# 3D Trajectory Optimization for Secure UAV Communication with CoMP Reception

## TL;DR

This paper introduces a 3D trajectory optimization method for UAVs to enhance secure communication with ground nodes using CoMP, outperforming traditional 2D approaches by leveraging altitude control.

## Contribution

It develops a joint 3D trajectory and power allocation optimization framework for UAVs with CoMP, incorporating vertical movement for improved secrecy performance.

## Key findings

- 3D trajectory optimization significantly improves secrecy rates.
- Vertical trajectory control offers substantial gains over 2D designs.
- Proposed alternating optimization approach effectively solves the non-convex problem.

## Abstract

This paper studies a secrecy unmanned aerial vehicle (UAV) communication system with coordinated multi-point (CoMP) reception, in which one UAV sends confidential messages to a set of distributed ground nodes (GNs) that can cooperate in signal detection, in the presence of several colluding suspicious eavesdroppers. Different from prior works considering the two-dimensional (2D) horizontal trajectory design in the non-CoMP scenario, this paper additionally exploits the UAV's vertical trajectory (or altitude) control for further improving the secrecy communication performance with CoMP. In particular, we jointly optimize the three dimensional (3D) trajectory and transmit power allocation of the UAV to maximize the average secrecy rate at GNs over a particular flight period, subject to the UAV's maximum flight speed and maximum transmit power constraints. To solve the non-convex optimization problem, we propose an alternating-optimization-based approach, which optimizes the transmit power allocation and trajectory design in an alternating manner, by convex optimization and successive convex approximation (SCA), respectively. Numerical results show that in the scenario with CoMP reception, our proposed 3D trajectory optimization significantly outperforms the conventional 2D horizontal trajectory design, by exploiting the additional degree of freedom in vertical trajectory.