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KEY TECHNOLOGIES AND DESIGN PRINCIPLES
High energy performance targeting reduced network energy consumption is a critical requirement of
5G. It enables reduced total cost of ownership, facilitates the extension of network connectivity to
remote areas, and provides network access in a sustainable and more resource-efficient way.
Key technologies to achieve this include ultra-lean design, advanced beamforming techniques,
and separation of user-data and system-control planes on the radio interface, as well as virtualized
network functionality and cloud technologies. This paper also defines two design principles on
which 5G systems with high energy performance should be built.
ericsson White paperUen 284 23-3265 | April 2015
5G Energy Performance
5G ENERGY PERFORMANCE • THE ROLE OF NETWORK ENERGY PERFORMANCE IN 5G 2
The role of network energy performance in 5G5G is the next step in the evolution of mobile communication. It will be a key component of the
Networked Society, and will help realize the vision of essentially unlimited access to information
and sharing of data anywhere and anytime for anyone and anything [1].
Energy performance has long played an important role in mobile communication on the device
side. High energy performance in devices has enabled longer battery life, and has been a vital
component behind the mobile revolution.
However, the need for high energy performance has also become a key factor for network
infrastructure. Reduced overall network energy consumption is being targeted, despite massive
increases in traffic and number of users. There are several important reasons for this development:
> High network energy performance is crucial to reducing operational cost, and is a driver for
better node and network dimensioning, which leads to reduced total cost of ownership (TCO).
> High network energy performance allows for off-grid network deployment relying on decently sized
solar panels as power supplies, enabling wireless connectivity to even the most remote areas.
> High network energy performance is part of a general operator aim to provide wireless access
in a sustainable and more resource-efficient way.
Consequently, network energy performance has an important role to play in 5G.
5G ENERGY PERFORMANCE • 5G – REQUIREMENTS AND EVALUATIONS 3
5G – Requirements and EvaluationsEach new generation of mobile-communication technology is preceded by extensive discussions
on what capabilities it should have and what requirements it has to meet. The expected
requirements and capabilities for 5G are more diverse than for previous generations. It will not
only require ubiquitous connectivity for human users but also end-to-end communication between
various kinds of machines and devices.
There are also stronger and more clearly defined requirements on high energy performance
than before. Operators explicitly mention a reduction of total network energy consumption by
50 percent despite an expected 1,000-fold traffic increase [2].
5G targets very high data rates everywhere. High data rates provide possibilities to transmit
the same or even more information in a shorter time. This results in more time without transmission
when equipment can enter various energy-saving or sleep modes.
“Everywhere” extends 5G data rates not only to current 3G and 4G mobile broadband coverage
but also beyond. Deploying 5G in very remote areas requires very high energy performance,
allowing for decent-sized solar panels or other cost-efficient onsite energy technologies. 5G
should also allow for deployment on the current grid of macro sites, as increased data rates and
network sharing, when applicable, can reduce the need for parallel network infrastructure. Avoiding
densification of macro sites in wide-area deployments as much as possible, for instance in rural
areas, will continue to be beneficial. The main reason is that even with infrastructure nodes
offering high energy performance, additional sites will inevitably add a certain fixed energy
consumption per site.
The diversity and amount of 5G capabilities and use cases has triggered requirements for
dramatically increased scalability and more modular network functions. For example, networks
should only have support functions and associated signaling for the use cases that they are to
support. However, common system support must still be extensive enough to provide the
necessary base for individual capabilities and use cases, such as the possibility to establish
network access.
TECHNOLOGY EVALUATIONS
In order to be certified as an International Mobile Telecommunications (IMT) technology, a radio-
access technology (RAT) must fulfill specific requirements defined by the International
Telecommunication Union (ITU). The requirements for next generation IMT technology are expected
to cover technology characteristics such as spectrum efficiency, traffic capacity, latency, data
rates and network energy performance. To be able to evaluate a technology in relation to ITU
requirements, common evaluation methodologies based on system simulations of different
scenarios need to be defined.
One potential extension of such evaluation methodologies that will also make it possible to
evaluate energy performance has been defined by the Energy Aware Radio and neTworking
tecHnologies (EARTH) project [3]. The Energy Efficiency Evaluation Framework (E3F) includes
power profiles for different types of base stations, a 24-hour traffic profile, and deployment
models on a regional scale with weight factors for different scenarios, thereby emphasizing low-
traffic scenarios.
