The rapid growth of mobile broadband is forcing operators
to add both coverage and capacity, applying a holistic spectrum strategy that
covers voice-centric and mobile broadband network deployments. As the
penetration of 3G-capable terminals increases, the 1800MHz spectrum used for
GSM services becomes an increasingly attractive candidate for refarming to
mobile broadband services based on LTE and HSPA.
The right band at the right time
It is vital that operators continue to deliver good
mobile broadband user experience as growing number of subscribers acquire smartphones, tablets, dongles and
other mobile broadband enabled devices.
Ensuring that there is sufficient network capacity
available to meet this growing demand for anywhere,anytime connectivity with the best possible performance
is the number-one priority.
Mobile broadband subscribers and traffic are growing at
an unprecedented rate. The number of mobile broadband subscriptions is estimated to hit the one
billion mark in 2011 and Ericsson estimates that this figure will grow exponentially to almost top
five billion by 2016. Some advanced markets have seen a doubling in mobile-data-traffic volumes every
six to 12 months over the past few years, primarily driven by rapid subscriber growth.
The main growth driver is the mass-market shift from
voice-centric feature phones to mobile broadband-enabled smartphones. In some markets, 90
percent of new handsets sold are smartphones of this type.
This transition represents a great opportunity for
operators because smartphone users generate significantly higher ARPU than users with voice-centric
phones. But it also represents a challenge:as subscribers become more reliant on mobile broadband
access as part of their daily lives, they are starting to cite reception quality as their primary concern – ahead of ease of use, screen size and extensive battery life.
In other words, the network is becoming the
differentiator, and one significant aspect of ensuring high-performance mobile broadband for the mass market is
having access to sufficient radio spectrum to deliver the required capacity and coverage.
Operators need to consider the most profitable way of
utilizing their total spectrum assets today and in the future. As mobile-data traffic continues to
grow, one clear candidate for delivering additional spectrum for mobile broadband is the 1800MHz band, today
available for deployment of GSM services to more than 350 operators in 148 countries around the
world.
By refarming this 1800MHz spectrum for use by mobile
broadband radio technologies, including LTE and HSPA, operators can gain the additional capacity,
higher performance, global accessibility and economies of scale that will ensure the continued success
of mobile broadband services.
The challenge of harmonization
To provide an excellent mobile broadband service,
operators need to ensure highest network quality; this means having the right coverage, capacity and latency to
accommodate the continuous growth of mobile – data traffic.
There are essentially three ways operators can achieve
this. The first is to improve spectral efficiency by introducing radio
technologies such as LTE and evolved HSPA. The second is to expand the amount
of radio spectrum available to mobile broadband through the deployment of new
carriers or new bands. The third is to densify the network with more cells and
layered architecture. For most operators around the world, meeting demand for
mobile broadband will mean engaging in a combination of these activities.
When expanding into new bands, it is important for
operators to choose a frequency and technology combination that gives them the potential
to create a global footprint, in order to leverage economies of scale and
simplify international roaming. This becomes even more important for a new
technology such as LTE, as there are a large number of deployment options. 3GPP
has identified 20 paired (FDD) and 11 unpaired (TDD) bands for use by LTE around
the world, as shown in Table 1. This provides a wide choice of bands for LTE
deployment.
The 1800MHz band already has a global footprint, as more than
350 operators in 148 countries have spectrum assets in that band, providing
great potential for global mobile broadband deployment. In the European Union,
initial licenses in the 900MHz and 1800MHz bands were dedicated to GSM technology.
This situation has now changed as Commission Decision 2009/766/EC has adopted
both HSPA and LTE as technologies that may be used in these bands.
Most EU countries have some face national competitive and
legal challenges in their markets, which threaten to delay deployment of new
technologies. Some member states, including the Netherlands and Switzerland,
have decided to hold off deployment of non-GSM technologies until current 3G
licenses expire.
