Design And Simulation On Narrowband Interference Suppression Technology For DS/FH Hybrid Spread Spectrum Communication System Based On Modulated DFT

Direct Sequence/Frequency Hopping(DS/FH) hybrid spread spectrum communi-cation system has very strong anti-jamming capability due to the advantagescombination of direct sequence spread spectrum systems and frequency hopping spreadspectrum system. It has been applied in military communications and civiliancommunications widely. According to the emergency needs, to further enhance theanti-jamming capability of the system, it is necessary to combine with interferencesuppression technology.Suppression technique for narrowband interference in DS/FH spread spectrumcommunication system is researched in deep. Based on the requirement analysis ofinterference suppression, a suppression method for narrowband interference, overlappedwindowing modulated Discrete Fourier Transform (DFT), is applied to received dataafter intermediate frequency. The principle of modulated DFT is deduced andimplementation structure of the method is provided. By modulated DFT, processing rateis decreased for high speed intermediate frequency data and the total length ofmodulated DFT data unchanged with the reduction of the length of FFT data. In result,the computation speed increases and suppression ability for narrowband interference isimproved. Simulation results show that side lobe interference signals dropped about92dB by adding Blackman-Harris window. So the effect of strong interference signalspectrum leak is decreased and makes it easy to identify and deal with the interference.Also, the loss of SNR introduced by windowing is reduced by overlapped windowing.In transform domain, anti-jamming performance of system is decided mainly byinterference detection and appropriate processing. To reduce the computationcomplexity of traditional double threshold algorithm, a fast algorithm based onfragmented detection is presented. The improved algorithm reduces the computationcomplexity of initial threshold greatly. Simulation results show that the new algorithmis simple, valid, robust and suitable to hardware implementation.Considered the loss of SNR and signal amplitude due to windowing, overlap-addand overlap-select are introduced to reduce the loss of SNR and improve signalamplitude. Different optimized schemes are compared. The requirement of hardwareresources for implementing every scheme is simulated and the rules for choice andimplementation of it are carried out. Focus on the loss of signal amplitude due towindowing and interference suppression, an adaptive amplitude recovery algorithm ispresented to recover signal amplitude processed by interference suppression.The methods and research results presented in the thesis have been applied toemergency communication system.