The Research And Realization Of Adaptive Narrow-band Jamming Suppression Algorithm

Direct sequence spread spectrum is a rapidly developed communication technology; therefore, it has been widely applied in the military field as well as in the civil. Its capability of narrow-band interference suppression is one of its outstanding advantages, but when outside interference might be more powerful than accepted tolerance, system can’t wok on the rails. Therefore it is necessary to introduce corresponding interference suppressing measures for improving system performance to make system achieve communications task efficiently in the powerful interference environment. A simplified signal model of digitalized receiver and the signal model of interference are provided. And it is analyzed in detail the capability of direct sequence spread spectrum communication systems in suppressing single tone interference, AR interference and partial band Gaussian interference.Currently, the time domain adaptive filtering method and the transform domain adaptive filtering method are methods commonly used for narrowband interference suppression. The frequency domain adaptive filter decomposed the signal energy to each sub-band by ways of applying FFT transform. But the spectrum of direct sequence is supposed as the White spectrum, where threshold are a constant. And, it will compare the preset energy threshold with signal energy in each sub-band. If the sub-band signal energy is greater than the sub-band B, the sub-band will be suppressed, or not. The time domain adaptive filter Adaptive iterative algorithm requires a certain convergence period. However, in the frequency domain, the frequency components in each sub-band have convergent properties independent. So it could convergence speed with the adaptive iterative algorithm.Because bandwidth is limited, the signal spectrum is no longer white spectrum in actual system. And then if the energy threshold B in each sub-band has the same value, the interference suppression performance will lose. According to the characteristic of the direct sequence spectrum, adaptive energy threshold was used to decide the thresholds of energy ruling dynamically. The results of narrowband interference suppressions simulations based on the adaptive energy threshold algorithm proves that the performance of the adaptive frequency domain filter behaves better.