Interference Suppression Technique Based On Time-varying Filter

With the explosion growth of wireless communication technologies and applications,various network systems coexist at the same time,causing the amount of wireless services increasing.Therefore,it is an urgent need to increase the system capacity and utilize the limited spectrum resources rationally.The network of different systems coexists in time domain,frequency domain,airspace domain and other different resource domain together which produce mutual influence inevitably.To deal with the complex interference problem in large-scale wireless network,this thesis aims at the anti-interference technology in joint time-frequency domain and conducts a series of studies,especially on the application of time-varying filtering in interference suppression.Firstly,the system model of spectrum resource allocation based on low-energy holes of energy distribution in the time-frequency domain of pulse shaping signals is studied.We analyze the feasibility of this model and the selection of shaping pulse.The mutual influence between useful signals and interference signals are analyzed in this scenario.We design the time-varying filter to suppress the interference,and optimize the tunable parameters to get filtered outputs with a higher signal to interference and noise ratio and reduce the system error rate.Then we verify the performance of the resource allocation system model under frequency-selection channel,with the single-carrier frequency domain equalization against fading.Secondly,we research the modeling method of fast time-varying channel.The fast time-varying channel makes the signal present dual dispersion characteristics in time and frequency domain.We improved the traditional time-varying channel modeling method to make it closer to the wide-sense stationary uncorrelated characteristics of the actual channel.And we introduce the method of time-frequency analysis to study the time-varying characteristics of double dispersive channel,depicting deep decline changes of wireless channel in time-frequency domain,from which we can obtain both global and local characteristics of channel,and compensate the influence on signals of channel in the time-frequency domain.Finally,we take the use of methods of time-varying filter to improve the channel equalizer in dual dispersion channel.The time-frequency domain representation is obtained by Short Time Fourier Transform after truncating reception signal according to the channel correlation time,and the equivalent timeinvariant approximation is made for the channel within the correlation time.The time-varying filter coefficients are designed according to the approximate time-invariant channel frequency domain transfer function to reduce the complexity of traditional equalization methods for inverting channel matrix and improve the equalization accuracy.