104 Urban Small Cells Overview

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DOCUMENT

Release Four: Urban

Overview

June 2014

104.04.01

scf.io/

SMALL CELL FORUM

RELEASE Four


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SMALL CELL FORUM

RELEASE Four

Small Cell Forum supports the wide-scale deployment of small cells. Its mission

is to accelerate small cell adoption to change the shape of mobile networks and

maximise the potential of mobile services.

Small cells is an umbrella term for operator-controlled, low-powered radio access nodes,

including those that operate in licensed spectrum and unlicensed carrier-grade Wi-Fi. Small

cells typically have a range from 10 metres to several hundred metres. These contrast with

a typical mobile macrocell that might have a range of up to several tens of kilometres. The

term small cells covers residential femtocells, picocells, microcells and metrocells.

Small Cell Forum is a not-for-profit, international organisation. Its membership is open

to any legally established corporation, individual firm, partnership, academic institution,

governmental body or international organisation supporting the promotion and worldwide

deployment of small cell technologies. At the time of writing, Small Cell Forum has around

150 members, including 68 operators representing more than 3 billion mobile subscribers

46 per cent of the global total as well as telecoms hardware and software vendors,

content providers and innovative start-ups.

Small Cell Forum is technology-agnostic and independent. It is not a standards-setting

body, but works with standards organisations and regulators worldwide to provide an

aggregated view of the small cell market.

This document forms part of Small Cell Forums Release Four: Urban. Urban small cells

are at an earlier stage in their commercial development than their more mature residential

and enterprise counterparts. As such, the present Release focuses on establishing the need,

evaluating the business case and identifying key barriers to commercial deployment. It

offers shared deployment learnings from leading operators and vendors, further refinement

of our technical works and reporting progress on our activities to strengthen the ecosystem

through improved multivendor interoperability.

Release Four also contains works clarifying market needs and addressing barriers to

deployment of residential, enterprise and rural small cells.

Small Cell Forum Release website can be found here: www.scf.io

All content in this document including links and references are for informational purposes only and

is provided as is with no warranties whatsoever including any warranty of merchantability, fitness

for any particular purpose, or any warranty otherwise arising out of any proposal, specification, or

sample.

No license, express or implied, to any intellectual property rights is granted or intended hereby.

2007-2014 All rights reserved in respect of articles, drawings, photographs etc published inhardcopy form or made available in electronic form by Small Cell Forum Ltd anywhere in the world.


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Report title: Urban small cells Release 4 overviewIssue date: 10 June 2014

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Executive summary

The mission of the Small Cell Forum is to accelerate adoption of small cell technologies

across a range of use cases including residential, enterprise, rural and urbanapplications. In this document we provide an overview of information we havepublished to support commercialization of urban small cells.

Urban small cells are defined as compact public-access base stations deployed byoperators to enhance capacity and coverage in dense environments such as city centerhot-zones, transportation hubs and retail. They are often referred to as microcells,picocells or metrocells.

We provide here a wide range of content covering the full range of issues that mayconcern an operator wishing to deploy urban small cells. We clarify drivers to deployand demonstrate how the business case can be evaluated. We also identifyingoperators main barriers to commercial deployment and look at the work underway

across the industry to address them, developing solutions in the different disciplines ofnetwork architecture, radio access, backhaul, deployment, regulatory and services. Wereport on progress towards multivendor interoperability in the standards and throughour Plugfest events, and we are also able to share some early experiences fromleading operator and vendors on their first urban small cell deployments.

Successful urban small cell deployments first require a good understanding of:

Market drivers: Our operator survey found the principal motivation to deployurban small cells is to provide an overall capacity increase, in order to offer higherdata rates and enable new services. Improving coverage and reducing the cost ofdata delivery were also cited as important drivers.

Key challenges: Operators report that providing backhaul and securing optimalsites are their two main concerns. Monetization and network management werealso raised as key issues, indicating a growing community of providers which arerefocusing their thoughts from logistics to commercial plans.

The Forum brings together a range of companies from across the ecosystem todevelop consensus around how the key challenges identified by operators can beaddressed.

Business case: A detailed analysis finds that the benefits of small cellsoutweighs the costs to yield a positive business case overall, even where an

operator plans to evolve both macrocell capacity and spectrum holdings as well.Although timing and quantity of deployment will vary markedly amongstoperators, we nevertheless see that a fully-featured small cell layer will be anessential component of future networks.

Interoperability: Recognized as anessential ingredient in the development of ahealthy competitive ecosystem around small cell technologies. Small Cell Forumand partner ETSI have an ongoing roadmap of Plugfest events to both debug

vendor implementations and drive resolution of standards ambiguities and gaps.Our review of standards shows that whilst basic multivendor HetNets are currentlypossible, further X2 standardization effort would enhance their performance.

Radio access: Self configuring and optimization of the small cell radio was a keyenabler for plug and play residential femtocells, and is equally necessary in theurban environment to ensure successful large scale deployments. We discussarchitectures and present process flows for a range of SON use cases, spanning

initial deployment and configuration through to optimization and maintenance.


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Network architecture: As the principal driver is to enhance capacity, urbansmall cells will need to be tightly integrated into existing macro cell networks. Weprovide architectural frameworks to show how key network functions such as

mobility, het net co-ordination, load balancing and synchronization can berealized. Specific architectures maybe extracted from the frameworks according

to the scale of the deployment. Security: Security is especially important for small cells where the form factor

and closer-to-user deployment makes them potential targets of various attacks.We provide a high level overview of various security considerations pertaining tosmall cell deployment and look to promote the adoption of best current practicesfor addressing such issues.

Backhaul:Our comprehensive analysis shows that a range of technical solutionsis available which together can fulfill the range of requirements for differentdeployment use cases envisaged. The total cost of ownership of small cells and

their backhaul are around a tenth of that for a macrocell, yielding a positivebusiness case overall. We provide an overview of the deployment process thatdevelops strategic guidelines to facilitate the subsequent stage of planning.

