AP Direct-Path Timestamping for Multipath Distance Measurement
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Solution Overview
Problem
In large-scale indoor wireless networks, traditional methods for determining the distance between access points (APs) using Fine Timing Measurement (FTM) protocol are inaccurate due to obstructions causing multipath signal propagation, leading to erroneous distance estimations and challenging timestamping tasks.
Innovation Solution
A method and system for classifying AP pairs as Line-of-Sight (LoS) or Non-Line-of-Sight (NLoS) using channel diversity and dynamically tuning timestamping parameters, such as search window and threshold values, to accurately timestamp direct wireless path signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional FTM protocol is used for distance measurement, then distance estimation can be performed, but measurement precision deteriorates due to multipath signal propagation caused by obstructions
Solution Approach 1:
The patent segments the received signal into multiple components corresponding to different propagation paths (direct path, reflected paths, diffracted paths). By identifying and isolating the direct path signal component from the multipath components, the system can timestamp only the direct path signal, thereby eliminating the harmful effects of multipath propagation on distance measurement accuracy.
Solution Approach 2:
The patent introduces an intermediary processing stage that analyzes the received signal to identify characteristics of direct path versus multipath signals. This intermediary analysis enables the system to distinguish and select the direct path signal for timestamping, resolving the contradiction between performing distance measurement and avoiding multipath interference.
2Measurement precision
If signal timestamping is performed without distinguishing path types, then timestamping can be completed, but position determination accuracy deteriorates due to inclusion of non-direct path signals
Solution Approach 1:
The patent employs dynamic threshold adjustment and adaptive parameter selection based on the received signal characteristics. The system dynamically identifies signal peaks, adjusts search windows, and selects appropriate timestamping parameters based on the detected signal environment, enabling accurate direct path signal identification without requiring overly complex fixed-rule systems.
Solution Approach 2:
The system performs self-service by automatically analyzing the received signal to identify direct path components without requiring external intervention or manual configuration. The timestamping mechanism uses the signal's own characteristics (arrival time, strength, propagation path indicators) to determine which components to timestamp, making the system self-sufficient in resolving the accuracy-complexity contradiction.
3Ease of operation
If APs are mounted on ceilings facing downward for client coverage, then client connectivity is improved, but direct wireless path signals between APs become difficult to obtain
Solution Approach 1:
The patent makes the AP serve multiple functions: it maintains its primary function of providing downward client coverage while simultaneously performing bidirectional communication with other APs for location determination. The system processes signals from multiple directions and uses signal analysis to identify direct path components regardless of AP orientation, enabling the same infrastructure to serve both client connectivity and precise location measurement purposes.
Solution Approach 2:
The patent changes the approach from relying on physical AP orientation to achieving direct path signals, instead using signal parameter analysis (arrival time, strength, propagation characteristics) to identify direct path components. This parameter-based identification method works regardless of how the APs are physically mounted or oriented, resolving the contradiction between optimal client coverage orientation and direct path signal detection.
Data Source
AI summary
An example method and an access point to timestamp a direct wireless path signal are presented. In an example method, a first AP receives a plurality of signals from a second AP and records a signal strength value and a time of arrival corresponding to each of the plurality of signals. Further, the first AP identifies one or more peak signal strength values in a search window preceding a highest signal strength value from the signal strength values. The first AP then selects a timestamp at a rising edge of an earliest peak greater than a threshold value as a time of arrival of the direct wireless path signal. Also, methods of dynamically tuning timestamping parameters, such as a search window and a threshold value are presented.