[简介] 6G无线系统作为6G系统的重要组成部分，其设计和关键技术的选择将直接影响通信、智能、感知、计算等多个维度的性能。预计6G系统设计将以沉浸宽带通信为基础，支持人工智能和通信融合、通信和通感一体化、泛在连接场景，并可与5G配合，全面支持物联网应用。针对这些典型场景，分析6G无线系统需要重点研究的技术要素。本研究可为面向6G的无线系统设计提供参考。

[简介]提出了5G-Advanced技术的总体愿景目标、主要演进方向以及六大应用场景，包括无缝万兆、全域通感、泛在智能、空天地一体、千亿物联、确定能力，并详细阐述了场景需求和关键技术。无缝万兆进一步提升网络速率和降低时延，全域通感将通信与感知功能结合，拓展无线网络边界，泛在智能通过AI赋能提升网络智能化水平，空天地一体实现星地融合，千亿物联支持高中低速全场景的物联接入，确定能力满足工业生产的高要求。5G-Advanced技术将持续提升5G网络能力，拓展应用场景，引领行业走向6G。

[Introduction] In the context of edge computing environments in general and the metaverse in particular, federated learning (FL) has emerged as a distributed machine learning paradigm that allows multiple users to collaborate on training a shared machine learning model locally, eliminating the need for uploading raw data to a central server. It is perhaps the only training paradigm that preserves the privacy of user data, which is essential for computing environments as personal as the metaverse. However, the original FL architecture proposed is not scalable to a large number of user devices in the metaverse community. To mitigate this problem, hierarchical federated learning (HFL) has been introduced as a general distributed learning paradigm, and has since then inspired and led to a number of research works. In this paper, we present several types of HFL architectures, with a special focus on the three-layer client-edge-cloud HFL architecture, which is most pertinent to the metaverse due to its delay-sensitive nature. We also examine works that take advantage of the natural layered organization of three-layer client-edge-cloud HFL to tackle some of the most challenging problems in FL within the metaverse. Finally, we outline some future research directions of HFL in the metaverse.

[Introduction] Femtosecond laser direct inscription is a technique especially useful for prototyping purposes due to its distinctive advantages such as high fabrication accuracy, true 3D processing flexibility, and no need for mold or photomask. In this paper, we demonstrate the design and fabrication of a planar lightwave circuit (PLC) power splitter encoded with waveguide Bragg gratings (WBG) using a femtosecond laser inscription technique for passive optical network (PON) fault localization application. Both the reflected wavelengths and intervals of WBGs can be conveniently tuned. In the experiment, we succeeded in directly inscribing WBGs in 1×4 PLC splitter chips with a wavelength interval of about 4 nm and an adjustable reflectivity of up to 70% in the C-band. The proposed method is suitable for the prototyping of a PLC splitter encoded with WBG for PON fault localization applications.