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The sixth-generation (6G) wireless communication network is expected to integrate the terrestrial, aerial, and maritime communications into a robust network which would be more reliable, fast, and can support a massive number of devices with ultra-low latency requirements. The researchers around the globe are proposing cutting edge technologies such as arti cial intelligence (AI)/machine learning (ML), quantum com- munication/quantum machine learning (QML), blockchain, tera-Hertz and millimeter waves communication, tactile Internet, non-orthogonal multiple access (NOMA), small cells communication, fog/edge computing, etc., as the key technologies in the realiza- tion of beyond 5G (B5G) and 6G communications. In this article, we provide a detailed overview of the 6G network dimensions with air interface and associated potential technologies. More speci cally, we highlight the use cases and applications of the proposed 6G networks in various dimensions. Furthermore, we also discuss the key performance indicators (KPI) for the B5G/6G network, challenges, and future research opportunities in this domain.
Content may be subject to copyright.
The shift to6G communications: vision
andrequirements
Muhammad Waseem Akhtar1, Syed Ali Hassan1, Rizwan Ghaffar2, Haejoon Jung3*, Sahil Garg4
and M. Shamim Hossain5*
Introduction
Next-generation communication systems aim to achieve high spectral and energy effi-
ciency, low latency, and massive connectivity because of extensive growth in the number
of Internet-of-ings(IoT) devices. ese IoT devices will realize advanced services such
as smart traffic, environment monitoring, and control, virtual reality(VR)/virtual naviga-
tion, telemedicine, digital sensing, high definition(HD), and full HD video transmission
in connected drones and robots. IoT devices are predicted to reach 25 billion by the year
2025[1], and therefore, it is very challenging for the existing multiple access techniques
to accommodate such a massive number of devices. Even fifth generation(5G) commu-
nication systems, which are being rolled out in the world at the moment, cannot sup-
port such a high number of IoT devices. ird generation partnership project(3GPP) is
already working on the development of 5G standard and has identified massive machine
type communication(mMTC), ultra-reliable and low latency communication(URLLC),
Abstract
The sixth-generation (6G) wireless communication network is expected to integrate
the terrestrial, aerial, and maritime communications into a robust network which would
be more reliable, fast, and can support a massive number of devices with ultra-low
latency requirements. The researchers around the globe are proposing cutting edge
technologies such as artificial intelligence (AI)/machine learning (ML), quantum com-
munication/quantum machine learning (QML), blockchain, tera-Hertz and millimeter
waves communication, tactile Internet, non-orthogonal multiple access (NOMA), small
cells communication, fog/edge computing, etc., as the key technologies in the realiza-
tion of beyond 5G (B5G) and 6G communications. In this article, we provide a detailed
overview of the 6G network dimensions with air interface and associated potential
technologies. More specifically, we highlight the use cases and applications of the
proposed 6G networks in various dimensions. Furthermore, we also discuss the key
performance indicators (KPI) for the B5G/6G network, challenges, and future research
opportunities in this domain.
Keywords: 6G, Machine learning, Artificial intelligence, Quantum communication,
Blockchain, Beyond 5G, IoT, Cloud
Open Access
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RESEARCH
Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
https://doi.org/10.1186/s13673-020-00258-2
*Correspondence:
haejoonjung@inu.ac.kr;
mshossain@ksu.edu.sa
3 Department of Information
and Telecommunication
Engineering, Incheon
National University,
Incheon 22012, Korea
5 Department of Software
Engineering, College
of Computer and Information
Sciences, King Saud
University, Riyadh 11543,
Saudi Arabia
Full list of author information
is available at the end of the
article
Page 2 of 27
Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
and enhanced mobile broad band(eMBB) as three main use cases for 5G in its Release
13(R13)[2].
At the same time, algorithms for the next generation communication systems, which
will have the performance higher than that of existing 5G networks, are being devel-
oped [3]. A typical 5G communication system has the capability to support at most
50,000 IoTs and/or narrowband IoT(NB-IoT) devices per cell[2]. Specifically, a more
robust network must be designed to realize the massive access in beyond 5G(B5G)/6G
communication systems. We now discuss comprehensive literature that has appeared on
various dimensions of 6G networks.
Vision andliterature survey
Currently, there is little information about the standards of 6G. However, it is estimated
that the international standardization bodies will sort out the standards for 6G by the
year 2030[4]. e work at some of the research centers has shown that 6G will be capa-
ble of transmitting a signal at a human computational capability by the year 2035[5].
While the rollout of 5G is still underway, the researchers across the world have started
working to bring a new generation of wireless networks. A tentative timeline for the
implementation of 5G, B5G, and 6G standards by international standardisation bodies
is shown in Fig.1 with respect to the vision of 6G wireless networks. International Tel-
ecommunication Union Radiocommunication sector (ITU-R) issued the requirements
of International Mobile Telecommunications-2020 (IMT-2020 Standard) in 2015 for the
5G network standards. At the same time, 3GPP issued R13 for 5G standards. It is pre-
dicted that ITU will complete the standardization of 6G(ITU-R IMT-2030) by the end
of the year 2030, whereas 3GPP will finalize its standardization of 6G in R23[5]. ITU has
established a focus workgroup for exploring the system technologies for B5G/6G sys-
tems in July 2018[7]. e Academy of Finland has founded, 6Genesis, a flagship pro-
gram focusing on 6G technologies, in 2018[8]. Similarly, China, the United States of
America, South Korea, Japan, Russia have also started the research for B5G/6G commu-
nication technologies[4, 5, 911].
e vision of 5G technologies is extended for the 6G networks by speculating the
visionary technologies for next-generation wireless systems in [5]. Different networking
scenarios are presented in[1215]. e authors in [12] and [13] give a predictive tech-
nical framework for industries in future generations of communication systems mainly
2013 2014 2015 2016 2017 2018 2019 2020 2021202220242023 2026
2025 2027 2028 2029
2012
2030
3GPP R14R13 R15 R16 R17R18 R19R20 R21R22 R23
ITU-5G
ITU-R IMT-2030
Traffic, Vision,Techs KPIProposalSpecs IMT-2020
Advanced
Traffic, Vision,Techs KPIProposal Specs
6G Study and Specifications B5G Study and Specifications 5G Study and Specifications
Fig. 1 A tentative timeline of standards development for 5G, B5G, and 6G [4, 6]
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Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
focusing on the specifications of future generations of the communication system. Cell-
less architecture, decentralized networking, and resource allocation, and three-dimen-
sional radio connectivity including the vertical direction are expected in next-generation
communication systems. e evolution of wireless systems from 1G to 6G is outlined
in[14]. e authors in[15] presented the role of intelligent surfaces in the architecture
of 6G networks.
e authors in[1619] presents the expected technologies, possible applications of
6G. e articles[2024] present the system-level perspective of the 6G scenario with use
cases, vision, and technologies. e authors in [25] analyze the application of blockchain
for the security and privacy measures in upcoming 6G networks. e potential role of
optical communication in 5G/B5G and 6G communication networks is described in[5].
e article[26] presents the feasibility of the application of mmWave communication in
satellite communication as an enabler of 6G networks. e article[27] gives an analysis
of potential applications of device-to-device communication in 6G. e authors in [9,
2830] elaborate on the multiple challenges in integrating artificial intelligence(AI) and
its potential role in future communication networks.
e authors in[31, 32], have focused on the vision for the next generation of wire-
less communication systems. Blockchain and AI are the potential technologies for the
next generation communication systems. Blockchain can be used for efficient resource
sharing and AI can be implemented for the robust, self-organizing, self-healing, and self-
optimizing wireless network[33].
