The Research And Simulation Of Spreading Code Synchronization Technology

Compared to narrowband communication system, spread spectrum communication system with the features of strong anti-interference, anti-interception capability,multiple-access communication etc, has become a very important means of communication recently. However, there are some complex technical issues in it and the spreading code synchronization technology has a vital role in Direct Sequence Spread Spectrum(DSSS) system.Now in the more commonly used capture methods, sliding correlation capture method has a simple structure and it is easy to implement, but its capture time is long; parallel search acquisition method has a short capture time, but a complex structure and a large hardware. They have better capture performance in the general white noise environment.In the case of a very low SNR, signal almost drowned in the noise, the undetected probability will increase and performance of the capture system will be reduced.In this paper, for Doppler frequency shift and Gaussian white noise environment it is proposed an improved algorithm of single integral sliding correlation method.Improvements are as follows: First, improve the fixed integration time to the change integration time. If Doppler shift turn large, then false alarm probability becomes large, at this time using long integration time to reduce false alarms probability. Conversely, small Doppler shift using shorter integration time, thus it reduces the acquisition time effectively.Second, change the fixed threshold to adaptive threshold. Threshold reached to self-adaption based on the integration time and noise. The threshold will increase if integration time increases; in the case of high-impact of noise on the correlation output,the false alarm probability becomes high, the threshold increases, whereas the corresponding threshold small, which can effectively reduce the probability of false alarm.Finally, this paper use the Matlab software to simulatie the false alarm probability and the average acquisition time under different Doppler shift and SNR. The result shows that this method can not only reduce the capture time, shorten and control the false alarm probability, but also improve catch performance effectively.