ericsson White paper
Uen 284 23-3262 | February 2015
RADIO SITE
TRANSFORMATION
Time to rethink high-capacity radio site design
More than ever, operators are being pressured by capacity demands, driven by unprecedented
consumer use of smartphones and tablets. Multi-standard networks (2G to 4G and later 5G) that
use multiple bands and layers (small cells and Wi-Fi) are being deployed in order to meet these
demands. However, to meet the requirements of multiple standards, bands and layers, operators
need a new approach to radio site design and building practice.
Efficiency in the
extreme
As operators strive to deliver excellent mobile broadband performance in the busiest parts of
their networks – city centers, business parks, transport hubs, public venues and hub sites – they
will need to deploy extreme capacity sites to efficiently serve the growing volumes of 2G, 3G,
4G, and future 5G, mobile traffic.
Ericsson measurements from live networks show that a relatively small number of sites carry
the vast majority of traffic, as illustrated in Figure 1. The performance of such sites is therefore
key to operator revenue generation and protection.
Capacity demand
Number of installed RBSs
Urban
(downtown)
Suburban
(residential and
industry)
Rural
(roads, villages)
Open
(roads, villages)
Figure 1: The majority of mobile traffic, and therefore revenue, is concentrated in a minority of cell sites.
To stay competitive, operators need to pay special attention to these revenue-critical sites, as
current site designs are unlikely to be able to deliver the required performance efficiently enough.
A systematic approach to radio site design is required: one that encompasses physical building
practice; the relative merits of distributed, centralized and coordinated radio architecture; fronthaul
and backhaul transport needs; as well as power requirements and energy efficiency.
RADIO SITE TRANSFORMATION • Efficiency in the extreme 2
Differentiating
where it counts
Most operators today offer excellent coverage for voice and accessing internet-based services,
but with growing levels of mobile broadband traffic (especially video traffic), speed and latency
are becoming the key issues, especially in high-density areas like city centers.
As people increasingly expect good connectivity and high data speeds wherever they go – even
to the extent of replacing their fixed home broadband services with mobile ones – low latency
and high throughput are becoming the key markers for differentiation.
Traffic growth hotspots
Mobile data traffic from smartphones, tablets and laptops is expected to grow at a compound
annual rate of 40 percent between 2014 and 2020 (as illustrated in Figure 2), resulting in an
eightfold increase in traffic by the end of 2020. Monthly traffic per active mobile subscription is
expected to grow from 900MB in 2014 to 3.5GB in 2020 [1].
30
Data: mobile PCs, tablets and mobile routers
Data: mobile phones
25
Voice
20
15
10
5
0
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
Figure 2: Global monthly mobile traffic (exabytes).
Much of this traffic growth is coming from cities, where there is the twin challenge of rising mobile
broadband adoption and use in parallel with rapid population growth. According to the United
Nations, more than half the world’s population already lives in cities, and this proportion is
expected to rise to two-thirds by 2050 [2].
People in cities are not only used to getting excellent mobile coverage, they also expect
instantaneous connectivity and rising data speeds.
At many city center sites, Ericsson field measurements show that capacity needs are doubling
roughly every 18 months. In areas like city centers, therefore, data-handling capacity is the main
driver for radio network development; maximizing peak rates and minimizing latency are key to
differentiation and user satisfaction.
In response, operators are rolling out new high-capacity radio technologies – including highspeed 3G, 4G and small cells – in a growing number of frequencies, as part of multilayered
networks. In very high traffic locations, where obtaining new radio sites is typically costly, difficult
and time-consuming, there is extreme pressure on existing radio sites to deliver more capacity,
more efficiently, in the same footprint. Backhaul throughput must also increase in line with radio
access capacities. Busier sites may require multi-gigabit capacities in the backhaul, which can
be provided with fiber or microwave.
New generations of cellular technology appear in shorter and shorter cycles, but it is not feasible for
operators to completely replace hardware each time a new technology comes along. Existing investments
need to be protected and reused, while new technologies are integrated smoothly and efficiently.
RADIO SITE TRANSFORMATION • Differentiating where it counts 3
Radio site trends
Multiband, multi-standard sites with as many as 10 separate frequency bands are becoming
more commonplace, driven by capacity demand and the need to reduce capex and opex. This
– in parallel with growing performance requirements, which include rising demand for network
sharing, better coverage and higher throughput – is increasing configuration complexity.
The main impact of rising traffic demand on radio sites is an increase in the amount of equipment
needed: more radios to handle the air interface; more baseband units to deliver radio features
for improved capacity, coverage and latency performance; more capable transmission units to
provide RAN connectivity (backhaul); more power backup systems to ensure continuous operation
during power outages; more site routers to handle connectivity within the site (fronthaul); and
more splitter units to make cabling more manageable. All this equipment must be economically
justified, engineered and installed in tight spaces.
