Line-of-Sight Probability for Outdoor-to-Indoor UAV-Assisted Emergency Networks

TL;DR

A model for the link in a UAV-assisted emergency location and/or communication system, given the importance of Line-of-Sight (LoS) links in localization as well as mmWave communication is developed and a closed-form expression for the LoS probability is derived.

Abstract

For emergency response scenarios like firefighting in urban environments, there is a need to both localize emergency responders inside the building and also support a high bandwidth communication link between the responders and a command-and-control center. The emergency networks for such scenarios can be established with the quick deployment of Unmanned Aerial Vehicles (UAVs). Further, the 3D mobility of UAVs can be leveraged to improve the quality of the wireless link by maneuvering them into advantageous locations. This has motivated recent propagation measurement campaigns to study low-altitude air-to-ground channels in both 5G-sub6 GHz and 5G-mmWave bands. In this paper, we develop a model for the link in a UAV-assisted emergency location and/or communication system. Specifically, given the importance of Line-of-Sight (LoS) links in localization as well as mmWave communication, we derive a closed-form expression for the LoS probability. This probability is parameterized by the UAV base station location, the size of the building, and the size of the window that offers the best propagation path. An expression for coverage probability is also derived. The LoS probability and coverage probabilities derived in this paper can be used to analyze the outdoor UAV-to-indoor propagation environment to determine optimal UAV positioning and the number of UAVs needed to achieve the desired performance of the emergency network.

Figures (10)

• Figure 1: Top view for the outdoor-to-indoor emergency network scenario with the UAV-mounted BS at point $A$, the MS at point $B$ inside a building represented by $\square R_1R_2R_3R_4$.
• Figure 2: Path loss as a function of the intrusion distance of an obstacle into the first Fresnel zone region for 5G-sub6 and 5G-mmWave frequencies for $d_1 = 8m$, $d_2=20m$.
• Figure 3: LoS region $\square FBDE$ when the back wall is illuminated by the UAV-BS at point $A$.
• Figure 4: Geometry for the scenario when the side wall is illuminated by the UAV-BS at point $A$.
• Figure 5: For the frequencies in consideration i.e. in 5G-sub6 bands and 5G-mmWave bands, the regime of operation is above the critical frequency. In the plot the we compare the closed form expression of the critical frequency vs its upper bound for room size $L_r=20m$ and window size $L_w=1m,\;2m,\;3m$.