27 research outputs found
Securing UAV Communications Via Trajectory Optimization
Unmanned aerial vehicle (UAV) communications has drawn significant interest
recently due to many advantages such as low cost, high mobility, and on-demand
deployment. This paper addresses the issue of physical-layer security in a UAV
communication system, where a UAV sends confidential information to a
legitimate receiver in the presence of a potential eavesdropper which are both
on the ground. We aim to maximize the secrecy rate of the system by jointly
optimizing the UAV's trajectory and transmit power over a finite horizon. In
contrast to the existing literature on wireless security with static nodes, we
exploit the mobility of the UAV in this paper to enhance the secrecy rate via a
new trajectory design. Although the formulated problem is non-convex and
challenging to solve, we propose an iterative algorithm to solve the problem
efficiently, based on the block coordinate descent and successive convex
optimization methods. Specifically, the UAV's transmit power and trajectory are
each optimized with the other fixed in an alternating manner until convergence.
Numerical results show that the proposed algorithm significantly improves the
secrecy rate of the UAV communication system, as compared to benchmark schemes
without transmit power control or trajectory optimization.Comment: Accepted by IEEE GLOBECOM 201
Throughput improvement for multi-hop UAV relaying
Unmanned aerial vehicle (UAV) relaying is one of the main technologies for UAV communications. It uses UAVs as relays in the sky to provide reliable wireless connection between remote users. In this paper, we consider a multi-hop UAV relaying system. To improve the spectrum efficiency of the system, we maximize the average end-to-end throughput from the source to the destination by jointly optimizing the bandwidth allocated to each hop, the transmit power for the source and relays, and the trajectories of the UAVs, subject to constraints on the total spectrum bandwidth, the average and peak transmit power, the UAV mobility and collision avoidance, and the information-causality of multi-hop relaying. The formulated optimization is non-convex. We propose an efficient algorithm to approximate and solve it, using the alternating optimization and successive convex optimization methods. Numerical results show that the proposed optimization significantly outperforms other benchmark schemes, verifying the effectiveness of our scheme
Beamforming Optimization for Active Intelligent Reflecting Surface-Aided SWIPT
In this paper, we study an active IRS-aided simultaneous wireless information
and power transfer (SWIPT) system. Specifically, an active IRS is deployed to
assist a multi-antenna access point (AP) to convey information and energy
simultaneously to multiple single-antenna information users (IUs) and energy
users (EUs). Two joint transmit and reflect beamforming optimization problems
are investigated with different practical objectives. The first problem
maximizes the weighted sum-power harvested by the EUs subject to individual
signal-to-interference-plus-noise ratio (SINR) constraints at the IUs, while
the second problem maximizes the weighted sum-rate of the IUs subject to
individual energy harvesting (EH) constraints at the EUs. The optimization
problems are non-convex and difficult to solve optimally. To tackle these two
problems, we first rigorously prove that dedicated energy beams are not
required for their corresponding semidefinite relaxation (SDR) reformulations
and the SDR is tight for the first problem, thus greatly simplifying the AP
precoding design. Then, by capitalizing on the techniques of alternating
optimization (AO), SDR, and successive convex approximation (SCA),
computationally efficient algorithms are developed to obtain suboptimal
solutions of the resulting optimization problems. Simulation results
demonstrate that, given the same total system power budget, significant
performance gains in terms of operating range of wireless power transfer (WPT),
total harvested energy, as well as achievable rate can be obtained by our
proposed designs over benchmark schemes (especially the one adopting a passive
IRS). Moreover, it is advisable to deploy an active IRS in the proximity of the
users for the effective operation of WPT/SWIPT.Comment: 32 pages, 10 figures, submitted to IEEE journal for possible
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