| Underwater towing systems are widely used in underwater exploration,environmental monitoring,submarine rescue,target search,etc.due to their high reliability and easy recov-ery characteristics.These applications require efficient and reliable underwater communication technology support to realize the real-time recovery of observation data and the timely com-munication of control commands.Therefore,research on real-time and efficient underwater communication methods is of great significance to the development of underwater towing sys-tems.Underwater streamer electromagnetic signal transmission method takes the electromag-netic signal with transmission characteristics as the information transmission carrier,and the closed loop composed of exposed towed steel cable and water as the channel,which has the advantages of high transmission rate,low development cost,simple operation and good confi-dentiality.However,the multipath delay,electromagnetic noise and natural noise in underwater towed cable electromagnetic channel seriously affect the research and development of electro-magnetic communication technology in the channel.Therefore,this paper mainly studies the transmission and communication of electromagnetic signal in the underwater streamer chan-nel,in order to achieve the efficient transmission of electromagnetic signal in the underwater streamer channel.The main work of this article are as follows:?1?Based on the equivalent transmission line theory,a dynamic model of the coaxial transmission line of the underwater towline is established;then according to the transmission characteristics of the underwater electromagnetic wave,the electrical model of the water is obtained,and the resistance coefficient of the water is analyzed using the COMSOL finite element simulation software;The coaxial transmission line model of the lower streamer and the electrical model of water are cascaded to establish the electromagnetic transmission channel model of the underwater streamer.By calculating the received signal voltage amplitude on the sampling resistor,the influence of the water conductivity,the length of the steel cable into the water,the signal frequency and the conductivity of the steel cable on the amplitude of the received signal voltage is analyzed,and the electromagnetic signal is revealed Attenuation characteristics of transmission in the channel.?2?The characteristics of the narrow bandwidth low-pass filter of the underwater streamer channel are studied,and the relationship between the transmission distance and the transmission frequency band is obtained;then the influence of the channel on the amplitude and phase during the dynamic change of the length of the streamer into the water is studied.Controlled modula-tion?ASK?and phase-shift keying modulation?PSK?are not suitable as digital communication methods for underwater streamer electromagnetic channels.With the help of COMSOL finite element software,the current density distribution of electrical signals in water was simulated,and the mathematical model of channel multipath transmission was established,and the param-eter calculation of the water channel multipath transmission model was completed.Finally,for the noise interference during underwater electromagnetic transmission,the characteristics of man-made noise and natural noise interference are analyzed,and the noise interference model of the channel is established.?3?According to the electromagnetic transmission characteristics of underwater steel ca-ble channels,the specific i mplementation p rocess o f O FDM-based u nderwater d ata electro-magnetic communication methods is analyzed,and a simulated communication system based on electromagnetic channels is built.When different modulation methods and different channel parameters are studied,the received signal noise Based on the relationship between the ratio and the bit error rate,a digital modulation method suitable for time-varying underwater streamer electromagnetic channels is proposed.The performance of multi-carrier OFDM communica-tion system and single-carrier FSK communication system in 500m underwater streamer elec-tromagnetic channel was compared and analyzed.A hardware circuit module based on FSK digital signal modulation and demodulation was designed to realize Carrier FSK modulation and demodulation function.?4?Taking hydrological cable as a special case of underwater towed system,an experi-mental platform of electromagnetic communication based on hydrological cable structure was built.The communication experiment based on single carrier FSK and the communication ex-periment based on multi-carrier OFDM are studied.The experiment verifies the reliability of the electromagnetic communication method of underwater streamer.The length of the steel cable immersed in water is 0-6m.When the single-carrier transmission rate is 2400bps,the average bit error rate is 7.02×10-3;when the multi-carrier transmission rate is 12kbps,the average bit error rate is 4.35×10-4.The experiment verifies t hat t he O FDM communication system is applied to When the channel is towed underwater,the transmission rate is increased and the accuracy is greatly improved. |
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