The Research And Design Of VLF Underwater Acoustic Communication Modem

In recent years,the application of wireless sensor networks has became increasingly popular,which has a revolutionary solution to many problems,although it is mainly used in ground,but in recent years,the human speeds up the development of ocean,the need for the application of underwater wireless network underwater is increasing.The modem is the basis of underwater wireless network,which has the important research value.Because the special of the underwater environment,electromagnetic wave can’t be used in long-distance communications,the cost of optical fiber communication is high,flexibility is limited.The acoustic signal is believed to be the only feasible medium in the underwater environment.In the existing technology,acoustic modem can achieve high bandwidth and long distance communication in underwater environment.However,there are acoustic modem transmission loss,propagation delay and Doppler effect,the refraction caused by changes in temperature and pressure,the problem of multipath effect and frequency attenuation,it is difficult to achieve long-distance communication due to attenuation and noise characteristic of underwater acoustic channel,to achieve long-distance communication must use very low frequency signals.The research content of this paper is the hardware structure and the modulation and demodulation scheme of the modem.In order to carry out the research and design of very low frequency acoustic modem,verify the feasibility of the hardware design and the modulation and demodulation scheme.In this paper,the experimental platform of acoustic communication is built and the corresponding experimental conditions are set up.Firstly,this article introduces the research status of very low frequency underwater acoustic communication modem,the characteristics of underwater acoustic channel and underwater acoustic communication modulation technology.Secondly,it introduces the concrete hardware implementation of very low frequency underwater acoustic communication experiment platform,which contains digital signal processing platform used TMS320C6747 DSP as the core,external transmit-receive circuit and underwater acoustic transducer.Then it describes the software design process of very low frequency underwater acoustic communication experimental platform.Finally,the experiment is designed to test the function of the experimental platform,and test the transceiver characteristics of the modulation technology such as frequency modulation,phase modulation,chirp modulation and so on.