5GrEEn: Towards Green 5G Mobile Networks
Magnus Olsson
Pål Frenger
Radio Access Technologies
Ericsson Research
Stockholm, Sweden
Wireless Access Networks
Ericsson Research
Linköping, Sweden
Cicek Cavdar and Sibel Tombaz
Dario Sabella
Wireless@KTH
Royal Institute of Technology
Stockholm, Sweden
Wireless Access Innovation
Telecom Italia
Turin, Italy
Riku Jäntti
Department of Communications and Networking
Aalto University
Helsinki, Finland
Abstract—In 2020, mobile access networks will experience
significant challenges as compared to the situation of today.
Traffic volumes are expected to increase 1000 times, and the
number of connected devices will be 10-100 times higher than
today in a networked society with unconstrained access to
information and sharing of data available anywhere and anytime
to anyone and anything. One of the big challenges is to provide
this 1000-fold capacity increase to billions of devices in an
affordable and sustainable way. Low energy consumption is the
key to achieve this. This paper takes as starting point the
situation of today, and tries to pinpoint important focus areas
and potential solutions when designing an energy efficient 5G
mobile network architecture. These include system architecture,
where a logical separation of data and control planes is seen as a
promising solution; network deployment, where (heterogeneous)
ultra dense layouts will have a positive effect; radio transmission,
where the introduction of massive antenna configurations is
identified as an important enabler; and, finally, backhauling
solutions that need to be more energy efficient than today.
Keywords—5G; green; energy efficiency; mobile network; radio
access; system architecture
I.
INTRODUCTION
Mobile communications have experienced a tremendous
journey since its introduction in the late 1970s. At that time
analog voice calls were the main application, while today we
have mobile broadband services capable of providing end user
data rates of tens, or even hundreds, megabits per second. Due
to the introduction of new devices such as smartphones and
tablets and associated applications and use cases, the data
traffic volumes in the networks have in principle exploded
during the last few years [1]. This trend is expected to continue
in the coming years [2]. In addition, future visions such as the
Internet-of-Things [3] is more and more becoming a reality,
and today all expertise agree that we are moving towards a
This work was carried out in 5GrEEn, which is an EIT-ICT Labs project
supported by the EIT, European Institute of Innovation and Technology.
networked society with unconstrained access to information
and sharing of data available anywhere and anytime to anyone
and anything.
Hence, a common conclusion is that mobile systems in the
future will need to cope with vastly different challenges and
expectations than today. Current 3G and 4G technologies such
as high speed packet access (HSPA) and long term evolution
(LTE) will evolve in that direction, but there are also initiatives
starting up focusing on new, 5G, technologies. One example is
the EU-funded FP7 project METIS [4], an industry-wide
consortium with the target to explore mobile and wireless
enablers for the 2020 information society.
One of the big challenges is to meet the future requirements
and expectations in an affordable and sustainable way. Low
energy consumption is the key to achieve this. Already today,
the mobile operator’s energy bill is an increasing part of their
OPEX, and with the future requirements and expectations there
is a clear risk that this may increase even further if nothing is
done. This is also important from a sustainability perspective;
even though mobile communications today only contributes to
a fraction of a percent of the global CO2 footprint [5], it is
important to maintain or even reduce this in the future. Hence,
low energy consumption is an important design target for
mobile communication systems in the future.
5GrEEn [6] is a joint effort of partners tightly connected to
the METIS project representing the telecom vendor
perspective, the mobile operator view, and leading academic
institutions. 5GrEEn will specifically focus on energy
efficiency aspects of 5G mobile networks, and will hence
contribute significantly to the important design target of low
energy consumption.
This paper takes as starting point the situation of today, and
tries to pinpoint important focus areas when designing an
energy efficient 5G mobile network architecture. The outline is
as follows: After a more in depth discussion on major
challenges for mobile networks in the future, the important
focus areas and some potential solutions are outlined. Finally, a
summary and concluding remarks are provided.
