started! General physical layer procedures In this section, we are going to analyze the structure of the 5G air interface and related physical layer procedures. We will explain the following: NR's general physical layer structure Improved spectral efficiency Channel structure of the radio interface and how it relates to LTE The NR cell concept and how it relates to LTE 5G Air Interface and Physical Layer Procedures - Part 1 The NR physical layer at a glance In NR, in general, adaptive Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency-Division Multiple Access (OFDMA) are used. We will go into detail about them later when we discuss downlink and uplink transmissions, which are Cyclic Prefix - Orthogonal Frequency Division Multiplexing (CP-OFDM) and Discrete Fourier Transform-spread-Orthogona Frequency Division Multiplexing (DFT-s-OFDM) respectively. OFDMA, in general, helps channel-dependent scheduling and link adaptation in time and frequency domains. In contrast to LTE, we have flexible numerology in NR, as shown in the following figure. User #2 A f=15, 30, 60, 120 kHz Scheduled User #1 Scheduled User #3 Scheduled 1 Slot frequency Figure 4.1 - Flexible numerology in NR Flexible numerology allows the Subcarrier Spacings (SCS) to be scalable, and the subcarrier spacings in this case are 15, 30, 60, 120, and 240 kHz. In the normal Cyclic Prefix (CP), there are 14 OFDM symbols, as there are in LTE. Similar to LTE, NR uses multiple antennas, both on mobile devices and in the gNB. There is high utilization of massive Multiple-Input Multiple-Output (MIMO) in NR. Figure 4.2 - Multiple antennas, both in the gNB and the Terminal The dedicated antenna beams from Massive MIMO antennas bring TX and RX diversity and help to reject and mitigate interference. This Massive MIMO will bring high bitrates and capacity, increased coverage, and energy efficiency. General physical layer procedures 20 MHz 400 MHz Figure 4.3 - Flexible bandwidth in NR As opposed to LTE, which has a maximum bandwidth of 20 MHz, we