低信噪比条件下数字通信系统码辅助同步技术研究

项目名称： 低信噪比条件下数字通信系统码辅助同步技术研究

项目编号： No.61501484

项目类型： 青年科学基金项目

立项/批准年度： 2016

项目学科： 无线电电子学、电信技术

项目作者： 满欣

作者单位： 中国人民解放军海军工程大学

项目金额： 21万元

中文摘要： 中继卫星高速数据传输技术是无线通信领域的研究热点，也是发展我国空间信息网络必须解决的关键技术。随着传输速率的快速增长，高速数传面临着频谱/功率受限的双重压力，而采用高阶调制与高效信道编码技术相结合将是缓解这一压力的有效途径。虽然Turbo/LDPC码的应用能极大降低译码门限，提高功率利用率，却给信号解调尤其是传统同步过程带来了巨大挑战，如何在低信噪比条件下完成有效同步成为实现高效编码增益的关键因素。本项目以提高低信噪比同步参数估计性能为切入点，试图从符合定时、载波同步和帧同步等方面建立码辅助的联合迭代同步框架。首先利用迭代译码过程产生的软信息构建代价函数，通过门限检测方法完成同步参数粗估计；然后将软信息引入到因子图和EM参数估计框架，改善同步参数估计精度；最后，根据不同参数之间的相互依赖关系，探讨一种低复杂度联合同步方案。研究成果将为低信噪比条件下高效同步系统的设计提供新思路和理论依据。

中文关键词： LDPC码；符号定时；载波同步；帧同步；低信噪比

英文摘要： High data rate transmission technologh in DRSS becomes an active reaearch field in wireless communication. With the rapid increase of transmission capacity, high data rate transmission technologh is faced with the double pressure of limited spectrum and power resource, which can be released by combining the high order modulation schemes with efficient channel codes. The application of efficient channel codes such as Turbo and LDPC codes can make the decoding threshold falling and power efficiency increasing. However, it also poses a great challenge to signal demodulation especially for traditional synchronization at low signal-to-noise ratios (SNR) to make the powerful coding gain come true. With the view of improving the estimation performance of synchronization parameters at low SNR in this research subject, the framework for joint iterative code-aided synchronization is managed to construct, which involved several aspects, such as symbol timing, carrier synchronization and frame synchronization. Firstly, the coarse estimation of synchronization parameters will be solved by comparing the presetted threshold with a cost function which is constructed by the soft information from iterative decoder. Secondly, the soft information will be introduced into a parameter estimation framework on the basis of factor graph and expectation-maximization (EM) algorithm to improve the estimation precision of synchronization parameters. Finally, the joint synchronization scheme with low computational complexity will be discussed based on the interdependence of different synchronization parameters. The findings may offer new guidance and theory foundation for the design of efficient synchronization system at low SNR.

英文关键词： LDPC code;Symbol Timing;Carrier Synchronization;Frame Synchronization;Low Signal-to-noise Ratios