Future 6G networks are envisioned to integrate low Earth orbit satellite mega-constellations to enable seamless global connectivity, particularly in underserved and remote areas. However, the deployment of dense mega-constellations introduces interference among satellites operating over shared frequency bands. This represents a rather new setup for studying spectrum sharing, which exacerbates the limited flexibility of conventional FDD systems based on fixed bands for downlink and uplink transmissions. We address this spectrum-sharing problem and propose dynamic re-assignment of FDD bands for improved interference management in dense deployments, as well as evaluate the performance gain of this approach. To this end, we formulate a joint optimization problem that incorporates dynamic band assignment, user scheduling, and power allocation in both directions. This non-convex mixed integer problem is solved using a combination of equivalence transforms, alternating optimization, and state-of-the-art industrial-grade mixed integer solvers. Numerical results demonstrate that the proposed approach of dynamic FDD band assignment significantly enhances system performance over conventional FDD, achieving up to 30\% improvement in throughput in dense deployments.

翻译：未来6G网络被设想整合低地球轨道卫星巨型星座，以实现无缝的全球连接，特别是在服务不足和偏远地区。然而，密集巨型星座的部署引入了在共享频段上运行的卫星之间的干扰。这代表了一种研究频谱共享的全新场景，加剧了基于固定下行和上行频段的传统FDD系统灵活性有限的特性。我们针对这一频谱共享问题，提出在密集部署中动态重新分配FDD频段以改善干扰管理，并评估该方法的性能提升。为此，我们制定了一个联合优化问题，该问题包括动态频段分配、用户调度以及双向功率分配。这个非凸混合整数问题通过结合等价变换、交替优化和先进工业级混合整数求解器来解决。数值结果表明，所提出的动态FDD频段分配方法相比传统FDD显著增强了系统性能，在密集部署中实现了高达30%的吞吐量提升。