5G Air Interface and Physical Layer Procedures – Part 1

In this chapter, we are going to introduce you to 5G New Radio (NR) physical layer procedures for control and user planes. We will start by looking at general physical layer procedures and then continue with waveform, numerology, and frame structure. Throughout the chapter, we will be comparing and contrasting NR and Long-Term Evolution (LTE).

After reading this chapter, you will have a good understanding of NR’s physical layer structure, downlink and uplink references, and synchronization signals. You will also have a good understanding of the numerology concept, which is the main difference between NR and LTE in the air interface.

In this chapter, we’ll cover the following topics:

• General physical layer procedures
• Waveform, numerology, and frame structure

Let’s get 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

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-Orthogonal 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...

Waveform, numerology, and frame structure

In this section, we will analyze NR waveform, numerology, and frame structure. We will first talk about scalable numerology, slot duration, and how they help to multiplex different numerologies. Then, we will talk about different NR scheduling schemes and related use cases.

Waveform

NR employs OFDM for downlink and uplink transmissions. These are the very same waveforms that were used in LTE.

Figure 4.12 – A visualization of an OFDM waveform

In the preceding figure, the visualization of an OFDM waveform is presented. It has a symmetric design, and the same waveform is used in downlink and uplink transmissions. Besides supporting MIMO in downlink and uplink transmissions, it also supports flexible numerology.

Within a given numerology, all other subcarriers are zero at sampling points. OFDM is a proven technology, and it has several benefits:

• Frequency diversity
• It’s robust against...

Summary

In this chapter, we introduced you to NR general physical layer procedures and channel structure. We made comparisons of bandwidths, energy efficiency, and spectral efficiency between LTE and NR.

Then, we covered all the important aspects regarding the NR waveform, numerology, and frame structure. We learned that NR is OFDM-based with scalable subcarrier spacing. This changes the slot durations to allow for different kinds of services, but it also presents challenges regarding how these different subcarrier spacings can be multiplexed in the frequency domain without interfering between them. We have also discovered that NR supports a slot-based scheduling mode. We saw that there are several interesting use cases that necessitate the introduction of this scheduling mode, such as LTE/NR coexistence or forward compatibility. Finally, we have described the dynamic TDD duplexing mode that NR introduces and how it is signaled to devices by using the slot format indication.

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