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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 ...

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.

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Refarming article slide Refarming article slide Document Transcript

  • What makes re-farming the bestapproach to efficient LTE roll-out or How to have cake and eat it too? by DATAX
  • INTRODUCTIONA mobile network operator that plans to roll-out its new LTE network has in principle twooptions: buy new spectrum or re-farm spectrum already in possession.Buying new spectrum is like building a new multiple lanes highway dedicated onlyfor modern vehicles. On the other hand, re-farming means reorganising managementmethods and rules on existing roads and enabling coexistence of very modern and legacyvehicles. The first method is time consuming and costly but at the end a high throughputcommunication way is achieved, whereas re-farming is remarkably cheaper and swift butrequires perfect planning and management.LTE SPECTRUM AUCTIONS VS. RE-FARMINGLTE 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 isperceived as a solution for satisfying market expectations regarding growing throughputfigures. Auctioned spectrum might be very expensive as exemplified by auctions of 3Gspectrum in Germany and UK at the start of the new Millennium. At that time, operatorspaid respectively 350 and 97 billion of Euros per MHz. At present time, final prices paidin 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 processis much cheaper as it builds on radio resources already owned by an operator. Re-farmingcost depends mainly on the network size that determines effort that must be spent byengineers, but the final price might be even less than 0.1% of the cost of buying newspectrum (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 2011800 MHz 59.6 M€/MHz 23.0 M€/MHz900 MHz - 16.9 M€/MHz1800 MHz 2.1 M€/MHz -2000 MHz 8.8 M€/MHz -2600 MHz Paired 1.8 M€/MHz 2.3 M€/MHz2600 MHz Unpaired 1.7 M€/MHz Offered but no bids for itIn Table 1, lower range spectrum (bands 900 MHz and 800 MHz) appears to be mostattractive for operators. This is mainly because of better propagation characteristics atlower frequencies. Specifically, radio waves in the frequency bands 900 MHz have lowerpropagation losses, undergo smaller attenuation as they pass through buildings as well as2 What makes re-farming the best approach to efficient LTE roll-out or How to have cake and eat it too?
  • better diffraction characteristics around obstacles in comparison to the frequency band2100 MHz. All these effects make 800 and 900 MHz very desirable for operators as theyallow them to reduce their costs in network deployment process (the same coveragearea requires 2 to 3 times fewer sites in comparison to 2100 MHz). Obtaining access tothese 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 thismost valuable spectrum at a very low cost.Also, a very good candidate for re-farming to LTE is GSM 1800 MHz band, which ispresently commonly used for voice communication. Coverage at 1800 MHz is lower thanat 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 factyields an opportunity to provide full LTE data speed (large spectrum blocks will enablecontiguous 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, especiallyin the bands occupied by GSM. However, at the same time operators face the challengeof avoiding compromising quality of the 2G networks in this process. Presently, 2Gtechnology is the most popular commercial communication system in the world withmore than 4 billion subscribers. Upward trend of GSM subscriptions is expected to becontinued within next few years in emerging markets, whereas in mature markets likeEurope, where mobile devices penetration already exceeds 130%, this trend is reversed.Nevertheless, high-tech terminals that nowadays are replacing former GSM mobiles alsosupport legacy technologies (from GSA statistics: approximately 84% HSPA terminalsalso support GSM EDGE) and in this way assure services continuity in case of WCDMA orLTE coverage problems (2G networks have been developed since early 90s and in somecountries cover almost 100% area). Moreover, GSM technology development is still on-going and features like Orthogonal Sub Channels will double voice channel capacity verysoon. Currently, main component of the GSM traffic is still voice but data transmissionand GERAN continuously rise and further growth is expected to be driven mainly by M2Mcommunications. In case of M2M communications, coverage, reliability and availability aremore important than bandwidth. Hence, 2G technology that is widely available in 73% ofmobile markets is perceived as a most attractive candidate to support M2M deployment.As an example, Sprint plans to provide its customers with global M2M connectivityoutside the U.S. in cooperation with Orange Business Services (announced on February7th 2012). By means of this partnership, Sprint-branded global M2M connectivity willbe available in 180 countries by using M2M-specific GSM SIM cards. While Sprint plansto 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?
  • plans to close its GSM networks by 2017. Few months before when AT&T decided to shutdown its GSM 1900 MHz PCS bands in New York, Apriva Wireless which is one of thebiggest players on the M2M markets and AT&T partner shifts part of its business to RacoT-Mobile M2M service provider. T-Mobile is re-farming its 2G network as well as other USoperators but keeps 25% of its 2G spectrum. Figure 1 shows DATAX forecasts of globalsubscriptions (by device types) and related global 2G traffic. It depicts slow decline ofhandsets devices share in 2G market and at the same time growth of M2M modules. Overthe time, traffic generated by M2M devices will rise. Hence, even with decreasing numberof 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 PROCESSIf re-farming makes so efficient solution for LTE spectrum acquisition and GSM still remainsan important technology, the question comes up whether it is possible to “have cake andeat it too”. Basically, it means deploying LTE in the GSM spectrum without compromising2G network’s quality. In a nutshell, re-farming is a process of removing part of spectrumallocated to GSM (freeing bandwidth for LTE) while reconfiguring appropriate networkparameters. A rule of thumb is that narrower spectrum means less capacity what maygive 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 transitionand 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?
  • narrower bandwidth available in GSM requires a new frequency plan that provides foroptimal interference conditions after re-farming. If environment is multi RAT, part of theGSM traffic can be offloaded to WCDMA by encouraging user terminals to select WCDMArather than GSM cell. Well done re-farming optimises overall network resources utilisationwithout impacting legacy users while providing an operator with a possibility to deployLTE 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 (newfrequency plan, reconfigurations of parameters, etc.) frees up spectrum for LTE roll-outand leads to the overall improvement of most of the KPIs while keeping the interferenceunder control.It goes without saying that LTE technology slowly becomes available across the nationafter the first products appear on the market. Mobile operators that want to meet marketexpectations 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 earlystage of LTE market development might not necessarily be the best way. Of course, inthe future a dedicated large spectrum block will be required for LTE but at present timere-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 amobile communication business. Hence, well performed re-farming that will not causeworsening of 2G services is a challenge, but is certainly possible. DATAX is a company thatis capable of meeting this challenge and manage cost-effectively re-farming of spectrumto provide room for LTE while keeping GSM services at optimal quality.ABOUT THE AUTHORSzymon Stefanski is a Radio Research Engineer at DATAX.He can be reached at szymon.stefanski@datax.plCONTACT USDATAX Sp. z o.o. (DATAX Ltd.)ul. Muchoborska 654-424 WrocławPOLANDsales@datax.plwww.datax.plwww.spectrumrefarming.com5 What makes re-farming the best approach to efficient LTE roll-out or How to have cake and eat it too?