5G ENERGY PERFORMANCE • ENERGY PERFORMANCE IN EXISTING TECHNOLOGIES 4
Energy performance in existing technologiesAn industry that has focused on providing high traffic capacity and high data rates is now also realizing
the importance of high energy performance when there is little, or no, data to transmit or process.
Vigorous research efforts, including activities within a number of joint research projects within the
telecom community, have been vital contributors to this understanding.
LOW AVERAGE TRAFFIC AND LARGE DYNAMIC TRAFFIC VARIATIONS
Peak traffic situations are very demanding to design and deploy for. They are, however, also comparably
rare in terms of where and how often they occur. The reality is that most cells and access nodes carry
comparably little traffic most of the time, adding up to rather low average traffic loads in mobile networks.
Understanding the distribution of traffic is vital for network planning, deployment and dimensioning
but also for identifying sweet spots for energy savings in mobile networks. Traffic analyses have yielded
three rules-of-thumb [4]:
> Traffic is unevenly distributed – the 5 percent most-loaded cells in a network jointly carry some 20
percent of total traffic, while the 50 percent least-loaded cells jointly carry only some 15 percent of
traffic.
> There are large spatial variations of traffic even within a given area – thus, even in a dense urban area
with high traffic load, there will be specific locations with low traffic loads.
> Traffic increases the most in areas that already have high traffic loads – this is important for correctly
estimating necessary capacity margins for future traffic growth.
Improved dimensioning through decreased discrepancies between dimensioned capacity and needed
capacity leads to reduced energy consumption and opex, as well as to reduced capex.
TRAFFIC MAKES LITTLE DIFFERENCE TO NETWORK ENERGY CONSUMPTION TODAY
Mobile networks are designed for continuous and highly reliable operation, which traditionally has been
associated with an “always on” design, implying that nodes and components are always on in order to
be immediately available when needed.
The combination of large load variations, low average traffic and “always on” network operation implies
that the primary limitation for energy performance is in fact not data traffic but the transmission of the
basic signals needed for devices to discover and access the system. Hence, the energy consumption in
existing networks is not very load dependent.
5G ENERGY PERFORMANCE • ENERGY PERFORMANCE IN EXISTING TECHNOLOGIES 5
In a typical LTE network, less than 10 percent of the sub-frames are used (when averaged over time and
area) and even in “extreme traffic” scenarios less than 20 percent of the sub-frames would be used – see
the left part of Figure 1. Even extreme traffic levels would only correspond to an increase in energy
consumption of less than 10 percent, compared with consumption when not transmitting any data.
Differently expressed, more than 90 percent of the energy consumption is needed just for the network to
be discoverable and accessible, indicated by the gray bars on the right side of Figure 1.
FROM “ALWAYS ON” TO “ALWAYS AVAILABLE”
Stronger requirements for improved energy performance in combination with the introduction of
packet-based services make it more attractive to switch to an “always available” design in access
nodes. In “always available” operation, all network functionality and components are not “always on.”
Rather, only the functionality needed for devices to access the network is always on, while the
remaining functionalities can be dynamically activated on a per-need basis, thus still being available
when needed. In practice, the advantage of this approach over traditional “always on” operation is
that components, subsystems and nodes can utilize a variety of advanced energy-saving modes
and sleep modes, which reduces network energy consumption.
“Always available” operation is also important in higher-level nodes that aggregate traffic from
several access nodes. Due to a combination of high node capacity and high requirements on reliability
and redundancy, it is rare that an entire node can be switched off with today’s specialized hardware.
However, different types of processor sleep modes may be applied to enhance energy performance.
Virtualization combined with more general-purpose hardware would also enable more efficient
resource allocation on fewer hardware units, which has the potential to increase the saving potential
even further.
Several steps have already been taken to achieve “always available” operation in current technologies
and their implementation. This will continue to be pursued within the evolution of LTE and Evolved
Packet Core.
Figure 1: Utilization and corresponding network energy consumption for different traffic loads.
5G ENERGY PERFORMANCE • 5G CHALLENGES AND DESIGN PRINCIPLES 6
5G Challenges and Design Principles5G is a unique opportunity to go beyond the energy-performance limitations of existing standards
and their evolutions. As the main part of the energy consumption in existing technologies is
associated with transmissions that enable devices to discover and access the system, this area
has the largest savings potential.