Guidelines consider operator specific holdings and market conditions to define atoolkit of backhaul solutions and accompanying selection rules. Subsequentplanning applies these to specific markets. Deployment may be phased to matchevolving demand and the changing mix of solutions over the planning lifecycle.

Regulatory: Wesupport regulators in ensuring that operators are permitted touse their existing spectrum and networks to achieve social and economic benefitsthat accrue to small cell users. For urban deployments, we encourage localauthorities to minimize unnecessary planning restrictions and avoid lengthy andcomplex planning application procedures for small cells. This will enable the fullcost and efficiency benefits to be realized from their introduction in areas of highmobile data traffic.

Deployment: We describe the people, tools and processes needed to plan,

design, build and maintain urban small cell networks. We consider how processes- which have typically been the domain of the mobile operator from a macro-cellperspective - could be streamlined and/or outsourced for potential cost savings in

large-scale small cell deployments. Value-added services:Small cells are capable of supporting custom applications

that can add value for operators. Bearing in mind operators want the subscriberexperience to be agnostic to the type of cell they connect to, these services are

aimed at providing enhanced analytics and/or performance which the operatorscan monetize. Examples of such include increasing the precision of locationinformation or on-cell caching to enhance subscriber QoE and reduce backhaul

traffic. We have made available an API emulator and associated programmersguide for developers to create and demonstrate location based applications to run

on small cells.

Deployment case studies: Wedescribe and share learnings from a number of

market leaders deployments in airports, theme parks, sporting venues, subwaysand at street level. These illustrate how partnerships in a number of countries arealready bringing small cells to new environments. Such deployments are also

bringing together small cells with a number of other technologies to meet thespecific challenges posed by the urban environment..

Overall we re-enforce the needs for urban small cells, and demonstrate how a positivebusiness case can be constructed. We capture operators main concerns and bringtogether companies and organizations from across the ecosystem to develop

consensus around how these can be addressed. Activities to improve multivendorinteroperability are underway and further recommendations provided. We believe that

a fully-featured small cell layer will be an essential component of future networks and


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all operators are advised to secure appropriate site and backhaul assets in the nearterm to ensure the efficiency of future deployments.

Small Cell Forum documents establishing needs and addressing barriers forurban small cells

To download visitwww.scf.io.
http://www.scf.io/http://www.scf.io/http://www.scf.io/document/096http://www.scf.io/document/049http://www.scf.io/document/095http://www.scf.io/


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Contents

1. Introduction .....................................................................2

1.1 The work of the Forum in accelerating adoption of urbansmall cells .......................................................................... 2

1.2 Value of Urban Release content for different audiences ............ 2

2. Market issues: drivers and challenges, business caseand market status ............................................................3

2.1 Drivers and challenges ......................................................... 3

2.2 Business case ..................................................................... 5

2.3 Small cell deployment case studies ........................................ 7

2.4 Market status ...................................................................... 7

3. Radio and physical layer ...................................................9

4. Interoperability .............................................................. 11

5. Network architecture ..................................................... 12

6. Backhaul ......................................................................... 15

7. Regulatory ...................................................................... 18

8. Deployment .................................................................... 20

9. Services .......................................................................... 22

10. Conclusion ...................................................................... 25

Figures

Figure 2-1 Top four drivers to deploy urban small cells ....................................... 4

Figure 2-2 Top three barriers to deploy urban small cells .................................... 4

Figure 2-3 Costs and savings for the 38km2dense urban case study .................... 6

Figure 2-4 Key small cell market statistics. Source: Mobile Experts...................... 8

Figure 4-1 Role of Plugfests in standards and product development and testing .... 11

Figure 5-1 Generic end-to-end urban small cell network ..................................... 12

Figure 6-1 Mix of last mile small cell backhaul technologies in macro launchedtopologies ..................................................................................... 16

Figure 6-2 Mix of last mile small cell backhaul technologies in street launchedtopologies ..................................................................................... 16

Figure 6-3 Process for planning and deploying small cells and their backhaul ........ 17

Figure 8-1 Deployment framework .................................................................. 20


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1. Introduction

1.1 The work of the Forum in accelerating adoption of urban smallcells

The Urban small cell represents an evolution of the technologies that have been

combined to make residential and enterprise small cells a success. They need to retaincharacteristics of being compact, easy to install, offering a scalable extension tonetwork coverage and capacity for operators. They additionally need to be deployable

in busy public spaces both indoors and out, and integrate with the existing coverageof macrocell networks.

The urban small cell market is less mature than residential and enterprisecounterparts, which already have significant volumes deployed commercially, asshown in our Market status report[SCF050]. As such, the work of the forum in

accelerating adoption of urban small cells must first focus on the foundational aspects

of establishing the market needs, demonstrating commercial viability and identifyingand addressing barriers in the disciplines of radio, architecture, backhaul, regulation,deployment and services. Success in all these areas is fundamental to making urbansmall cells a mass-market reality which we believe they can and will be.

Different types of small cell are discussed further in Small cells, whats the bigidea? [SCF030]. This document summarizes a range of useful information includingterminology, interference management, backhaul, forms of access and the positioningof small cells relative to adjacent technologies including DAS, Wi-Fi and Cloud RAN. Itlooks at five very different use cases and shows how the momentum behind small cellsis growing.

Looking ahead, the Small Cell Forum will continue to support the adoption of all types

of small cell technologies, residential, enterprise, urban, rural and potentially others,as their markets mature at different rates and times. Our Release structureroadmap[SCF100]outlines our anticipated areas of focus for upcoming releasetimeframes.

