As the excellent tools for aiding communication,intelligent reflecting surface (IRS) and unmanned aerial vehicle (UAV) can extend the coverage area, remove blind area, and achieve a dramatic rate improvement. In this paper, we improve the secrecy rate (SR) performance at directional modulation (DM) networks using IRS and UAV in combination. To fully explore the benefits of IRS and UAV, two efficient methods are proposed to enhance SR performance. The first approach computes the confidential message (CM) beamforming vector by maximizing the SR, and the signal-to-leakage-noise ratio (SLNR) method is used to optimize the IRS phase shift matrix, which is called Max-SR-SLNR. Here, Eve is maximally interfered by transmitting artificial noise (AN) along the direct path and null-space projection (NSP) on the remaining two channels. To reduce the computational complexity, the CM, AN beamforming and IRS phase shift design are independently designed in the following methods. The CM beamforming vector is constructed based on maximum ratio transmission (MRT) criteria along the channel from Alice-to-IRS, and phase shift matrix of IRS is directly given by phase alignment (PA) method. This method is called MRT-NSP-PA. Simulation results show that the SR performance of the Max-SR-SLNR method outperforms the MRT-NSP-PA method in the cases of small-scale and medium-scale IRSs, and the latter approaches the former in performance as IRS tends to lager-scale.

翻译：作为辅助通信的卓越工具，智能反射面（IRS）和无人机（UAV）能够扩展覆盖区域、消除盲区，并实现速率的大幅提升。本文通过结合使用IRS和UAV，提高了定向调制（DM）网络中的保密速率（SR）性能。为充分挖掘IRS和UAV的优势，我们提出了两种高效方法来增强SR性能。第一种方法通过最大化保密率来计算机密信息（CM）波束成形矢量，并采用信号-泄漏-噪声比（SLNR）方法优化IRS相移矩阵，称为Max-SR-SLNR。在此方法中，通过沿直射路径发射人工噪声（AN）并在剩余两条信道上进行零空间投影（NSP），对窃听者施加最大干扰。为降低计算复杂度，以下方法独立设计了CM、AN波束成形及IRS相移矩阵。CM波束成形矢量基于沿Alice到IRS信道最大比传输（MRT）准则构建，IRS相移矩阵直接通过相位对齐（PA）方法给出，该方法称为MRT-NSP-PA。仿真结果表明，在中小规模IRS场景下，Max-SR-SLNR方法的保密率性能优于MRT-NSP-PA方法；而随着IRS趋于大规模，后者的性能逐渐接近前者。