Algorithm Research And Implementation For Underwater Acoustic Communication Modem

Underwater acoustic communication Modem is a major component of underwaterinformation network.A stable and reliable communication between Modems is a prerequisitefor underwater information network Orthogonal Frequency Division Multiplexing (OFDM)becomes a focus in the field of underwater acoustic communication in recent years withadvantage of high spectrum efficiency, resistance to multipath.In this paper, the main task is to study and implement the algorithm of OFDMcommunication in the Modem’s physical layer, and complete data transmission with theModem’s data link layer.The communication processing platform of the Modem makeshigh-performance digital signal processor TMS320C6455as the main processor, and a FPGAchip, X4series procuced by the Xilinx company is used for logic control. The Modem can usesound pressure transducers or vector sensor as the receiving unit. In order to improve thequality of communication, based on OFDM algorithm, the Modem uses channel coding,diversity, vector signal process, channel estimation, etc. In the program development process,in order to transmit data between the link layer and physical layer, the networkcommunication based on the NDK was researched. In order to realize efficient performance,C64x+core peripheral drive configuration and the integration of the used for coding theTCP/VCP coprocessor were studied, meanwhile.the theoretical algorithm was improved. Theimproved communication system increases its processing ability and communication effect.The OFDM system was developed based on DSP/BIOS, including the networkcommunication thread, OFDM modulation thread and OFDM demodulation thread. Networkcommunication thread is mainly responsible for receiving PC command and data which needto be sended, and transmiting raw data and demodulation results. OFDM modulation thread isto modulate data and start to send. OFDM demodulation thread is to receive data anddemodulate it. The system need to build reasonable system frame, arrange each thread, andrealize real-time data processing.The Modem made experiments in Underwater Acoustic Laboratory, Harbin EngineeringUniversity, Songhua river, and Yellow Sea near Dalian. The results of the experiments showthat the Modem is stable and reliable, and achieve the desired requirements.