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A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz, Jan Heitmann and Christian Renner 17th GI/ITG KuVS Fachgesprch "Sensornetze", Braunschweig September 13 th , 2018 Research Group

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SLIDE 1

A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters

Fabian Steinmetz, Jan Heitmann and Christian Renner

17th GI/ITG KuVS Fachgespräch "Sensornetze", Braunschweig

September 13th, 2018

TUHH TUHH

Research Group smartPORT Research Group smartPORT Hamburg University of Technology Hamburg University of Technology

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SLIDE 2

Motivation

Micro autonomous underwater vehicles (µAUVs) and underwater

wireless sensor networks (UWSNs)

Possible applications

  • Localization of pollution
  • Tracking and inspection of ships

µAUVs and UWSNs need a stable and low-power

communication interface

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 1 1

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SLIDE 3

Underwater Channel (I)

Acoustic wave

⇒ speed of sound c ≈ 1500 m/s

Reflections and scattering

⇒ frequency-selective and time-dependent channel

Shallow water scenarios

⇒ high impact of the surface reflection

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 2 2

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SLIDE 4

Underwater Channel II

1 s band-limited pseudo-random noise 10 kHz - 100 kHz Strong frequency dependency

25 50 75 100 20 40 60 80

frequency (kHz) amplitude (mV)

Transmitted Noise

25 50 75 100 20 40 60 80

frequency (kHz) amplitude (mV)

2.1 m Channel

25 50 75 100 20 40 60 80

frequency (kHz) amplitude (mV)

5.1 m Channel

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 3 3

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SLIDE 5

smartPORT Acoustic Underwater Modem

Small and low-power device Contains of:

  • Mainboard with power supply and

Cortex M4 microcontroller

  • Receiver with amplifiers, band-pass

filter and AD-converter

  • Transmitter with DA-converter and

power-amplifier

  • External hydrophone

Frequency Shift Keying (FSK) based

synchronization and data transmission

Range up to 150 m and data rate

260 bit/s

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 4 4

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SLIDE 6

FSK and Chirp Keying

Frequency Shift Keying (FSK)

  • A bit is transmitted with a constant frequency
  • Non-coherent detection (currently implemented)
  • Problem: synchronization

Chirp Keying

  • Frequency sweep from fs to fe

◮ fs < fe ⇒ up-chirp ◮ fs > fe ⇒ down-chirp

  • Bandwidth B = |fe − fs|
  • Spread the information over spectrum
  • Cross-correlation detection
  • Good correlation properties

0.5 1

  • 1

1

t/T → s(t)

Up-Chirp

0.5 1

  • 1

1

t/T → s(t)

Down-Chirp

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 5 5

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SLIDE 7

FSK and Chirp Keying - Comparison

1 2 3 4

  • 2
  • 1

1 2

t/T

FSK Non-Coherent

1 2 3 4

  • 2
  • 1

1 2

t/T

FSK Cross-Correlation

1 2 3 4

  • 2
  • 1

1 2

t/T

Chirp Cross-Correlation

1 2 3 4 0.5 1

t/T

1 2 3 4

  • 1

1

t/T

1 2 3 4

  • 1

1

t/T

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 6 6

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SLIDE 8

FSK and Chirp Keying - Comparison

1 2 3 4

  • 2
  • 1

1 2

t/T

FSK Non-Coherent

1 2 3 4

  • 2
  • 1

1 2

t/T

FSK Cross-Correlation

1 2 3 4

  • 2
  • 1

1 2

t/T

Chirp Cross-Correlation

1 2 3 4 0.5 1

t/T

1 2 3 4

  • 1

1

t/T

1 2 3 4

  • 1

1

t/T

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 6 6

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SLIDE 9

FSK and Chirp Keying - Comparison

1 2 3 4

  • 2
  • 1

1 2

t/T

FSK Non-Coherent

1 2 3 4

  • 2
  • 1

1 2

t/T

FSK Cross-Correlation

1 2 3 4

  • 2
  • 1

1 2

t/T

Chirp Cross-Correlation

1 2 3 4 0.5 1

t/T

1 2 3 4

  • 1

1

t/T

1 2 3 4

  • 1

1

t/T

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 6 6

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SLIDE 10

FSK and Chirp Keying - Comparison

1 2 3 4

  • 2
  • 1

1 2

t/T

FSK Non-Coherent

1 2 3 4

  • 2
  • 1

1 2

t/T

FSK Cross-Correlation

1 2 3 4

  • 2
  • 1

1 2

t/T

Chirp Cross-Correlation

1 2 3 4 0.5 1

t/T

1 2 3 4

  • 1

1

t/T

1 2 3 4

  • 1

1

t/T

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 6 6

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SLIDE 11

Preamble Based Synchronization

Packet-based transmission Preamble and starting frame delimiter (SFD)

before each data-packet

Preamble with alternating symbols

  • Up- and down-chirps
  • Sinusoidal symbols with two frequencies

Previous evaluations: Good sync ⇒ correct

data reception

Parameter Settings:

