OFDM Underwater Acoustic Communication System Based On DM642

Underwater acoustic communication technology is an important part of underwateracoustic technology. More and more attention is paid to the underwater acousticcommunication technology as the fast development of ocean exploitation. Underwateracoustic communication is economic, flexible, convenient, and wireless. It is widely used inmilitary field and civil field and plays an important role. Underwater acoustic channel hastwo interfaces which are not flat, and it is a random and uneven medium channel. The signaltransmitted into the channel is time variable, space variable and interfered by multi-path,Doppler, noise and so on. The bandwidth of underwater acoustic channel is restricted,because energy is losing as the increasing of the distance and frequency. The purpose ofunderwater acoustic communication is transmitting the information from the source to theend through the underwater acoustic channel reliably at high speed, and so finding acommunicaton scheme which is high-speed, reliable and fit for underwater acoustic channelis pivotal in underwater acoustic communicaton technology.Orthogonal frequency division multiplexing (OFDM) technology is a sort of multiplecarrier wave modulation. Informaton is transmitted in parallel by assigning high-speed bitstream to sub carrier in OFDM, and frequency is fully used. OFDM can effectively resistmultipath interference by adding cyclic prefix. OFDM communication system is simplebecause that OFDM can be carried out by FFT/IFFT algorithm. So OFDM underwateracoustic communication has a good development in the underwater acoustic communication.An OFDM underwater acoustic data communication system is designed in the paper.The hardware is based on TI TMS320DM642DSP chip. Peripheral circuits include powercircuit, clock circuit, reset circuit, JTAG circuit, external memory circuit, audio circuit,network circuit and so on. All the peripheral ciucuit is detailed introduced in the paper. Thesoftware is made up of transmitter program, receiving program and PC controlling program.PC control program takes charge of data exchange between PC and DSP through networkmodule. Transmitter program receives the data from PC, and the data which is modulated byOFDM is transmitted into underwater acustic channel. When the signal is detected fromunderwater acoustic channel, receiving program demodulates the information data throughOFDM demodulation, and the data is sending to PC by network module. In order to ensurethat the communication system is real time, transmitter program and receiving program isoptimized through DSP program optimizing method. An experiment is taken in the channel cistern in order to validate the feasibility of the system. The results of the experiment showthat the system is reliable and can real-time transmit data.