By using millimeter-wave (mmWave) and terahertz(THz) frequency bands, massive
bandwidth, and highly directive antennas will be available to the 6G mobile devices to
enable new applications and seamless coverage [33]. Federal Communications Commis-
sion(FCC) has commercialized these frequency bands in 2019[34]. Ultra-high-precise
positioning will become available with 6G due to high-end imaging and direction-find-
ing sensors, just like human eyes and ears. 6G mobile phones could be equipped with
capable robots and intelligent algorithms[5].
e latency of the network in 6G will be minimized by using super-fast and high com-
putational power processors both at the network and end devices. e mobile phone of
the future network will be intelligent enough to sense the environment and give the pre-
cautionary and preventive measures. For example, these mobile phones will be capable
to detect the air pollution level, toxic food materials, and explosive materials around us.
ese phones will replace the wallet, hard cash, and wristwatches by providing digital
currencies, and smartwatches, respectively. Similarly, smart goggles will replace glasses
and smartphones. It is anticipated that 6G cellphones, coupled with the incredibly high
directive and beam-steering antennas, would be capable enough to see through the walls
by reconstructing the images by receiving the signals from multiple levels of density of
the environment in the vicinity[9]. is feature would be useful for extracting minerals
and elements from rocks, exploring underground natural reserves, and detecting arms.
Apart from this, 6G mobile phones will have tremendous features of providing position,
location, and range with very high accuracy. is will be helpful for maritime and under-
water communication and positioning.
Self-driving cars, which are already being developed in the initial phase these days,
would make human life safer and more comfortable[5]. Holographic technologies and
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Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
VR/augmented reality(AR) will break the barrier of distances. e digital revolution has
transformed the way we play, talk, or work. In the recent era of the digital revolution, 5G
has become the center of attention for everyone. Soon the mobile devices in our pockets
will get the wireless speed approaching the fiber optic transmission speed, bringing 3D
imagery, television, online games, and many other applications that we never imagined
into our tablets or mobiles.
Special attention is paid to the improvement of the traffic prediction in [35]. Follow-
ing the 6G vision and service requirements, some use case scenarios for the 6G, such
as autonomous vehicles, smart cities, flying networks, holographic, telemedicine, and
Tactile Internet, are discussed in [36]. Moreover, the reliability of the future wireless net-
work is forecasted to be at the same or higher level as that of today’s wired communica-
tion networks.
Some potential key enabling technologies encompassing blockchain-aided decen-
tralization of the network and machine learning(ML)-based intelligent communication
system for the 6G are discussed in [37]. A comparative analysis between the key per-
formance indicators(KPIs) for 5G and 6G is carried out in [31]. Practical applications
including holography, ML, VR, Internet-of-ings, visible light communication(VLC),
automated driving is discussed in [38].
Contribution
e objective of this article is to draw a complete picture of “how the 6G will look like?”.
We cover different dimensions and aspects of 6G focusing on the projected 6G system
architecture, potential technologies, network dimensions, KPIs, applications, and use
cases. e taxonomy of the paper is shown in Fig.2, which gives a pictorial view of all
sections and subsection presented in this paper. e contributions of this article are
summarized as follows.
– We discuss in detail about the projected 6G system architecture. We highlight all
the essential network elements of 6G system architecture and discuss the new air
interface development, application of AI and ML, utilization of new spectrum, the
coexistence of variable radio access technologies(RATs), and intelligent and smart
beamforming, etc.
6G network dimensions that include, cloudification/fog/edge computing, intelli-
gence, softwarization, and slicing are discussed in detail.
Tactile Internet is one of the main use cases of 6G networks and holographic verti-
cals are the potential application. Space tourism and communication in space, han-
dled by 6G networks, is discussed.
Towards the end, we discuss multiple challenges and research directions that include
the increase in chip size, beamforming for mobile users, pre-emptive scheduling, low
latency, and high reliability, and variable bandwidth and coverage issues that will be
faced due to the coexistence of all networks.
e remaining paper is outlined as follows. e next-generation wireless networks sys-
tem architecture is described in Sect. "6G system architecture". Next-generation net-
work dimensions are given in Sect. "Network dimensions". Some prominent use cases
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Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
and applications of 6G communication systems are presented in Sect. "Potential tech-
nologies", followed by potential key enabling technologies for 6G are given in Sect. "6G
application". Sect. "Key Performance Indicators(KPIs)" describes KPIs for 6G. Research
challenges and future directions are given in Sect. "Research challenges and directions"
and finally, the paper is concluded in Sect. "Conclusion".
6G system architecture
Next-generation wireless networks will consist of massive number of connected devices
and with the base stations(BSs)/access points(APs) leading to mMTC. Multiple BSs/
APs may serve one or more devices simultaneously to form a coordinated multi-
point(CoMP) transmission[39]. e huge amount of data produced by massive devices
will require very high-performance processing units and robust backhauling links. e
central processing units may utilize ML and AI algorithms and the backhauling links
may utilize optical fiber and or photonic communications. Remote user, in 6G commu-
nication systems, can use several relays or transmitters for a remote user to transmit,
and the user’s SINR may be improved by using the technique of diversity as in virtual
MIMO systems.
By intelligent networking, all the end devices would be aware of the location and fea-
tures of BSs/APs in their vicinity, and all of the BSs/APs would be aware of the loca-
tions, features, and QoS requirements of devices in their vicinity. Robust interference
management/optimization techniques can be applied to maximize the efficiency of the
wireless network. Central processing units will be fast enough to manage and switch the
resources(bandwidth, time, power) among multiple end-users, and data processing will
be conducted at the base-band processing units(BPUs). Figure3 depicts some of the
Air Inte rface
New
Spectrum
Machine
Learning and
Artificial
Intelligence
Advanced
Beamforming
with Ve ry
Large Scale
Antenna
Coexistance
of Variable
Radio Access
Technologies
Intelligence
Cloudification
/Fog/Edge
Softwarization
Virtua lization
Slicing
Quantum
Communi cation
and Quantum
Machine
Learning
Blockchain
Tactile Internet
Free Du plexing
and Spectrum
Sharing
E-Health and
Digita l/Bio
Sensing
Holographic
Transmissions
Communication
in
Space and Deep
Sea
Robotics and
Automated
Vehicles for
Beyond Industry
4.0 Era
Peak Da ta Rate
Mobility
Massive
Connectivity
Area Tr affic
Capac ity
Energy
Efficiency
Hardware Complexity
& Increase in Ch ip
Size
Variable Radio
Resource Allocation
Ultra Lo w Power &
High Pr ocessing
Circui t Design
Pre-Em ption
Security and
Privacy
The Shift to 6G Communications: Vi sion and Requirements
eRLLCS
Spectral
Efficiency
Seamless
Coexistence of
Multiple RATs
Section 2
6G Network
Architecture
Section 3
Network
Dimensions
Section 4
Potential
Technologies
Section 5
6G Use
Cases
Section 6
Key
Performa nce
Indicators
Section 7
Research
Challenges and
Direct ions
Fig. 2 Taxonomy of the paper
Page 6 of 27
Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
major components in the 6G system architecture, that will cause a major paradigm shift
towards the realization of 6G standards. e air interface is the main component that
causes a major improvement in the wireless generations. Orthogonal frequency division
multiplexing(OFDM) played a major role in the development of 4G, as code division
multiple access(CDMA) was the key player in 3G. Similarly, the development of the new
air interface will be an essential component of 6G system architecture.
AI and ML is another crucial component of the 6G system architecture. AI and ML
will play an important role in the self-organization, self-healing, self-configuration of 6G
wireless systems. Spectrum congestion has also pushed the 6G to adopt a new spectrum
for communication. erefore, this new spectrum will also be an active component in
the 6G system architecture. Since 6G will accommodate a wide range of communica-
tion devices ranging from IoTs to live HD video transmission, 6G will need to be in line
with all previous technologies. erefore, a flexible and multi-radio access technolo-
gies(RAT) system architecture will be an essential component in the 6G network.
