Ultrasonic Locationing via Phase Difference Correlation

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Solution Overview

Problem

Ultrasonic locationing systems face challenges due to acoustic reverberations and noise interference, which affect the accuracy of time difference of arrival (TDOA) measurements, especially with closely spaced microphones, leading to incorrect location calculations.

Innovation Solution

The system derives two frequencies from the ultrasonic burst and correlates the phase difference between them to improve TDOA accuracy, using band pass filters and digital multipliers to enhance correlation strength and immunity to noise, allowing for precise locationing with microphones as close as one foot apart.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a high Q receiver is used to reject acoustic noise, then noise rejection is improved, but amplifier response time increases resulting in poor correlation margin

Engineering Contradiction:

Improveacoustic noise rejectionVSAvoidcorrelation margin

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent segments the ultrasonic burst into multiple individual cycles, treating each cycle as a separate correlation input. This allows the system to process multiple correlated signals from the same burst, effectively utilizing the narrow bandwidth receiver while maintaining adequate correlation margin through the aggregation of multiple measurement opportunities.

Inventive Principle:

Principle #1Segmentation

2Object-generated harmful factors

If a very short burst width is used to avoid multipath reflections, then multipath interference is reduced, but the signal becomes more susceptible to noise

Engineering Contradiction:

Improvemultipath reflection interferenceVSAvoidnoise susceptibility

Core Design Contradiction:

Object-generated harmful factorsVSObject-affected harmful factors

Solution Approach 1:

The patent merges multiple individual cycle correlations into a single composite TDOA measurement. By combining the correlation results from multiple cycles within the same ultrasonic burst, the system achieves noise reduction through signal averaging while maintaining the short burst width necessary to avoid multipath reflections.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The system uses the correlation results from individual cycles as feedback to determine the optimal TDOA measurement. By analyzing the correlation peaks from multiple cycles and selecting or averaging the best results, the system achieves robust noise rejection while maintaining immunity to multipath interference.

Inventive Principle:

Principle #23Feedback

3Length of stationary object

If microphones are spaced less than one foot apart, then device size is reduced, but TDOA measurement accuracy deteriorates due to poor correlation margin

Engineering Contradiction:

Improvemicrophone spacingVSAvoidTDOA measurement accuracy

Core Design Contradiction:

Length of stationary objectVSMeasurement precision

Solution Approach 1:

The patent ensures continuous useful action by utilizing every cycle of the ultrasonic burst for correlation measurements. Instead of relying on a single correlation opportunity, the system continuously processes multiple cycles, ensuring that adequate measurement data is accumulated even with closely spaced microphones that produce small TDOA differences.

Inventive Principle:

Principle #20Continuity of useful action

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

This approach significantly increases the margin between correct and adjacent correlation peaks, providing accurate TDOA measurements and improved locationing accuracy, even in noisy environments, and offers immunity to multipath signals and noise interference.

Implementation Method 1

The ultrasonic emitter can transmit ultrasonic energy in a short burst which can be received by an ultrasonic transducer (microphone)

Methodology Applied

Scientific EffectUltrasonic emission: Ultrasound

Implementation Method 2

derives two frequencies from the ultrasonic burst and correlates the phase difference between them to improve TDOA accuracy

Methodology Applied

Scientific EffectPhase difference correlation:

Data Source

PatentUS9151826B2Locationing via phase difference correlation between two frequency pulses derived from a single frequency emitter ultrasonic burst

Publication Date: 2015.10.06 SYMBOL TECHNOLOGIES LLC

AI summary

Ultrasonic locationing of a tag with an emitter transducer operable to emit a single frequency ultrasonic burst. A receiver with at least two microphones is operable to receive the ultrasonic burst. Each microphone receiver contains two narrowband filters to extract frequencies above and below the ultrasonic burst frequency. A processor derives a low frequency waveform indicative of the phase difference between the dual frequency pulses coming from each microphone receiver. A correlator then determines the time difference of arrival (TDOA) between each microphone receiver by correlating the phase difference waveforms. This invention enables the creation of an ultrasonic locationing system requiring microsecond accuracy on TDOA data, as is necessary with microphone spacing of less than one foot, while using a simple single high frequency emitter source.