Simulation Research Of Space-time Coding Techniques In Underwater Acoustic Channel

Underwater acoustic communication technology is a research hotspot. Underwater acoustic channel as transmission medium is a complex time-varying and space -varying channel, and the transmission characteristics such as the multi-path effect, sound transmission loss and the Doppler Effect, etc. seriously influence to the performance of the underwater acoustic communication. In addition, the lower carrier frequency, limited transmission bandwidth and lower data transfer rate have become constraining factors in the development of underwater acoustic communication. Therefore, reliable high-speed transmission technology is the research focus on the field of underwater acoustic communications. Space-time coding techniques are developing rapidly in recent years. It can be used in conjunction with the modulation technique, so that a marked improvement occurred in spectrum efficiency. At the same time, diversity gain and coding gain can be obtained, and the data can be transmitted reliably at high rate. By comparing several space-time coding techniques, space-time block coding technique have been paid wide spread attention for its low complexity and high performance. Also the orthogonal frequency division multiplexing (OFDM) can transmit data effectively in frequency selective fading channel.In this thesis, the space-time coding and OFDM technique are joint designed and applied in underwater acoustic channel to raise data transfer rate and enhance reliability. The thesis constructs a model according to the characteristics of the underwater acoustic channel; makes a review of diversity and multiple input multiple output technology; discusses the classification of space-time coding, encoding and decoding methods and their performances and characteristics; focuses on the space-time block code encoding and decoding methods, and simulates and compares the performances of error code in cases of different number of transmitter and receiver diversities. Then, the STBC-OFDM transmission system proposed, and applied to the underwater acoustic channel model. In different conditions of data transfer rates, the performance of the transmit diversity and receive diversity are simulated and researched. The simulation results show that STBC-OFDM can improves the performance of underwater acoustic communication system.