1. 1
5G: The Next Generation of Wireless Networks
Zhen-Yuan Bo, Communication Research Group, University of Toronto
Student Number: 999232762
Email: zhenyuan.bo@mail.utoronto.ca

Abstract—5G wireless networks are envisioned to
expand current network capacity and to support
connections for at least 100 billion devices with
speed up to 10 GB/s. With the advent of 5G
technologies, users will experience extremely low
latency and response time. The ultimate goal of 5G
is to realize networks that can provide zero-distance
connectivity between users and connected
machines. The technology vision of 5G is to design
a true wireless world that has not yet been achieved
by earlier generations. This paper first presents an
introduction to 5G technologies, and then highlights
key concepts of 5G, its features, its underlying
hardware, reviews its network architecture and
identifies possible research challenges of such
future networks. The last section concludes this
paper and leaves readers an extra room to think
beyond what has been done thus far.
Index Terms—5G, CDMA, SDN, UWB, MIMO,
Interference, M2M, D2D
I. INTRODUCTION
There has been a tremendous technical
breakthrough on mobile phones over the past few
decades, starting from one with a minuscule screen
and little processing power to a one with long battery
life, high resolution and palm-sized screen. The latter
one is commonly called ‘smart phone’. Its smartness
is illustrated through the usage of a variety of mobile
apps that in some ways can make users’
life better. The transformation from monochrome
device to smart model has also triggered the needs
for more sophisticated network technology. Upon
till now, there have been four generations of
network deployed to the public. One of major
reasons for upgrading one to the other is to
accommodate higher data rates to mobile users.
As the current 4G networks reaches its technical
bottleneck, engineers and scientists are turning
attention towards 5G technologies. Similar to 4G, 5G
stands for 5
th
Generation Mobile technology. While
meeting the demand for higher data rate, it is also
designed to be 1) significantly more efficient on
energy, resource utilization, and more cost effective
than today’s technology 2) able to support a variety of
network devices with various requirements, and 3)
capable of providing better scalability in terms of
number of connected devices and access points.
5G technologies are destined to bring a revolution
to the networks world. As such, many parts of
existing networks will be redesigned from scratch.
These include air-interface and RAN systems. The
purpose of doing so is to meet increasing demand
for massive capacity and ultra-fast network speeds.
As of now, network engineers around the globe still
do not have a consensus on what 5G will eventually
look like and are currently in their research stage.
However, one common belief shared among them is
that this next generation will consist of a number of
interconnected communication standards and
protocols, which will provide desired throughput
and user experiences as per the requirement of a
particular scenario.
In general, the capabilities of 5G technologies
must extend far beyond previous generations of

2. mobile communication. The realization of 5G will
help build the networked society in which individuals
will be granted unlimited access to information and
data can be shared with anyone at anytime and
anywhere. By individuals, the scope is no longer
limited to people. It could refer to ubiquitous
communication between connected devices and
applications. In this sense, 5G should not be
considered as a specific radio access technology any
longer. Instead, it provides an overall wireless-access
solution that addresses demands and more
complicated requirements beyond 2020. This is the
time point at which the 5G era begins.
II. KEY CONCEPTS OF 5G [1]
5G wireless networks will zone out any limitation
imposed by current and previous network
technologies in order to realize a real wireless world.
IPv4 will be replaced by IPv6 to support the
communications involved in 5G networks. Users
inside such communication environment can
simultaneously set up connections with multiple
wireless access technologies and freely move between
them without any restriction. Such simultaneous
connection is supported by cognitive radio
technology, which allows data to be transferred
concurrently over multiple paths. The concurrency is
the point of interest for this technology and is the
result of efficient use of spectrum. To ensure higher
data volume, it consistently looks for unused spectrum
and adapts the transmission scheme to the
requirements of different users. 5G, essentially, aims
to realize the integration of networks. In the future,
networks will be heterogeneous that consists of
multiple tiers. Due to such fact, one unified global
standard is recommended. This avoids possible
conflicts merely because of regional differences.
III. FEATURES OF 5G NETWORKS TECHNOLOGY
1) Heterogeneous Networks
The following diagram shows how
such networks look like.
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Figure 1: Heterogeneous Networks
i. Small Cells [2]
Size of cells has a direct impact on the data rate.
Intuitively speaking, in the smaller cells, number of
UEs will be largely reduced, which reduces the
interference and improves the quality of transmitted
data. In other words, when a communication
channel becomes less congested than before, data
transmission rate will be increased. Meanwhile,
smaller cells will trigger higher frequency reuse,
which increases the spectral efficiency. Also,
reducing the size of cells can be seen as a solution
to resolve some problems. For example, transmitters
whose power is not strong enough favors a lot on
the idea of deploying small cells as the transmission
distance will be greatly reduced. Similar to
transmitters, receivers may not always perform as
expected. Having smaller cells indoor can offload
some traffic from macro cells, which in turn
improves the quality of reception.
ii. Separation of User/Control Plane [3]
The decoupling of user and control plane is
currently being discussed to see if it is suitable for the
future 5G wireless networks. The idea behind is very
simple and easy to understand. UE will have
connections to two base stations at the same time, one
is located in a macro cell and the other is in a small
cell. The signal coming from the macro cell provides
connectivity using lower frequency bands, while
higher frequency bands are used to support
transportation of data in the small cell. The motivation
of this proposal is to save as much energy as possible
and to reduce any avoidable inter-cell

