Research On Blind Detection And Parameters Estimation Of Direct Sequence Spread Spectrum

Because of the fast development in modern communication technology and detection technology, research in military Communication Counter-Measures field has been made a great progress. As a signal with large bandwidth and difficult detection, spread spectrum signals have low probability of being intercepted and captured, strong discrimination ability, so the Spread Spectrum technology has got wide usage upon mobile communication, radar, navigation and orientation. People have great interest in DS-SS detection and have developed the research work with high passion.A lot of DS-SS signals estimation methods have been developed. These methods are almost based upon the theory of conventional signal detection and estimation. However the DS-SS signals are wide-band weak signals, they are not in conformity with the theory of conventional signal processing, so when the signal to noise ratios of the received signals becomes lower, the performance of the methods take a turn for the worse, the methods don not work. Presently, the development of DS-SS signal estimation is slow, it is almost in study of conception and concrete method, is far from comprehensive and mature.In this dissertation, three detection methods: square frequency detection, time-domain correlation detection and higher-order cumulant are applied to detect the DS-SS signal. Every method can estimate a different parameter of the signal with good performance. The square frequency detection combined with correlation accumulate technique can pick up the carrier frequencies, and the algorithm is simple and has great performance. But this method can't recognize the signal as spread spectrum signal. Time- domain correlation combined with second spectrum, using the periodicity of the DS autocorrelation function, can estimate the symbol and its second moment also can estimate the carrier frequency. A sort of detectors based on fourth-order statistics slices are presented to detect the presence of signal and estimate the carrier frequency and symbol period of DS-SS/BPSK signal. Because the detector based on the fourth-order cumulant 2-D slice, which has better ability to suppress Gaussian noise, possesses both characters of square detector and correlation detector, it can estimate not only the carrier frequency, but also the symbol period.