Design And Simulation Of Narrow-Band Interference Suppression Filters In SSC Systems

Because Spread Spectrum Communication (SSC) has unique advantages of anti-jamming, information hiding, easy encryption, arbitrary location, ease of networking and etc., This technology has been widely used in military communications, electronic countermeasures, as well as positioning, measurement, mobile communication and other fields since the U.S. Military started the study in the mid-1950s. Since Spread spectrum communication system, reconnaissance, jamming and anti-jamming communications, electronic warfare have became research hotspots, Many countries are vigorously developing SSC anti-interference system. The mechanism of spread-spectrum technology is the use of a relatively wide frequency band, and will provide greater possibilities for interference which could be constant time-varying narrowband interference, impulse interference and other interference. Therefore, the research and application of SSC has important theoretical and practical significance.At present, narrowband interference suppression technologies in time domain and transform-domain are widely studied. Based on the previous studies, further improvements are made in this master dissertation and the presented methods have better performance in view of the current existing problems. The master dissertation is organized as follows:Firstly the basic theory and principle of SSC are introduced, which include the characteristics of SSC and pseudo-random code used in SSC. Taking the direct sequence spread spectrum communication system as an example, we analyzed the anti-jamming performance of spread spectrum communication system.Secondly, we simulated and discussed the interference suppression filter in time domain and transform domain respectively. The interference signals used in this process are mainly polyphony signal with fixed frequencies and chirp signal whose frequency is sweeping all the time.The filters in time domain includes horizontal adaptive filters, lattice adaptive filters, and the combination of horizontal and lattice adaptive filters. As shown in this paper, we studied and simulated these three types of filters. We made some alteration on some algorithms in the simulation process and made it have better performance in narrow-band interference suppression and more improvement on SNR. In simulation, we applied the LMS adaptive algorithm, because this algorithm with fast convergence characteristics is easy to implement. We compared and discussed the performance of SNR improvement of these algorithms.In transform domain, narrow band interference suppression technology based on real-time frequency domain is not sensitive to disturbance frequency, number and energy changes. It can effectively suppress narrow-band interference and time-continuous, fast changing interference. This technique may use fast algorithm for real-time processing, and can dramatically save the system resources. So we studied the frequency domain interference suppression. The filtering algorithms in the frequency domain includes TZ(threshold Zeroize), TC(threshold Clipping), CMF(Condition Median Filter) and so on. We make some alteration on some algorithms in the simulation process.The improved algorithms were simulated with the MATLAB platform and proved to have better performance in narrow-band interference suppression. In the FFT and IFFT transform process, we used some signal processing methods such as windowing and lapped processing. A section was written to introduce the interference suppression techniques based on filter bank.Finally, We summarized all the work we did for this research. And also we compared the narrow-band suppression performance in time domain and the one in transform domain.