A Survey on the 5th Generation of Mobile Communications: Scope, Technologies and Challenges


1

A Survey on the 5th Generation of Mobile Communications:
Scope, Technologies and Challenges
M. Sousaacd, P. Vieirabd, M. P. Queluzad, A. Rodriguesad

aDepartamento de Engenharia Electrotécnica e de Computadores, Instituto Superior Técnico, Portugal
bDepartamento de Engenharia Electrónica e Telecomunicações e de Computadores, Instituto Superior de

Engenharia de Lisboa, Portugal
cCELFINET, Consultoria em Telecomunicações, Lda.

dInstituto de Telecomunicações, Lisboa, Portugal
marco.sousa@celfinet.com pvieira@deetc.isel.pt [paula.queluz, ar]@lx.it.pt

Abstract— The 5th Generation (5G) of mobile communications
will impact the costumers Quality of Experience (QoE) by ad-
dressing the current mobile networks usage trends and providing
the technological foundation for new and emerging services.
Additionally, 5G may provide a unified mobile communication
platform, with multiple purposes, leveraging industries, services
and economic sectors. In this paper, a 5G tutorial is presented,
including the 5G drivers, main use cases, vertical markets and
a current status of the standardization process. Furthermore,
several 5G key enabling technologies are presented, concerning
the Radio Access Network (RAN) and Core Network (CN)
perspectives. Finally, a brief outline over the Internet of Things
(IoT) concept and current research topics is presented.

Keywords: 5G, eMBB, mMTC, URLLC, SDN, NFV,
mMIMO, mWaves, MEC.

I. INTRODUCTION

Mobile wireless communication networks have been expe-
riencing enormous advances throughout its successive gen-
erations. Starting with 1st Generation (1G), which was an
analog technology only for voice calls in the 1980s, industry
moved on to 2nd Generation (2G), that entered into the
digital domain in the 1990s; besides voice, it also supported
Short Message Services (SMSs). The breakthrough of the 3rd

Generation (3G) was the global access to mobile data services,
video streaming, web browsing, e-mail, etc, in the 2000s.
The introduction of the 4th Generation (4G) eliminated the
circuit switching domain to embrace an all Internet Protocol
(IP) network, enhancing data services, in the 2010s. Finally,
the 5th Generation (5G) will be disruptive in the sense that
while previous generations had the purpose of connecting
people, 5G will connect not only people but also the physical
world (things). Also, the 5G will provide the technological
foundation for a wide range of new applications and services,
headed for an increasingly connected world.

In the economy field, the concept of General Purpose
Technologies (GPT), identifies technologies whose adoption
introduce changes that redefine work processes as well as
the rules of competitive economic advantages [1]; the printed
press, the Internet, and the computer, are a few winning
examples. According to [1] from IHS Markit, the 5G has
the potential to enter the exclusive group of GPTs, as a
technological breakthrough.

In this paper, a state of the art about the 5G is presented.
As mentioned, 5G is significantly different from previous
generations and will have a significant impact in society
and economy. In that sense, besides the 5G technological
foundations, also the new services/applications and economic
sectors, which are likely to adopt or benefit from the 5G, will
be considered.

This paper is organized as follows. In Section II, the
development scope of the 5G is presented; it includes the
technology drivers, the main 5G use cases and the regulatory
perspective of 5G. In Section III, an overview of possible
technologies to facilitate the 5G networks, is presented; it
includes key technologies for both Radio Access Network
(RAN) and Core Network (CN). Section IV, is dedicated
to the Internet of Things (IoT), in light of being one key
difference between 5G and legacy networks. Finally, in Section
V conclusions are draw.

II. 5G SCOPE

This section provides a wide scope analysis of 5G networks,
starting with the main drivers for its development and foreseen
use cases. Since the Mobile Network Operators (MNOs)
business approach will be also transformed along with 5G
deployment, new vertical players are anticipated, such as
the automotive industry, which has shown a strong interest
in taking advantage of the upcoming networks. The efforts
with standardization and regulation, from entities such as the
3rd Generation Partnership Project (3GPP) and International
Telecommunication Union (ITU), are crucial for the first 5G
commercial deployments, and will be also overviewed in this
section.

A. 5G Drivers

The 5G networks drivers can be loosely classified as cos-
tumer or industry associated. With respect to mobile network
costumers, there are several key trends. Firstly, the number of
mobile subscriptions is growing at 6% annual rate [2], reaching
7.8 billion in the third quarter of 2017 (Q3), and the respective
grow rate for mobile broadband subscriptions is around 20%
year-on-year [2]. Besides the mobile subscriptions up rise
trend, the mobile data traffic generated by each subscriber is
also increasing. Latest statistics account 65% annual increase

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in mobile traffic between the 3rd quarter of 2016 and 2017 [2],
and the momentum is expected to continue and reach a 8-fold
increase in 2023. Currently, more than 50% of the mobile
traffic is video streaming [2], being the leading application in
traffic generation.