Air interface
Since 6G will concentrate on the current terahertz frequency range with extremely wide
bandwidths available, it will bring up new obstacles to interact efficiently at these fre-
quencies. Getting a secure transmission infrastructure that has an adequate range and
isn’t power-hungry will be the answer here. e availability of incredibly wide band-
widths would change the emphasis from spectrally optimized solutions to improved
coverage solutions. In these new frequency spectrums, the tradeoff between spectrum
performance, power efficiency, and coverage will play a key role in developing devices.
is will lead to the design of a modern air interface where more consideration can
be paid to single-carrier systems. e OFDM scheme would be revisited for lower fre-
quency ranges where spectral efficiency will be important as it does not use the energy
effectively because of the cyclic prefix, which is just the duplication of information and
does not hold any additional information. Furthermore, a high peak-to-average power
ratio(PAPR) makes the power amplifiers complex and expensive.
Many researchers have proposed the non-orthogonal multiple access (NOMA) as
a promising new scheme for the B5G/6G mobile networks[4042]. In NOMA, all of
6G
Air Interface
New Spectrum
Artificial
Intelligence and
Machine
Learning
Advanced
Beamforming
with Very Large
Scale Antenna
Coexistence
of Variable
Radio Access
Technologies
Fig. 3 6G wireless network elements
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Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
the users are allowed to access the complete resource(frequency band) simultaneously.
Some researchers have suggested the rate-splitting multiple access(RSMA) as a new
access technology for 6G communication systems[4345]. Both NOMA and RSMA rely
on the successive interference cancellations(SIC) to decode the information for the user.
RSMA uses the SICs to decode the common message firstly and then decode the private
message. Both schemes need to be matured enough before practical deployment. A new
AI-based software-defined air interface is presented in [46], where the authors proposed
an intelligent air interface switching system for user QoS enhancement.
3GPP release 15, reveals the specifications for the 5G-New Radios(NR), in which mul-
tiple waveform configurations and two sets of frequencies are defined. By adopting the
variable numerologies(symbol duration, sub-carrier spacing, and pilot spacing), we can
give the transmitter leverage to self-organize and self-configure according to the chan-
nel conditions and service required. is is often useful on different measurements. For
instance, by reducing the symbol length, low latency can be achieved, and increasing the
spacing of the sub-carrier can be helpful in reducing the phase noise in mmWave and
sub-mmWave. In high mobility situations, optimizing the sub-carrier width can also be
helpful for Doppler shift compensation.
New spectrum
mmWave is already a candidate for 5G, but it is not exploited to its full potential as
the beamforming algorithms are not mature enough. It requires improvements in
the networks when personal BSs and satellite connectivity can get merged into cellu-
lar communication. In the previous generations, the spectrum is divided for multiple
services, for instance, television(TV) services, military communications, and cellular
communication[47].
erefore, the idea of using an unlicensed spectrum is proposed, i.e., to use the
mmWave, THz band, and visible light spectrum, simultaneously[4852]. ese bands
are never used for any communication. e problem with the higher frequency band,
though, is that the signal is attenuated very rapidly about the distance traveled. For
example, a 3G or 4G BS can have a coverage of about several miles whereas a 5G or 6G
BS coverage may limit to only a few hundreds of meters. To resolve this issue in mmWave
and THz communications, the idea of using massive multiple inputs and multiple out-
puts(MIMO) and beamforming emerged, which is described in the next subsections.
Articial intelligence/machine learning
By offering pervasive, secure, and close proximity-instant wireless networking for
humans and computers, 6G wireless communication networks would be the core of
society’s digital transition. A broad variety of emerging developments, such as self-
driving cars and voice assistants, have been made possible by recent advancements in
ML research. B5G/6G wireless networks have increased complexity, requiring smarter
methods for handling any losses and handling network features, detecting anomalies,
and understanding KPI trends. is can be done by introducing solutions for ML and
SDN. In order to preserve a certain level of KPI, ML/AI will boost the decision-mak-
ing process. e operation and implementation of RAN for 6G needs a new strategy.
Incorporating AI in wireless algorithms (e.g., for channel estimation, for channel state
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Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
information(CSI) feedback, and decoding, etc.) may bring a change in the direction of
these algorithms[53]. Application of ML, DL [54], and AI algorithms to the communica-
tion network, we can instantly manage the resources as per the user requirements. e
probability of choosing the best solution is improved in this way and the network can
maintain its optimum state.
Advanced beamforming withvery large scale antenna(VLSA)
e idea of beamforming is to steer the beam to only the desired direction or user. Since
energy is not spread in all directions, the transmission range is thus improved by con-
centrating the beam in one direction.
Intelligent reecting surfaces(IRSs)
Intelligent Reflecting Surfaces (IRSs) can be the potential area for beamforming in
6G[55]. IRSs are composed of thin electromagnetic materials, which can reflect/config-
ure the incoming electromagnetic rays in an intelligent way by configuring the phase of
reflected rays by a software[55]. Indeed, IRSs use at a large number of low-power and
low-cost passive elements to reflect the incident signals with configurable phase shifts
without the requirements of additional power, encoding, decoding, modulation, demod-
ulation requirements. IRSs are installed on the important points and locations such as
high-rise buildings, advertising panels, vehicles (cars, airplanes, unmanned aerial vehi-
cles (UAVs)), and even the clothes of the pedestrians. e main advantage of the IRS is
that it can enhance the signal-to-interference-plus-noise-ratio(SINR) with no change in
the infrastructure or the hardware of the communication network. Also, there is no need
for extra power required for the installation.
IRS can reduce the hardware complexity at the receiver and the transmitter by reduc-
ing the number of antennae installed at them, thereby, reducing the radio frequency(RF)
chains at the transmitter and the receiver. IRS can replace the conventional relays sys-
tem due to its advantages in terms of power, spectral efficiency, and reduced hardware
complexity[56]. IRS can be used in the deep-fade and non-line-of-sight(NLOS) com-
munication environment. e principle by which SINR is enhanced at the receiver is
optimally controlling the phases of the incident ray at multiple elements of the IRS, to
produce useful beamforming at the receiver[56]. Degradation factors such as noise and
interference have no impact on the IRS. All these features of the IRS make it a promising
technique for the B5G/6G communication systems.
Orbital angular momentum(OAM)‑aided MIMO
A new dimensional property of the electromagnetic waves(EW) was discovered in the
1990s termed as the orbital angular momentum(OAM). is discovery promised the
transmission of multiple data streams over the same spatial channel. An EM wave carry-
ing the OAM has the phase rotation factor of
exp(
jlφ)
, where l is OAM state number
represented in integer and
φ
is transverse azimuth angle[5759]. e main advantage of
OAM over other beamforming techniques is that OAM can have an unlimited number
of orthogonal modes, which allows the EW to multiplex multiple data streams over the
same spatial channel, thereby, enhancing the spectral efficiency and transmission capac-
ity. OAM support a high number of user in mode division multiple access(MDMA)
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Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
scheme without utilizing extra resources(i.e., frequency, time, and power). e flexibil-
ity of OAM to be used in narrowband and wideband frequency hopping scheme makes
it an attractive scheme for low probability of interception(LPI) applications. OAM-
based MIMO systems have advantages over the conventional MIMO systems in terms of
capacity and long-distance line-of-sight(LoS) coverage[60]. erefore, OAM has great
potential for applications in 6G wireless networks.
