Recently, urban air mobility (UAM) has attracted attention as an emerging technology that will bring innovation to urban transportation and aviation systems. Since the UAM systems pursue fully autonomous flight without a pilot, wireless communication is a key function not only for flight control signals, but also for navigation and safety information. The essential information is called a command and control (C2) message, and the UAM networks must be configured so that the UAM can receive the C2 message by securing a continuous link stability without any interruptions. Nevertheless, a lot of prior works have focused only on improving the average performance without solving the low-reliability in the cell edges and coverage holes of urban areas. In this dissertation, we identify the factors that hinder the communication link reliability in considering three-dimensional (3D) urban environments, and propose a antenna configuration, resource utilization, and transmission strategy to enable UAM receiving C2 messages regardless of time and space. First, through stochastic geometry modeling, we analyze the signal blockage effects caused by the urban buildings. The blockage probability is calculated according to the shape, height, and density of the buildings, and the coverage probability of the received signal is derived by reflecting the blockage events. Furthermore, the low-reliability area is identified by analyzing the coverage performance according to the positions of the UAMs. To overcome the low-reliability region, we propose three methods for UAM network operation: i) optimization of antennas elevation tilting, ii) frequency reuse with multi-layered narrow beam, and iii) assistive transmissions by the master UAM.

翻译：近年来，城市空中交通作为一种新兴技术，因其将为城市交通与航空系统带来革新而备受关注。由于城市空中交通系统追求无需飞行员的完全自主飞行，无线通信不仅是飞行控制信号的关键功能，也是导航与安全信息传输的核心。此类关键信息被称为指挥与控制消息，城市空中交通网络必须配置为能够通过确保连续链路稳定性而实现无中断的指挥与控制消息接收。然而，现有研究大多仅关注提升平均性能，未能解决城市区域中小区边缘与覆盖盲区的低可靠性问题。本论文通过三维城市环境建模，识别了影响通信链路可靠性的关键因素，并提出了一种天线配置方案、资源利用策略与传输方法，以实现城市空中交通设备在任意时间与空间条件下均能可靠接收指挥与控制消息。首先，通过随机几何建模，我们分析了城市建筑导致的信号遮挡效应。根据建筑物的形态、高度与密度计算了遮挡概率，并通过反映遮挡事件推导了接收信号的覆盖概率。进一步地，通过分析不同城市空中交通设备位置下的覆盖性能，识别了低可靠性区域。为克服低可靠性区域问题，我们提出了三种城市空中交通网络运行方法：i) 天线俯仰角优化配置，ii) 基于多层窄波束的频率复用技术，iii) 主控城市空中交通设备的辅助传输机制。