The 4G networks are not fully developed yet, for in-
stance Self-Organizing Networks (SON) features, as covered
in [3] [4] can improve network performance, also MNOs are
starting to evolve their Long Term Evolution (LTE) networks
to Long Term Evolution - Advanced (LTE-A), enhancing
the 4G network performance. Nonetheless, even considering
such solutions, 4G networks will not be able to cope with
the subscribers increasing demand. Furthermore, considering
services such as video streaming, where the uprising trend
in video resolution will generate more content in 4K or even
8K, or considering the appearance of new services, like virtual
reality and augmented reality, its feasibility with the current
mobile networks is limited. Overall, such services require high
throughputs, and constitute the first main 5G use case, the
Enhanced Mobile Broadband (eMBB) [5].

On another perspective, the fourth industrial revolution
known as “Industry 4.0” is starting. According to [6], Industry
4.0 is defined as the digitalization process of the manufacturing
sector; it consists on embedding sensors for monitoring all
products and equipment, using cyber physical systems, and
in applying cognitive analysis to all collected data. From the
technological point of view, 5G will be an important facilitator
in the full realization of the Industry 4.0 concept. Accordingly,
the second main use case, defined by ITU, is the Massive
Machine Type Communications (mMTC) [5]. In essence, it
is characterized by a large number of connected devices,
collecting and sending non-delay-sensitive data [5]; it can also
be seen as one of the applications of IoT [7].

Lastly, ITU also defined the Ultra-Reliable Low Latency
Communications (URLLC) [5] requirements. This will es-
tablish the technological foundations for the self-driving [8]
endeavor. There is a strong economic interest from the automo-
tive industry in developing not only the autonomous vehicles,
but also a connected and intelligent infrastructure. It requires
both Vehicle-to-Vehicle (V2V) communications and Vehicle-
to-Infrastructure (V2I). Along this way, the transmitted data is
as time sensitive as intolerant to failures and errors. Satisfying
the above mentioned requisites entails in the development of
wireless communication systems with high availability, ultra
reliable and with very low latency. Similarly to the automotive
industry, other sectors may also develop new services based
on URLLC, such as Wireless Tele Surgery (WTS) [9] in the
health care sector.

B. Use Cases

Figure 1 presents the main 5G applications in a three
dimensional space, where each dimension corresponds to one
of the main 5G requirements (eMBB, mMTC and URLLC).

These requirements are deeply analyzed in the following
subsections.

1) Enhanced Mobile Broadband: The eMBB essentially
deals with the human centric use cases, aiming to deliver

Fig. 1: Usage scenarios of IMT for 2020 and beyond [5].

multimedia content and data services. It depends on the
ability to provide high throughputs, especially when con-
sidering high quality video streaming or 3D video services.
In a recent survey [10], the authors identified that network
throughput and security are the factors that mostly condition
the subscribers expectations about the upcoming 5G networks
which is aligned with the eMBB requirements. In [11], the
authors classified eMBB as the first 5G “killer app”, based
on a costumer survey where the experienced bottlenecks, of
smartphone users, were identified as one of the factors that
most impact the Quality of Experience (QoE).

ITU has defined minimum requirements for the main net-
work capabilities [12]. Nonetheless, depending on the usage
scenario, some capabilities are more relevant than others. This
relative importance is depicted in Figure 2.

Fig. 2: Relative importance of key capabilities in different
usage scenarios [5].

Considering the eMBB, the key capabilities are: network
energy efficiency, area traffic capacity, peak data rate, user ex-
perienced data rate, spectrum efficiency and mobility. In [11],
and considering the RAN, the authors identified three pillars to
address the requirements of eMBB, densify networks, deliver
higher spectral efficiency and the usage of new spectrum
bands. In this matter, the development and standardization of
the 5G New Radio (NR), that is an ongoing process, will
provide the technology to deliver the performance require-

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ments for eMBB. The main key aspects of the 5G NR are
the shared access scheme, Ortoghonal Frequency Division
Multiplexing (OFDM) based or Non-Orthogonal Multiple Ac-
cess (NOMA), new system architectures enabling Cloud Radio
Access Network (C-RAN) and network slicing, new spatial-
domain processing techniques including Massive Multiple-
Input Multiple-Output (mMIMO) and 3D beamforming, and
also the use of Millimeter Wave (mmWave) bands.

