A mobile network operator that plans to roll-out its new LTE network has in principle two options: buy new spectrum or re-farm spectrum already in possession. Based on the tools, know-how and experience in networks’ reconfiguration at DATAX, we believe that well performed re-farming, if accompanied by GSM optimisation (new frequency plan, reconfigurations of parameters, etc.) frees up spectrum for LTE roll-out and leads to the overall improvement of most of the KPIs while keeping the interference under control. It goes without saying that LTE technology slowly becomes available across the nation after the first products appear on the market. Mobile operators that want to meet market expectations have to start this new technology roll-out process and gain free spectrum. But experience from UMTS history show that investments in a new spectrum in the early stage of LTE market development might not necessarily be the best way. Of course, in the future a dedicated large spectrum block will be required for LTE but at present time re-farming seems to be the best way to obtain spectrum quickly and cheaply. However, as discussed, mature 2G technology will remain for many years an important part of a mobile communication business. Hence, well performed re-farming that will not cause worsening of 2G services is a challenge, but is certainly possible. DATAX is a company that is capable of meeting this challenge and manage cost-effectively re-farming of spectrum to provide room for LTE while keeping GSM services at optimal quality.If re-farming makes so efficient solution for LTE spectrum acquisition and GSM still remains an important technology, the question comes up whether it is possible to “have cake and eat it too”. Basically, it means deploying LTE in the GSM spectrum without compromising 2G network’s quality. In a nutshell, re-farming is a process of removing part of spectrum allocated to GSM (freeing bandwidth for LTE) while reconfiguring appropriate network parameters.

1. What makes re-farming the best
approach to efficient LTE roll-out or
How to have cake and eat it too?
by DATAX

2. INTRODUCTION
A mobile network operator that plans to roll-out its new LTE network has in principle two
options: buy new spectrum or re-farm spectrum already in possession.
Buying new spectrum is like building a new multiple lanes highway dedicated only
for modern vehicles. On the other hand, re-farming means reorganising management
methods and rules on existing roads and enabling coexistence of very modern and legacy
vehicles. The first method is time consuming and costly but at the end a high throughput
communication way is achieved, whereas re-farming is remarkably cheaper and swift but
requires perfect planning and management.
LTE SPECTRUM AUCTIONS VS. RE-FARMING
LTE technology very efficiently utilises radio resources ( LTE spectral efficiency is 16.3 bit/s/
MHz in comparison to 8.4 and 1.92 bit/s/MHz of HSDPA and GSM + EDGE, respectively)
and can be easily built on top of existing 3GPP networks architecture. This technology is
perceived as a solution for satisfying market expectations regarding growing throughput
figures. Auctioned spectrum might be very expensive as exemplified by auctions of 3G
spectrum in Germany and UK at the start of the new Millennium. At that time, operators
paid respectively 350 and 97 billion of Euros per MHz. At present time, final prices paid
in auctions are lower, except for the most desirable bands like “digital dividend”.
On the other hand, spectrum acquisition for LTE roll-out by means of re-farming process
is much cheaper as it builds on radio resources already owned by an operator. Re-farming
cost depends mainly on the network size that determines effort that must be spent by
engineers, but the final price might be even less than 0.1% of the cost of buying new
spectrum (e.g. shown in Table 1).
Table 1 Price paid in recent German and Spanish auctions for 4G spectrum.
Germany, Spain,
Band
Auctioned May 2010 Auctioned July 2011
800 MHz 59.6 M€/MHz 23.0 M€/MHz
900 MHz - 16.9 M€/MHz
1800 MHz 2.1 M€/MHz -
2000 MHz 8.8 M€/MHz -
2600 MHz Paired 1.8 M€/MHz 2.3 M€/MHz
2600 MHz Unpaired 1.7 M€/MHz Offered but no bids for it
In Table 1, lower range spectrum (bands 900 MHz and 800 MHz) appears to be most
attractive for operators. This is mainly because of better propagation characteristics at
lower frequencies. Specifically, radio waves in the frequency bands 900 MHz have lower
propagation losses, undergo smaller attenuation as they pass through buildings as well as
2 What makes re-farming the best approach to efficient
LTE roll-out or How to have cake and eat it too?

