Adaptive Algorithms Of Suppression Narrow-Band Interference In DSSS

Spread spectrum communication is used widely in the CDMA system and military communication because it can suppress narrow-band interference (NBI) in the common degree. The small center frequency difference between NBI and spread spectrum signal or the large NBI power will make spread spectrum communication invalid. So the work on the suppression NBI in the spread spectrum communication will be significative.The valid NBI suppression algorithms of spread spectrum communications must be adaptive algorithms which can change parameters adaptively, because the optimizing suppression algorithms relates to the statistic characteristic of NBI. On the basis of the time-domain adaptive algorithms and frequency-domain adaptive algorithms, the modified ones are proposed which performances are demonstrated.Firstly, the frequency-domain adaptive filter which is used to suppress NBI in the spread spectrum system is modified. Because the DS with color spectrum influ -ences the performance of algorithm to suppress NBI, the AET algorithm based on channel estimation and CF one based on combination filter are proposed. AET can design the sub-band energy thresholds, and CF can generate optimized sub band energy thresholds. So algorithms can suppress NBI in the spread spectrum system effectively, and the adaptability of CF is improved.Secondly, this paper summarizes the system info of LSL algorithms, as well as performances of LSL predictor, LSL interpolator and QRD-LSL interpolator to suppress NBI are analyzes contrastively. A novel variable (intermediate forward /backward predictor error substitutes for forward /backward predictor error to stru -cture improved QRD-LSL interpolator. So the calculation efficiency and robustne -ss are advanced, and it adapt well to finite precision occasion.The interior characteristic of the improved algorithms is analyzed chiefly in order to optimize the improved QRD-LSL interpolator to suppress NBI in spread spectrum system.At last, nonlinear mode of QRD-LSL interpolator is discussed. On the foun-dation of the nonlinear mode of ACM-QRD-LSL interpolator, the paper proposes the modified nonlinear QRD-LSL interpolator (CYC-QRD-LSL interpolator). Exp -eriments indicate that CYC-QRD-LSL interpolator can depress the eflfection of color spectrum of DS to the performance of QRD-LSL interpolator to suppress NBI.