1.2 Value of Urban Release content for different audiences

Operators can use the recommendations and case studies to develop their own smallcell strategy taking into account specifics of their markets and asset holdings. Theycan find out about the state of the art of small cell related technologies and

understand the roadmap to wide scale commercial deployment. They can benefit frombest practices and shared learnings from leading operators who do so to help drive

scale and bring down costs for the benefits of all.

Vendorscan better understand operator thinking around their motivations to deploy,together with their key challenges and technical requirements. It will help to refinetheir roadmaps to ensure they will deliver features and performance aligned withindustry requirements.

Regulators, investors and municipalities can all benefit from the collective view ofissues that will need to be resolved to facilitate deployment of small cells in denseenvironments, bringing the social and economic benefits of enhanced mobileconnectivity.

Partner organisations can better understand how the Forum is positioned relative totheir activities.
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2. Market issues: drivers and challenges, business case andmarket status

2.1 Drivers and challenges

Establishing the need is the starting point for every operator when considering a newtechnology deployment. This underpinning theme is discussed in: Urban marketdrivers [SCF086].

Smartphone-driven demand for mobile broadband is growing rapidly but notuniformly; it may spike in specific areas, at certain times of day, week, year or during

certain events. Operators need to continuously update their networks to keep pacewith this growing and non-uniform demand. They will do so with a combination ofadditional spectrum, new radio technology to increase spectral efficiency, and topologydensification. Of these three, by far the greatest capacity increases have historically,

and will in future, come from network densification. Small cells are a certainty, and

virtually all operators already include them in their future strategies.

Small cells not only increase capacity, but also add coverage and enhance end userexperience. They allow operators to generate additional revenue from increased usageand, potentially, new services. In addition, there are measurable societal benefits fromimproved mobile broadband services. Further elaboration on the fundamental driversand benefits of small cells can be found in our business case analysis in [SCF087]

Our market drivers paper includes a 2014 global survey of tier one and tier twooperators on their main drivers to deploy urban small cells and key perceivedchallenges.

Figure 2-1 illustrates the top four urban small cell drivers ranked in order (1 being

most significant). Increasing overall capacity is widely agreed to be the principledriver, for the reasons already discussed; 25% of respondents stated this as theirmain priority, and 60% include it in their top four. Financial drivers of reducing cost of

data and supporting new revenue generating services also featured highly, as did bothextending coverage depth, and filling holes in capacity. Regional variations in thesedrivers are discussed further in [SCF086].

Figure 2-2 shows operators top three barriers to urban small cell deployment, whichare of particular importance to the forum as they define the foci of our efforts. Theirmain concern is backhaul availability and cost a topic which The Forum has and willcontinue to address in detail, as described in section6.

Another widely perceived challenge cited by half of respondents in their top three isbeing able to secure optimalsite locations as distinct from site acquisition per se.We have considered the trade off between the benefit maximizing siting of the small

cell versus the additional cost to extend backhaul to these locations in our businesscase analysis [SCF087]. In the chosen case study, we found that business case wasonly weakly sensitive to the exact positioning of the site.

Monetization and network management were also raised as key issues, indicating agrowing community of providers which are refocusing their thoughts from logistics to

commercial plans. Regional variations discussed in the paper reveal a shifting in thetypes of concern in relation to the commercial maturity of market.
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Figure 2-1 Top four drivers to deploy urban small cells

Figure 2-2 Top three barriers to deploy urban small cells

Source: Maravedis Rethink survey of tier one and two mobile operators worldwide,January 2014. Top drivers and barriers ranked in order, with 1 being most significant


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2.2 Business case

A Business case for urban small cells [SCF087], conducted independently by Real

Wireless, weighs up the benefits brought by deploying urban small cells against thecosts of doing so. Different case studies are analyzed representing a capacity drivenoutdoor deployment, one that is coverage driven and a deployment in a transportationhub.

Network densification only makes sense if it can be done cost-effectively comparedwith other sources of capacity. The associated costs depend on the details of theexisting network assets, including both the existing macrocells and the range ofbackhaul options that are available. The analysis considers a time varying evolution ofvarious aspects of the network as follows:

Explicit account of existing macrocell density and wireline backhaul; Account of varying wireless backhaul solutions, architectures, performance

and costs;

A detailed model of small cell costs, including initial planning and deploymentcosts and on-going operational and replacement costs, validated againstindustry data and interviews with key vendors and operators;

A backdrop of increasing spectrum and spectrum efficiency during the studyperiod on the existing macrocell network; and

Determination of the required density of small cells to meet a non-uniformprofile of demand across the study area based on both coverage capabilitiesand capacity.

Key results for the baseline case are shown inFigure 2-3.The analysis focused on a

dense urban area of 37.6 km2, with LTE traffic growing at a compound annual growthrate of 35% over the period 2014-2020. It was found that the deployment of small

cells to enhance capacity yields a benefit of $48.6m (present value) for a TCO of$29.8m (undiscounted) providing a positive net present value for operators of $28m.

This represents a highly cost-effective investment with a RoI of 136%, and paybackperiod within 4 years.

The report notes that specific outcomes depend on the assumed parameters and maydiffer significantly amongst operators and markets. A series of sensitivityinvestigations are included in the paper to determine the robustness of the business

case to various factors. Overall, however, the paper concludes that the capacityenhancement-based market driver is an important one with a strong business case given a carefully planned deployment.

For coverage enhancement, the role small cells can play in improving the depth of

coverage provided by an operator that does not have any low (< 1 GHz) frequencyspectrum and that wishes to achieve similar coverage to its competitors isexamined. If the small cells are targeted at the cell edge areas where macrocellsdeliver unacceptable coverage, cost savings can be achieved compared to achievingthe same target by macro layer augmentation.

Additional benefits include the quality of experience enhancement in the form of anincrease in the median throughput delivered to all network users (not only those onthe small cells). This could yield a strong economic benefit for users via improvedworking efficiencies and enhanced operator revenues. This coverage augmentationand performance improvement can be achieved without requiring additional spectrum,leveraging a reuse of the existing spectrum in a small cell layer that will deliver
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additional economic benefits to the operator. Further benefits, such as increasedcapacity and reduced churn, are also likely.

