074 Alternative Enterprise Small Cell Extension (1)

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Alternative enterprise small cell extension solutions

December 2013

074.04.01

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RELEASE FourSmall 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-prot, international organisation. Its membership is open to any legally established corporation, individual rm, 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 re nement 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 and an overview of all the material in Release Four: Urban can be found here: www.scf.io/doc/104

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Report title: Alternative enterprise small cell solutions Issue date: 03 December 2013 Version: 074.04.01

Scope

In the development of the Small Cell Forums Release Two: Enterprise, the question of what is an enterprise? has had plenty of airtime. As with most definitions, there are multiple answers to the question, depending on the viewpoint of the questioner.

This document describes small cell technologies that can be deployed in enterprises in addition to or alongside the traditional small cell solutions such as picocells, metrocells, nanocells, femtocells, etc.

Not all such applications of this document are fully developed at this version. In common with the Small Cell Forum itself, this document is driven by member contributions and as such, any new application space for this document is welcomed for future editions.


Executive summary

This document describes solutions that expand the ability of small cells to help mobile operators address in a cost effective way the coverage and capacity needs of their subscribers in a variety of indoor configurations.

The two architectures described are:

Smart signal booster that provides rich indoor coverage for enterprises that dont have access to usable backhaul (suburban areas very often have inconsistent fiber-optic coverage). The existing macro-network is used as signal source in this small cell approach.

The small cell enterprise RAN that leverages conventional RNC/NodeB functional decomposition enabling management of many indoor small cells as one system and looks to the core as a single Iuh connection.


Contents

1. Background and introduction ...........................................1 2. Small cell RAN with enterprise-based radio controller ......2 2.1 Architecture ........................................................................ 2 2.2 Benefits.............................................................................. 4 3. Smart signal boosters (SSBs) ...........................................5 3.1 Regulatory context .............................................................. 6 3.2 SSB architecture ................................................................. 6 3.3 Applications of SSBs within enterprises .................................. 7 3.3.1 Enterprises without usable backhaul ...................................... 7 3.3.2 Small cell coverage extension within enterprises ..................... 7 3.3.3 SSB use case summary ...................................................... 12 4. Proposed improvements and next steps for later

editions .......................................................................... 13 References ................................................................................ 14

Tables Table 3-1 SSB deployment scenarios .............................................................. 12 Figures Figure 2-1 E-SCC architecture .......................................................................... 2 Figure 2-2 Small cell RAN architecture .............................................................. 3 Figure 3-1 SSB architecture ............................................................................. 6 Figure 3-2 Smart signal booster extends small cell coverage ............................... 8 Figure 3-3 SSBs used to extend small cell coverage to the back of a warehouse..... 9 Figure 3-4 Using an SSB to extend small cell coverage into a basement ............... 10 Figure 3-5 Small cell coverage extension results basement location .................. 11

Report title: Alternative enterprise small cell solutions Issue date: 03 December 2013 Version: 074.04.01 1

1. Background and introduction

The application of small cells within enterprises is not new, but the codifying of the enterprise application within the Small Cell Forum Release Program has led to a rich discussion of possible interpretations of the word enterprise, and this has led to more formal definitions of classes of enterprise within the Small Cell Forum Release Two documentation set.

Within a given enterprise classification (based on size, building, construction, number of users, traffic profile, etc.) multiple potential implementations are possible (for instance more smaller cells, fewer, larger cells). See Small Cell Forums Market drivers for enterprise small cells [1] and the Small Cell Forums Business case for enterprise small cells [2] for a detailed discussion of enterprise indoor structure sizing.

The enterprise small cell technologies and architectures described in this paper augment the traditional small cell definitions of picocell, metrocell, nanocell, femtocell, etc. that have been largely derived from standardization of H(e)NB approached by 3GPP, offering additional tools in the armoury of network operators to provide high quality and cost effective enterprise services.


2. Small cell RAN with enterprise-based radio controller

Most of the architectures and small cell solutions described in Release Two documents make the implicit assumption that small cells are essentially H(e)NBs, connecting to the core network directly over Iuh/S1 interfaces, as illustrated in Figure 1. In this section we discuss an alternative realization of an enterprise small cell RAN that in principle relies on the more traditional 3GPP UTRAN functionality split between NodeB and RNC.

This architecture is effectively a split, multi-radio H(e)NB. The multiple attached small cells are presented to the mobile core as a single HNB and can be managed as a single entity - e.g., from a SON perspective. An enterprise-based radio controller (ERC) element includes conventional RNC functionality and is able to aggregate all the small cells in an enterprise, manages mobility and interference across them, integrates them with the enterprise s Intranet, and provides a single Iuh interface to the core network.

