The DSSS System Transform Domain Interference Suppression Technology Research

Direct sequence spread spectrum (DSSS) system has been payed sufficientattention in the field of both military and civil communications, espacially in theaspacts of anti-jam communication, satellite communication, navigation, and secretcommunication, because of its strong anti-jam capability, strong concealmentcapability, the performance of CDMA systems, the anti-fading performance and thecapability of anti multi-path interference.Whereas its anti-interference capabilitywould be quickly decreased when the strength of the jammer exceeds the jammingmargin of the system.So the technique of interference suppression in DSSS systembecomes one hot spot of research on military communication.This thesis conducts a research on the narrowband interference and LFMinterference in DSSS system by FFT and FRFT in the transform domain.The maincontents of this thesis are given as follows:1. The basic principle of anti-interference in DSSS system, the basic theory ofFFT and FRFT (Fractional Fourier Transform) are researched. Several commoninterference signals are also introduced and their FFT and FRFT are also analyzed.2. A better interference threshold algorithm of successive interference excision isstudied to set the interference threshold of narrowband interference suppression byFFT. The analysis of simulation results shows that this new algorithm furtherdecreases the bit error rate(BER) of system and is more adaptable to changinginterference environments and it can suppress the interference in the strong andmutlti-narrowband interference environment than the fixed interference thresholdalgorithm.3. The thesis contributes to the study of wideband LFM interference in the FRFTdomain because FFT is hard to suppress the LFM interference. The key point ofsuppressing LFM in FRFT domain is to find the best rotation angle of LFM. BecauseLFM interference has the best aggregation in a proper rotation angle in FRFT domain,this thesis studies a new method of searching the best rotation angle. Simulationresults show that this new method can precisely find out the best rotation angle of LFM in FRFT domain and suppress LFM interference sufficiently.