Research On Parameter Estimation Methods For Direct Sequence Spread Spectrum Signals

Direct Sequence Spread Spectrum (DSSS) systems have been widely applied in military communications field, due to their good anti-jam performance, high counterreconnaissance ability, and low intercept probability. Usually, a receiver can extract information from the signal through correlation operation by the spread code. However, without the spread code, a scout has to achieve 6dB or higher SNR to demodulate the DSSS signals, which have low PSD (Power spectrum density) and are always submerged in noise. To meet the future demand of electronic reconnaissance techniques, it is of great significance to study parameter estimation methods for DSSS signals under low SNRs.This paper mainly deals with the estimation of the carrier frequency and the chip rate of DSSS signals. Firstly, the basic theories of cyclic spectrum estimation are introduced. By searching the peaks on the f = 0 envelope of cyclic spectrum of the DSSS-BPSK signals, the carrier frequency and chip rate can be estimated. Secondly, after detailed study of the instantaneous correlation function of DSSS-BPSK signals, an estimation method for the carrier frequency and the chip rate of DSSS-BPSK signals is presented, which is based on the power spectrum of instantaneous correlation function for DSSS-BPSK signal. To overcome the influence of noise, a chip interval pre-estimation approach is proposed, which is based on the autocorrelation of signal segments and is shown to improve the estimation performance greatly. Finally, based on the analysis of DSSS-QPSK, a quadratic transformation is used to convert a DSSS-QPSK signal into a new DSSS-BPSK signal, for which the cyclic spectrum approach and the instantaneous correlation function based approach can be applied to estimate the carrier frequency and chip rate. Experimental results show that these methods are effective and are of great application potentials.