Functionally the proposed implementation is similar to Option 2 of the Small Cell Forums Enterprise small cell network architectures white paper [3] illustrated in Figure 2-1.

Figure 2-1 E-SCC architecture

Although in principle the proposed solution relies on the UTRAN hierarchical RNC/NodeB architecture, the enterprise-based radio controller implements among other things functionalities of an ESCC (enterprise small cell concentrator) and optionally the ESCG (enterprise small cell gateway). The implementation of enhanced ESCC functionality, as described in section 4.3 of [3], enables the support of LTE small cells in addition to 3G and presents a single, standard, S1 interface to the EPC, delivering benefits of enhanced mobility hiding described in detail in [3].

2.1 Architecture

The architecture, shown in the Figure 2-2 below, is built upon a local, enterprise-based, small cell radio controller to address the main requirements of deploying a scalable small cell network inside an enterprise.


Figure 2-2 Small cell RAN architecture

The solution consists of two network elements:

Small cells Enterprise small cell radio controller

Each small cell acts as a single sector (e)NB and can support 3G and/or LTE air interfaces. Small cells are connected to the enterprise small cell radio controller through an Ethernet LAN. The radio controller acts as a self-organizing network (SON) manager, an optional cellular-enterprise integration gateway, and in the case of a 3G deployment as a radio network controller (RNC). It aggregates all the small cells and appears as a single multi-sector (e)NB to the core network. The radio controller connects to the 3G core network using an Iuh interface. and to the LTE EPC using S1. It can also connect to neighboring macro eNBs using X2 and to macro RNCs using Iur.

The system relies on enterprise LAN to provide connectivity between the radio controller and the small cell - e.g., using the options described in [SCF068] [4] small cells and radio controller form a self-managed IP network, and all user and signaling traffic between them is carried inside an IPSec tunnel.

As with the E-SCC approach described in [3], this architecture enables all UE sessions to be anchored on premise, in this alternative at the enterprise radio controller. As a result, a UEs session does not have to be relocated when it moves within the small cell network. The centralized radio controller also manages interference between small cells. The radio controller architecture can simultaneously send voice traffic through multiple small cells, rapidly select the best serving cell for HSDPA, and combine signals on the uplink. All these methods for managing inter-cell interference have been proven in macro-cellular network, and can be further optimized for operation inside buildings.


As with the E-SCC approach described in [3], this architecture supports soft handover between 3G small cells, allowing all small cells in the deployment to operate on the same channel. Soft handover improves coverage, eliminates interference between small cells, and ensures that users can move from one small cell to another without dropping calls. However, in contrast to the architecture presented in [3], the radio controller acts as a radio network controller for small cells connected to it and uses 3GPP standards-based mechanisms for handovers. This can be contrasted with the Iurh based soft handover as described in [3] that requires the small cell acting as source HNB to anchor session state and forward traffic to the small cell acting as target HNB while UEs are in soft handover.

Note, enterprise femtocell deployment guidelines described in [SCF032] [5] has investigated the usefulness of soft handover from an RF perspective and concluded that the benefits of SHO will depend on office type.

In addition to acting as the RNC, the radio controller also implements a SON manager. It is responsible for auto configuring, optimizing and managing the enterprise small cells. When a new enterprise small cell is added to the network, it discovers the radio controller. From that point on, the radio controller takes responsibility for providing the small cell with its radio configuration. If an enterprise small cell goes out of service, the controller can adjust the configuration of neighboring nodes to fill the coverage hole. All the complexity of configuring, managing and optimizing scores of small cells stays hidden from the mobile operators core network.

In its role as a cellular-enterprise integration gateway, the radio controller can optionally include enterprise small cell gateway functionality, including interfacing to an enterprise AAA server to authorize enterprise users and, based on policies, locally switch traffic from enterprise users to the Intranet. Refer to the Small Cell Forums Enterprise small cell networks architectures [3] for a definition of an enterprise small cell gateway and its role in the support of local IP access (LIPA) and selective IP traffic offload (SIPTO).

2.2 Benefits

In addition to the benefits delivered by an ESCC, and optionally an ESCG, which are presented in [3], this architecture provides the following benefits:

1. Consistent throughput Since all UE HSDPA sessions are anchored on the radio controller, the radio controller can serve each UE from the best cell, increasing average HSDPA throughputs. On the uplink, the radio controller can combine signals received at multiple cells. Smart power-control algorithms may be used to maximize diversity gains.