In several EU member states, the competitive situation
changes if operators with spectrum in 900MHz and 1800MHz are allowed to use
WCDMA or other IMT technologies in addition to GSM. In some countries,
including Denmark, Italy and Sweden, this has been resolved by reallocating
spectrum in the 900MHz band to incorporate operators that only had spectrum in
2100MHz. In other markets, including Germany and the UK, regulators do not
enforce reallocation in the 900MHz band, but instead are applying restrictions
to existing 900MHz license holders in their upcoming auctions of 800MHz Digital
Dividend spectrum.
The regulatory situation for countries outside Europe
varies. Many countries allow the 900MHz and 1800MHz bands to be used for any
technology, while in others they are earmarked for GSM only.
Maximizing spectrum utilization
The question for operators with access to 1800MHz
spectrum is: how can they make best use of this resource as part of a holistic
spectrum strategy for mobile broadband growth?
1800MHZ: The advantages
Today, the 1800MHz band is almost entirely used for GSM
traffic, often as a higher band complement to GSM in the 900MHz band.
Typically, the higher band is used for delivering capacity and the lower band
for coverage.
In many markets, subscribers are migrating to 3G-enabled
smartphones, and offloading GSM traffic from the 1800MHz spectrum. Combined
with good 3G coverage, this migration simplifies the process of refarming this
spectrum for use by mobile broadband radio technologies such as LTE and HSPA.
There are a number of advantages offered by the 1800MHz
band when used by mobile broadband radio technologies. In most markets, it
offers 2 x 75MHz spectrum bands – often in slots of 10MHz or wider – that are
typically not fragmented and often only partially utilized.
LTE supports flexible carrier bandwidths, from 1.4MHz up
to 20MHz. It also supports both FDD and TDD modes. This makes the technology
extremely efficient at utilizing spectrum even in narrow, fragmented bands.
For existing GSM1800 operators, this opens up the
opportunity to refarm some, or all, of their 1800MHz spectrum for LTE use in a
very efficient way. As LTE and GSM do not interfere with each other, they can
be deployed together in adjacent frequencies without the need for guard bands.
This gives GSM operators the option of gradually shifting the amount of 1800MHz
bandwidth assigned to LTE in line with demand.
For operators with sufficient HSPA capacity to meet
projected mobile broadband growth from smartphones, rolling out LTE in the
1800MHz band is an obvious choice. However, if the HSPA spectrum assets are not
sufficient to meet this need, using the 1800MHz band for HSPA should also be
considered as an option.
As part of their spectrum strategy, operators also need
to consider refarming lower-band GSM spectrum (such as 900MHz) to HSPA, in order to improve HSPA
coverage for the smartphone mass market. When carrying out this low-band HSPA refarming, there may be
implications for the GSM load in 1800MHz, as GSM traffic is shifted from the 900MHz to the 1800MHz
network. These potential effects also need to be considered as part of a 1800MHz refarming decision.
Overall, operators need to strike a balance between
driving innovative, market-leading LTE services, serving the profitable and growing HSPA mass market, and
continuing to manage voice-centric GSM traffic well.
A commercial decision
The choice of which technology route to take LTE1800 or
HSPA1800 – will depend on a range of factors.
These include: the operator’s current market situation;
the penetration of smartphones and other mobile broadband devices; the
availability of other spectrum (especially that offering the capacity, and
coverage, to cater for mobile broadband growth); the geography of the
operator’s service area; and local regulatory conditions.
From a technical perspective, either route is perfectly
feasible. Spectrum refarming is a tried and trusted approach, and the
deployment of multi-standard equipment can leave the decision open, even if the
operator decides to modernize its network. Several GSM operators around the
world have conducted major refarming projects to implement WCDMA/HSPA in the
900MHz band. Experience of running both GSM and WCDMA/HSPA networks has already
shown how both technologies can continue to evolve in parallel, and how spectrum
can be refarmed from GSM to WCDMA/HSPA in line with commercial needs.
