临近空间协同Turbo信号接收技术研究

Recently, near space communications (e.g.unmanned aerial vehicle airborne communications) have become the hot-spots in the space information science research at home and abroad, due to their potentially huge value in politics, militaries and economies. But they still have several problems as follows. First of all, in the near space communications, the signal reception at low signal-to-noise ratio is very hard. Then,the wireless multipath fading channels are usually very complex. Finally, the estimation and detection of the large range variation of the high dynamic signals are also difficult. According to these problems, this project researches the fundamental theories and key technologies of the sparse graph framework based coordinated Turbo signal reception in near space to solve all these problems in the field of space communications. In theoretic aspects, it mainly investigates the construction and analysis of high performance structured quasi-cyclic accumulate-repeat-accumulate (QCARA) protograph extended low-density parity-check (LDPC) codes, low complexity coordinated decoded synchronization with iterative synchronization and noise parameter estimation, iterative estimation and detection of the parameters from complex wireless multipath fading channels, multi-antenna general single-input multi-output(SIMO) joint coordinate iterative detection and some other related theoretic problems. In practical aspects, it focuses on the efficient software and hardware related simulation and verification platform for the above research theories. The innovation of this project mainly consists in these aspects as follows. The channel codewords are constructed and analyzed by stochastic graph models. By the means of soft probability metric propagation, the stochastic sparse graph based framework of the coordinated decoding and signal detection/demodulation can eleminate the mutual information loss, which mainly occurs in traditional communication and information systems without joint processing, thus it improves the performance of the joint coordination system. Also the efficient mutual information accumulation based coordinated signal processing via multiple relays is applied for better performance. The anticipated fruits of this project will help contribute to the implementation and programming of the near space communication systems in our country.

目前，临近空间通信(如无人机机载通信)因潜在的重大政治、军事、经济等应用价值，已成为国内外空间信息科学研究热点。但其存在低信噪比信号接收困难，低仰角多径衰落信道复杂，大范围高动态信号参数检测不易等问题。针对这些问题，本项目拟在空间通信领域，以稀疏图为信号处理框架，开展临近空间协同Turbo信号接收基础理论与关键技术研究。在理论上研究：高性能累积重复累积结构原模图扩展的低密度奇偶校验码构造与分析；低复杂度迭代同步及噪声参数估计的协同译码同步；复杂无线多径衰落信道参数的迭代估计与检测；多天线广义单输入多输出联合协同信号接收与检测等基础理论问题。在应用上研究上述理论的软硬件仿真验证平台。创新在于：随机图码字构造及随机度分析；基于稀疏图的协同译码检测与解调，以软概率消息传递为手段，消除传统分立处理引起的互信息损失；多中继互信息累积协同信号处理。预期成果有助于促进我国临近空间通信系统的实施和规划。

目前，临近空间通信因潜在的重大政治、军事、经济等应用价值，已成为国内外空间信息科学研究热点。但其存在低信噪比信号接收困难，低仰角多径衰落信道复杂，大范围高动态信号参数检测不易等问题。针对这些问题，本项目在空间通信领域，以稀疏图为信号处理框架，开展了临近空间协同Turbo信号接收的基础理论与关键技术研究。理论成果如下：(1)联合编码构造：修正EXIT图与扩展渐进图外消息度的ARA结构原模图高编码增益G-LDPC码构造；可重构围长优化可变码率LDPC码空间通信应用；准循环QC-LDPC预编码喷泉码及联合稀疏码分多址接入等编码调制构造；(2)协同译码解调：高动态微弱卫星信号的多环嵌套锁频-锁相环载波捕获与跟踪；接近Cramer-Rao理论界的低复杂度MAP定时恢复;高效LDPC译码硬判决辅助联合多用户迭代VBLAST检测; 极低SNR下LDPC编码QPSK系统的迭代载波恢复；修正ISM频域的高效宽带卫星波束成形；(3)迭代稀疏检测：多任务贝叶斯压缩感知的高灵敏度宽带频谱检测；协作认知网络误码率约束的联合能耗优化与中继频谱协同检测；高速两级并行CMA-LMS自适应均衡与联合微弱稀疏信号接收；判决聚合模式模糊集GPS微弱信号检测与抗干扰；中椭圆轨道卫星多普勒频移快速估计；稀疏OFDM信道估计的改进同伦法检测；循环PN相关时域同步OFDM频偏估计检测；(4)广义协同接收：改进的低阶量化转发机制下的优化中继选择与功率分配优化；多中继AF协作网络中继链路筛选排除法的优化选择；基于门限决策的选择译码转发SDF中继选择策略；混合译码放大转发的增强选择策略；功率优化单中继LAR协议优化。在应用研究方面，重点研究了临近空间Turbo接收系统编译码构造与性能仿真，协同Turbo接收性能验证等核心算法软件仿真平台和基于FPGA的高速光无线传输等迭代接收自主无线电硬件仿真验证平台，研制了临近空间通信自主无线电软硬件仿真验证平台，且申请了较多关键算法专利，并获得了较好经济效益及相关科技进步奖励。该项目研究成果将有助于我国临近空间通信理论与技术发展，并对我国空间探测与通信规划和实施有积极促进作用。