Boosting Cellular Signals Indoors


New technology trends are in motion to help organizations extend cellular coverage and capacity inside their buildings to meet today's exploding wireless traffic demands.

For example, front and center at last week's Mobile World Congress (MWC) in Barcelona, Spain, were new "small-cell" in-building wireless solutions, some of which integrated multiple technologies such as distributed antenna systems (DASs), femtocells and Wi-Fi access points (APs).

MWC is an annual, GSM Association-sponsored conference and exhibition. In addition to yielding volumes of new consumer device announcements and mobile WAN backbone products, MWC also showcases the latest in-building licensed wireless network amplification and signal-delivery systems. Generally, the systems are adopted by mobile WAN operators, who, in turn, sell them to enterprise customers directly or via resellers. More recently, Wi-Fi offload - whereby mobile operators can use unlicensed Wi-Fi spectrum to supplement their networks for additional capacity - has been a big theme at MWC, too.

The Road to In-Building Success

There are many reasons to boost licensed mobile broadband signals indoors. Some buildings are too far from the nearest macro cellular tower(s) to pick up a signal, for example. Other buildings might consist of materials that the signals can't penetrate.

Other organizations might want to transmit and receive over public safety network frequencies in an emergency. In fact, public safety is likely to soon get more attention, given that late last month, U.S. President Barack Obama signed into law that the 700MHz "D" block of spectrum will be used to build a nationwide public-safety network.

Whatever the in-building wireless driver, traditionally in-building solutions have taken the form of a DAS, targeted at larger enterprises with deep pockets and carrier clout. A DAS takes signals from an in-building cellular signal source, such as a base station, and distributes them to antennas that have been traffic-engineered and installed all over the building. Signal distribution is via fiber, coaxial cable, a fiber/coax hybrid or, in some cases, your Ethernet backbone.

At the other end of the spectrum, so to speak, are femtocells. These "miniature  in-building cell towers" were initially created for homes and small businesses covering up to about 5000 square feet.

And in-building options are finally emerging for mid-sized enterprises, largely overlooked until now. DASs are moving down market, while femtos  are moving up market, for example, with Sprint leading the enterprise femto pack. There are also entirely new in-building approaches, such as SpiderCloud Wireless' Small-Cell Cluster Solution (see sidebar and table).

Obsession with Small Cells

TNWireless-March 5-Sidebar.jpgThe small-cell trend is about reusing full spectrum as often as possible. You do this by placing signal sources closer together in a high-density design, thereby creating more, smaller cells, each with full capacity. This contrasts with traditional designs with fewer sources blasting out signals across long distances. In those networks, the signals are strongest near the source and the faintest at the outside edge of the big cell. Those setups aren't cutting it, indoors or out, with so many wireless users now vying for capacity and exchanging large data and video files.

"We need more stuff," says Joe Madden, principal analyst at Mobile Experts, a wireless consultancy in Campbell, Calif.  "Nowadays, cell towers are fully occupied with users who are nearby; bandwidth isn't available to penetrate all the buildings. We need to reuse spectrum as much as possible. DASs are starting to include...femtos, and I think that's a good idea. We're also seeing consumer-grade femtocells scaling up for enterprises."

Small-cell, or high-density, wireless network designs are growing desirable in both licensed mobile broadband networks and unlicensed-spectrum Wi-Fi networks. And Wi-Fi is getting mixed in with operators' licensed-frequency network designs to boost capacity - an option particularly favored by AT&T. Traditional cellular network suppliers Alcatel Lucent and Nokia Siemens Networks, for example, announced at MWC that their small-cell portfolios will include support for Wi-Fi. Cisco unveiled a Small Cell Gateway, which the company said integrates 2G, 3G and 4G LTE networks with femtocells and Wi-Fi hotspots.

Conversely, Wi-Fi supplier Ruckus Wireless announced that it would be adding support for licensed-frequency small cells to its public hotspot technology.

And "more DAS providers will add Wi-Fi to their signal mix," says John Byrne, research director, wireless infrastructure at IDC.

Higher density designs for both mobile WANs and Wi-Fi are needed for stronger signals (more wireless bandwidth) everywhere there is coverage. In fact, the U.K.'s Informa Telecoms & Media issued an inaugural report on small cells during the MWC show reflecting this trend. The firm predicts that small cell deployments will grow from 3.2 million in 2012 to 62.4 million by 2016 - a 2000% (or 20x) increase.

TNWireless-March 5-Table.jpg

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The in-building availability of 3G/4G signals seems to be an area that will only increase in importance. Even though many devices could automagically switch from cellular to Wi-Fi, staying with a single infrastructure certainly has its advantages.


