Bringing Cellular IndoorsBringing Cellular Indoors

This article originally appeared in the December 2007 issue of Business Communications Review

By Joanie Wexler

Enterprises seeking high-quality mobile voice communications inside their buildings have several wireless alternatives. Organizations that have already installed very dense wireless LANs might be using or investigating voice over WiFi (Vo-Fi). Others, with cellular phone usage deeply ingrained in their cultures, are turning to newly enhanced indoor cellular technology to do the trick.

The basic in-building cellular problem to be solved is generally well understood: Certain buildings receive poor service indoors. Coverage can be blocked or degraded because the building is in an area too far from the closest cell tower to pick up a strong signal, for example. Or the building’s composition—such as thick concrete or metallic walls and windows with low-emission glass—can block or degrade signals.

Cosmetics company Mary Kay Inc., in Addison, TX, now uses an in-building cellular system to enhance wireless coverage and performance. “We got a bit of signal from multiple cell towers, but not enough from any one tower,” said Brent Frerck, senior technical engineer in the company’s information services and technologies group. “That meant we were getting constant tower-to-tower handoffs and terrible service inside the building.”

Onto Enterprise Radars

Situations like these have long existed, but there are a few reasons why enhancing in-building cellular performance is now moving swiftly onto enterprise radars:

* About 60 percent of U.S. cellular phone calls are made from indoors, according to researcher Ovum, Ltd. The desire for a single device and phone number is causing users—particularly so-called “prosumers,” who combine business and personal tasks on integrated smartphones—to make and receive more calls indoors.

* Advances in IP-PBXs allow multiple handsets to ring or to follow users from their business PBX extensions to other numbers, which is helping businesses justify beefing up cellular network coverage indoors.

* The latest in-building cellular equipment from companies such as InnerWireless, LGC Wireless (currently being acquired by ADC) and Mobile Access supports multiple frequencies and networks in a single system. This prevents enterprises from having to purchase, install and manage several overlay systems if they want to extend network coverage from more than one operator. InnerWireless and Mobile Access will also distribute WiFi signals from a centralized, secured bank of access points, and LGC Wireless and Mobile Access have recently announced that they are adding WiMAX modules to their systems.

* It’s becoming common for organizations to expand their buildings underground to gain extra real estate in municipalities that enforce height restrictions. Basement locations are notoriously impervious to cellular signals, so enterprises need a way to gain coverage in these areas.

These conditions are among the reasons that ABI Research anticipates that in-building wireless deployments will increase at a compound annual growth rate (CAGR) of nearly 20 percent over the next five years. Worldwide revenues for in-building wireless systems were more than $1.3 billion in 2006 and will likely grow to $3.6 billion in 2011, according to the researcher.

There are several technological approaches to bringing the outdoor cellular network inside. There are also funding, regulatory and administrative issues to work out with mobile network operators, who own the licensed spectrum that transports the cellular traffic. The rest of this article will explore the ins and outs of these issues.

Approaches To Indoor Mobility

In-building systems extend cellular voice coverage, data coverage or both indoors. At this juncture, it is common to use WiFi for indoor data applications, given that WiFi bandwidth, once installed, is “free,” with no usage charges. WiFi is widely available and most laptops ship with a WiFi card for connections. However, users in locations without WiFi infrastructure might rely on cellular data network connections to access the Internet and internal data resources.

Currently, though, most enterprises looking at in-building cellular systems are attempting to accommodate internal mobile voice requirements. Of those that prefer cellular technology to Wi-Fi (Figure 1), many are very large and have enough revenue clout with the mobile carrier that the carrier will actually build and manage the system at no cost to the enterprise. For some such large organizations, this is preferable to footing the bill in-house to build out WiFi densely enough for full voice coverage and contending with inter-access point handoff issues that still pose performance and reliability challenges for large-scale Vo-Fi.

For example, a worldwide consumer products company based in the Pacific Northwest has built out WiFi infrastructure in conference rooms and lobbies for mobile data access, but does not have blanket coverage across its 2.4 million-square-foot headquarters campus. Rather than shelling out another $400,000 to $500,000 for the dense wireless LAN infrastructure required to successfully support mobile voice sessions without interruption, the company had its mobile operator, AT&T, pick up a $750,000 tab to extend coverage indoors with micro base stations and distributed access systems (DASs), according to the company’s global network manager.

