The Design And Implementation Of Underwater Long-wave Transceiver System

Underwater communication technology has a broad application in the fields of marine exploration,water monitoring and underwater sensor networks.Underwater communication can be divided into wired mode and wireless mode.In certain circumstances,the wireless communication has more advantages.Therefore,the research of underwater communication technology is of great value.Underwater wireless communication mainly includesunderwater acoustic communication,underwater laser communication and underwater electromagnetic communication.Under thecircumstances of shallow andmuddy water,underwater acoustic communications or underwater laser communication is difficult to achieve the desired effect,whileusing long-wave as a carrier in underwater wireless communication has good adaptability to the environment,and will be able to overcome the enormous underwater electromagnetic wave attenuation.To develop underwater long-wave communication equipment,this paper proposedan underwater long-wave transceivers experimental platform,and the expected effect was gained.This paper described the structure of underwater long-wave experiment platform.In response to the features of underwater wireless communication,digital wireless communication technology wasusedto design the system,andspread spectrum communication technology was added to meet reliability requirementsofthe severe channel environments.Programmable logic device(FPGA)was used in the system,implement most of the signal processing circuitry on a single FPGA chip other than using conventional discrete components,which was able to improve reliability andreduce power dissipation of the system.Underwater experimental platform is divided into ground part and underwater part.The underwater portion includes the transceiver circuit,antenna and battery,while theground portion comprises a portable data acquisition card and a computer.In the transmitting system,weaccomplished signal encoding,M-sequence generation,Direct Sequence Spread Spectrum(DSSS),the carrier generation,the digital-analog conversion and power amplification and 2FSK modulation based on FPGA.In the receiving system,hardware circuitwas used tocomplete 2FSK demodulation.Demodulated signals were collected by the portable data acquisition card.The correlation dispreading,symbol decision and FM0 decoding of spread-spectrum signals was achieved based on software programming.Finally,the performance of the underwater transceiver system was tested.For the underwater experimental platform,multi-level transmitting power was set upin the transmitting system.The experimental data ofdifferent transmitting power was collectedin different distances,which showed the effective transmission range of each level of transmitting power.Comparative experiment of the system with and without spread-spectrum communication technologywas carried out,and the effect of spread-spectrum communication technology on transmitting range was analyzed.The results showed that the system with spread-spectrum communication technology could receive signals with lower SNR correctly,and the transmitting rangewas increased,which improved the reliability of the system.When the expected effective transmission distances were the same,using the spread spectrum communication technologycould reduce the transmission power.