At the same time, there is a growing focus on energy-efficiency, driven by cost pressure and
regulatory requirements.
Deployment flexibility is increasingly important as more and more equipment is needed on
site: floor space is limited and wall space is often needed to install equipment.
Moving to main-remote
The proportion of main-remote deployments, with radios placed outside the cabinet nearer to
the antenna, as well as antenna-integrated radios is steadily increasing, driven by performance
advantages, lower energy consumption and deployment flexibility.
A basic principle of cell site design is that higher output power offers greater options for
delivering better network performance in terms of coverage, capacity and latency. There will
always be some power loss in the feeders between antennas and radios, meaning longer feeders
are detrimental to network performance: it is better to place the radio as close as possible to
the antenna. This makes main-remote radios that can be placed outdoors better than a cabinet
radio, since they can be placed very close to the antenna (which a cabinet radio usually cannot).
The lower power losses of these main-remote designs also reduce power consumption for the
same network performance.
Another reason for the popularity of main-remote designs is a practical one. Cabinet radios
need to be installed on the floor. In space-limited sites, there may not be enough floor space to
accommodate a cabinet with all the radio units needed to match current and future traffic demand.
In such locations, it is essential to use all available space, including wall space, which can be
done with main-remote designs.
One other practical aspect is that some site equipment is better centralized (such as transmission
and power backup), while other equipment is better distributed (such as radios close to antennas).
This means that using cabinet radios also increases equipment costs if radios need to be located
close to the antenna for a three-sector site (because this requires three cabinets instead of one).
These effects are then multiplied in multiband and multilayer sites. In addition, radio features
like carrier aggregation and multiple-input, multiple-output (MIMO) further add to the need for
cabling between radios and baseband units.
Building extreme capacity sites that support multiple frequency bands cost-efficiently presents
significant challenges. Site acquisition has always been an issue in areas like city centers, and
is becoming more difficult and costly. This means that developing extreme capacity solutions
within existing sites is likely to be the favored option for most operators.
Operators need to plan and map out their next steps for these revenue-critical sites.
RADIO SITE TRANSFORMATION • Differentiating where it counts 4
Delivering
efficient growth
One way in which operators are meeting mobile broadband capacity needs in high-density areas
where site acquisition options are limited is through the deployment of additional bandwidth in
the form of new radio technologies or additional frequency bands, or both.
By 2020, it will not be uncommon to see radio sites with as many as 10 frequency bands across
different technologies.
Meeting the needs of multiple radio bands across multiple radio technologies – 2G, 3G, 4G
and later 5G – within the existing site footprint will call for solutions that incorporate a much
higher number of radios, baseband and transmission units than before. However, today’s hardware
is simply too large and insufficiently systematized to enable extreme capacity sites to be built
efficiently in existing locations.
Balancing site design
It is important to balance the dimensioning between the four main types of equipment on a site:
radio, baseband, transmission and power. The capacity and latency delivered are only as good
as the weakest link in the radio-baseband-transmission chain.
The power solution, including backup, must take into consideration the other three equipment
types. When defining and dimensioning the transmission part, it is important to consider the
backhaul capacity needed and the latency of the fiber or microwave connection used. With
centralized baseband, it may be better to use wavelength division multiplexing (WDM) fiber for
fronthaul since it simplifies practical transmission aspects when using radio features like carrier
aggregation and coordination. In some scenarios, wireless fronthaul can be used when fiber is
not viable.
Planning the power solution with respect to power consumption and power losses is extremely
important in high-capacity sites, where any interruption in operation could have a significant
impact on revenue and reputation. Here, the choice between AC and DC solutions could be
crucial: AC exhibits less power loss but comes with bigger safety risks. Intelligent power
consumption algorithms for traffic handling during power outages and battery charging can make
a big difference to overall power consumption.
Common building practice
As the trend continues toward placing (smaller) radio units outside cabinets, closer to the antennas
(to minimize losses and latency), with a growing number of frequencies and sectors per site, more
and more (fronthaul) transmission branches are needed to connect the growing number of radios
efficiently to a growing number of baseband units and maximize the overall performance and
reliability of the cell. In addition, access to the power supply is needed not just at the cabinet, but
also for the radios. This is leading to a massive increase in the amount and complexity of cabling.
A new approach to designing and building site solutions is needed that offers systematic
characteristics – in terms of ease of construction, ease of expansion, power-efficiency and safety
– that deliver the desired network performance at the right lifetime cost. Revenue-critical sites
will demand highly efficient modular systems that are easy to install, configure, expand and
adapt to new mobile broadband demands.
