Research And FPGA Realization Of Narrow-band Interference Suppression Techniques Based On Time-domain Adaptive Filter

Direct sequence spread spectrum (DSSS) communication systems have been widelyemployed in civilian and military fields, for its good performance in anti-interference,interception, confidentiality and Code Division Multiple Access(CDMA) communication.Spread spectrum for itself bares a certain amount of anti-interference ability, butinterference rejection shall be adopted in improving system performance when jammingintensity exceeds the interference limits.Because of its less resource consumption, lowalgorithm complexity and interference suppression performance advantages, thetime-domain adaptive filteringing algorithms is widely used in interference suppression ofspread spectrum communications.This paper firstly studies the time-domain adaptive filtering narrowband interferencesuppression technique based on the minimum mean square (LMS) algorithm, and goes on asimulation by Matlab with the project background and index requirements of this paper. ABit Error Rate(BER) simulation results can be see, this scheme is effective and feasible, andhas an excellent performance.Secondly，the effect of time-domain adaptive filteringing algorithms on PseudorandomCode Zero Value in PN code ranging system is presented. The equivalent filter model forclassic NBI suppression algorithm is used to establish the model of analyzing the effect ofNBI suppression on Code Phase bias. Then, the article works out the relationship betweenthe code phase zero value bias and equivalent filter, and gives the simplified analyticalmodel. Both theoretical analysis and simulations illustrate that, linear phase filter has noeffect on code phase zero value; Nonlinear phase filter has an effect on carrier phase zerovalue, which is directly related to the convolution results of filter and Pseudo-codeautocorrelation function.Then, this article presents a study in order to solve the problem of spread spectrumsignal distortion caused by raised correlation between the samples, when generaltime-domain adaptive filtering narrowband interference suppression method is used in theoversampling direct sequence spread spectrum system. The proposed algorithm is on thebasis of interpolating transversal filter with two-sided taps and the minimum mean squarealgorithm for updating the weights adaptively, combined with downsample-upsample structure. It could effectively suppress narrowband interference. Both theoretical analysisand simulations illustrate that, the proposed algorithm has not only lower Signal-to-noiseRatio loss, but also such excellent characteristics as small distortion of desired signal in thehigh Signal-to-Noise Ratio(SNR) conditions, meanwhile it has a slight advantage in BERperformance in the low SNR conditions.Finally, a FPGA implementation and hardware simulation for the time-domainadaptive filtering narrowband interference suppression technique based on the interpolatingtransversal filter with two-sided taps this paper proposed are carried out, so as to verify theperformance and feasibility of the scheme.