Research On The Application Of R Combination Spread Spectrum And OFDM In Underwater Acoustic Communication

In recent years,as people's understanding of the ocean has gradually improved,people's interest in marine rights and interests has gradually increased.“Towards the ocean” is already an inevitable trend.However,severe marine environment causes serious distortions in the sound propagation process,such as serious multi-passage expansion,rapid changes in time-frequency domain,severe Doppler frequency deviation,large transmission attenuation,severe noise interference,and limited communication bandwidth.OFDM is a communication technology with high spectrum utilization rate.In recent years,its application in underwater acoustic communication has also been widely studied.However,OFDM technology is greatly affected by the environment,resulting in poor robustness.Although the robustness of spread-spectrum underwater acoustic communication is relatively high,the communication rate is too low,which severely limits its application in practical engineering.This thesis makes full use of the characteristics of OFDM technology and spread spectrum technology,studies multi-carrier spread-spectrum underwater acoustic communication methods,and fuses their respective characteristics,and proposes a r-combination and spread-frequency OFDM underwater acoustic communication algorithm.Firstly,this paper introduces the basic principles of spread spectrum technology and OFDM technology,and proposes new algorithms for spread spectrum underwater acoustic communication receivers such as spread spectrum energy detectors,differential energy detectors,and differential differential spread spectrum detectors,and analyzes each algorithm.The applicable conditions focus on the channel estimation method in OFDM underwater acoustic communication and the peak-to-average power ratio suppression technique based on the partial transmission sequence method.Secondly,this paper combines spread spectrum and OFDM underwater acoustic communication technologies,and proposes multi-carrier spread spectrum underwater acoustic communication technologies such as frequency domain multi-carrier spread spectrum,time-domain orthogonal multi-carrier spread spectrum,and time-domain multi-tone spread spectrum,etc.The mathematical expressions that implement the block diagram and the modulated signal are given.Thirdly,this paper applies the r-combination technique in frequency-domain spread spectrum to obtain r-combination frequency domain multi-carrier spread spectrum and r-combination time-domain orthogonal multi-carrier spread spectrum algorithms,and the requirements from the receiver,algorithm implementation complexity,and environment Puller frequency deviation requirements and other aspects of the analysis of the advantages and disadvantages of the two algorithms.Finally,the paper simulates the communication algorithm of r-combination frequency domain multi-carrier spread spectrum: select M=32,r=5,M=64,r=6,M=128,and r=7.Combining,comparing the number of spreading code selections and the size of spreading code base,affects the overall system error rate and information carrying capacity.Based on this,a r-combination frequency domain multi-carrier spread spectrum algorithm based on time-reversal mirror technology is further constructed.The simulation results show that the time-reversal mirror technology helps to improve the system's adaptability and anti-interference,and can effectively suppress Signal distortion.At last,this thesis carried out the pool test and the Songhuajiang field test to verify the performance of r-combination and spread-spectrum OFDM underwater acoustic communication.The pool test not only completed the fixed-point data acquisition but also carried out the mobile data acquisition.Both the pool and field test data processing achieve low BER data transmission,verifying the effectiveness and robustness of the r-combination spread-spectrum OFDM algorithm.