Research For Technology Of Suppressing Narrow-band Interferences In DSSS Communication Systems

Modern communications is a important driving force of the social civilization and progress. As a method of the spread spectrum communication, the Direct Sequence Spread Spectrum(DSSS) communication has been widely used in military and civilian defense communications mobile communication. With the anti-jamming ability and being benefit for resolving the nervous things of frequency resource, DSSS system is favored by people. Though it has strong anti-jamming performance in theory analysis, its anti-interference ability becomes bad because of the various restrictions in practical engineering application. It is easy to make the communication performance of DSSS system seriously deteriorating by high power narrow-band interference. Therefore, research for improving the anti-jamming ability of DSSS system through signal processing method has very vital and profound significance.Firstly, this paper introduces the study background and importance for suppressing interference in Spread Spectrum system, which also summarize and analyzes the techniques and methods. Secondly, basing on reading up large number of relevant literature, the article researches three narrow-band interference suppression algorithms, and makes appropriate simulation. At last, it gives some discussions and concussions and conclusion as well as future study directions. The main tasks completed in the thesis are as follow.(1)Study of adaptive threshold in suppression narrow band interference based on wavelet packet transformsFrom the theoretical foundation knowledge of wavelet and wavelet packet transformation, this article analyzes and researches narrow-band interference suppression algorithm based on wavelet packet transform in DSSS. Improving the algorithm on the basis, and it hand out the method of adaptive feature threshold narrowband interference suppression based on wavelet packet transform. The simulation results show that interference suppression and robust has improved, compared with the traditional fixed threshold algorithm.(2)The research on interference estimation and cancellation algorithm Based on singular value decomposition of matrixThrough researched, The data observation space of the DSSS signal can be composed into the jamming signal subspace of interference and the noise sub-space by the DS signal and background noise signal, and that the two sub-space are orthogonal mutually, what estimate and reject the interfere with the jamming signal subspace to realize restrain off narrowband interference. The method through the singular decomposition is able to accurately estimate the narrowband interference from computer simulation, which makes the interference cancellation effect better. At the same time, this algorithm will not wear down the useful signal and insensitive to the change of the interference, and with good robustness.(3) Study of estimation and cancellation interference by the propagation operatorThe method of interference estimation through the propagation operator is also way of based on subspace decomposition algorithm, likely the singular value decomposition. But the propagation operator method is more superiority than the singular value decomposition in the time complexity of algorithm. By the way, the estimation algorithm based on communication operators to better estimate of single interference, but bad for dual and sound of narrowband interference estimate.From the above, from interference eliminate and cancellation two perspective, the paper improved the existing reject algorithm, and put forward that based on the subspace decomposition theory to estimate and reject interference. It Improved narrowband interference inhibitory ability of DSSS, and improve the system of communication performance and strengthened robustness of anti-jamming of system, with certain practical value.