Ofdm Technology Applied Research In Underwater Acoustic Communication System

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier digital modulation technique. Its conception has come out for a long time, however, it is recently that it's recognized as an proposed method in broadband bi-direction wireless data communications with the development of multimedia services. With the development of DSP chip techniques and the introduction of some mature techniques, such as TCM, adaptive channel equalization, the insertion of Guard Interval and so on, people are starting to focus on the application of OFDM in the field of mobile communications. The main content of this paper include the followings. Design criteria and analysis procedures for a practical OFDM underwater communications system are presented. A new broadband underwater channel model with Doppler time scaling effect is developed. A two-dimensional MMSE scheme using time and frequency pilots is employed for channel estimation. Doppler frequency shift is estimated using cyclic prefix and is compensated by a digital sampling rate conversion procedure. Numerical simulations demonstrate that OFDM technique is robust with respect to frequency selectivity and time selectivity.