Page 23 - 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

• ”always‐ON” terrestrial‐aerial‐satellite network, architecture. In this sense, 6G will inally complete the
paradigm shift from store‐and‐forward to compute‐and‐
• frame error rate (reliability) equal to 1 − 10 −9 [21], forward [1], [58] or, more precisely, 6G will bring a “holis‐
• very high energy ef iciency also supporting ”battery‐ tic management of communication” (including comput‐
free IoT devices” (10‐100 times the one of 5G [56]) ing, caching, and control resources) as de ined in [21].
and especially equal to 1 pJ bit −1 [21], The vision of 6G has also been enhancing the idea of

• connected intelligence, ’ecosystem’ of networks (or network of networks), pre‐
liminarily started with 5G. This has been making 6G
• jitter equal to 1 µs [21], closer and closer to the concept of the ’Web of Every‐
thing Everywhere’ [59]. In fact, the research commu‐
• spectrum ef iciency greater than three times the one
nity agrees that there will inally be a full integration and
of 5G [22],
interoperation between satellite, aerial and terrestrial
network, merged in a unique dynamic‐adaptive network
• receiver sensitivity less than −130 dBm [22].
infrastructure [60]–[62]. Moreover, some researchers
• a connectivity density ten times the one provided have also envisioned the possibility of integrating under‐
by 5G, with an area traf ic capacity of up to water communication networks into the whole 6G net‐
1 Gbit s −1 m −2 (10 Gbit s −1 in 3D [21]), work in order to provide seamless connectivity from the
ocean/sea loor to the space [56]. Regarding the air to
6
• density of connected devices greater than 10 km −2 ground link, authors of [62] showed the link budget for
[22], the employment of 71 −76 GHz and 81 −86 GHz in the
• localisation precision equal to 1 cm in three dimen‐ the air‐to‐ground link. This so‐called 3D networking will
sions [21]. signi icantly affect the design of 6G Layer 3/Layer 4 new
network and transport protocols, which can be capable
Moreover, in the very recent literature on 6G, this concept to ef iciently and effectively exploit the three‐dimensional
of KPI has been considered to be incomplete. Because of characteristics of the communication networks [54]. Fur‐
that, KPI and Key Value Indicators (KVI) have been placed thermore, the 3D network architecture has embraced the
side by side [2], [57]. The term KVI is based on the con‐ actual operators’ network since, for example, it has been
cept of value, which is de ined as “[...] intangible yet im‐ de ined the concept of 3D core network [22]. The High‐
portant human and societal needs such as sustainability, Altitude Platforms (HAP) and the low cost of nanosatel‐
trustworthiness, and inclusion. [...]” [2]. The KVI are lites’ constellations will represent a pivotal means to en‐
grouped into three main categories [57]: growth, sustain‐ hance and ensure the complete and reliable connectivity
ability, and ef iciency. The irst is principally related to to the rural areas [63].
economic growth, and the creation of new values, busi‐
ness ecosystems and models. The second and the third As previously mentioned D2D communications were ini‐
mainly refers to digital inclusion, zero energy devices, re‐ tially introduced in LTE networks. Next, 5G vision sig‐
source ef iciency and users’ privacy. Additionally to the ni icantly stressed the employment of D2D technologies
(together with mobile small cells [64]) in order to allow
ones introduced for 5G in Section 3.1, other de initions of
for the provision of effective connectivity in dense sce‐
concept of quality have been introduced. The concept of
narios. Nowadays, the D2D paradigm has also been in‐
Quality‐of‐Physical‐Experience (QoPE) [54] is an attempt
to complete and to unify the evaluation separately given cluded in the 6G vision [65]. The ultra‐dense scenar‐
by QoS and QoE, by combining them with other physical ios envisioned in 6G, if we also consider the complexity
aspects of humans such as brain cognition, body charac‐ added by ’hybrid verticals’ such as MBRLLC and massive
teristics, and gestures. URLLC, have been identi ied as important justi ications
for a massive and seamless integration of D2D communi‐
ITU has not yet started discussing requirements for “sys‐ cations and mobile small cells (possibly cooperative) into
tems beyond IMT‐2020”. As part of the to be applied IMT‐ the future 6G ecosystem of networks.
process, ITU‐R will produce a Report on “Technical per‐
formance requirements” (e.g. like ITU‐R M.2410 for IMT‐ 6G communication networks will be the irst generation
2020) at a later stage. of networks with native AI. This means that AI will not
merely be an application but an inherent part of the in‐
frastructure, and of the network management and op‐
4.2 Targeted architectural characteristics
erations [66]. The usage of AI for physical, network,
By looking at the architectural characteristics of 5G and and application layers was described in [67]. While
the current respective trends, everybody in the scien‐ for network and application layers the ideas come from
ti ic and industrial community argues that 6G architec‐ existing research in ML and Self‐Organising Networks
ture will be completely softwarized and lexible. The cur‐ (SON)/autonomic networking, the additional novel as‐
rent convergence between ETSI and 3GPP on this (pre‐ pect is the full application of AI within the physical layer.
viously cited for MEC) will extend to the full network The idea is to make intelligent operations such as channel

© International Telecommunication Union, 2021 11