The Research Of Narrowband Interference Suppression On Variable Step Size LMS Algorithm

Direct sequence spread spectrum (DSSS) communication technology has the secrecy, extremely flexible channel allocation ability and strong resistance multipath and anti interference ability, is widely used in the military communication, civil communication and satellite communication and other aerospace measurement and control fields. Anti interference method of direct sequence spread spectrum communication system is without increasing the spreading gain conditions, using the difference of the useful signal and interference signal spectrum, by processing the received signal, to achieve the purpose of suppressing interference. However, because of the artificial malicious interference, regular DSSS don’t completely satisfy the ability of interference suppression in the actual communication, therefore we need to use various algorithms and interference rejection technology to handle the interference in the communication process.The purpose of this paper is to narrowband interference suppression in DSSS communication system, emphasis on the time domain interference in DSSS system suppression algorithm, the simulation analysis of performance of adaptive LSL filtering algorithm for narrowband interference suppression, through analysis the LMS adaptive filtering algorithm and the adjustment rule of step, put forward a new interference suppression algorithm with variable step size adaptive. The advantage of this algorithm compared to previous algorithm, can converge fast, steady performance and more stable. The main work is as follows:1 Build simulation platform on MATLAB software, analyzes the model and modulation in DSSS system, simulation the ability of the anti interference, verify the performance of direct sequence spread spectrum system, and through experiments in under the narrowband interference in DSSS system necessity of adding interference suppression, analysis of audio interference and autoregressive (AR) mathematical model and the characteristics of interference.2 This paper studied the adaptive filtering technique in time domain, analyses the condition, commonly used linear filtering and nonlinear filtering algorithm, analysis LMS adaptive filtering algorithm and the normalized LMS adaptive algorithm. The structure of the traditional transversal filter, LSL lattice algorithm can based on forward prediction error and the backward prediction error, to solve the difficult coordination problems of LMS algorithm in stability maladjustment and convergence speed. Through simulation, the algorithm not only combines advantages of fast efficiency and convergence of the LMS algorithm, but also can greatly improve the rejection of narrowband performance in spread spectrum communication system.3.For the rejection of narrowband signal and reduce the interference of the DSSS communication system, research on a new variable step size LMS algorithm for signal processing. According to the step size adjustment principle, on the research step size LMS algorithm conditions, combined with hyperbolic secant function to adjust the step size μ(n) and the error of e(n) nonlinear relationship. The performance of the algorithm and learning curve for theoretical analysis shows that, this algorithm improves the convergence speed, upgrades the convergence precision, and reduces the steady state error. In MATLAB through building DSSS communication system, the research result indicates that this algorithm superior to the existing algorithm, can be more accurate prediction and suppression audio signal interference, enhance the anti interference performance of DSSS communication system.The thesis focuses on the study of direct sequence spread spectrum communication system, through deeply analysis of LMS adaptive filtering algorithm, improved narrowband interference suppression performance of the system.