Figure 2-3 Costs and savings for the 38km2dense urban case study

The business case for indoor urban small cells is also assessed in this paper. This isbased on the need to provide cost-effective service to indoor areas with ultra-densedemand requirements that are often encountered in large public buildings like

shopping malls and railway stations. In this context, urban small cells aredemonstrated to be a highly cost-effective means of carrying capacity whilstsimultaneously providing the flexibility to respond to changing usage patterns.

The overall findings of the business case paper are that urban small cells, in bothoutdoor and indoor incarnations, are an essential tool for operators and can yield apositive business case even when an operator plans to evolve both macrocell capacityand spectrum holdings. However the timing and quantity of deployment will varymarkedly among operators, who should carefully determine the appropriate market

drivers for them and take full account of existing network and spectrum assets anddemand expectations when planning their deployments. The business case paperadvises operators to secure appropriate site and backhaul assets in the near term toensure the efficiency of future deployments. They are also advised to consider market

drivers for small cells well beyond capacity enhancement in order to maximize theircompetitive position and service offering.


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2.3 Small cell deployment case studies

Urban case studies[SCF098]describes a number of urban small cell networkrollouts that have already been developed in some important markets by a number of

operator and vendor partners.

Notable in particular for their diversity, these rollouts take place in airports, themeparks, sporting venues, subways and at street level, and illustrate how partnerships in

a number of countries are already bringing small cells to new environments. Suchdeployments are also bringing together small cells and a number of other technologiesto meet the specific challenges posed by urban small cell rollout.

An example of this is the AT&T deployment for Disney Parks and Resort. It covered anumber of major visitor destinations across the US and enabled reliable high qualitycoverage for staff and visitors. It involved not only more than 350 small cells thecompany's biggest small cell deployment to date but also 25 DAS systems and 40repeaters.

Similarly Alcatel-Lucents work for a tier one operator in a major urban subway

system, a sporting venue and a variety of university and city deployments shows thegrowing trend towards large-scale integration of small cells as part of a HetNet.

Other concerns are driving the choice of vendor partner for some operators. Forexample, to deal with the needs of the vast Beijing Capital Airport, China Unicomturned to Huawei for a solution that is intended to address not only customer needs

but speed of rollout, control of capex and opex, technical evolution and serviceinnovation.

Speed is certainly an important consideration even if urban small cells are a relatively

new market. When Korea Telecom (KT) and Radisys Corporation partnered for a large-scale deployment of indoor and outdoor LTE small cells the aim was not only to boostnetwork capacity and improve customer experience but to do so quickly in a highlycompetitive market.

But QoS and security implications also need to be kept in mind. SK Telecom in theKorean market has been quick to deal with the QoS considerations that handover in amacro and small cell environment could imply, as well as potential security threats.

The final case study in [SCF098]addresses the challenges that street-level

deployment and RF-co-existence may bring up. Nokia decided to gain operatorexperience of urban small cell rollout through deployment of a small cell solutioncovering all phases from planning to operations. The results are both interesting andvaluable and like the other case studies surveyed in this document show that

urban small cells are already making their mark in very diverse contexts in the realworld.

2.4 Market status

The forum provides regular updates on state of market adoption for the different typesof small cell technology with the latest statistics provided by Mobile Experts. The latestresults can always be accessed via our Market status report[SCF050].

At the time of writing, the number of small cells shipped has grown to more than 8.4million units, still dominated by residential femtocell units. Deployment grew in key
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areas such as enterprise and urban small cells during 2013, concentrated in pocketswhere extremely high traffic density justified the investment.

In addition, mobile operators continue to migrate from their initial implementation of

residential femtocells to the use of enterprise small cells and some carrier-deployed

urban small cells. Many different mobile operators that have not been structured topursue enterprise customers are now adopting enterprise femtocells along with newstrategies to sell mobile services in the business world.

Figure 2-4 Key small cell market statistics. Source: Mobile Experts

Through March 31, 2014, the number of small cells shipped has reached substantiallevels:

8.4 million small cells overall;

8.1 million residential femtocells;

123,000 enterprise small cells;

120,000 indoor urban small Cells;

6,980 outdoor urban small cells; and

More than 2,050 rural small cells are deployed worldwide.

More than 64 operators use small cells

commercially in their networks:

45+ operators have residential

femtocells;

44+ operators use Enterprise SmallCells; and

22+ operators use Urban Small Cells


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3. Radio and physical layer

SON use cases [SCF077]covers the SON functions as they pertain to urban small cell

networks. It aims to highlight, in as much detail as possible, without infringing on

architecture or algorithm choices, use cases for the SON functions.

The broad goal of SON is to enable the configuration, deployment, optimization,operation, maintenance and healing of dense networks across multiple scales withvery low or no manual input or feedback and this spirit is maintained in the document.

The following topics are addressed by the SON use cases document:

Urban SON use cases addressing the two predominant radio accesstechnologies UTRAN and EUTRAN;

SON use cases addressing the full life cycle of the network from initialdeployment and configuration through self-optimization as well asmaintenance aspects;

SON functionality specifically addressing the 3GPP identified areas such asself-configuration, self-optimization (neighbor discovery, parameters(PCI/PSC) optimization, resource sharing for interference management andcapacity optimization as final goals, load balancing, robust handoff and RACH

parameter optimization) and self-healing; and In addition SON aspects related to maintenance use cases are introduced.

Concerns about interoperability between multivendor small cells and macros arealready being addressed through our ongoing and very successful Plugfests andexisting documents such as LTE SC-API [SCF082]. This document is part of SmallCell Forums Small Cell Forums SCAPI (small cell application platform interface)initiative to encourage competition and innovation within the small cell industry

between suppliers of platform hardware, platform software and application softwareby providing a common API around which suppliers of each component can compete.A layer 1 API for 3G small cells can be found in 3G SC-API [SCF048].

