# UAV Communication Recovery under Meteorological Conditions
## 2 System Model
### Excessive Path Loss  
Excess path loss refers to the signal degradation beyond the free-space path loss, characterized by a Gaussian distribution [33; 34; 35]. The additional losses arise due to the scattering or reflection of electromagnetic waves when they interact with obstacles such as buildings, trees, and other obstructions on the ground. In this study, we focus on the average value of the additional path loss rather than its stochastic nature, as discussed in [17]. To determine the excessive path loss in the four selected regions, we employed MATLAB's Communications Toolbox to perform ray tracing simulations at two distinct frequencies, 28 GHz and 71 GHz. Specifically, the ray tracing simulation platform (PC) is equipped with an Intel(r) Core(tm) i7-11700F Processor (2.50 GHz) and 16 GB of RAM. In MATLAB, the command to initiate the ray tracing model is expressed as raytrace(tx, rx), where tx and rx represent predefined transmitter and receiver site objectives, respectively [32]. We use a site viewer object to display transmitter and receiver sites, as well as visualizations of ray propagation. We have employed omnidirectional antennas at both transmitter and receiver ends. It is worth mentioning that, in many practical cases, omnidirectional antennas are used for A2G communications due to their ability to radiate the signal uniformly in all directions. This allows for broader coverage and facilitates communication with aircraft regardless of their position or trajectory. Omnidirectional antennas are particularly suitable when the primary objective is to provide widespread coverage to a large area or a fleet of aircraft. By default, the site viewer presents a 3D view of the globe with geographic coordinates. For our simulation, the terrain and building data defined within the site viewer are based on the Open Street Map (OSM) file. We utilized the shooting and bouncing rays (SBR) method, allowing for up to three reflections, to create the ray tracing model. The interaction types within the SBR method encompass reflection effects but exclude diffraction, refraction, or scattering effects. In our ray tracing simulation, both building and terrain materials are designated as concrete due to its widespread usage in urban settings. The four selected rectangular regions have dimensions of approximately 840 m in length and 450 m in width. To maintain simulation consistency, we employ the same UAV deployment scheme across all four regions. For example, in one region, the UAV's projected coordinates on the ground are positioned at the center of the rectangle, with a height of 300 m. Taking into account an equal number of receivers per unit area, we  
Figure 1: LoS probability in four representative urban environments. distribute a specific number of receivers uniformly on the ground within the four regions. The quantities of the ground receivers in these regions are 24,947, 19,543, 12,144, and 11,209, respectively. The declining number of ground receivers across the regions is due to our selection of suburban, urban, dense urban, and high-rise urban environments. As the ratio of the building area to the total area within each region increases, the number of accommodated users on the ground decreases. Furthermore, the transmitter has an output power of 10 watts (40 dBm), and both the transmitter and receiver antennas are isotropic. Figure 2 displays the LoS and NLoS points, along with varying reflection numbers, at a 28 GHz carrier frequency across the four regions. It is important to note that we differentiate these reflection points based on the reflection number of the first ray that reaches the receiver. Based on Equation (3) from [17], we compute the excessive path loss \(\eta\) for each receiver across four regions. In Equation (3), \(\text{PL}_{n}\) and \(\text{FSPL}_{n}\) represent the total path loss and free-space path loss between the UAV and the nth receiver, respectively.