MARINE TECHNOLOGY - Elac-Nautik

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MARINE
TECHNOLOGY
R E P O R T E R
June 2010
www.seadiscovery.com
Subsea Defense
Opening In-Water Communication Lines
Deepwater Dilemma
The Crisis Continues
Fiber Optics
In Subsea Environ

Reprinted from the June 2010 Edition of Marine Technology Reporter
Faster, more secure and more precise
Digital Underwater Telephones
by Edward Lundquist
Subsea Defense & Underwater Communication
Ulrike Schulte-Rahde of L-3 ELAC Nautik in Kiel, Germany,
says her company’s UT3000 Underwater Communication System
can be used as secure interrogation system, similar to IFF
(Identification Friend or Foe) used for aircraft.
“The IFS (Identification of friendly submarines) system can
secure identification of friendly submarines to ensure they are not
identified as hostile combatants. It must be secure, robust, and
able to operate at long ranges in all environments. IFS must be
covert so that the friendly submarines would not reveal themselves
to the enemy. With a defensible Low Probability of Intercept
(LPI), only friendly units who have the capability to detect and
decode such a signal will recognize the interrogated one,” she says.
“This is vital for secure communications between submarines and
other submarines, ships, AUVs, helicopters with dipping sonars or
other vehicles and shore or seafloor stations.”
With the UT3000, call signs, position information and other
sensitive data are sent digitally and may even be encrypted. The
system uses a projector and hydrophone receiver, and includes a
human interface (HMI) graphic display and keyboard.
Schulte-Rahde says the UT3000 can send four different types of
messages in IFS mode:
• Interrogation message (‘int’)
• Reply message (‘rep’)
• Do Not Answer message (‘dna’)
• Emergency message (‘sos’)
Depending on the selected transducer configuration, the multifunctional
UT 3000 can be used in different modes, based upon
the chosen modulation and the environmental conditions to offer
analogue telephony and digital data transfer rates up to 3840bps,
as well as a large number of additional optional functions in a wide
and long-range robust data rate (LDR) (up to 90 bps) in variable
frequency ranges. Schulte-Rahde says that the output power and
frequency is adjustable so that it can even be used to communicate
with divers as well as other vessels, and can be either directional or
omni-directional.
Gerald Baden, director marketing and sales for L-3
Communications ELAC Nautik says new advances in digital
underwater communications transcends sending simple messages,
but secure identification, as well. In much the same way as
transponders on friendly aircraft “squawk” when interrogated by
Identification Friend or Foe (IFF), the IFS system can verify the
presence of a friendly underwater contact. “IFS currently being
integrated as a function into the UT3000. IFS is only possible
with digital communications.”
IFS is presently a study carried out together with the COE CSW
(Center of Excellence for coastal and shallow waters and the
Research Branch for Waterborne Sound and Geophysics (FWG),
a Division within the Bundeswehr Technical Center for Ships and
Naval Weapons, Maritime Technology and Research, according to
Kai Duehrkop, L-3 ELAC Nautic’s manager of marketing and
sales. “The primary mode is manual. A signal is only sent at the
discretion of the submarine commander. The secondary mode is
automatic, which can be used for unmanned underwater vehicles,
gateway buoys and underwater stations.”
The data can actually be transmitted so that it “hides” within the
ambient noise in the water by spreading the signal energy over the
frequency band over time using an algorithm known to friendly
forces. To compromise the exchange, the enemy would need that
algorithm as well. “That’s something you can’t do can’t do with
analog,” says Baden
Analog underwater communications are bound to certain modulation
on a specific frequency. “You have all the problems and
limitations you have with voice communications. When giving
position data you have to repeat yourself. You can’t distribute
complex information,” Baden says.
Non Coherent Modulation Scheme
To “hide” the transmission, Schulte-Rahde says a non coherent
modulation scheme is used. “Non coherent modulation means in
general that digital information is transmitted through discrete frequency
changes of a carrier wave. The simplest non coherent modulation
scheme is the binary FSK (frequency shift key), that
implies using one discrete frequency to transmit binary (0 and 1)
information. The detector tries to find out, if the carrier is set (->1
is transmitted) or not (->0 is transmitted).”
“Multiple frequency-shift keying (MFSK) applied in the UT
3000 is a variation of FSK that uses more than one frequency, distributed
over the transmission band. The principles in detection
and evaluation are nearly the same,” Schulte-Rahde says. “The
data rate increases with the amount of carriers you take within one
transmitted symbol.”
“The data rate with digital communications is relatively high,
according to Baden, about 3,800 bits per second. It’s faster and
more precise than voice,” he says. “It takes about 30 seconds to
give a position report using an underwater telephone in the analog
voice mode, and that can be garbled. Using digital, it takes less
time with less ambiguity. There is no need to repeat, and it is
harder to intercept.”
All kind of digital data can be sent, including ASCII and binary,
which is a totally new approach in underwater comms. This
includes complex data gathered by autonomous underwater vehicles.
“It is possible to send a plot of the surface situation, target

Reprinted from the June 2010 Edition of Marine Technology Reporter
Subsea Defense & Underwater Communication
information and all other info down to a submarine at speed and
depth (or vice versa), and done so encrypted,“ Schulte-Rahde says.
Baden says ELAC Nautik’s systems are found on virtually all conventional
subs world wide.
The UT 12 underwater telephone is still found on some submarines.
The UT2000 analog system has been in use for 15 years
and is found on many submarines around the world. The latest
UT3000 model was introduced three years ago.
“The UT3000 can replace the 2000. They are able to work with
the same transducers. All that is required is an exchange of the
main unit.”
The system employs open architecture, according to Duehrkop.
It is easy to update the software with new functions, or to customize
the system, such as a customer wanting to install his own
encryption.
Because the system can monitor the full frequency range from 1
to 60 khz, including upper and lower sidebands, it has the ability
to intercept transmissions, such as a hostile sub trying to contact
the surface.
“This is all new,” says Baden. “We’re finding new applications
every day.”