II.
MAJOR CHALLENGES
As already touched upon in the introduction above, there
are a number of different challenges and requirements that
mobile networks need to be able to handle in the future. Some
of the most important ones from a green design perspective
will be discussed in the following subsections.
A. Data Traffic Volumes
Today, there are over 2 billion mobile broadband
subscriptions worldwide, a figure that has grown 40% annually
over the last six years, making mobile broadband the most
dynamic market in the entire ICT sector [1]. Furthermore,
forecasts predict that data traffic volumes will experience an
exponential growth in the coming years [2], as illustrated in
Fig. 1. For example, it can be seen that the data traffic volumes
are expected to increase approximately 10 times between 2012
and 2018. By extrapolation of this, one easily realizes that a
several hundred-fold, or even a thousand-fold, increase can be
expected somewhere beyond 2020. This is well in line with
other forecasts [7][8]. For example, [7] predicts that per-user
data rates are expected to grow by a factor of up to 50-100; on
the other hand the density of mobile Internet users is expected
to increase by a factor of up to 10, implying a factor of 1000x
capacity demand in the 2020 time frame.
Fig. 1. Evolution of mobile data traffic per month up to 2018
Hence, it is obvious that mobile systems in the future need
to be capable of delivering significantly more capacity than
today. This trend is important also from a green design
perspective, since the mobile network evolution (additional
deployment of legacy 2G-3G-4G equipment and installation of
new and efficient 5G technology) should be performed by
avoiding the risk of an unreasonable over-provisioning of the
network that in this scenario will become more and more
unsustainable in terms of costs. In fact, up to now mobile
network were dimensioned by taking into account the peak
capacity, but this approach, this an exponential grow rate will
imply a costly network deployment. Instead, evolved mobile
networks should satisfy the increasing traffic demand by a
flexible availability of capacity (in time and space) in order to
sustain the data rate development that has been observed
during recent decades.
B. Number of Connected Devices
Today, there are almost 7 billion mobile subscriptions, and
thereby wireless connected devices, worldwide. Most of them
are devices used by humans such as mobile phones, laptop
computers, or tablets. However, in the future this is predicted to
change, as different kinds of machines such as smart grid
devices, sensors and surveillance cameras will be connected to
the networks. This is usually referred to as Internet-of-things
[3] or machine-to-machine (M2M) communication, and means
that everything that can benefit from a wireless connection will
have a wireless connection. Just by considering the number of
devices in a normal home, one realizes that the number of
connected devices in the future will be 10-100 times higher
than today [9].
This kind of evolution will also introduce new
characteristics of the traffic in the networks, e.g. due to the
presence of a large number of M2M devices requiring small
amount of bits, but requiring a relatively high overhead in
terms of signaling. In this sense, the need of an efficient
signaling management will be crucial also in terms of offering
to the network nodes the possibility to be de-activated during
no traffic periods. From this point of view the M2M traffic will
introduce additional challenges for a green network design.
C. Diverse Requirements
In the evolutionary scenario discussed in the present paper,
5G will include a myriad of applications with a wide range of
requirements and characteristics, some of them vastly different
than what is the case in mobile systems of today. Some
applications may require low latency, for example time-critical
control functions in industrial applications. The same type of
applications typically also requires very high reliability, while
others such as simple sensors can have lower reliability
requirements. Certain applications such as surveillance
cameras may have to convey enormous amounts of data while
others have very small data amounts to send.
This challenge need to be taken care of in the system
design, as this sets up new and varying quality-of-service
(QoS) requirements. This may have a significant impact on the
green design, as the minimization of network power
consumption should not have impacts on the correct and
efficient management of the QoS in the system.
D. Energy Consumption
Perhaps the most important challenge is to meet the above
mentioned challenges and requirements in an affordable and
sustainable way. Cost is an important issue to consider, and
will be so also in the future. CAPEX and OPEX need to be at a
level where services can be provided at a reasonable end user
price and with attractive business cases for the mobile
operators.
