Recently, intelligent reflecting surface (IRS) and unmanned aerial vehicle (UAV) have been introduced into wireless communication systems to enhance the performance of air-ground transmission. To make a good balance between performance, cost, and power consumption, a hybrid-IRS-and-UAV-assisted directional modulation (DM) network is investigated in this paper, where the hybrid IRS consists of passive and active reflecting elements. To maximize the achievable rate, three optimization algorithms, called maximum signal-to-noise ratio (SNR)-fractional programming (FP) (Max-SNR-FP), maximum SNR-equal amplitude reflecting (EAR) (Max-SNR-EAR), and maximum SNR-majorization-minimization (MM) (Max-SNR-MM), are proposed to jointly design the beamforming vector and phase shift matrix (PSM) of hybrid IRS by alternately optimizing one and giving another. The Max-SNR-FP method employs the successive convex approximation and FP methods to derive the beamforming vector and hybrid IRS PSM. The Max-SNR-EAR method adopts the maximum signal-to-leakage-noise ratio method and the criteria of phase alignment and EAR to design them. In addition, the Max-SNR-MM method utilizes the MM criterion to derive the IRS PSM. Simulation results show that the rates harvested by the proposed three methods are slightly lower than those of active IRS with higher power consumption, which are 35 percent higher than those of no IRS and random phase IRS, while passive IRS achieves only about 17 percent rate gain over the latter. Moreover, compared to Max-SNR-FP, the proposed Max-SNR-EAR and Max-SNR-MM methods make an obvious complexity degradation at the price of a slight performance loss.

翻译：近期，智能反射面（IRS）和无人机（UAV）已被引入无线通信系统以提升空地传输性能。为在性能、成本和功耗间取得良好平衡，本文研究了一种混合IRS与无人机辅助的定向调制（DM）网络，其中混合IRS由无源和有源反射单元组成。为最大化可达速率，提出了三种优化算法——最大信噪比-分数规划（Max-SNR-FP）、最大信噪比-等幅反射（Max-SNR-EAR）和最大信噪比-最小最大化（Max-SNR-MM）——通过交替优化波束成形向量和混合IRS相移矩阵（PSM）实现联合设计。Max-SNR-FP方法采用逐次凸近似和分数规划方法推导波束成形向量与混合IRS的PSM；Max-SNR-EAR方法采用最大信泄噪比方法结合相位对齐与等幅反射准则进行设计；Max-SNR-MM方法则利用最小最大化准则推导IRS的PSM。仿真结果表明，所提三种方法获取的速率略低于功耗更高的有源IRS方案，但相较无IRS和随机相位IRS方案提升35%，而被动IRS仅比后者获得约17%的速率增益。此外，与Max-SNR-FP相比，所提Max-SNR-EAR和Max-SNR-MM方法在轻微性能损失下实现了显著的复杂度降低。