Solution Approach 2:
The patent focuses on detecting changes in timing parameters rather than directly measuring distance. By monitoring variations in transmission and reception timestamps and analyzing the pattern of parameter changes over time, the system can detect small distance changes that would be lost in the quantization of direct distance measurements
Data Source
AI summary
In one aspect, a method for detecting changes in distance between a first wireless device and a second wireless device is provided. The method comprises determining a variation of a parameter over time, based on measurements of first timing signals transmitted between the first and second wireless devices. The variation of the parameter depends on a distance between the wireless devices, and comprises periodic step transitions as a result of relative clock drift between the wireless devices. The method further comprises predicting a time at which a periodic step transition is expected to occur based on the variation of the parameter, and determining a value of the parameter based on measurements of second timing signals. In response to a determination that the determined value of the parameter differs from an expected value of the parameter, it is determined that the distance between the wireless devices has changed.