3. better diffraction characteristics around obstacles in comparison to the frequency band
2100 MHz. All these effects make 800 and 900 MHz very desirable for operators as they
allow them to reduce their costs in network deployment process (the same coverage
area requires 2 to 3 times fewer sites in comparison to 2100 MHz). Obtaining access to
these lower frequency bands through auctions in order to deploy LTE is very expensive.
At the same time, the lower frequency bands are already at a disposal of many operators,
as first 2G mobile networks were very often rolled out in 900MHz bands. In consequence,
spectrum re-farming emerges as a possibility to allow these operators deploy LTE in this
most valuable spectrum at a very low cost.
Also, a very good candidate for re-farming to LTE is GSM 1800 MHz band, which is
presently commonly used for voice communication. Coverage at 1800 MHz is lower than
at 900 MHz but still almost 2 times larger than at 2600 MHz. Hence, operators may roll-
out new LTE network with good coverage at a reasonable cost. What is also important,
many operators already possess blocks of 20 MHz and more in 1800 MHz bands. This fact
yields an opportunity to provide full LTE data speed (large spectrum blocks will enable
contiguous carrier aggregation to exploit LTE-A feature).
WHY 2G WILL REMAIN IMPORTANT?
Obviously, re-farming can speed up LTE deployment in a cost effective manner, especially
in the bands occupied by GSM. However, at the same time operators face the challenge
of avoiding compromising quality of the 2G networks in this process. Presently, 2G
technology is the most popular commercial communication system in the world with
more than 4 billion subscribers. Upward trend of GSM subscriptions is expected to be
continued within next few years in emerging markets, whereas in mature markets like
Europe, where mobile devices penetration already exceeds 130%, this trend is reversed.
Nevertheless, high-tech terminals that nowadays are replacing former GSM mobiles also
support legacy technologies (from GSA statistics: approximately 84% HSPA terminals
also support GSM EDGE) and in this way assure services continuity in case of WCDMA or
LTE coverage problems (2G networks have been developed since early 90s and in some
countries cover almost 100% area). Moreover, GSM technology development is still on-
going and features like Orthogonal Sub Channels will double voice channel capacity very
soon. Currently, main component of the GSM traffic is still voice but data transmission
and GERAN continuously rise and further growth is expected to be driven mainly by M2M
communications. In case of M2M communications, coverage, reliability and availability are
more important than bandwidth. Hence, 2G technology that is widely available in 73% of
mobile markets is perceived as a most attractive candidate to support M2M deployment.
As an example, Sprint plans to provide its customers with global M2M connectivity
outside the U.S. in cooperation with Orange Business Services (announced on February
7th 2012). By means of this partnership, Sprint-branded global M2M connectivity will
be available in 180 countries by using M2M-specific GSM SIM cards. While Sprint plans
to expand its M2M business to GSM worldwide market, AT&T announced (August 2012)
3 What makes re-farming the best approach to efficient
LTE roll-out or How to have cake and eat it too?

4. plans to close its GSM networks by 2017. Few months before when AT&T decided to shut
down its GSM 1900 MHz PCS bands in New York, Apriva Wireless which is one of the
biggest players on the M2M markets and AT&T partner shifts part of its business to Raco
T-Mobile M2M service provider. T-Mobile is re-farming its 2G network as well as other US
operators but keeps 25% of its 2G spectrum. Figure 1 shows DATAX forecasts of global
subscriptions (by device types) and related global 2G traffic. It depicts slow decline of
handsets devices share in 2G market and at the same time growth of M2M modules. Over
the time, traffic generated by M2M devices will rise. Hence, even with decreasing number
of handsets in the market, the total 2G data traffic will be growing within next few years.
Figure 1 2G subscriptions and traffic forecast.
SUCCESSFUL RE-FARMING PROCESS
If re-farming makes so efficient solution for LTE spectrum acquisition and GSM still remains
an important technology, the question comes up whether it is possible to “have cake and
eat it too”. Basically, it means deploying LTE in the GSM spectrum without compromising
2G network’s quality. In a nutshell, re-farming is a process of removing part of spectrum
allocated to GSM (freeing bandwidth for LTE) while reconfiguring appropriate network
parameters. A rule of thumb is that narrower spectrum means less capacity what may
give rise to concerns of worse quality experienced by customers (e.g. higher interference,
lower throughput). Of course, GSM customers do not want to be affected by the transition
and thus new network configuration shall avoid main KPIs degradation. Furthermore,
4 What makes re-farming the best approach to efficient
LTE roll-out or How to have cake and eat it too?

5. narrower bandwidth available in GSM requires a new frequency plan that provides for
optimal interference conditions after re-farming. If environment is multi RAT, part of the
GSM traffic can be offloaded to WCDMA by encouraging user terminals to select WCDMA
rather than GSM cell. Well done re-farming optimises overall network resources utilisation
without impacting legacy users while providing an operator with a possibility to deploy
LTE services.
Based on the tools, know-how and experience in networks’ reconfiguration at DATAX,
we believe that well performed re-farming, if accompanied by GSM optimisation (new
frequency plan, reconfigurations of parameters, etc.) frees up spectrum for LTE roll-out
and leads to the overall improvement of most of the KPIs while keeping the interference
under control.
It goes without saying that LTE technology slowly becomes available across the nation
after the first products appear on the market. Mobile operators that want to meet market
expectations have to start this new technology roll-out process and gain free spectrum.
But experience from UMTS history show that investments in a new spectrum in the early
stage of LTE market development might not necessarily be the best way. Of course, in
the future a dedicated large spectrum block will be required for LTE but at present time
re-farming seems to be the best way to obtain spectrum quickly and cheaply. However,
as discussed, mature 2G technology will remain for many years an important part of a
mobile communication business. Hence, well performed re-farming that will not cause
worsening of 2G services is a challenge, but is certainly possible. DATAX is a company that
is capable of meeting this challenge and manage cost-effectively re-farming of spectrum
to provide room for LTE while keeping GSM services at optimal quality.
ABOUT THE AUTHOR
Szymon Stefanski is a Radio Research Engineer at DATAX.
He can be reached at szymon.stefanski@datax.pl
CONTACT US
DATAX Sp. z o.o. (DATAX Ltd.)
ul. Muchoborska 6
54-424 Wrocław
POLAND
sales@datax.pl
www.datax.pl
www.spectrumrefarming.com
5 What makes re-farming the best approach to efficient
LTE roll-out or How to have cake and eat it too?