Research Of Coding Technology For Long Distance Underwater Acoustic Communication

With the rapid development of ocean exploitation, recently long range underwater acoustic communication with submarine has been one of the international focuses in researches. And the technique of channel coding is one of the key points for safe and low bit error rate (BER) long-range communication with submarine.In thesis, the channel coding technique suitable for long range underwater communication is researched. At first, characteristics of underwater acoustic channel are introduced, and two models of long distance underwater acoustic channel are given with relevant channel parameters. Then, the RS code which belongs to the linear block codes and the convolutional code are researched with computer simulation, including the principles of encoding and decoding, the expression form and the Viterbi algorithm etc.. Combining the pseudorandom interleaving technology, the BER performance of the concatenated code is given.Main researches concentrate on the principles and performance of turbo codes. The encoding architecture and decoding method of the turbo codes are explained, and some decoding algorithms, such as MAP algorithm, Log-MAP algorithm and soft output Viterbi algorithm (SOVA) are analyzed in detail. The complexity and performance of these algorithms are also compared. The performances of turbo codes with different design parameters are compared and the simulation results are given.Based on the analysis of underwater acoustic channel, in the simulation of overall performance of the system using channel coding, the scheme of long range underwater acoustic communication system is designed at first, and some key techniques are analyzed such as modulation, channel equalization etc., the simulation results for some classic codes including RS code, convolutional code and the relative concatenated code are given. Against the soft input characteristic in the decoding process of turbo codes, the equalization algorithm is modified appropriately to have a soft output result which will be the input data in decoding of turbo codes. Then a scheme of receiver for underwater acoustic communication is proposed, basing on the iterative principle combining equalization and decoding. The scheme is also called turbo equalization, and has shown a better performance in simulation results.