Wi-Fi Positioning System Using Leakage Signal Delay Cancellation
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Solution Overview
Problem
Wi-Fi based positioning solutions using measured time-of-flight signals have limited accuracy due to delays in AP functioning and internal latencies, affecting the precision of indoor positioning.
Innovation Solution
A method and system utilizing multiple WLAN devices to measure distances with high accuracy by canceling internal delays, employing a Wi-Fi radar capability to detect location and movements, and using fine timing measurement protocols to estimate the location of Wi-Fi enabled devices without the need for timing synchronization between transmitter and receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Wi-Fi based positioning uses measured time-of-flight signals, then positioning function is achieved, but positioning accuracy is limited due to internal delays
Solution Approach 1:
The system uses a feedback mechanism where the target device sends back an acknowledgment signal that allows the initiating device to calculate the time of flight. By measuring the round-trip time and subtracting the known processing delay at the target device, the system compensates for internal delays and achieves accurate distance measurement.
Solution Approach 2:
Each device measures its own internal processing delay by detecting leakage signals from its own transmitter through its receiver. This self-measured delay information is then used to compensate for internal delays in the time of flight calculation, enabling accurate positioning without requiring external calibration.
2Reliability
If multiple WLAN devices are used for positioning, then positioning reliability is improved, but system complexity increases
Solution Approach 1:
The positioning function is segmented into multiple independent device pairs, where each pair independently measures distance using the time of flight method. The final position is determined by combining measurements from multiple pairs, which improves reliability through redundancy while keeping each individual measurement process simple and standardized.
Solution Approach 2:
The same time of flight measurement protocol is used universally across all WLAN device pairs in the system. This multi-functional approach allows any device to serve as both initiator and target, simplifying the overall system architecture while improving reliability through multiple measurement opportunities.
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
The system achieves accurate positioning with an accuracy of several centimeters by removing internal device-related delays and utilizing Wi-Fi radar sensing to improve positioning reliability, especially for moving targets, and can perform both positioning and radar sensing simultaneously.
Implementation Method 1
calculating a first time difference between a time the second WLAN signal was sent and a time the first leakage signal was detected, (e) calculating a second time difference between a time the first WLAN signal was sent and a time the second leakage signal was detected, and (f) subtracting the second time difference from the first time difference to obtain a time-of-flight that corresponds to the distance
Data Source
AI summary
A method for estimating a location of a target Wireless Local-Area Network (WLAN) device includes obtaining relative locations of three or more WLAN devices. Respective distances are measured between each of the WLAN devices and the target WLAN device. The location of the target WLAN device is estimated based on the locations of the WLAN devices and on the measured distances, wherein measuring a distance between a WLAN device and the target WLAN device includes: exchanging WLAN signals, detecting a first leakage signal by a receiver of the WLAN device, detecting a second leakage signal by the receiver of the target WLAN device, calculating time differences between a time a WLAN signal was sent and a time a leakage signal was detected, and subtracting the time differences one from the other to obtain a time-of-flight that corresponds to the distance between the WLAN device and the target WLAN device.