Coexistence ofvariable radio access technologies
6G can lead to a ubiquitous networking infrastructure where users would not only be
left with the option of selecting the best communication network. Each node in this net-
work would, however, be intelligent enough to sense the conditions of the channel and
the specifications of QoS at any other node. For example, the use case and the availability
of network will decide the network as cellular, wireless LAN, Bluetooth, and ultra-wide-
band (UWB), etc. 6G communication standard should, therefore, be designed in such
a way that it will converge all of the wireless technologies. Communication with Wi-Fi,
Bluetooth, UWB, VLC, UAVs, biosensors, and satellite communications can all integrate
into 6G and should fall under one standard such that all of them can connect with each
other. e Wi-Fi operating at 2.4 GHz has already entered deeply into IoTs as most of the
appliances are now connected through this network[6163].
By merging all these technologies, 6G would be able to utilize the massive infrastruc-
ture deployed by previous technologies, which otherwise can cost 6G a huge revenue.
e features in the previous technologies, such as network densification, high spec-
tral efficiency, high throughput, low latency, high reliability, and massive connectivity
should be converged in 6G. 6G technology should also keep the trend of offering new
services by applying the new technologies, such as AI/ML, VLC, quantum communica-
tions(QC), and quantum machine learning(QML). ese services may include but are
not limited to smart cars, smart homes, smart wearable, and 3D mapping[64].
Figure4 gives an overview of the evolution of the wireless generation, with timelines,
from 1G to 6G with respect to applications, KPIs, network characteristics, and tech-
nology. Figure4a shows that a major leap in the application is observed with 4G. 4G
introduced mobile Internet, mobile TV, and HD videos. AR/VR, ultra-HD(UHD) vid-
eos, wearable devices, vehicle-to-infrastructure(V2X), smart city, telemedicine, and IoTs
concepts are introduced in 5G. 6G is projected to have applications such as space tour-
ism, Tactile Internet, fully automated cars, holographic verticals, deep-sea sight, digital
sensing, and Internet-of-bio-Nano-things(IoBNT). Figure4b shows that how KPIs are
changing with the evolution of wireless generations from 1G to 6G. Figure4c shows the
evolution of the network characteristics with wireless generations. All Internet proto-
col(IP) and the ultra-broadband concept is introduced in 4G. e concepts of cloudifi-
cation, softwarization, slicing, virtualization, and wireless worldwide web(WWW) are
introduced in 5G. Integration of intelligence with cloudification, softwarization, slicing,
and virtualization will be introduced in 6G communication systems. Figure4d depicts
the evolution of technologies with the development of wireless communication genera-
tions. e initial stage of the wireless communication system is the development of the
advanced mobile phone system(AMPS). Global systems for mobile(GSM) and general
packet radio systems(GPRS) family is developed in 2G wireless systems. Code-division
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Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
multiple access (CDMA) family shifted the wireless systems from 2G to the 3G.
OFDM with the integration of turbo codes and MIMO systems is the key technology
for 4G communication systems. 5G communication systems brought some new tech-
nologies such as cloud/fog/edge computing, massive MIMO, SDN, mmWave and sub
mmWave(NR) along with low-density parity-check(LDPC) and polar codes. ML, AI,
blockchain, THz communication, orbital angular momentum multiplexing(OAM Mux),
spatial Modulation(SM)-MIMO and intelligent re-configurable reflecting surfaces are
the new technological domains in 6G.
Network dimensions
In this section, we give an overview of the network dimensions of 6G networks. Network
intelligence will be an essential component of 6G networks and the network will take
actions dynamically according to the environmental conditions. e idea of clouds, fog,
and edge computing is applied for fast access to services. e features of self-optimi-
zation, self-organization, self-reconfiguration will be achieved through softwarization,
virtualization, and slicing. e detailed discussion on each network dimension is given
as follows.
d
c
1G
1980
2G
1990
3G
2000
4G
2010
5G
2020
6G
2030
SM-
MIMO
THz Comm.
RIS
OAM Mux
Machine
Learning
LDPC and
Polar Codes
Carrier
Aggregation
Cloud/Fog/Edge
Blockchain
D2D
Comm.Flexible
Frame
Structure
ICIC
NOMA
Turbo
Code Quantum
Comm.
MIMO
OFDM
Hetnet
Massive
MIMO
Mm-Wave
Comm./NR
SDN/NFC
RSMA
AI
GPRS
EDGE
CDMA
WCDMA
GSM
UMTS
TDMA CDMA
2000
AMPS
1G
1980
2G
1990
3G
2000
4G
2010
5G
2020
6G
2030
Voice
Text
Multimedia
Mobile
Internet
Mobile TV
Mobile PayHolographic
Verticals
Tele-
medicine
Wearable
Devices
HD Videos
V2X
IoT
Smart City
Voice
Voice
Fully
Automated
Cars
VR/AR/360°
Videos
UHD Videos
Tactile
Internet
Space
Tourism
Deep-Sea
Sight
IoBNT
Digital
Sensing
a
1G
1980
2G
1990
3G
2000
4G
2010
5G
2020
6G
2030
Intelligence
Slicing
All-IP
Cloudi-
zation
Softwari-
zation
Virtuali-
zation
Slicing
Digital
voice Virtuali-
zation
Cloudi-
zation
Softwari-
zation
Circuit
Switching
for voice
Packet
Switching
for data
Packet
Switching
Packet
Switching
Packet
Switching
Broad
band Ultra
Broad
band Wireless
WWW
b
1G
1980
2G
1990
3G
2000
4G
2010
5G
2020
6G
2030
100Mbps
20Gbps
≥1Tbps
350Km/h
500Km/h
≥1,000Km/h
10ms 1ms
10-100µs
0.1
10
1,000
1 ×
3 ×
15 ×
1 ×
100 ×
10 ×
Peak Data Rate
Mobility
Latency
Spectral Efficiency
Network Energy
Efficiency
21Mbps
2
Mbps/m
7
10
6
10
5
10
2
Devices/Km
100ms
300ms
4
10
0.001
0.1 ×
0.01× 0.6 ×
Fig. 4 Evolution of wireless communication, with timeline, from 1G to 6G based on (a) Applications (b) KPIs
(c) Network characteristics and (d) Technological development
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Intelligence
Researchers believe that AI will play a defining role in the IoTs and IoBNTs driven world
[65]. e potential shift from 5G to the 6G will be to determine an efficient way to trans-
mit data. e ideal system will be the one that is free from human intervention at all[66].
Cloudication/fog/edge
ousands of sensors are installed in the industries and hundreds of the sensors are
installed in homes. It is very difficult to connect all these sensors with wires[67], and,
all these devices can produce a large amount of data. Also, these devices are smart
and intelligent, capable of making smart decisions and less processing power. ere-
fore, we need to offload the data from cloud to edge and device end. To reduce the
processing delay, we need to shift the process near to end devices in terms of cloud/
fog. We need to place the workload closer to the edge for a better quality of service.
Softwarization
Main driving force behind the development of B5G and 6G networks is to provide
services such as self-organization, configurability, programmability, flexibility, and
heterogeneous use-cases. It is difficult to install the hardware equipment which pro-
vides all of the mentioned functionalities. By realizing the functionalities by under-
lying networks, softwarization and virtualization have emerged as the two most
demanding paradigms for B5G/6G networks[68].
Softwarization is the term used for the set of interfaces and protocols which can
allow the network to be configured in software by decoupling the control and user
plane. e user plan usually consists of a set of distributed and stateless routing tables
at which packet switching is performed at a very high speed. ese tables are updated
by the centralized control plan which maintains the end-to-end routing informa-
tion for multiple services. Data and control management operations are exchanged
between the service consumer and the SDN provider[36]. SDN provider ultimately
forwards the required service to the service consumer. ese services are controlled
by the service consumer by taking acting on these virtual resources.
