The integration of non-terrestrial networks (NTNs) and terrestrial networks (TNs) is fundamental for extending connectivity to rural and underserved areas that lack coverage from traditional cellular infrastructure. However, this integration presents several challenges. For instance, TNs mainly operate in Time Division Duplexing (TDD). However, for NTN via satellites, TDD is complicated due to synchronization problems in large cells, and the significant impact of guard periods and long propagation delays. In this paper, we propose a novel slot allocation mechanism to enable TDD in NTN. This approach permits to allocate additional transmissions during the guard period between a downlink slot and the corresponding uplink slot to reduce the overhead, provided that they do not interfere with other concurrent transmissions. Moreover, we propose two scheduling methods to select the users that transmit based on considerations related to the Signal-to-Noise Ratio (SNR) or the propagation delay. Simulations demonstrate that our proposal can increase the network capacity compared to a benchmark scheme that does not schedule transmissions in guard periods.

翻译：非地面网络（NTN）与地面网络（TN）的融合对于将连接扩展至传统蜂窝基础设施无法覆盖的农村和服务欠缺地区至关重要。然而，这种融合带来了若干挑战。例如，地面网络主要采用时分双工（TDD）模式。但对于通过卫星实现的非地面网络，由于大覆盖范围小区中的同步问题、保护时段的显著影响以及较长的传播延迟，TDD的实现变得复杂。本文提出了一种新颖的时隙分配机制，以在非地面网络中实现TDD。该方法允许在下行时隙与相应上行时隙之间的保护时段内分配额外的传输，以减少开销，前提是这些传输不会干扰其他并发传输。此外，我们提出了两种调度方法，基于信噪比（SNR）或传播延迟的相关考量来选择进行传输的用户。仿真结果表明，与不在保护时段内调度传输的基准方案相比，我们的方案能够提升网络容量。