Studying On Narrowband And Impulse Interference Suppression In LEO Satellite Spread Spectrum Communication Systems

Micro-satellite technology and system has a good application outlook in communication, remote sensing, science research, technique demonstration, interstellar exploration, education, and so on. The availability of low orbit satellite communication, which mainly operates with short message service, is impacted by the complicated radio environment in China and Southeast Asia.It is one of the key techniques in low orbit satellite communication system to suppress the in-band interference and jamming with some effective measures. This technique is significant in both theory and application.In this dissertation, some methods for narrowband interference suppression and impulse interference rejection in the low orbit satellite spread spectrum communication are studied.Firstly, the capability of some time-domain filters and frequency-domain filters for suppressing the narrowband interference in the received spread spectrum signal, which involves fixed multi-tone interference or non-stationary chirp jamming, are simulated. In these filters, some time-domain filters involve LMS-based linear and nonlinear transversal filters, Lattice-based linear and non-linear filters, other frequency-domain filters include TZ, TC, CMF, and so on, which use some signal processing methods such as windowing and overlapped processing.Based on above simulations, some modified algorithms are put forward: 1) a new non-linear LT.I filter in time-domain, 2) a simplified algorithm for estimating threshold between interference and others, and a method of attenuating the interference magnitude linearly in frequency-domain. These methods simplified the complexity in realization.Secondly, a double time constant automatic gain control is introduced for rejecting the impulse jamming in low IF received signals, and performance is analyzed. Based on the analysis result, a modified AGC is presented, with better performance of suppressing impulse interference over the former. The robustness of the receiver is enhanced by it.In the end, the research work in this dissertation and some latest narrowband interference suppressing methods in spread spectrum communication are summarized, which would prompt the following research.