Research On Carrier Frequency Estimation And Narrow-Band Interference Suppression Inhalf-Blind DSSS

Direct sequence spread spectrum communication system (DSSS) has been widely used in recent years for its advantages of low Signal-to-Noise ratio (SNR) and anti-multipath effect.As a common co-channel interference overlapping on spread spectrum, the effect of Narrow-band Interference (NBI) could not be neglected. Although spread spectrum systems could suppress NBI themselves to certain extent, the effective rejection techniques used for NBI suppression would enhance the performance greatly. Therefore, corresponding DSSS electronic counter technique has become an urgent problem to solve in electronic warfare domain.The work of thesis is as follows. Firstly, research on carrier frequency estimation and narrow-band interference suppression have been introduced in detail, simulation and analysis have also been done on common NBI.Secondly, basic model and ways of working in DSSS have been introduced. Then, modulation model is built on using matlab. Aimed at researching on carrier frequency estimation and NBI suppression, the functional block diagram is designed.Thirdly, Carrier frequency estimation is a key technology in realizing the blind estimation of DSSS signal, thus, this thesis is aimed at reducing error of the traditional FFT algorithm (assuming the receiver has already finished demodulation of spread-spectrum sequence), A new algorithm using squared or quartic filtering is proposed which is based on the traditional FFT algorithm. Simulations results show estimation precision is improved greatly.Fourthly, the narrow-band interference suppression technology based on windowed DFT in DSSS communication system is discussed in this dissertation. An improved algorithm is proposed which is based on transform domain, the overlap-add algorithm and the time delay in each path are employed to reduce the distortion of signal. Simulation results show that system performance of the bit error rate (BER) is improved greatly and the narrowband interference is suppressed effectively.Finally, summing up the whole thesis and analyzing the coming unsolved problems.