Research On Low Probability Intercept Spread Spectrum Signal Detection Algorithm

Spread spectrum communication is a communication mode which uses the pseudo random code to modulate the information data to be transmitted, and it realizes spectral spreading before information transmission. As a major operating mode of spread spectrum communication, direct sequence spread spectrum communication has advantage with low probability of intercept, strong anti-interference, high security, working in low SNR environment, it is widely used in mobile communications, radar, navigation and measurement field. At the same time, DSSS signal detection and parameter estimation has always been an important research topic in the field of communication countermeasure.Currently, there are many method about DSSS signal detection and estimation, but these methods are based on the conventional signal(fixed frequency signal) detection and estimation, and the power density spectrum of DSSS signal is low, which usually buried in the noise background and is difficult to find. Therefore, when the DS signal is operating in a lower SNR environment, the performance of these traditional detection methods deterioration, estimates results may even be wrong. In short, at the present stage the research about detection and estimation of DSSS signal is not comprehensive mature enough.In this paper, we focus on BPSK modulated DS signal, the DSSS signal detection and parameter estimation were studied. This paper used four different methods to estimate the carrier frequency, PN sequence rate and PN sequence period.The main results are as follows:1. Carrier detection algorithm was adopted to estimate the carrier frequency parameter of direct sequence spread spectrum signal, the algorithm structure is simple and easy to implement, but the signal to noise ratio tolerance is low. In order to improve its detection performance, we propose a joint carrier detection-MUSIC estimation, MUSIC algorithm which can attain high accuracy of frequency estimation. Simulation results shows the performance of the joint estimation algorithm is good and it is easy to implement.2. Based on the delay multiplication algorithm, this paper analyzes its characteristic which can detect DS signal and estimate its PN code rate,and combined the characters of autocorrelation function to average noise, the performance of algorithm was improved. At low SNR background, this algorithm can accurate estimate the PN code rate of DSSS signal.3. For PN code period parameter estimation of DSSS signal, this article analyzes spectrum reprocessing method and autocorrelation detection method. Due to the work conditions of autocorrelation detector normally extremely harsh, so we use spectrum reprocessing method to estimate PN code period, and introduced delays multiplied algorithm to improve its amplitude periodic components in the frequency domain. Simulation results showed that the improved algorithm estimation has smaller error and better detection performance.4. Combining the above improved algorithm, a DSSS signal parameter detection system was proposed, the system can estimate DSSS signal carrier frequency, pseudo-random code chip and pseudo-random code period.