智能交通场景下无人机对地无线传播信道的测量、参数提取和建模研究

Time variant Unmanned Aerial Vehicle (UAV) to ground channel model is essential for the development and testing of communication and navigation algorithms. It has significant impact on the applications of UAV in the future intelligent traffic and transportation system. However, the state-of-the-art UAV-ground channel model does not fulfill the requirements of communication and navigation applications. Therefore, the proposed project aims at characterizing and modeling the UAV-ground propagation channel in terms of narrowband and wideband based on channel measurement campaigns. In narrowband analysis, the UAV height and distance dependent path loss, large and small scale fading models are going to be established and validated based on measurement data. In wideband analysis, the path parameters of time variant channel impulse response (CIR) are estimated by a developed combination of superresolution algorithm (i.e., SAGE) and a recursive Bayesian estimator. Regarding each estimated time variant path, analysis will be conducted in terms of the propagation phenomena, scatterer position and characteristics, the fading process of the envelope due to unresolvable closely-spaced multipath components. Further, the diffraction caused by building and the diffuse scattering caused by large rough ground surface will be addressed by applying physical methods like the 3D uniform theory of diffraction (UTD) and the Backmann’s radar cross section calculation. Finally, the physical models will be combined with the geometry-based stochastic channel model (GSCM) in order to accurately model the UAV-ground wireless channel for communication and navigation applications.

无人机对地时变信道模型对于通信以及定位导航技术相关算法的开发和测试有着至关重要的作用，对于无人机在智能交通系统中的应用有着重要的科学研究价值和意义。然而，目前国内外对无人机对地信道测量和建模的研究还无法满足相关通信和导航技术测试的要求。本项目旨在通过无人机对地信道测量开展无线信道特征分析及建模的研究。揭示路径损耗，大、小尺度衰落同距离、无人机高度之间的关系特征和规律；发展适合无人机对地无线电传播信道的高分辨率时变多路径参数估计和追踪算法；阐明多路径传播的变化特性和传播机理，建立点散射体的参数模型；提出基于物理方法的针对不同地形地貌的无线电信号散射模型；将衍射、漫散射物理方法和基于几何方法的的随机信道模型相结合，提出适合无人机对地通信导航技术测试的无线信道模型。

准确理解交通环境下无人机对地无线电信号传播的特征，是无人机系统中通信和定位技术开发和测试的重要基础，对无人机在智能交通中的应用有着重要意义。现有无人机信道研究还存在着信道参数与无人机高度之间关联性研究较少、无人机对地场景下丰富漫散射制约传统时变信道参数估计方法的性能、无人机信道模型准确度和复杂度之间失衡等问题。针对这些问题和智能交通场景中低空小型无人机通信、导航技术测试对信道模型的实际需求，本项目开展了无人机对地信道测量、参数提取和建模方法优化的研究并取得了重要研究进展。项目研究并提出了基于小型USRP的系统层面多链路无人机对地时变无线信道测量方案，通过机载原子钟校正实现收发端的准确同步；针对真实环境中漫散射分量的大量存在造成的参数估计模型不匹配的问题，提出了基于自回归滤波和最大似然法的信道参数估计方法，实现了镜面反射参数和漫散射参数的同时估计；此外，项目利用测量间隔大小对大尺度多径参数的影响较小这一特点来解决间隔过大时造成的小尺度参数无法准确预测及初始化问题。随后，项目研究了无人机对地多链路信道的时变和相关性特征，重点分析了单个链路随时空变化的自相关特性和不同链路之间的链路间互相关特性，揭示了无人机高度和时空相关性之间的关联，建立了和高度距离等参数相关的路径损耗和衰落模型，对于系统层面的通信和定位算法测试提供了理论基础。项目针对不同情况下的地面反射与散射特征及模拟方法展开研究，根据地貌粗糙度等参数发展有效计算地面散射系数的物理方法，优化信道模型，在信道模拟准确度与复杂度之间达到性能平衡。项目成果发表高水平期刊论文19篇，其中英文期刊14篇，获得授权中国发明专利5项。本项目实现了小型无人机对地信道测量方案、提出了更具有鲁棒性和适用范围的信道参数估计方法、建立了基于物理和统计方法的信道模型，提升了信道模型的准确度，项目成果对无人机在智能交通系统中的应用具有重要的理论意义和应用价值。