Application Of Time-frequency Modulation In Underwater Electromagnetic Communication

Underwater electromagnetic communication, which is widely used in underwaterexploration, is currently the priority research in the field of underwatercommunication. Underwater electromagnetic can achieve a faster traffic rate sinceelectromagnetic wave travels much faster than sound. Another advantage of usingelectromagnetic is that the suspended substance or other impurities will exert littleimpact on the communication system, making electromagnetic communication anindispensable way for underwater communication.Time-frequency modulation using multiple frequencies, send different frequency indifferent time slot to express different information. Benefits from frequency diversity,time-frequency modulation works well to prevent frequency selective fading. Byseparate a same frequency with another frequency, signal can hardly interfere itself orother frequency, it makes time-frequency modulation has a characteristic ofanti-fading and anti-interfere.Aiming on short distance communicate scenario, this paper designed an underwatercommunication system which is based on time frequency modulation. Combined withtime frequency modulation, frequency diversity, orthogonal encoding and powerreceiver, this system uses megahertz level electromagnetic waves which caneffectively resist frequency selective fading. There are several special requirementsfor the electromagnetic wave used in an underwater communication system due to thedifferent medium parameters compared with those in atmosphere. This paper analyzedthe effect made by different carrier frequency and pulse width, explained the way ofselecting a applicable pulse to use in underwater communication based on the study inprecursor field, skin effect and attenuation. The system BER shows an excellent errorcorrecting capability as well as resisting disturbance, which obviously overmatch pulse position modulation.