【作者】 雷剑梅；

【导师】 杨士中；

【作者基本信息】 重庆大学 ， 电路与系统， 2002， 硕士

【摘要】 扩频通信是当今通信领域讨论得最多的一种通信体制，尤其在今天日益复杂的信道环境以及个人通信倍受关注的社会需求环境中，扩频通信优秀的抗噪声性能和保密性就显得十分重要。在整个扩频系统中，接收端对发端扩频码的捕获和同步，是一项决定整个系统成败的至关重要的技术。而传统的PN码捕获方法存在捕获时间长或电路结构复杂等缺点，普遍不能完成低信噪比下长PN码捕获的要求。本文主要研究了大步进快速捕获法，该方法是针对低信噪比下长扩频码的捕获和同步问题提出的。本文着重从理论和电路设计两方面对大步进快速捕获方法和大步进快速捕获延迟锁定环进行讨论。在理论方面，本文利用圆形状态图对大步进快速捕获法的工作原理进行研究和分析，导出由相关处理时间、大步进时间、虚警概率、检测概率和虚警“代价”时间表示的捕获时间平均值及其方差的表达式。通过将分析结果与单步进搜索方案进行比较，证明了大步进延迟锁定环可以使捕获时间缩短至单步进的m分之一（m=10-100），实现PN码的快速捕获。同时也对解扩相关器在接收端噪声为加性白高斯噪声情况下的输出成分进行了详细分析，推导得出大步进搜索的虚警概率和检测概率的公式。在电路设计方面，由于全数字化存在成本过高的弊端，全模拟实现又存在电路复杂度过大的弊端，折中考虑后，采用了数字和模拟并存并高度集成化的设计方案，并最终给出实验结果。在对大步进快速捕获延迟锁定环中关键电路进行数字化和集成化的过程中，采用了美国著名可编程器件生产商ALTERA公司的开发软件MAXPLUSⅡ，结合VHDL语言进行逻辑电路的编程、仿真，并使用该公司的MAX7000系列复杂可编程逻辑器件，自制开发板，完成程序下载和信号引出，实现所需逻辑功能。更多还原

【Abstract】 Spread spectrum communication is one of the most popular topics in the communication field. With the increasing requirement for personal communication and the increasing complexity of channel condition, the advantages of spread spectrum communication in secrecy and resisting noise has been more and more important. In the spread spectrum communication system, the synchronization of receiver’s Persedo-Noise (PN) code to the transmitter’s PN code is such an important part that the whole system can’t work at all without it. But the traditional method to capture the PN code are either too slow or too complicated to satisfy the need of today’s communication system.This article works over a mathod named Large Step Fast Acquisition to capture the PN code in the receiver, which was originally put forward for the acquisition and synchronization of long PN code under the condition of low signal to noise ratio(S/N). The principle of Large Step Fast Acquisition and the circuit design of Large Step Fast Acquisition Delay Lock Loop (LSDLL) are disgussed as the emphasis. When analyzing the principle and performance of the LSDLL, circular flowgraph is used. The expression for "penalty" time and mean and variance of the acquisition time is derived from the circular flowgraph of Large Step Acquisition method. And the output components of the despread correlator under the condition of additive white gaussian noise (AWGN) are analyzed to derive the expressions for the false alarm probability and the detection probability. When discussing the digitalization and integration of the LSDLL circuit, the CPLD developing software MAXPLUSⅡ of ALTERA is used to program the logic circuit and simulate it’s function. And the MAX7000 device of ALTERA is used to realize the logic circuit.更多还原