To boost the secrecy rate (SR) of the conventional directional modulation (DM) network and overcome the double fading effect of the cascaded channels of passive intelligent reflecting surface (IRS), a novel active IRS-assisted DM system with a power adjusting strategy between transmitter and active IRS is proposed in this paper. Then, a joint optimization of maximizing the SR is cast by alternately optimizing the power allocation (PA) factors, transmit beamforming at the BS, and reflect beamforming at the active IRS, subject to the power constraint at IRS. To tackle the formulated non-convex optimization problem, a high-performance scheme of maximizing SR based on fractional programming (FP) and successive convex approximation (SCA) (Max-SR-FS) is proposed, where the FP and SCA methods are employed to optimize the PA factor of confidential message and the PA factor of power allocated to the BS, and the SCA algorithm is also utilized to design the transmit beamforming and phase shift matrix of the IRS. To reduce the high complexity, a low-complexity scheme, named maximizing SR based on derivative operation (DO) and general power iterative (GPI) (Max-SR-DG), is developed, where the DO and methods of the equal amplitude reflecting (EAR) and GPI are adopted to derive the PA factors and IRS phase shift matrix, respectively. Simulation results show that with the same power constraint, both the proposed schemes harvest about 12 percent and 70 percent rate gains over the equal PA and passive IRS schemes, respectively.

翻译：为提升传统定向调制网络的安全速率并克服无源智能反射面级联信道的双衰落效应，本文提出一种在发射机与有源IRS间采用功率调整策略的新型有源IRS辅助DM系统。通过交替优化基站处的功率分配因子与发射波束成形、有源IRS处的反射波束成形，在IRS功率约束下构建了最大化安全速率的联合优化问题。针对该非凸优化问题，提出基于分数规划与逐次凸逼近的高性能安全速率最大化方案（Max-SR-FS），其中采用FP与SCA方法优化机密消息的PA因子及分配给基站的PA因子，并利用SCA算法设计发射波束成形与IRS相移矩阵。为降低高计算复杂度，进一步开发了低复杂度方案——基于导数运算与通用功率迭代的安全速率最大化方案（Max-SR-DG），分别采用DO方法与等幅反射及GPI方法推导PA因子与IRS相移矩阵。仿真结果表明，在相同功率约束下，所提两种方案相比等功率分配方案和无源IRS方案分别获得约12%与70%的速率增益。