The other challenge to coverage is that the wireless carriers will not let go of control/management of the BDAs and other repeaters transmitting on their licensed frequencies. Who pays install costs varies from deal to deal. The FCC is sitting on a long pending rulemaking on the subject. It is an open question, at best, whether the FCC will adopt a "self-help/self-install option," using carrier pre-approved equipment, for building owners. This would include some sort of prior coordination with the carriers This approach would address many concerns discussed below.

Joanie, given enterprise trending towards BYOD, it seems that enterprise femtocell is growing less viable?

Back when employers purchased all employee cellular handsets, they picked the carrier - and could choose a compatible femtocell. There were still big issues with capacity and coverage but at least a business could blanket a facility with one kind of femtocell.

With BYOD, enterprises would need to ensure indoor coverage for multiple cellular networks. As you noted, for femotocells, that means one for ATTWS, another for VzW, etc. Leveraging one enterprise WLAN to carry all of those calls sure starts to sounds more attractive than extending every carrier's network inside my building.

I know that DAS can be outfitted with uplinks to each carrier network. How do "small cell cluster" solutions deal with supporting multiple carriers within the same building?

"Small cell" designs address the high-density/capacity issue. Historically, folks wanted to bring signals indoors so people could make voice calls on their phones, so basic coverage was the name of the game. Now, of course, data is front and center. So whether you favor cellular or Wi-Fi indoors, you need stronger signals near everyone, which means more Wi-Fi APs or cellular signal sources in more places, which create smaller but more potent coverage areas (cells). In the case of cellular, it's impractical to install multiple base stations or picocells throughout the enterprise because of size, real estate, cost and so forth. Femtos can work and their price is right; but as you point out, Lisa, they are currently single-frequency devices.

The need to support multiple frequencies is another problem altogether. The DAS providers have been ahead of the game in this area, because most offer "neutral host" systems that can accept signal feeds from multiple frequencies (signal sources) and carry said signals to pre-traffic-engineered antennas throughout the building. In other words, you can "distribute" multiple carriers' services, as well as even services on multiple frequencies coming from a single carrier (AT&T in the U.S. has three, for example) across one infrastructure.

The challenge here - particularly for hotels and other venues serving the public and also for enterprises addressing BYOD, as you mention, Lisa - is that you need as many signal sources to distribute as services/frequencies you wish to support. Getting the signal source down to something smaller than a base station, like a picocell or even a femtocell, at least addresses capex, power and HVAC issues associated with these multiple pieces of equipment, which can feed a DAS. But finding the real estate for all of them is still a big deal (unless the carrier(s) is doing it on your behalf, and that presumes you're a pretty big company). Now, TE Connectivity has bundled a 1900 MHz WCDMA femtocell into its DAS (currently in prototype), so that helps by giving you another signal source. And companies like Ericsson have made noises about bundling multiple frequencies into picocells - again, just one box that feeds the DAS helps solve the multifrequency issue. Small cell is somewhat addressed in DASs, in that the antennas are traffic engineered for optimum coverage; however, the spectrum is not reused at each antenna.

So still at issue with DAS is reusing spectrum, which is fundamental to maximizing capacity everywhere. Perhaps a small-cell solution like SpiderCloud's - which literally puts a signal source everywhere there's an antenna - could eventually gain support for multiple frequencies/carriers so that both problems - spectrum reuse and need to support multiple frequencies/carriers/services - could be met. Time will tell!


Enterprise femtocells and enterprise small cell clusters are normally paid for by the carrier; i.e., they require no or relatively small investment by the enterprise. The carrier makes this investment to retain existing subscribers and to acquire new ones (if ATTWS had 5-bars in your building and VzW did not have signal, wouldn't people switch?). Carriers can afford to provide small cell systems at no/small cost because these systems cost less than multi-operator systems. In contrast, enterprises often have to bear majority of cost of systems that support multiple operators, with few or no options to recover this cost in the future.

With BYOD, employees are choosing. So, if a particular carrier is ready to improve coverage in your building at no cost, why stop that carrier? Let him provide coverage/capacity in your building, and let employees decide if they want to switch to that carrier.

Multi-operator systems like DAS make business sense for public areas, like hotels, convention centers, and airports, where property owners can recover their investment by leasing the DAS to multiple operators. However, it is unlikely that a 250-500 employee office can lease out its DAS to 4 mobile carriers and recover its investment.


Purveyors of multicarrier DAS want the enterprise to install new building-wide coax networks to support RF. With WiFi, this wasn't necessary as the industry coalesced around structured tw-pr wiring and Ethernet. We want a solution that lets use the the wire plant we already have installed.

Of course, just because we want it doesn't mean we'll get it. So perhaps this is just a rant.


A challenge for MDU environments is that residents have subscribe to multiple wireless carriers and each wireless carriers have their individual sets of backward compatible frequencies in their handsets.
In single tenant/owner environments the likelihood of a single wireless carrier offering service to individuals working in the facility is higher.

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