WiFi Requester Location Privacy via Randomized SIFS
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Solution Overview
Problem
Existing time measurement-based positioning methods in WiFi networks, such as those using IEEE 802.11 standards, can compromise the privacy of the requester's location as responders can accurately calculate the location based on time stamps, which may not account for variations in actual short interframe spacing used by the requester.
Innovation Solution
The requester randomly generates a short interframe spacing within a specified fluctuation range of the nominal SIFS, preventing the responder from accurately calculating the time stamp (t3-t2) and thus maintaining location privacy by using this randomly generated SIFS as the interframe spacing between measurement and acknowledgement frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the requester uses a fixed nominal SIFS value for time measurement, then the positioning accuracy is improved, but the location privacy of the requester is compromised
Solution Approach 1:
The patent changes the SIFS parameter from a fixed nominal value to a randomly selected value within a specified range. The requester selects an actual SIFS value differently from the nominal SIFS value used in standard IEEE 802.11 protocols, introducing uncertainty into the time measurement process. This prevents responders from accurately calculating the requester's location while maintaining acceptable positioning functionality.
Solution Approach 2:
The patent introduces dynamic variation in the SIFS parameter by allowing the requester to randomly select different actual SIFS values for different time measurement processes. This dynamic approach contrasts with the static nominal SIFS value, making it impossible for responders to predict or accurately calculate the time stamps, thereby protecting location privacy.
2Loss of information
If the requester randomly generates actual SIFS within fluctuation range, then location privacy is protected, but measurement precision deteriorates
Solution Approach 1:
The patent deliberately introduces parameter variation by selecting actual SIFS values that differ from the nominal value within a controlled fluctuation range. This parameter change creates measurement uncertainty that protects privacy while the bounded nature of the fluctuation range ensures that positioning accuracy remains within acceptable limits.
Solution Approach 2:
The patent creates a modified version of the standard SIFS parameter - instead of using the exact nominal value, the requester uses a copied/adapted value that follows the same general protocol requirements but introduces protective variation. This allows the system to function while preventing precise location calculation by responders.
3Adaptability or versatility
If responders use standard IEEE 802.11 SIFS calculation, then protocol compatibility is maintained, but requester location can be accurately determined
Solution Approach 1:
The patent inverts the usual approach by having the requester (rather than the responder) introduce variation into the SIFS parameter. The requester selects an actual SIFS value that differs from the nominal value, causing the responder's standard calculations to fail. This inversion of who controls the parameter variation protects privacy while maintaining protocol compatibility.
Solution Approach 2:
The patent changes the SIFS parameter value used by the requester to be different from the nominal value expected by standard IEEE 802.11 protocols. This parameter change maintains basic protocol compatibility (the communication still works) while preventing responders from accurately calculating location based on time stamps.
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 effectively enhances the privacy of the requester's location by introducing uncertainty in the calculated location, ensuring that the responder cannot accurately determine the requester's position, thereby protecting location privacy.
Implementation Method 1
a time of a one-way flight (ToF) of a message (the measurement frame or the acknowledgement frame) between the access point and the station is equal to [(t4−t1)−(t3−t2)]/2
Data Source
AI summary
A method includes: separately performing, by a requester, time measurement with a plurality of responders, and calculating a location of the requester based on a measurement result. A measurement result obtained by the requester by performing time measurement with each responder includes time stamps t1, t2, t3, and t4, where t1 is a time when the responder sends a measurement frame, t2 is a time at which the requester receives the measurement frame, t3 is a time when the requester sends an acknowledgement frame in response to the measurement frame, and t4 is a time when the responder receives the acknowledgement frame. The acknowledgement frame is sent by the requester after waiting for a randomly generated short interframe spacing after receiving a last symbol of the measurement frame. The randomly generated short interframe spacing is randomly generated within a specified fluctuation range of a nominal short interframe spacing.