04-06-2012, 02:14 PM
A Survey of Techniques and Challenges in Underwater Localization
[attachment=24161]
Abstract
Underwater Wireless Sensor Networks (UWSNs) are expected to support a
variety of civilian and military applications. Sensed data can only be interpreted
meaningfully when referenced to the location of the sensor, making
localization an important problem. While Global Positioning System (GPS)
receivers are commonly used in terrestrial WSNs to achieve this, this is infeasible
in UWSNs as GPS signals do not propagate through water.
Introduction
During the last couple of years, we could observe a growing interest in
Underwater Wireless Sensor Networks (UWSNs). One important reason is
that they can improve ocean exploration and fulfil the needs of a multitude of
underwater applications, including: oceanographic data collection, warning
systems for natural disasters (e.g., seismic and tsunami monitoring), ecological
applications (e.g., pollution, water quality and biological monitoring),
military underwater surveillance, assisted navigation, industrial applications
(offshore exploration), etc.
• High Accuracy
The location of the sensor for which sensed data is derived should be accurate
and unambiguous for meaningful interpretation of data. Localization
protocols usually minimizes the distance between the estimated
and true locations.
• Fast Convergence
Since nodes may drift due to water currents, the localization procedure
should be fast so that it reports the actual location when data is sensed.
• Wide Coverage
The localization scheme should ensure that most of the nodes in the
network can be localized.
Range-based Underwater Localization
Range-based localization typically comprises the following steps:
• Step 1a: Range measurement (Reference node within com-
munication range of ordinary node)
Each ordinary node estimates its distance from each reference node
using the following methods:
– Received Signal Strength Indicator (RSSI)
Each ordinary node determines its distance from a reference node
by measuring the Received Signal Strength and comparing it with
a range dependent signal attenuation model. However, it is difficult
to achieve accurate ranging when multipath and shadow fading
effects exist (Burdic, 2002). Since the path loss in underwater
acoustic channels is usually time varying and multipath effect can
result in significant energy fading, the RSSI method is not the
primary choice for underwater localization.
– Time Difference of Arrival (TDoA)
For indoor localization, the TDoA method utilizes the time difference
between two different transmission mediums, namely, radio
transmission and acoustic transmission, to calculate the distance
between objects (Gu et al., 2006). Based on the two received signals,
the distance to the transmitter can be determined. However,
it is unsuitable for underwater localization because radio does not
propagate well in water.
[attachment=24161]
Abstract
Underwater Wireless Sensor Networks (UWSNs) are expected to support a
variety of civilian and military applications. Sensed data can only be interpreted
meaningfully when referenced to the location of the sensor, making
localization an important problem. While Global Positioning System (GPS)
receivers are commonly used in terrestrial WSNs to achieve this, this is infeasible
in UWSNs as GPS signals do not propagate through water.
Introduction
During the last couple of years, we could observe a growing interest in
Underwater Wireless Sensor Networks (UWSNs). One important reason is
that they can improve ocean exploration and fulfil the needs of a multitude of
underwater applications, including: oceanographic data collection, warning
systems for natural disasters (e.g., seismic and tsunami monitoring), ecological
applications (e.g., pollution, water quality and biological monitoring),
military underwater surveillance, assisted navigation, industrial applications
(offshore exploration), etc.
• High Accuracy
The location of the sensor for which sensed data is derived should be accurate
and unambiguous for meaningful interpretation of data. Localization
protocols usually minimizes the distance between the estimated
and true locations.
• Fast Convergence
Since nodes may drift due to water currents, the localization procedure
should be fast so that it reports the actual location when data is sensed.
• Wide Coverage
The localization scheme should ensure that most of the nodes in the
network can be localized.
Range-based Underwater Localization
Range-based localization typically comprises the following steps:
• Step 1a: Range measurement (Reference node within com-
munication range of ordinary node)
Each ordinary node estimates its distance from each reference node
using the following methods:
– Received Signal Strength Indicator (RSSI)
Each ordinary node determines its distance from a reference node
by measuring the Received Signal Strength and comparing it with
a range dependent signal attenuation model. However, it is difficult
to achieve accurate ranging when multipath and shadow fading
effects exist (Burdic, 2002). Since the path loss in underwater
acoustic channels is usually time varying and multipath effect can
result in significant energy fading, the RSSI method is not the
primary choice for underwater localization.
– Time Difference of Arrival (TDoA)
For indoor localization, the TDoA method utilizes the time difference
between two different transmission mediums, namely, radio
transmission and acoustic transmission, to calculate the distance
between objects (Gu et al., 2006). Based on the two received signals,
the distance to the transmitter can be determined. However,
it is unsuitable for underwater localization because radio does not
propagate well in water.