31-05-2012, 02:07 PM
Overview of Networking Protocols for Underwater Wireless Communications
[attachment=23700]
INTRODUCTION
Underwater wireless communications can enable
many civilian and military applications such as
oceanographic data collection, scientific ocean
sampling, pollution and environmental monitoring,
climate recording, offshore exploration, disaster
prevention, assisted navigation, distributed
tactical surveillance, and mine reconnaissance.
Some of these applications can be supported by
underwater acoustic sensor networks (UWASNs)
[1], which consist of devices with sensing,
processing, and communication capabilities that
are deployed to perform collaborative monitoring
tasks (Fig. 1). Wireless signal transmission is
also crucial to remotely control instruments in
ocean observatories and to enable coordination
of swarms of autonomous underwater vehicles
(AUVs) and robots, which will play the role of
mobile nodes in future ocean observation networks
by virtue of their flexibility and reconfigurability.
MEDIUM ACCESS CONTROL PROTOCOLS
Due to the unique characteristics of the propagation
of acoustic waves in the underwater environment,
existing terrestrial MAC solutions are
unsuitable for this environment. Channel access
control in wireless underwater networks, in fact,
poses additional challenges due to the limited
bandwidth, very high and variable propagation
delays, high bit error rates, temporary losses of
connectivity, channel asymmetry, and heavy multipath
and fading phenomena. Current underwater
MAC solutions are mainly focused on
carrier-sense multiple access (CSMA) or codedivision
multiple access (CDMA).
ROUTING PROTOCOLS
There are several drawbacks with respect to the
suitability of the existing terrestrial routing solutions
for underwater wireless communications.
Routing protocols can be divided into three categories,
namely, proactive, reactive, and geographical.
Proactive protocols (e.g., destinationsequenced
distance vector [DSDV], optimized
link state routing [OLSR]) provoke a large signaling
overhead to establish routes for the first
time and each time the network topology is
modified because of mobility, node failures, or
channel state changes because updated topology
information must be propagated to all network
devices. In this way, each device can establish a
path to any other node in the network, which
may not be required in underwater networks.
Also, scalability is an important issue for this
family of routing schemes. For these reasons,
proactive protocols may not be suitable for
underwater networks.
TRANSPORT-LAYER PROTOCOLS
A transport-layer protocol is required to achieve
reliable transport of event features and to perform
flow and congestion control. Most existing
Transport Control Protocol (TCP) implementations
are unsuited for the underwater environment
because the flow control functionality
relies on window-based mechanisms that require
an accurate estimate of the round trip time
(RTT). The long RTT, which is caused by the
low sound speed affecting the propagation delay
on each underwater link composing the end-toend
path, would affect the throughput of most
TCP implementations.
[attachment=23700]
INTRODUCTION
Underwater wireless communications can enable
many civilian and military applications such as
oceanographic data collection, scientific ocean
sampling, pollution and environmental monitoring,
climate recording, offshore exploration, disaster
prevention, assisted navigation, distributed
tactical surveillance, and mine reconnaissance.
Some of these applications can be supported by
underwater acoustic sensor networks (UWASNs)
[1], which consist of devices with sensing,
processing, and communication capabilities that
are deployed to perform collaborative monitoring
tasks (Fig. 1). Wireless signal transmission is
also crucial to remotely control instruments in
ocean observatories and to enable coordination
of swarms of autonomous underwater vehicles
(AUVs) and robots, which will play the role of
mobile nodes in future ocean observation networks
by virtue of their flexibility and reconfigurability.
MEDIUM ACCESS CONTROL PROTOCOLS
Due to the unique characteristics of the propagation
of acoustic waves in the underwater environment,
existing terrestrial MAC solutions are
unsuitable for this environment. Channel access
control in wireless underwater networks, in fact,
poses additional challenges due to the limited
bandwidth, very high and variable propagation
delays, high bit error rates, temporary losses of
connectivity, channel asymmetry, and heavy multipath
and fading phenomena. Current underwater
MAC solutions are mainly focused on
carrier-sense multiple access (CSMA) or codedivision
multiple access (CDMA).
ROUTING PROTOCOLS
There are several drawbacks with respect to the
suitability of the existing terrestrial routing solutions
for underwater wireless communications.
Routing protocols can be divided into three categories,
namely, proactive, reactive, and geographical.
Proactive protocols (e.g., destinationsequenced
distance vector [DSDV], optimized
link state routing [OLSR]) provoke a large signaling
overhead to establish routes for the first
time and each time the network topology is
modified because of mobility, node failures, or
channel state changes because updated topology
information must be propagated to all network
devices. In this way, each device can establish a
path to any other node in the network, which
may not be required in underwater networks.
Also, scalability is an important issue for this
family of routing schemes. For these reasons,
proactive protocols may not be suitable for
underwater networks.
TRANSPORT-LAYER PROTOCOLS
A transport-layer protocol is required to achieve
reliable transport of event features and to perform
flow and congestion control. Most existing
Transport Control Protocol (TCP) implementations
are unsuited for the underwater environment
because the flow control functionality
relies on window-based mechanisms that require
an accurate estimate of the round trip time
(RTT). The long RTT, which is caused by the
low sound speed affecting the propagation delay
on each underwater link composing the end-toend
path, would affect the throughput of most
TCP implementations.