2) Massive Machine Type Communications: The services
belonging to the mMTC are such that machine-type devices
are used for monitoring, sensing and metering. On a 5G per-
spective, the network is expected to support a large number of
these machine-type devices, typically requiring low throughput
and sparse communications. Also, it is required to support a
high connection density of these devices [13]. Basically, 5G
mMTC encompasses the IoT use cases which are non delay-
sensitive, using a standardized technological solution. The
3GPP group has already standardized the Narrowband Internet
of Things (NB-IOT), in LTE Release 13 and LTE Release 14,
to provide wide-area mMTC connectivity for IoT [14]. Besides
this licensed band standard, other proprietary solutions, such
as Sigfox and Lora, were developed in unlicensed bands [15].
Nonetheless, these solutions are struggling in a scenario where
the number of devices significantly overpass the resources. As
these solutions rely on orthogonal transmission principles, in
recent years non-orthogonal strategies have been also proposed
to accommodate more users than the more classical orthogonal
approaches [13].

The 5G eMBB and the mMTC require two completely
different communication system designs. Not only the eMBB
service category is heavily focused on the downlink com-
munication, while the mMTC service is focused on the
uplink, but also the eMBB requires high packet sizes and
throughputs, whereas the mMTC requires low values of these
parameters [16]. Consequently, the mMTC advocates a set of
technologies that are quite different from those of the eMBB
use case. The first main difference is, as mentioned before, the
medium access scheme, in order to support the highest number
of connected devices. While the orthogonal medium access
tightly sets the available resources according to the number of
supported users, a non-orthogonal medium access allows some
degree of resources overloading [16]. Moreover, the grant-
based access, used in LTE, requires a good prediction of uplink
requests and additional signaling, which is not ideal for the
mMTC scenario. In that sense, a grant-free solution is expected
to enhance the requirements feasibility of mMTC [16]. Both
solutions imply a complexity increase from the base station
in order to simplify the devices complexity and achieve the
stipulated requirements. Technologies such as Sparse Code
Multiple Access (SCMA), Compressed Sensing based Multi
User Detection (CS-MUD) and Continuous Phase Modulation
(CPM) can be strong candidates to enable massive access.

3) Ultra-reliable and Low Latency Communications: The
URLLC supports the applications that are latency sensitive
as remote control and autonomous driving [17]. Another
emerging application is tactile internet [18]; it allows humans
to control real and virtual objects wirelessly, and hence, equiv-
alent to human touch, visual and auditive perceptions would

be transmitted seamlessly via data networks. This application
requires 1 ms end-to-end latency [19]. Other services for 5G
URLLC require latencies in the range of 1-10 ms. Currently,
LTE networks are characterized by latencies in the range of
30 to 100 ms [13]. This end-to-end latency values are due
to the best-effort policies, typically used in the backbone
network. In order to comply with the latency requirements
of the 5G URLLC, changes have to be conducted not only
in the backbone network but also in the RAN. The use
of Software Defined Networks (SDNs), Network Function
Virtualization (NFV), and the concept of network slicing,
can establish dedicated connections for URLLC services [17].
Likewise, the use of Multi-Access Edge Computing (MEC)
can reduce the latency even more [20]. On the RAN, given
that a large portion of the latency is introduced by the control
signaling [13], the communication overhead for URLLC has to
be reduced. To accomplish this, the packet and frame structure,
and the scheduling schemes, have to be revisited [17]. The
use of polar codes for large-sized packet and of Sparse Vector
Coding (SVC) for small-sized ones are technological enablers
to achieve the latency requirements.

C. New Players

Even though the number of mobile subscribers has been
rising, the MNOs revenues have been flatting out in the past
years [21]. With the anticipated capabilities of 5G, MNOs can
achieve a much larger growth, addressing key challenges in
digitalization of manufacturing, automotive and other indus-
tries, also known as vertical markets. In this ecosystem, MNOs
can become, besides network developers, service enablers or
even service creators [21]. In this new reality, the role of
MNOs, might evolve from Business-to-Consumer (B2C) to
Business-to-Business (B2B) providers. In the following text,
an overview of main vertical markets, in a 5G perspective, is
presented.

1) Automotive: The automotive industries have been adopt-
ing several connectivity technologies pursuing the long term
goal of autonomous driving. In that sense, the automotive
industry is clearly interested in the possibilities that 5G might
enable. The 5G can improve the Vehicle-to-Everything (V2X)
communications [22] and also the in car “infotainment” [23].
Other new use cases such as Platooning [24] or teleoperated
vehicles [25] might be developed with the support of 5G
networks.

2) Manufacturing: Within the manufacturing industry, and
as pursued by the Industry 4.0, 5G networks will be able
to provide the underlying unified communication platform to
fulfill the digital transformation [26]. The 5G can be a key
enabler for remote assistance and robot control, logistics track-
ing or process automation within factories [23]. Throughout,
efficiency improvements and automation, all over the supply
chain and product’s life cycle, are expected.

