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White Paper

Technical Considerations for a SuccessfuNeutral Host DASNestor SalvadoDirector, Channel Sales In-Building Wireless February 2015


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Historically, Distributed Antenna Systems (DAS) have been deployed by individual carriewanted to extend their service into buildings, open-air venues and campus environments. Tsystems were typically owned by a single mobile network carrier who would be responsib

negotiating with the building owner, working with the local regulating authorities to securenecessary permits and authorizations, funding the deployment of the DAS and managing tsystem afterwards. In order to offset the operating costs, the carrier often leases portions oDAS system’s resources to other carriers in order to monetize their investment over time.

Today, DAS networks support a wide variety of locations, including universities, sports arstadiums, hotels, casinos, malls, airports and subways. As commercial trends such as “brin

your-own-device” (BYOD) and the public’s demand for ubiquitous connectivity have growthe number of DAS installations has steadily increased. By 2017, DAS deployments couldmore than 300 percent growth.1 Driven in part by rising bandwidth requirements and qualityof service expectations, the cost to deploy and maintain today’s advanced DAS systems isgrowing as well. As a result, the wireless industry as a whole is pursuing a variety of servidelivery models designed to offset the high CapEx and OpEx costs while ensuring reliableprotable in-building coverage and capacity. One of the models receiving a lot of attentionthe neutral host DAS.

A neutral host DAS shifts the ownership of the system from the carrier to either the buildinowner, DAS integrator or a third-party system provider. Under the neutral host model, thisindependent third-party host assumes all nancial3, regulatory, legal and technical responsibilityfor deploying, installing and maintaining the system, and leases space or access to the systto one or more operators.

The neutral host model provides a number of attractive benets for all parties involved.

• Participation by multiple carriers ensures more end-users can utilize their carrier’s netwinstead of having to roam.

• Because the DAS is owned and managed by a third party, no carrier has anunfair advantage.

• The ability for venue owners, DAS integrators and even DAS system providers to serveneutral hosts, increases the number of players who are able and willing to help satisfy thgrowing demand in the market.

Much of the literature on neutral host DAS systems deals with the various funding modelsownership and usage rights and the sometimes complex relationships between carrieroperators, venue owner and neutral host. This paper, instead, provides an overview ofthe some of the more common technical issues involved in designing, commissioning andmaintaining a neutral host DAS. It is based on CommScope’s extensive experience in thedesign and implementation of multi-carrier, multi-band DAS solutions.

The design process

Of the various processes in the development of a neutral host DAS solution, arguably the mcomplex and important is the design phase. It is in this stage that the potential conicts anproblems regarding a multi-operator system arise. Depending on the number of carriers whhave signed on, the design stage involves half a dozen or more parties, each with their ownexpectations, specications and limitations.

The rst step in the design process involves the carriers dening the specic frequencies,wireless technologies and sectorization schemes they want to use. This information enablethe neutral host to develop the initial DAS design which may or may not include input frombuilding owner as well. This preliminary design will typically include technology-specicbudgets, initial antenna placements, possible cable pathways, and RF heat maps.

“Typical DAS contracts for hardware

only (hubs, nodes, remote radio heads,antennas, etc.) now range from $5 to $10million, compared to just $1 million a fewyears ago.”

– Infonetics Research, April 20142

Carrier Signal source:RF repeateror BTS

Neutral Host

Neutral Host

DAS activeequipment

DAS passiveequipment

Neutral host with carrier providingsignal source.


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After reviewing the initial design with all the carriers, the neutral host will now have a mubetter understanding of many of the performance requirements and other details necessarya successful project. This translates into a more precise layout of where the remote units aantennas must be located, the required power levels for each, the basic cabling infrastructuand the location of the carrier BTS units and the DAS headend.

Each carrier enters into the relationship wanting to maximize their own revenue by gettingmost favorable design for their network and users. This is where using the neutral host moproves highly benecial. By denition, the owner of a neutral host solution—responsible fcoordinating the process and mediating any conicts—is not one of the participating moboperators. Therefore the playing eld is level for all the carriers involved.

This point becomes important in contextualizing some of the more important technical dethat follow. These include issues such as allocating resources to compensate for changes incapacity and coverage, interference control, and the commissioning and optimization of thnal DAS solution.

