Autonomous Underwater Vehicle Docking 16.5 Coupling Power and Communications 399
Part B | 16.5
16.5 Coupling Power and Communications
As outlined previously, many docking scenarios are
motivated by the desire to extend undersea deployment
of an AUV. Initially such scenarios were oceanographically driven, however, as outlined in the introduction,
commercial and military operational scenarios are incorporating docking as a way to extend deployment
durations of AUVs. The need to recharge AUV batteries
and to extract data and send new commands is common
to almost every extended deployment scenario. Furthermore, when the dock is connected to the shore, the dock
provides the physical portal through which an operator
can interact with the vehicle. For example, docking tests
of the Dorado AUV [16.2] used the Naval Postgraduate School (NPS) Monterey Inner Shelf Observatory
(MISO) cabled observatory, allowing video monitoring
of the docking and undocking process in real time from
the shore. Once docked, the vehicle effectively became
a part of the shore network, with all the advantages such
connectivity brings.
Even when the dock is not connected to the network, there are strong motivations for enabling the
vehicle to download data to the dock. In effect, the dock
is usually the safe part of the system, so it is the logical
location in which to save data. The alternative, in which
the vehicle simply accumulates data, creates a situation
where each successive operation of the vehicle puts at
risk both the vehicle, and all previous data taken by the
vehicle. At some point, the risks of operation will outweigh the potential benefit of additional data.
The ability to recharge an AUV’s batteries at sea
is a key feature of many docking systems. AUVs
that carry power hungry payloads like mapping sonar
are most often attended by a ship and recovered on
a daily schedule for servicing. Recharging an AUV at
a dock creates the opportunity to simultaneously support a power hungry payload and remain deployed for
extended periods.
16.5.1 Establishing a Communications Link
Communication techniques that have been employed
for connecting an AUV and a dock include optical,
inductive, radio frequency, and direct electrical connection. Each of these technologies is driven by large
commercial markets, and thus the technical foundation
is constantly evolving. Factors influencing the choice
of communication link include the amount of data that
will be transferred; the nature of the engagement and
capture mechanisms; the role of communications in
the docking and undocking process; the characteristics
of the dock environment; and the type of AUV being
employed.
Bandwidth requirements for communication connectivity is largely driven by the intersection of data
download and operational duty cycle needs. Communication between the AUV and the dock is employed
for a variety of reasons, including:
Downloading mission data from the vehicle to the
dock
Uploading mission scripts from the dock to the vehicle
Commanding the vehicle to start a mission
Modifying the vehicle software configuration.
Interacting with the vehicle to upload and start
new missions and to modify vehicle software can be
accomplished over comparatively low bandwidth connections. In contrast, high bandwidth sensors like multibeam sonar and sidescan sonar generate on the order of 300 kb=s. So if the vehicle can download data
at 1 Mb=s, the vehicle must spend roughly 1 h downloading data for every 3 h of mission. Camera systems
can generate even more data. Consequently, highbandwidth connection between the vehicle and the dock
can be critical if rapid turn-around of the vehicle between missions is important.
Optical communications was used by the Flying
Plug docking system [16.36], inductive coupling by the
Odyssey IIb [16.48], radio frequency communications
by the Dorado [16.2], and direct electrical connection by the REMUS [16.8]. The advantage of both
optical and inductive communications is that no electrical connection need be exposed to seawater or mated
via an underwater connector. The advantage of the
direct electrical system is that it is relatively simple
and uses off-the-shelf hardware and software. The radio frequency (RF) communication system used by the
Dorado employed off-the-shelf 802.11 hardware and
provided 10 Mb=s communications through seawater at
separations up to 6:25 cm.
The RF-based communication link used by the Dorado offered the particular attraction that the dock and
the vehicle established a communication link while the
vehicle was not yet fully docked. When the dock is cabled to shore, as in the Dorado tests that occurred at the
MISO cabled observatory [16.49], the potential exists
for human intervention in the docking process. For example, the Dorado tests could be monitored by a video
camera on the dock, and when the dock established
a communication link with the vehicle, that communication link by extension allowed operator interaction with
the vehicle. With the appropriate interface to the vehicle,
this allows the operator to take control of the vehicle and
manually control docking should the need arise.