3) Agriculture: Even more traditional sectors, such as agri-
culture, are undertaking profound technological innovations.
With IoT, agriculture can move to smart farming and precision
agriculture [23]. The baseline is to monitor crop yields,
moisture levels and/or terrain, providing more data to support

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assertive farming decisions. The 5G can provide a robust
network for IoT and also for remote control of the farming
machinery [23].

4) Energy and Utilities: Regarding the energy and utilities
environment, the energy industry is facing some challenges;
the increased electricity consumption associated with some
degree of uncertainty in modeling the demand, and considering
several sources of energy generation (renewable sources),
contribute with additional threats. In this complex scenario,
emerging concepts as smart metering and smart grids [27],
have been investigated. The smart metering can be considered
part of the mMTC applications whereas the smart grid concept
might be more challenging. The smart grid concept requires
communication between sensors, control systems, energy gen-
eration and storage to monitor and to optimize the grid in real-
time. The 5G can support this use case, specially where fiber
based access is not cost effective [28].

D. Regulation

The regularization and the full standardization of 5G is
a lengthy process, involving several entities and organiza-
tions, private and public ones. Around 2014, the International
Telecommunication Union Radiocommunication Sector (ITU-
R) started working in the definition towards the 5G technology
performance requirements, as outline in Figure 3.

Fig. 3: Timeline for IMT-2020 in ITU-R [29].

Within ITU-R, the 5G is known as International Mobile
Telecommunications - 2020 (IMT-2020). In 2016, ITU-R
produced the first draft of the IMT-2020 performance require-
ments. The submitted proposals, for the new radio interfaces,
to be included in IMT-2020 specification, will be evaluated by
independent external groups. The whole process is expected to
be due by 2020, with the approval of the specifications [29].

Meanwhile, the 3GPP is developing its proposal for the
IMT-2020 call from ITU-R. The final specifications for the
IMT-2020 are planned to be completed with Release 16, by
the end of 2019, as shown in Figure 4.

The 3GPP group has released an early drop of Release 15
containing the Non-Standalone (NSA) 5G radio specifications.
The full Release 15 will include the standalone version of
the 5G NR by mid 2018. While the Release 15 focus on the
eMBB, Release 16 is expected to evolve more in depth the
mMTC and the URLLC specifications.

Fig. 4: 3GPP Timeline towards 5G [30].

III. TECHNOLOGIES

In the previous section, the 5G environment and the three
major use cases were considered. Several technologies were
identified as key enablers to meet the 5G requirements. In
this section, these technologies are presented considering RAN
and CN domains, respectively. Moreover, the different network
architectures that are being developed within the 3GPP group,
are also considered.

A. Architecture

Regarding the upcoming 5G network architecture, there are
two distinct architecture approaches: the NSA 5G architec-
ture and the standalone 5G architecture. The 3GPP group,
in a early drop version of Release 15, focused their effort
mainly towards the specification of the NSA 5G network. The
complete Release 15 should include also the standalone 5G
architecture specification. The left side of Figure 5 presents the
NSA architecture, that should be used on the first commercial
deployments of 5G; the right side of the Figure 5 displays the
standalone option for 5G.

Fig. 5: Proposed 5G architectures in 3GPP Release 15 [31].

According to the specifications, the NSA 5G architecture,
should have a 5G Base Station (BS) anchored in a LTE
network. A User Equipment (UE) is expected to be connected
to the LTE BS, using this link for user and control plane, and
while connected with a 5G BS for user plane only. Also, the
5G BS is connected with the LTE Evolved Packet Core (EPC).
Considering the standalone option, the 5G RAN is connected

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only with the 5G Core Network (5G-CN) providing both user
and control planes, forming a full 5G network.

B. Radio Access Network

Taking into account the 5G RAN, there are several expected
evolutions compared with current networks, that are described
next.

1) Massive MIMO: Traditional Multiple-Input Multiple-
Output (MIMO) systems, improve the Signal-to-Noise Ratio
(SNR) in uplink due to the diversity gain, mitigating the fading
effects and increasing capacity due to the achieved spatial
multiplexing gain [32]. There are two major MIMO types:
Single-User MIMO (SU-MIMO) and Multi-User MIMO (MU-
MIMO). Whereas SU-MIMO allocates the time-frequency
resources to a single user, MU-MIMO simultaneously serves
several users in the same time-frequency resource using beam-
forming [33]. Finally, mMIMO is a form of MU-MIMO [33],
where the number of BS antennas is much larger [34] than in
MU-MIMO. The MU-MIMO requires a highly reliable Chan-
nel State Information (CSI), which is unlikely and complex
in practical scenarios [32]. Additionally, in [35] the authors
showed that when considering a large number of antennas at
the BS MU-MIMO allows the simplest sort of precoding on
the forward link and processing on the reverse link. Thus,
mMIMO deliver high throughputs (high spectral efficiency)
reliably, both in the uplink and downlink channels, and in
fast-changing propagation environments, without the effects
of uncorrelated noise and fast fading. It only remains the
inter-cellular interference due to pilot contamination [35].
Even though, work is being developed to mitigate the pi-
lot contamination using: protocol based methods [36], blind
methods [37], precoding [38], Genetic Algorithm (GA) based
allocation scheme [39] or the use of dual pilot sequences [40].
Hence, mMIMO will be a key enabler for the 5G use cases.
Moreover, combining the high antenna gains (mMIMO) with
large available bandwidths (mmWave), 5G network throughput
barriers can be pushed even further.