AT&T chose the components, built the indoor network and manages it, he said.

“The hassles of voice over WiFi, multiple devices, battery life, and shifting back and forth between WiFi and cellular [when roaming in and out of buildings] make my head spin,” the company’s global network manager said. “I’d rather deal with the carrier in filling their black holes than building and operating a voice WiFi infrastructure myself.”

When Will The Carrier Pay?

In the case of very large companies like these, carriers find it’s often worth their while to finance and manage such projects because of the additional cellular usage revenues the carrier will reap when indoor calls are made on the cell network instead of on the internal corporate network. Smaller companies, however, often don’t have the luxury of simply handing over their mobility problems to their carrier, because the return on investment (ROI) for carriers is simply not strong enough.

“If the customer is willing to pay [for the in-building equipment], I’m happy,” said Jim Erickson, director of in-building solutions in the wireless unit of AT&T. “But we decide what we’ll spend based on what revenue we are likely to get on our investment, like any other business transaction. We treat each customer situation as an independent evaluation.”

Companies not large enough to make the cut either pay for the equipment themselves or share the equipment and deployment costs with the carrier. Sometimes they negotiate these deals themselves; in other instances, an integrator or the in-building equipment vendor might step into the picture to remove some of the complexity from the shoulders of the enterprise.

K&L Gates, an international law firm in Washington, DC, sprang for a $50,000 Verizon Wireless base station and a $20,000 T-Mobile base station as part of its effort to push cellular signals indoors. The DAS component—supplied by LGC Wireless and installed by integrator Glasgow Group Inc. of Great Falls, VA—cost between $80,000 and $100,000, according to Rodney Carson, K&L’s local director of administration. Carson noted that the overall DAS cost was lower than it might have been because it was installed during initial construction of the firm’s new 13-story DC office building.

“The building was wide open with no ceilings or walls” to drill or break through, lowering labor costs, he explained.

In-building Components

The exact components that the enterprise (or the enterprise’s integrator or carrier) select will depend on the square footage requiring coverage, how many different wireless networks are to be supported, and the number of floors comprising the building. But the two basic components required to blanket a building or campus with strong cellular signals are a cellular radio-frequency (RF) signal source and a DAS.

* Micro base stations—The cellular source in larger organizations (100,000 square feet and up) is likely to be a small base station installed in the enterprise’s building and supplied by the enterprise’s mobile carrier(s), who owns the license to use the cellular spectrum. Some enterprise-sized base stations are called microcells; smaller versions are called picocells. Still smaller is an emerging class of product called femtocells, which are currently being deployed in residences by mobile network operators. Femtocells hold promise for distributed deployment throughout the enterprise without the need for a DAS (Table 1), but are not available yet as an enterprise-grade product.

“Femtocells will probably be the next big push,” said AT&T’s Erickson. “We’re right in the middle of evaluating what’s out there, the pluses and challenges.”

* Repeaters—An alternative to a small base station as an in-building RF source might be a nearby cell tower, whose signal strength is enhanced by a repeater supplied by an operator-certified third party and installed either on the roof or inside the building. Smart repeaters offer some management of the signal and are generally used in buildings requiring coverage of less than 100,000 square feet.

Spotwave is one supplier of smart repeaters for sites needing less than 50,000 square feet of coverage. Its equipment has been certified by all the major North American mobile network operators. Most Spotwave installations cost less than $10,000, according to Mike Roper, the company’s chief technology officer. Microcells, picocells and smart repeaters are often used with distributed antenna systems.

* DASs—The DAS transports the carrier’s signals from antenna to antenna throughout the building via cabling. There are various architectural approaches to DASs. The differences, most notably, are whether the system uses passive or active components; the type of cabling it uses; and whether or not it supports more than one frequency and network type.

