Design And Implementation Of Environment-adaptive Dual-mode Communicator Software

Underwater acoustic channel has the characteristics of limited bandwidth resources,severe Doppler spread,large multi-way delay,strong time varying,and high environmental noise,which brings great challenges to the research of underwater acoustic communication.Underwater acoustic spread spectrum communication technology has good concealment and anti-interference ability.It still has strong environmental adaptability under the condition of low signal-to-noise ratio;Underwater acoustic OFDM communication technology has a high communication rate,but its application scenarios are strict,whose anti-interference ability of anti-Doppler is weak and environmental adaptability is poor.This paper combines the characteristics of the two communication systems,comprehensively considers the application scenarios and designs a dual-mode communication machine for environmental interaction to achieve efficient underwater acoustic communication combining communication speed and robustness.This paper first reviews the two underwater acoustic communication technologies of spread spectrum and OFDM.Based on the analysis of the environmental characteristics of the underwater acoustic channel,a time-varying underwater acoustic channel model is established,and the Bellhop software is used to simulate the underwater acoustic channel of different communication distances.Sound channel classification discussion.Then two kinds of communication systems,direct spread spectrum and OFDM,are studied.Aiming at the underwater acoustic spread spectrum communication system,the differential energy detector and the improved differential energy detector are studied respectively,and the influence of different length spread spectrum codes on the communication system is analyzed,and the improved differential energy detector is emphatically verified in the Doppler scene.decoding performance.For the OFDM communication system,two methods of Doppler estimation,block estimation and null subcarrier estimation,are studied.Based on this,channel coding,channel estimation and channel equalization methods are further studied.Finally,the performance of the two communication systems with different channel multi-way delays is also analyzed,and the respective application scopes of direct spread spectrum underwater acoustic communication and OFDM underwater acoustic communication are clarified.After that,this paper studies the environment-adaptive OFDM underwater acoustic communication system.The signal-to-noise ratio and the maximum multi-path delay of the communication link are used as the basis for adjusting the adaptive transmission coding and modulation mode.And the channel information is fed back by the spread spectrum communication system.Considering the real-time nature of the system,the SBLA algorithm is used in this paper to reduce the amount of calculation.The communication frequency band is divided and the same modulation method is used in the same subband to reduce the feedback signal overhead.ESNR is used as the criterion for adaptive modulation of OFDM system.Thus the channel state can be described more comprehensively.After that,an expert system is constructed.OFDM and spread spectrum are combined to form an environment-adaptive dualmode communication system according to their respective characteristics.In this paper,spread spectrum technology is used as the default communication mode of the communication system,so that the communication performance of the system is guaranteed.Based on the above theory,this paper develops and designs the software of environmentadaptive dual-mode underwater acoustic communication machine.The software is designed and developed based on QT and uses UDP protocol for real-time data interaction with the hydrophone data acquisition system,mainly including the transmitting part and the receiving part.Finally,the practicability of the software system is verified through the channel pool test and the sea test.