Study Of The Underwater E-mail Transmission System

With the development of the modern mobile technology,we can freely keep up with others in air or on land. But it is very difficult under water. Electromagnetic waves do not propagate over long distances under water except at extremely low frequencies. However,the transmission of signals at such low frequencies is prohibitively expensive because of the large and powerful transmitters required. So the acoustic wave is the only practical solution in this channel.An underwater acoustic channel is characterized as a multi-path channel due to signal reflections from the surface and the bottom of the sea. Because of wave motion,the signal multi-path components undergo time-varying propagation delays that result in signal fading and inter-symbol interference (ISI). It is very difficult to design a high-quality underwater acoustic data transmission system.In our study,we use Frequency diversity and Frequency-hopped technology. This method is an effective solution for the ISI and Signal Fading. With this tech,we design a high-efficient & robust MFSK data transmission system.But in Frequency diversity of MFSK system,it is very difficult to tell whichdiversity is the correct carrier frequency. Now we use the Temporary phase swift (IPS) method to solve the difficulty. The TPS method is the most important result in our study.In 2000,American navy successfully sends E-mail through the link of the underwater acoustic channel. To take the pace with the developed country,we design an E-mail transmission system. In the end of the paper,the complete & specific set of hardware circuits and software program scheme is presented.The performance of the underwater E-mail transmission system is practical. It is tested in the lab. In the future,we will increase the number of the Frequency-hopped sub-bands. It will solve the inter-symbol interference (ISI) perfectly. Then the system will be used on the test out of labs.