Passive vs. Active DASs

There are both passive and active DAS types, as well as some hybrid passive/active devices. Active DASs usually transport cellular signals from the RF source across fiber cabling in risers and either fiber or Category 5e Ethernet-grade copper cabling serving each floor. Active DASs are smart, in that they amplify, condition and adapt the signal to deliver overall consistent coverage and performance. In addition to the active RF source from the carrier, active systems make use of expansion hubs on each floor connected to remote access units (RAUs) distributed around the floor, with antennas mounted upon them.

Passive DASs usually distribute signals using “leaky” coaxial cable, whereby notches in the cabling act as distributed antennas. These devices simply pass signals along without any enhancement. Their primary advantage is that they cost less than an active system and there are no active electronics between nodes to break.

But attenuation over distance can degrade the signal and, thus, service.

“In areas where there is high usage, you take some chances with passive systems, because they are designed to support a particular capacity,” explained Dan Shey, principal analyst, business mobility, at ABI Research. In places where there are dense spots of usage, “a passive system won’t adjust for additional capacity and power requirements to provide a good experience, and you’ll suffer dropped calls,” he said.

There is also a category of DAS that is hybrid. It combines active components, installed between the RF source and the floors, and, usually, coaxial cable for passive transmission across the last few feet on each floor. These systems offer some of the signal management and adaptation of the active system and some of the cost savings of the passive system.

Multi-network Support

Historically, DASs could accept input from just one carrier’s micro base station. This left corporate customers with the limited options of supporting just one carrier’s service within their building or installing multiple DASs, which was an expensive proposition. Now, however, some DASs can accept multiple carrier signal feeds, making the DAS alternative potentially more compelling, particularly for mid-sized organizations that are either sharing the cost of the equipment with the carrier, or paying for it in its entirety (Table 2).

“I would not have been able to get the money for multiple DASs,” said Tommy Russo, chief technology officer at Akridge, a real estate company headquartered in Washington, DC, that uses a Mobile Access hybrid DAS. His 12-story building stretches 500,000 square feet both above and below ground and serves both internal Akridge employees and other office tenants—a total of about 1,000 users a day.

Because Akridge and its tenants use any number of carrier services, Russo installed the Mobile Access DAS in June 2006 to support three of the four major carriers, some Wi-Fi, and 900MHz/800MHz private walkie-talkie networks in a single system. The project cost about $300,000, Russo said.

At the other end of the spectrum is The Venetian casino and hotel in Las Vegas, a Sands Corp. property that supports 40,000 users wandering the property at any given time. Its in-building system was installed about seven years ago and, as such, supports five different overlay DASs to distribute cellular signals from the AT&T, Verizon Wireless, Sprint Nextel, legacy Nextel iDEN and T-Mobile networks.

“We have multiple DASs, because back then the operators didn’t want to share the other guys’ antennas,” said Steve Vollmer, The Venetian’s vice president of IT and chief technology officer. On the other hand, The Venetian brings in enough business to motivate the carriers to fund and operate the systems. With the operators assuming full responsibility for the indoor installation, operations management and service levels, the complexity of the installation is more or less irrelevant to the property’s owners/managers. And The Venetian’s capex/opex is $0.

“Now, there are DASs available that will share antennas,” said Vollmer, who has invited all the carriers to the table to discuss covering the new 3,000-room Palazzo Resort, Hotel and Casino—another Sands property set to open in Las Vegas this month. “We will let the carriers call that shot [to use such systems] if they care to.”

Procurement Options And Issues

In-building systems can be procured from the carrier, an integrator, or directly from the DAS supplier. “Carriers are a big channel, but we’re seeing enterprises more actively searching for in-building solutions,” said John Spindler, vice president of marketing at LGC Wireless. “So we now sell direct to them.”

Operators will generally work with large customers or their DAS supplier or integrator up front to determine what needs to be done to boost indoor coverage. Sometimes minor antenna adjustments to the macro network can improve coverage, or a new cell site might be coming to the area, said AT&T’s Erickson.

Phil Martin, managing partner at Oxys LLC, a wireless consultancy in Jupiter, FL, said that if the implementer “doesn’t work with the network guy, all other things become second. The DAS vendor won’t know all the macro cell issues in that location.”

