Research Against Multipath Effect In OFDM Underwater Acoustic Communication System

The higher reliability and effectiveness of underwater information transmission have been required with the development of marine resources and national defense,so underwater acoustic(UWA)communication systems of high speed and high reliability gradually attach great importance and research by each country.The serious multipath interference is one of the major factors of hindering the development of UWA communication,and orthogonal frequency division multiplexing(OFDM)technique has higher spectrum efficiency,stronger resistance to multipath interference and better adaptability to frequency-selective fading.So it has the very high theoretical and practical value for the research of OFDM technology in the UWA communication.It is mainly in the thesis studied how to against serious multipath interference in UWA channel for OFDM systems and the model of UWA communication system based on OFDM is designed,which can effectively resist multipath interference and noise of UWA channel and is suitable for the mobile UWA environment with higher data transfer rate.The mainly contents are as following:1)Physical characteristics of UWA channel and the basic principle of OFDM are introduced and the advantages and disadvantages of OFDM are discussed in UWA channel.Analyze the influence of multipath effect for OFDM symbols and ways to overcome the multipath interference.2)OFDM synchronization and channel estimation technology is studied,and an OFDM symbol synchronization and frequency offset estimation algorithm is presented,and the DFT channel estimation algorithm is improved.3)A parallel DFT spread spectrum method is put forward based on DFT spread spectrum OFDM,which not only can effectively reduce the peak-to-average power ratio(PAPR)of OFDM symbols,but also is simple and is not affected by the subcarrier number.4)Combining orthogonal spread spectrum and OFDM reduce the influence of the multipath effect and noise on the premise of guarantee data transfer rate,thus to improve the anti-interference ability.5)It has been verified by the MATLAB simulation and pool experiment for the validity and reliability of the proposed UWA communication system,which have obtained well results and showed the fine performance.