Through its support of both FDD and TDD modes, LTE helps
drive the global convergence of radio access for paired and unpaired spectrum
into a single globally-adopted technology. LTE and HSPA are both highly capable
radio-access technologies for mobile broadband. While LTE and its evolution
will ultimately offer superior throughput and spectral efficiency, evolved HSPA
performs as well as LTE in most areas and for most applications. Decisions on
how fast to evolve HSPA networks and how soon to deploy LTE will be based on
individual operators’ circumstances. There are well-defined evolution paths for
both technologies.
The decision to refarm the 1800MHz spectrum for HSPA or
LTE is therefore mainly a commercial one, rather than a technical one: there
are tried and trusted approaches for refarming the spectrum in either
direction.
Shaping the eco-system
To encourage the transition of mobile broadband
subscribers to higher-speed, higher-capacity radio technologies like HSPA and
LTE, operators need to manage the evolution of their networks and terminal fleets
in tandem. For existing GSM1800 operators, this means rolling out network
features and terminals that reduce the load from GSM services in the 1800MHz
spectrum.
Operators can accelerate the process of freeing up
1800MHz bands through frequency replanning and the deployment of GSM
modernization technologies that enhance voice spectral efficiency – essentially
squeezing the spectrum needed by GSM traffic. As the number of global GSM
subscriptions continues to rise, further investments are being made into
serving these subscribers more efficiently.
As refarming means less spectrum is available for GSM,
operators need to be sure they put in place a process for maintaining
performance, and minimize the effects of interference in the narrower spectrum used,
as shown in Figure 1. The old cell plan is unlikely to be optimal, meaning the
process will need to include some replanning and retuning of the network.
The second step in this process is to identify which
features are to be implemented in the GSM network to prepare it for refarming.
There are many techniques available to do this, including 1/1 reuse, Adaptive
Multi-Rate (AMR) techniques and Voice services over Adaptive Multi-user channels
on One Slot (VAMOS), to name a few.
Not all of these features need to be implemented at the
same time, and will differ for each network case. Here, the vendor’s experience
of real-life refarming projects becomes very important in maintaining network performance,
especially in areas such as radio optimization, tuning, replanning and
monitoring.
As GSM operators modernize their networks to become more
energy- and spectrum-efficient, they are increasingly deploying
multi-frequency, multi-standard radio base stations that can handle all 3GPP
radio technologies in one system. This enables smooth evolution to new mobile
broadband radio technologies without significant additional capital investment,
while allowing operators to serve the significant GSM subscriber base
efficiently in line with market needs.
GSM1800 operators that also have HSPA implemented in the
2100MHz band will be able to reuse their existing 2100MHz radio sites for
LTE1800 (and LTE2600), as they offer roughly the same levels of coverage. In
addition, GSM antennas typically designed for x-polarization (Rx diversity), as
well as other site assets, can be reused for 2×2 multiple-input,
multiple-output (MIMO) operation in LTE and HSPA.
Another way in which operators can encourage load
reduction on the GSM network is by actively steering new terminal sales towards
3G-capable devices that make less use of GSM. Some operators have proactively made
the decision to offer only HSPA-enabled devices to their subscribers. In this
way, the vast majority of devices will eventually be using the HSPA network,
with its higher spectral efficiency for voice and data.
Of course, as part of this strategy, it is important to
ensure 3G coverage is sufficient to enable HSPA devices to continue with the 3G
access, without the need to use GSM for voice or data calls.
The successful use of 1800MHz spectrum for mobile
broadband will require mobile broadband-enabled devices that can use the band.
Furthermore, these devices must offer multiple standards (multi-mode) and bands
(multi-band) within each mode. As it resides roughly in between the other bands
allocated for use by LTE, the 1800MHz band provides a good complement to either
low” bands, such as the 800MHz band, or high” bands, such as the 2600MHz band
used for LTE in Europe.
In recent years, great advancements have been made in
areas such as filter technology, which means chipset makers have been able to
produce multi-band, multi-mode devices more cost-effectively than before. Several
device-chipset makers have introduced or announced multi-band LTE/HSPA
products, and these are starting to be shipped in commercial volumes. Ericsson
has conducted extensive interoperability tests with ST-Ericsson and other
suppliers.