A key area of standardization needed to support small cells relates to procedures toassist co-ordination with macrocells over LTEs X2 interface. [SCF059]X2interoperability in multivendor HetNetssurveys standards currently in place tosupport the following four key procedures:

ICIC (frequency domain interference coordination)

Signaling appears designed for cell-edge to cell-edge interaction,unsuitable in its current form for multi-vendor HetNet use

eICIC (time domain interference coordination)

signaling is well designed for multi-vendor HetNet use, but issues exist incoordinating small cell layer transmissions, especially where the smallcell layer itself is multi-vendor

MRO (mobility robustness)

Broadly multi-vendor interoperable

MLB (mobility load balancing)

Almost completely non-interoperable for either intra-RAT or inter-RAT
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Recommendations are made regarding workarounds or standards changes that maybe adopted to improve interoperability. Our findings are consistent with our partnerthe NGMNs study of MLB and MRO in their Recommended practices for multi-vendor

SON deployment, and we also provide additional analysis of ICIC and eICIC. Overallwe find that whilst current standards support basic multivendor HetNets operation,

further X2 standardization effort would enhance their performance.


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4. Interoperability

A strong small cell ecosystem requires that operators have a wide choice of

interoperable equipment from a range of suppliers from which to build their

heterogeneous networks. Manufacturers also benefit from the economies of scale thata successful ecosystem brings.

Achieving a state of ecosystem interoperability requires both good quality standardsand equipment that conforms to them. Our Value of small cell forum Plugfests[SCF085]paper describes the role of interoperability testing as shown inFigure 4-1.

Figure 4-1 Role of Plugfests in standards and product development and testing

Equipment from different manufacturers is connected and operated in arange of real life scenarios. This tests both the suppliers implementation of

the standards, as well as the quality of the standards themselves.

Failed tests drive debugging of implementations, as well as resolution ofambiguities, gaps and incompatible options in standards.

Successful testing demonstrates mature and interoperable standards andequipment.

Conformance testing later checks that products correctly implement therequirements of the interoperable standard.

The SCF and ETSI have been working together since 2010 to conduct Plugfests to

accelerate alignment of small cell network technologies. At the time of writing, fourevents have tested interoperability of 3G and LTE small cells networks, and a fifth setfor June 2014 will include testing of multi-vendor SON functionality in heterogeneous

networks (with the cooperation of the NGMN Alliance).


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5. Network architecture

What are the functional requirements for an urban small cell network? What are the

network architecture options for urban small cells? Are new boxes and interfaces

needed? How should policy be implemented to manage UEs on to small cell, macroand Wi-Fi layers? What about loading and mobility? These are just a few of theconcerns raised by operators. They are discussed in Urban small cell networkarchitectures[SCF088].

Figure 5-1 Generic end-to-end urban small cell network

This paper starts by listing some important deployment scenarios and presents anend-to-end architectural framework. It is a framework that allows specific

architectures to be built for specific scenarios. The framework identifies a number ofarchitectural domains, such as the small cell RAN, the macro RAN, backhaul transportand the operator core network. Each of these domains consists of several functionalentities, which are then listed and described. This is followed by individual discussionson various sub-architectural frameworks, such as X2-support (including aspectsrelated to the X2-gateway being introduced in 3GPP Release 12), SON-support andBackhaul-considerations (e.g. VLAN usage, QoS etc.).

Next, a number of system-wide functions and procedures are discussed that involveone or more of the architectural domains. For example, key characteristics of urbansmall cell networks include HetNet aspects (i.e. where small cells and macro cellsprovide complementary as well as overlapping coverage and capacity) and Multi-RAT

aspects (i.e. where the small and macro cells may be of 3G, LTE and Wi-Fi type). Thepaper looks at key scalability challenges of urban small cell networks, examining theinteractions and consequential signaling requirements of deploying small cells foraddressing coverage use cases.

Urban small cell networks have the potential to realize various types of services and

applications, which are being addressed by the Service Working Group of the SCF.Accordingly, the small cell architectural aspects of supporting local and cached contentas well as precise location are introduced.

Another network architecture-related topic that operators highlighted is howsynchronization is actually achieved. This is a long-standing study area addressed inearlier releases and specifically in Synchronization for LTE small cells[SCF075]
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As the paper explains, all cellular radio base stations require synchronization, includingsmall cells. This may be frequency synchronization, phase alignment to other basestations, or in the case of CDMA and CDMA2000, time synchronization. In earlier 3GPP

releases, synchronization was delivered using a TDM network or GNSS. Today, withall-IP asynchronous networks and indoor small cell deployments, operators need to

rethink their synchronization delivery strategy.

Broadly speaking, FDD systems require only frequency synchronization of 50 250ppb(parts per billion), but TDD systems have an additional requirement for phasealignment of less than 3s, relative to other cells with overlapping coverage.

For some LTE-A features (for example eICIC, CoMP and MBSFN), no synchronizationrequirements have been specified but that does not mean no requirements exist.Rather, there is a soft limit based on vendor implementation and operatordeployment type. This limit is in the region of 1-5s relative phase alignment betweenneighbouring base stations.

For LTE small cells, the level and type of synchronization required depends as much onthe cell location as it does on the technology used. For example, a small cell usingTDD technology, but located in a remote area with no overlapping macrocell coverage,will only need frequency synchronization, since there is no reference for any phase

alignment. Similarly, FDD small cells in less dense environments will not require LTE-Afeatures such as eICIC or CoMP, and may therefore only require frequency. However,a small cell in a dense urban environment may require both phase and frequency tosupport LTE-A.

