| The ocean contains rich resources,providing important support and guarantee for the survival and development of human beings.Underwater information transmission is an indispensable part of human protection of the ocean and strategy of the ocean,however,the complex underwater channel conditions make underwater wireless communication face severe challenges.Magnetic induction communication uses the induction field to transmit information,which has the advantages of channel stability,low delay,small coil antenna size and low power consumption,and is expected to achieve efficient and stable information interaction in underwater scenes.Therefore,the design of underwater frequency division duplex communication system is studied based on magnetic induction communication technology.Firstly,the paper analyzes the electromagnetic characteristics of the single-turn coil of the magnetic induction communication transceiver coil,establishes the magnetic induction communication transceiver model and the channel model in the medium,and compares the performance of different modulation and demodulation methods.In this process,the coil parameters,working frequency band and modulation and demodulation method of the frequency division duplex magnetic induction communication system are determined,which provides theoretical support for the system parameter setting.Secondly,the paper studies the magnetic induction communication resonant circuit,proposes a dual-frequency resonant circuit design,analyzes and simulates the circuit,and the actual test results show that the design meets the design requirements of transmitting and receiving signals of different frequencies on the single-coil antenna,and lays the foundation for the design of frequency division duplex magnetic induction communication system.Subsequently,for the self-interference problem in the frequency division duplex magnetic induction communication system,the self-interference suppression method based on out-ofband spectrum suppression and the self-interference suppression method based on selfinterference signal cancellation are adopted successively.By comparing the eye diagram and constellation diagram of the demodulated signal before and after self-interference suppression,the self-interference suppression effect of these two methods is intuitively illustrated.In addition,the measured experimental results show that the signal-to-interference-plus-noise ratio of communication node 1 and communication node 2 are improved by 9.63 d B and 9.27 d B,respectively,which verifies the effectiveness of this method to improve the received signal-tointerference-plus-noise ratio.Finally,the frequency division duplex magnetic induction communication system is built,and the system design is introduced.After testing,the system realizes the frequency division duplex magnetic induction communication of 3.4m in air and 1m underwater under the condition that the coil driving power is less than 1.25 m W,and completes the two-way information exchange between air and underwater at 1500 bps,which verifies the feasibility of the design.In summary,the main contributions of the thesis include : applying magnetic induction communication technology to underwater duplex communication;a dual-frequency resonant circuit is designed to improve the utilization of the antenna,and the design of the transceiver resonant circuit of the single-coil frequency division duplex magnetic induction communication system is completed.Aiming at the problem of self-interference in frequency division duplex magnetic induction communication system,the method of out-of-band spectrum suppression and self-interference signal cancellation is adopted to effectively reduce the influence of selfinterference signal and improve the communication quality. |