2) Millimeter Waves: The limited available spectrum, and
its cost, have always been a concern for MNOs. In that sense,
efforts such as spectrum refarming, through the re-purposing
of the terrestrial TV spectrum [34], or by refarming the 2G
bands to other technologies, have been implemented. Also,
spectrum sharing techniques [41] [42] have been proposed.
Nonetheless, some open issues remain to be solved [34],
as how to increase the available bandwidth at microwave
frequencies. Alternatively, there is a great available bandwidth
at the mmWave, ranging from 3 to 300 MHz [34]. Due to
the associated high pathloss for higher frequencies, the use
of mmWave towards 5G networks was initially considered
for short-range indoor locations [43]. More recently, it has
been tested in outdoor Non-Line-of-Sight (NLoS) environ-
ments, with satisfactory results [44] [45]. Moreover, combin-
ing mmWave with other techniques, such as beamforming, can
enhance the outdoor mmWave performance [46].

Besides some regulatory constraints, key technical con-
straints prevent the use of mmWaves. The high pathloss, the as-
sumption of needed Line-of-Sight (LoS), the infeasible nature

of some hardware components due to technical limitations and
the high Doppler shift, remain as key challenges [47]. More
recently, all these challenges have been subject of important
developments.

Regarding the high pathloss, it can be mitigated with
the use of smart antennas, with high gains [45] [48]. The
LoS requirement can be solved by exploiting the multipath
reflections [45]. Considering the hardware limitations, new
antenna array designs have been proposed [49], but there
are still some challenges, as the linear relationship between
power consumption and the sampling rate, in the analog to
digital converters, which is even more critical at millimeter
bands [49]. Finally, the Doppler shift is also mitigated when
considering directional antennas [48].

Aside from the mmWave applications for the RAN, back-
haul and relay solutions [50] are also available.

3) Others: Some other 5G RAN technologies, not included
in the previous items, can be considered. The RAN random
access scheme proposed in the 3GPP Release 15, is OFDM
based. Nonetheless, new waveform candidates are expected
in future releases. For instance, non-orthogonal waveform
enables higher spectral-efficiency compared with the orthog-
onal ones [51]. Some of the non-orthogonal access schemes
are the NOMA [52], the SCMA [53], the Multi-user Shared
Access (MUSA) [54], the Pattern Division Multiple Access
(PDMA) and Successive Interference Cancellation Amenable
Multiple Access (SAMA) [55]. All these schemes achieve
higher throughputs, or spectral-efficiencies, than Orthogo-
nal Frequency-Division Multiple Access (OFDMA) based
schemes.

Other key technology towards 5G is Full-Duplex (FD)
wireless systems, which enables a radio transceiver to receive
and transmit simultaneously in the same frequency and time
frame [56]. It can potentially double the system capacity
and increase the spectrum utilization efficiency. The main
challenge of these systems is Self-Interference (SI) miti-
gation [57] [58]; in fact, although feasible, some practical
imperfections still limit its performance [56].

Aiming to target the spectrum shortage problem and the
problem of spectrum under-utilization (spatial and/or tempo-
ral), the Dynamic Spectrum Sharing (DSS) concept has been
investigated [59].

Another, key technology towards 5G is network slicing [60].
The concept was initially proposed for the 5G-CN [61] and
was extended for End-to-End (E2E) network slicing. In [61],
the authors evaluate the impact of network slicing in the RAN,
namely traffic differentiation, efficient management mechanics
to setup and operate new slices, among others.

C. Core Network

Moving on to the 5G-CN, there are also new technologies
and concepts being introduced.

1) Cloud Radio Access Network: The current RAN ar-
chitecture in mobile networks contributes to the network
resources underutilization [62], in the sense that the network
load at different locations and time instances varies due to the
user movements; hence, some BSs can be overloaded while

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others are idle (e.g., office locations vs. residential areas during
the day). Consequently, the BS processing power is being
underutilized in some BSs and used at the maximum in other
BSs [63]. To overcome this challenge, the concept of C-RAN
was proposed [64], which consists in physically separate the
Baseband Units (BBUs) from the Remote Radio Units (RRUs),
by centralizing the BBUs into a shared BBU Pool.