Already today, the mobile operator’s energy bill is a
substantial and increasing part of their OPEX, and with the
future requirements and expectations there is a clear risk that
this may increase even further if nothing is done. Hence, low
energy consumption is very important, and we have above
discussed the impact of the other challenges on this.
The energy consumption should at least be kept at the same
level as today (despite the traffic growth, the massive amount
of devices, and new requirements), but we believe that it is
possible to go further than that. The EARTH project showed
that it is possible to cut the energy consumption of LTE by a
factor of 4 with a 2012 baseline [10], and recently the
GreenTouch consortium issued a press release [11] saying that
they could cut the energy consumption of current systems by a
factor of 10 with a 2010 baseline. 5GrEEn will target a factor
of 10 lower energy consumption compared to today, while
fulfilling the requirements stated in the previous subsections.
III.
FOCUS AREAS AND POTENTIAL SOLUTIONS
A. System Architecture
The system architecture constitutes a fundamental limit on
how low energy consumption that is possible to achieve. An
energy efficient system needs to be efficient both when
transmitting data as well as when we are not transmitting data.
The system architecture in particular affects the latter, as it
(explicitly or implicitly) mandates a certain amount of
mandatory idle mode network functionalities. In current
cellular systems these by far dominate energy consumption,
and hence this is an important area to address. When the
network is in idle mode we need to improve e.g. the
distribution of access information, paging, and idle mode
mobility.
To do this, we will assume a logical separation between
idle mode functions (such as transmission of system
information) and user plane data transmission and reception,
see Fig. 2. Such an architecture was first proposed in the
EARTH project [12][13], and will in 5GrEEn be further
developed into a more mature state.
Fig. 2. Logical separation between idle mode and active mode network
functionalities enable very efficient use of DTX and DRX in the network
nodes as well as very high gain antenna beam-forming to active UEs.
In this architectural design, cells can be viewed as UE
specific resources for data transfer that are dynamically created
and configured to support only the currently active UEs. The
use of dynamic cells very efficiently enables the use of
DTX/DRX in the network nodes as well as very high gain
antenna beam-forming. In current cellular systems there is a
fixed relationship between the “cell”, “physical cell identity”
and “access point”. By a decoupling of the access point and
“cell” the “cell” becomes more flexible. For example, the same
physical cell identity may be used in several adjacent access
points, in other words, the area covered by the cell is the union
of the coverage of all the access points that uses the physical
cell identity used by this cell. Moreover, an access point may
be utilized by more than one cell. Also, a dynamic cell may
fully utilize reconfigurable antenna system (using e.g. beamwidth and tilt optimization) at the access point(s) in order to
shape the coverage in the best way. This makes it easier to
allow that the number of access points turned on is dynamically
adapted to the traffic condition.
In telecommunication systems we usually talk about the
control plane, user plane and management plane. The control
plane carries control information (also known as signalling);
the user plane carries the network's users’ traffic; the
management plane carries the operations and administration
traffic required for network management. Broadcast of system
information also belongs to the management plane. By
separation of the network into these planes we facilitate e.g.
independent utilization of access points by the planes, i.e. a
given access point may be used by a subset of the planes. For
example, we may have an access point which is exclusively
used for broadcast of system information. Such separation
allows for independent scaling of control/user/management
plane entities. Hence independent deployment of the different
plane entities can be done at the most energy efficient location.
B. Network Deployment
Energy efficiency improvements through network
deployment strategies have been touched upon in several
projects for state-of-art technologies [14][15]. Example of
these deployment strategies are different topologies of cells,
distributed antenna systems and base station cooperation.
Especially heterogeneous network deployments, where small
cells are deployed under an umbrella macro cellular coverage,
have gained great interest and have been presented as a
promising solution for improving energy efficiency of LTE
[13]. This is due to the fact that if correctly placed the small
cells can significantly offload the macro cells with an overall
energy saving as result.
