Study On High Rate Transmission Over Underwater Acoustic Channel

With the development of oceanic exploiture and communication industry, the need to high rate underwater acoustic communication is more and more urgent. The goal to get high-rate and high credibility communication has gived rise to a popular research interest in acoustic communication research field.This dissertation focuses on the modulation and equalization under acoustic channel. Firstly, the physics characteristic of acoustic channel is introduced as well as the effect of channel to signal transmission is analyzed, Secondly, comparison between underwater acoustic channel and wireless channel is done and the model of channel is established. Both the error rate under flat Rayleigh fading channel and the effect of transmission distance and phase noise to error rate are studied by simulation. Thirdly, the advantages and disadvantages of OFDM applied in underwater acoustic channel are analyzed. Focus on the problem of occurring ICI when there is doppler frequency shift, an equalizer is designed to eliminate ICI which has get high SINR gains. After the thorough research,a conclusion is concluded:it had better adopt low-complexity equalizer under acoustic channel because that traditional equalizer used in wireless communication system has high complexity.Later,we bring forward a low-complexity equalizer which can eliminate ICI in underwater acoustic OFDM system.It makes the channel matrix sparse by preprocessing,then gets the sending signal using iterative estimation. On the base of above, a new low-complexity equalizer is designed. Signal passes through a filter who eliminates ICI further after preprocessing and the scheme saves computation instead of iterative estimation. Lastly, we propose to adopt MIMO DFE to improve the performance. Comparison and simulation have been done between this scheme and traditional MMSE linear equalization. It enlarges the channel capacity by using MIMO structure.