Page 24 - 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

modelling and estimation, spectrum management, power targeted data rates [74]. For example, some initial chan‐
control, handover management, etc. Next, traf ic and mo‐ nel models for future 6G communication networks have
bility prediction, together with supervised ML manage‐ been presented in [75].
ment of policies were additionally mentioned by [68],
in the context of URLLC. The authors in [69] envisioned The authors of [76] proposed some key physical‐layer
an intelligent protocol stack, in which AI handles analy‐ problems to be solved to move from 5G to 6G physical
sis, management, and optimisation of the operations per layer. In particular, 6G should improve 5G via the ex‐
layer. The employment of AI for the physical layer’s op‐ ploitation of higher frequency bands (mmWaves and es‐
erations was also highlighted by [70]. Instead of focus‐ pecially Terahertz), of smart radio technologies such as
ing on a protocol‐stack perspective, the authors of [70] Recon igurable Intelligent Surface (RIS), and the full real‐
discussed the usage of AI from the RAN perspective. The isation of a cell‐less massive MIMO wireless system. The
study and design of an intelligent RAN for 6G will impact main characteristic of cell‐free or cell‐less systems is that
not only on the performance, management, and opera‐ the ’usual’ concept of cell is abandoned and access points
tions but also on the design and future standardization and base stations in the RAN coherently serve end users,
of RAN internal devices and technologies [70]. Next, [71] using the same time‐frequency resources in a speci ic cov‐
dealt with the design of an intelligent edge. ered area. This can imply the elimination of cells’ bound‐
ary effects [76].
Each generation of wireless cellular networks has been
promising an increase in data rate. In order to do that, a As shown in Fig. 7, the imagined 6G RAN has also been tar‐
combination of augmenting spectral ef iciency and band‐ geting the exploitation of frequencies in the visible‐light
width should be employed. This is something that 6G spectrum.
has also been promising [58]. The former can be ob‐ Since the beginning of 6G research, Visible Light Com‐
tained by going on employing massive MIMO antennas; munications (VLC) have been considered by industry and
the latter by going towards higher and higher frequen‐ academia as an excellent candidate complementary tech‐
cies. Next, wireless communications using THz frequen‐ nology to provide optical ibre‐like connectivity perfor‐
cies are the solution to achieve Tbit s −1 data rates. The mance [21], [77]. The use of visible light spectrum with
pro of these frequencies is the provisioning of very nar‐ VLC offers the potential to create short‐range (less than
row beams, which can eventually mitigate interference 10 m) high‐capacity links with ultrahigh bandwidth (Ter‐
and help in augmenting the possible number of antennas ahertz), and zero electromagnetic interference with radio
into the base stations [56]. Fig. 7 clearly shows the 5G NR frequencies. Today available VLC products have limited
−1
operating bands together with the targeted 6G RAN oper‐ performance from few tens of Mbit s over short ranges
ating band [72]. The table in the igure also speci ies what (up to 5 m). As explained in [21], at the horizon of 2024,
bands are assigned for the Time‐Division Duplex (TDD), upcoming new light sources based on micro‐LED technol‐
theFrequency‐DivisionDuplex(FDD),the Supplementary ogy will unlock such limitations, enabling the use of 1 GHz
−1
Uplink (SUL), and the Supplementary Downlink (SDL). bandwidth (and more), and achieving tens of Gbit s
with single‐diode LEDs (even up to several hundreds of
−1
The vision of 6G has also pictured the realisation of a Gbit s , thanks to the coming availability of micro‐LED
wireless 6G RAN lexibly using time‐frequency‐space re‐ matrices and dedicated optical beamforming algorithms
sources [73]. Regarding frequency, it has been envisioned allowing for spatial separation of users). Next, in a few
the usage of mmWave and Terahertz bands, and likely years’ time (by 2027), it is expected that by adding mas‐
visible‐light band. By referring to time, 6G could tar‐ sive parallelisation of micro‐LED arrays and dedicated
get a subsequent reduction of the duration of the time wavelength division multiplexing techniques, VLC will be
slot in order to better serve very low‐latency verticals. able to offer, similarly to sub‐THz communications, to tar‐
In the space domain, it could further enhance the trend get Tbit s −1 aggregated throughput (see Fig. 8).
of 5G, by employing base stations equipped with ultra‐
massive MIMO technologies. Base stations transmitting Further above, we have alluded to RIS employment within
within the Terahertz band will guarantee a coverage of 6G. A irst step into a radical change, that has been of‐
about 5 m to guarantee a User Datagram Protocol (UDP) fered to future 6G networks, is the inclusion of an RIS con‐
data rate of 1 Tbit s −1 [72]. For distances greater than cept within the wireless network architecture. 5G com‐
7 −10 m mmWaves will be able to achieve greater data munication networks have been following the Shannon’s
rates [72]. Wireless links so directive and so short will communication paradigm, which establishes the princi‐
need the design of new medium access techniques in or‐ ples for the reliable transmission of symbols over a noisy
der to ef iciently exploit the new bandwidths, as under‐ communication channel [78]. However, current wireless
lined in [72]. On the other hand, these characteristics can communications extend their role from pure communica‐
make Terahertz frequencies interesting as backhaul links tion systems to much more complex ones, involving the
[72]. Highly important is also the design of new anten‐ interaction between natural and arti icial intelligence, re‐
nas with speci ic geometries and physical characteristics sponding to multifold requirements, and being able to
in order to ef iciently provision the connectivity and the exploit revolutionary techniques to control various

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