【作者】 张桂华；

【导师】 姬红兵；

【作者基本信息】 西安电子科技大学 ， 模式识别与智能系统， 2008， 博士

【摘要】 深空测控通信系统对在遥远的空间探测器进行通信、测量和控制,包括跟踪、遥测、指令控制和数传,对深空探测器的整个飞行过程进行测控以保证其飞行轨道的准确,并获取探测过程中的回传科学信息。本文在对深空测控系统通信体制的特点分析的基础上,研究了高增益信道编码和微弱信号的接收处理等关键技术提出了一系列适用于深空探测的信道编码和微弱信号接收的新方法。针对深空探测实际需求,提出了一种易于工程实现的Turbo码编译码算法。该方法采用线性拟合Log-Map算法有效逼近Log-Map算法,大大减少了计算量;应用二次置换多项式交织器,有效地解决了并行译码的访问冲突问题,缩短了Turbo码译码时延。该算法性能优良,算法简单,解交织与交织结构相同,所需存储空间少,易于硬件实现。综合EXIT图法和自适应微粒群优化(APSO)算法的优点,提出了一种基于EXIT图和APSO算法的非正则LDPC码度分布对优化方法。该方法设计了衡量EXIT曲线匹配程度的全局代价函数,并运用APSO算法对度分布对进行快速迭代优化,迭代过程中不需要固定CND曲线,可以获得EXIT曲线更加匹配的优化度分布对,以及更高的噪声门限。仿真结果表明,该方法在码结构优化方面有着很好的性能,且优化速度较高斯逼近法有了很大的提高。在针对围长的校验矩阵构造方法中,提出了一种新的QCE-PEG算法,给出了实现具体步骤和设计实例。该算法将构造过程分解,结合准循环扩展技术和渐进边增长构造方法的优点,既能满足度分布对的需要,又保证了平均围长尽可能大的要求,提高了LDPC编码的速度和性能。用该方法设计的中短长度非正则LDPC码,其性能优于渐进边增长方法构造的PEG码,且设计简单,编码快速,便于工程实现。为进一步提高LDPC纠错性能,在基于QCE-PEG构造校验矩阵基础上,研究了以LDPC码为水平码、单奇偶校验码为垂直码的LDPC-SPC联合编码技术,有效地降低了LDPC码的译码门限与误码平层,能够在较短码长就能达到在信噪比0.7dB下误比特率为10-5,大大减少存储空间,满足深空探测要求。为解决深空测控领域中低信噪比下微弱信号的捕获、跟踪问题,实现高精度测速、测距功能,设计了微弱信号接收机方案。采用二维捕获方案,并行捕获下行信号的多普勒频率和多普勒频率变化率;利用二阶锁频环和三阶锁相环联合工作方式进行载波跟踪。系统性能满足深空探测指标要求。最后对全文进行了总结,并对后续工作进行了展望。更多还原

【Abstract】 The TT&C system of deep space exploration functions as telemetry, tracking and command for the faraway detector in space, which keeps a reliable commmunication and data transmission with the object so as to ensure the orbit accuracy and acquire the scientic information. Based on the analysis of the characteristic of a representative TT&C system, several new solution for its key technique such as high gain channel coding and weak signal detection is presented.A practical Turbo coding scheme using quadratic permutation polynomial (QPP) interleaver and linear Log-Map algorithm is presented. The adoption of linear Log-Map algorithm reduces the computation complexity sharply, and the application of QPP interleaver avoids the access collision problem in parallel decoding effectively. The algorithm has some advantages such as good performance, simple algorithm, the same structure for both interleaver and deinterleaver, few storage space and easy hardware implementation.Based on EXIT chart and APSO algorithm, a new method to optimize the degree distributions of irregular LDPC codes is proposed. An overall cost function is first designed to measure the matching extent of EXIT curves. Then the degree distributions are optimized iteratively by using the adaptive particle swam optimizer (APSO) algorithm. Such a procedure needs not to fasten the CND curve. Therefore, some new degree distributions with higher noise threshold are obtained. Simulation results show that the algorithm has a good performance to achieve optimal code structures, more effective than Gaussian Approximation in computation.To enable the practicability of the low density parity check codes, a QCE-PEG algorithm is presented, followed by the description of the implementation approach and a design case in detail. The algorithm divides the construction into two process, combining the quasi-cyclic extension method and progressive edge-growth technique. It has several advantages such as good degree distribution, long average girth, rapid encoding process and good performance. The irregular LDPC codes the algorithm constructed has good performance, simple and practicable.To improve the correcting error performance of LDPC code, the LDPC-SPC technique is introduced which based on the check matrix construction of QCE-PEG. It uses LDPC code as horizontal code and single parity code as vertical code. Thus it can not only fall the decoding threshold and error floor effectively, but also reaches BER less than 10-5, while SNR is 0.7dB with shorter frame length.To overcome the capturing and tracking problem of weak signal under the low SNR environment of deep space and to obtain the precise measurement for the speed and distance, a practical receiver scheme is designed. In the scheme, A 2D capture method was applied to capture both the Doppler frequency and Doppler variety rate of downlink signal in parallel mood. A 2-rank FLL associate with 3-rank PLL mode to track carrier is presented. Simulation and test results show that the system performance of our design can satisfy the requirement of deep space exploration.Finally, a summary of the whole paper is given and a prospect of the issues concerned in this field is also made from the author’s research perspective.更多还原