nokia optimising mobile broadband performance by spectrum refarming white paper

Optimizing mobile broadband performance by spectrum refarming

Nokia Networks

networks.nokia.comPage 2

Contents

1. Executive summary 3

2. Why refarming? 3

3. Mastering refarming 7

3.1 Sustain business with users who have GSM-only phones, serve M2M traffic

7

3.2 Maximizing mobile broadband performance through HSPA and LTE

9

3.2.1 Flexible carrier spacing and bandwidth for HSPA

10

3.2.2 Narrower carrier spacing for LTE solutions

10

3.3 Minimize operational expenditure associated with refarming

11

4. How to do refarming 13

5. Nokia solutions 14

5.1 Committed to spectrum refarming 15


1. Executive summaryRefarming offers operators a unique, cost efficient method to improve mobile broadband capacity and coverage. As GSM traffic is decreasing, spectrum can be reallocated to HSPA1 and LTE, ensuring improved mobile broadband performance. At a later point the LTE capacity can be increased by refarming frequencies from HSPA to LTE.

Lower frequencies are particularly attractive, as they provide excellent coverage in rural areas, while also providing indoor coverage in urban areas. And given the expected growth in mobile broadband traffic during the coming years, refarming on higher frequencies can provide the much needed capacity.

Operators can also expect better network quality to help reduce churn, as well as higher data traffic and revenue from HSPA and LTE subscribers than from GSM subscribers.

Nokia Networks solutions maximize the opportunity for refarming, allowing an HSPA carrier to be refarmed within 3.8 MHz and enabling dual cell HSPA+ service within 7.6 MHz. On the LTE side, through narrower carrier spacing, a 10 MHz LTE carrier can be provided within 9.2 MHz. In order to maintain good GSM service in less spectrum, a number of advanced features, such as Orthogonal SubChannels (OSC) and Smart Dual Beam (SDB) are available.These solutions can be used to optimise the amount of spectrum given to the different systems and are further described and discussed in this whitepaper.

Having refarmed over 125 commercial radio networks, Nokia Networks has gained extensive experience and is a trusted partner. (September2014).

2. Why refarming? It is well known that mobile data traffic is growing fast, alongside the expectations of mobile users, who want a consistently high quality experience when it comes to using applications like video streaming, social media and web browsing, regardless of whether they are located, indoors or outdoors, in the city or countryside. This growth in traffic volumes and user expectations force operators to rethink the use of their spectrum assets and look towards refarming their GSM spectrum to deploy more spectral efficient HSPA or LTE. With the introduction of Voice over LTE (VoLTE) operators can evolve their old circuit-switch (CS) voice network towards LTE and complement VoLTE with e.g. HD voice and multimedia messaging. This enables further

1 The term HSPA is used for 3G, also covering WCDMA.


refarming of GSM and HSPA towards LTE. VoLTE has been commercially launched in the United States and Asia, while European operators are expected to follow during 2014. GSM networks will still be utilized during the next few decades to accommodate voice users and M2M traffic, which is typically based on long-term contracts. However, the amount of GSM traffic in mature markets is expected to decline and can be handled with a GSM system featuring fewer frequencies than are used today. As GSM is the dominant technology in many cases for the 850, 900 and 1800/1900 MHz band, this frees-up frequencies in these bands for HSPA or LTE use.

The quantity of spectrum to be allocated to HSPA and LTE depends on a number of factors, like the amount of subscriptions in each of the technologies, the available terminals in the network and the target QoS per technology. Figure 1 shows the mobile subscription growth globally per technology over the next years. While LTE appears to be accelerating, 3G is still the dominant mobile broadband technology in coming years and. GSM is decreasing rapidly. It should be noted, however that there are large regional differences as illustrated in Figure 2.

