Grand visions of the enterprise mobile warrior conjure images of productive employees staying in touch with the office and clients between appointments by effortlessly communicating while on the move via a cell phone, PDA, laptop computer or other wireless device.

But this ideal of efficiency often contrasts sharply with reality. At most large public facilities, signs that untethered nirvana has not yet arrived are readily apparent: cell-phone users glaring at handsets unable to get a reliable signal, a row of mobile-device owners leaning against a window or stepping outside a building in an effort to get a signal, and the groups of non-coffee drinkers frequenting Starbucks so they can get access to a Wi-Fi connection.

Coverage always has been an issue in the wireless world, especially inside buildings. Otherwise strong wireless signals often don't penetrate building walls well and sometimes are stopped altogether. The problem is particularly severe in larger buildings that typically serve more wireless users — not only do these buildings feature sturdier materials that block radio signals, the large number of people they serve during peak periods can create capacity issues for any in-building coverage system that is deployed.

As a result, in-building coverage is a sore subject for many wireless service providers.

“The fact is, sometimes [in-building coverage strategies] work, and sometimes they don't,” said a spokesman for one prominent wireless carrier. “We don't care to talk about it.”

One of the more intriguing developments on the in-building-coverage front has been the introduction of dual-mode phones that support both voice-over-Wi-Fi (or VoWi-Fi) and cellular calls. Although just introduced last year, the market for such dual-mode phones is expected to blossom over the next few years, resulting in 100 million such handsets sold by 2010, according to ABI Research senior analyst Philip Solis.

By leveraging its Wi-Fi network and such dual-mode phones, an enterprise could reduce the number of cellular minutes used by its employees, who also could have one point-of-contact number instead of separate numbers for wireline and wireless voice communications.

Enabling such seamless mobility is a priority for service providers that serve enterprise customers, said Eric Shepcaro, AT&T's vice president of business strategy and development. While the potential for in-house communications over an enterprise Wi-Fi network has great potential, Shepcaro said the notion of letting visitors use the enterprise's Wi-Fi network may not happen until security and network-capacity concerns can be resolved — particularly without some compensation coming to the enterprise that owns the network.

Solis said he believes firewalls can provide needed security and that enterprises will not be concerned with deriving revenues from visitors calling from inside their buildings.

“I think it will be done as a business courtesy — just as you let a visitor use your landline phone today, you would let that visitor use your Wi-Fi network to make calls in the future,” Solis said.

Regardless of such policies, traditional Wi-Fi networks have many practical drawbacks. Although they can be deployed relatively cheaply, Wi-Fi access points have limited range, making it difficult for a building owner to provide ubiquitous coverage without over saturating with access points, which creates additional installation costs, greater maintenance costs and voice applications of uneven quality, because handoffs between access points as a mobile user moves from one cell to another have not been perfected.

“Wi-Fi phones are great if you're standing under an access point, but they're not so great when you're standing further away from the access point or are on the move, creating the need for a handoff between access points,” said David Heckaman, principal of the Heckaman Group.

Ernie Cormier, Nextel Communications' vice president of product management, agreed that VoWi-Fi is not something that can be provided in a haphazard manner.

“You have to design your network to support voice; you can't just take your existing data network and run voice over it,” Cormier said.

Furthermore, deploying lots of 802.11 hot spots won't necessarily provide all of the in-building wireless coverage needed in the facility. For example, the presence of dual-mode phones may mean that voice-enabled Wi-Fi networks also support cellular coverage, but such network deployments typically do not enhance coverage for legacy wireless technologies such as pagers and two-way radios, much less future standards such as WiMAX.

Attempting to balance all of these variables for a wireless deployment at Children's Memorial Hospital of Chicago was William Brook, the hospital's director of information technology. One of Brook's priorities in selecting an in-building system was to deploy a solution that would support the broadest array of mobile devices used by hospital staff and patrons while limiting maintenance time and effort.

“We didn't want to go up in the ceiling any more than we have to, because that disrupts patient care and can create dust,” said Brook, noting that “there's no off hours in a hospital” in which maintenance on a network can be done conveniently in the ceiling of a patient's room.

With this in mind, solutions requiring multiple access points on each floor quickly were eliminated from consideration, because the potential maintenance would be too great. Brook eventually chose a system from InnerWireless, which provides ubiquitous wireless coverage throughout a facility by deploying radiated cable in the ceiling above each floor (see graphic on page 26).

