Altitude design for quasi-static UAV-BS maximizing physical layer security

Abstract

In this study, the altitude of an unmanned aerial vehicle base station (UAV-BS) is optimized to maximize an average worst-case secrecy rate (AWSR) without eavesdropper location information. AWSR denotes the lower bound of the network secrecy rate. The air-to-ground channels are modeled based on the derived line-of-sight probability under a general urban model with {\it Poisson point process} and {\it Rayleigh distribution} for the {\it locations} and {\it heights} of the buildings, respectively. To solve the AWSR maximization problem, which is intractable, I reformulate it with first-order Taylor series approximation using the density information of eavesdroppers and apply a Davies-Swann-Campey algorithm to effectively find the solution of the modified AWSR maximization problem. Numerical results verify that the altitude of UAV-BS affects the secrecy rate significantly and that the proposed UAV-BS can improve the secrecy rate compared to a static terrestrial BS. The results show the benefits of UAV-BS having flexibility in placement. Furthermore, the suggestion of UAV-BS altitude placement in terms of urban environmental parameters, eavesdroppers' density, and leitimate user's horizontal distance is provided.