Statistical Modeling of the FSO Fronthaul Channel for UAV-Based Communications

Abstract

In this paper, we investigate the statistics of the free space optics (FSO) communication channel between a hovering unmanned aerial vehicle (UAV) and a central unit. Two unique characteristics make UAV-based FSO systems significantly different from conventional FSO systems with static transceivers. First, for UAV-based FSO systems, the incident laser beam is not always orthogonal to the receiver lens plane. Second, both position and orientation of the UAV fluctuate over time due to dynamic wind load, inherent random air fluctuations in the atmosphere around the UAV, and internal vibrations of the UAV. On the contrary, for conventional FSO systems, the laser beam is always perpendicular to the receiver lens plane and the relative movement of the transceivers is limited. In this paper, we develop a novel channel model for UAV-based FSO systems by quantifying the corresponding geometric and misalignment losses (GML), while taking into account the non-orthogonality of the laser beam and the random fluctuations of the position and orientation of the UAV. In particular, for diverse weather conditions, we propose different fluctuation models for the position and orientation of the UAV and derive corresponding statistical models for the GML. We further analyze the performance of a UAV-based FSO link in terms of outage probability and ergodic rate and simplify the resulting analytical expressions for the high signal-to-noise ratio (SNR) regime. Finally, simulations validate the accuracy of the presented analysis and provide important insights for system design. For instance, we show that for a given variance of the fluctuations, the beam width should be properly adjusted to minimize the outage probability. introduce the following new challenges: i) For conventional FSO links, it is typically assumed that the laser beam is orthogonal with respect to (w.r.t.) the receiver lens plane, as orthogonality maximizes the amount of laser power collected by the photo-detector (PD) located behind the lens [12]. However, orthogonality may not hold for UAV-based FSO communication systems. For example, the position of a UAV may depend on the locations and traffic needs of the users, while the CU may not be able to adjust the orientation of the receiver lens due to limited mechanical capabilities. In addition, using one receiver lens and multiple PDs [15], [16], the CU may receive data from several UAVs having different positions. Hence, it is not possible to orthogonally align the laser beams of all UAVs with the receiver lens plane. ii) Unlike 1 The receiver can only capture the fraction of power that falls on its lens. This phenomenon is known as geometric loss. Moreover, misalignment of the center of the optical beam and the center of the receiver lens further increases the geometric loss. This phenomenon is known as misalignment loss [12].

Ergodic Sum Rate Analysis of UAV-Based Relay Networks With Mixed RF-FSO Channels

“…Second, the instability of the UAV, i.e., the random vibrations of the UAV, introduces a random power loss. Taking these effects into account, the point-to-point UAV-based FSO channel, g, can be modeled as follows [30], [31]…”

Performance of UAV-to-Ground FSO Communications with APD and Pointing Errors

“…In these cases, free-space optical (FSO) communications, a cost-effective, license-free, easy-to-deploy, high-bandwidth, and secure access technique, is being viewed as a potential candidate for the front-hauling transmission of multimedia data collected by flying UAVs from the CP [6][7][8][9][10][11]. For these reasons, FSO communication technology was naturally incorporated with UAV technology in order to establish high-speed optical communication networks in ground-to-air, air-to-ground, and air-to-air situations.…”

“…UAV-based FSO communication links have been relatively well studied in the literature [6,7,[15][16][17][18][19]. In particular, the author in [6] proposed an approach of flying platforms for relaying the FSO backhaul or front-haul data traffic from the access-to-core networks.…”

Analytical Channel Model and Link Design Optimization for Ground-to-HAP Free-Space Optical Communications

“…However, the authors in [33], [34] ignored the effects of the side-lobes of optical Airy pattern at the receiver which result in an outage probability floor. Meanwhile, based on the assumption of non-orthogonal incident beam to the photo detector (PD) plane, a statistical model was proposed for the geometrical and misalignment losses of the FSO channel for unmanned aerial vehicles (UAVs)-based networks [35], where the background noise was assumed as the dominant noise source at the PD. However, in this noise regime, the receiver field-of-view (FOV) was not optimized to mitigate the effects of background noise and orientation deviations of the UAV.…”