2. Management This architecture offers the operator with a single point of management for each enterprise small cell deployment. It ensures that all small cells are running the same software image. Faults are aggregated and correlated before they are forwarded to a management system in the core. Performance counters are managed on a per-cell basis as well as for the entire system. Operators can monitor and manage the performance of each enterprise small cell system, and differentiate themselves by offering SLAs to large enterprise accounts.

3. Self-organizing The architecture enables SON algorithms to be located in the radio controller where they can have visibility of the operation of the entire enterprise small cell network. SON operation can be coordinated across multiple enterprise small cells.


3. Smart signal boosters (SSBs)

Smart signal boosters (SSBs) are devices that enhance or boost the signal to and from mobile devices; they implement the features of a traditional repeater, as specified in 3GPP TS25.106, TS35.106 and a number of additional advanced features:

SSBs are operator-specific (configured to boost only a particular network operators frequencies).

This can be achieved by configuration of specific frequencies over an O&M link, or by the SSB actively reading the broadcast parameters of the network to find and verify the PLMN-ID1 and frequencies2.

SSBs implement features to protect the (e)Node B uplink (and hence the uplink capacity of the cell) from noise introduced by the booster.

This is typically created when the noise floor at the uplink receiver of the booster is amplified towards the base station. The base station can be protected using a number of different schemes, including:

Turning off the uplink transmission if no mobile devices are active (so zero noise at the base station receiver generated in this case).

By adaptively controlling the gain of the SSB to ensure that the noise floor of the Node B is not affected by the transmissions from the SSB.

The classic signal booster problem is that the noise floor at the uplink receiver of the booster is amplified towards the base station, in addition to the uplink signal form the active mobile(s).

This noise component is diminished by the path-loss between the booster uplink transmitter and the (e)Node B uplink receiver. If the noise component is sufficiently small compared to the path-loss, then it is insignificant however, if the noise component is too large compared to the path-loss then it will contribute to the noise floor at the (e)Node B receiver and affect uplink performance.

An SSB knows (a) the path-loss to the serving (and nearest) cell and (b) the likely footprint of the cell, based on pilot transmit power. It can use this knowledge to control the ratio of uplink noise it introduces to the pathloss. This can be descried as a localized SON as the self-configuration is done in the device itself.

An SSB should typically be configured such that at least 100 SSBs can be deployed in a macro cell sector without affecting the uplink noise floor of the macro cell and at least 5 SSBs can be deployed in a very small cell (defined as pilot power


SSBs self-organise:

SSB will automatically sense the environment and adapt its operating parameters to adjust to the small cell network, the macro network as well as other SSBs5 that are used to extend coverage in the same area.

3.1 Regulatory context

Some regulatory authorities recognise the concept of the smart signal booster and allow customer self-installation within the terms of mobile network operators licenses:

Ofcom in the UK use the term smart repeater to describe such devices, that operate under the same regulatory umbrella as femtocells [6].

FCC in the USA use the term provider specific consumer booster; within this context, the FCC regulations [7] allow devices implementing smart signal booster advanced features greater flexibility of deployment and higher performance.

ACMA in the Australia use the term smart repeater to describe such devices; they operate under the control of the network operators, but can be self-installed by end-users [8].

3.2 SSB architecture

The basic SSB architecture is illustrated below:

Figure 3-1 SSB architecture

The two green boxes represent a single smart signal booster:

Donor ant: this is the antenna that picks up the donor signal from the small cell.

4 I.e. setting specific pre-agreed values in SIB parameters on the mobile network broadcast channel to control the SSBs. 5 SSBs introduce a time-delay, measured in microseconds, between the incoming donor signal and the boosted signal re-transmitted by the SSB. Therefore SSBs incorporate echo-canceller technology to prevent problems related to feedback loops. This echo-canceller technology is the enabler to detect other SSBs in the vicinity by their effect (e.g. where there is a 10 micro-second delay, and an echo is seen at 10 micro-seconds and 20 microseconds then there are 2 SSBs in the path of the signal and the SSBs can configure themselves accordingly).

Legend 1 Donor UMTS/LTE signal 2 Donor Ant SSB Link 3 Relayed UMTS/LTE signal Donor Ant Antenna system that communicates with the cell SSB Smart signal booster service unit that relays the signal from/to the cell

Ant

SSB

Implements 3GPP TS25.106 Plus additional smart features

Donor Ant


SSB: This is the part of the smart signal booster that provides the additional coverage; in repeater parlance this would be the service antenna.

