Detection And Parameters Estimation Of Direct Sequence Spread Spectrum Signal

Direct sequence spread spectrum signals have been widely used for secure commu- nication and mobile communication known as Code Division Multiple Access System. Because DS signals have many advantages such as anti-jamming capability, low probability of interception, multiple access capability and so on.In this paper , an efficient algorithm for detecting and estimating the parameters of the four BPSK,QPSK,16QAM,64QAM/DSSS signals in low S/N ratio without any prior knowledge is proposed in this paper. Cyclic spectrum is applied to detect the DSSS signals and estimate the chip rate and carrier frequency. The reprocessed power spectrum of DSSS is used to estimate the period of pseudo-noise sequence. The PN sequence is estimated based on the feature vectors of the autocorrelative matrix accumulation. Then other four detection and parameters estimation algorithms are studied . It is found that the square detection is so poor although the speed is fast when detecting the signal and estimating the carrier frequency; The Correlation In Time Field can performed periodic detection and estimate the chip width. But it cannot restrain the noise effectively because it is the average of noise ;Cepstrum Detection can detect the period of PN code after two fft operations and one logarithm of DSSS .The performance is not satisfying; 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 signal. It can restrain the noise a certain extent but the performance was not very well.Simulations show that the algorithm proposed can despread the DS signal blindly and receive best performance in low S/N ratio.