Page 145 - ITU Journal, Future and evolving technologies - Volume 1 (2020), Issue 1, Inaugural issue

ITU Journal on Future and Evolving Technologies, Volume 1 (2020), Issue 1

Space,
Waveform Aerial,
Coexistence, Terrestrial,
mmWave
Flexible and Undersea
and NOMA Free Duplex Flying Network Cell Free
microWave THz Multidimensional Communications Access Points Integration Networks
Modulation &
Waveform
FLEXIBLE MULTI-BAND ULTRA FLEXIBLE ULTRA FLEXIBLE
UTILIZATION PHY & MAC HETEREGENOUS
NETWORKS
Spectrum
Coexistence Enhanced Advanced RAN Slicing
and Visible Hybrid Scheduling Coordinated and
and
and
Dynamic Light Equalization User Centralized Network
Spectrum Association Networks Virtualization
Access
Pervasive/ Edge AI Ambient
Radio Collective and Backscattering
Environment Big Data AI Distributed and Wireless ISAC Security PHY Security
Map Context Intelligence Energy Power Transfer
Awareness Harvesting
INTEGRATED INTELLIGENT SECURE
SENSING and GREEN
COMMUNICATIONS COMMUNICATIONS COMMUNICATIONS COMMUNICATIONS

ISAC in ISAC in Intelligent Holographic Zero-energy Cross Layer
and
Radar Wi-Fi SWIPT MAC Security
Systems Networks Surfaces MIMO Narrow-band Security
IoT
Fig. 4 – Categorization of the promising 6G key enablers under the ultra- lexible perspective.

of dealing with the spectrum scarcity issue by providing 3.2 Ultra-Flexible PHY and MAC
an additional degree of lexibility in assigning the most
suitable frequency resources for given scenarios [46]. One of the unique features of 5G, speci ically in the
context of PHY design, is the introduction of numerol-
ogy concept where different con igurations of the
time-frequency lattice are used to address the varying
Apart from mmWave and THz communications, Visible requirements [88]. While the numerology concept paves
Light Communications (VLC) also provides spec- the way for lexibility in beyond 5G networks, it is rather
trum lexibility as a candidate key enabler for 6G limited considering the competing nature of require-
networks [27, 52, 61]. Moreover, a new degree of free- ments expected for future 6G networks [25]. In addition
dom that is information source lexibility is exploited to the standardized activities, the use of lexible Cyclic
using visible light sources.
Pre ix (CP) con igurations (e.g., individual CP, common
CP, etc.) is explored to enhance the multi-numerology
systems for 6G [89].
Spectrum coexistence is another important issue in need
of lexible spectrum utilization [50, 74]. Indeed, the Taking one step beyond the use of different realiza-
coexistence of cellular communications, Wi-Fi, satellite tions of the same parent waveform as in 5G, multiple
networks, and radar systems is inevitable in the future waveforms can be accommodated in a single frame for
due to both scarce resources and increasing growth in achieving 6G goals [49, 90]. In line with this, multi-
user demands. To exemplify, the coexistence of radar and numerology structures can be designed for promising
cellular communications in mmWave frequency bands alternative waveforms, that are more suitable for pro-
becomes more popular nowadays [87]. Moreover, the viding additional parameterization options. Having
idea of Dynamic Spectrum Access (DSA) relies on the these options enhances lexibility in the PHY layer via
spectrum coexistence [56].
increased adaptation capability for meeting a large
number of requirements. Moreover, waveform coexis-
tence in the same frame gives the opportunity to serve
As it is seen, there are several aspects of lexible multi- multiple networks such as radar sensing [91] and Wi-Fi
band utilization in 6G systems. Flexibility sources can communications together with 6G communications in
be summarized under three main perspectives: 1) multi- a lexible manner. There are also several waveform-
band lexibility, 2) information source lexibility, and 3) domain NOMA studies that exploit different resource
spectrum coexistence lexibility. utilization aspects in the literature [92–95]. Moreover,

© International Telecommunication Union, 2020 125