Joint Obstacle Avoidance and 3D Deployment for Securing UAV-Enabled Cellular Communications

Unmanned aerial vehicle (UAV) can enable cellular mobile communications in unexpected or temporary scenarios, but there are information security problems raised in such applications. Physical layer security is now emerging as a promising alternative technology to realize secrecy in wireless communications. In the UAV-enabled communication systems, the fully controllable mobility of UAV provides new design degrees of freedom for enhancing physical layer security. This paper investigates an UAV-enabled cellular communication system where an ultralow-altitude UAV is equipped with a base station to serve a ground user in the presence of an eavesdropper. The probability of non-zero secrecy capacity is maximized subject to the airspace and obstacle constraints by adaptively optimizing the UAV’s three-dimensional positions. The optimization problem is simplified by equivalent transformation and then solved by semidefinite relaxation (SDR). Two approaches termed as eigenvector approximation and random sampling are addressed to extract an approximation solution for the primal problem from the solution obtained by the SDR. Simulation results show that there is a slight difference between the probability of non-zero secrecy capacity achieved by the two solution approximation approaches.