The connection between the donor antenna and SSB can be via a variety of media, wireless or wired.

Regardless of how the connection is achieved, the amount of boost that the system can add to the signal received at the donor antenna to the signal relayed by the SSB (and thus the SSBs footprint) is directly related to the RF isolation between the donor antenna and SSB. The measuring of this isolation and therefore the sizing of the SSB footprint must be fully automatic and require no user input, other than repositioning the donor ant and/or SSB.

3.3 Applications of SSBs within enterprises

The classic scenario for deployment of SSBs within enterprises is as a coverage solution for indoor areas not served by the macro network, or by other small cell technologies. There are two main use cases:

3.3.1 Enterprises without usable backhaul

Backhaul can be a limiting factor, preventing small cell deployment in some cases, for instance:

In the same way that mobile-only households exist, without a fixed phone line or fixed broadband connection, in certain countries and within certain demographics mobile-only enterprises are a reality. If such a (typically small) enterprise is located in a building with poor indoor coverage their only option to receive mobile service of sufficient quality, may be to deploy an SSB.

Another factor in some places can be poor quality rural broadband. In rural areas, in both well-developed and less developed countries, fixed broadband connections can be relatively slow (0.5 1.0 Mbps in the downlink and 128 kBps or even less in the uplink). At these sorts of rates, running a small cell over the broadband link may be challenging, but if a reasonable rural 3G or 4G macro cell signal is available, an SSB can solve an indoor coverage issue for the rural enterprise.

Finally some enterprises may have IT policies that prevent connection of a small cell to the corporate LAN (e.g. a satellite office of a corporation whose LAN is connected directly via a permanent VPN link to another country, where the Internet gateway lives). In that case an SSB can provide indoor coverage where a conventional small cell cannot be deployed.

3.3.2 Small cell coverage extension within enterprises

Small cells provide coverage, capacity and additional value-added services in areas that require it. Some scenarios are more capacity driven and some are more coverage driven. In scenarios where coverage is the driving factor there is a cost/complexity trade-off where it can be quicker and easier to extend the coverage of an existing small cell with a SSB rather than installing more small cells.

By extending the coverage of an existing small cell, services, such as, for example PBX integration, are preserved.


Figure 3-2 Smart signal booster extends small cell coverage

The following sections list some common small cell deployment scenarios with coverage challenges that can potentially be aided with a smart signal booster.

Warehouses Warehouses are characterised as being large buildings with relatively few people in them (low capacity requirement); they are classic locations that suffer mobile network coverage problems, as they are typically metal-skinned.

A typical warehouse design is to have an office area at the front of the building, a large area behind it and loading docks at the back or on the side.

SSB Ant

Small cell


Figure 3-3 SSBs used to extend small cell coverage to the back of a warehouse

A small cell would typically be installed in the office area at the front of the warehouse, but its coverage might not reach all the way to the back of the warehouse; an SSB could be used to extend the coverage to the back of the warehouse.

Small and medium-sized factories and industrial units Construction and layout of small and medium industrial units used for manufacturing and other industries such as vehicle maintenance are very similar to warehouses described above and suffer similar coverage problems that can be solved by extending a small cells coverage using SSBs. (Capacity is generally not an issue as the numbers of people are small, relative to the area covered.)

Basement areas Basement areas of many industrial and commercial buildings are not occupied, they do typically contain ancillary equipment such as central heating boilers, patch panels for building wiring, gas, electricity and water meters, etc..

The requirements in such areas for mobile network coverage are twofold:

Maintenance staff will occasionally be present and need mobile network coverage.

Typically low-speed M2M connections for telemetry purposes such as smart-meters for power consumption are increasingly likely to be required in these areas.

Because the bandwidth requirements are so small, it may often be easier to extend the small cell coverage from the ground floor into the basement using a smart signal booster.

Ant SSB


Figure 3-4 Using an SSB to extend small cell coverage into a basement

Deployment guidelines for small cell coverage extension within enterprises The Small Cell Forums Radio and Physical Layer working group studied small cell coverage extension in two networks [9]. This yielded the following outcomes:

Effects of SSB delay SSBs typically add an additional delay to the signal received at the mobile device in the range of 6 12 microseconds6. This equates to an equivalent distance of the mobile from the small cell of between 1.8 and 3.6km. Therefore to accommodate mobiles who are connected via the extended coverage of a SSB, the small cell must be capable of supporting a cell radius measured in a few km rather than tens of metres.