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

4G

3G

2G

Source: Informa, 06/2014

Subs

cription

s

0

2

4

6

8

Fig. 1. Mobile subscribers per Technology in the World (Informa June 2014)


World0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

North America Middle Eastand Africa

Asia and Pacific Asia and Pacific Latin America

4G

3G

2G

Fig. 2. Estimated global distribution of 2G, 3G and 4G subscribers for 2017 (Informa June 2014)

Operators may want to offer differentiated service on HSPA and LTE by offering different throughputs, for instance. This may be done directly in the subscription offering or indirectly to ensure that users experience the 4G effect, and insist on upgrading from their 3G connections. This should to be taken into account when deciding how much spectrum is set aside for each technology.

A typical band allocation of the different technologies can be seen in Figure 3. The 900 and 1800 MHz bands are traditionally used by GSM, whereas in order to benefit from the low frequencies the 900 MHz band is being refarmed to 3G (further details provided in our 3G refarming white paper) and for that reason will likely be the last GSM and HSPA carrier to be refarmed towards HSPA and LTE respectively. Likewise, the 800 MHz band is also typically used for LTE. The 2100 MHz and 2600 MHz bands are typically used by HSPA and LTE respectively, whereas we see signs of the 2100 MHz band now being refarmed towards LTE for capacity reasons. In networks where GSM traffic is on a steep decline, the 1800 MHz band is an obvious candidate for refarming to LTE as it leads to OPEXand CAPEX savings compared to having LTE in the 2600 MHz band.


Other bands are also available or becoming available in many countries, such as the 700 and 3500 MHz band, which is targeted to LTE.

Low frequencies provide good coverage: the lower the carrier frequency, the further radio signals can travel. This means it takes fewer radio cells to cover the same area, making it the perfect solution for extending mobile network coverage. Whats more: a radio signal traveling through the walls of a building at a lower carrier frequency is less susceptible to signal attenuation (penetration loss). With the benefit of this property, the usage of lower frequencies can extend indoor coverage and improve service in metro areas (see Figure 4). Perhaps most important to operators, it can do all this at remarkably low cost and with compelling efficiency. Measurements and experiences with a multitude of commercial HSPA 900 networks have demonstrated these advantages in practice.

2600 MHz

2100 MHz

1800 MHz

900 MHz

800 MHz

LTE

LTEGSM

LTEHSPA

GSM HSPA

LTE

Fig. 3. Typical band allocations across different technologies over time


700 MHz

0.0

Cell area (km2)

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0

800 MHz

900 MHz

1800 MHz

2100 MHz

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Fig. 4. Typical 3 sector site LTE coverage area in urban environment, including indoor coverage, at different frequencies acheiving a minimum data rate of 1 Mbps

3. Mastering refarmingOperators seeking to capitalize on the potential of refarming must protect legacy business interests, sustain current operations and find a way to contain rollout costs. In other words, operators aiming to refarm frequencies must resolve three major issues:

1. Sustain business with users who have GSM-only phones, and serve Machine Type Traffic (MTC) traffic.

2. Maximize mobile broadband performance through HSPA and LTE.

3. Minimize operational expenditure associated with refarming.

3.1 Sustain business with users who have GSM-only phones, serve M2M traffic

Using GSM spectrum more efficiently is a way of creating more spectrum for mobile broadband and making the most of the remaining GSM carriers capacity, such that it can take care of


the traffic of the remaining GSM-only phones and serve M2M traffic. Frequency hopping techniques, dynamic power control and discontinuous transmission are three well-known methods of boosting GSM spectral efficiency. Other advanced methods to further increase GSM spectral efficiency include:

Orthogonal Sub Channel (OSC) can provide up to double the number of radio channels for circuit switched voice traffic. With OSC, fewer GSM hardware radio timeslot resources are needed for voice and data services.

Smart Resource Adaptation (SRA) allocates downlink radio timeslot resources as needed. In conventional networks, radio resources are allocated by mobile device multi-slot class. Today, however, most transferred packets are small, meaning that multi-slot allocation is inefficient, as one user may reserve five resources. With SRA, shallow packet inspection (SPI) is used to allocate only one timeslot for small packets, allowing for up to five times more users, or fewer radio resources to be used, which is particularly relevant for MTC traffic.

