Research On TVAR Modeling For Wideband Interference And Suppression Methods In DSSS System

At recent years, the wideband time-varying interferences which have a great impact on direct sequence spread-spectrum (DSSS) systems attract more researchers'attention. Among them, frequency-modulation interference is a common type of time-varying interferences. It includes two categories: linear (LFM) time-frequency structure and nonlinear (SFM) time-frequency structure. At present, domestic and foreign researchers have acquired some wideband time-varying interference identification technologies based on non-parametric methods such as the time-frequency distribution. Compared with narrowband interference, the processing algorithm of wideband time-varying interference is more complex and difficult. Moreover, for those interferences with nonlinear time-frequency structure, the interference suppression technologies are often useless.We all know that sine signal in white-noise can be represented by AR modeling , recently research indicate that FM signal in white-noise can also be represented by parametric modeling. the model parameter is allowed to varying with time to catch up the time-varying frequency of the FM signal .This paper aims TVAR modeling of the linear and non-linear frequency-modulation interference that often appeared in DSSS systems, efficient iterative method to calculate the time-varying coefficient is also referred.This thesis focus on how to choose the model order, how to choose the basisfunctions and the dimension of the basis function.Thesis selects three simulation modeling of typical FM interference - LFM-interference, non-linear single-component FM interference and the two components of the LFM interference to study, practical conclusions were received.Limitations in using the proposed method for estimating the time-varying frequency or the spectrum of non-stationary signals are also mainly discussed.TVAR has been successfully shown for modeling linear and non-linear FM signal, once the instantaneous frequency of the FM signal been calculated, many interference suppression methods can successfully mitigate the jammer signal.