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：作为通信辅助的卓越工具，智能反射面（IRS）和无人机（UAV）能够扩展覆盖范围、消除盲区并实现显著的速率提升。本文通过联合运用IRS与UAV来提升定向调制（DM）网络的保密速率（SR）性能。为充分挖掘IRS与UAV的潜力，我们提出了两种增强SR性能的高效方法。第一种方法通过最大化SR计算机密消息（CM）波束赋形向量，并采用信漏噪比（SLNR）方法优化IRS相位偏移矩阵，称为Max-SR-SLNR方法。该方法中，窃听者（Eve）受到沿直接路径发射人工噪声（AN）并对剩余两条信道进行零空间投影（NSP）的最大化干扰。为降低计算复杂度，后续方法将CM波束赋形、AN波束赋形及IRS相位偏移设计独立处理：基于Alice到IRS信道的最大比传输（MRT）准则构建CM波束赋形向量，并采用相位对齐（PA）方法直接给出IRS相位偏移矩阵，称为MRT-NSP-PA方法。仿真结果表明，在小规模与中规模IRS场景下，Max-SR-SLNR方法的SR性能优于MRT-NSP-PA方法；当IRS趋于大规模时，后者性能接近前者。