Page 14 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 6 – Wireless communication systems in beyond 5G era

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 6

and private communities. Some consortia have al‐ Access Network (E‐UTRAN), and the core network. The
ready started working on the inition and characteri‐ term E‐UTRAN means the Radio Access Network (RAN)
sation of future 6G communication networks, preparing of Long Term Evolution (LTE) together with UMTS Ter‐
the ground for its standardization by 2030. In Europe, restrial Radio Access Network (UTRAN) and GSM RAN
some of the major projects are the EU Flagship Hexa‐ (GERAN), interconnected via the EPC.
X [2], the 5GPPP CORDIS RISE‐6G [3], and the 5GPPP
RIA DEDICAT 6G [4]. In parallel, US has also started the The Global System for Mobile Communications (GSM)
Next G Alliance [5]. All those results are expected to be and the Universal Mobile Telecommunications System
contributed towards the ITU Radiocommunication Sector (UMTS) represents the 2nd and 3rd Generation of wire‐
(ITU‐R), which has initiated the work on “systems beyond less cellular networks, standardization efforts of Euro‐
IMT‐2020” (see Section 4). pean Telecommunications Standards Institute (ETSI) and
However, various promises made by 5G are still not satis‐ 3GPP respectively. As it is possible to notice in the context
ied and there is the feeling in part of the community that of wireless cellular networks, the term ’generation’ (iden‐
6G could just be a 5G+. Moreover, network softwarization ti ied by ’⋅ G’) has been representing a signi icant change
brought 5G closer to the Internet community, which does in the characteristics and performances of the RAN – 1G
not use any ’generation’ terminology, but it provides con‐ and 2G, or in how different RANs are interconnected, 3G
tinuous network upgrades and software updates. Next, and 4G. The switch of generations has maintained a peri‐
5G has already promised support to many verticals, which odicity of about ten years.
are still waiting to receive the promised low‐latency reli‐
able connectivity and almost continuous service availabil‐ At the end of the 1990s, the deployment of 3G started,
ity. In such conceptual/technical still ’liquid’ and chang‐ under the ications of ITU International Mobile
Telecommunications‐2000 (IMT‐2000). The scope of 3G
ing situation, this article tries to state some important
was to support a variety of mobile broadband services
conceptual, terminological, and technical characteristics
not only wireless voice telephony but also mobile Inter‐
and guidelines that will make 6G. In this sense, this paper
will try to give a solid answer to questions such as What net access, video telephony, and mobile television. With
can 6G be? Do we really need 6G? Because of that, the fol‐ this generation, data started becoming the core aspect
of wireless cellular communications. Next, this standard
lowing provides a signi icant analysis of the literature and
of the evolution of the characteristics of 5G and 6G, in or‐ was also guaranteeing global mobility via a harmonisa‐
der to propose some stable reasons for justifying the cur‐ tion of the frequency bands, which set some common
rent standardization and research effort towards 6G. bands worldwide.
Finally, the deployment of the 4th Generation‐L TE started
First, Section 2 ly introduces the path towards 4G,
around 2009. The objective of 4G was to improve the per‐
and origins of the concepts of virtualisation and cloud
formance at the RAN also extending the initial focus on
computing. Next, Section 3 describes the advent of 5G, its
data started with 3G, providing a wireless cellular net‐
characteristics, requirements, and the kinds of services it
targets. With Section 4, the objective is to survey a sig‐ work architecture with full access to the Internet. The
de inition of the EPC provided a core network, which uni‐
ni icant part of the literature in order to give a review of
the current proposed metrics, characteristics, and verti‐ ied the different radio access technologies under a sin‐
gle infrastructure. Additionally, L TE also started the in‐
cals proposed within 6G. This section is important to state
tegration with non‐3GPP radio access technologies. This
the conceptual basics, which are critically discussed in
Section 5 in order to highlight the main fundamental as‐ is clearly visible in the part of the standard focused on
interworking between L TE and Wireless Local Area Net‐
pects of 6G together with the issues and the trade offs that
work (WLAN) – embodied by the Institute of Electrical
will require signi icant investigation withing the scienti ic
community and the industry. and Electronics Engineers (IEEE) 802.11 standard [6],[7].
2. THE COMMUNICATION P ANORAMA Fig. 1 depicts the structure of the 4G RAN and its EPC.
BEFORE 5G There are various logical blocks in the EPS, each one
grouping logical nodes that interwork to provide a spe‐
2.1 The standardization and architecture of ci ic set of functions in the network. From the RAN per‐
wireless cellular networks spective, all the 2G‐4G RANs coexist and connect to the
EPC. There is also the domain called ’non‐3GPP access
In September 2014, Release 8 of the standard 3GPP Sys‐ networks’, which denotes any packet data access network
tem Architecture Evolution Speci ication (SAES) was pub‐ that is not de ined by 3GPP standards such as IEEE 802.11
lished. This is the irst document introducing the concept WLAN and WiMAX. Side by side, the core network also
of Evolved Packet Core (EPC) [6] – more generally labelled consists of multiple domains such as circuit core, packet
Evolved Packet System (EPS). In fact, the term EPS rep‐ core and IP‐Multimedia Subsystem (IMS). The user man‐
resents the end‐to‐end system, which mainly consists of agement domain provides coordinated subscriber infor‐
User Equipment (UE), Evolved Universal Terrestrial Radio mation and supports roaming and mobility between and

2 © International Telecommunication Union, 2021