Introduction

Today, The technology of Wireless communication  has become part of our daily life, but still the idea of wireless undersea communications seem unachievable. However, several researches are going over a decade on designing the methods for wireless data transmission underwater. Our knowledge and understanding about the world’s water resources mainly oceans which covers the major part of our planet, rests on our ability to gather information from remote undersea locations. In the past decades, the major discovery which we all are familiar is the remains of TITANIC, was made using cabled submersibles. Although such system remains very important, if high-speed communication link is to exists between the remote end and the surface, it is natural to wonder what one could accomplish without the use  of heavy cables. Here comes our topic , Wireless Underwater Communications.  With the help of sensor technology and vehicular technology, wireless communications will enable new applications ranging from environmental monitoring to gathering of oceanographic data, marine archaeology, and search and rescue missions.

Definition

                    A technique of transmitting and receiving information or data below water is known as Underwater wireless communication.There are several ways of employing such communication but the most common is by using hydrophones.

                  Deep in the ocean radio waves cannot be used to transmit signals  as electro-magnetic waves propagate only very short distances. Instead of that we use acoustic waves which can propagate over long distances. Inspite of that, there are some factors which make underwater acoustic channel difficult for a system designer. The three factors or characteristics of this channel :

  1. Frequency-dependent propagation loss
  2. Severe multipath
  3. Low speed of sound propagation.

 None of these characteristics are seen in land-based radio channels, the fact that makes underwater wireless communication extremely difficult.

Multipath propagation

 If an acoustic signal can propagated by multiple paths, it is called multipath propagation. In addition to the actual or direct path ,the acoustic wave gets reflected from the water surface and bottom .Vertical channels are characterized by little time dispersion, whereas horizontal channels may have extremely long multi-path spreads, whose value depend on the water depth.

Path loss

Path loss occurs due to the reflection of waves,refraction of water while propagating and so on .This path loss or attenuation is given by A=dka(f)d, here k is the path loss exponent whose value is between 1 and 2, a(f) is the absorption factor that depends on the frequency of the acoustic waves. This dependence severely limits the available bandwidth.

APPLICATIONS

In last several years, Underwater Communication Network has found enormous applications and benefits in various domains such as

  1. Environmental Research
  2. Autonomous Underwater Vehicle (AUV) operation
  3. Oil-rig maintenance
  4. Collection Of Data For Water Monitoring
  5.  Linking Submarines To Land
  6. Coastal surveillance system, etc..

CONCLUSION

            These are the basic stuffs in wireless Underwater communication. Researches had been going in this field to develop acoustic communication in various aspects and to achieve advanced technologies. This is an emerging part in communication domain in future.