Monash University AUSTRALIA 1A Real Time DSP Sonar Echo Processor - IROS’2000

A Real Time DSP Sonar EchoProcessor#

by

Andrew Heale and Lindsay Kleeman

Intelligent Robotics Research Centre

Department of Electrical and Computer Systems Engineering

Monash University, Victoria, AUSTRALIA

www.ecse.monash.edu.au/centres/IRRC

# Funded by an Australian Research Council Large Grant

Monash University AUSTRALIA 2A Real Time DSP Sonar Echo Processor - IROS’2000

Contents

u Introduction

u Processing

u Results

u Conclusions

Monash University AUSTRALIA 3A Real Time DSP Sonar Echo Processor - IROS’2000

Introduction

u Robot systems are often sensor bound:– eg map building, localisation, obstacle avoidance

are limited by sensors, not algorithms

– require reliable, fast, accurate cheap sensing.

u Sonar has been seen as unreliable, inaccurate.– eg Polaroid ranging module is a poor angle sensor

u DSPs allow sonar echo real time processingwith more accurate range/bearing than laserrange finders.

Monash University AUSTRALIA 4A Real Time DSP Sonar Echo Processor - IROS’2000

Introduction (continued)

u This paper introduces a new DSP sonarsensor that achieves optimal signalprocessing at near real time rates.

u Sensor reports range and bearing to targetsto 5.4 m at 27 Hz.– Speed of sound alone imposes a limit of 30 Hz.

u Bearing and ranges errors are dominated byair conditions - typical still air gives:– 0.1 degrees, 0.2 mm error standard deviations.

Monash University AUSTRALIA 5A Real Time DSP Sonar Echo Processor - IROS’2000

DSP Sonar System

DSP Sonar system

T T

R R

Werrimbi

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Custom Built Receiver

u 1MHzsampling on2 channels

u All in one box– reduces noise levels

u Fast processing by DSP

33MHz AD2181 DSP

+ ROM

LPF + 12 bit ADCs

High speed buffered UART

300 V FETTransmitter

Drive Circuit

Gain

PC

T

R1

R2

Monash University AUSTRALIA 7A Real Time DSP Sonar Echo Processor - IROS’2000

Overview of DSP Processing

u On the fly pulse extraction

u Template matching– parabolic interpolation for sub sample

estimation

u Correspondence

u Triangulation

Monash University AUSTRALIA 8A Real Time DSP Sonar Echo Processor - IROS’2000

Example of a Receiver Signal

Monash University AUSTRALIA 9A Real Time DSP Sonar Echo Processor - IROS’2000

Apply threshold = multiple of standarddeviation of noise.

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Remove inter-pulse signal below thresholdfor at least 30 samples before and after pulses.

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Summary of thresholding with pre andpost triggering

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Pulse Splitting - based on signal peaksthat are clear of surrounding peaks.

Monash University AUSTRALIA 13A Real Time DSP Sonar Echo Processor - IROS’2000

Template Matching

u Templates are pre-computed echo pulseshapes used in the arrival time estimation.

u Shape depends on arrival angle and range.

u This dependency has been accuratelymodelled - see [Kleeman&Kuc IJRR 1995]

u Thus the template set can be generated froma measured echo at normal incidence at 1m.

Monash University AUSTRALIA 14A Real Time DSP Sonar Echo Processor - IROS’2000

Template shape varies withangle to transducer

0 deg 2 deg 4 deg6 deg

8 deg 10 deg 12 deg 14 deg

Transducer

Monash University AUSTRALIA 15A Real Time DSP Sonar Echo Processor - IROS’2000

Templates shifted to best match the pulses using correlationof the template with the pulse. Shape (not amplitude) are matched by a correlation.

Template Matching

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Receiver Data Association

u Left and right receiver arrival times areassociated based on:– arrival times consistent with small receiver

spacing

– amplitudes matched

– correlation coefficients > 95%

Monash University AUSTRALIA 18A Real Time DSP Sonar Echo Processor - IROS’2000

Door jamb experiment

Reported sensor readings

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MappingExperiment Sonar features from

moving sensor

Mouldings

RobotPositions

Wall

Mouldings

Door jamb

Monash University AUSTRALIA 20A Real Time DSP Sonar Echo Processor - IROS’2000

Fused Targets

Raw target data in closeproximity is fused basedon a weighted average.

Weights are determinedby amplitude andcorrelation values.

Monash University AUSTRALIA 21A Real Time DSP Sonar Echo Processor - IROS’2000

Conclusions and Future Work

u DSP sonar implementation allows:– local processing obviating high speed data

communications

– real time processing is achieved

– portability.

u Futher work:– real time on the fly target classification.

– interference rejection with double pulse coding(presented ACRA 2000, Melbourne Australia).

– Real time SLAM.