It also remains crucial to improve energy performance when transmitting data. This requires
a more user-centric system in which every transmission can be specifically tailored to the intended
receiver in a flexible and adaptable way. From an application perspective, a user-centric system
implies increased precision in resource allocation depending on application needs – something
that is crucial considering all the possible use cases a 5G system will face. Application needs
determine the tolerable delays that indirectly affect how aggressive energy-saving mode may be
pursued in the underlying hardware equipment. Furthermore, resources can be dynamically
adapted per user to avoid overprovisioning of network resources and also to facilitate better
utilization of the resources that are active.
User-centric RANs can be obtained by user-specific directional transmissions, for example,
beamforming. Optimizing the radio transmission for a specific user, however, must not impact
access coverage.
A system that does not transmit anything unless there is an ongoing user-data transaction
would not be able to support initial access or access mobility for users. This requires additional
broadcast information to be transmitted over the coverage area, for instance to support random
access.
The optimization of basic system functions that is required for initial access and access mobility
over large areas is fundamentally different from the optimization of individual radio links between
base stations and user terminals. This type of broadcasted information is traditionally associated
with cells. There is, however, nothing in the functionality for initial access and access mobility
that requires cells. On the contrary, moving away from the traditional cell concept would rather
enable a more scalable and efficient system design.
Note that rethinking the cell concept would also be beneficial to managing the increasing
complexity associated with advanced antenna techniques, which are used for dedicated data
transmissions. With LTE, cooperative multi-point transmission techniques are already “bypassing”
the cell concept by focusing on transmission points rather than cell sites. 5G networks will need
to handle more sites, antennas and frequency bands with faster adaptation. Here, the dynamically
optimized radio links between system and individual users become the central entity, while static
cell concepts have little to offer.
Regarding core-network nodes and other aggregating network nodes, the main challenge is
increased scalability and manageability, in order to efficiently handle the wide variety of use
cases foreseen in the future.
DESIGN PRINCIPLES
These challenges can be transformed into design principles to obtain high energy performance in
mobile networks:
> to only be active and transmit when needed
> to only be active and transmit where needed.
“To only be active when needed” implies an “always available” approach with dynamic activation from
“inactivity” and default state on several levels: nodes, functionality, subsystems and components.
5G ENERGY PERFORMANCE • 5G CHALLENGES AND DESIGN PRINCIPLES 7
“To only transmit when needed” refers in particular to minimized transmissions not directly related
to the delivery of user data. For radio access, such transmissions include signals for synchronization,
network acquisition and channel estimation, as well as the broadcast of different types of system
and control information. This can also be interpreted as: transmitting as seldom as possible but
as often as needed.
“To only be active where needed” covers the spatial domain of “always available” and may
refer both to the same levels as above but with the addition of an extra dimension to distributed
architectures.
“To only transmit where needed” refers to the previously discussed distinction between the
needs for dedicated, directional (also referred to as beamformed) transmissions and broadcasted
omni-present transmissions to several users. Furthermore, this may also imply a preference for
dedicated transmissions from shorter distances with lower power; that is, more localized
transmissions, when applicable. Adding additional access nodes, thereby reducing the access-
node-to-device distance, also reduces the required transmission power for a certain data rate.
This, however, only translates into decreased network energy consumption when the added
energy consumption from the new node is smaller than the gained transmission energy.
5G ENERGY PERFORMANCE • KEY TECHNOLOGY CONCEPTS FOR SUPERIOR ENERGY PERFORMANCE 8
Key technology concepts for superior energy performance
Based on the discussed design principles, a number of key technology concepts can be identified
as crucial for outstanding network energy performance:
ULTRA-LEAN DESIGN
Ultra-lean design targets the design principle to “only transmit when needed.” It aims to minimize
any transmissions not directly related to the delivery of user data.
Ultra-lean design provides two main benefits in terms of energy performance. Firstly, it provides
more time without transmission compared with existing cellular technologies; that is, it provides
more time during which equipment can be in sleep mode. Figure 2 shows the difference between
sleep-mode possibilities in LTE and an example of ultra-lean design.
Secondly, longer periods without transmissions also enable equipment to enter more extensive,
or deeper, sleep-mode levels. Consequently, even larger energy saving is possible since equipment
may not only sleep longer but also save more energy when in sleep mode.
Note that ultra-lean design is also an important enabler for higher achievable data rates by
reducing the overall system interference level from non-user-data-related transmissions. Ultra-
lean design is applicable to and beneficial for all kinds of deployments, including macro
deployments.
System-control planeUltra-lean design
0 100 200 (ms)
New RATDuty cycle 0.5%DTX 100ms
0 5 10 (ms)
LTEDuty cycle 50%DTX 0.2ms
Figure 2: Increased potential for sleep mode with ultra-lean design – in this example 100 times lower duty cycle and 500 times longer discontinuous transmission (DTX) compared with LTE.