System capacity and coverageFrom a mobile network perspective, the landscape within a building, venue or campus isconstantly in ux. As end-users arrive and leave, the demands on the DAS network changnot only per carrier but per channel. Therefore, the DAS needs to be able to easily adapt aexpand to address the possible changes in frequency bands, sectorization, coverage andcapacity according to the needs of each carrier.

Consider, as an example, AT&T Stadium in Dallas, TX, home of pro football’s Dallas CowIn 2009, the stadium installed its rst DAS system, a multi-carrier, multi-band, multi-technsolution designed by CommScope. On any given day, a majority of fans who attend aCowboy’s game will typically be AT&T subscribers because the strength of the carrier in tregion. As a result, AT&T will require more base station resources then the other carriers osystem. This has signicant implications on how the wireless trafc for each carrier must sectorized. More importantly the systems have to enable growth.

This situation is hardly unique to sports venues; virtually any DAS system serving the neea large, diverse and transient population must have the exibility to alter sectorization schbased on the changing needs of individual carriers. This includes convention centers, largehotel properties, international airports and cosmopolitan shopping malls. This exibility iscritical in order to satisfy the shifts in wireless trafc as large numbers of end-users move one part of the venue to another.

Coverage and capacity are directly linked to power requirements, making system exibilita key feature when comparing the technical capabilities of DAS solutions. Deploymentexibility among providers runs the gamut from none to the ability to re-congure coveracapacity—by carrier and zone—on the y.

Most neutral host DAS solutions today offer some dynamic capacity capability. Typically,altering the sectorization plan for an individual carrier will require some re-cabling. Moreadvanced solutions, like the CommScope ION-U, enable stadiums to modify and optimizesectorization scheme within minutes via a simple software connection.

“DAS vendors and integrators haveadvanced their equipment to meet a wider

range of frequency bands and higherpower outputs...

Key performance indicators for DAS designinclude frequency bands, signal protocols,sectors, coverage and interference, amongother parameters.”

– DAS Forum; November 20114


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Potential InterferenceAs with a macro network, there can be potential Intermodulation issues in a neutral host D

environment. These are typically limited to the more commonly used frequency bands suc700 MHz and 800 MHz bands. Because the system is centrally monitored and managed,any interference issues can usually be adequately resolved by adjusting power levels onthe DAS headend and by the use of RF remote radio units that have integrated interferencemitigation lters.

While the potential for Intermodulation is relatively low, the neutral DAS host should not ithe risk during the vendor selection and system design phases. This is especially importancarriers continue to add more frequency bands and channels that must co-exist in the sameecosystem in closer proximity to one another. Check to make sure there is adequate interfemonitoring and power control functionalities in the system.

In a multi-operator DAS, the greater risk regarding interference comes in the form of passinter-modulation (PIM) interference. In multi-operator DAS environments a growing num

of components in the RF path increase the potential for PIM generation. Because PIMis a hardware-based issue—potentially caused by physical imperfections in the DASheadend, cabling and connectorization, or remote and amplier construction—the qualityof manufacturing and installation become paramount.

The minimum PIM specication for each and every component is improving continually. Pspecications for RF components (splitters, couplers, etc.) and antennas have transitioned –140 dBc to –150 dBc and now are moving to –153 dBc and –160 dBc. With the passivecomponents—splitters, hybrid couplers, and directional couplers—being placed closer to tsignal sources in these systems, it is critical that the PIM specication for these devices arewith highest performance levels.

From PIM levels and signal loss to service availability, each carrier will have their ownperformance standards the DAS must meet. Overall, the system is expected to meet therequirements of the most restrictive carrier. In most cases, however, carriers’ expectations metrics like quality of service are fairly similar. Therefore, the difference between the mosleast restrictive should not be wide enough so as to make the project unsustainable.

System commissioning and optimizationThe nal stage of deployment is the system commissioning and optimization. During this prepresentatives from all parties involved participate in a walk-through of the entire facilityensure the DAS is performing as expected. Specic verications include thorough sweep aisolation testing of the cabling infrastructure, checking power levels for all carriers and chainvestigating and correcting any sources of interference and a nal coverage assessment.