This passive architecture lets users store all active electronics in a secured closet, which greatly simplified maintenance and upgrade procedures.

“Let's say Cisco buys a company and uses its technology to upgrade an access point,” Brook said. “[With an active system], if we wanted to upgrade to the latest gear, we'd have to replace all those access points, which would require going into the ceiling and disrupting patient care. With InnerWireless, you just install the new access point in the secure closet on each floor and you've upgraded the entire network.”

As a consultant working on the Time Warner building construction project in New York, Heckaman found that InnerWireless's system provided an enormous savings in the number of access points that needed to be deployed. Instead of 300 access points needed to serve the hotel in the complex, only 26 access points were needed, he said.

In addition, InnerWireless's distributed antenna system provides more even coverage, allows for greater capacity through layering of channels (see graphic on page 26) and eliminates the need for handoffs, because all the access points are stored in the electronics closet, he said.

“Besides being a great way to distribute signals, it also solves a lot of other inherent problems, especially for VoIP,” Heckaman said.

InnerWireless certainly is not the only company to boast a passive distributed cable system, but its system is more flexible than its competitors, Heckaman said. Most passive systems support only cellular and 802.11 technologies, but the InnerWireless system also supports paging and two-way radio communications.

Indeed, InnerWireless senior vice president of product management Ed Jungerman said his company's basic package supports wireless technologies with signals operating from 380 MHz to 2.5 GHz. Customers can opt for packages that extend the lower frequencies — where older paging systems operate — or provide frequencies up to 6 GHz that are earmarked for 802.11(g) and public-safety broadband data services.

“We're the only one that offers a broadband passive system,” Jungerman said. “Other companies that offer passive systems only support a service or two.”

This flexibility eases the task for network managers, who otherwise might be placed in the uncomfortable position of designing networks while trying to predict which wireless technology will be desired next. With the passive InnerWireless infrastructure in place, the decision to plug in an access point to support a new technology like WiMAX can be done relatively easily when the market demands it.

“After the [InnerWireless system was installed in the Time Warner building], somebody said, ‘We want to add a pager channel,’” Heckaman said. “Initially, we were worried, but it turned out that plug-in was just a fraction of what it would have cost us to deploy another network just to provide that service — less than $1000.”

The InnerWireless system is not cheap, with Heckaman noting that the “initial sticker shock is tough” for some to overlook. But the value of being able to efficiently add services in the future instead of reinvesting in an entirely new network to support the latest wireless technology is worth the added expense, Brook said.

“It was certainly more than just buying access points — but not much more, if you look at it from an installation and long-term investment-protection standpoint,” Brooks said. “But, if you look at it from a two-year standpoint, it's tough to justify the cost.”

Another oft-overlooked benefit of the distributed antenna system is that its ubiquitous coverage means an antenna is never far away, so devices can operate at low power. Not only does this extend the battery life of mobile devices, but the lower power makes it less likely that the devices' signals will “leak” so far outside the building that hackers can use them to get unauthorized access to a network, Heckaman said.

“[Security] is not something people talk about a lot, but that edge could be a make-or-break issue for doing an installation, particularly for a health-care facility or a bank building,” he said. “One of the biggest security threats you have is your wireless data system.”

From another security angle, Heckaman said the fact that the InnerWireless system can carry public-safety two-way radio signals makes the architecture particularly attractive to building owners that are required to provide in-building support to first-responder communications — a characteristic that appears in an increasing number of codes for new buildings, he said.

“I would think it [distributed wireless] should be part of the building code, if only for first responders,” Heckaman said.

Jungerman also said he can foresee a day when supporting public-safety radios will be a requirement for all buildings, noting that sprinkler systems evolved from a feature only in large, high-end facilities — much like distributed antenna systems today — into a requirement for the vast majority of structures.

The fact that building owners can use this same infrastructure to generate revenue by providing services directly, striking deals with service providers or making their properties more valuable to tenants makes InnerWireless optimistic about the future, Jungerman said.

“It was a particularly long time [for sprinkler systems to become commonplace], especially for older buildings,” he said. “But the wireless utility we offer helps solve the economic impediment, so there's an incentive for building owners to do it.”