Rotatable antenna (RA) technology has emerged as a promising solution to enhance spectrum efficiency by exploiting additional spatial degrees of freedom (DoFs) in multiple access networks. However, the relative performance superiority among different multiple access schemes remains largely unclear due to the unique capability of RA in reconfiguring the directional gain pattern. In this letter, we conduct a theoretical comparison between non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) schemes in RA-assisted communication systems in terms of transmit power minimization, subject to constraints on antenna rotational range and users' target rates. To address the associated non-convex optimization problem, a particle swarm optimization (PSO) algorithm is employed to optimize the rotational angle. Simulation results demonstrate that RA-assisted schemes significantly reduce transmit power compared to fixed-antenna benchmarks. Furthermore, RA-assisted NOMA may perform worse than time-division multiple access (TDMA) for symmetric user deployments, while it exhibits superior robustness and energy efficiency in asymmetric scenarios.

翻译：可旋转天线技术通过利用多址接入网络中额外的空间自由度，已成为提升频谱效率的前沿方案。然而，由于可旋转天线在重构方向增益模式方面具有独特能力，不同多址接入方案的相对性能优势仍不明确。本文在旋转角度范围与用户目标速率约束下，以发射功率最小化为目标，对可旋转天线辅助通信系统中非正交多址接入与正交多址接入方案进行了理论比较。针对其非凸优化问题，采用粒子群优化算法进行旋转角度优化。仿真结果表明，与固定天线基准方案相比，可旋转天线辅助方案能显著降低发射功率。此外，对称用户部署场景下，可旋转天线辅助NOMA的性能可能劣于时分多址接入，但在非对称场景中表现出更强的鲁棒性与能效优势。