3. interference. In this scenario, the base station in a
macro cell is active all the time while the one in a
small cell can switch on and off depending on
whether there is data needs to be transported. Such
separation great improves overall network
performance and user experiences. More noticeably,
this separation scheme benefits users at cell edge by
improving their data throughput up to 70 percent
and reducing total energy consumption around 20
percent.
iii. Full-Duplex Communication [3]
FD communication scheme is expected to be
available in 5G networks. In such scheme, device is
capable of transmitting and receiving signals on the
same frequency band at the same time. It was
unachievable few years back as transmission and
reception happen simultaneously will incur self-
interference, which is very difficult to be minimized
and eliminated. Recently, the advancement on RF
interference cancellation techniques and digital
baseband technologies makes such technology
become true. Though it is still in its testing stage, it
is viewed as an alternative and feasible method to
address current issues in existing wireless networks,
including long end-to-end delay, low data rate, low
throughput and hidden terminals.
iv. Energy Harvesting [3]
Minimizing energy consumption is one of main
goals for 5G wireless networks. As most of wireless
devices are constrained by battery life, a cost effective
technique is needed to improve overall energy
efficiency of the network. One innovative method is to
harvest energy from energy sources. These sources
could be either natural or RF signals. Natural sources
may include solar and wind energy. However, natural
resources cannot provide a reliable energy supply to
UEs. In contrast, harvesting energy from RF signals is
more favorable, especially for those QoS-constrained
devices. The reason behind is that RF sources have
continuous and fixed electric supply. Such supply will
not be interfered with external forces and is static with
respect to time. In this sense, the amount of energy
harvested from RF sources will also tend to be fixed.
This ensures the
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continuous operation of UEs.
In addition to extract energy from RF signals,
obtaining information from the same RF input
signals is also possible and feasible. To implement
this scheme, two ideas have been proposed. First
idea is to design an antenna to perform time
switching, meaning periodically switch between
information decoding and energy harvesting
circuits. Second idea is to split the received signals
into two streams for information reception and
energy harvesting. As of now, there is no firm
answer as to which one is better. Ongoing research
efforts are underway to provide the best solution.
The following block diagram shows how the
energy from RF signal is harvested and transferred
to the load (i.e. UE).
Figure 2: Energy Harvester
v. Device to Device Communications [2]
This communication scheme is used to alleviate
and mitigate problems faced by highly dense
network. In this scheme, devices can talk to each
other directly without the assistance of base
station to route the information in between. One
attractive point of this scheme is that it can reduce
interference. In previous generations, this
technology is not available. Information has to be
routed through the base tower even though the
two UEs are close to each other. Such routing
strategy is extremely inefficient and adds
unnecessary traffic load to the base station. D2D
is the desirable way to work around the problem.
D2D has been utilized in some scenarios at this

