Rotatable antenna (RA) provides additional spatial degrees of freedom (DoFs) for communication systems by enabling per-antenna dynamic boresight adjustment, which is attractive for fairness-oriented multicast transmission. This letter investigates an RA-enhanced downlink multi-group multicast system. Specifically, we aim to maximize the minimum signal-to-interference-plus-noise ratio (SINR) among all users by jointly optimizing the multicast beamforming vectors and the RA boresight directions under transmit power and rotation constraints. To solve this non-convex problem, we first reformulate the max-min SINR objective via quadratic transform. Then, we develop an alternating optimization (AO) algorithm that iteratively updates the multicast beamforming and RA boresight directions. The beamforming vectors are obtained from a convex subproblem, while the boresight directions are refined using a successive convex approximation (SCA) procedure. Simulation results verify that the proposed RA-based scheme substantially enhances the fairness performance compared with fixed antenna-based and random-orientation benchmarks.

翻译：可旋转天线通过实现每根天线的动态波束指向调整，为通信系统提供了额外的空间自由度，这对于面向公平性的多播传输具有吸引力。本文研究了一种可旋转天线增强的下行多组多播系统。具体而言，我们通过联合优化多播波束成形向量和可旋转天线的波束指向方向，在发射功率和旋转约束下最大化所有用户中的最小信干噪比。为解决这一非凸问题，我们首先通过二次变换重新表述了最大-最小信干噪比目标，随后开发了一种交替优化算法，该算法迭代更新多播波束成形和可旋转天线的波束指向方向。波束成形向量由一个凸子问题求解得到，而波束指向方向则通过逐次凸近似过程进行优化。仿真结果表明，与基于固定天线和随机指向的基准方案相比，所提出的可旋转天线方案显著提升了公平性性能。