Research On Multicarrier MFSK Underwater Acoustic Communication And Modem Implementation

The marine safety is becoming more and more important,the marine resources development is increasing day by day.The demand for marine equipment is increasing day by day.Especially,the research of underwater communication technology in the world has led to the rapid development of ocean communication equipment.Acoustic waves are the most effective information carriers found in water so far,so underwater communication is often carried out using underwater acoustic devices.Underwater communication from point-to-point communication to the present underwater network communication,the formation of robust and reliable underwater communication network has become a hot research underwater communication,underwater communication network key infrastructure is underwater acoustic modems.Underwater acoustic channel has many problems,such as strong multi-channel interference,narrow band of available frequency,randomly change with time and space,doppler spread.The complicated underwater acoustic channel environment makes it necessary to study robust and reliable underwater acoustic modems.Multi-Carrier Frequency Shift Keying has the advantages of multi-carrier anti-jamming and orthogonal subcarriers saving bandwidth,which can achieve the purpose of underwater robust communication.Complex channel estimation algorithms are not needed.This paper designs a half-duplex multi-carrier MFSK underwater acoustic modem.The system uses low power floating-point DSP-TMS320C6748 as the core processor to realize digital signal processing tasks.Modem system DSP driver on the one hand to achieve multi-carrier MFSK algorithm to provide on-board hardware resources interface program,on the other hand with the file system to achieve SD card storage function,it can store collected data and record the operating parameters.In this paper,based on the multi-carrier MFSK algorithm,the CRC check is added to verify the consistency of the information between the transmitter and the receiver,and the influence of channel random error is reduced by scrambling and interleaving.Channel coding using mature convolutional coding,channel decoding using Viterbi decoding.The transmitter uses Hadamard code modulation and two single frequency signals are used to estimate the Doppler in the data frame.The frame synchronization is performed at the receiver by the improved overlap correlation method,and the Doppler is compensated by the high power FFT.In order to control the collected acoustic signal in the appropriate range,the receiving end of the data acquisition of automatic gain control to achieve adaptive adjustment of the amplitude of the acquisition signal.The host computer GUI software is programmed to achieve the control of the modem and display modem contentwith the communicationof the host computer and DSP.Finally,the program is optimized,and the system-level electrical connection experiment and the pool experiment are carried out.The program of each module is tested and the communication performance of the multi-carrier MFSK algorithm is tested in the pool communication experiment.It is proved that the multi-carrier MFSK-Modem is reliable,can be used as a key equipment underwater communication network equipment.