There are several different types of small cell deployment. The type of deployment willhelp to define which LTE and LTE-A features are likely to be used, as well as the leveland type of synchronization required.

A number of different techniques may be used to synchronize small cells, each withtheir own advantages and disadvantages. They include:

Precision time protocol (PTP);

Network time protocol (NTP); Synchronous Ethernet (SyncE);

Global navigation satellite systems (GNSS, e.g. GPS);

Cellular network listening;

PTP/NTP combined with assisted GNSS; Cellular network listening combined with assisted GNSS; SyncE combined with assisted GNSS; and PTP combined with SyncE.

In addition the synchronization capabilities of different backhaul technologies willaffect the choices for small cell synchronization.

The paper also addresses the consequences of poor synchronization. In the case ofFDD systems, if base station frequency is more than 250ppb out it could meananything from a minor degradation in the data throughput to complete inability toprovide service. For TDD systems too, a reduction in data throughput will begin to

accumulate, along with a potential to interfere with reception of the primary controlformat indicator channel (PCFICH), and consequent loss of an entire sub-frame ofdata.

The paper suggests that network maintenance and troubleshooting as well as

synchronization monitoring and assurance will therefore need to be part of an


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operators practices. However, it adds, this is an area that will continue to rewardstudy as more potential backhaul solutions and network issues arise, not just inrelation to the enterprise, but also to urban and rural deployments.


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6. Backhaul

Our survey in [SCF086]found backhaul to be one of the key concerns of operators

considering urban small cell rollout from both a technology and a cost perspective.

We provide a number of documents to help allay these concerns as follows:

Backhaul for urban small cells: A topic brief [SCF095]helps operators andbackhaul providers to understand the particular needs of urban small cells from abackhaul perspective. It summarises key aspects that must be considered whendesigning and deploying the transport network, and points to sources of furtherinformation.

Backhaul performance requirements vary with the operators motivation to deploy,and relaxations on hard requirements are possible in different deployment scenarios:

For capacity driven deployments, backhaul should be provisioned to match thecapabilities of the small cells (provided). For coverage driven deployments, backhaul

can be provisioned according to end use demand rather than the limitations of thesmall cell RAN.

HetNet interference co-ordination may require small and macro cells to be tightlysynchronized. Achieving this with packet synchronisation techniques drives transportdelay performance more so than the control plane co-ordination signaling over X2,

which is more delay tolerant. [SCF075]contains a detailed analysis of small cellsynchronization requirements and solutions.

Last mile backhaul to the small cell site is particularly challenging, and the wide rangeof wireless and wireline solutions available are discussed in detail in Backhaul forsmall cells: use cases, requirements and solutions [SCF049]. This document

develops technical requirements and compares them to the characteristics of thedifferent solutions. Although there is no one solution that works in every case, we findthat a combination can be used to address the different use cases envisaged.

Our urban backhaul topic brief[SCF095]also considers the different transport

topologies, which are largely determined by the last mile technology choice. Thetopology refers to the way that individual links are combined to provide the end-endconnectivity. The paper defines two general topologies, illustrated in Figure 5-1:

Street launched: wireline solutions typically provide connectivity to street-level cabinets. This may be trenched to reach the nearest small cells site, and

then a wireless solution used to extend connectivity to nearby sites.

Macro launched: an operators existing macro rooftop backhaul is extendeddown to the street-level small cell sites using wireless links.
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Figure 6-1 Mix of last mile small cell backhaul technologies in macro launched topologies

Figure 6-2 Mix of last mile small cell backhaul technologies in street launched topologies

The business case analysis for urban small cells in [SCF087]confirms that an evolvingmix of technologies and thus topologies will be needed to keep backhaul costs toa minimum. Overall the business case analysis finds positive value for operators todeploy and operate small cells compared to keeping up with increasing traffic usingonly a macro approach. In addition, a range of commercial models could be applied tothis value chain, where entities such as site shares, neutral hosts or leased capacity

may be able to bring economies of scale by providing sites, backhaul or other aspectsto a number of operators.

Even though we have shown that there are a number of backhaul solutions which cantogether meet the varying requirements of different use cases, there is still achallenge for operators to select which type of backhaul to use in which situation.Figure 6-3 illustrates a process by which operators first define strategic guidelinesbased on their particular holdings and costs in a given region, and then use this as astructure to facilitate the planning process for individual cities or markets. Theguidelines define a toolkit of backhaul solutions with associated rules which help

planners decide which one to use in a given scenario. Guidelines are defined to meetboth performance and budgetary requirements. Planning then leads onto deployment,which is discussed in our deployment issues document [SCF096]
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Figure 6-3 Process for planning and deploying small cells and their backhaul


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7. Regulatory

Regulation is an ongoing concern and one that will clearly differ from one use case to

another. Operators therefore want to know more about the regulatory requirements

they must consider for urban small cells and what regulators are doing to help suchdeployments. In addition operators have asked the Small Cell Forum about theregulatory impact on sharing sites, spectrum and backhaul, and E911 device location,and lawful intercept in the context of small cells.

Given the numerous administrations involved across dozens of countries, these issuesare constantly developing and changing. The baseline document for discussion of this,however, is our Regulatory white paper [SCF076].

In general, small cells create several opportunities to meet the objectives thatregulators set out to achieve. For example, small cells provide a cost-effective means

of improving consumer access to mobile services in a number of both indoor andoutdoor environments without recourse to large numbers of macro base stations. They

tend to be visually unobtrusive. They are spectrum efficient. In addition, by reducingthe deployment and operating cost of mobile broadband services, small cells increasethe value of services for both consumers and service providers. They increase therange of service models available to operators, encouraging competition andefficiency. They also enable newer technologies to be delivered to customers more

quickly and provide a platform for delivering new applications and services to existingdevices with attractive tariffs.