Under a C-RAN architecture, depicted in Figure 6, all
computational resources are concentrated in a cloud platform
which includes the BBU Pool; the BS contains only the
RRU to receive and transmit the radio signals to the cloud
platform [62].

Fig. 6: Schematic of C-RAN architecture [65].

The BBU pool will serve a particular area providing all
the processing to the macro and small cells, allowing BSs
to share computational resources. The distance between the
cloud platform and the BSs can be up to 40 km where the
distance limitation comes from the propagation delay [64].
The fronthaul communications are analyzed in dept in [66].

Another advantage of the C-RAN architecture is the network
energy efficiency [64], as a result of a more efficient use of
the computational resources. Additionally, as the BSs became
less complex, containing only the RRU, the deployment and
maintenance cost of new BS is expected to drop [64]. The C-
RAN concept will take a key role towards the 5G networks.

2) Multi-Access Edge Computing: Another important con-
cept towards 5G is the MEC. Recent years have seen a
paradigm shift towards decentralized computing and cloud
platforms, with its realization in MEC, in mobile commu-
nications. This aims to push computing, storage and control
resources to the edges of the network, thus near the final
users. In the MEC architecture, presented in Figure 7, the
latency experienced by the users is reduced, while enabling
a more efficient usage of the network backhaul and of the
core network [67].

MEC results from a strong synergy between Information

Fig. 7: Mobile edge computing architecture [68].

Technology (IT) and mobile networks domains, which is a
current trend, in the sector. Thus, the MEC, can leverage
the development of a wide range of new services and ap-
plications, especially if information such as contextual infor-
mation and location awareness, is used to deliver, in real-
time, a customized mobile broadband experience to users [69].
Also, as MEC offers an open radio network edge platform,
MNOs can monetize it, by allowing third-parties to access
the storage and processing capabilities; this may facilitate
service enhancements, or even new services, towards not
only mobile subscribers but also to enterprises and vertical
segments. This should be a secure cloud platform that, through
Application Programming Interfaces (APIs), shares access to
third-parties [69].

Similar to MEC, there are several related concepts, such as
Mobile Cloud Computing (MCC), Local Cloud, Cloudlet and
Fog Computing.

MCC takes advantage of mobile computing and cloud
computing to enable virtualized computing and storage re-
sources [68], for mobile end-users. It provides all resource-
intensive computing executed in clouds without a device with
a powerful configuration. Also, it extends the battery life and
storage of the end-users devices.

Local Cloud is managed by internal or external sources and
are intended to provide services exclusively to a group or
institution [68]. In [70], the authors proposed a cooperative
scheduling algorithm to manage the local cloud resources
together with Internet cloud resources.

Cloudlet is an emerging paradigm, where a small-box data
center is deployed at one wireless hop away from mobile
devices [68]. It is the middle entity between the mobile device
and the cloud, with data routing and security functionality [71].
Thus, cloudlet aims latency and resource sensitive mobile
applications. It can be deployed in public places such as
hospitals, shopping centers, etc.

Fog Computing is also known as edge computing, sup-
porting ubiquitous connected devices [68]. In this concept,
processing is carried out in the local area network or in the
IoT gateway. In fog computing, one could retrieve data from
several sensors and act accordingly, without having to access
a remote cloud platform [68].

As a concluding remark, MEC is highly complementary
with C-RAN [72]. Not only the collocation of both technolo-
gies allows a more cost effective investment for MNOs but
also the MEC APIs can provide access to RAN information

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which, otherwise, would not be trivial, enabling other services.
3) Software Defined Networks/Network Function Virtualiza-

tion: MNOs have high expectations on these two technologies,
SDN and NFV, as they promise to reduce network costs,
improve the network scalability and flexibility and provide the
base ground for a more dynamic and efficient network.

Firstly, SDN is a centralized networking paradigm where
there is a key separation between control and user
data [73] [74], as seen in Figure 8.

Fig. 8: SDN architecture overview [73].

Moreover, as the network control functions are centralized
in one or more SDN controllers, it enables to simplify the
data forwarding of applications and network services [73].
The communication between control and data planes is man-
aged through a communication protocol, being OpenFlow the
most used [75]. This is an open source protocol which is
controlled by Open Networking Foundation (ONF) [76], and
allows to access the flow tables [75] that control the traffic
routing in switches and routers. Nonetheless, other protocols
exist, such as the Internet Engineering Task Force (IETF)
ForCES [77] protocol. As already stated, a key element in a
SDN architecture is the SDN controller. It should be not only
a platform for deploying SDN applications but also a SDN
application development environment [78]. There are several
controller implementations, such as the OpenDayLight [78]
or the ONOS [79]. Overall, SDN applications interact with
the SDN controllers using, as interfaces, Representational
State Transfer (REST) and JavaScript Object Notation (JSON);
the SDN controller uses communication protocols such as
OpenFlow [75].

