Lenovo s executive headquarters are in purchase , new york , usa with principal operations in beijing , china , and raleigh , north carolina , usa and an enterprise sales organisation worldwide . the company employs more than 19 , 000 people worldwide 联想决策总部位于美国纽约州玻切斯purchase ，主要营运据点在中国北京与美国北卡罗莱州拉雷raleigh ，且销售地点遍及全世界，全球员工超过19000人。
Appropriate data compression methods are needed to assure the random nature of the information source and to enlarge its entropy . in this thesis , first , we present the theory of sess system , then the acquisition method of sess system is discussed in detail , finally , a acquisition model of sess system is built and simulated in the awgn channel , in the raleigh fading channel and in multi - address interfere condition . the simulation results show the acquisition method of sess system can be just as reliable as the conventional dsss systems 本文首先对自编码扩频通信的基本原理,自编码扩频序列的产生方法及其产生的序列的特性进行了概述,然后详细讨论了直扩通信系统中的扩频码的捕获跟踪问题,根据自编码扩频通信的特点,设计了其捕获跟踪方案,并在加性高斯白噪声信道、瑞利衰落信道和多址干扰情况下进行了仿真。
In this thesis , first , we present the theory of sess system , the generation of the sess spreading code and its characteristics and the acquisition theory of conventional spread spectrum communication system . an efficient acquisition scheme based on periodically transmitting the synchronization head , which is composed of binary chaotic codes , using the matched filter and automatic decision threshold - level control based on a so - called constant false alarm criterion for sess system is present . the acquisition model of sess system is built and simulated in the awgn channel , the raleigh fading channel and imulti - address interfere condition 本文首先概述了自编码扩频通信的原理、自编码扩频序列的产生方法及其特性和扩频通信系统编码同步的理论,然后针对自编码扩频通信系统提出了扩频序列捕获方案:周期性地加入混沌序列同步码,并采用恒虚警率匹配滤波器捕获法;在加性白高斯噪声信道、瑞利衰落信道和多址干扰情况下进行了仿真,分析了各种捕获性能:在选择性能最优的混沌序列、适当的序列长度、虚警概率及门限值的情况下,可以获得较短的捕获时间和较大的捕获概率。