More equipment on site requires a common building practice in order to optimize site cost
and network performance. Form factor becomes critical: size (volume) and weight must be
minimized in order to enhance installation flexibility (such as wall mounting), and make equipment
easier to handle.
Traditional main-remote radios have occupied 20-40 liters and weighed roughly 20-40 kg. With
high-capacity sites most likely needing to support as many as 10 frequency bands, there may
be 30 radios on a three-sector site. When baseband units, transmission units, site routers and
cabling are also included, it is easy to see the practical importance of form factor.
A common form factor for the different equipment types is important to make installation as
flexible as possible. It is also important that connectors are placed in such a way that the units
can be easily installed in different ways to increase installation flexibility.
To reduce the number of cables needed between radios and baseband units, for example, Common
RADIO SITE TRANSFORMATION • Delivering efficient growth 5
Public Radio Interface (CPRI) splitter units can be used. These also have the advantage of reducing the
number of ports needed in the baseband unit (as shown in Figure 3).
Radio
Baseband
Baseband
Radio
Radio
CPRI splitter
Radio
Radio
Radio
Common
Radio
Radio
Radio
Radio
CPRI cable/port reduction
Figure 3: CPRI splitters reduce both the amount of cabling and the number of ports needed in the
baseband unit at radio sites.
Enhancing overall efficiency
New performance-enhancing radio techniques – such as carrier aggregation, MIMO and increasing
antenna element arrays – are driving a rapid increase in demand for digital signal processing power needed
to handle radio signaling.
This in turn is driving the need for more energy-efficient site solutions, especially as the radio network
represents the dominant proportion of overall mobile network energy use. The processing needs at
radio sites will only become greater as traffic volumes rise and new radio technologies, including 5G,
are rolled out.
To reduce overall energy costs, operators could introduce energy management schemes that adapt
power usage to traffic levels. For example, features for dynamically reconfiguring three-sector sites to
omni-operation, reconfiguring antennas from MIMO to single-input, multiple-output (SIMO) mode, and
discontinuous transmission are all based on traffic load. As a result, the radio system makes a shift from
being ‘always on’ to ‘always available.’ At multi-standard, multiband sites, it is possible to shut down certain
bands during low-traffic periods to reduce energy use. Transmission equipment can be handled in a
similar way.
Distributed, centralized or virtualized
One important aspect of improving overall efficiency is how to handle the increasing baseband
processing requirements.
At a strategic level, operators need to decide where the switching, routing and ‘intelligence’ to handle
the growing volumes of internet traffic in their networks will reside. The basic choice is to make such
functionality, including baseband hardware, centralized, distributed or even virtualized.
As the number of radios per site increases, and the variety of advanced techniques for deriving extra
capacity and throughput from each channel grows, the need for baseband processing increases. Essentially,
this is driving the need for more baseband units, with progressively more digital signal processing power
over time.
The performance of baseband units has increased dramatically in recent years, with the availability of
Many Core Architecture processors that enable several thousand active users to be simultaneously handled
by a single board, for example.
Traditionally, baseband units are placed near the radio units to minimize latency. Where WDM fiber
is available, operators have the option of deploying locally centralized ‘baseband hotels’ to coordinate
processing power between clusters of cell sites. The coordination gains are initially significant, but tail
off as the size of the coordination clusters grows (as shown in Figure 4), while the maximum distance
between the coordinated baseband resources and the radios is limited by acceptable levels of delay,
latency and jitter. The location of cluster borders and the availability of suitable power supplies also
need to be considered carefully when adopting a centralized approach.
There are practical limitations to the deployment of such baseband hotels, because the CPRI interface
they require has significantly higher data rate and latency requirements than the Iub, X2 and S1 interfaces
typically used between baseband units and the core nodes Evolved Packet Core (EPC) and radio network
controller (RNC). The dark fiber or WDM connections needed are not widely available.
Virtualizing baseband digital signal processing – essentially, putting processing resources in the cloud
– presents significant risks to overall performance. Furthermore, it is unlikely that the commercial, off-theshelf hardware used in virtualized solutions will be viable from a performance or energy-efficiency
perspective.
RADIO SITE TRANSFORMATION • Delivering efficient growth 6
As operators deploy a mix of macro cells, small cells and Wi-Fi to meet rising capacity needs,
RAN architecture will evolve to incorporate a mix of distributed and centralized RAN approaches.
Techniques like Coordinated Multi-Point (CoMP), in which users are served by multiple cell sites
to maximize throughput performance, will be key to delivering spectral efficiency and lower total
cost of ownership.
