Multicasting in wireless access networks is a functionality that, by leveraging group communications, turns out to be essential for reducing the amount of resources needed to serve users requesting the same content. The support of this functionality in the modern 5G New Radio (NR) and future sub-Terahertz (sub-THz) 6G systems faces critical challenges related to the utilization of massive antenna arrays forming directional radiation patterns, multi-beam functionality, and use of multiple Radio Access Technologys (RATs) having distinctively different coverage and technological specifics. As a result, optimal multicasting in these systems requires novel solutions. This article aims to provide an exhaustive treatment of performance optimization methods for 5G/6G mmWave/sub-THz systems and discuss the associated challenges and opportunities. We start by surveying 3rd Generation Partnership Project (3GPP) mechanisms to support multicasting at the NR radio interface and approaches to modeling the 5G/6G radio segment. Then, we illustrate optimal multicast solutions for different 5G NR deployments and antenna patterns, including single- and multi-beam antenna arrays and single- and multiple RAT deployments. Further, we survey new advanced functionalities for improving multicasting performance in 5G/6G systems, encompassing Reflective Intelligent Surfaces (RISs), NR-sidelink technology, and mobile edge enhancements, among many others. Finally, we outline perspectives of multicasting in future 6G networks.

中文翻译：

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5G/6G 毫米波和亚太赫兹系统中的组播模型、方法和解决方案

无线接入网络中的多播功能通过利用组通信，对于减少为请求相同内容的用户提供服务所需的资源量至关重要。在现代 5G 新无线电 (NR) 和未来亚太赫兹 (sub-THz) 6G 系统中支持此功能面临着与利用形成定向辐射图的大规模天线阵列、多波束功能以及使用多种无线接入技术 (RAT) 具有明显不同的覆盖范围和技术细节。因此，这些系统中的最佳多播需要新颖的解决方案。本文旨在详尽介绍 5G/6G 毫米波/亚太赫兹系统的性能优化方法，并讨论相关的挑战和机遇。我们首先调查支持 NR 无线电接口多播的第三代合作伙伴项目 (3GPP) 机制以及对 5G/6G 无线电段进行建模的方法。然后，我们阐述了针对不同 5G NR 部署和天线模式的最佳多播解决方案，包括单波束和多波束天线阵列以及单和多 RAT 部署。此外，我们还调查了用于提高 5G/6G 系统中多播性能的新高级功能，包括反射智能表面 (RIS)、NR 侧链路技术和移动边缘增强等。最后，我们概述了未来 6G 网络中组播的前景。