Precise paging a network will page all cells to alert the base station for incoming voice, data calls and text messages. Conventionally, common control signaling channels are added if there are enough frequencies. However, the Precise Paging feature will page only the cell where the mobile station was last known, as well as adjacent cells. The feature also increases paging capacity by up to 70% in both Air and Abis interfaces, raising paging success for a better perceived quality for the subscriber.

Dynamic Frequency and Channel Allocation doubles base station site traffic capacity using a powerful base station controller (BSC) algorithm that optimizes the call quality in radio channel allocation for every new call and incoming handover. Dynamic allocation allows a more comprehensive re-use of GSM channels, helping operators to add more hardware capacity per MHz. This enables GSM implementation in less spectrum, or more traffic to run within the existing spectrum.

Flexible MCPA Tx power pooling - conventionally, Multi Carrier Power Amplifier (MCPA) power is shared equally between carriers. This GSM Software Suite feature allows output power to be shared dynamically between GSM carriers. This cuts the RF power needed for GSM, reducing energy consumption and providing more power for HSPA and LTE.

Energy Efficient Coverage (EEC) similar in operation to Multiple Input Multiple Output (MIMO) in LTE networks, EEC can up to double the amount of traffic carried at the cell level using existing GSM spectrum.


It can also achieve the same GSM performance using less spectrum, thus freeing up more spectrum and transmitter power for spectrum refarming. In addition, the feature can improve coverage by typically 4 dB.

Smart Dual Beam (SDB) Smart Dual Beam introduces a method of realizing higher order sectorization without the need to increase the number of BCCH frequencies employed. This way it enables operators to benefit either from 50% more GSM capacity in their existing spectrum and base station sites, or by refarming 20% spectrum for HSPA and LTE deployments.

3.2 Maximizing mobile broadband performance through HSPA and LTE

Spectrum comes in defined blocks and it may be challenging to fit the different systems into those blocks, for instance HSPA comes in carriers of 5MHz. LTE is more flexible as it comes in multiple bandwidths as illustrated in Figure 5, where the bandwidths and the peak data rates are shown. Release 10 specifies carrier aggregation for LTE, enabling aggregation across different carriers, whereas for HSPA, 3GPP has specified dual cell aggregation in release 8 and aggregation across 8 carriers in release 112 .

1.4 MHz

3.0 MHz

5 MHz

10 MHz

15 MHz

20 MHz

9 Mbps

22 Mbps

37 Mbps

74 Mbps

110 Mbps

150 Mbps

Fig. 5. Various LTE bandwidths and peak data rates

2 Note that not all bandwidths and band combinations can be aggregated. 3GPP adds new combinations in every release of the specifications.


In order to provide the best possible fit to the available spectrum, Nokia Networks offers solutions to deploy HSPA and LTE carriers with narrower bandwidth by means of flexible/narrower carrier spacing.

3.2.1 Flexible carrier spacing and bandwidth for HSPA

3GPP calls for a carrier spacing of 5.4 MHz between HSPA and GSM carriers. 3GPPs assumption is based on the performance of typical radio frequency (RF) filters in base stations and, on a worst case power level scenario, in adjacent carriers. 3GPPs recommended carrier spacing poses a challenge for a 2G/3G operator wishing to introduce HSPA 900. The easy solution is to save bandwidth by condensing carrier spacing. Nokia Networks Configurable Carrier Bandwidth technology allows operators to use software to configure HSPA bandwidth in 3.8 MHz or 4.2 MHz.

When refarming to HSPA, this flexibility allows operators to keep more spectrum in GSM and maintain service to GSM customers or to leave more spectrum for LTE. In fact, the 3.8 MHz HSPA bandwidth allows many operators with restricted GSM frequency allocation to start providing HSPA or LTE services while continuing to deliver GSM services.

Configurable carrier bandwidth allows operators to deploy Dual Cell HSPA+ refarming services on the 7.6 MHz (2 x 3.8 MHz) bandwidth, which is substantially less than the 10 MHz conventionally needed by networks for two-carrier solutions. Such industry-leading spectral efficiency allows many operators to offer Dual Cell HSPA+ for the first time, while still continuing to provide GSM services. Alternatively this solution may be used to provide more spectrum to LTE. In 2012, the worlds first commercial re-farmed Dual Cell HSPA+ 900 network was by provided by Nokia Networks in New Zealand.

