21-05-2012, 03:58 PM
Design of a High Speed,Short Range UnderwaterCommunication System
[attachment=22603]
Abstract
The present report describes the rst part of the development of a high-speed, short range underwater communication system to be used by the NARO sh. It is found that the acoustic communication approach matches best the given requirements of the NARO project. Constitutive parts of this rst stage of the project are thus on one hand the design of the needed electro-acoustic circuitry and on the other hand the development of a powerful but highly specialised simulation of the acoustic underwater channel.
Introduction
Two systems developed in the tensions of the cold war illustrate like nothing else the technical challenges involved with underwater communication - the american Sanguine and the sowjet ZEVS system. Both systems use electromagnetic waves in the ELF (extremely low frequency) domain to transfer information to submerged submarines up to a depth of around 300m. Waves situated in the ELF spectrum with frequencies between 30Hz and 300Hz have the ability to penetrate in a great measure the electrically conducting seawater, explaining this large possible depth. But there are huge drawbacks related with waves in this low frequency region. On one hand only very low data rates in the range of a few bits per minute are possible. On the other hand these frequencies have wavelengths of between 100km and 100000km and since a good transmitting antenna has a length of a multiple of =4,
gigantic structures are needed to transmit signals in the ELF spectrum. The ZEVS system for example uses a transmitting ground dipole of an alleged length of 106km!
Target Application
The present work focusses on the development of a high speed, short range underwater communication system for shallow water environments. The selection of this application eld is not occasional but follows the main operational area of the parent project of this work - the NARO sh.
2.1 NARO - Nautical Robot
The project NARO - NARO stands for nautical robot - is concerned with the development of an arti cial sh. The main goal of the project lies in the imitation of the natural sh movement, which has a locomotion eciency that excels by far all human built devices down to the present day. The design of the NARO sh is oriented by the shape and motion of a tuna sh - a sh that has an average locomotion speed of 20km/h and can reach velocities up to 70km/h on short distances! Figure 2.1 shows a concept study of the arti cial sh. The partition of the sh in six distinct segments is visible, which should ensure that the sh could use a nature
like motion although tuna shes generate most of their acceleration by the tail n.
State of the Art inUnderwater Communication
Since during and after the second world war submarines gained more and more importance in the naval warfare, research in the area of underwater communication was strongly intensi ed. In the last decades, applications with sensor networks for oceonagraphic research and for the o shore oil and gas industry also strengthened the demand after fast and reliable underwater communication links. Through these application elds, many di erent approaches to communicate underwater were invented and pursued in the last century. In the following, the di erent kind of approaches are presented together with their advantages and disadvantages.
3.1 Di erent Approaches to Communicate Underwater
There are basically three completely di erent ideas, how information could be transfered through the underwater channel. The rst approach uses general electromagnetic waves and in special optical waves. The second approach tries to communicate via electric current waves without making use of the electromagnetic.
[attachment=22603]
Abstract
The present report describes the rst part of the development of a high-speed, short range underwater communication system to be used by the NARO sh. It is found that the acoustic communication approach matches best the given requirements of the NARO project. Constitutive parts of this rst stage of the project are thus on one hand the design of the needed electro-acoustic circuitry and on the other hand the development of a powerful but highly specialised simulation of the acoustic underwater channel.
Introduction
Two systems developed in the tensions of the cold war illustrate like nothing else the technical challenges involved with underwater communication - the american Sanguine and the sowjet ZEVS system. Both systems use electromagnetic waves in the ELF (extremely low frequency) domain to transfer information to submerged submarines up to a depth of around 300m. Waves situated in the ELF spectrum with frequencies between 30Hz and 300Hz have the ability to penetrate in a great measure the electrically conducting seawater, explaining this large possible depth. But there are huge drawbacks related with waves in this low frequency region. On one hand only very low data rates in the range of a few bits per minute are possible. On the other hand these frequencies have wavelengths of between 100km and 100000km and since a good transmitting antenna has a length of a multiple of =4,
gigantic structures are needed to transmit signals in the ELF spectrum. The ZEVS system for example uses a transmitting ground dipole of an alleged length of 106km!
Target Application
The present work focusses on the development of a high speed, short range underwater communication system for shallow water environments. The selection of this application eld is not occasional but follows the main operational area of the parent project of this work - the NARO sh.
2.1 NARO - Nautical Robot
The project NARO - NARO stands for nautical robot - is concerned with the development of an arti cial sh. The main goal of the project lies in the imitation of the natural sh movement, which has a locomotion eciency that excels by far all human built devices down to the present day. The design of the NARO sh is oriented by the shape and motion of a tuna sh - a sh that has an average locomotion speed of 20km/h and can reach velocities up to 70km/h on short distances! Figure 2.1 shows a concept study of the arti cial sh. The partition of the sh in six distinct segments is visible, which should ensure that the sh could use a nature
like motion although tuna shes generate most of their acceleration by the tail n.
State of the Art inUnderwater Communication
Since during and after the second world war submarines gained more and more importance in the naval warfare, research in the area of underwater communication was strongly intensi ed. In the last decades, applications with sensor networks for oceonagraphic research and for the o shore oil and gas industry also strengthened the demand after fast and reliable underwater communication links. Through these application elds, many di erent approaches to communicate underwater were invented and pursued in the last century. In the following, the di erent kind of approaches are presented together with their advantages and disadvantages.
3.1 Di erent Approaches to Communicate Underwater
There are basically three completely di erent ideas, how information could be transfered through the underwater channel. The rst approach uses general electromagnetic waves and in special optical waves. The second approach tries to communicate via electric current waves without making use of the electromagnetic.