ABI’s Shey agreed: “Clearly, there has to be a relationship between the DAS vendor and the carrier.” He added that where the relationships get thorny is in multi-tenant office buildings.

“If in-building coverage is poor, typically the building owner will expect the operator to finance and install an in-building system. However, operators typically do not do this in buildings where it is hard to determine how many tenants are their customers and how long they will reside in that location.”

In addition, each carrier has its own approach to CPE, said Richard Glasgow, president of integrator Glasgow Group.

“Verizon wants you to take their signal off the air via a rooftop antenna and mini-base station, then distribute it via the DAS. T-Mobile wants a T1 interface into your building from its own central office,” he said.

The main issue with the carriers, he said, is that, “unless the enterprise has leverage, you’re at the carrier’s mercy. No carriers have said ‘no’ [to supplying a base station],” Glasgow said. “But they tend to be extremely busy and this is not a priority.”

K&L Gates, for example, saw its LGC Wireless dual-network DAS installed, but had to wait 18 months for Verizon Wireless to supply an RF source for its CDMA-based network, even though K&L was able and willing to pay for it, said Carson. The reason? K&L was not a Verizon Wireless business customer; it was installing the Verizon in-building system to serve the personal needs of its employees and, in particular, to get them coverage in the subterranean floors of its new building.

However, the law firm received its base station from T-Mobile—with whom it is a subscriber to BlackBerry service for about 800 handsets—in about three months.

“If the enterprise is willing to pay, in almost all cases, the carrier will be willing to make [internal coverage] happen,” said Jeff Kunst, vice president of marketing at Mobile Access. “But the timetable is questionable, particularly for a multiservice system where there is just a small population of users for a given carrier.”

Carrier Certification Important

Each mobile operator has a list of equipment that it has certified to use on its licensed airwaves. When it comes to repeaters, which are less expensive than microcells and DASs, a number on the market are not certified. Uncertified equipment can cause problems in the outdoor (“macro”) cellular network and provide unreliable performance, so certification is important.

Technically, selling repeaters that have not been certified by the carrier who owns the licensed spectrum with which it will work is illegal, noted AT&T’s Erickson.

“It’s our spectrum, and we guard it jealously,” he said. “You can go to the Internet and take your pick of repeaters that could interfere with our network; it happens every day. There have been situations that, because of the way a repeater was installed, we’ve had quality-of-service problems in the surrounding cell sites.”

Erickson said AT&T is working with the cellular industry’s association, the CTIA, to “get the FCC to put more teeth into this.”

Implications For FMC

What does the uptake of in-building cellular systems mean for fixed-mobile convergence, or FMC, whereby a single device works seamlessly across multiple types of cabled and wireless networks without dropping sessions?

The turning point will come when dual-mode cellular/WiFi handsets grow abundant, said Craig Mathias, principal at Farpoint Group, a wireless consultancy in Ashland, MA. “If you only have a single-mode [cell] phone, you need in-building cellular,” he said. Mathias estimates that there are about 100 dual-mode phone models available worldwide and about 50 available in the U.S.

For The Venetian’s employees, “We have an interest in combining the PBX with mobility,” said Vollmer. “We’re looking to blend our PBX with the cellular network, take advantage of better rates and run [usage] through the call accounting system to track calls.”

Akridge’s Russo, too, sees cellular as the mobility foundation for his organization. His opinion is that “WiFi phones aren’t prime time. I’m not going to spend half a million dollars on a [WiFi/IP-PBX] phone system.”

Mary Kay’s Brent Frerck agreed, saying he doesn’t consider WiFi to be a mobile solution. “I know there are early solutions that hand off from WiFi to cellular, but I hear they don’t work right, and calls still drop. It complicates the infrastructure more than is necessary,” he said.

He said he sees the future for cellular “only getting brighter” for the applications at Mary Kay: “We want the vice president of manufacturing to be able to leave the plant 15 miles away, be on a conference call while driving to headquarters, pull into our garage, get in the elevator and not lose his connection.”

He said he envisions one day having no desktop phones and having the PBX functions on a wireless device. “But we want to be able to cost-justify it and we want it to be stable first.”

Joanie Wexler is a freelance technology editor/writer based in California's Silicon Valley.