Virtualization
Network function virtualization enables the software functions to be performed in
the virtual machines and allows the access of common shared physical resources such
as storage, networking, and computations. Containers are used to instantiate multi-
ple functions within the same virtual machine. Dynamically varying network demand
such as offered services and network traffic can be handled by dynamically instantiat-
ing the virtual machines.
e services, which can be virtualized, include but are not limited to load manage-
ment, mobility management, baseband processing unit services, evolved packet
core(EPC) functions. Network function virtualization(NFV), unlike traditional mobile
networks, provides the leverage to route the packet of each service between virtual net-
work functions(VNFs)[69]. Further, the routing services are provided with very few
overheads. Also, routing and traffic flow are smoothly maintained without any interrup-
tion even if a new VNF is added or removed according to the traffic demands.
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Slicing
One of the key network abilities that will allow us to build a flexible network on top of
the common physical infrastructure is network slicing. As 5G continues to take shape,
network slicing will become the fundamental technology to enable a wide range of
use cases. Taking a single piece of network infrastructure and being able to cost-effec-
tively deliver multiple logical networks over the same common physical infrastruc-
ture[69]. e slices can be allocated to some specific use-cases such that we can have
a slice for IoTs, slices can be allocated to a class of service, slices can be allocated to a
class of customers, slices can be allocated to some specific mobile network operators,
slices can also be allocated to network types such as wireless vs wired or consumer vs
businesses.
In network slicing, the biggest difficulty is configuring new slices, since it affects all the
network components. However, with the need to create customized services and deliver
a service with a very specific requirement, we can create slices such as slice for automo-
tive, healthcare, utility.
Figure5 gives a pictorial overview of the 6G wireless network that covers all aerial-
ground-sea communications. As shown in Fig.5, 6G will make it possible to commu-
nicate with the devices with very low data-rates such as biosensor and IoTs, and at the
Fig. 5 A depiction of space-air-ground-sea based integrated next-generation communication system with a
wide range of applications
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same time, it will enable high data rate communication such as HD video transmission
in smart cities. Communication will be possible in a fast-moving bullet train, airplane.
It also shows that all of the networks will be merged all together. Further, the buildings
and surfaces in smart cities can be equipped with the IRS that could enhance the cover-
age and quality of service (QoS) of each communicating device. For the maritime com-
munication scenarios, the robust underwater data links will enable the communication
between ships, submarines, and sensors at the deep sea level [70, 71]. Besides, innovative
technologies such as AR/VR, haptics, and ML will further reduce the effect of physical
distances around the globe.
Figure6 depicts a comparative analysis of the network architecture of 5G and 6G. e
6G core network is shown to have upgraded to the basic 5G core network based on intel-
ligence, high computational power, and high capacity. By integrating BSs/APs, satellites,
and UAVs, the access network is upgraded similarly. ere is a vertical hand-off in 6G in
addition to the horizontal as in that of 5G. Besides, fog computing and MEC are an inte-
gral component of the 6G network infrastructure, that reduces latency and bandwidth
utilization for regularly needed services by a massive number of devices on the user plan.
Potential technologies
Based on the vision of 6G and its network architecture, we now elaborate on the key
enabling technologies for 6G wireless networks in this section. Various state-of-the-art
technologies must be utilized together to enable the key features of 6G.
Fig. 6 A comparative analysis between 5G and 6G network architecture
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Quantum communication andquantum ML
Quantum technology uses the properties of quantum mechanics, such as the interaction
of molecules, atoms, and even photons and electrons, to create devices and systems such
as ultra-accurate clocks, medical imaging, and quantum computers. However, the full
potential remains to be explored. A quantum Internet is a way of connecting quantum
computers, simulators, and sensors via quantum networks and distributing information
and resources securely worldwide[72].
In October 2018, the European Commission launched the Quantum Flagship, a 1
billion Euro project for over ten years involving 5000 scientists to support quantum
research in the EU with the goal of creating a quantum Internet[72]. For the next dec-
ade, the EU plans to develop and deploy a secure pan-European QC infrastructure (QCI)
to become the backbone of a quantum Internet. QCI will make quantum cryptography
a part of conventional communication networks, protecting the EU sensitive data and
digital infrastructure and making it possible to exchange information between different
countries securely. QCI will combine terrestrial and satellite segments, where the ter-
restrial one will use the existing fiber communication networks linking the strategic sites
within and between countries, the satellite segment will be deployed to cover very long
distances across a large area.
Quantum key distribution will be the first service to run this infrastructure [73].
It provides the sender and the recipient of an encrypted message with an intrinsically
secure random key in such a way that an attacker cannot eavesdrop or control the sys-
tem. It will secure important confidential communication even against code-breaking by
future quantum computers. It will provide services such as securely sharing information,
digital signatures, authentication services, and clock synchronization. is infrastruc-
ture would be beneficial for the economy and society and ensure the security of sensitive
government information both from earth, sea, and in the space [74].
e QC and the QML can be key players in 6G wireless networks. e QC can provide
the solutions for the 6G networks in the domain of increased channel capacity, e.g., new
multiple access technologies, such as NOMA, RSMA demand very high power on run
time for computation of SIC. Similarly, QC and QML can have a considerable role in 6G
in the field of channel estimation, channel coding(quantum turbo codes), localization,
load balancing, routing, and multiuser transmissions[75]. In the communication net-
work core side, QC and QML can solve complex problems such as multi-object exhaus-
tive search by providing fast and optimum path selection to the data-packets in ad hoc
sensor networks and Cloud IoT [76].
Blockchain
Blockchain is bringing the revolution to some of the huge industries such as finance,
supply chain management, banking, and international remittance[77]. e concept of
blockchain is opening new avenues to conduct businesses. Blockchain provides trust,
transparency, security, autonomy among all the participating individuals in the net-
work [78]. As far as the telecommunication industry is concerned, innovation in a
competitive environment with reduced cost is the most important parameter for the
successful businesses in the telecommunication industry. e blockchain industry can
benefit the telecommunication industry in the following various aspects.
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Internal network operations
Smart contracts in Ethereum, which is the second generation of blockchain technolo-
gies, have revolutionized the automation system in various applications. Smart contracts
allow the computer code to automatically execute when a certain event is triggered.
Because of this fact, blockchain has an immense attraction for its applications in the tel-
ecommunication industry to automate various operations such as billing, supply chain
management, and roaming. Blockchain can prevent the fraudulent traffic in the telecom-
munication network thereby saving a lot of bandwidth and resources and ultimately
increasing the revenue of the operators[79]. Blockchain can save time for the telecom-
munication industries and reducing the cumbersome post-billing audit process apply-
ing the smart contracts for the authentication and clearance of the bills. rough this
process, telecommunication industries can automate accounting and auditing processes.
Blockchain‑based digital services
Telecommunication operators can generate new revenues by proving customers with
new blockchain-based services such as mobile games, digital asset transactions, music,
payments, and other services. Telecommunication industries can also generate some
new revenue streams by allowing the customers to transfer money from the user to
user[79].
Digital identity verication
Digital identity verification already costs the government millions of dollars every year.
A blockchain-based digital identity verification system can be implemented in the next
generation of communication networks which will replace the existing identity verifica-
tion systems[79].
Ecosystem forecient cooperation
Next-generation wireless systems aim to provide a variety of new digital services. Block-
chain is an attractive application for the complex transactions initiated for these ser-
vices. Blockchain can also be used in the advertising industry by using user information
effectively [31]. is will trigger a massive machine-to-machine (M2M) transactions.
Telecommunication operators can take the initiative of using blockchain in this specific
area and usher the next generation of digital services.
e demand for massive connectivity in 6G has triggered the network resource man-
agement such as power distribution, spectrum sharing, computational resources dis-
tribution as the main challenges[61, 77]. Blockchain can provide solutions to the 6G
network in these domains by managing the relationship between operators and users
with the application of smart contracts. Similarly, blockchain can solve the unlicensed
spectrum management and energy management problems. Blockchain can also be used
in seamless environmental protection and monitoring, smart healthcare, cyber-crime
rate reduction[80, 81].