Typically, small femtocells are not set-up to support cell radii of this size and we have seen that SSBs effectively put mobiles out of range and unable to communicate with the femtocell. In networks where SSBs and femtocells co-exist then this is typically mitigated by the SSB detecting the femtocell7 and not relaying the carrier frequency that the femtocell is transmitting.

Proven coverage extension for low-traffic areas In enterprise small cell deployments where the small cells can tolerate the additional delay, SSBs have been shown to provide a good and easily deployed solution to cover low-traffic areas, such as basements, and have no detrimental effect on network KPIs.

For instance, the figures below are taken from the results of the small cell coverage extension study Error! Reference source not found.of an area described by employees as the bunker a basement area in a concrete and steel construction office building.

6 Typical causes of the additional delay to the signal propagation between serving cell and the mobile are the transmission link between ant and SSB units, and delays due to signal processing, such as echo-cancellation. 7 This is easiest done based on knowledge in the SSB about particular broadcast parameters that indicate a femtocell, e.g. pilot TX power below a certain threshold, or primary scrambling codes within a certain range or cell IDs within a certain range.

Ant

SSB


Figure 3-5 Small cell coverage extension results basement location

2000 ft (185 m2)

Small Enterprise deployment characteristic

~5 to 10 permanent employees + transient employee and courier traffic

2000 ft (185 m2)

Small Enterprise deployment characteristic

~5 to 10 permanent employees + transient employee and courier traffic

SSB

SSB Location


3.3.3 SSB use case summary

Enterprise Profile Deployment Scenario 0-10 active

users in area 10-25 active users in area

>25 active users in area

Suitable available Internet connection available

No suitable available Internet connection available

Enterprise small cell supports effective cell radius >2km

Enterprise small cell does not support effective cell radius >2km

Legend: = suitable for enterprise small cells = suitable for stand-alone SSB = suitable for small cell coverage extension with SSB

Table 3-1 SSB deployment scenarios


4. Proposed improvements and next steps for later editions

Add cross-reference to the Enterprise SON use cases document [10] (after the proposed update of that document to include the enterprise small cell coverage extension case).

Add further field experience of enterprise SSB deployment.


References

1 SCF061 Enterprise Market Drivers, Small Cell Forum, Dec 2013, http://scf.io/document/061

2 SCF062 Enterprise Business Case, Small Cell Forum, Dec 2013, http://scf.io/document/062

3 SCF 067 E-SCN Network Architectures, Small Cell Forum, Dec 2013, http://scf.io/document/067

4 SCF 068 Enterprise small cell & it networks, Small Cell Forum, Dec 2013, http://scf.io/document/068

5 SCF 032 Small Cell Forum, Dec 2013, http://scf.io/document/032 6 Web-page Femtocells and Smart Repeaters Ofcom website:

http://licensing.ofcom.org.uk/radiocommunication-licences/mobile-wireless-broadband/cellular-wireless-broadband/policy-and-background/femtocells-smart-repeaters/

7 Federal Communications Commission; 47 CFR Parts 1, 2, 20, 22, 24, 27, and 90; [WT Docket No. 104; FCC 1321]; Signal Booster Rules

8 Cellular mobile repeaters proposed changes to the Radiocommunications Regulations 1993, ACMA Discussion Paper, April 2013

9 Developing guidelines for the joint deployment of Small Cells and Smart Signal Boosters to balance coverage and capacity in enterprise and other environments [SCF WG2 study by AT&T and Nextivity]: http://www.femtoforum.org.uk/sites/home/wg2/Session%20documents/Forms/AllItems.aspx?RootFolder=%2fsites%2fhome%2fwg2%2fSession%20documents%2f2013%20London%20ad%2dhoc%20documents&FolderCTID=&View=%7bCBB52DC5%2d1B0C%2d48DF%2dA4BA%2dEE29A4B287B7%7d

10 SCF 066 Enterprise SON use cases, Small Cell Forum, Dec 2013, http://scf.io/document/066

ScopeExecutive summaryContentsTablesFigures1. Background and introduction2. Small cell RAN with enterprise-based radio controller2.1 Architecture2.2 Benefits

3. Smart signal boosters (SSBs)3.1 Regulatory context3.2 SSB architecture3.3 Applications of SSBs within enterprises

4. Proposed improvements and next steps for later editionsReferences

Documents

074 Alternative Enterprise Small Cell Extension (1)