Thus, SDN presents itself as an alternative to standardized
networking protocols, by providing the same role as a central-
ized software application.

Regarding the NFV [80], it is basically the process of
replacing dedicated hardware with software instances which
run on cloud environments or general purpose servers [73].
Within this concept, each conventional Network Function (NF)
runs in a Virtual Machine (VM) or even in multiple VMs. Each
implementation of a NF, using VMs, is called Virtual Network
Function (VNF). These instances are deployed and executed
in a Network Function Virtualization Infrastructure (NFVI).
This is composed by physical resources (computing, storage
and networking) which are used through a virtualization layer

by the VNFs. Ultimately, and using as example the LTE
EPC, each core entity (e.g., Mobility Management Entity
(MME), Serving Gateway (S-GW), etc.) could be virtualized
as VNFs, where each type of VNF, by forming a common
pool, can be scaled independently and according with the
network requirements and resources [73]. Towards 5G, not
only NFV but also SDN will be key technologies. Many
components of a 5G network can be turned into VNFs,
allowing accelerated service deployment, when compared to
the traditional hardware deployment, network flexibility, scal-
ability and capacity. Above all, VNFs enable network slicing,
where the same physical infrastructure can be used to provide
multiple and independent logical networks, where the users
experience similar conditions as having a dedicated physical
infrastructure [81].

Additionally, even though SDN and NFV are independent
technologies, both can be enhanced when used together due
to their complementary traits. Explicitly, NFV can serve an
SDN architecture by virtualizing components such as the SDN
controllers or the forwarding data entities. Also, SDN can
serve NFV by allowing programmable and dynamic network
connectivity between VNFs [73]. This synergy between SDN
and NFV is called Software Defined Network Virtualization
(SDNV) [82], and is an emerging research area. Both SDN and
NFV have the potential to redefine the evolution of network
architectures and the potential to be key enablers for the 5G
networks.

IV. INTERNET OF THINGS

Although IoT [7] has been an active research topic in the
past years, the concept of a network of smart devices has
been around since the mid 80s. Concretely, Mark Weiser’s
paper about ubiquitous computing [83], in 1991, set some
cornerstones of the actual IoT concept.

The IoT concept of a network of connected physical objects,
cyber-systems and sensors everywhere, combined with recent
technological advances, opens up the range of IoT applications
in different environments, which are being proposed and
developed. Besides, the applications mentioned in Section
II-C, the concept of smart home [84] and the smart cities
are other examples of IoT applications. Extensive work has
been developed in creating applications towards enhancing the
user lifestyle, especially through the retrieval and analysis of
relevant city information [85]. Also, the concepts of Intelligent
Transportation System (ITS) and smart healthcare have been
receiving important contributions by the IoT community [86].

A. Design Requirements

To fully implement the proposed IoT use cases, including
the 5G mMTC and URLLC scenarios, there are some main key
design principles. A low device (e.g., a IoT sensor) cost will be
a key enabler for mass-market IoT applications within the 5G
mMTC use case. The IoT network deployment cost, including
both Capital Expenditure (CapEx) and Operating Expense
(OpEx) must be minimized in order to provide massive IoT
through a feasible economic perspective [86]. In this scenario,

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the usage of cellular networks, compared to dedicated Low-
Power Wide-Area (LPWA) networks, might be preferred. Also,
a key point is energy efficiency, mainly on the IoT device
side. Considering that these devices are battery powered and
are expected to have a time span of years, without human
intervention, energy efficiency is crucial. Thus, the develop-
ment of lightweight protocols and scheduling optimization are
important research areas [86] [87]. Other design principle,
specially towards smart metering, is the coverage requirement.
Some smart meter locations are in deep indoor scenarios,
which require enhanced coverage [88]. Another key topic in
the IoT design is the security and privacy of personal data [89].
In [89], the author describes extensively the main concerns in
providing security in a IoT environment.

B. Architecture
The IoT generic architecture is organized in three layers:

the application layer, the transport layer and the sensing layer
[90]. The sensing layer is composed by all cyber-physical
objects and sensors. All these devices may collect any kind
of data, which is then delivered to the application layer
through the transport layer. In the application layer, the data is
aggregated and analyzed using intelligent computing, in order
to extract valuable information or to trigger actions towards
the sensing layer devices [90]. A general IoT architecture is
presented in Figure 9.

Fig. 9: General Architecture of IoT [90].

Nonetheless, since it is expected that IoT networks will con-
tain millions of devices, large scale IoT (scalable and flexible
architecture) is required. Thus, in [91] the authors proposed a
self-configuration peer-to-peer architecture. This architecture
type, provides automatic discovery mechanisms, enabling the
absence of human intervention in the configuration phase.