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Tactile internet
With the evolution of mobile Internet, sharing of data, videos are enabled on mobile
devices. e next stage is the evolution of IoTs, in which communication between smart
devices is enabled. Tactile Internet is the next evolution of the Internet of networks,
which integrated the real-time interaction of M2M and human-to-machine(H2M) com-
munication by adding a new dimension of haptic sensations and tactile to this field. Tac-
tile Internet is the term used for transmission of touch over a long distance. Some of the
researchers termed it “Internet of Senses”[82].
ITU has termed the Tactile Internet as the Internet of networks with very high per-
formance, ultra-low latency, high reliability, and high security. Tactile Internet will allow
the human and the machines to communicate in the real-time with the environment in a
certain range. Haptic interactions will be enabled through Tactile Internet.
Creating pressure against the skin without any physical object is one of the main chal-
lenges for Tactile Internet. One of the methods to produce such a sense of touch is by
intense pressured sound waves. Ultrahaptics, a British company, is working on produc-
ing the haptic sensation by using ultrasounds[83]. e ultrasonic transducers can create
a sense of touch by controlled production of ultrasonic waves by multiple transducers.
ese transducers integrated with in-depth cameras can detect the position of the body
to react accordingly. Microsoft is also working on the development of haptic sensation
using air vortex rings, which are resembling speaker diaphragm[84]. e concentrated
waves from the tiny holes can move with a resolution of 4 inches and to the distance
of 8.2 feet[85], which has a greater range and much less precise than the ultrasound
system.
Free duplexing andspectrum sharing(FDSS)
In previous wireless generations, wireless systems were using either fixed duplex-
ing(TDD/FDD) such as in the case of 1G, 2G, 3G, and 4G or flexible duplexing in the
case of 5G[8688]. Whereas, with the progress in the development of duplexing tech-
nologies, 6G is expected to use full free duplex in which all users are allowed to use
complete resources simultaneously. Users can use all resources (i.e., space, time, and fre-
quency) in a free duplex mode that eventually improves latency and throughput.
Presently, government bodies are monitoring the spectrum and allocating the spec-
trum to the operators. e owner of the spectrum has the full right to use that spectrum.
Any other operator cannot use the spectrum allocated to some other operator. is is
only due to the non-development of efficient spectrum monitoring or spectrum manag-
ing techniques at present. erefore, as AI and blockchain are anticipated as key tech-
nologies in 6G, robust spectrum monitoring and spectrum management strategies are
expected to be developed for the 6G roll-out. e network resources can be dynamically
controlled by AI-aided 6G systems. erefore, free spectrum sharing will become a real-
ity in 6G.
In the context of free spectrum sharing techniques, NOMA is proposed to be a prom-
ising multiple access candidate for B5G/6G communication systems. In NOMA, a
complete resource block (frequency band and time slot) is assigned to all users simul-
taneously, whereas the users are distributed in the power domain. e weakest user
receives the maximum power from the BS, whereas the strong users apply the SIC to
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the composite NOMA signal to cancel out the messages of the weak users and finally
extract their own messages. However, the number of SIC increases exponentially with
the increase in the number of users, which increases the complexity of the NOMA sys-
tem. User cooperation in NOMA can be used to alleviate outage problems of weak users
and to provide diversity at the expense of more time slots. However, the number of SICs
even becomes larger with the number of cooperating time slots. Space-time block cod-
ing-based NOMA (STBC-NOMA) is proposed as an alternative to reduce the number of
time slots while keeping the same diversity order [89].
Apart from imperfect SIC, the imperfection in the channel state information (CSI)
also affects the performance of NOMA systems. We present a comparative analysis of
the impact of imperfect CSI on the performance of non-cooperative NOMA, conven-
tional cooperative NOMA (CCN), STBC-aided cooperative NOMA, and conventional
orthogonal multiple access (OMA) schemes in Fig.7. For a fair comparison between all
schemes, we use the same total power budget for all of them. e channel from BS to the
users and between users is considered as flat-fading Rayleigh channel. Fig.7a shows the
average capacity of the weakest user vs. the total number of users for OMA, non-coop-
erative NOMA, STBC-NOMA [90, 91], and conventional cooperative NOMA (CCN)
[40] schemes with perfect CSI. Fig.7b and Fig.7c depict that with perfect channel state
information (pCSI), CCN outperforms OMA, non-cooperative NOMA, and STBC-
NOMA schemes. However, with the impairments of imperfect CSI (ipCSI), the perfor-
mance of CCN is severely degraded, where the impact of ipCSI on the STBC-NOMA
is much lesser than that of CCN. As shown in Fig.7c, with the ipCSI = -15 dBm, the
STBC-NOMA outperforms the CCN scheme, whereas the impact of ipCSI on the OMA
scheme is negligible. ese schemes can be further explored in the future for providing
massive connectivity with band-limited applications.
6G application
Modern society is influenced by intelligent and smart machines. ese machines can
communicate with each other and with human beings. ey can be utilized to help
human-being in various aspects of life ranging from medical/e-health, transport, food
industry, agriculture, education, etc. In this section, we will introduce some of the
important use cases of 6G that will utilize the ideas mentioned above.
Total number of users [K]
20 40 60 80 100
Av. capacity of the weakest user (bps/Hz)
0
1
2
3
4
5
6
7
OMA with pCSI
Non-cooperative NOMA with pCSI
STBC-NOMA with pCSI
CCN with pCSI
a
Total number of users [K]
20 40 60 80 100
Av. capacity of the weakest user (bps/Hz)
0
1
2
3
4
5
6
7
OMA with ipCSI = -30dBm
Non-cooperative NOMA with ipCSI = -30dBm
STBC-NOMA with ipCSI = -30dBm
CCN with ipCSI = -30dBm
b
Total number of users [K]
20 40 60 80 100
Av. capacity of the weakest user (bps/Hz)
0
1
2
3
4
5
6
7
OMA with ipCSI = -15dBm
Non-cooperative NOMA with ipCSI = -15dBm
STBC-NOMA with ipCSI = -15dBm
CCN with ipCSI = -15dBm
c
Fig. 7 The average capacity vs. total number of users for OMA, non-cooperative NOMA, STBC-NOMA, and
CCN with (a) pCSI (b) ipCSI = -30 dBm (c) ipCSI = -15 dBm
Page 18 of 27
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E‑health anddigital/bio sensing
Recently, a widespread pandemic of coronaviruses, a class of viruses that cause sick-
ness in human and animal species, has emerged as a serious threat to the health and
life of mankind. e COVID-19 is linked to the family of Severe Acute Respiratory Syn-
drome(SARS) which affects the respiratory system of humans and animals[92]. With
the growing number of COVID-19 infections, there is a requirement for the develop-
ment of biosensors that are precise, accurate, sensitive, easy-to-use, and specific to
detect and monitor infectious diseases. With the development of 6G, these biosen-
sors can be integrated into the smartphones to give an early warning and control the
pandemics[9397].
With the integration of QC, ML, and biotechnology, 6G networks can be capable of
effectively detecting viral diseases by observing the body temperature of infected indi-
viduals efficiently. Optical biosensors may also be used to track the pathological func-
tioning of biorecognition substances, such as antibodies, enzymes, whole cells, and
DNAzymes, to better detect multiple diseases[96]. In other areas of electronic health
(e-health) such as control of environmental conditions (e.g., temperature, percentage of
gases, and light condition), 6G can also be helpful. In various health operations such
as emergency care, medical checkups, cleaning contaminated floors, and the supply of
medication in rural areas, autonomous robotics can be used.