4. point. For example, Bluetooth is an application that
allows two devices to communicate directly with
each other. The voice call in some cars is realized
using Bluetooth. Prior to setting up this feature, a
cellphone needs to have an exchange of information
with a particular application in the car.
Such exchange doesn’t involve any third party such
as base station. Since current D2D applications are
running over the unlicensed spectrum, they are not
very robust to interference. To massively implement
D2D communication, base station is still required to
provide connectivity in order to avoid intra-cell
interference.
2) Software Defined Cellular Networks [4]
Network virtualization will become one of the
main trends in 5G wireless networks. Software
Defined Network (SDN) has recently gathered its
momentum in the networking industry and will be
used to abstract low level networking functionality
into virtual services and resources. These resources
will be shared among different consumers (e.g.
service providers). There are several motivation
drivers to apply SDN to mobile networks. First, it
can help operators simplify their network
management. Second, it enables high resource
utilization, improves overall system performance
and provides new services with better quality-of-
service (QoS) to meet exponential traffic growth
envisaged for 5G networks.
With the virtualization of networks, SDN can
separate network services from underlying physical
infrastructure. Such physical resource is owned by
infrastructure provider (InP) in a virtualized
wireless network. InP leases the resources to mobile
virtual network operator (MVNO), which creates
virtual resources and assigns them to subscribers.
To MVNO, there is no need for them to know the
underneath physical resource architecture.
There are two types of virtualization in the
virtualized wireless network: cross-infrastructure
virtualization and limited intra-infrastructure
virtualization. The first one allows multiple InPs to
share the same physical network. The second one
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refers to the sharing of radio spectrum and access
network among different MVNOs.
Additionally, SDN architecture can be categorized
into two forms: centralized and distributed. It still
needs some time for engineers to justify which one is
better or to make a decision as to which one excels
more under a certain circumstance.
To the general public, SDN appears to be able to
provide an open, flexible and programmable
solution to future wireless networks. However, its
advantage could possibly shed some negative
impacts on the overall network performance. As an
open solution, SDN might be susceptible to
interference, which raises the security concern.
Also, there is yet no consensus on how flexible it
can be programmed. There must be some trade-offs
in between. Rather, the most important two factors
that should be considered as top priorities to
engineers are scalability and robustness. Failing to
resolve these outstanding issues will deter the
massive deployment of SDN.
The following diagram entails a high level
understanding of a virtualized network.
Figure 3: C-RAN Architecture
3) Massive MIMO [3]
MIMO is defined as multiple inputs and multiple
outputs. Massive MIMO simply consists of a large
array of antennas at each base station. Such design is

5. aimed to increase the system capacity on the order of
10 and to increase the energy efficiency on the order
of 100 times. In addition to these two benefits, there
are still some concerns and problems remain to be
addressed in coming years.
First, Massive MIMO is considered impractical for
FDD systems since beamforming requires a large
amount of channel state information, which is
problematic for the downlink channel. As of now, it
can only be used in TDD systems.
Second, a massive amount of data will be generated
from this scheme and to ensure low latency and
response time, a fast processing algorithm is needed.
Third, Massive MIMO suffers a lot from pilot
contamination. The meaning of such contamination is
that the channel state estimation at the base station
will be contaminated if two transmitters located in
adjacent cells use the same pilot sets.
The following diagram illustrates the pilot
contamination.
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technologies tends to appear in an ad hoc and
piecemeal manner. In this sense, a consistent and
standardized horizontal approach is needed to realize a
true M2M world.
Another challenge specific to M2M is the security
and privacy. Different M2M services and applications
have different privacy requirements. Such
requirements must be taken into consideration at the
beginning of system design.
The following diagram illustrates a new M2M
solution for Oil & Gas Industry, launched by Norsat
International Inc.
Figure 4: Pilot Contamination
4) Machine to Machine Communications (M2M) [2]
One example of M2M communication is that the
latest in-car satellite navigation system communicates
with built-in cellular modems to download traffic
information updates invisibly in the background. As a
matter of fact, M2M has already been commercialized
in today’s market. Unfortunately, there are still some
challenges that need to be resolved before it realizes
its full potential in the future 5G networks.
One challenge is that the M2M traffic does not flow
readily within the current network architectures. To
resolve such technical issue, some modifications and
technology extension have been developed and
deployed. However, the development of these new
Figure 5: Remote Site Data Monitoring and Control
This solution utilizes the concept of M2M to
provide remote site data monitoring and control in real
time through flexible communication services and
intuitive web-based interface. Such solution can be
used in any other industries such as weather
forecasting, air and water quality monitoring.
5) Localize Traffic Flows [3]
The end-to-end (E2E) latency performance is of
paramount importance to massive machine
communication. According to the delay analysis of
legacy technologies, most of the delays originate from
the Internet and the core network parts of the E2E
connection. Therefore, instead of having connections

