 ms. Furthermore, cell phones and tablets now use primarily touch interaction, a "tactile interaction" that requires a more rigorous delay control, such as 1 ms. A promising heterogeneous and hybrid network architecture is shown in Figure 1.5. It contains small BS (SBS), marco BS (MBS), remote radio head (RRH), and network slice. 1.3 Book Outline In face of several challenges by 5G and beyond system, this book focuses on technologies that can improve spectral, energy, and computation efficiency. As mentioned above, we 1.3 Book Outline Intra-user communication BBU pools/Data server Cloud server Inter-user communication SDN controlled Communication with BS/Edge Backhaul Backhaul Backhaul ((--)) Fronthaul ((e)) (((-))) (((a))) ((o)) SBS/Edge SBS/Edge SBS/Edge (((-))) (((i))) SBS/Edge Network resource slices ((i-))) Figure 1.5 A promising network architecture for pervasive loT communication needs. mainly study physical layer techniques. Specifically, our first focus (Chapters 1-6) is to pro- vide reader with latest research efforts on 5G NOMA. We have studied NOMA in a system- atic way, including applying NOMA to address spectral efficiency and number of connected devices challenges under various network schemes. Our next focus (Chapters 7 and 8) is MEC. MEC is used to reduce computation delay, and we primarily investigate its role for computation offloading. Chapter 9 discusses the emerging wireless paradigm to facilitate distributed machine learning. Chapters 10 and 11 review secure spectrum sharing with machine learning techniques. Lastly, Chapter 12 concludes this book and discusses current and further research directions on 5G and beyond wireless systems. 5G Wireless Networks with Underlaid D2D Communications Background 2.1.1 MU-MIMO The narrow beam enabled by massive MIMO brings unprecedented spatial multiplexing. Hundreds of beams can be generated from the BS toward each user, with little interference in the space. This brings new opportunity for multi-user MIMO (MU-MIMO) in the 5G era. MU-MIMO is one type of 