Nevertheless, as a relatively new technology, the various types of small cells do raisequestions as to the way they fit with existing regulations. Small Cell Forums membershave considered these questions and in general believe that very few changes, if any,to regulations are required.

For example, all types of small cells operate as part of the operators existing network.The operator remains in control of the emission boundaries of the small cell at alltimes and is therefore able to continue to comply with its existing technical licenseconditions. Small cells have to comply with the same safety limits that are applied to

other wireless devices such as mobile phones and their antenna sites. Power levelsvary (rural and urban cells use more power than enterprise, which use more powerthan residential) but all remain within accepted limits. Operator control means userscannot transmit with small cells on unauthorized frequencies or locations.

The security of small cells is a factor that has been considered and engineered fromthe start. Security standards that have been, or are being, developed in various

standards bodies will provide adequate security to facilitate safe and securecommunications based on small cells and operator core networks. Mechanisms have

also been defined to ensure that the security of an individual users identity isrespected and their privacy is maintained when new types of location based servicesare offered via small cells. Small cell security: topic brief[SCF099]presents a highlevel overview of various security considerations pertaining to small cell deploymentand the standards in place to address them.

Other regulatory issues include the possibility that administrations may requireoperators to register small cell locations, as they do for macro base stations. TheSmall Cell Forum considers, however, that for small cells this would create anexcessive burden on operators and regulators alike.
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Also, in some cases, there could be a requirement for qualified personnel to installbase stations, or for substantial sums to be charged for operation of each base station.Such requirements would be disproportionate if applied to small cells and would be adisincentive to their commercial deployment.

Small cell technology is moving outside homes and offices and into the street. Couldthis have specific regulatory consequences? In fact these devices operate within themobile operators licensed spectrum, remain under the control of the operator andrequire no additional licenses or special regulatory conditions to be applied. In urbanand rural areas local administrations may need to consider the visual impact on theenvironment, but the small form factor of these access points allows them to bepositioned discreetly.

As for whether small cells are open or closed devices, they can support a variety ofoperating approaches with respect to user access. In many cases residential

femtocells used in the home will have a closed user group, with the femtocellcustomer controlling which mobile users can access the device. In other cases, often

in the enterprise or outdoors, small cells will be open or semi-open access. In allcases, however, only registered users of the relevant mobile network are permittedaccess and the full authentication and security mechanisms typically used in mobilenetworks are applied.

Small cells can enable a more flexible approach to provision of mobile networks,where the infrastructure may be owned by the end user, the operator or another

intermediary. The regulatory paper makes clear the Small Cell Forums belief thatregulation should be shaped to facilitate any of these approaches since all servespecific purposes to efficiently provide valued mobile services to the user community.

Some regulatory aspects of storing content locally in a small cell network (so-callededge caching) are also described in the paper. These include considerations of lawfulintercept regulations, copyright laws and prevention of unlawful material.

Finally, several national and international regulatory bodies have taken specific stepsto clarify issues of policy and regulation relating to small cells and some have revisedtheir regulatory requirements to facilitate their deployment. Several examples aredescribed in our Regulatory white paper. Most bodies take into account the positiverole of small cells in helping to guarantee mobile services and the control thatoperators can exert over small cells as part of their existing network. The Small CellForum is maintaining a register of applicable regulations in locations of interest to itsmembers and helping to spread examples of regulatory best practice.


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8. Deployment

The Deployment issues for urban small cells [SCF096]document has been

produced to expand on the topics explored within Deployment Issues for Enterprise

Small Cells [SCF079].

This paper begins by arguing that the processes needed to build and run small cellnetworks have the potential to be notably cheaper than the traditional techniquesused in existing macro networks, as the methods used can be extensively streamlineddepending upon the established service level agreements (SLAs) between thecustomer and mobile operator.

Figure 8-1 Deployment framework

However, to date there has been a relatively limited volume of urban small cell

deployments for which the tower/rooftop macro-centric infrastructure methodologieshave been extended, using a mini-macro way of thinking.

To truly find the most successful methodology and unlock the potential of the businesscase, traditional presumptions and misconceptions will need to be challenged. The keymessages of this document are therefore:

Urban commercial modelsUrban commercial models can take severalforms, from operator installed, owned, and maintained, to neutral host leasedcapacity including variants where a third party provides certain capabilities.

Capability designThere are many documents published by the Small Cell

Forum that help to illustrate how an operator can utilize the new technology

inside its existing estate. A list of appropriate documents is given. Physical designPhysical design should be driven by small cell installation

locations and aesthetics, local rules and environmental requirements. The

objective is to reduce equipment, installation, and operation cost withoutcompromising coverage and capacity requirements.

Geographical designComplex urban environments require proper sitesurveys to be conducted prior to the design and deployment phase.Additionally, RF simulations should take into account the surrounding macroenvironment such that coverage and capacity KPIs can be appropriately met.

RegulatorySimilar licensing and spectrum regulatory considerations are

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Installation, commission and acceptance Installation and commissioningshould comply with a well-documented design, while the list of acceptancetests should provide flexibility to network operators requirements.

Central operations Small cells must be visible to the NOC and serviceable Field forceThe process steps remain essentially the same but the ability to

have other organizations enacting roles in the process can significantlyreduce operational costs.

Performance assuranceKPIs are similar to those in the macro network butthe thresholds for action need to be weighted and relevant to the businessproposition. It is imperative to make sure the organizations size is assessedaccordingly.

As we have already indicated, the regulations that apply to small cell deployment,

among them safety, failsafe, zoning and power consumption, are discussed both hereand in Regulatory white paper [SCF076]. SON use cases[SCF066]also offersvaluable deployment information.


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9. Services

In the longer term, urban small cells may be able to support value added services.

What operators want to know is precisely what value added services could be possible

with urban small cells. The Small Cell Forum addresses this question with Small cellservices in urban environments [SCF090].

