The Study Of PN Code Acquisition Detection Method For DSSS Based On Wavelet Analysis

1,IntroductionSpread spectrum technology in the field of navigation and communication both the most influential and most well-know system is the Global Positioning System (GPS) and Code Division Multiple Access (CDMA) mobile communication system business. In spread spectrum communication system, the focus of concern at the issue of PN code synchronization. Taking into account the spread spectrum receiver just between machines transceiver group phase error codes do not know anything, in order to enable the receiver to restore the correct code information must be generated by the receiver for dispreading of pseudo-random code and the sending end of the pseudo-random code synchronization. Pseudo-random code synchronization generally has tow-step. The first step is to search and capture the receiving end of the pseudo-random code of the initial phase so that the sending end and the code phase error is less than 1 bit, that is, code capture (capture sequence); the second step is at the basis of the initial synchronization, so that further reduce the code phase error and maintain synchronization, this step is usually called tracking. It can be seen that the study of capture are important, and the questions how to determine whether the success of capture is also an important one.2,The energy detections of PN code acquisitionIn direct spread spectrum communication system, the pseudo-code acquisition is to get the initial PN code phase at the receiver end. Analysis the widely used detection methods now, we found that there are a fixed integration time detection, the presence of many time detection and sequence detection. Analysis of the three testing found that they received the signal in a period of time and the accumulation of band. After energy accumulation some values, then determining whether the signal existence. This is method, except to average the white Gaussian noise; it shouldn't more effectively fight against its suppression and the existence and impact. In the stationary random processing, for spectrum communication signal to be reliably detected, even though now made all kinds of improvements, but the basic principles and fundamental approach has not changed. The fundamental reason is not proposed a fully using the characteristics of the spread spectrum signal. In order to solve the already capture signals'the veracity, rapid and effective detection. More, in order to lower PN code acquisition time, false alarm probability, improve detection probability at low signal to noise ratio (SNR).3,The PN code acquisition detection for DSSS on wavelet analysisWavelet analysis as a new mathematical method, more and more applications in the broad fields of engineering, because of the characteristics of multi-scale, made wavelet analysis largeness using in the signal de-noising, signal compression and data processing fields. Compared to Fourier transform, the Fourier transform can not detect localized signals as well as the singularity of the whole. Moreover wavelet transform and wavelet transform-based signal have the tools of detection signal the whole and the local singularity. In spread spectrum communication, the synchronization signal'detected usually by means of energy detection. Since the PN code is not captured, this time only the existence of Gaussian white noise. In the wavelet transform, the white noise of the Lipschitz's indexα< 0, so the amplitude maxima of wavelet transform with the scale of wavelet transform j increase, it decrease. When achieve the PN code capture time, the capture signal is BPSK or QPSK signal polluted by Gaussian white noise. And this signal exist phase transition characteristics. It has singularity. In the wavelet transform, the Lipschitz index 0 <α< of the signal singular points, which signals correspond to the singular points of the wavelet transform modulus maxima. When these extreme points appear on this system, it achieved capture. So we can choose the appropriate scale factor and establish the threshold to distinguish two situations in order to achieve the purpose of detection of captured moments.4,Simulation results and conclusionsAccording to this paper in the DSSS system, we choose the white Gaussian noise channel. Firstly we analysis the success capture and the failure capture signal time domain characteristics. The successful capture of the BPSK signal with Gaussian white noise signals in mixed-signal and non-successful capture of the Gaussian white noise signal. Form the simulation results can be seen mixed with Gaussian white noise of BPSK modulated signals with time-domain variability of the phase jump that is, each symbol of the carrier phase relative to the desirability of the baseline phase 0,π. The relative phase-shift in the latter when the symbol if the carrier phase relative to the baseline phase for 0, so the before and after the element is the carrier phase continuous; Otherwise, the carrier phase element in the two codes take place sudden jump. And we simulate the two signals by MATLAB. Secondly I analysis the singularity characteristics of the two signal. Then simulate the two signals and compare them. Proof wavelet determined methods reasonableness. On this basis I simulate the important parameters of the wavelet determine method. Comparison of three of the Daubechies series wavelet, through experimental analysis and comparison of three detection probability and false alarm probability, then I got it that choosing wavelet Db3 is more appropriate through experimental analysis results. Finally, about the wavelet method and traditional energy captured method, I simulate the average acquisition time and compare with the traditional one. Found that this method can effectively reduce the average acquisition time. At low signal to noise ratio, the various parameters have improved. While the majority of spread spectrum system is to work at low SNR, this method proves that there is a certain degree of theoretical and application value.