  • Orthogonal symbols with T = 2.5 ms
  • Chirp bandwidth B = 2.342 kHz
  • FSK with 400 Hz symbol spacing
  • 16 preamble symbols + 4 SFD symbols

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 7 7

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SLIDE 12

Experimental Setup

Signal generation and processing with

MATLAB

USB oscilloscope and waveform generator Low sampling rate (200 kHz) RX and TX circuits Marina in Hamburg with LOS conditions long wide-band chirp (10 kHz to 100 kHz,

100 ms) to obtain a ground-truth

2.1 m and 5.1 m distance, 0.5 m depth

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 8 8

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SLIDE 13

Synchronization Macroscope

100 synchronizations per frequency band

  • ver 5.1 m

40 kHz - 90 kHz in 2 kHz steps

−500 −250 250 500 40 50 60 70 80 90

synchronization error (µs) frequency (kHz)

FSK Non-Coherent

5 10 15 20 25

relative freq. (%)

−500 −250 250 500 40 50 60 70 80 90

synchronization error (µs) frequency (kHz)

FSK Cross-Correlation

5 10 15 20 25

relative freq. (%)

−500 −250 250 500 40 50 60 70 80 90

synchronization error (µs) frequency (kHz)

Chirp Cross-Correlation

5 10 15 20 25

relative freq. (%)

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 9 9

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SLIDE 14

Synchronization Microscope (I)

1000 synchronizations over 2.1 m and 5.1 m Fixed frequencies

  • Chirp: 62.4 kHz - 64.8 kHz
  • FSK: 62.4 kHz and 62.8 kHz

−250 250 2 4 6 8 10

synchronization error (µs) relative freq. (%)

FSK Non-Coherent

20 40 60 80 100

CDF (%)

FSK Non-Coherent

−250 250 2 4 6 8 10

synchronization error (µs) relative freq. (%)

FSK Cross-Correlation

20 40 60 80 100

CDF (%)

FSK Cross-Correlation

−250 250 2 4 6 8 10

synchronization error (µs) relative freq. (%)

Chirp Cross-Correlation

20 40 60 80 100

CDF (%)

Chirp Cross-Correlation

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 10 10

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SLIDE 15

Synchronization Microscope (II)

FSK non-coh FSK xcorr Chirp xcorr 2.1 m Channel Inside 10 % margin 72.8 % 77.9 % 91.6 % Average sync. error 137.1 µs 122.2 µs 120.1 µs Standard deviation 77.2 µs 76.7 µs 73.6 µs 5.1 m Channel Inside 10 % margin 76.7 % 72.3 % 100 % Average sync. error 74.7 µs 62.3 µs 50.5 µs Standard deviation 87.7 µs 70.6 µs 48.7 µs

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 11 11

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SLIDE 16

Conclusion and Outlook

A chirp-based synchronization enhances:

  • The number of received synchronizations

72 % ⇒ 100 %

  • The accuracy

71 µs ⇒ 49 µs (standard deviation)

  • The precision

62 µs ⇒ 51 µs (average sync. error)

Outlook:

  • smartPORT modem implementation
  • Chirps with a larger bandwidth
  • Research on chirp-based data transmission

Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters Fabian Steinmetz A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters 12 12

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SLIDE 17

A Case for Chirp Modulation for Low-Power Acoustic Communication in Shallow Waters

Fabian Steinmetz, Jan Heitmann and Christian Renner

17th GI/ITG KuVS Fachgespräch "Sensornetze", Braunschweig

September 13th, 2018

TUHH TUHH

Research Group smartPORT Research Group smartPORT Hamburg University of Technology Hamburg University of Technology Fabian Steinmetz

PhD Student at Research Group smartPORT Phone +49 / (0)40 42878 4887 e-Mail fabian.steinmetz@tuhh.de http://www.tuhh.de/smartport