Page 22 - 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

Among the various proposed verticals, Augmented Real‐ used to manage the communication network infrastruc‐
ity (AR) and Virtual Reality (VR) have been the main and ture, to process/act on data, to enforce security, etc. Thus,
most popular drivers of 6G vision. Even if already pro‐ the paradigm of digital twins will open signi icant chal‐
posed in a preliminary form during 5G, now AR and VR lenges to Machine Learning (ML) algorithms.
visions have signi icantly been extended towards the re‐
alisation of 3D holographic video representations and in‐ As just brie ly mentioned above, multiple contexts of ap‐
plications of digital twins have been identi ied. The irst
teractions. Some initial studies have estimated that “[...] a
use case was industrial manufacturing [46]. Next, var‐
raw hologram, without any compression, with colors, full
parallax, and 30 fps, would require 4.32 Tbit s −1 . The ious other ones appeared such as remote surgery [47],
latency requirement will hit sub‐millisecond, and thou‐ construction industry [48], aviation [49] and aeronautics
[50], oil and gas industry [45], [51], itness [49]. From
sands of synchronized view angles will be necessary
the standardization perspectives, the authors in [52] pro‐
[...]” [40]. Additionally, the idea has also been to make
posed the digital twins’ standardization effort as the ini‐
holo‐grams physically perceptible by associating not
tial convergence from standards ISO/IEEE 11073, includ‐
only au‐diovisual information but also haptic data as in
the Tactile Internet. ing X73 compliant devices.
These initial speculations have also brought to the po‐ As previously mentioned in Section 3.1, 5G verticals have
been grouped intothe three main categorieseMBB, uMTC,
tential realisation within communication networks of a
more advanced concept, called digital twin. A Digital Twin and mMTC. In the context of 6G, these groups may respec‐
tively evolve to the ubiquitous Mobile Ultra‐Broadband
[41] can be de ined as a virtual representation of either
physical objects, lows, or generally speaking sys‐ (uMUB), ultra‐High‐Speed Low‐latency Communications
tems. The great initial interest has grown into the indus‐ (uHSLLC), and ultra‐High Data Density (uHDD) [53]. An‐
other consideration was proposed by [54], which sug‐
trial community driving business speci ically within the
gested to include a new hybrid category of services called
IoT [42]. In the context of the Industry 4.0, the design and
Mobile‐Broadband Reliable Low‐latency Communication
production of speci ic products (e.g. bicycles, cars, etc.)
(MBRLLC). In particular, this group of verticals includes
can be enhanced and better managed via the interaction
services that jointly target the KPI of eMBB and uMTC ap‐
with the products’ digital twin. A large number of sensors
have to be applied on the real object to represent the phys‐ plications. Side by side, it became the de inition of mas‐
sive URLLC [54], which jointly addressed verticals both
ical characteristics into the virtual reality. This can help to
targeting the KPI of mMTC and uMTC. This can imply an
ind faults and to solve problems before the real‐product
creation. The concept of digital twin has also been ex‐ important conceptual observation. Until 4G‐LTE, there
was mainly a single mobile‐broadband vertical. With 5G,
tended from nonliving to living physical entities such as
three distinct categories have been de ined. In the context
humans [42], [43]. According to what has just been said,
of 6G, the taxonomy of verticals is going to become more
it clearly appears that the quality of the virtual model, and
and more elaborated, requiring more complex sets of KPI.
of the big data collected and processed are pivotal [44],
This means the categorisation of services is going to show
[45].
intersections among the groups.
Some aspects have already been listed in the literature
to start characterising the idea of digital twin [43]. First,
all the digital twins will have a unique ier. Sensors 4.1 Envisioned performance and metrics
and actuators will be fundamental to guarantee complete As previously mentioned in Section 3.1, 5G has made re‐
and correct replication of the real twin into the virtual quirements on the KPI more and more stringent, by also
reality. These sensors will convey all possible kinds of adding their concurrent satisfaction on a end‐to‐end per‐
data, not only audiovisual but also haptic, hearing, taste, spective. According to the use cases that 6G vision has
smell, etc. Next, communication will also be critical. Dig‐ been targeting like the ones mentioned above, the prelim‐
ital and physical twin will have to experience real‐time inary list of requirements that has been set includes [21],
sensing and interactions. The phenomenology of the Dig‐ [55], [56]:
ital Twin can assume different forms such as virtual (i.e.
−1
a 3D avatar), holographic, physical‐robotic (e.g. a hu‐ • throughput/data rate up to 1 Tbit s ,
manoid social robot), or software‐based (i.e. via a set of −1
software components without a recognisable form). Fi‐ • user‐experienced data rate of 1 Gbit s (ten times
nally, trust (real twins must trust their digital counter‐ the one targeted by 5G),
parts) and privacy and security (a huge quantity of sensi‐ • end‐to‐end latency less than 1 ms,
tive data is collected and processed) are fundamental pil‐
lars in the realisation and employment of digital twins. In • an ’over‐the‐air’ latency of 10 −100 µs with mobility
this whole context, the role of Arti icial Intelligence (AI) up to 1000 km h −1
will be critical under many different angles. AI will be
• very broad bandwidth with frequencies reaching
1 −3 THz,

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