In June 2011, the Global mobile Suppliers Association
(GSA) estimated that about 10 percent of LTE devices already support the
1800MHz band. Some operators have taken the step of pre-populating their terminal
fleets with such multi-mode, multi-band devices that will be ready to make use
of new radio-network technologies as soon as the network is enabled.
Evolution scenarios
The ultimate shape that operators’ mobile broadband
networks will take – and the route and timing of the journey taken to get there – will vary from case to case. As an illustration of the possible alternative
routes that could be taken by three different operators, Figures 2 and 3 show
the start points and end points of the evolution to a high-performance mobile
broadband network using different radio-access technologies. Typical European
frequencies are used to illustrate the strategies for this evolution.
Scenario 1: This operator has no early access to either
2600MHz or 800MHz spectrum for LTE. Here, the first step is to refarm the
900MHz spectrum to HSPA in order to boost 3G coverage and capacity, especially
in rural areas. As GSM traffic diminishes as a result of the greater HSPA capacity,
the operator can refarm the 1800MHz spectrum either for LTE or HSPA to provide
high-performance mobile broadband in urban and suburban areas. The technology choice
will depend on the operator’s market position, the current and projected device
fleet, the ability to serve mass-market volumes of HSPA smartphones in existing
3GPP bands, and the availability of other bands for LTE. In this scenario, the
operator is able to roll out LTE in other bands as it becomes available.
Scenario 2: This operator has already deployed WCDMA/HSPA
in the 900MHz, as well as in the 2100MHz band. The total spectrum in these deployments
is sufficient to cater for mass HSPA smartphone uptake. By driving the uptake
of 3G-capable devices that use 3G access for voice and data, and rolling out
GSM efficiency improvements, GSM traffic can be served within the 900MHz spectrum.
This frees up the 1800MHz spectrum for LTE deployment.
Scenario 3: This operator has early access to 2600MHz
spectrum for LTE, as well as the option for rolling out LTE in the Digital
Dividend 800MHz band (made available following the shutdown of Europe’s analog
TV networks). The operator’s first step is to refarm 900MHz spectrum to
WCDMA/HSPA to provide wider and deeper 3G coverage and capacity, especially for
rural and indoor areas. Increasing use of WCDMA/HSPA in the wide area gradually
reduces load on the GSM/EDGE network.
In addition, the operator deploys LTE in the 2600MHz band
in urban hotspots to provide a high-speed mobile-broadband service to
complement the HSPA access. After this, the operator rolls out LTE in the 800MHz
band to provide high-performance broadband in the wide area, including rural
areas.
Ultimately, when GSM traffic has diminished
significantly, the operator can refarm the 1800MHz spectrum for LTE as well to
provide a further capacity and boost coverage. Alternatively, if the need for
additional HSPA capacity is more pressing at this time, the operator has the
option of deploying HSPA in the 1800MHz spectrum.
Conclusion
The popularity and rapid growth of mobile broadband
services are a result of the value people derive from having anywhere, anytime
connectivity to the internet. To maintain and enhance mobile broadband user
experience – especially as user devices and applications become more powerful
and data-hungry – operators need to deploy ever-faster connections, along with
greater network capacity and broad coverage.
As two key components of this unified mobile broadband
network, LTE and HSPA are both capable of delivering the additional capacity,
coverage and performance that operators need. The 1800MHz band is a strong
candidate for such deployments, due to its large footprint. Whichever
technology path operators choose to take, they will benefit from access to
additional radio spectrum that will enhance their subscribers’ mobile broadband
experience in their own networks and as they roam.
Ultimately, the technology ecosystem will be shaped by
the commercial decisions that operators make for their own markets. But one
thing is for certain: the 1800MHz band represents a major asset for enabling
mobile broadband growth in the coming years. As the first roll outs of mobile
broadband in 1800MHz are already under way, the trend appears to be
unstoppable.
By Ericsson
[email protected]
