In this paper, a novel wavelet packet modulated direct sequence spread spectrum system is introduced, and an anti-jamming algorithm is also developed to suppress narrow band jamming signals. According to the time series theory, Fisher's test can detect the hidden sinusoids in an AWGN environment, which give us a clue to detect the jamming signal. We generalize this algorithm so that we can detect the hidden wavelet packet components in an AWGN environment. The normalized energy distribution of the wavelet packet transformed signal is derived, a threshold is determined and the jamming signal is excised. Jamming signals with different strength and different bandwidth are investigated. Based on the simulation results, the generalized Fisher's test can effectively suppress interference in wide ranges.
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