Turn-Around Calibration Factor Estimation for WLAN Positioning
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Solution Overview
Problem
Legacy wireless stations (STAs) lack the capability to perform Fine Timing Measurement (FTM) procedures, relying on non-FTM procedures for RTT measurements, which require knowledge of the access point's turn-around calibration factor (TCF), leading to inaccuracies in position determination due to unknown delays.
Innovation Solution
Implement a method where wireless stations perform both FTM and non-FTM procedures to calculate a TCF estimate, with the FTM procedure providing accurate RTT measurements and the non-FTM procedure accounting for delays, allowing for the calculation of TCF, which is then sent to a server for aggregation and distribution to legacy STAs for accurate RTT measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If non-FTM procedure is used for RTT measurement, then legacy STAs can perform positioning, but measurement accuracy deteriorates due to unknown TCF
Solution Approach 1:
The patent introduces FTM-capable STAs as intermediaries that measure the TCF by performing both FTM and non-FTM procedures, then report the measured TCF to the server. This mediator approach allows legacy STAs to benefit from accurate TCF values without requiring them to perform FTM procedures themselves.
Solution Approach 2:
The system implements a feedback mechanism where TCF measurements obtained by FTM-capable STAs are reported to the server, which then distributes these TCF values to legacy STAs. This feedback loop enables continuous improvement of positioning accuracy for legacy devices based on real-world measurements from capable devices.
2Measurement precision
If FTM procedure is used for RTT measurement, then measurement accuracy improves, but legacy STAs cannot perform positioning
Solution Approach 1:
The patent creates a copy of the TCF measurement capability by having FTM-capable STAs perform the measurements and report results to a server. Legacy STAs then obtain TCF values through this copied mechanism without needing to implement FTM hardware or software themselves.
Solution Approach 2:
The server acts as an intermediary that collects TCF measurements from FTM-capable STAs and distributes them to legacy STAs. This intermediary mechanism bridges the capability gap between different STA types, allowing legacy devices to access accurate TCF values without direct FTM capability.
3Ease of operation
If TCF is unknown, then non-FTM RTT measurements can be performed, but positioning accuracy deteriorates
Solution Approach 1:
The system performs preliminary TCF measurement actions by FTM-capable STAs before legacy STAs perform their non-FTM RTT measurements. The TCF values are pre-measured and stored in the server, so when legacy STAs need positioning, they can retrieve accurate TCF values without having to measure them themselves.
Solution Approach 2:
FTM-capable STAs perform self-service by autonomously measuring TCF values and reporting them to the server. This self-service mechanism eliminates the need for manual TCF configuration or complex calibration procedures, allowing the system to automatically maintain accurate TCF values for use by legacy STAs.
Data Source
AI summary
In one aspect, a method includes performing, by a wireless station, a fine timing measurement (FTM) procedure that includes exchanging one or more FTM messages between the wireless station and an access point to obtain a first round-trip time (RTT) between the wireless station and the access point. The method also includes performing, by the wireless station, a non-FTM procedure to obtain a second RTT between the wireless station and the access point. The wireless station then calculates a turn-around calibration factor (TCF) estimate of the access point based on a difference between the second RTT and the first RTT. Data representative of the TCF estimate of the access point may then be sent to a server.