Research On Jamming Rejection In DS System Based On Smart Antenna

Currently,Spread-Spectrum(SS) technique has been widely applied both in Military and in eivilian communications for its many advantages,which make it Suitable for the environments of wireless communication.The best advantage is its out standing ability to anti-jam if the processing gain is large enough.However,its ability of inter ference suppression is always limited.The system performance is dramatically degraded and its capaeity is largely reduced if the Processing gain is not sufficiently large and no other methods can be adopted to suppress strong interference.Therefore,interference suppression is crucial issue in SS systems. It is necessary to apply the special suppression techniques in new detection structures. In this paper the figures of sending end and receiving end of the direct sequence spread spectrum system are in troduced.Also it deseribes the realization process of DS-SS system from the maththeory.At the same time various adaptation algorithms used in CDMA system are discussed,such as SGD,LMS,NLMS,decision-direct algorithm,MOE and Griffthms,algorlthm.This paper over views some commnonly used cost function of the adaptation algorithms that minimize them and analyse convergence simply.this paper simply in troduces the emergence,development,basic working theory,characteristics and the merits of smart antenna.Then,the advanced algorithms of DOA estimation on this paper are the multiple signal classification method,esprition of signal paramenters via rotational invariance techniques algorithm and estimation of spatial two-dimension DOA. All of the methods above introduce the algorithms basic theory and array models,and by computer simulation, analyzing the validity and performance of this algorithm deeply.Finally according to the MVDR algorithm, propose one based on the smart antenna aspect improvement algorithm,which can greatly depress the interference, is proposed. within the null space of the steering vectors vectors matrix of interference signals, the weight vector which is closest to the steering vector of the expected signal and deeply depresses the interference signals simultaneously comed be obtained with least square method through the linear combination of orthogonal basis. Computer simulation is carried out to validate the above feasibilities by the research tool of the software MATLAB.