Urban small cells provide a foundational platform that enables additional services to bebuilt that can be leveraged by commercial entities for opt-in location and presence-based services. Additionally, the backhaul and quality of experience (QoE) can beoptimized by allowing content publishers to take advantage of the storage capabilitiespresent in small cells. The various sections in the paper describe the opportunity forselect merchant services businesses and mobile operators to make use of the

capabilities delivered by small cells. In particular, the opportunity to leverage location-based services and presence capabilities in small cells creates unique opportunities toinnovate merchant services business systems in ways that have not previously beeneasily available.

Many emerging context-aware services rely on location information. In the simplestcase, a service or application will behave differently depending on whether the mobiledevice is inside or outside of the targeted venue. As indoor location becomes moreprecise and user friendly, new compelling services become possible. Turn-by-turn

navigation can guide employees to a rendezvous with a product or service deliverypoint. Location-enhanced search from an attendee device in a large event at theappropriate time provides enough context to return rich service options with the clickof a button.

To enable these rich context-aware services to mobile devices, the underlying locationtracking technology must offer both the necessary precision and ease of use in the

urban setting. Furthermore, it must do so with the greatest economy. The mobilelocation information must also be accessible to applications required by a given app.

Emerging small cell technologies can provide indoor location accuracy in the order ofunder 3 meters using 3G, LTE and/or Wi-Fi radio technologies. Location streaming,

precise indoor location and geofencing are all applications that can be enabled bysmall cells.

Cost is also minimized with small cell-based location solutions. Public venuesdeploying small cells to solve indoor coverage and capacity issues will be able to

leverage the small cell radios for indoor location measurements. As a result, theincremental cost for precise indoor location is minimized since there is no need to

deploy parallel location hardware.

Commercial service providers with context-aware components must be able toidentify, purchase and consume location-based information meeting their specificneeds. Based on this reality, the small cell industry is moving towards location serviceexposure through standardized, web-friendly, open APIs. It may then be possible toselectively deploy the most appropriate set of context-aware applications from avariety of third party sources or develop applications internally. Mobile operators mayadditionally offer services based on these APIs.

Another potential advantage of small cell-based location technologies is the ease withwhich the location data can feed into existing mobile operator location functionsutilizing A-GPS and macro network technologies. This, however, requires that the

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the system upon configuration. This also includes the assumption that the small cellsdo not move once they are placed. If they are moved, the location data source wouldneed to either be automatically or manually recalibrated.

To authorized applications, location information becomes ubiquitous and transparent

irrespective of whether the device is serviced through the small cell infrastructure orvia the mobile core.

There is a growing M2M market evolving around the need to monitor the location andstate of various enterprise assets. With deployment of small cell technologies, SIM-enabled devices integrated into equipment may be discovered, located and queried by

commercial applications. For example, a drinks vending machine can know localoutdoor temperature, sales velocity, and estimated time before being out of stock.This information can be used for intelligent dispatching and routing to restock themachine and maximize the generated revenue.

Again, once the small cell infrastructure is in place, support of M2M services becomes

only a small incremental investment. To ease the development of small cell-basedM2M services, the small cell industry adopts already standardized APIs (via the OpenMobile Alliance) and protocols to consistently identify and track devices and to providea common discovery mechanism between devices.

Given small cell integration into mobile operator networks, M2M location planners

dont need worry about delivering a network to the M2M device. Thus, one less painand cost point for commercial M2M vendors is greatly reduced.

The rich contextual environment associated with small cells also makes it possible tointelligently utilize the storage often present in small cells. Doing so presents a win-win for the operator, which is able to deliver the content to the user without loading it

core network); and the user, who experiences improved QoE because the content isserviced from a near-by location. Moreover, it brings additional benefits to theoperator in the form of a new value-add service that it can offer to content providers

and distributors, while enable content providers to delivery targeted, context-awarecontent to their users.

The strong context associated with small cells makes it possible for operators andcontent providers to properly determine what content is best stored in what smallcells. For example, the storage in a small cell located in a coffee shop in an urban

plaza can be well utilized with information and advertisement about the shopsofferings, the services available elsewhere in the plaza as well as a selection of mostpopular news sites (newspapers and magazines that people are likely to pull up whileat the coffee shop).

As with other types of services, the small cells industry is moving towards providing aset of standardized web-friendly open APIs that enable operators to provision andexpose small cell storage to content providers and content distribution networks actingon behalf of content providers.

In summary, once small cells have been deployed in the urban environment, they canbecome the shortest and most cost-effective path to a rich set of context-aware

services, while supporting the needs for emerging location, presence, richcommunications and M2M applications. Furthermore, devices or machine services canbe supported in a more ubiquitous manner both on the small cell and, eventually, onthe macro network. While some of these services may seem futuristic, the Small Cell

Forum is working to describe how these services could work and defining APIs toenable these benefits for enterprises.


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Small cell programmers reference guide [SCF091]is the place to go if you wanttips on how to write your own small cell services. This developers guide providesguidance on building location-based applications based on small cell technologies andthe Small Cell Forum's Zonal Presence API using a developer sandbox environment.

Requirements on a location based API[SCF092]recommends a path towardsobtaining a standardized set of precision indoor location APIs that will be recognizedby the small cell industry as a standard for vendor implementation. It sets out arange of use cases and derives a common set of requirements and surveys a range ofexisting relevant industry APIs.

Extensions of small cell zone API supporting small cell contentmanagement [093]provides operational definition for enhancing the existing smallcell zone APIs with the capability to support operator-managed caching solutions usingsmall cell-based storage.
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10.Conclusion

We are grateful to our operator audience for their help and support in keeping us

aware of their questions and concerns relating to urban small cells and their work,

alongside vendors and industry experts, in helping to resolve them. Many of the issuesraised by operators are addressed in the current release. Our aim, however, is toensure that we continue to address your concerns as the small cell landscape changes.

104 Urban Small Cells Overview

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