Understanding 5G – Part 1 – Introduction

This is the first blog post in a planned series on 5G technology researched from 5G specifications from 3GPP organization. The following is a starting point for future posts in the series. Additional posts and will be seen under the related tag “5G-Overview”. Over the course of these posts we hope to familiarize reader with the terms of 5G, how the technology works, and where it is going from a technical perspective. Feel free to submit questions through the “Contact Us” section of the site. Don’t forget to also checkout some video overviews on YouTube. Let’s get started with a basic start point of what is defined as 5G.

What Does 3GPP Call “5G”?

3GPP specifications tend to make use two sets of acronyms to describe 5G technologies:

• NG: “Next Generation”
• NR: “New Radio” Access

Thus, the 5G Radio Access Network is known as NG-RAN. NR also features prominently in documentation to differentiate 5G information references from LTE. For example, NR-ARFCN is used to refer to the 5G channel number as compared to EARFCN for LTE.

A First Look at NR Physical Layer Scheme

Though 5G radio layer is referred to as “New Radio”, there is much in the technology being carried over from LTE. Initial 5G releases will use OFDM grid structure with physical resource blocks. However, for the uplink DFT spreading is optional. Though mmWave is a key feature of 5G, there are in fact, two frequency design ranges so low band deployment is possible. There is also more flexibility in how bandwidth is used and subcarrier spacings (abbreviated as SCS in 3GPP) range from 15kHz to 120kHz. Note that the supported SCS settings depend on frequency range. More details on NR physical layer will be revealed in future articles.

Basic Architecture

Figure 1: 5G Overall Architecture

In the above diagram, for 5G access NG-RAN consists of gNBs where your RRM functions take place. Note though the internals of the gNBs are detailed also in the specifications. NG-RAN may also have ng-eNBs which can be thought of as a hybrid technology. These provide LTE service as functioning eNodeBs to UE but are connected to 5G core over NG interface. NG-RAN nodes are interconnected via an Xn interface which supports handover data forwarding, as with LTE X2 interface.

For 5G, the core network is termed 5GC and consists of an Access Mobility Function (AMF) and User Plane Function (UPF), and connect to the NG-RAN via an NG interface.

The AMF can be considered analogous to the MME in LTE. It handles the control plane from NG-RAN including idle state mobility and NAS signaling (including security). The UPF handles the user plane from NG-RAN. As with LTE SGW, it provides an anchor point for mobility, as well as packet forwarding & routing.

More to Come

This is just a brief introduction – there is plenty more to cover in future articles, including the physical and RRC aspects.

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