Research For Narrow-Band Interference Suppression Technology In DSSS Based On Wavelet Packet Transform

The technique of spreading spectrum has got rapid progress because of its inherent anti-jamming character. Direct sequence spread spectrum (DSSS) is a typical spreading spectrum techinque. The anti-jamming ability of DSSS system is decided by its processing gain, which can be increased by augmenting the bandwidth. However, processing gain is always finite because there are some restrictions in bandwidth and techniques in a practical system. A narrowband interference (NBI) has a greater power spectral density. Thus it will bring more strong devastation to the DSSS system than a broadband one does.So it is difficult for DSSS system to ensure a high quality of communication by itself when strong interference exists, even communication may be intermitted. Therefore researching more efficient techniques to suppress the narrowband interference has great practical significance.Firstly,Many kinds of filter techniques are presented in this paper, e.g. linear and nonlinear filters in the time domain and filters in the frequency domain.These traditional filters have some limitations and defects for suppressing narrowband interference.Due to its multiresolution and good time-frequency properties ,wavelet-packet transform can track the spectrum varieties of the input signals. And then the interference is localized in a definite frequency domain. So the application of wavelet-packet transform to interference-excision has hold people's interest.Through comparing and summarizing the traditional filters, anovel adaptive interference suppression scheme based on Adaptive Time-frequency (ATF) is put forward. In this scheme, the decomposition of the received signal realized by adaptive time-frequency in DSSS systems is studied.The performance evaluation of the excision techniques via ATF is presented. The optimal adaptive NBI rejection arithmetic is also proposed using the adaptive filter instead of sub-band excision, which suppresses NBI efficiently and impoves loss of the avail signal. Analyzed and simulation results show that the interference suppression method of adaptive wavelet packet decomposition based on the ATF algorithm will obtain better performance than that of conventional sub-band elimination. Additionally the orientation speed of the adaptive algorithm can be increased. NBI can be suppressed effectively.