本文为中国香港大学（作者：Yu Ngok Li）的博士论文，共219页。

第五代（5G）无线网络旨在支持包括增强型移动宽带（eMBB）、大规模机器型通信（mMTC）和超可靠低延迟通信（URLLC）在内的多种用途，对世界的技术、经济和工业发展具有重要意义。要实现5G的愿景，关键是要在5G新无线电（NR）标准第一次发布的基础上，学习5G的初始部署，并在随后的5G及以后的标准发布中及时解决问题。大规模MIMO是5G标准的一个重要组成部分，用于提高5G系统的频谱效率和网络性能，以达到其目标的千兆吞吐量。对于5G NR系统，与4G系统的关键区别之一是除了6GHz以下的频带之外，还利用毫米波（mmWave）频带。为了降低复杂度和实现成本，大规模天线阵列的模拟-数字混合波束形成已成为解决高传输损耗问题和提高毫米波频谱效率的常用设计方法。5G NR标准提供了对不同波束形成架构和部署场景的支持。在这篇论文中，我们解决了5G NR标准化过程中遇到的一些主要挑战，并提出了一些对5G演进有用的波束管理和信道状态信息（CSI）获取的新技术。这些技术包括基于组的波束管理和先进的线性组合码本设计。

超密集网络部署是下一代网络发展的必然趋势。为了实现小区的灵活部署，自回程小区体系结构是未来超密集网络体系结构的重要类型之一。在这篇论文中，我们提出了一个新的网络架构，在小区和用户两方面支持加密和虚拟化。提出并评价了考虑多用户多输入多输出（MU-MIMO）和虚拟多输入多输出（virtual MIMO）自适应的用户虚拟化方法。此外，我们提出了一种新的软混合自动重复请求（HARQ）反馈方案来改善云系统中设备之间的链路自适应。能量效率是NR网络的关键性能指标之一。必须仔细考虑能源效率和其他性能方面（如延迟、吞吐量、连接密度和可靠性）之间的权衡。能量效率对于用户设备（UE）侧和基站侧都是重要的。在UE方面，UE的电池寿命对用户体验有很大的影响。在不影响5G手机电池寿命的前提下，在其他性能方面改善UE体验是一个挑战。在基站方面，从环境和运营成本的角度来看，高效的网络实现是至关重要的。为了适应不同的要求和取舍，5G NR标准在网络运行模式上具有很大的灵活性。本文提出了5G-NR标准所采用的节能技术，包括两步随机接入和MIMO层自适应。在现有标准化技术的基础上，提出了绿色通信的一些主要发展趋势，并对未来5G标准中的潜在技术进行了展望。

The fifth generation (5G) wireless network, aiming at supporting diversified use cases including enhanced mobile broadband (eMBB), massive machine type communications (mMTC) and ultra-reliable and low latency communications (URLLC), is important for technological, economical and industrial development in the world. To realize the vision of 5G, it is crucial to learn from the initial 5G deployment based on the first release of 5G New Radio (NR) standard and address the issues promptly in the subsequent releases of the standards for 5G and beyond. Massive MIMO is an important component of the 5G standard to improve the spectral efficiency and network performance for reaching its targeted multi-gigabit throughput in 5G systems. For 5G NR systems, one of the key differences from 4G systems is the utilization of millimeter wave (mmWave) bands in addition to sub6GHz bands. To keep the complexity and implementation cost low, hybrid analogdigital beam-forming with large-scale antenna arrays has become a common design approach for addressing the issue of high propagation loss as well as improving the mmWave spectral efficiency. The 5G NR standard providesthe support of different beam-forming architectures and deployment scenarios. In this thesis, we tackle some major challenges encountered in the 5G NR standardization process and present some novel techniques for beam management and Channel State Information (CSI) acquisition which are useful for 5G evolution. These techniques include group based beam management and advanced linear combination codebook design.

Ultra-dense network deployment is a clear trend considered for the next generation networks. To allow flexible deployment of small cells, self-backhauled small cell architecture is one of the important types of the future ultra-dense network architecture. In this thesis, we propose a new network architecture supporting densification and virtualization in both cell and user aspects. User virtualization considering adaptation between MU-MIMO and virtual MIMO is proposed and evaluated. In addition, we present a novel soft Hybrid Automatic Repeat Request (HARQ) feedback scheme to improve the link adaptation between devices in a cloud. Energy efficiency is one of the key performance indicators in NR networks. Tradeoffs have to be carefully considered between energy efficiency and other performance aspects such as latency, throughput, connection densities and reliability. Energy efficiency is important for both user equipment (UE) side and base station side. On UE side, UE battery life has great impact on user experience. It is challenging to improve UE experience in other performance aspects without affecting battery life of 5G handsets. On the base station side, efficient network implementation is critical in both environmental and operation cost standpoints. To adapt different requirements and trade-offs, the 5G NR standard is designed to have great flexibility on network operation modes. This thesis provides the proposals of power saving techniques adopted by 5G NR standard including 2-step random access procedure and MIMO layer adaptation. In addition to the existing standardized techniques, some major development trends of green communication and the future potential techniques expected in the beyond-5G standards are proposed and discussed.

1.       引言

2. 波束管理技术

3. 信道状态信息获取

4. 基于MIMO的自适应小区和用户可视化

5. 5G及超5G的功率节约技术

6. 结论与展望

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