Part B | 16.5
16.5 Coupling Power and Communications
As outlined previously, many docking scenarios are
motivated by the desire to extend undersea deployment
of an AUV. Initially such scenarios were oceanographically driven, however, as outlined in the introduction,
commercial and military operational scenarios are incorporating docking as a way to extend deployment
durations of AUVs. The need to recharge AUV batteries
and to extract data and send new commands is common
to almost every extended deployment scenario. Furthermore, when the dock is connected to the shore, the dock
provides the physical portal through which an operator
can interact with the vehicle. For example, docking tests
of the Dorado AUV [16.2] used the Naval Postgraduate School (NPS) Monterey Inner Shelf Observatory
(MISO) cabled observatory, allowing video monitoring
of the docking and undocking process in real time from
the shore. Once docked, the vehicle effectively became
a part of the shore network, with all the advantages such
connectivity brings.
Even when the dock is not connected to the network, there are strong motivations for enabling the
vehicle to download data to the dock. In effect, the dock
is usually the safe part of the system, so it is the logical
location in which to save data. The alternative, in which
the vehicle simply accumulates data, creates a situation
where each successive operation of the vehicle puts at
risk both the vehicle, and all previous data taken by the
vehicle. At some point, the risks of operation will outweigh the potential benefit of additional data.
The ability to recharge an AUV’s batteries at sea
is a key feature of many docking systems. AUVs
that carry power hungry payloads like mapping sonar
are most often attended by a ship and recovered on
a daily schedule for servicing. Recharging an AUV at
a dock creates the opportunity to simultaneously support a power hungry payload and remain deployed for
extended periods.
16.5.1 Establishing a Communications Link
Communication techniques that have been employed
for connecting an AUV and a dock include optical,
inductive, radio frequency, and direct electrical connection. Each of these technologies is driven by large
commercial markets, and thus the technical foundation
is constantly evolving. Factors influencing the choice
of communication link include the amount of data that
will be transferred; the nature of the engagement and
capture mechanisms; the role of communications in
the docking and undocking process; the characteristics
of the dock environment; and the type of AUV being
employed.
Bandwidth requirements for communication connectivity is largely driven by the intersection of data
download and operational duty cycle needs. Communication between the AUV and the dock is employed
for a variety of reasons, including:
Downloading mission data from the vehicle to the
dock
Uploading mission scripts from the dock to the vehicle
Commanding the vehicle to start a mission
Modifying the vehicle software configuration.
Interacting with the vehicle to upload and start
new missions and to modify vehicle software can be
accomplished over comparatively low bandwidth connections. In contrast, high bandwidth sensors like multibeam sonar and sidescan sonar generate on the order of 300 kb=s. So if the vehicle can download data
at 1 Mb=s, the vehicle must spend roughly 1 h downloading data for every 3 h of mission. Camera systems
can generate even more data. Consequently, highbandwidth connection between the vehicle and the dock
can be critical if rapid turn-around of the vehicle between missions is important.
Optical communications was used by the Flying
Plug docking system [16.36], inductive coupling by the
Odyssey IIb [16.48], radio frequency communications
by the Dorado [16.2], and direct electrical connection by the REMUS [16.8]. The advantage of both
optical and inductive communications is that no electrical connection need be exposed to seawater or mated
via an underwater connector. The advantage of the
direct electrical system is that it is relatively simple
and uses off-the-shelf hardware and software. The radio frequency (RF) communication system used by the
Dorado employed off-the-shelf 802.11 hardware and
provided 10 Mb=s communications through seawater at
separations up to 6:25 cm.
The RF-based communication link used by the Dorado offered the particular attraction that the dock and
the vehicle established a communication link while the
vehicle was not yet fully docked. When the dock is cabled to shore, as in the Dorado tests that occurred at the
MISO cabled observatory [16.49], the potential exists
for human intervention in the docking process. For example, the Dorado tests could be monitored by a video
camera on the dock, and when the dock established
a communication link with the vehicle, that communication link by extension allowed operator interaction with
the vehicle. With the appropriate interface to the vehicle,
this allows the operator to take control of the vehicle and
manually control docking should the need arise.