Research And Design Of Broadband Magnetic Induction Communication System Based On Orthogonal Frequency Division Multiplexing

Due to the influence of soil,rock and water medium in complex condition such as underwater and underground,it is extremely difficulty to realization of wireless communication in these complex environments.Magnetic Induction（MI）communication has become wireless communication technology that is expected to replace the traditional electromagnetic wave communication to be applied to underwater,underground and other complex environments due to its advantages of stable transmission channel,less susceptible to environmental factors,small coil size and lower cost,which has research significance.The traditional Magnetic Induction（MI）communication system is faced with the problems of narrow channel bandwidth,smaller channel capacity and higher frequency selective fading channel characteristics.To solve these problems,this article uses the frequency splitting phenomenon when the MI intensity between the two coils is in a strong coupling area in the process of MI communication to generate multiple communication channel,then improves channel bandwidth and channel capacity of MI communication.The adaptive modulation and coding（AMC）method based on Orthogonal Frequency Division Multiplexing（OFDM）is applied to magnetic induction communication systems,which overcomes the frequency selective fading problem of MI communication channel and improves the transmission performance ofthe system.Firstly,this paper discuss the frequency splitting phenomenon in the direct MI communication system and waveguide MI communication system.Among them,the magnetic induction intensity between the coils in the waveguide MI communication system will also be enhanced in the case of frequency splitting Therefore,the magnetic induction of multiple adjacent coils is also considered in the waveguide MI communication system model.Secondly,based on the above two MI communication systems,the impacts of different circuit parameters on system path loss,channel bandwidth,channel capacity and channel transfer function are analyzed.It is proved that when the frequency splitting occurs,the MI communication system will produce multiple communication channel,so as to improve the channel bandwidth（above 20 k Hz）and channel capacity(above 200 kb·s^-1)of the system.It also shows necessity of consider the magnetic induction of multiple adjacent coils in waveguide MI communication system and the characteristics of high frequency selective fading of the MI channel.Finally,based on the above research conclusion,the design and performance analysis of the OFDM-based adaptive modlation and coding MI communication system are completed.The system parameter of OFDM are reasonably designed according to the select of MI system parameters,and then the fixed threshold algorithm with low algorithm complexity is selected as the adaptive modulation coding algorithm to inspect the bit error rate,frame error rate and throughput of the system.Theoretical analysis and simulation result show that the adaptive modulation and coding MI communication system based on OFDM designed in this article can Maximize the system throughput under the premise that target bit error rate is lower than 10^-2 and the target frame error rate is lower than10^-1,so as to ensure the effectiveness and reliability of MI communication.