Capacity increase
100
80
60
40
20
0
1
2
3
4
5
6
Size of coordination clusters
3
1
3
1
2
7
8
9
3
1
2
2
Figure 4: Incremental capacity gains diminish as the number of cells
included in a coordination cluster increases.
Figure 5: Uncoordinated network cluster size 1.
Figure 6: Coordinated network cluster size 3.
RADIO
SITE TRANSFORMATION • Delivering efficient growth
7
Advanced radio integrated transport
Whether they employ distributed or centralized baseband, extreme capacity solutions will require
tight radio and backhaul transport integration to ensure superior user experience and maximum
efficiency. They will need fronthaul, access routers and backhaul that can support the new
capacity levels and strict timing requirements, as well as provide more efficient provisioning and
maintenance. To keep operating costs down and increase agility, fronthaul and backhaul network
provisioning needs to be fully integrated with rest of the RAN. The solutions will also need a very
resilient backhaul transport solution because of their critical value, where no single point of failure
should determine their continuous operation.
Meeting the strict latency requirements of centralized and coordinated RAN architecture will
require a fronthaul network that can deliver very high capacity with minimal latency, over CPRI
connections. Low-latency (sub-100 microseconds) transport of CPRI enables the coordination
of various radio sites for maximum capacity (through CoMP).
Operators need to invest in transport hardware that can enable them to skip an upgrade cycle
or two by seamlessly keeping pace with traffic growth in ever-shortening capex cycles. In extreme
cases, traffic in backhaul links at baseband hotels is already reaching multi-Gigabit Ethernet
(GE) levels and could well reach 100GE interfaces within a few years. At the cell sites, keeping
up with traffic growth will require multiple 10GE interfaces within five years. Operators can break
frequent and expensive capex cycles by adopting a 7-10 year view, perhaps with solutions that
enable ‘pay-as-you-grow’ capacity licenses.
Managing backhaul latency and packet loss is critical in ensuring the QoE for users in a mobile
network. Advanced integration between backhaul network and RAN enables key information
exchange across each domain in order to enable more intelligent and automatic mitigations. This
way, the network can automatically heal a congested connection when possible by using softwaredefined networking and traffic engineering capabilities. For example, users may be load-balanced
to different eNodeBs that have a backhaul connection that is healthier. If this fails, then in extreme
scenarios such as a stadium event, admission control may be used by the RAN instead.
In addition, making the backhaul more aware of each individual subscriber in a radio network
enables more granularity in how traffic is engineered and load balanced, further improving
utilization of the network and improving QoE. Greater granularity also enables Network Functions
Virtualization and orchestration to be introduced more easily for mobility anchor points such as
an Evolved Packet Gateway. Subscriber-aware backhaul enables individual users or even individual
user applications, such as video, to be handled in a way that goes far beyond simple QoS
mechanisms.
Advanced, radio-integrated transport plays a pivotal role in handling performance at these
revenue-critical sites.
RADIO
SITE TRANSFORMATION • Delivering efficient growth
8
Conclusion
Operators need to meet growing traffic capacity demands, especially in busy, densely
populated areas, with their current mobile network as the starting point. Existing site
solutions and strategies are unlikely to be able to address the coming site challenges. A
radio site transformation is needed for high-capacity radio site design.
With operators deploying a mix of distributed, centralized and coordinated radio architecture,
there will also be a significant impact on the transport network. The transport solution will
need to be fully integrated with the rest of the site in order to make installation and operation
as simple and seamless as possible.
Any system is only as good as its weakest link, so all site equipment – including the antenna
system, cabling, fronthaul and backhaul – needs to be carefully chosen and dimensioned.
Operators will benefit from deploying site solutions that are compact, systematic and
modular in design, in order to take care of radio functionality, baseband processing,
transmission, power and battery backup as efficiently as possible.
RADIO SITE TRANSFORMATION • conclusion
9
GLOSSARY
CoMP
CPRI
GE
MIMO
SIMO
WDM
Coordinated Multi-Point
Common Public Radio Interface
Gigabit Ethernet
multiple-input, multiple-output
single-input, multiple-output
wavelength division multiplexing
RADIO SITE TRANSFORMATION • glossary
10
References
1.
Ericsson, November 2014, Ericsson Mobility Report, available at:
http://www.ericsson.com/res/docs/2014/ericsson-mobility-report-november-2014.pdf
2.
United Nations, accessed February 2015, Global Issues – Human Settlement, available at:
http://www.un.org/en/globalissues/humansettlements/
RADIO SITE TRANSFORMATION • REFERENCES
11