Wireless Station Location Detection Using Time of Flight
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Solution Overview
Problem
Existing methods for locating rogue devices in wireless networks, such as using RSSI and TDOA, are flawed due to unknown client transmit power and unsynchronized clocks, leading to inaccurate device location and potential service disruption when trying to eliminate rogue devices.
Innovation Solution
A technique involving transmitting frames and calculating the time for signal passage between access points and devices to estimate distance, using multiple access points to determine device location in two or three dimensions, allowing for precise location without disrupting network service.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RSSI is used to locate devices, then device distance can be estimated, but location accuracy deteriorates due to unknown client transmit power and unavailable radio environment models
Solution Approach 1:
The patent introduces a clock synchronization mechanism as an intermediary to enable accurate TDOA measurements. By using synchronized clocks between access points and client devices, the system can accurately measure time differences of arrival without the information loss that plagues RSSI-based methods. The synchronization protocol acts as a mediator that establishes a common time reference across the network.
2Measurement precision
If TDOA is used to locate devices, then signal attenuation is removed from calculation, but location accuracy deteriorates due to unsynchronized clocks and varying signal paths
Solution Approach 1:
The patent applies preliminary action by synchronizing clocks before performing TDOA measurements. The system establishes time synchronization in advance through a coordination protocol between access points and client devices, ensuring that when location measurements are taken, all devices are operating from a common time reference. This preliminary synchronization eliminates the reliability issues that would otherwise plague TDOA measurements.
3Measurement precision
If multiple access points are used to improve location accuracy, then measurement quantity increases, but path variation causes TDOA quality to deteriorate
Solution Approach 1:
The patent segments the location determination process into multiple independent TDOA measurement pairs. Instead of attempting to process all access point signals simultaneously and dealing with path variations as a unified complex problem, the system divides the problem into separate bilateral measurements between pairs of access points and the client device. Each pair's TDOA is calculated independently, and the results are combined to determine location, simplifying the management of varying signal paths.
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
Enables effective identification and elimination of rogue devices without interrupting network service, allowing for secure and uninterrupted operation by providing accurate device location without suppressing service.
Implementation Method 1
The amount of time for a signal to pass between the AP and the device may be estimated and multiplied by the speed of light to find the distance between the AP and the device
Data Source
AI summary
A technique for locating a device uses connectivity to find a distance between an access point (AP) and a device. The AP transmits a frame to a device and receives an acknowledgement frame from the device. The amount of time for a signal to pass between the AP and the device is estimated and multiplied by the speed of light to find the distance between the AP and the device.