Movable antenna (MA) is an emerging technology which can reconfigure wireless channels via adaptive antenna position adjustments at transceivers, thereby bringing additional spatial degrees of freedom for improving system performance. In this paper, from a security perspective, we exploit the MAenabled legitimate jammer (MAJ) to subvert suspicious multiuser downlink communications consisting of one suspicious transmitter (ST) and multiple suspicious receivers (SRs). Specifically, our objective is to minimize the benefit (the sum rate of all SRs or the minimum rate among all SRs) of such suspicious communications, by jointly optimizing antenna positions and the jamming beamforming at the MAJ. However, the key challenge lies in that given the MAJ's actions, the ST can reactively adjust its power allocations to instead maximize its benefit for mitigating the unfavorable interference. Such flexible behavior of the ST confuses the optimization design of the MAJ to a certain extent. Facing this difficulty, corresponding to the above two different benefits: i) we respectively determine the optimal behavior of the ST given the MAJ's actions; ii) armed with these, we arrive at two simplified problems and then develop effective alternating optimization based algorithms to iteratively solve them. In addition to these, we also focus on the special case of two SRs, and reveal insightful conclusions about the deployment rule of antenna positions at the MAJ. Furthermore, we analyze the ideal antenna deployment scheme at the MAJ for achieving the globally performance lower bound. Numerical results demonstrate the effectiveness of our proposed schemes compared to conventional fixed-position antenna (FPA) and other competitive benchmarks.

翻译：可移动天线（MA）是一种新兴技术，它能够通过调整收发端天线位置来重构无线信道，从而为提升系统性能提供额外的空间自由度。本文从安全视角出发，利用可移动天线赋能的合法干扰器（MAJ）来颠覆由单个可疑发射器（ST）与多个可疑接收器（SR）构成的可疑多用户下行通信。具体而言，我们的目标是通过联合优化MAJ的天线位置与干扰波束成形，最小化此类可疑通信的收益（所有SR的和速率或所有SR中的最小速率）。然而，关键挑战在于：给定MAJ的动作，ST可以反应性地调整其功率分配，转而最大化其收益以减轻不利干扰。ST的这种灵活行为在一定程度上干扰了MAJ的优化设计。面对这一困难，针对上述两种不同收益：i）我们分别确定了给定MAJ动作下ST的最优行为；ii）基于此，我们得到了两个简化问题，并开发了有效的基于交替优化的算法来迭代求解它们。除此之外，我们还关注两个SR的特殊情况，并揭示了关于MAJ天线位置部署规则的深刻结论。此外，我们分析了MAJ为实现全局性能下界所需的天线理想部署方案。数值结果表明，与传统的固定位置天线（FPA）及其他竞争基准相比，我们提出的方案具有显著优势。