Each representative, also known as an “authority having jurisdiction” (AHJ), will have diftesting requirements and often use disparate test equipment. Due to the number of AHJs inin a multi-carrier DAS project, the commissioning and optimization process can be compland time-consuming. Readings from one piece of equipment may not always agree with thof another. When conicts in individual results or issues with performance are identied, tprocess stops until the problem is resolved.

Some of the DAS systems available today provide additional functionality that enables theneutral host to reduce the time required for commissioning and optimization. These systemhave integrated routines designed to perform the same checks that the individual AHJs arerequired to perform. These include sweep testing of the cabling infrastructure to ensure theintegrity of all ber and coax cable and connections, using internal test signals to illuminasectors and measuring the signal interaction between sectors.

2018

2023

WHAT IS PIM?

WHEN TWO OR MORE WIRELESS SIGNALS MIXTOGETHER, THEY CAN PRODUCE AN ADDITIONAL,UNDESIRED FREQUENCY THAT INTERFERES WITHTHE DESIRED SIGNALS.

THIS IS CALLED PASSIVEINTERMODULATION, OR...PIM

A DROP OF JUST1 DECIBELIN UPLINK SENSITIVITY

DUE TO PIM

WHEN THE PIM LEVEL WAS SLIGHTLY INCREASED

DRIVE TESTS REVEALED

~18% DROP IN DOWNLOAD SPEED

WIRELESS COVERAGE BY

11 PERCENTI N A M A C R O

NETWORK

C A N R E D

U C E

I

M U L T I P L EOPERATORS

3 – 5 operators in urban areas

TECHNOLOGIES 2G, 3G, 4G, WiFi

FREQUENCY BANDS48 different 4G bands alone

There are multiple considerations to address when

designing an indoor wireless system including:


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If the DAS system also provides for automatic system leveling, this eliminates the need tore-adjust and re-test the channel power settings each time a change must be made. Systemwith advanced commissioning and optimization may also feature an internal test signal

generator as part of their commissioning sub-system. This allows for independent testingwithout having to connect to the carriers’ BTS. It also ensures all participants are basing tassessments on results from the same testing equipment and eliminates the need for them bring their own equipment.

Return on DAS investment relies on system functionalWorldwide spending on DAS systems is exploding. Forecasted total for 2014 is expected be 4.4 billion dollars. By 2019, it is projected to grow to more than 8 billion, a 14 percentcompound annual growth rate (CAGR). The increase is coming from in-building as well aoutside deployments, with sports venues and transportation applications leading the way ashopping malls, healthcare, hotels, and resorts close behind.5

As carriers, facility owners and integrators look to cut their deployment costs, the neutral hDAS model will continue to be popular. While multi-carrier DAS systems have existed fo

years, the neutral host approach as a business model is still relatively new and developing

Today, the considerations involved in deploying a neutral host solution go beyond the issuof ownership and nancing. Serious thought must be given to technical issues regarding thsystem’s ability to adequately support the interests of all parties involved.

As the deployment of neutral host DAS systems increases, the demands on system performwill grow. Selecting a DAS solution that provides advanced functionality—independentcarrier sectorization, automated power leveling, and system commissioning and optimizatroutines—will help ensure all parties realize a better return on their DAS investment.

Resources1 U.S. DAS Market Forecast: 2012 to 2017 Installations, Tenancy, OpEx and CapE; iGR Research; Q4 20132 Infonetics Research, DAS Equipment Biannual Market Size, Share and Forecast; April 20143 Determining the best DAS funding model for your Enterprise; CommScope, white paper; October 2013.4 The DAS Forum; Considerations for an In-Building Distributed Antenna System; November 15, 20115 In-Building Wireless Market Reaches $8.5B in 2019; ABI Research, press release; February 2014

www.commscope.comVisit our website or contact your local CommScope representative for more information.

© 2015 CommScope, Inc. All rights reserved.

All trademarks identied by ® or ™ are registered trademarks or trademarks, respectively, of CommScope, Inc.This document is for planning purposes only and is not intended to modify or supplement any specications or warranties relating to CommScope products or services.

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