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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