Research On The Application Of OFDM Techonlogy In The Underwater Acoustic Communication

The underwater acoustic channel is very complex where cochannel interference,Doppler frequency offsets,narrow bandwidth and time and frequency selective deep fades obstructs the development of high speed and fidelity underwater data transmissions. Thus projects of high speed and fidelity underwater signal transmissions become a hotspot in the fields of world academic circles. The conventional serial communication must use adaptive equalizer to combat the multipath in real-time. Since the underwater channel is nonstationary and the fades is frequency-selective,it is hard to use the real-time channel equalization technology. However,the paralleling communication can meet the requirements of high speed and fidelity in underwater signal transmissions. OFDM is a kind of novel paralleling transmission technology. The principle of OFDM is that the whole bandwidth can be divided into some subchannels,the high-speed serial signal stream is modulated by some orthogonal subcarriers. By using OFDM technology,we can reduce the baud rate with a high frequency spectrum utility factor. Another advantage of this technology is that the transmission can combat the intersymbol interference (ISI) at the receiver without complex adaptive equalizer. Furthermore,combined with FEC and interleaving,OFDM shows a high priority in countering the frequency-selective fades and ISI caused by multipath propagation. Employing the DSP technology,we can carry out the real-time FFT algorithm,which is the kernel in OFDM technology. With the developing of DSP and VLSI technology,OFDM develops rapidly and becomes a promising high-speed signal transmission technology in practical applications. In this thesis,for the merits of high frequency spectrum utility factor and high-speed data communication,the OFDM is introduced into the underwater acoustic communication. Combined with FEC to combat the frequency-selective fades and ISI in the underwater acoustic channel,high speed data transmission is realized by employing OFDM technology. Based on the two existing underwater acoustic channel models (the rice model and the rayleigh model),we simulated the effects on the image signal underwater transmission with different OFDM parameters. By selecting appropriate OFDM parameters,we realize a simple offline communication system. Besides,parts of programs based on TI TMS320C62X are realized in this thesis.