In order to handle the future capacity demands and the
massive amounts of different devices, it is expected that even
denser deployments, so-called ultra dense deployments (see
Fig. 3), will be necessary. These deployments are of particular
interest in areas where extremely high data rates and capacity is
needed, for example in offices, shopping malls, and subway
stations. As these typically are located indoor, we can expect
this to be beneficial from an energy consumption perspective
due to the avoidance of power consuming wall penetration.
Despite this rather obvious expectation, an important question
from an energy perspective is how to design the ultra-dense
network deployments in order to minimize the energy
consumption, and at the same time considering the vastly
different challenges and expectations of today with a new
system architecture. For example, if care is not taken in the
design a small cell deployment can even result in increased
energy consumption [16]. The new system architecture will
relax the constraints established by the state-of-art standards
designed without any energy concern and thus provide more
degrees of freedom.
State-of-the-art mobile communication systems of today are
already very efficient in this discipline; they employ adaptive
modulation and coding, and also precoded multiple-input
multiple-output (MIMO) transmission which allows both
multi-layer transmission for increased data rates, and
beamforming to certain extent. The result is high spectral
efficiency which also is good from an energy efficiency
perspective as it means high data rates and more time for
potential node sleep.
Fig. 3. Ultra dense deployment.
The architectural solution with a logical separation between
the ability to establish availability of the network (transmission
of system information) and the ability to provide functionality
or service will have impact on how to design an energy
efficient network deployment. This new system architecture
will enable network-wide traffic adaptation with DTX and
DRX functionality as well as high gain antenna beam forming
to active users. The former will change base station power
consumption, and the latter will increase the link-level energy
efficiency. New energy-optimized network deployment
solutions need to consider these new features due to the
foreseen changes in node power consumption (different level
of sleep modes) and network performance assessment.
5GrEEn will develop energy-optimized heterogeneous
network deployment strategies for different traffic distributions
and environments that will provide capacity where it is actually
needed and will bring maximum benefit from the additional
flexibility created by the new system architecture. The most
significant difference in deployment level will arise from the
fact that future network dimensioning will not only consider
the busy hour traffic and aim to minimize the total power
consumption for the worst case scenario -as is currently being
applied- but it will take the daily traffic variation into account
to minimize the overall energy consumption. New network
deployment solutions need to be developed that minimize the
energy consumption through long- and short-term sleep
opportunities by exploiting the flexibility in the new system
architecture. This includes how to distribute the controlmanagement- and user-planes among the access points, as
discussed in the system architecture section above.
C. Radio Transmission
As already mentioned in the system architecture section
above, an energy efficient system needs to be efficient both
when transmitting data as well as when we are not transmitting
data. In order to be energy efficient when transmitting data, all
we need to do is to “send the packet to the receiver”. We
should do it quickly and we should try to avoid sending signals
in directions that does not reach the receiver.
We believe that the MIMO technology has further
potential. Recently, massive antenna configurations, or very
large MIMO, have gained increased interest [17]. Proper use of
such technology will further boost peak data rates and system
capacity, which can benefit energy efficiency in two ways;
higher peak data rates means more time for sleep, higher
system capacity means that a future traffic demand can be
served without a corresponding densification of the network.
The large number of antenna elements can also be used for
very selective beamformed transmission to a recipient while
reducing interference to others, which means that the
transmission power in the network is reduced. Such high gain
beamforming, in combination with the system architecture
solutions mentioned above, can allow increased inter-site
distances with maintained system capacity, which of course is
beneficial from an energy efficiency point of view.
However, there are some issues that need to be considered.
The first is to make sure that the energy consumption of the
baseband processing does not explode, and the other is to make
sure that data transmission protocols are improved. Today we
spend a lot of energy of preparing the channel for optimum
transmissions, and here we need to improve.
