Based On The Transform Domain Narrowband Interference Suppression Technology Research And The Fpga Implementation

Direct Sequence Spread Spectrum technology is an important means of communication, it usually used in some current and future cellular communication systems because it has many advantages, applied to the field of Global Positioning System (GPS), satellite communications, short-range wireless communications. Although the direct sequence spread spectrum technology with certain narrow-band interference suppression, its narrow band interference suppression capacity mainly restricted by spreading gain and SIR, and the pseudo-random sequence cycle of Direct Sequence Spread Spectrum can’t increase indefinitely because of the restriction of hardware implementation and other factors, dispreading module of the receiving end can’t expand the spectrum broadband of narrowband interference unlimitedly. So it is necessary to research on the narrowband interference suppression method of Direct Sequence Spread Spectrum, in order to reduce the impact of narrowband interference on the performance of Direct Sequence Spread Spectrum.This paper mainly studied on transform domain narrowband interference suppression, the main process is projected the time-domain signal to frequency domain, adopted a kind of certain measure to detect narrow-band interference signals, eliminate it and then transform it to restorative signals; this paper also researched deeply on narrowband interference suppression which based on FFT and wavelet packet transform, select the former as project realization, Using Verilog HDL language designed a hardware circuit for FPGA.Firstly, this paper studied on the narrowband interference suppression which based on FFT, based on the accurate discrimination of narrow-band interference resides band, in the light of some features, such as the performance of spread spectrum signal is relatively flat, the interference amplitude of narrow band is relatively large and the frequency band is relatively narrow, implemented reset processing on narrowband interference resides sub-band in order to suppress narrowband interference; focused on Discussing the relationship between various windowing functions and the SNR loss, used overlapping complex method to decrease the degree of signal distortion which is made by the interruption of data; and then introduced some common threshold algorithms, such as segment threshold method median filtering algorithm and λ algorithm, an appropriate interference threshold is the key to this kind of algorithms. The MATLAB simulation results showed that this algorithm can completely filtered out of the narrowband interference in direct sequence spread spectrum systems on the premise of the precise positioning of narrowband interference resides sub-band and reasonable threshold algorithm.Secondly, the wavelet packet transform have the ability to suppress interference signals, but it will removed all signals including the useful signals. The suppression algorithm the author adopted in this paper is to combine wavelet packet transform with LMS algorithm, the wavelet packet transform is equivalent to an ideal filter group, it made the binary tree decomposition of input signal come true, it could determine the location of interference sub-band by the energy gathered and the around node power rate, then adopted LMS algorithm to adjust adaptively for the filter tap coefficients, executed larger attenuation factor on sub-band which disturbed seriously, able to suppress the narrowband interfere effectively. The MATLAB simulation results indicated that the process realization of this algorithm is longer, more complex and it has large amount of calculation, but the interference position is faster and the effect of suppression is more obvious.Lastly, the FFT transform narrowband interference suppression algorithm which is based on FPGA is consist of Hamming window module, FFT/IFFT module and auto-adapted disturbance threshold module, the realization of each module is by Verilog HDL language, the simulation analysis showed that the circuit can achieve the desired performance; it can suppress the narrowband interference effectively, so its accuracy has been verified.