.ds / Qpsk Signal Blind Detection And Estimation Algorithm

Direct sequence spread spectrum (DSSS) communication systems has been widely used in these years for its advantage of wide spectrum, low working Signal-to-Noise ratio (SNR), anti-interference, anti-multipath effect and capability of LPI and LPD. They are increasingly replacing conventional communication forms and obtaining extensively applications in modern military and commercial communication systems, for example, CDMA communication system, GPS , measuring and control system, satellite chain, identification of friend or foe and etc. Therefore, corresponding DSSS electronic counter technique becomes a big problem to solve in electronic warfare domain. DSSS electronic counter technique including blind detection, blind parameter estimation and spreading sequences estimation. For the issue of DSSS electronic counter technique of DSSS/QPSK signal damaged by strong additive white Gaussian noise (AWGN), the main research content in this dissertation as follow.1,Both synchronous and asynchronous DSSS baseband signal are created and modulated to create DSSS/QPSK signal. At the same time, we introduce the demodulated method of DSSS/QPSK signal.2,The characteristics of power spectrum, time-domain correlation and high-order statistics of the DSSS/QPSK signal are used to detect the signal. And the computer simulation is launched to analyze and compare the capability of different detection method.3,Base on the adequate analysis of the characteristic of DSSS/QPSK signal, this dissertation mainly used carrier doubler method (CDM), auto-correlation method (ACM) and delay-and-multiply (DM) method to estimate the carrier frequency, the symbol period and the chip rate of DSSS/QPSK signal. At the same time, we introduced fourth-order cumulant 2-D slice method to realize multi-parameter estimate.4,Several usual blind code synchronization and spreading sequences estimation methods, including matrix eigenvalue decomposition (EVD) and subspace tracking algorithms, are summed up and analyzed by computer simulations. Base upon the theoretics of subspace tracking, this dissertation introduce the algorithm based on fast subspace tracking by a Novel Information Criterion to solve the problem of blind estimation of DS/SS spreading sequence. Computer simulations show that this algorithm descends the storage consuming memory, is prone to hardware realization and has fast convergence properties, and this algorithm can estimate PN spreading sequence quickly and accurately at low SNR.5,Finally, we established an associated system to process DSSS/QPSK signal including detection, parameter estimate and spreading sequences estimation. And the computer simulation was launched to analyze and compare the capability of different method combination.