Research Of Synchronization Technology In DS/SS

This thesis investigates the synchronization of digitalized DSSS receiver in high-dynamic and low SNR environment, presents the methods of fast acquisition and precise tracking for PN code and carrier. Firstly, the fundamental theory of DSSS and the correlation performance of m code and Gold code are introduced. After establishing the model of IF DSSS receiver, comparing and analyzing several conventional code acquisition methods, code and carrier 2-dirnention fast acquisition scheme based on FFT is proposed. Secondly, according to the characteristics of FLL and PLL, based on the analyzing several tracking methods of code and carrier, LL-DPLL for code tracking and digital complex soft loop for carrier tracking, which combined by cross-product automatic frequency control and Costas phase locked loop, are provided here. The design methods for loop filters are also discussed in this part. Finally this thesis shows the digital simulation model based on Simulink, and some part of implementation on DSSS receiver.The simulation result shows that, comparing to the conventional acquisition methods, code & carrier 2-dimention fast acquisition scheme based on FFT can dramatically shorten the acquisition time and simply the hardware complexity. Digital complex soft loop using for carrier tracking also makes the IF DSSS receiver obtain better dynamic and noise performance.