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

Rong-Rong Lu,Qinglin Wang,Jin-Yuan Wang,Yang Ma,Sheng-Hong Lin,Bingyuan Zhang

doi:10.3390/e23121596

Abstract

This paper focuses on an unmanned aerial vehicle (UAV) assisted hybrid free-space optical (FSO)/radio frequency (RF) communication system. Considering the rate imbalance between the FSO and RF links, a buffer is employed at the UAV. Initially, theoretical models of energy consumption and throughput are obtained for the hybrid system. Based on these models, the theoretical expression of the energy efficiency is derived. Then, a nonconvex trajectory optimization problem is formulated by maximizing the energy efficiency of the hybrid system under the buffer constraint, velocity constraint, acceleration constraint, start–end position constraint, and start–end velocity constraint. By using the sequential convex optimization and first-order Taylor approximation, the nonconvex problem is transformed into a convex one. An iterative algorithm is proposed to solve the problem. Numerical results verify the efficiency of the proposed algorithm and also show the effects of buffer size on a UAV’s trajectory.

Highlights

Different from terrestrial static relay, unmanned aerial vehicle (UAV)-based relay has low cost and high mobility, which plays an important role in many application scenarios [1]
The narrow beams of Free-space optical (FSO) communications facilitate secure and interference-free communications. These advantages of FSO communication come at the expense of some challenges: (1) FSO communication relies on the availability of a line-of-sight (LoS), which introduces critical limitations for mobile nodes
Only a few studies focus on hybrid FSO/radio frequency (RF) systems with UAV mobile relays

Summary

Introduction

Different from terrestrial static relay, unmanned aerial vehicle (UAV)-based relay has low cost and high mobility, which plays an important role in many application scenarios (such as emergency responses and delay-tolerant applications) [1]. The UAV-assisted wireless communications have attracted increasing interest. The narrow beams of FSO communications facilitate secure and interference-free communications These advantages of FSO communication come at the expense of some challenges: (1) FSO communication relies on the availability of a line-of-sight (LoS), which introduces critical limitations for mobile nodes. To mitigate the unpredictable connectivity of FSO links, both the RF and FSO techniques can be utilized to constitute a hybrid system (i.e., so-called hybrid FSO/RF system). In such systems, both the advantages of RF and FSO links can be exploited. Only a few studies focus on hybrid FSO/RF systems with UAV mobile relays. In [10], the energy efficiency for a UAV-based RF system was analyzed

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Conclusion