D. Backhauling Solutions
Despite the relative scarce attention paid to the role of
backhaul in optimizing the overall power budget of mobile
radio networks, recent studies have highlighted its remarkable
impact especially when heterogeneous deployments are
considered [18]. The results showed that there is a tradeoff
between the power saved by using small and low power base
stations and the baseline power that has to be spent to backhaul
their traffic. This is mainly due to the fact that the power
consumption for the backhaul becomes almost comparable
with the small cells consumption itself [18]. Therefore, with a
potential evolution towards even more heterogeneous network
deployments (i.e., where a massive number of ultra dense
nodes will be used to meet the increased need for coverage and
capacity envisioned for 2020) the power consumption of
backhaul may become one of the bottlenecks for future green
wireless access networks. In this regard, there are a series of
questions that need to be answered to get a holistic
understanding of how to achieve a green backhaul solution.
In 5GrEEn, we will tackle these questions and study
various existing and future backhaul technologies. We will
consider the advantages/disadvantages of different backhaul
technologies, e.g., microwave, fiber, copper, for different
deployment scenarios as shown in Fig. 4. For example fiberbased backhaul has higher CAPEX and longer deployment
time but offer long-term support with respect to increasing
capacity requirements. Microwave is an appealing solution due
to its quick and relatively cheap deployment potential. On the
other hand, there is still a great interest on copper based
solution in order to increase their capacity so that the existing
infrastructure can still be exploited at its maximum. Therefore,
a “one solution fits all” may not be viable. A good backhaul
architecture may not necessarily have to rely on one single
technology but it may be the result of a mix of fiber,
microwave and copper, depending on several factors, e.g.,
existing infrastructure, spectrum and licence costs, availability
of equipment, operator business modeling, and QoS level to be
provided. In this regard, we will assess the power consumption
of some hybrid backhauling solutions that can cope with the
massive demand in 2020. This will be done for different
heterogeneous network layouts considering their limitations
with respect to capacity, distance, availability etc. These
properties will be used to define which technology is the most
suitable candidate at different aggregation levels in the
backhaul network, thus enabling us to identify the most energy
efficient backhaul solution for different scenarios. With this
knowledge it will also be possible to define new and holistic
wireless deployment strategies tailored for specific backhaul
architectures to avoid the bottleneck in the backhaul power
consumption.
introduction of massive antenna configurations is identified as
an important enabler; and, finally, backhauling solutions that
need to be more energy efficient than today.
All these areas are important in order to meet the future
challenges and requirements with a green 5G network design.
Due to the partners’ tight connection to the METIS project,
5GrEEn will influence the work in METIS which will take
benefits from the guidelines and recommendations provided by
5GrEEn in their overall design of future mobile technologies.
Furthermore, some of the focus areas and solutions are also
relevant and applicable in current mobile network technologies,
and when possible 5GrEEn partners will contribute to relevant
standard bodies such as the ETSI EE technical committee and
3GPP in order to make sure that all future mobile networks will
be as green as possible.
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Fig. 4. Illustration of possible backhauling solutions.
IV.
[10]
[11]
CONCLUDING REMARKS
This paper has provided an outlook on green aspects and
solutions for 5G mobile network design that will be worked on
in the 5GrEEn project.
In 2020, mobile access networks will experience significant
challenges as compared to the situation of today. Traffic
volumes are expected to increase 1000 times, and the number
of connected devices will be 10-100 times higher than today in
a networked society with unconstrained access to information
and sharing of data available anywhere and anytime to anyone
and anything. One of the big challenges is to provide this 1000fold capacity increase to billions of devices in an affordable
and sustainable way. Low energy consumption is the key to
achieve this. Important focus areas to achieve this include
system architecture, where a logical separation of data and
control planes is seen as a promising solution; network
deployment, where (heterogeneous) ultra dense layouts will
have a positive effect; radio transmission, where the
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