【作者】 邓志鑫；

【导师】 郝燕玲；

【作者基本信息】 哈尔滨工程大学 ， 导航、制导与控制， 2009， 博士

【摘要】 迭代伪码捕获算法就是将基于因子图的迭代消息传递算法应用于伪随机码的捕获,其主要思路是根据伪随机码自身存在的约束关系,建立因子图模型,然后利用软信道初始信息在因子图上执行消息传递算法,通过迭代处理,得到本地对接收序列的最大后验估计,并据此生成本地码,从而完成伪码的捕获。该方法因为其捕获时间短、实现复杂度低而获得人们的广泛重视,对于该方法的研究国内外刚刚起步,本文对迭代伪码捕获算法从理论和仿真角度上进行了深入的研究,主要研究内容如下：首先为了得到任意因子图上的消息传递算法,本文以无向图及其消息传递算法为基础,以边缘函数和表达式树为分析工具,推导了因子图上和积算法的运算规则。然后将迭代伪码捕获算法的两个应用背景用统一的信号模型表示,这些作为迭代伪码捕获的理论基础。为了将消息传递算法应用于m序列捕获,本文首先给出一种因子图的建立方法,然后详细分析了单路信号不同消息传递算法与不同因子图结构的迭代伪码捕获运算步骤与算法流程,并进行了仿真分析。最后分析多路信号迭代伪码捕获算法,提出了两个重要的改进方法——多路联合初始信息进化方法与多重迭代方法,并最终给出两种改进方法相结合的多路迭代捕获方案。以m序列捕获为基础,本文分析了Gold码的迭代捕获算法。首先给出了一种Gold码等效稀疏校验关系的求取方法,然后分析了校验关系特性,找到了求取最优校验关系的方法。然后针对Gold码的冗余校验捕获法,提出了一种改进的运算方法——顺次校验方法；针对分层校验捕获法,给出了分层因子图的优化方法。在对各种迭代捕获算法进行直观分析的基础上,本文对算法的性能进行更深入的理论分析。首先用密度进化方法和EXIT图方法对迭代捕获算法进行了收敛性分析,然后提出了几种迭代后初始向量估计方法,并进行了检测概率、捕获时间与复杂度分析。最后对软信道初始信息获取过程中的载波同步和采样率进行分析,给出了一种载波同步方法,并分析了增加采样率对提高捕获性能的作用。码元同步是迭代伪码捕获算法的前提条件。本文分析了码元相位差对迭代捕获的影响,然后给出一种搜索同步法,提出了基于重采样和三阶相关的码元相位同步方法,并给出各方法的适用范围。本文的最后针对两个应用领域给出了迭代伪码捕获算法的两个应用实例。在无线电导航天波捕获应用实例中,提出了m序列码元同步与载波同步相互配合的方法,并给出了无线电导航系统3路天波的迭代捕获方案。在超宽带应用实例中,求出了适用于迭代捕获的最佳Gold码族,并给出了一种多路迭代捕获方案。更多还原

【Abstract】 The principle of iterative PN code acquisition algorithms is using iterative message passing algorithms(MPAs) based on factor graphs(FGs) to acquire PN codes. The process is first building FG models according to the constraint relationship of PN codes, secondly performing MPA on FGs using soft-channel-messages. After iterative processing, the Maximum a Posteriori(MAP) is got, from which local codes are chosen, thereby the PN code has been synchronized. Because of its short acquisition time and low complexity, this method has got vast attention. Researchs of this method are newly started. On the basis of previous work, further researchs has been made on the algorithms by theoretical analysis and simulation in the thesis, and some valuable improvements has been got.For getting MPAs of arbitrary FGs, on the basis of nondirectional graphs and its MPAs, using brink functions and expression trees as analyzing tools, computing rule of sum-product algorithms on FGs was exported. Then two applying models of iterative PN code acquisition algorithms were expressed by uniform signal model.For the purpose of using MPAs to acquire m-sequense, a building method of FGs was showed. Then the PN code acquisition computing steps with different MPAs and different FG structure when single station exists was analized, and some simulation results were got. Finally, the condision of multi-path existing was discussed. Two improved methods were proposed, one is multi-path union initial message evolution method, the other is multi-iterative method, and a multi-path iterative acquisition scheme was showed.On the basis of m-sequence iterative acquisition, the method using Gold codes was discussed. First a method of calculating equivalent sparse checking relationship was proposed, characteristics of the checking relationship were analyzed, and a route to acquire optimal checking relationship is found. Then contraposing redundancy checking acquisition, improved computing steps called ordinal checking method was proposed. Contraposing hiberachy checking acquisition, an optimizing method of hiberachical FGs was given.After simulation analysis of each iterative acquisition algorithms, the performance of the algorithms was researched in detail theoretically. First two kinds of convergence analytical methods of iterative acquisition algorithms were showed, one is density evolution method, the other is EXIT graph method. Secondly, acquisition time and complexity for different vector reckoning methods were disscussed. Finally carrier synchronization and sample rate in the process of acquiring initial soft-channel- messages were discussed.Since iterative methods use soft-channel-messages to initialize, symbol timing is the premise condition of acquisition methods. In the thesis, the influence on iterative acquisition made by symbol phase error was analyzed, and then two useful symbol phase synchronization methods were showed after presenting the searching method, one is re-sampling method, the other is three-order correlation method. Simultaneously, applying scale for each method was showed.At the end of the thesis, two instances of iterative acquisition algorithm were showed. In wireless navigation instance, an improved method was proposed in which wave synchronization and symbol timing can work together to reduce complexity, and 3-user iterative acquisition scheme was also presented. In UWB instance, the best Gold codes which suit in iterative acquisition was got by computing, and then an interative acquisition scheme for UWB systems was presented.更多还原