【作者】 李宏飞；

【导师】 廉保旺；

【作者基本信息】 西北工业大学 ， 通信与信息系统， 2005， 硕士

【摘要】 本文对应用于高动态、低信噪比下的数字化中频直扩接收机中的同步技术进行了研究,提出了伪码载波快速捕获及精密跟踪的方法。文章首先介绍了直接序列扩频通信系统的基本原理,以及伪随机码m序列和Gold序列的相关特性。在建立了中频直扩接收机的模型之后,对常用的伪码捕获方法做了详细的分析和比较,最后提出基于FFT技术的伪码载波二维快速捕获方案。其次在分析了常用的伪码及载波跟踪方法的基础上,结合锁相环和锁频环的特性,提出了采用超前-滞后型非相干数字延迟锁相环来实现伪码跟踪,叉积自动频率跟踪和科斯塔斯环相结合的数字复合软环来实现载波跟踪的新算法。文中还详细讨论了伪码及载波环路滤波器的具体实现方法。文章最后给出了以上系统基于Simulink(的数字化仿真模型,以及在接收机上部分实现的效果分析。实验结果表明,基于FFT的伪码载波二维捕获系统较之于传统方法,大大地缩短了捕获时间和硬件复杂度,数字复合软环在载波跟踪中的使用也使得本接收机具有较好的动态性能和抗噪性能。更多还原

【Abstract】 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.更多还原