Page 28 - 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

duction of transmission, queuing, and processing latency, crease to optimise the coverage and the usage of spectrum
for example, if we take into account the virtualisation of in very dense urban scenarios, and also it will augment to
signal processing in the context of C‐RAN and BBU split‐ support fog computing within the IoT network layer (see
ting. Fig. 5).

Another critical aspect among 6G KPI is energy ef iciency. According to what has been seen in Section 4, we can as‐
The very high data rate, the massive application of virtu‐ sume that 6G will see an increased importance of QoE ver‐
alisation, native AI with continuous data mining and pro‐ sus QoS, compared to what has been for 5G. This is due to
cessing (so‐called connected intelligence) will increase the increased focus on users’ experience quality and satis‐
in‐network computing to an unprecedented level. Next, faction, together with the prominent immersion of users
an ’always ON’ 6G network (i.e. experiencing no failures) into the VR. Even in the ’natural’ reality, the users are ex‐
will require the presence of backup virtual network func‐ pected to seamlessly interact with virtual entities, the so‐
tions, always ready for a replacement. Moreover, a large called AR. AR will especially become more and more ex‐
density of UEs, together with several of them needing treme starting from 3D holographic images, towards ob‐
Tbit s −1 data rate, will greatly augment the computing re‐ jects and avatars. These holograms will change the way
quired per user at the BBU. Especially, this will be a virtual we work, we experience reality, and more generally will
BBU according to the C‐RAN paradigm. Thus, this huge create ’cross‐reality’ users (either humans or machines),
stress on edge and cloud data centres will signi icantly in‐ acting in a ’mixed’ or ’extended’ [102] reality between VR
crease the end‐to‐end energy usage. Next, in order to im‐ and the ’natural’ reality. In this context, the advancements
prove power ef iciency for coverage and battery life, the of the research in neuroscience and psychology will be
network operating region will have to enlarge in both the pivotal for the success of these technologies in communi‐
regions of the power and spectral ef iciency [58]. As also cations and 6G, and for the measurement of their quality.
mentioned in [58], it will be hard for 6G to concurrently Given these considerations, we can also agree with the in‐
enhance coverage, cost, and battery life. We also agree troduction of hybrid metrics combining QoS and QoE as
with [58] that higher data rates and ef iciency will make the previously mentioned QoPE (see Section 5.1).
the possibility of increasing battery life more dif icult. All On the other hand, other metrics such as KVI [2], [57] may
these observations about energy underline some incon‐ create confusion and not be really effective in evaluating
sistencies among the KPI, that will be extremely hard to performance and in providing useful design guidelines.
solve by just evolving the current ’classic’ technologies. As previously quoted, the de inition of value indicator
6G could be a quite successful story for energy usage just refers to an ’intangible human and societal need’. How‐
by creating a full intelligent autonomic network while sat‐ ever, in the moment of design and measurement, an in‐
isfying the KPI originally established for 5G (in fact, this tangible need is always mapped into either objective (e.g.
energy target has not been reached yet).
QoS) or subjective (e.g. QoE) metrics, or into a combina‐
tion of both (e.g. QoPE). For example, the same can hap‐
In contradiction with the reduction of energy usage ad‐ pen for the mentioned value ’sustainability’, which can be
vertised within 6G, there is also the technological trend de ined as “[...] the long‐term viability of a community, set
of mobile small cells and fog computing at the UEs, for of social institutions, or societal practice. In general, sus‐
very low latency. Mobile small cells integrate the concept tainability is understood as a form of inter‐generational
of mobile relay stations with ixed small cells and can be ethics in which the environmental and economic actions
deployed into vehicles such as public transport systems taken by present persons do not diminish the opportu‐
[98]. In [99], authors showed that mobile cells can im‐ nities of future persons to enjoy similar levels of wealth,
prove spectrum ef iciency, throughput, and signal quality utility, or welfare [...]” [103]. From this de inition, it ap‐
of users. Future communication is expected to be a net‐ pears clear that, in order to measure and to target ’sus‐
work of a large number of mobile users that will interact tainability’ within 6G design and development, it has to
together with many applications such as VR/AR games or be mapped into its economic, societal, and environmen‐
streaming videos requiring low response times. There‐ tal KPI.
fore, mobile small cells can be deployed via cluster of UEs
using D2D technology [100], [101]. This type of small After having critically discussed potential 6G use cases
cell can also be deployed to cover the urban landscape. and performance metrics, the following deals with 6G
These cells can be formed using mobile UEs or low‐cost technological and architectural aspects.
nodes such as RRHs which are connected to aggregation
nodes through wireless links [64]. The base stations of 5.2 Network virtualisation and campus net‐
these cells mainly perform a transceiver’s functionalities works in 6G
and are less involved than fully functional eNodeBs. In the
literature, mobile small cells are also called on‐demand By looking at Section 3, it is possible to see the distance
because they can lexibly be deployed in case of signi i‐ between the promises referred to 5G network virtualisa‐
cant traf ic variations in short‐time ranges, etc. All these tion and the actual virtual‐architectural characteristics,
considerations show that battery life will necessarily in‐ provided by the current standardization and develop‐

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