Holographic transmissions
Holography is a technique for capturing an object’s full 3D image. e methodology was
suggested in 1947 by Gabor[98]. e term holography derives from the Greek words
‘Holo’ implies ‘complete’ and ‘graphic’ implies ‘writing’. An ordinary photograph records
the picture’s two-dimensional image because it records only the distribution of ampli-
tude or intensity. erefore, in holography, both the intensity and the phase of light
waves are recorded. Physical light effects such as interference, reflection, refraction, and
diffraction were recorded in holography, and the archive is called the hologram [99]. It is
possible to play each hologram repeatedly. Although a hologram does not have an object
resemblance, it has all the object information in optical forms. Just as mobile cameras
have replaced still cameras, video calling and video recording, such as movies, will be
replaced by holography.
Communication inspace anddeep sea
Space tourism has the immense potential for the next decade both in economic and sci-
entific perspective[100]. Humans from every aspect of life will be traveling to space.
Several firms are planning to launch sub-orbital commercial flights for space tourism.
After some successful and profitable space launches, the next step will be to ensure the
availability of space hotels and space hospitals for the customers[101]. Apart from com-
mercial space flights, space research is another potential application[102].
6G will expand the range of activities throughout the globe with the availability of easy
and effective tools of communication. Autonomous and intelligent robots will be placed
in the harsh environmental areas for communication and research purposes [103].
e mysteries of the globe could be solved with the aid of the powerful and enormous
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capabilities of 6G networks. Deep-sea exploration such as oil exploration and mineral
exploration can become a reality.
Robotics andautomated vehicles forbeyondindustry 4.0 era
Industry 4.0 is the term used for the fourth industrial revolution[104]. Industry 4.0
factories have fully automated machines that can self-organize and self-optimize and
include processes such as cloud computing, NFV, slicing, and industrial IoT. 6G will
bring a new industrial revolution termed as beyond the Industrial 4.0 era.
Robots and fully automated vehicles will take part in the real-time diagnostics, opera-
tions, monitoring, and maintenance processes in a very efficient and cost-effective man-
ner [104106]. Extremely high reliability and self-organizing feature of automation will
come into all aspects of daily life. Swarms of UAVs, through advanced hardware, ML,
and QML algorithms, will be used in various operations such as fire control, construc-
tion, emergency first response, and agriculture.
Key performance indicators(KPIs)
In this section, we discuss the main KPIs of 6G wireless systems. ese KPIs include
peak data rate, mobility requirements, connected devices per Km
2
, area traffic capacity,
latency, reliability, network spectral, and energy efficiency.
Peak data rate
One of the use cases for next-generation wireless communication is eMBB, which simply
implies high data rates. Hence we can download HD videos in a few seconds. e data
rate requirements of users are increasing since the birth of wireless communications.
As shown in Fig.4, 1G had the data rates of a few kbps, which further increased to a few
Gbps in 5G. ese data rates are still not enough for some applications. erefore, we
require the development of some standard and communication protocols that have data
rates in the range of 10-100Gbps[107].
Mobility
More mobility robustness is also required in next-generation communication systems.
High data rates should be maintained in highly mobile devices. For instance, if we are
moving in the airplanes or high-speed bullet trains, the communication should not be
disturbed, and data rates should be maintained. e mobility requirements for 6G, as
defined by ITU, is >1000Km/hr[107].
Massive connectivity(devices/Km
2
)
Another use case for next-generation wireless communication is mMTC. is is the
domain where the IoTs comes in and is machine type communication without the inter-
action of human beings. e calls, messages, and commands are from machine to the
other machine. e actions are not carried out by a human. Rather, it is the machines
that are communicating with each other. Next-generation wireless networks technology
is expected to accommodate
107
devices/Km
2
[108].
Sensor networks and IoTs will be connected to each other in a cooperative way and
with several BS. Devices and applications in this category include wearable devices,
Page 20 of 27
Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
control and monitoring devices, self-driving cars, smart grids, industrial automation and
control devices, and medical and health-related devices. e communication between
these devices may be through peer-to-peer or cooperative multi-hop relay manner.
Different applications or devices require different network infrastructure design which
could manage different content-driven applications/network. erefore, keeping all of
these requirements in view, next-generation wireless networks would require a com-
pletely different approach for planning and optimization.
Area trac capacity(Mbps/m
2
)
With the increase in the number of connected devices per unit area, demand for the
higher capacity channels and back-hauling also increased. A highly dense deployed sen-
sor network produces more than tara bytes(TB) of data on daily basis [107]. is data
production needs a high capacity back-hauling channel to accommodate the traffic.
In the previous wireless generations(1G-to-5G), wireless protocols are designed for
some specific applications. However, with the development of massive IoTs or mMTC,
we need to have some power-efficient and cost-efficient devices to be designed. is
massive IoTs communication leads to the development of vehicular communication such
as autonomous driving termed as V2X(vehicle-to-infrastructure). e vehicle needs to
interact with another vehicle, with pedestrians, and many other sensors installed in the
vehicle. All these communication needs to be extremely reliable and with low latency
and security. Industrial automation is another example where a lot of sensors are com-
municating and generating a huge amount of data. e minimum area traffic capacity
limit for 6G is 1000Mbps/m
2
[107].
Extremely‑high reliability andlow latency withsecurity(eRLLCS)
Low latency means quick and fast communication. We want our packets to be transmit-
ted in a very short amount of time and there should not be much processing delays. e
maximum allowable latency in 6G is 10
sec[107, 108]. e future network of intelligent
mobiles and robots will require high reliability and ultra-low latency. Future cities will
comprise of smart homes, smart cars, smart industries, smart schools/universities, and
smart industries. Smart cities will need to be connected to airplanes, ships, bullet trains,
and UAVs. Some of the critical applications which include health care, defense sector,
monitoring, and surveillance will require ultra-reliability and low delay.
Online gaming services demand high reliability and low latency. e eRLLCS in 6G
wireless systems will integrate the security features with mMTC and URLLC in 5G with
greater requirements of reliability of higher than 99.9999999
%
(Nine 9’s) [107]. Autono-
mous vehicles will be connected to each other and the communication between them
should be ultra-reliable, otherwise it may lead to the loss of lives in accidents. In 6G sys-
tems, a lot of households and other sensors will be communicating with each other also
require ultra-reliability to prevent any mishap to occur.
A QoS‑aware spectral ecient network
e future intelligent wireless network will comprise of intelligent/smart factories, intel-
ligent/smart hospitals, schools, universities, and autonomous robots. is will require
a highly spectral efficient network having high computing power. A high-density and
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Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
high-rate network will require high bandwidth. e scarcity of the bandwidth will
increase with the increase of data in the network. For reliable communication, an ultra-
spectral efficient network would therefore be needed while at the same time satisfy-
ing the criteria for QoS of all users in next-generation wireless networks, which will be
smart enough to move to a new state with changing environmental conditions.
With the increasing number of mobile devices and communication types, the scarcity
of the radio wireless spectrum has increased. erefore, some communication protocols
are needed to be designed for spectral efficient communication. So that the bandwidth
resource is effectively utilized. e spectral efficiency of 6G networks is supposed to be
>15 times that of 3G[107].
Energy ecient network
e next-generation wireless communication system will consist of massive self-organ-
izing and self-healing robots. All these intelligent robots/devices will require high com-
putation power. erefore, the need for energy will be increasing with the increase in
intelligent robots. Currently, traditional GPUs are not meeting the energy efficiency
requirements of next-generation wireless networks communication networks. In such a
scenario, an energy-efficient and scalable intelligent network design will be required. e
industry has moved towards IoTs, IoEV and IoBTs[107, 109]. We have sensors deployed
Table 1 A critical analyses ofdierent techniques proposed forB5G/6G systems
Technology
enabler Pros Cons Use cases Research initiatives
Quantum Commu-
nication (QC) and
QML [72, 75]
Faster
High-performance
processing Power
Costly
Complex Drug industry
Radar industry
Mathematics
D-Wave Systems Inc.
