Underwater Acoustic Communication Waveform Design And Research

With the increase of the world’s population,the per capita land resources have decreased,countries around the world have increased their research on the ocean,and underwater acoustic communication technology has also been promoted.Electromagnetic wave communication,optical fiber communication,optical communication and other methods are difficult to transmit in underwater acoustic channels.Underwater acoustic communication becomes the main way of underwater communication because of its low attenuation and long-distance communication.Underwater acoustic channels have serious noise interference,path transmission loss,Doppler frequency shift and multipath effect.Therefore,this paper mainly studies and designs the waveform of underwater acoustic communication aiming at the reliability of data transmission in harsh underwater acoustic communication channel.Based on IEEE802.15.4a standard,Chirp spread spectrum and differential quadrature phase shift keying(DQPSK)hybrid modulation techniques are used to design and implement the whole transmitting and receiving process.Chirp signal itself as a spread spectrum signal and has good autocorrelation and pulse compression characteristics,which can effectively combat channel fading.MATLAB software is used to simulate the bit error rate curve of the system under the conditions of Gaussian white noise channel and multipath channel respectively.Using Verilog language to design each module of the system,and passed the behavior level simulation.In order to solve the problem of serious crosstalk between symbols in the design of underwater acoustic communication waveform based on standard implementation in multipath channel,equalization technique is used to improve the bit error performance.The passive and virtual time reversal mirror techniques used in this paper are less complex to implement than other equalization methods and can effectively use the reciprocity of underwater acoustic channels.The bit error rate curve under the condition of multipath channel is simulated by MATLAB.The results show that when the signalto-noise ratio is large,the two kinds of time reversal mirror equalization can effectively reduce the bit error rate.The virtual time reversal mirror is improved from three aspects,and the feasibility of the improved scheme is verified by simulation.In order to improve the ability of error correction and detection in the case of low signal-to-noise ratio,this paper proposes to replace the biorthogonal mapping coding given by the standard with low density parity check channel(LDPC)coding technology.The bit error rate curve under the condition of multipath channel is simulated by MATLAB.The results show that the signal-to-noise ratio is small,and the combination of time reversal mirror equalization and LDPC channel coding with underwater acoustic communication system also has good bit error performance,which verifies the feasibility of the improved LDPC channel coding scheme.