A New OFDM-CR Channel Estimation Algorithm Used In Dynamic Channels Based On Fractal Theory

With the rapid development of mobile communication technology in recent years,the mobile Internet is also showing a thriving scence and more and more various new types of communication methods emerge.Meanwhile,people have higher requirements for the speed,bandwith and quality of communication.This will make the wireless spectrum resources which is limited and short in nature face severer challenges.Cognitive Radio(CR)is regarded as an effective method to solve the problem publicly.Channel estimation is one of the key technologies in CR systems.Except influcing the bit error rate(BER),the accuracy of channel estimation also influce the spectrum allocation and efficiency in CR systems.The traditional channel estimation methods usually assume that the transmitted signal is smooth and differentiable,so the linear mathematical theory can be used to model the channel.However,most of the natural phenomena and social phenomena are nonlinear in real life.The nature of multipath fading signal is a nonlinear dynamic evolution process under the combined action of environment.However,the traditional channel estimation method ignores the "saw tooth" part of the signal waveform and think the waveform is smooth,so the details of the signal waveform can not be modeled.When the channel becomes dynamic,unflat and fading-fast,the traditional channel estimation method will be unable to estimate the channel state of cognitive radio effectively.Fractal theory is a nonlinear science.Firstly,a new OFDM-CR channel estimation algorithm used in fast time-varying fading channels based on fractal theory is proposed in this paper,which analyzes the channel of OFDM-CR systems in a viewpoint of nonlinear dynalics and try to use a new method to research.Secondly,we use the fractal dimension to characterize the variety law of multipath fading signals under the combined action of environment,which is more consistent with the transmission nature of multipath fading signals.At last,A new interpolation algorithm based on the fractional Brown motion model is proposed,which can effectively reflect the micro changes of multipath fading signals.Simulation results show that the proposed algorithm can track and estimate the dynamic channel of CR systems better.Compared with the traditional algorithm,the algorithm proposed in this paper has lower error rate in dynamic channel.