A UAV-Mounted Free Space Optical Communication: Trajectory Optimization for Flight Time

Abstract

In this work, we address the trajectory optimization of a fixed-wing unmanned aerial vehicle (UAV) using free space optical communication (FSOC). Here, we focus on maximizing the flight time of the UAV by considering practical constraints for wireless UAV communication, including limited propulsion energy and required data rates. We find optimized trajectories in various atmospheric environments (e.g., moderate-fog and heavy-fog conditions), while also considering the channel characteristics of FSOC. In addition to maximizing the flight time, we consider the energy efficiency maximization and operation-time minimization problem to find the suboptimal solutions required to meet those constraints.Furthermore, we introduce a low-complexity approach to the proposed framework. In order to address the optimization problem, we conduct a bisection method and sequential programming and introduce a new feasibility check algorithm. Although our design considers suboptimal solutions owing to the nonconvexity of the problems, our simulations indicate that the proposed scheme exhibits a gain of approximately 44.12% in terms of service time when compared to the conventional scheme. Free space optical communication (FSOC), wireless communications with an unmanned aerial vehicle (UAV), UAV-mounted FSOC, flight time maximization, trajectory design. I. INTRODUCTION Recently, unmanned aerial vehicles (UAVs) have attracted a great deal of attention in the area of wireless communication networks. Owing to their mobility and flexibility, UAVs can be dispatched as a mobile entity in a network. It can provide new opportunities in various communication applications and have the capability to complement conventional fixed networks. UAV-assisted communications can efficiently support already existing terrestrial communication infrastructure, including data offloading at a hot spot [1], [2]. For example, in case of a catastrophic event, UAV-mounted infrastructures can temporarily support service recovery initiatives and local interim communication facilities for potentially damaged infrastructures [3]. In addition, UAV-assisted relaying can help to extend base station connectivity, from one station to another, in situations where the nodes are widely scattered and/or obstacles such as hills or large buildings are present [4].Principally, we envision that most future networks will be highly user-centric, increasing the user demand information due to an exponential increase in the internet of things (IoT), fifth-generation (5G) mobile networks, and beyond-5G wireless networks. Accordingly, UAVmounted fronthaul and backhaul frameworks have been considered as a promising approach to handle unexpected or temporarily large amounts of information that is commonly required by user terminals [5], [6]. By leveraging the UAV-mounted fronthaul and backhaul links, large-scale projects are now underway in several research groups and information technology companies,including Global Access to the Internet for All (GAIA) [7], Project Loon by Google [8], and...

Energy-Efficient Trajectory Optimization for UAV-Based Hybrid FSO/RF Communications with Buffer Constraints

“…This is reasonable because the air link is more likely to have a LoS link compared to the ground link. Moreover, the fast fading that may occur with the location and movement of the UAV is perfectly compensated [ 12 ]. Therefore, the RF channel is mainly characterized by path loss, which can be expressed as where is the reference channel gain at , is path loss exponent, and is the distance of the RF link.…”

“…To make full use of the UAVs’ high maneuverability, researchers have concentrated on optimizing the trajectory of the UAVs. For a UAV-based dual-hop RF relaying system, the UAV’s trajectory was optimized by minimizing the energy consumption [ 11 ] or maximizing the UAV’s flight time [ 12 ]. In mixed FSO/RF systems, the rate imbalance problem caused by using different types of links is a major concern, the buffer-assisted UAV relaying was proposed [ 10 , 13 ].…”

“…In this paper, we will analyze the energy efficiency and then optimize the UAV’s trajectory for a hybrid FSO/RF communication system. The main contributions of the paper are listed as follows: Different from [ 9 , 10 , 11 , 12 ] focusing on the UAV based RF scenarios, we consider a UAV based hybrid FSO/RF system with a buffer, which is a promising solution to the emerging wireless backbone network. Unlike [ 5 , 6 , 7 , 8 ], we focus on analyzing the energy efficiency of the system.…”

“…Different from [ 9 , 10 , 11 , 12 ] focusing on the UAV based RF scenarios, we consider a UAV based hybrid FSO/RF system with a buffer, which is a promising solution to the emerging wireless backbone network. Unlike [ 5 , 6 , 7 , 8 ], we focus on analyzing the energy efficiency of the system.…”

UAV Trajectory and Communication Co-design: Flexible Path Discretization and Path Compression

“…Specifically, different from TD that imposes equal time-slot length on all line segments, the authors proposed to divide the entire time horizon into three sub-horizons with different time-slot lengths so as to reduce the number of design variables in each time-window. Alternatively, to maximize the UAV flight time given fixed propulsion energy supply, a customized low-complexity UAV trajectory design was proposed in [24] that optimizes only a UAV trajectory fragment in a short time horizon, while it treats the overall trajectory as the rotated and replicated ones of the trajectory fragment with certain rotation angles. In [25], the authors proposed to fit the UAV trajectory over time by finite Fourier series with TD, based on which the complicated UAV waypoint optimization can be reduced into finding optimal values of finite Fourier series coefficients.…”