Research On Underwater Acoustic LDPC-OFDM System And Underwater Acoustic Time Varying Channel Simulation

With the rapid development of ocean exploitation, underwater acoustic communication has become a hot research spot. The multi-path interference and doppler spread are underwater acoustic channel's characteristics, which make signal go through time and frequency selective fading, resulting in serious inter symbol interference and signal fading, and bringing great obstacles to underwater acoustic communication. To improve communication speed and reduce multi-path influence introduced by acoustic channel, OFDM (Orthogonal Frequency Division Multiplexing) is stuided. OFDM is a multi-carrier digital modulation technique and proved to be a good method for high-speed wireless data communication, which can avoid ISI and reduce ICI. Besides, to ensure the transmitted data and achieve reliable communication, channel coding is introduced. Compared to the traditional channel correcting coding, LDPC (Low-Density Parity-Check Codes)'s characteristics are very close to Shannon limit, low error flat, easy to be described and achieved. So, LDPC has become a hot research spot in the area of error correcting codes.Firstly, the channel's characteristics and its important position in acoustic communication are studied; based on its statistical characteristics, its modeling and simulation are also studied. Then, the performance of LDPC is studied through combining LDPC and OFDM. The main work includes: the simulation of different check-matrix construction used in LDPC; the influence applied by the code's length in the LDPC-OFDM system; simulation of different mapping in LDPC-OFDM; the contrast between the LDPC codes and converlutional code in OFDM system; performance of LDPC in different underwater acoustic channels.Simulation results indicate that, the modeling method of underwater acoustic time varying channel can simulate the propagation of signal and reflect the characteristics correctly, which is very important to underwater communications. LDPC-OFDM systems turns out to be a good choice in underwater acoustic communication and exhibit excellent performance in severe acoustic channel.