The Research On DSSS Signals Detection And Parameters Estimation

The spread spectrum communication has the advantages of low signal noise ratio (SNR), good anti-jamming, low probability of interception and the capability of anti-multipath interference. It is widely used in mobile communications, radar, navigation and orientation. With the development of the electron and information technology, the detection of the Direct Sequence Spread Spectrum (DSSS) signal and its parameters estimation have become an important research direction on condition of little prior knowledge and low SNR.A lot of DSSS signal estimation methods have been developed. These methods are mostly based upon the theory of conventional signal detection and estimation. However, DSSS signals are wide-band weak signals, and they are impracticable to the theory of conventional signal processing. Therefore, when the SNR of the received signals becomes lower, the performance of the methods is worsened. At Present, the methods of detecting DSSS signals and estimating its parameters are far from mature. Although there have been some methods for the detection, most of them can only estimate a different parameter of the signal with good performance but can not make a systematic detection for all parameters. In this paper, some methods for the high-order cumulant, the high-order cyclic cumulant, the delay-multiply and autocorrelation are discussed. The improved methods based on predecessors are presented.1. The fourth-order cumulant theoretically can suppress the Gaussian White Noise and the adaptive noise cancellation can also eliminate noises effectively. Based on the fourth-order cumulant, this paper proposes a method of estimating the carrier frequency of DSSS signals on the condition of the low SNR. This method can solve the difficult problem of the carrier frequency detection. The validity of this method is shown by the computer simulation.2. The cyclic-character of cyclic-cumulant embodies the frequency of cyclic stable signals, and the high-order cyclic-cumulant can suppress the stationary and non-stationary Gaussian coloured noise. Based on the high-order cyclic cumulant, this paper proposes a method of estimating the carrier frequency and the chip rate of DSSS signals. This method can solve the difficult problem of detection for the carrier frequency and the chip rate. The validity of this method is shown by the computer simulation.3. The delay-multiply can estimate the chip rate and the carrier frequency of DSSS signals. And the autocorrelation processing can detect the period of DSSS signals. Based on delay-multiply and autocorrelation, this paper proposes a method of delay-multiply multi-autocorrelation. This method not only can estimate the carrier frequency, the chip rate, but also detect the period detection of the long Pseudo Noise (PN) code. The validity of this method is shown by the computer simulation.The above mentioned three methods can estimate parameters for DSSS signals effectively with little prior knowledge, which have significance for the blind estimation. The simulations show that they can achieve good precision on the condition of low SNR.