WLAN Geo-location via Clock Drift Compensation
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Solution Overview
Problem
Current geo-location methods for WLAN devices, particularly those based on IEEE 802.11 technology, often require multiple measuring devices and are prone to errors due to clock drift between the wireless device and measuring receivers, which can lead to inaccurate location determination.
Innovation Solution
A method and system that utilize a single mobile measuring receiver to determine the relative clock drift between the wireless device and the measuring receiver by analyzing the Time of Arrival (TOA) and Time of Departure (TOD) of beacons, allowing for accurate location calculation even when the positions differ by less than a predetermined distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple measuring devices are used to determine location, then location accuracy is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple measuring devices into a single mobile measuring station that integrates TOA measurement capability, GPS positioning, and clock drift compensation functions. This single device performs location determination by measuring TOA of beacons from the target WLAN device, determining its own position via GPS, and calculating clock drift between measurements, thereby achieving accurate location determination without requiring multiple separate devices.
Solution Approach 2:
The patent changes the operational parameters of the single measuring device by having it move to different positions and perform measurements at multiple time points. By varying the position parameter and time parameter, the device collects multiple TOA measurements that, when combined with clock drift compensation, enable accurate location determination equivalent to using multiple stationary devices.
2Measurement precision
If TOA measurements are taken at different positions, then location determination is improved, but clock drift errors increase
Solution Approach 1:
The patent implements a feedback mechanism where the measuring station determines its own position via GPS, calculates the clock drift based on the change in position and the time elapsed between measurements, and then uses this calculated drift to compensate subsequent TOA measurements. This closed-loop feedback approach continuously corrects for clock drift errors, maintaining measurement reliability even as the device moves to different positions.
Solution Approach 2:
The patent performs preliminary actions by having the measuring station determine its position via GPS and calculate the clock drift before using these measurements for location determination of the target device. By pre-calculating the clock drift parameter based on known position changes, the system prepares compensation values in advance that are then applied to correct the TOA measurements, thereby eliminating drift errors before they affect location accuracy.
Data Source
AI summary
A passive geo-location method for determining the location of a wireless device. The method includes receiving, by a measuring receiver at a first position, a first beacon transmitted to the measuring receiver by the wireless device, and receiving, by the measuring receiver at a second position, a second beacon transmitted to the measuring receiver by the wireless device. When the first position differs from the second position by less than a predetermined distance, the method further includes determining a relative drift between a clock associated with the wireless device and a clock associated with the measuring receiver, and determining a location of the wireless device based at least on the determined relative drift.