6. between every single device and the outside world, a
traffic-flow concentrator can be implemented to first
aggregate all the traffic flows within a network and
then forward them all to the Internet. Such approach
facilitates direct communication among sensors
located in capillary network and alleviates the traffic
congestion in the core network gateway.
The use of concentrator is essential for delay-
sensitive services, such as road safety applications. As
the road circumstance is monitored in real time, a low
latency of less than 5 ms can provide users with the
most updated and accurate information.
The two figures below highlights the difference
between the one with concentrator and the one without.
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limited, researchers are motivated to look beyond 6
GHz and are currently testing the feasibility of
millimeter band. This band spans from 30 GHz to 300
GHz. Such sufficient room in spectrum can certainly
help system designers meet the burgeoning demand in
future networks. At the time this paper is written,
there are already some ongoing efforts to conduct
extensive study over frequencies of 28 GHz and 38
GHz. It is believed that such study paves a promising
way for millimeter wave to be used in the near future.
The figure below visualizes the spectrum used for
both current and future communications.
Before
Figure 8: Spectrum View
Figure 6: Connection without Concentrator
After
Figure 7: Connection with Concentrator
6) Millimeter Wave [2]
Higher throughput is what network engineers aim to
achieve for the future 5G wireless networks. To generate
high throughput, more bandwidth resources are needed.
As the available bandwidth below 6 GHz is
7) Spectrum Sharing [3]
As discussed in the point 6, expansion of spectrum is
done for the purpose of increasing data rate and
throughput. In some scenarios, such expansion cannot
eliminate the problem of frequency shortage
completely. To patch such shortage, sharing licensed
spectrum could be considered as an alternative
solution. In order to prevent any further conflicts
caused by this sharing scheme, only authorized users
who possess permission given by the licensee of the
spectrum is eligible to access a particular spectrum.
This increases the effectiveness of under-utilized
spectrum and will not bring any negative impacts on
the holder of the spectrum.
An analogy can be made to help understand the
practice of this sharing method. When someone wants
to rent an apartment from its owner, he or she must be
currently employed or must have a sufficient amount
of deposit in a bank. Otherwise, this person will not be
eligible for renting this apartment. That being said, if
such apartment is successfully rented out, this
transaction brings benefits to both parties. From
owner’s point of view, his or her under-utilized
apartment can bring him or her some revenue. For
tenants, they have somewhere to live. The relation

7. between the owner and the tenant is exactly the same as
the one between the holder of a spectrum and its users.
IV. HARDWARE OF 5G [2]
i. Ultra-wideband Networks (UWB)
Ultra-wideband, also known as UWB, is a radio
technology that consumes little amount of energy for
short-range, high-bandwidth communications. This
technology is ideal for wireless personal area
networks (WPANs). Different from spread
spectrum, the transmission of UWB does not
interfere with conventional narrowband and carrier
wave. Such fact allows this technology to share the
same spectrum with others. As such, networks using
this technology can provide cost-effective, power-
efficient and high bandwidth solution to conduct
relay between devices within an immediate area.
ii. Bandwidth
The bandwidth used for 5G networks is expected
to be 4000 Mb/s. This value is 400 times faster than
today’s wireless technology. Larger bandwidth
allows higher data rate and throughput.
iii. Antennas
a. Switched Beam Antennas: such antennas
support radio positioning by using the
information collected from nearby devices.
The beams can switch from one place to the
other depending on the location of the user
terminal. The diagram below shows the
switched-beam antenna system.
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Figure 9: Switched-beam Antenna System
b. Adaptive Array Antennas: these antennas
utilize a smart signal processing algorithm to
calculate beam forming vectors to track and
locate the antenna beam on a target. The use
of these smart antennas can improve
interference rejection, accuracy on location
positioning and channel models based on
Angle of Arrival (AOA) channel sounding
measurements.
The diagram below depicts the adaptive
antenna system.
Figure 10: Adaptive Array System
As shown in the diagram, the adaptive
algorithm is using the concept of a closed-
loop control system to conduct adjustments
in order to target desired beam with strong
enough power at the user terminal.

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iv. Multiplexing Scheme
Code Division Multiple Access (CDMA) will be
employed in the future 5G networks. At the
transmitter, a code generator (built by shift register)
produces a number of codes to vary the frequency
of a transmitted signal. Once such signal arrives at
the receiver, to decode and extract information,
receiver side also generates a series of code. Only
the same code as being transmitted can perform
signal decoding and output desired data. In 5G era,
there will be trillions of possible frequency-
sequencing codes. This strengthens the robustness
of future networks.
The following three diagrams are: 1) code
assignment to a transmitted signal; 2) block diagram
of a code generator; 3) Inside view of a code
generator.
Figure 11: Code Assignment
Figure 12: Block Diagram of a Code Generator
Figure 13: Inside View of a Code Generator
V. 5G MOBILE NETWORK ARCHITECTURE [3]
Figure 14 (shown below) illustrates a system-
level design of network architecture for 5G mobile
systems. This future technology will be IP based
and the network systems mainly consist of a user
terminal and a number of independent, autonomous
radio access technologies (RAT). Each RAT is seen
as an IP link that connects the user terminal to the
outside world. There is no direct connection
between these RATs, meaning if we need to have
all user terminals connected with the core network,
all the corresponding RATs in these terminals must
be active at the same time. Otherwise, the
architecture is not considered functional.
Figure 14: System-Level View of 5G Network

