Research Of Interference Suppression Methods In DSSS System Based On Matched Signal Transform

At recent years, the wideband time-varying interferences which have a great impact on direct sequence spread-spectrum (DSSS) systems attract more researchers'attention. Among them, chirp-like interference is a common type of time-varying interferences. It includes two categories: linear (LFM) time-frequency structure and nonlinear (HFM) time-frequency structure. At present, domestic and foreign researchers have acquired some wideband time-varying interference suppression technologies based on the time-frequency distribution. Compared with narrowband interference, the processing algorithm of wideband time-varying interference is more complex and difficult. Moreover, for those interferences with nonlinear time-frequency structure, the interference suppression technologies are often useless.The research results of the current matched signal transform (MST) show that the MST of the received signal mixed with interference have a very obvious feature in the frequency modulation rate Domain (FMR), which makes the parameters estimation very easy.This paper aims at the chirp-like interference that often appeared in DSSS systems, and several effective MST interference suppression algorithms are proposed: adaptive time-varying filtering algorithm, peaks-holding algorithm and interference reconstruction based on twice MST algorithm. Adaptive time-varying filtering algorithm is mature now and is combined with MST, which become a new algorithm. Peaks-holding algorithm is based on fast MST algorithm and the original interference suppression algorithm which includes thresholding and masking. Interference reconstruction algorithm is an interference estimating algorithm, which needs MST transform to get the interferences'amplitudes and frequency-modulation rates (FM). These algorithms have a key point that is the estimation of FM rate or the thresholding value. So the paper also presents two estimation algorithms.Research results show that the new interference suppression algorithms have lots of strongpoints such as lower bit error rate (BER), well robustness, a small amount of computation, realizing easily, all of which lead to broad application prospects.