Program Book - Oceans'10 IEEE Sydney

T07: Underwater Communications
Dr Milica Stojanovic & Lee Freitag
Time: 0830 – 1200
Room: Bayside 104
Wireless information transmission is an
enabling technology for the
development of future oceanobservation
systems, whose
applications range from marine biology
to oil industry, and involve the
emerging concepts of cooperating
autonomous vehicles and ad-hoc
deployable sensor networks.
Communication between such devices
often relies on transmission of acoustic
waves, since electro-magnetic waves
propagate only over very short
distances underwater. However,
acoustic signals are confined to low
frequencies (usually no more than
several tens of kHz) making the
available bandwidth extremely limited.
Within a constrained bandwidth, acoustic communications are
governed by propagation that occurs over multiple paths and at
low speed (nominally 1500 m/s). Delay spreading over tens or
even hundreds of milliseconds results in a frequency-selective
signal distortion, while motion creates an extreme Doppler
effect. The worst properties of radio channels—poor link quality
of a mobile terrestrial channel, and long delay of a satellite
channel—thus appear combined in an underwater acoustic
channel, which is generally recognized as one of the most
difficult communication media in use today.
The quest for high rate communications over these channels is
tightly coupled with the use of bandwidth-efficient modulation
methods and signal processing solutions that can counteract
the channel distortions. Since the early 90‘s, when adaptive
equalization was employed to demonstrate the feasibility of
phase-coherent detection underwater, research has yielded
innovative signal processing solutions, as well as the first
networking concepts for underwater acoustic systems.
This lecture offers a top-level overview of the basic concepts of
acoustic communications:
• Channel characteristics: attenuation, noise, multipath and
Doppler spreading
• Modulation/detection: single-carrier and multi-carrier (OFDM)
broadband methods; equalization, synchronizations, diversity
combining; multi-input multi-output (MIMO) communication
• Networking: topology/architecture selection, resource
allocation
• Multiple access and channel sharing: deterministic (e.g.,
TDMA/CDMA) and random (MAC, routing).
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