面向宽带移动通信的平流层大规模MIMO用户接入关键技术

High Altitude Platform Station (HAPS) will play essential roles in the futuristic space-air-ground integrated high speed network by relaying the terrestrial network with the LEO/MEO satellite network, enabling ground-air cooperative transmission and providing high throughput wireless coverage. HAPS will support stable connections in the topologically dynamic space-ground network, which makes it possible a broadband access anytime and anywhere. .However, the traditional HAPS networks suffer from high side-lobe interference, overlaying of neighboring cells and inaccuracy of beam focusing. To solve these problems, this research program will exploits the new transmission technology of Large Scale Antenna System (LSAS) in the HAPS networks, with the specially developed channel models for antenna systems in HAPS. Moreover, this research will explore the cooperative transmission between multiple networks, which include the HAPS network, the satellite network and the terrestrial tower network. Especially, this research will investigate the cooperative scenario when HAPS networks are acting as relays for the LEO/MEO satellite. These cooperative transmissions in the space-air-ground integrated network will provide better interference management, stabilized the link quality and improve the user fairness. Using the LSAS and the cooperative transmission, this research program will explore the analytical and empirical schemes that facilitate the deployment of HAPS to achieve the higher throughputs. These schemes cannot be achieved by simply extending what are available in the ground communication systems. New theories and methodologies are required. To achieve this goal, this research will manipulate multiple theoretical tools such as random process, random matrix theory, network information theory and convex optimization. Based on these theoretical foundations, this research will propose insightful results and invent new methods. The research will be attempted and exploratory.

平流层通信平台可以作为中、低轨道卫星与地面通信系统的高空中继节点，结合平流层通信为地面通信终端提供的大容量宽带接入机制，共同打造空天地一体化高速无线通信系统，为解决高动态断续条件下空间信息的时空连续性支持问题发挥重要作用。. 本项目针对平流层通信的特点，以平流层通信传播特性、大规模阵列天线信道建模为基础，通过大规模MIMO技术，解决传统平流层通信方案中的旁瓣干扰、小区重叠、用户跟踪困难等问题，同时，针对空天地立体多层网络，开展卫星/平流层/地面网络协同通信与干扰管理技术的研究，在改善用户接入公平性的条件下，探索可实现平流层宽带无线大容量接入的新理论与新方法。这些研究并不能通过现有的地面宽带无线通信系统相关研究成果的简单扩展和延伸来解决，而是需要在很好地掌握随机过程、矩阵理论、网络信息论、凸优化理论等工具的基础上，通过深入的分析和研究，提出一些新的理论与方法。

本课题对基于面向宽带移动通信的平流层大规模MIMO用户接入技术从信道建模、大规模MIMO预编码算法设计、平台协作下的干扰抑制算法设计以及中继辅助的编码协作几个方面开展了研究。在信道建模方面提出了基于散射体动态演进的宽带MIMO信道模型，采用马尔科夫过程描述散射体“消失”和再次“出现”的动态特性，得到散射体存在和消失的稳态概率与高仰角平台下的测量结果可以很好地吻合。其次，针对城市环境散射体比较丰富的场景，提出了一种双圆柱体窄带信道模型，考虑等向散射和非等向散射的散射体，其接收端空间相关性函数和城市环境下的高仰角测量数据可以很好地吻合，验证了模型的有效性。最后，基于上述模型提出了一种热点区域下的平流层大规模MIMO用户相关性信道模型。在预编码算法方面提出了大规模MIMO系统基于模块化架构的迫零预编码(MZF)算法，通过模块间的并行处理缩短了基站总的基带处理时间，并通过接收端不同模块间的数据信号叠加，使干扰信号和噪声彼此随机消除，提升了频谱效率。其次，针对平流层通信中高仰角地区用户数较多，提出了机会波束成型-用户分组联合优化方案。该算法仅需用户信道的统计信息，和现有k-means分组算法相比，算法复杂度明显降低。此外，我们为抑制导频信道干扰提出了多天线接收端波束成形算法，通过用户端到不同基站相关性矩阵的差异来抑制相邻小区基站的干扰，所提方法要明显优于现有的小区联合信道估计(CAE)方法。在平台协作方面：采用本课题提出的信道模型，设计了多天线接收端波束成形算法抑制相邻平台间的干扰信号，在莱斯信道模型下，相对于单天线用户，当接收端配置4天线时，其可达速率可以提升200%左右。其次，针对平流层通信系统中存在严重同信道干扰情况，提出了可适用于平流层通信系统的基于中继辅助的编码协作通信方法以及相应的最优的中继节点（中继平台）选取方案。所提出的方案充分利用了中继辅助编码协作通信方式，有效提升了平流层通信系统容量。