Wi-Fi Ranging Accuracy via Multi-Path Interference Filtering

Solution Overview

Problem

Wi-Fi ranging using the IEEE 802.11mc standard is unreliable due to multi-path interference, which introduces noise into round trip time (RTT) measurements, leading to inaccurate distance estimates.

Innovation Solution

A method that involves receiving fine time measurement (FTM) messages, extracting channel state information (CSI), determining the probability of multi-path interference using a channel condition classifier, and discarding FTM messages if the probability exceeds a threshold, thereby improving the accuracy of RTT measurements and distance calculations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If FTM messages are used for Wi-Fi ranging, then distance measurement capability is provided, but measurement precision deteriorates due to multi-path interference

Engineering Contradiction:

ImproveRTT measurement accuracyVSAvoidmulti-path interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and removes FTM messages identified as being affected by multi-path interference from the set of measurements used for RTT calculation. By separating out the corrupted measurements, the system preserves only the reliable line-of-sight measurements for distance calculation, thereby improving measurement precision while eliminating the harmful effect of multi-path interference.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent implements a feedback mechanism where the system evaluates the quality of each FTM message (likely through signal strength, consistency checks, or multi-path detection algorithms) and uses this information to determine whether to include or exclude the message from RTT calculations. This feedback loop allows the system to adaptively filter out measurements degraded by multi-path interference, resolving the contradiction between maintaining measurement capability and ensuring measurement precision.

Inventive Principle:

Principle #23Feedback

2Productivity

If all FTM messages are processed, then productivity is improved, but reliability deteriorates due to inclusion of noisy multi-path messages

Engineering Contradiction:

Improveranging operation speedVSAvoiddistance estimation accuracy

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent extracts and removes FTM messages identified as being affected by multi-path interference from the set of measurements used for RTT calculation. By separating out the corrupted measurements, the system preserves only the reliable line-of-sight measurements for distance calculation, thereby improving measurement precision while eliminating the harmful effect of multi-path interference.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the parameter of measurement selection from including all FTM messages to selectively including only those messages that meet quality criteria. By adjusting the selection parameters (such as signal strength thresholds, consistency requirements, or multi-path detection metrics), the system maintains high productivity by processing multiple messages while ensuring reliability by excluding noisy measurements from the final calculation.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12127157B2Methods, systems, and non-transitory mediums for augmented fine time measurement

Publication Date: 2024.10.22 TOYOTA JIDOSHA KK

AI summary

A method for measuring a distance is provided. The method includes receiving a fine time measurement (FTM) message, extracting channel state information (CSI) from the FTM message, determining with a channel condition classifier a probability that the FTM message is multi-path based on the corresponding CSI, and discarding the FTM message in response to the probability that the FTM message is multi-path is above a threshold level of probability.