Distributed Antenna Systems
ACTI Briefing Note
ACTI Communications, Collaboration, and Mobility Group (ACTI-CCM)
www.educause.edu/acti
October 2012
This briefing note provides an overview of distributed antenna system (DAS) solutions for
in-building wireless coverage for cellular voice services on higher education campuses. It:
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Describes what DAS is,
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Highlights some non-DAS alternatives, and
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Provides useful advice to campuses looking to buy and fund a DAS solution.
The paper ends with a brief look at the future of indoor cellular coverage.
Although students, faculty, and staff expect the voice and data capabilities of their mobile
devices to simply work everywhere, there are significant technical and financial challenges
to making this a reality in most campus environments. The rise of Wi-Fi-capable
smartphones and the investments colleges and universities have made in campus Wi-Fi
networks has, to a large extent, solved the data connectivity issue. However, in-building
wireless coverage for cellular voice services remains a significant challenge on most
campuses. Many campuses are working to solve in-building cellular coverage problems
with a distributed antenna system (DAS) solution, in which large numbers of small cellular
antennas are installed inside campus buildings. The addition of a few on-campus cellular
towers is fundamentally different from the implementation of a DAS and is not the focus of
this document. The on-campus cellular tower approach might be viable in smaller campus
environments, but it is unlikely to be a solution for larger campuses.
© 2012 EDUCAUSE
This work is licensed under a Creative Commons
Attribution-NonCommercial-NoDerivs 3.0 License.
http://creativecommons.org/licenses/by-nc-nd/3.0/
Distributed Antenna Systems
What is a DAS?
In a generic technical sense, a distributed antenna system is a solution that places a large
number of very small antennas throughout a building or set of buildings.1 DAS antenna
spacing is often similar to the placement of Wi-Fi access points in a building. These antennas
are powered by a series of small transmitters that are distributed throughout the DAS
network. Fiber optic cable is typically used to connect the DAS network in buildings to the
campus central DAS electronics location. This central location is where wireless carriers will
install their equipment. The cellular carriers require a significant amount of space, power,
and cooling in this central location because they typically install several racks of equipment.
One alternative—often referred to as an “outdoor DAS” by some vendors—is to install a
series of antennas on the exterior of campus buildings. Outdoor DAS solutions require a
much smaller number of antennas and do assist with cellular coverage, but they often fail to
provide reliable coverage inside buildings.
Campus DAS systems typically operate as carrier-neutral solutions, and are specifically
designed to provide transport for the frequencies and services that several or all of the
cellular carriers in the area use to provide service. Sometimes the installation and operation
of a DAS system is bundled as part of a contract for campus cellular services. In these cases,
the DAS will often be designed to provide enhanced coverage only for the single carrier that
holds the services contract. Carrier-neutral DAS solutions are popular in higher education
environments because schools rarely know what brand of cell phone their students are
likely to bring to campus.
Non-DAS Solutions
A full, in-building DAS solution is expensive to install and operate. Initial five-year costs to
install and operate a DAS for the residence-hall portions of a typical large campus can range
into the millions of dollars. Because the wireless industry incorporates new technology at a
rapid pace, additional system expansion will almost certainly be needed during the initial
five-year period. In-building wireless coverage can also be enhanced using solutions other
than a full DAS:

Enhanced Outdoor Coverage
Carriers are often willing to install small cell sites on campus to enhance outdoor
coverage and assist with indoor coverage. While these sites provide excellent
outdoor coverage, they often fail to provide high-quality indoor coverage due to
topography and building construction materials. The same new construction
materials that make buildings energy efficient also degrade cellular radio signals.
Specialized “leaky” coaxial cable is also sometimes used instead of relatively large numbers of antennas. While
the technical implementations differ, both of these solutions can deliver excellent cellular coverage in a building.
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Distributed Antenna Systems
Moreover, the addition of large numbers of outdoor cellular antennas is often
complicated in a campus environment for aesthetic reasons.
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
Donor Antenna Solutions
DAS-like functionality within a single building or section of a building can often be
achieved with a donor-antenna solution. A smaller number of antennas are installed
in a building and connected via an amplifier system to a cellular antenna located on
the roof. These types of solutions work well for a small area and are very cost
effective but do not grow to become large-scale solutions. While this type of solution
enhances wireless coverage, it does not add capacity for larger numbers of cellular
users within a building in the manner of a full DAS solution.
Picocell Systems (sometimes called Femtocell)
Cellular carriers manufacture devices to provide coverage within a small home.
These devices receive connectivity from the local LAN and provide cellular coverage
to a small number of devices in a limited area for a single carrier. Although these
devices can work well in a house and can be used on campus to cover, for example, a
small number of faculty offices, coordination of coverage and overlapping
transmitters make these types of devices unsuitable for the general campus
environment. These devices also typically require a GPS signal and thus must be
installed near a window.
Buying and Funding a DAS Solution
Funding for campus DAS solutions is a complex and multifaceted challenge involving costs
for both the initial construction of the system and for long-term maintenance and upgrades
as wireless technology advances. Most campuses prefer to have cellular carriers or a thirdparty integrator fund the system because it is the carriers that bill users for services and
make the profits. For that reason, however, cellular carriers really only have an incentive to
fund DAS solutions that focus on large numbers of their own users. In addition, carrier
coverage priorities don’t necessarily match the locations that are important in a campus
environment. While each carrier values the assets a campus brings to the negotiating table
somewhat differently, the ability to provide excellent coverage in stadiums, arenas, and
residence halls appears to be a high priority for all carriers. We recommend that you work
to ensure that carriers or the third-party integrator funds coverage for your institution’s
high-priority locations (or the whole campus) as part of the agreement when you provide
access to residence halls, stadiums, and arenas.
There are a few common procurement approaches for a campus DAS system. Some of the
tradeoffs for each these approaches are highlighted below:
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Distributed Antenna Systems

Campus-Developed DAS
A campus with strong wireless industry expertise could design and install a carrierneutral DAS solution. Potential obstacles to this approach include staff resources and
the school’s ability to convince the carriers to invest millions of dollars in a project
run by staff who may not have previously implemented DAS solutions.

