Low SNR OFDM Signal Enhancement Based On Intra-Well Stochastic Resonance Of Bistable

Orthogonal Frequency Division Multiplexing(OFDM)is a high-speed data transmission technology,which is widely used in mobile communication transmission system,wireless LAN and other fields.Considering the influence of a large number of background noise in complex electromagnetic environment,the received signal presents the characteristics of low signal-to-noise ratio,which is not conducive to the correct demodulation of data.In this thesis,the stochastic resonance(SR)method is applied to the enhancement of OFDM signal with low SNR to improve the demodulation performance of OFDM system.The main contents of the thesis are as follows:(1)The basic principle of OFDM and the basic theory of nonlinear stochastic resonance are introduced.The principle of OFDM modulation is described and the OFDM system model is built;The mathematical model of bistable stochastic resonance is derived by using nonlinear theory analysis method,and the essence of stochastic resonance is analyzed by changing system parameters or noise intensity.(2)The signal enhancement mechanism of bistable stochastic resonance is introduced.The numerical iterative algorithm for stochastic resonance is derived,and the interwell stochastic resonance and intrawell stochastic resonance are deeply compared.This thesis discusses the essence of the enhanced signal of stochastic resonance,and verifies the feasibility of the enhanced output of stochastic resonance system when the input is single carrier signal and multi carrier signal.The significance of applying stochastic resonance to OFDM signal enhancement processing is introduced,and a method of OFDM signal enhancement and demodulation based on intrawell stochastic resonance of bistable is proposed.(3)The internal mechanism of enhancing OFDM signal with low SNR is studied.The analytical expression of transient response time required for the intrawell stochastic resonance system excited by multicarrier signal is derived,and the energy loss in OFDM symbol caused by transient response is analyzed;The analytical expression of steady-state output of nonlinear system is derived,and the problem of superimposing DC bias component on the subcarrier modulated signal is analyzed.On this basis,the OFDM baseband complex signal is enhanced by simulation,and then the OFDM signal is demodulated by FFT and constellation inverse mapping.In this thesis,the stochastic resonance method is combined with the process of OFDM communication signal enhancement and demodulation,and the influence of different types of stochastic resonance on the output state of the system is analyzed in different parameter settings.It is proved that under the appropriate parameter selection,the cooperative effect of signal and noise in the well is realized,and the bit error rate of OFDM signal demodulation is reduced,It provides a method to improve the performance of OFDM communication system.