Other architectures have been proposed, such as the
SDN [92] and the cloud computing based [93].

C. Communication Technologies
IoT networks have been widely investigated on the last

years, resulting in several IoT communication technologies,

which solve the transport layer on the IoT general architecture.
There are three types of technologies: long-range, short-range
and cellular networks [86]. Long-range networks, or LPWA
technologies, are among the most popular IoT approaches. One
of them is LoRa [94], which is a physical layer protocol target-
ing low-cost, low-power and long-range communications [86].
LoRa architecture is a star shaped network where each device
has a direct connection with a LoRa gateway.

Also in the long-range IoT, Sigfox [95] technol-
ogy offers end-to-end IoT connectivity. Sigfox relies on
Ultra-Narrowband (UNB) communication technologies, well
adapted to a wide range of conventional IoT use cases, that
rely on sparse and low throughput communications require-
ments [96].

Others, as DASH7 [97] or Weightless [98] are also promis-
ing long-range solutions.

On the short-range IoT, one of the most used is the
Bluetooth [99]. Even though Bluetooth was standardized by
the Institute of Electrical and Electronics Engineers (IEEE)
as a communication technology for replacing wires in mobile
devices, it has evolved to other applications, especially in IoT
smart home. The main drawback of Bluetooth is the restriction
of only one-to-one communication. In that sense, the Bluetooth
Smart Mesh working group was proposed to standardize a new
mesh architecture aimed at IoT use cases.

ZigBee, which is developed on top of the physical and
data link layers defined in IEEE 802.15.4, is also a short-
range communication base for IoT [86]. The main difference
of ZigBee compared with Bluetooth, is the range. Whereas
Bluetooth operates around a 50 meters range, ZigBee can
provide service through hundreds of meters.

Also in the short-range communication domain the Wireless
Local-Area Network (WLAN) technology is widely used.
Initially, it was designed to support high bandwidth com-
munications between devices. As it does not verifies the
modern IoT network requirements, IEEE proposed a low
power WLAN, IEEE 802.11ah [100], as an amendment to
the legacy standard. WLAN based IoT applications include
parking metering, autonomous lightning, smart security, smart
home thermostats, etc., [101].

While IoT essentially aims to interconnect a great number
of devices and extract value from all collected data, a new
paradigm has recently emerged to enhance even more IoT,
called Cognitive Internet of Things (CIOT) [102]. The CIOT
arises from the application of cognitive abilities to the IoT
network. Within the scope of CIOT, heterogeneous smart
objects inter-operate through a cognitive centralized entity.
This adds an intelligent decision making layer to conventional
IoTs networks [102]. Compared with IoT, CIOT is a new and
hot research topic.

V. CONCLUSION

The next generation of mobile communications, 5G, is
around the corner. Besides MNOs, several economic sectors
glimpse at 5G as a key promoter for socio-economic develop-
ment. Clearly, the mobile network costumers are enthusiastic
concerning the upcoming 5G networks and associated services.

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The evolution of the current mobile networks to 5G is
expected to be gradual, minimizing the CapEx for MNOs. The
first 5G commercial deployments are expected by the end of
2018, in a NSA solution, where 5G BSs are anchored in the
LTE EPC.

In this paper, apart from an overview of the 5G ecosystem,
several key technologies were pinpointed. Concerning the 5G
RAN, mMIMO and mmWave will be crucial to accomplish the
eMBB requirements. Nonetheless, these two topics are still
open research areas. In mMIMO systems, the channel esti-
mation techniques, pilot contamination and the rich scattering
environments dependence are still being investigated. Also, the
joint operation of mMIMO and mmWave is being explored.

The 5G-CN will constitute an advance of mobile core
networks, being empowered by several IT driven concepts. C-
RAN, MEC, SDN and NFV are candidate solutions heading
for the 5G-CN, where work is in motion to solve associated
open issues. Overall, these technologies are associated with
practical constraints, regarding system inter-operation, orches-
tration, resource management, flexibility and scalability. The
association of multiple technologies, from the ones mentioned,
is again a research area of importance.

Also, E2E network slicing is a promising solution towards
the development of the future 5G networks. As open chal-
lenges, dynamic slicing, end-to-end slice provisioning, slice
isolation, are front runners.

As a concluding remark, from the technological point of
view, 5G can be considered an evolution of LTE, specially in
the early 5G phase. From a socio-economic point of view, it
certainly can be seen as a revolution.

VI. ACKNOWLEDGEMENTS
The authors would like to thank FCT for the support by

the project UID/EEA/50008/2013. Moreover, our acknowl-
edgement concerning project MESMOQoE (n◦ 023110 -
16/SI/2016) supported by Norte Portugal Regional Opera-
tional Programme (NORTE 2020), under the PORTUGAL
2020 Partnership Agreement, through the European Regional
Development Fund (ERDF).

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