| 摘 要： |
As part of 3GPP standardization work for Release 17, non-terrestrial networks (NTNs) aim to bring 5G New Radio (NR) communications to unserved and isolated areas. Constellations of low Earth orbit (LEO) satellites have emerged as a promising asset for NTNs and a key enabler technology to provide truly seamless and ubiquitous connectivity through 5G. Varying and longer propagation delays compared to terrestrial networks, limited radio link budget and the inherent high-speed movement of LEO satellites introduce new challenges in the mobility management procedures. To guarantee robust service continuity and satisfactory user experience, the handover (HO) procedure in LEO satellite systems is critical. Motivated by this fact, this paper presents a first performance analysis of the conventional 5G NR HO algorithm in a LEO-based NTN deployment. We provide system-level simulations obtained for different values of HO margin and time-to-trigger. Furthermore, we compare the HO performance in NTN with two 3GPP terrestrial scenarios - urban macro and high-speed train. The simulation results show HO failures and radio link failures are a factor 10 higher for the NTN scenario, while the corresponding time in outage is 5 times longer. Finally, we analyze the key issues and suggest potential mobility enhancements.
作为3GPP第17版标准化工作的一部分，非地面网络（NTNs）旨在将5G新空频（NR）通信技术引入未覆盖和偏远地区。低地球轨道（LEO）卫星星座已成为NTNs的有力支撑，是实现5G真正无缝、无处不在连接的关键技术。与地面网络相比，LEO卫星具有不同的传播延迟、有限的无线电链路预算以及固有的高速移动特性，这些因素给移动性管理带来了新的挑战。为确保服务连续性和良好的用户体验，LEO卫星系统中的切换（HO）过程至关重要。基于这一背景，本文首次对基于LEO的NTN部署中传统5G NR HO算法进行了性能分析。我们提供了针对不同HO余量和触发时间值的系统级仿真结果，并进一步将NTN中的HO性能与两种3GPP地面场景——城市宏站和高速列车进行对比。仿真结果表明，在NTN场景下，HO失败和无线链路失败的发生率高出10倍，相应的中断时间也延长了5倍。最后，我们分析了主要问题，并提出了可能的移动性改进方案。 |
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