9. In addition, the 5G network architecture is
designed to be scalable, flexible and service-
oriented. All these three key aspects have to closely
work with each other in order to ensure that a
diverse set of 5G technologies can fulfill a broad
range of service requirements. One such scenario is
that scalability is assisted by flexibility to meet the
requirements of extremely contradicting services,
such as MMC vs. Multi-User Ultra High Definition
(UHD) telepresence. In general, both existing and
emerging technologies will coexist in the 5G
networks. This coexistence provides a smooth
transition between the 4G and the 5G and makes
devices to be compatible with old-fashioned
technologies. The following figure sketches a
generic 5G network architecture.
Figure 15: Generic 5G Network Architecture
VI. RESEARCH CHALLENGES AND NEW
OPPORTUNITIES [2]
In this section, I first discuss the measurement
and test challenges on 5G technologies. Then, I
present some possible new research opportunities.
1) Measurement Challenges
 Spatial distributions and mobility:
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The existing channel models are drop-based,
meaning the scattering environment is randomly
created for each link. As the density of links is
expected to increase in 5G networks, a consistent
manner has to be employed to model these links
in order to support different network nodes
residing in the heterogeneous networks.
 Large-scale antenna arrays and the use of
Millimeter wave
The large-scale antenna arrays require spherical
wave modeling instead of the currently used
plane-wave approximation. As mentioned
before, the use of millimeter wave provides a
promising way to increase the capacity of 5G
networks. However, prior to using it, some
characteristics such as highly resolved angular
properties and non-line-of-sight path loss have
to be figured out.
2) Testing Challenges
 Testing on 5G BS (base station)
Unlike traditional BSs, future BSs are expected to
implement radio resource control, including
admission control, load balancing, radio mobility
decisions, on top of the traditional layer 1 and
layer 2. Such complexity poses challenges to
researchers as they have to simulate future
scenarios using conventional BSs.
 Testing on 5G UE (User Equipment)
One of challenges specific to this testing is to
ensure that the requirements of state change
response are met. Researchers only show interests
into two modes of UEs, one is idle mode and the
other is connected mode. In idle mode, devices are
in the low power consumption state and only wake
up periodically to check for paging signals. In the
connected mode, devices must be awake and
respond any information sent from the base
station. To ensure these two modes can flexibly
switch from each other, a stress test and battery
drain test must be performed.

10. 3) New Opportunities
Some other issues such as resource discovery,
interference rejection, mobility management
and price-based allocation open up new
research opportunities for network engineers.
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challenges", IEEE Instrum. Meas. Mag., vol. 18, no.
3, pp. 11-21, 2015.
VII. CONCLUSION
This paper provides an overview of the current
research studies on 5G wireless networks and
incorporates author’s own understandings specific to
some interesting concepts. 5G technologies are
envisioned to be available since 2020. By that time,
the whole world will be connected more closely and a
true wireless networked society will no longer be
legendary. Compared to preceding network
technologies, 5G networks are designed to be more
reliable in terms of data rates and throughput, more
affordable in the market. While the public is waiting
for the arrival of new era on telecommunications,
several challenges have to be resolved. One of the
biggest challenges is to ensure that all involved
enabling technologies can work well with each other
and make every user’s life much better than before.
VIII. REFERENCES
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[2] W. Chin, Z. Fan and R. Haines, "Emerging
technologies and research challenges for 5G
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21, no. 2, pp. 106-112, 2014.
[3] J. Monserrat, G. Mange, V. Braun, H. Tullberg,
G. Zimmermann and Ö. Bulakci, "METIS research
advances towards the 5G mobile and wireless
system definition", EURASIP J Wirel Commun
Netw, vol. 2015, no. 1, p. 53, 2015.
[4] E. Hossain and M. Hasan, "5G cellular:
key enabling technologies and research