Research On Chaotic Communication Technology Of Underwater Conduction Current Field

Underwater conduction current field communication technology is a means of communication which is based on water as a medium and uses electric dipole antenna to sense field changes to get information.However,since the degree of attenuation of the received signal is inversely proportional to the third power of the communication distance,it is very difficult for the digital receiver to receive the signal when the signal-to-noise ratio is very low.DUFFING Chaos oscillator has a very high sensitivity to specific frequency signals and a strong out-of-band signal filtering ability to receive signals at very low signal-to-noise ratios.In this paper,the characteristics of DUFFING chaotic oscillator are used to improve the communication distance of underwater conduction current field,improve the anti-interference performance of the system and reduce the error rate of the system.This paper mainly studies the following aspects.?1?The mathematical model and communication principle of underwater conduction current field communication are analyzed.Aiming at the problem that the digital receiver can hardly receive the signal when the signal-to-noise ratio is low and the communication distance is far,this paper proposes to use chaos communication as a means.By analyzing a variety of chaotic communication models,a special kind of DUFFING chaotic oscillator model is found to solve the corresponding problems.Then the MATLAB simulation of the existing DUFFING chaotic oscillator model is analyzed.Based on this,an improved mathematical model of DUFFING chaotic oscillator is proposed,which is simulated by MATLAB and simulated by MULTISIM.The phase diagram fully proved that it does have chaotic characteristics.The dynamic behavior of the improved DUFFING chaotic oscillator model is analyzed in detail.The anti-noise performance of the improved DUFFING chaotic oscillator model is analyzed and simulated in theory and by MATLAB.?2?For the underwater conduction current field communication system which uses FSK as the modulation mode,the improved DUFFING chaotic oscillator model is taken as the demodulation means and the method of two-frequency single-phase filtering counting is proposed,that is,two-frequency improved oscillators processing,low pass filtering,selecting absolute values,sampling soft judgment,adopting statistics to eliminate interference,code decision are put forward to obtain the baseband signal.This method is simple and easy to realize by chip.The performance of this communication system is analyzed by bit error rate curve.In particular,we show that this systems presents the 2FSK communication with information transmission rate of 39.2bps,with BER of3*10^-4 and the SNR of-16dB.It effectively improves the communication distance and reliability of the underwater conduction current field communication.The corresponding hardware implementation system is designed.In order to solve the problem that the carrier signal frequency in the hardware is slight different from the MATLAB simulation,A two-frequency four-phase filter counting method is proposed.The use of hardware description language Verilog completed the preparation of the corresponding modem,and physical implementation.?3?Aiming at the underwater conduction current field communication system which uses PSK as the modulation mode,same as the method of FSK chaotic demodulation,That is,using single-frequency two-phase filtering counting method.According to the bit error rate curve,this systems presents the 2PSK communication with information transmission rate of39.2bps,with BER of6*10^-5 and the SNR of-16dB.In case of frequency difference,two methods are proposed,one is based on the hopping point eight-phase filter counting method,that is,the eight phases are demodulated at the same time,using the processed data value jump to obtain the baseband signal.The other is similar to the previous one,except that only four phases are demodulated at the same time,and the transition point is judged by determining the period state of less than half of the time length.Simulation and analysis with MATLAB and the use of FPGA physics to achieve underwater conduction current field voice signal and digital signal transmission.In this paper,the underwater conduction current field chaotic communication system with FSK modulation and PSK as modulation mode can communicate at lower signal-to-noise ratio and improve the distance and reliability of underwater conduction current field communication.At the same time,it also retains the abilities of underwater conduction current field communication about strong adaptation to the environment and high flexibility.