Neutral Integration Firm
An approach used by many institutions is to hire a firm that is in the business of
building large DAS solutions for carriers in airports and other large venues. These
firms typically have the technical knowledge to design and build an efficient
multicarrier solution, and the carriers trust them. Integration firms also bring
wireless industry business expertise and can greatly assist with the carrier
negotiations needed to fund the construction and operation of the system, including
the integration firm’s costs. These firms are also often willing to operate the DAS
system on behalf of the institution if desired. This solution typically results in a
solution that is owned by the campus but funded by the carriers. Carrier funding
normally includes the cost for maintenance to operate the system and the costs for
future upgrades.

Third-Party Integration Firm
Another common approach is to hire a third-party firm to fund, install, and maintain
the DAS under contract to the campus. This solution typically results in a system
that is owned and operated by the third-party integrator. Third-party integrators
make their money by charging carriers to access and use the DAS. This type of
solution has worked well for some institutions. When negotiating a contract with a
third-party integration firm, we recommend that the contract contain strong
performance provisions that include significant financial penalties if the integrator
fails to have a sufficiently large number of carriers use the DAS. The main goal for
most campus DAS solutions is enhanced cellular coverage in as many areas and for
as many carriers as possible. Coverage is usually much more important than any
royalties that the third-party integration firm might offer.

Cellular Carriers
There are also some cases of a cellular carrier acting as either a neutral integration or
third-party integration firm, where the carrier will allow other carriers’ traffic
(typically for a fee) on the DAS that they own and operate. This solution can work
well because the carriers tend to trust each other (at least in a technical sense). The
same caveats as for third-party integration firms are appropriate here in that it is
most likely critical to the campus that multiple carriers actually use the system.
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Distributed Antenna Systems
The Future of Indoor Cellular Coverage
DAS-based solutions to the cellular coverage problem will likely continue to remain
important for the foreseeable future, even though technical alternatives exist. Technologies
that enable a user’s smartphone to leverage an available Wi-Fi network instead of the
carrier’s cellular network have been available for years, but, aside from T-Mobile, are not
widely deployed in the United States. Likewise, while VoIP applications (such as Skype)
that function over both a smartphone’s cellular and Wi-Fi radios are widely available, they
are typically not well integrated with the handset and do not deliver the experience users
expect.
When Wi-Fi access point manufacturers are asked why they choose not to manufacture
devices that support both advanced Wi-Fi and cellular radios, their answer is that such
devices would be much more complex and costly and that the integration would be of
dubious benefit. One of the compelling core issues cited is that the pace of change in the WiFi and cellular industries is different and thus the timing for needed equipment upgrades
would nearly always be unsynchronized.
Some newer DAS technologies are able to leverage Cat-5e+ (twisted pair network) cable at
the distribution layer, potentially simplifying DAS installation and lowering the one-time
costs. Other systems are able to provide wiring-closet aggregation of Wi-Fi access points
and the distribution of Wi-Fi signals via the DAS antennas that carry cellular services.
Summary
DAS technology will continue to evolve, synergies with Wi-Fi will wax and wane, and the
regulatory environment will change.2 Still, the need to provide effective service to the
mobile devices that students and employees bring to campus is a long-term issue that is
only likely to increase in the near future. Most campuses will find that they lack either the
technical expertise or the cellular industry credibility needed to extract large sums of money
from cellular carriers—that is, to persuade cellular carriers to make significant investments
in campus-based infrastructure—and will choose to employ external resources to build and
even operate their campus DAS solution.
There are often state and national building codes that must be observed when designing campus DAS
solutions. Public safety needs can often be accommodated via the same DAS that is used to enhance cellular
coverage. For more information, see the National Public Safety Telecommunications Council page on in-building
communications available at http://www.npstc.org/inBuilding.jsp.
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Distributed Antenna Systems
Acknowledgments
This briefing note was written by ACTI Communication, Collaboration, and Mobility cochair James A. Jokl, Associate Vice President and Chief Enterprise Architect, University of
Virginia, with input and support of the following ACTI-CCM contributors:
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David Beyerle, Communications Engineer, The Pennsylvania State University
Douglas Carlson, Associate Vice President, Communications & Computing Services,
New York University
Richard Hach, Associate Director, Network Administration Special Projects and
Initiatives, Virginia Tech
Kurt J. Jeschke, Manager, Network Engineering, The Pennsylvania State University
Mark Katsouros, ACTI-CCM co-chair and Director, Network Planning and
Integration, The Pennsylvania State University

Timothy Lance, President and Board Chair, NYSERNet, Inc.
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John Nichols, Information Technology Manager, Virginia Tech

Steve Troester, IT Director, University of Iowa

Steve Updegrove, Senior Director, Telecommunications & Networking Services, The
Pennsylvania State University
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