Achieving Secrecy Energy Efficiency Fairness in UAV-Enabled Multi-User Communication Systems

This letter investigates the secrecy energy efficiency (SEE) fairness of unmanned aerial vehicle (UAV)-enabled multi-user communication systems where a UAV disseminates data to multiple ground users (GUs) in the presence of an eavesdropper (EVE). Taking into account the security threats from EVE, the limited on-board energy of UAV and the fairness among GUs, we formulate a user-oriented SEE maximization problem to maximize the minimum GU’s SEE by jointly optimizing the UAV trajectory and resource allocation subject to the UAV motion constraints and resource budgets. Due to the difficulty in solving this problem that arises from the fractional structure of SEE and the coupling characteristic of optimization variables, we first exploit the successive convex approximation to transform the original problem to a convex one, which is further converted into a second order cone program to reduce the computational complexity. Then, a convergent iterative algorithm is designed to find the suboptimal solution. Simulation results show that the proposed scheme significantly improves SEE fairness of GUs as compared to some benchmark schemes.

I. Introduction

Owing to highly controllable mobility, flexible and on-demand deployment as well as easily available line-of-sight (LoS) links, the unmanned aerial vehicle (UAV)-enabled communication systems (UCSs) can significantly enhance network coverage, connectivity and throughput, compared to the traditional terrestrial communication systems (TCSs) [1]. However, due to the broadcast nature of wireless channels, the UCSs face some challenges from potential eavesdroppers (EVEs) on the ground. To guarantee secure UAV communications, the physical layer security technologies were exploited to maximize secrecy rate (SR) by jointly optimizing the UAV trajectory and power allocation in both spatial domain and power domain simultaneously [2]. In addition, the limited on-board energy of the UAV is another critical challenge in UCSs, since besides the conventional communication-related energy consumption (CEC), the propulsion energy consumption (PEC) should also be required to maintain UAV aloft. By taking this issue into account, the authors in [3] defined the energy efficiency (EE) of fixed-wing UAV as the total information bits per UAV’s PEC unit and designed an energy-efficient trajectory with a single ground user (GU).