ttempted to take a more generic and systematic approach to the design of physical layer for the IMT-2020 wireless systems SO that the reader can understand and apply the learnings to the design and implementation of any OFDM-based physical layer irrespective of the radio access technology. 5G NR. DOI: https://doi.org/10.1016/B978-0-08-102267-2.00003-8 © 2019 Elsevier Inc. All rights reserved. Chapter 3 NR protocol structure Non access stratum OSI seven-layer network (NAS) Internet protocol (IP) model Application layer Radio resource control (RRC) Presentation layer QoS Flows Session layer Service data adaptation Control/ protocol (SDAP) configuration Transport layer Radio bearers RRC PDUs Packet data convergence Network layer protocol (PDCP) Control/configuration Data-link layer RLC channels Radio link control (RLC) Physical layer Control/configuration Logical channels Medium access control (MAC) Control/configuration Transport channels Physical layer (PHY) Control/configuration/ physical layer measurements Physical channels Figure 3.1 The physical layer in NR protocol stack [19]. In this chapter, we start with the study of the fundamental concepts and common fea- tures/functions in downlink and uplink of the new radio, which include review of the characteristics of wireless channels in sub-6 GHz and mmWave frequency regions as well as the analysis of two-dimensional (2D) and three-dimensional (3D) channel mod- els and propagation effects. We will then begin our top-down approach to physical layer protocols starting with waveforms, orthogonal and non-orthogonal multiple- access schemes, and duplex schemes as well as the operating frequencies of the new radio. The frame structure, OFDM numerologies, time-frequency resources, and resource allocation techniques will be discussed and analyzed from theoretical and practical point of views. New Radio Access Physical Layer Aspects (Part 1) 287 3.1 Channel Models and Propagation Characteristics 3.1.1 Characteristics of Wireless Channels In a wireless communication system