5G ENERGY PERFORMANCE • KEY TECHNOLOGY CONCEPTS FOR SUPERIOR ENERGY PERFORMANCE 9
ADVANCED ANTENNA TECHNIQUES AND BEAMFORMING
Advanced antenna techniques already play an important role for current generations of mobile
communication, and will play an even more important role in 5G. They are vital to meet requirements
for increasing data rates by better utilization of the spatial domain, as well as to improve service
coverage.
From an energy performance perspective, advanced antenna techniques have several benefits.
Higher data rates enable more time for sleep mode, and increased system capacity also enables
extreme future traffic to be served without a corresponding densification of the network.
The most interesting multi-antenna technique for high energy performance is, however, to
utilize a large number of antenna elements for very selective beamformed transmission; that is
to “only transmit where needed.”
Selective beamforming provides several benefits: decreased interference which enables
reduced overall transmission power in networks; and extended service coverage which also
provides high data rates in sparse deployments. Alternatively, it enables more sparse networks
with maintained system performance. All of these contribute to high network energy performance.
SEPARATING USER-DATA AND SYSTEM-CONTROL PLANE FUNCTIONALITY
Decoupling user-data and system-control plane functionality is an important tool for obtaining
superior energy performance. The system-control plane includes the provisioning of system
information, including procedures needed for devices to access the system.
Such a decoupling in the radio interface allows separate scaling of user-plane capacity and
fundamental system-connectivity functionality. User data may then be delivered by a dense layer
of access nodes, activated on demand, while system information is only provided via an overlaid
layer, a layer on which devices also initially access the system. Consequently, this is related to
the design principles – to only transmit “when” and “where” needed.
Note that user-data/system-control plane separation is also an important component for 5G
deployments that rely heavily on beamforming for user-data delivery. Combining ultra-lean design
with a logical separation of user-plane data delivery and basic system-connectivity functionality
will enable a much higher degree of user-centric network optimization of the active radio links
in the network.
Since only the system-control plane in an ultra-lean design needs to be static, it is possible
to design a system in which almost everything can be dynamically optimized in real time. Therefore,
a separation of user-data and system-control plane functionality is a prerequisite for full utilization
of advanced antenna systems, as well as for harvesting all the benefits of the ultra-lean design,
as illustrated in Figure 3.
Figure 3: Separation of system-control plane (green) and user-data plane (blue) allows full utilization of advanced antenna systems.
5G ENERGY PERFORMANCE • KEY TECHNOLOGY CONCEPTS FOR SUPERIOR ENERGY PERFORMANCE 10
Furthermore, ultra-lean design combined with user-data/system-control plane separation also
provides desirable flexibility in terms of evolution of the RAT, since with such separation the
user-data plane is able to evolve while retaining system-control functionality, something that
provides benefits both for modular network design and forward compatibility.
VIRTUALIZED NETWORK FUNCTIONALITY AND CLOUD
In contrast to radio access nodes, core network nodes manage enormous amounts of aggregated
traffic and users from a large number of access nodes. Hence, the need for extremely fast
energy-saving mechanisms is smaller in core network nodes than in access network nodes, as
the load is more likely to change at a slower rate due to the higher degree of aggregation.
Nevertheless, managing fast traffic and subscriber growth – and, in the future, emerging new
use cases – in a resource- and cost-efficient way still requires high degrees of flexibility, adaptability
and scalability.
ONE NETWORK – MULTIPLE USE CASES
Traditional network-function applications are strongly connected to the type of purpose-built
hardware they run on. 5G systems will have to cope with many different use cases and
requirements. In traditional network models, use cases with vastly different requirements and
characteristics would typically be implemented as separate physical networks. However, from
an energy-consumption and cost perspective, it is preferred to support as many use cases as
possible over a single physical network infrastructure.
This can be realized by network slicing, which provides the possibility to create logically
separated network partitions over a shared physical network infrastructure [5]. This enables
operators to deliver network connectivity tailored to specific application needs, as illustrated in
Figure 4. In addition to the offered flexibility in connectivity, network slicing allows the 5G system
to provide for a large variety of the different communication needs of the Networked Society.
This will largely reduce, or even eliminate, the need to spend resources and operational energy
on parallel infrastructures for specialized needs.
Virtualized network functionality and cloud technologies are important tools when designing
systems with a higher degree of abstraction, which improves network flexibility and enables the
concept of network slicing.
