Research On Narrowband Interference Suppression In Spread Spectrum System Based On Adaptive Convex Combination Algorithm

In military field, spread spectrum communication system often suffer human deliberate interference, the most common situation is narrowband interference. Narrowband interference has a great impact on system, even make the system can not work. In order to eliminate the impact of narrowband interference and ensure the spread spectrum communication systems work well, the method of interference suppression based on convex combination of adaptive filter is studied in this paper.Firstly, the theory of spread spectrum communication technology is introduced in this paper, including the basic theory, classification and characteristics. Three mathematical models of narrowband interference are set up, including audio interference model, autoregressive interference model and low data rate digital interference model. The methods of narrowband interference suppression are researched, including time-domain prediction technology, transform domain interference suppression technology and code-aided optimal filtering technology, and the performance, advantage and disadvantage of the three methods are analyzed.Secondly, based on researching the single adaptive filter algorithm, the stationary performance and the tracking performance are analyzed. Furthermore, the characteristic of convex combination which can get the advantages of components is proved in theory. To further improve the performance of convex combination method, several different adaptive convex combination algorithms are analyzed, and the shortcomings of normal convex combination method are indicated. The reasonable improved methods are proposed, which include improving the performance of component filter, quickening the updating speed of the weight cost of the slow filter at the beginning of the algorithm, changing the adaptive process of the auxiliary parameter, enhancing the information utilization of the convex combination filter and component filter. Based on the proposed methods, the normal convex combination of steady step-size LMS (CLMS) method is improved, a new method which is called convex combination of variable step-size LMS (VSS-CLMS) algorithm is proposed, the new method designs the steady step-size and combined step-size to variable step-size, uses the fast filter to quicken the speed of the slow filter at the beginning of the algorithm, and validly utilizes the information of component filters and the overall filter, so it can be adaptively adjusted base on the changing environment, and the overall convergence speed is further improved.Finally, the adaptive convex combination algorithm is proposed to be applied to spread spectrum system, to suppress the common narrow-band interference, and the adaptive convex combination of notch filter is designed by combining the advantage of adaptive notch filter, to suppress the single frequency interference. The computer simulation results show that the adaptive convex combination algorithm has a good narrowband interference suppression capability.