Acoustic Com
359
Part B | 15
15. Acoustic Communication
Milica Stojanovic, Pierre-Philippe J. Beaujean
In this chapter, we discuss acoustic communication methods which are used to provide
wireless connection between remote nodes operating in an underwater environment. We begin
with an introductory overview of the history
of acoustic communication, and an outline of
current and emerging applications. We then
provide a summary of communication channel
characteristics, with an eye towards acoustic propagation mechanisms and the ways in
which they differ from radio propagation. The
main focus of our treatment is on two major aspects of communication system design:
the physical link and the networking functions.
On the physical link level, we discuss noncoherent and coherent modulation/detection
methods, paying attention to both single-carrier
modulation and multicarrier broadband techniques. Specifically, we discuss signal processing
methods for synchronization, equalization, and
multichannel (transmit and receive) combining.
On the networking level, we discuss protocols
for channel sharing using both deterministic division of resources (frequency, time, and
code-division multiple access) and random access, and we also overview recent results on
routing for peer-to-peer acoustic networks. We
conclude with an outline of topics for future
research.
15.1 A Brief History ..................................... 360
15.2 Current and Emerging
Modem Applications ............................ 360
15.3 Existing Technology ............................. 361
15.3.1 System Requirements ................ 361
15.3.2 Commercially Available Modems . 362
15.3.3 Field Tests................................. 363
15.4 Propagation Channel ........................... 364
15.4.1 Attenuation and Noise............... 364
15.4.2 Multipath Propagation ............... 365
15.4.3 Time Variability:
Motion-Induced
Doppler Distortion ..................... 369
15.4.4 Time Variability:
Random Effects (Fading) ............ 370
15.4.5 System Constraints..................... 372
15.5 Point-to-Point Links:
Signal Processing ................................. 374
15.5.1 Noncoherent
Modulation/Detection ................ 374
15.5.2 Coherent Modulation/Detection .. 375
15.5.3 Data Link Reliability................... 378
15.5.4 Turbo Equalization .................... 378
15.5.5 Adapting to the Environment ..... 379
15.5.6 Networks .................................. 379
15.5.7 Channel Sharing........................ 381
15.5.8 Routing
and Cross-Layer Integration ....... 382
15.6 Future Trends ...................................... 383
References................................................... 383
Wireless transmission of signals underwater over distances in excess of a 100 m relies almost exclusively
on acoustic waves. Radio waves do not propagate well
underwater, except at low frequencies and over extremely short distances (a few meters at 10 kHz) [15.1].
Optical signals, which are best used in the blue–
green region (around 500 nm), also suffer from attenuation and do not propagate beyond about 100 m,
although they do offer high bandwidths (on the order of MHz) [15.2]. Hence, sound is used for wireless transmission over anything but very short distances. Sound propagates as a pressure wave, and it
can thus easily travel over kilometers, or even hundreds of kilometers, but to cover a longer distance,
a lower frequency has to be used. In general, acoustic communications are confined to bandwidths that are
low compared to those used for terrestrial radio communications. Acoustic modems that are in use today
typically operate in bandwidths on the order of a few
kHz, at a comparably low center frequency (5 centered at 10 kHz) [15.3]. While such frequencies will
cover distances on the order of a kilometer, acoustic frequencies in the 100 kHz region can be used for
shorter distances, while frequencies below a kHz are
used for longer distances. Underwater acoustic communication over basin scales (several thousand kilometers) can be established in a single hop as well;
however, the attendant bandwidth will be only on the
359
Part B | 15
15. Acoustic Communication
Milica Stojanovic, Pierre-Philippe J. Beaujean
In this chapter, we discuss acoustic communication methods which are used to provide
wireless connection between remote nodes operating in an underwater environment. We begin
with an introductory overview of the history
of acoustic communication, and an outline of
current and emerging applications. We then
provide a summary of communication channel
characteristics, with an eye towards acoustic propagation mechanisms and the ways in
which they differ from radio propagation. The
main focus of our treatment is on two major aspects of communication system design:
the physical link and the networking functions.
On the physical link level, we discuss noncoherent and coherent modulation/detection
methods, paying attention to both single-carrier
modulation and multicarrier broadband techniques. Specifically, we discuss signal processing
methods for synchronization, equalization, and
multichannel (transmit and receive) combining.
On the networking level, we discuss protocols
for channel sharing using both deterministic division of resources (frequency, time, and
code-division multiple access) and random access, and we also overview recent results on
routing for peer-to-peer acoustic networks. We
conclude with an outline of topics for future
research.
15.1 A Brief History ..................................... 360
15.2 Current and Emerging
Modem Applications ............................ 360
15.3 Existing Technology ............................. 361
15.3.1 System Requirements ................ 361
15.3.2 Commercially Available Modems . 362
15.3.3 Field Tests................................. 363
15.4 Propagation Channel ........................... 364
15.4.1 Attenuation and Noise............... 364
15.4.2 Multipath Propagation ............... 365
15.4.3 Time Variability:
Motion-Induced
Doppler Distortion ..................... 369
15.4.4 Time Variability:
Random Effects (Fading) ............ 370
15.4.5 System Constraints..................... 372
15.5 Point-to-Point Links:
Signal Processing ................................. 374
15.5.1 Noncoherent
Modulation/Detection ................ 374
15.5.2 Coherent Modulation/Detection .. 375
15.5.3 Data Link Reliability................... 378
15.5.4 Turbo Equalization .................... 378
15.5.5 Adapting to the Environment ..... 379
15.5.6 Networks .................................. 379
15.5.7 Channel Sharing........................ 381
15.5.8 Routing
and Cross-Layer Integration ....... 382
15.6 Future Trends ...................................... 383
References................................................... 383
Wireless transmission of signals underwater over distances in excess of a 100 m relies almost exclusively
on acoustic waves. Radio waves do not propagate well
underwater, except at low frequencies and over extremely short distances (a few meters at 10 kHz) [15.1].
Optical signals, which are best used in the blue–
green region (around 500 nm), also suffer from attenuation and do not propagate beyond about 100 m,
although they do offer high bandwidths (on the order of MHz) [15.2]. Hence, sound is used for wireless transmission over anything but very short distances. Sound propagates as a pressure wave, and it
can thus easily travel over kilometers, or even hundreds of kilometers, but to cover a longer distance,
a lower frequency has to be used. In general, acoustic communications are confined to bandwidths that are
low compared to those used for terrestrial radio communications. Acoustic modems that are in use today
typically operate in bandwidths on the order of a few
kHz, at a comparably low center frequency (5 centered at 10 kHz) [15.3]. While such frequencies will
cover distances on the order of a kilometer, acoustic frequencies in the 100 kHz region can be used for
shorter distances, while frequencies below a kHz are
used for longer distances. Underwater acoustic communication over basin scales (several thousand kilometers) can be established in a single hop as well;
however, the attendant bandwidth will be only on the