Advanced massive MIMO and power saving techniques for 5G and beyond

Abstract

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 sub-6GHz bands. To keep the complexity and implementation cost low, hybrid analog-digital 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 provides the 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. Trade-offs 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.