3.2.2 Narrower carrier spacing for LTE solutions

LTE already offers more flexibility through the different available bandwidth solutions. Additionally, Nokia Networks offers narrower carrier to carrier spacing for refarming in the 1800 MHz layer. This is illustrated in Figure 6. The concept consists of two elements:

1. Narrow LTE carrier bandwidth for allowing additional GSM carriers within the LTE nominal bandwidth in RF sharing mode.


2. Nearest Offset BTS (NOB) is required for maximum performance: minimizes the mutual inter-system interference and optimizes GSM and LTE performance. NOB allows only strong GSM users on overlapping channels, thus minimizing impact of GSM transmissions on HSPA/LTE.

This feature allows LTE and GSM to coexist within smaller bandwidth. When combined with earlier mentioned features such as SDB and DFCA, considerable bandwidth savings can be achieved.

3.3 Minimize operational expenditure associated with refarming

Introducing another radio access layer adds to the operational effort. This extra effort may be minimized by making intelligent use of synergies at all levels. Nokia Single RAN offers an excellent opportunity to save costs, operating different radio technologies on a single multi-purpose hardware platform.

Single RAN is already helping many operators to achieve substantial benefits but the coming years will see the technology evolve

Fig. 6. Example of a narrower carrier spacing solution

10 MHz LTE GSM GSM

15.4 MHz

9.2 MHz LTE GSM

13 MHz

GSM

2.7 MHz 2.7 MHz

1.9 MHz 1.9 MHz

4.7 MHz carrier spacing instead of 5.1 MHz

4+4+4 GSM capacity delivered in less spectrum due to usage of advanced GSM features like SDB, DFCA, NOB.


significantly. One of the benefits of Nokia Single RAN-Advanced solution today is that legacy base station equipment can be re-used. An existing GSM RF module, for example, can be re-used in re-farming by GSM-LTE RF sharing, which enables operators to avoid adding LTE RF modules. This RF sharing is enabled by Flexi Multiradio 10 Base Station hardware, in practice changing from Single Carrier Power Amplifiers (SCPA) in GSM to Multi Carrier Power Amplifiers (MCPA) as used in LTE and HSPA networks. This positions re-farming as a simple software upgrade, and the existing base station RF can now be used simultaneously for both GSM and LTE, or GSM and HSPA, depending on the frequency band. HSPA and LTE RF sharing is commercially available today.

Current products also support triple sharing, but this has not yet materialized in commercial networks. When the same spectrum is shared, RF power and front haul transport can be shared by different RF technologies and we can expect these capabilities to develop further in future product generations.

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Condential

RF sharing

Two dedicated RF One shared RF

LTE RF

GSM RF

LTE-GSM RF

WCDMA RF

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Fig. 7. Examples of RF sharing


Today, all vendors baseband products support one RF technology at a time, but baseband miniaturization will enable baseband module sharing to further reduce the number of modules and simplifying networks even more.

Nokia Networks multicontroller platform allows for step-by-step refarming with the possibility of re-using a hardware module between GSM/EDGE and HSPA controllers. However, the current understanding for LTE is that centralized LTE scheduling and a new controller network element could be beneficial in the small cells layer, but not in the macro base station layer though this requires further investigation.

4. How to do refarmingThe previous section described the different building blocks used in refarming, but the question of when and how much still remains.

Figure 8 offers a simplified diagram of the refarming process.

Prior to starting, its necessary to consider which technologies are the candidates for each band in addition to the currently deployed technology. Key factors include the band support in the network terminals, available site locations and coverage requirements. In the candidate selection, its important to consider future developments such as expected growth in subscriber and data traffic for each technology.

The second step is checking every radio access technology to determine whether the spectrum needs are fulfilled or whether some adjustments are required. For GSM, this can be based on the amount of voice traffic and MTC traffic in the existing GSM network in addition to MTC traffic growth expectations. Spectrum can thus be adjusted, taking into account the coverage needs. This typically means utilizing a part of the 900 MHz band for GSM to ensure indoor voice coverage as well as meters, which are often a large part of the indoor GSM MTC traffic.