IBM Corporation
Intel Corporation
Cambridge Quantum
Computing Limited
Blockchain [61, 77,
78, 80]Distributed
Stability
Integrity
Immutability
Traceability
Inefficient
High storage
Privacy concerns
Decentralize
Supply-chain
Voting
Healthcare
Security
Digital identity
IBM
Alibaba Group (China)
Fujitsu (Japan)
Mastercard
ING Groep (Dutch
banking firm)
Reconfigurable
Intelligent Sur-
faces (RIS)s [55, 56]
Low complexity
Power efficient
Low cost
Difficulty in phase
configuration Comm. and Defense
industry - World-wide
Tactile Internet and
Haptics [35, 84, 85]Online gaming
Revolutionize the
life of disabled
peoples
Noise
Less energy efficient
Costly
Mining
Automation
Online gaming
VR and AR
TU of Dresden in
Germany
Kings College London
Ericsson and Microsoft
Ultrahaptics UK
Access Technologies
[40, 4345]Improved network
efficiency Economic Loss due
to replacement
of existing equip-
ment
Variable use cases World-wide
New Spectrum
-mmWaves
THz
VLC [4752]
Higher bandwidth
availability Low penetration
power Variable use cases World-wide
Internet-of-Every-
thing (IoE) [66, 68,
110]
Low latency
Higher data rates Low energy effi-
ciency Variable use cases Worldwide
Page 22 of 27
Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
everywhere. ere is a sensor in our door, in our air conditioner, in our car, on the TV, in
the refrigerator, in offices. All these sensors need energy-efficient communication.
Table 1 gives a critical analysis of the potential 6G technologies, which will enable
communications in the B5G/6G era. Advantages and disadvantages along with the
research initiative in these technologies are also described.
Research challenges anddirections
In this section, We discuss some of the main research problems and directions for the
deployment of B5G/6G networks.
Hardware complexity andincrease inchip size
Next-generation mobile communication will integrate multiple communication devices
ranging from sensors to HD video transmission devices or communication with high-
speed trains and airplanes. Such devices will require variable packet sizes to be transmit-
ted, contrary to the previous mobile communication technologies with fixed packet size.
With the variable packet size to be transmitted, the hardware complexity is
increased. Since the frame/packet size is not known to the mobile station a priori,
it must select its signal processing and RF chains according to the incoming packet,
which means that the chip size will be increasing, which will ultimately increase the
mobile size. is will again increase the processing time which is not desirable in
next-generation wireless communication.
6G communication network will cover a large bandwidth ranging from 3GHz to
60GHz. erefore, to enable communication, at any frequency in this band, the com-
plexity of the hardware circuitry is increased. For each, the communication, antenna,
RF filters, amplifiers have to be designed accordingly. To cover all the band in next-
generation communication systems, multiple RF and signal processing chains would
be required, which would ultimately increase the chip size and hardware. erefore, a
lot of focus needs to be paid to the field of open research.
Variable radio resource allocation
With variable QoS requirements, a variable radio resource has to be assigned to the
user. is may be variable bandwidth, power, or both. Another challenging aspect of
6G is that with propagation frequency, the signal can attenuate rapidly and have high
penetration loss at high frequencies. e signal is also automatically attenuated upon
accessing houses, residences, or workplaces. With the increasing frequency, as the
radio waves get attenuated, it could have trouble penetrating walls in buildings and
houses, while affecting the QoS requirements of the users. It is therefore of great sig-
nificance to develop stable, fast, precise algorithms to manage the 6G communication
requirements by dynamically allocating variable resources.
Ultra‑low power circuits withhigh‑performance processing capabilities
To cope with latency-critical scenarios such as automated cars and medical/health
applications, the communication needs to be accomplished in a very short duration of
time. To attain the latency of only a few milliseconds is quite challenging. To achieve
Page 23 of 27
Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
low latency and ultra-high reliability, it is essential to develop powerful high-end pro-
cessors that consume low power.
Pre‑emptive Scheduling inMassive Connectivity
In the wireless communication, a network node assigns the radio resources to other
nodes as per their priorities [111]. However, in the case of 6G wireless networks,
where a massive number of devices will be connected to each other, setting the prior-
ity level for all these devices and maintaining the latency and packet loss requirements
of 6G will be quite challenging. In order to carry out such pre-empted communica-
tion on the 6G wireless network, which is another open research field, some appropri-
ate algorithms would be required.
Seamless coexistence ofmultiple RATs
With multiple interfaces, 6G can incorporate multiple RATs. is ensures that 6G will
coexist with and interoperate with other technologies, such as Wi-Fi, Bluetooth, net-
works of ad hoc sensors, and IoTs, etc. For the change in the user’s radio environment,
the air interface can dynamically change. It is still an open challenge to develop scalable
techniques that guarantee interoperability while meeting the KPI requirements of 6G.
Security andprivacy
In the last few years, the number of IoT devices has grown exponentially. ese devices
include personal IoT, health care IoT, and industrial IoT, which are connected to form a
mesh network. 6G is expected to be an enabler for large-scale cyber operations including
IoT applications. As IoT devices are connected to the internet, broad-scale distributed
denial of service (DDoS) attacks could be more common. is large-scale DDoS attack
will serve as an enabler in a 6G IoT system that can lead to security, privacy, and trust
issues in the network. is is therefore an open research challenge for 6G networks, too.
Conclusion
Technology has a great impact on the lifestyle of human beings. Wireless technolo-
gies have revolutionized businesses, living standards, infrastructure, and many other
aspects of human life. Mankind is in a constant struggle to find elegant solutions to vari-
ous problems and is in search of new avenues to progress. is desire of mankind has
evolved wireless communication from 1G to 5G. However, this development has not
stopped here. e researchers around the world are working hard for the development
of 6G communication network, which is expected to be rolled out by 2030.
In this paper, we covered various aspects of 6G wireless networks with different per-
spectives. We provided a vision for B5G/6G communications, 6G network architecture,
KPI requirements, key enabling technologies, their use-cases, and network dimensions
that will landmark the next generation communication systems. Furthermore, a way out
is discussed how these potential technologies will meet the KPI requirements for these
systems. Finally, the opportunities and research challenges such as hardware complexity,
variable radio resource allocation, pre-emptive scheduling, power efficiency, the coex-
istence of multiple RATs, and security, privacy and trust issues for these technologies
Page 24 of 27
Akhtaretal. Hum. Cent. Comput. Inf. Sci. (2020) 10:53
on the way to the commercialization of next-generation communication networks are
presented.
Acknowledgements
Not applicable.
Authors’ contributions
MWA, SAH, RG suggested and conceived the core conception of this research work. RG presented the case study, find-
ings and discussion. SG, MSH and HJ defined the overall organization of the manuscript. MSH has carried out thorough
oversight of this work. The final manuscript was read and accepted by all contributors. All authors read and approved the
final manuscript.
Funding
This work was supported in part by the Researchers Supporting Project number (RSP-2020/32), King Saud University,
Riyadh, Saudi Arabia and in part by the Incheon National University Research Grant in 2020.
Availability of data and materials
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Author details
1 School of Electrical Engineering and Computer Science (SEECS), National University of Sciences and Technology
(NUST), Islamabad, Pakistan. 2 Wi-Fi division of Broadcom, San Jose, CA, USA. 3 Department of Information and Telecom-
munication Engineering, Incheon National University, Incheon 22012, Korea. 4 Electrical Engineering Department, École
de Technologie Supérieure, Montréal, QC H3C 1K3, Canada. 5 Department of Software Engineering, College of Computer
and Information Sciences, King Saud University, Riyadh 11543, Saudi Arabia.
Received: 8 September 2020 Accepted: 5 December 2020
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