For some of the virtualized network functions (VNFs), higher centralization in larger data centers
allows better infrastructure scaling and less computational redundancy, and may therefore improve
the energy consumption footprint. For other VNFs, however, sharper requirements on delay,
availability and transport decongestion are likely to create an opposite trend of distributing
functionality toward the access network. The cloud infrastructure will provide flexible deployment
and runtime functionality that allows the functions to run at the best place and time based on
requirements for delay, throughput, data locality, availability, and high energy performance.
Figure 4: One shared network infrastructure supporting multiple use cases via network slicing.
5G ENERGY PERFORMANCE • KEY TECHNOLOGY CONCEPTS FOR SUPERIOR ENERGY PERFORMANCE 11
CONSTRUCTIVE INTERACTION BETWEEN VNFS AND PHYSICAL HOSTS
High energy performance relies on constructive hardware and software interaction. Decoupling
them via virtualization may therefore seem a contradiction. It does not, however, exclude
constructive interplay between them. On the contrary, in virtualized networks the crucial hardware
coordination is handled by an orchestrator. This reduces the existing diversity in specialized
hardware to fewer, more generic types. The VNFs inform the orchestrator about their needs, and
the orchestrator ensures that hardware resources are available when required but also that non-
utilized hardware remains in optimal energy-saving modes.
The orchestration allows the cloud to consolidate the running VNFs on a subset of the available
hardware, which will run with a higher grade of utilization, while the rest can be powered down
or put in standby mode. Aggregating several VNFs on the same generic hardware, such as
servers, enables even more efficient utilization of the active hardware. This enables higher energy
performance during low load, while providing possibilities to quickly scale up or down to handle
peak usage.
Furthermore, the software-hardware decoupling through virtualization allows easy porting of
network functions to the latest hardware generations with state-of-the-art energy-saving
functionality, thus ensuring continuously improved energy performance.
5G ENERGY PERFORMANCE • CONCLUSION 12
Conclusion5G will have to fulfill many requirements, and a critical one is to deliver high network energy
performance. This is crucial in order to reduce operational cost and TCO, to facilitate network
connectivity in remote areas, and to provide network access in a sustainable and resource-
efficient way.
High energy performance requires a fundamental change of design principles and implementation
practices within the mobile telecom industry. There has been a long-standing focus on providing
high traffic capacity and high data rates, but many in the industry are now realizing that high energy
performance is equally important even when there is little, or no, data to transmit or process.
5G systems with high energy performance should be built on two design principles:
> to only be active and transmit when needed
> to only be active and transmit where needed.
This will allow for a scalable, manageable, and flexible network design that both facilitates truly
load-dependent energy consumption and maximizes energy-saving possibilities.
Key technologies to achieve this include ultra-lean design, advanced beamforming techniques,
and separation of user-data and system-control planes on the radio interface, as well as virtualized
network functionality and cloud technologies.
5G ENERGY PERFORMANCE • REFERENCES 13
[1] Ericsson, February 2015, White paper: 5G radio access – technology and capabilities,
available at: http://www.ericsson.com/res/docs/whitepapers/wp-5g.pdf
[2] NGMN Alliance, February 2015, NGMN 5G White paper, available at: https://www.ngmn.
org/uploads/media/NGMN_5G_White_Paper_V1_0.pdf
[3] Auer et al, IEEE Wireless Communications Magazine, October 2011, How much energy is
needed to run a wireless network?, synopsis available at: http://ieeexplore.ieee.org/xpl/login.js
p?tp=&arnumber=6056691&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F7742%2F6
056680%2F06056691.pdf%3Farnumber%3D6056691
[4] Frenger et al, Ericsson Review, February 2014, Radio Network Energy Performance:
Changing the Game from Power to Precision, available at: http://www.ericsson.com/res/
thecompany/docs/publications/ericsson_review/2014/er-radio-network-energy-performance.pdf
[5] Ericsson, January 2015, White paper: 5G systems – enabling industry and society transformation,
available at: http://www.ericsson.com/co/res/docs/whitepapers/what-is-a-5g-system.pdf
References
5G ENERGY PERFORMANCE • GLOSSARY 14
GLOSSARYDTX discontinuous transmission
EARTH Energy Aware Radio and neTworking tecHnologies (EU FP7 research project)
E3F Energy Efficiency Evaluation Framework
IMT International Mobile Telecommunications
ITU International Telecommunication Union
RAT radio-access technology
TCO total cost of ownership
VNF virtualized network function
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