For HSPA and LTE, data throughputs can also be taken into account. Operators targets typically include the number of satisfied users on HSPA and LTE, e.g. 95% of users must experience throughput above a certain level. Different target throughputs can be used for 3G/HSPA and LTE as the end user expectation is usually that LTE is better than 3G. Based on the current data throughputs and predictions, it can be estimated whether the spectrum of HSPA and LTE should be adjusted. If both HSPA and LTE require more spectrum, and there are no additional frequencies available, the target throughputs or thresholds


should be adjusted to the most optimal configuration. If the number of unsatisfied users exceeds the threshold on only one technology, then the option to move some spectrum towards this technology can be considered, bearing in mind the overall benefit, the future proofness of the decision, and the cost of refarming, etc.

5. Nokia solutionNokia Networks considers refarming as an excellent opportunity to boost the mobile broadband performance for the mobile users, through better rural and indoor coverage. Nokia Networks has developed network planning services as well as the Single RAN Advanced solution for stepwise refarming.

Planning services are based on a methodology proven in projects around the world, helping operators to maximize the returns from spectrum refarming, make the most of legacy assets, and mitigate any technical risks. Nokia Networks engineers tailor the best refarming solution for a given scenario, selecting the appropriate spectrum allocation and spectral efficiency features to satisfy the operators needs. Powerful tools then help to optimize performance across all technologies and layers in the network.

Fig. 8. Simplified diagram of the refarming process

Decide candidate technologies for each frequency band

Evaluate for each radio access technology the specrum needs

versus the current spectrum

Adjust the spectrum in order to fulfill the spectrum needs or

adjust the requirements


Nokia Networks offers solutions to facilitate refarming by reducing the HSPA bandwidth from 5.4 MHz to 3.8 MHz and narrowing the LTE carrier bandwidth to allow additional GSM carriers within the LTE nominal bandwidth in RF sharing mode. Packaged with several unique GSM features, operators can ensure good GSM performance while offering mobile broadband through HSPA and LTE.

Compact, modular, and engineered to consume less power, the Flexi Base Station enables effective site acquisition and re-use. Flexi Multiradio 10 Base Station is the latest generation of the market-leading Flexi Base Station family. It is based on the latest, third generation platform developed to support higher GSM, HSPA+, LTE and LTE-A capacities and a wider variety of base station site configurations with a minimum of equipment and lower power consumption.

Flexi Multiradio 10 Base Station is the worlds smallest software-defined, multi-technology, high-capacity base station. No additional cabinet or shelter is needed as the base station is perfectly suited for indoor and outdoor use. Thanks to its modular design, operators can begin with small configurations and scale up as markets grow. Expansions are easy, starting with remote software upgrades, adding capacity sub-modules and chaining additional modules.

Nokia Networks was the first company to provide radio frequency sharing, offering this facility in 2008 with Flexi Multiradio Base Station. With a simple software upgrade, the existing base station RF can be used simultaneously for both GSM and LTE, or GSM and HSPA, depending on the frequency band. Nokia RF sharing has opened the door to refarming for many operators, as it is a cost-efficient configuration one less RF module is needed, while it also offers fast rollout and re-use of assets.

5.1 Committed to spectrum refarmingConfident in the validity of frequency re-allocation, Nokia Networks has made a strong commitment to refarming and is successful in commercializing it. Having refarmed over 125 commercial radio networks, Nokia Networks has gained extensive experience and is a trusted partner (September 2014).


PublicNokia is a registered trademark of Nokia Corporation. Other product and company names mentioned herein may be trademarks or trade names of their respective owners.

Nokia Nokia Solutions and Networks Oy P.O. Box 1 FI-02022 Finland

Visiting address: Karaportti 3, ESPOO, Finland Switchboard +358 71 400 4000

Product code C401-01090-WP-201410-1-EN

Nokia Solutions and Networks 2014

nokia optimising mobile broadband performance by spectrum refarming white paper

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