The broadcast characteristics of sixth-generation (6G) low-earth orbit (LEO) satellite communications raise serious security issues. Movable antenna (MA) technology offers a promising physical layer security (PLS) solution by flexibly reconfiguring antenna positions to exploit additional spatial degrees of freedom. However, in highly dense LEO satellite constellations, the legitimate satellite and potential eavesdropping satellites may exhibit small angular separations, which poses significant challenges for the design of secure transmission schemes. To address this challenge, this paper proposes an MA-assisted secure transmission scheme for time-varying LEO satellite communications, where a ground station equipped with an MA array communicates with a serving satellite, while the other visible satellites are regarded as potential eavesdroppers. We maximize the average secrecy rate by jointly optimizing the transmit beamforming and MA positions. An alternating optimization (AO) framework is developed, where semidefinite relaxation is adopted for the beamforming optimization subproblem, while high-accuracy successive convex approximation (SCA) and low-complexity differential evolution (DE) algorithms are proposed for the MA position optimization subproblem. Numerical results demonstrate that the proposed MA-assisted LEO secure transmission scheme consistently achieves superior performance compared to the conventional fixed-position antenna scheme.

翻译：第六代（6G）低地球轨道（LEO）卫星通信的广播特性引发了严重的安全问题。移动天线（MA）技术通过灵活重构天线位置以利用额外的空间自由度，为物理层安全（PLS）提供了一种有前景的解决方案。然而，在高度密集的LEO卫星星座中，合法卫星与潜在窃听卫星可能出现较小的角度间隔，这对安全传输方案的设计构成了重大挑战。为应对这一挑战，本文提出了一种面向时变LEO卫星通信的MA辅助安全传输方案，其中配备MA阵列的地面站与一颗服务卫星通信，而其他可视卫星被视为潜在窃听者。我们通过联合优化发射波束成形和MA位置来最大化平均保密速率。开发了交替优化（AO）框架，其中采用半定松弛求解波束成形优化子问题，并针对MA位置优化子问题分别提出了高精度逐次凸近似（SCA）和低复杂度差分进化（DE）算法。数值结果表明，与传统固定位置天线方案相比，所提出的MA辅助LEO安全传输方案始终能获得更优的性能。