Questions and answers with a DAS expert
We recently had a wide-ranging discussion on the topic of in-building distributed antenna systems (DAS) with Allen Dixon.
Technical, business and standards issues are discussed in this Q-and-A exchange with the chair of the DAS Forum.
By Patrick Mclaughlin
We recently had a wide-ranging discussion on the topic of in-building distributed antenna systems (DAS) with Allen Dixon. Dixon is national channel development manager for Corning MobileAccess (www.mobileaccess.com) and currently serves as chair of the DAS Forum (www.thedasforum.org). Our conversation touched on a number of topics related to in-building DAS and the cabling that supports these systems.
CI&M: Can you provide a “soup-to-nuts” type list of the physical elements, products and technologies that make up a distributed antenna system?
Dixon: By definition, a DAS is spread over a structured or geographic area, and connected by a medium to a common RF [radio frequency] source. So one element needed is an RF source, which typically comes from the carrier. The source provides input to the DAS. Next is a headend element, which takes the incoming source or sources and does something with them. That “something” can be any number of functions, including the combining or cleaning-up of sources. From there the signals go onto a transfer medium. In our case, that medium is singlemode fiber. The next piece of equipment can be called a few different things, including remote element or expansion hub. We use the term remote. That element essentially “undoes” whatever the headend did, for example converting the signal from optical back to electrical. A coaxial cable takes the signal from the remote to the DAS antenna.
CI&M: Is there a template for the type of cabling that is necessary to support a system of distributed antennas? Or do the cabling requirements depend on factors like a DAS’s spatial reach, number of antennas, or other factors?
Dixon: The distributed antenna systems available today are proprietary and each provider does things a little differently. For example, some have higher power within remotes than others. These systems with higher-power remotes can drive higher power on a coaxial cable, potentially to multiple antennas. The answer is, there are certain elements that are common. But every opportunity is a custom-engineered opportunity, depending on the construction of the environment. It may be open and cavernous, or enclosed like a hospital environment.
Standards bodies are taking interest in DAS. The TIA [Telecommunications Industry Association] has inquired about a way to begin to standardize [on DAS infrastructure]. BICSI (www.bicsi.org) is looking at DAS from the perspective of best practices. This is not structured cabling, but it goes into the same venues where structured cabling is installed. The basic tenet of structured cabling is: If I build the cabling infrastructure, it does not matter what plugs into it; it will work. Here, with DAS, you start at the end, with the connected devices, which are the antennas.
CI&M: Can any or all parts of a DAS coexist with local area network (LAN) equipment, in the same telecommunications rooms, racks, pathways, etc.?
Dixon: Historically, separateness has been maintained. But that probably is an artifact of the fact that the DAS has gone in afterward. There is no reason it could not share the same racks and pathways. It can even share the same singlemode fiber. If you have a singlemode backbone, you can use that backbone as part of our DAS.
We say there are three pieces of a DAS installation—parts, heart and smarts. Parts are what we [at Corning MobileAccess and other manufacturer organizations] provide—active gear, splitters etc. “Hearts” is the installation labor—the individuals who typically have the relationship with the enterprise customer. And “smarts” come in the form of the systems integrator or RF VAR [value added reseller]. Historically, if you look at where the DAS market has come from and where it’s going, there have been a lot of changes, particularly in the past three years. Venues historically do not buy DAS. The systems were installed by the big carriers. Now that these venues see a DAS as an asset, they are installing them. You can put other systems onto a DAS; it is multi-carrier, multi-technology capable. Wireless medical telemetry is an example. Health-care providers are changing the way they carry the patient signal from one point to another. Many drivers have led to growth in the installation of DAS by end-users. As that has happened, the core base of RF systems integrators has gotten stretched pretty thin. Some professionals are seeing this opportunity and moving into that space.
CI&M: Turning a little more attention to the business side of DAS installations, I understand it can be difficult to get carriers to participate and bear some of the capital costs of a project. Is there a strategy or formula that strikes a balance, for everyone involved, between capital outlay and benefit from the establishment of a DAS?
Dixon: This comes up constantly in conversations with our customers. It boils down to the fact that we do need carrier participation. They own the spectrum. Their willingness to participate is predicated on a number of things, boiling down to what kind of return they’ll get on their investment. If the carrier is going to spend $80,000 on a base station, they have to justify it by a significant number of users in the network. There are less-expensive solutions; a repeater costs $10,000 to $15,000. But that amount still must be justified. Historically, if the user is willing to establish the DAS itself, the carrier usually is willing to provide the signal. As we move toward data-heavy wireless traffic, rather than voice-heavy, it is becoming necessary to use more-expensive, more-powerful sources. If there is a strategy or formula, it comes back to the “heart” and “smarts”: Make sure you have a systems integrator who has an excellent relationship with local-market radio-frequency engineers.
CI&M: Can a DAS be constructed to support multiple wireless carriers?
Dixon: There are two sides to this question. From a technical standpoint, if you can support one carrier, you can support multiple. In terms of the headend, make sure you have multiple inputs to support multiple carriers. You will need additional inputs at the remote as well. The other side of it is, once a carrier finds out another carrier is involved, they typically don’t want to be left out. It is a matter of finding that first carrier. And again, a lot depends on their internal return-on-investment calculations.
CI&M: Is there anything an enterprise end-user organization can do to prepare for an eventual DAS installation that will not happen immediately?
Dixon: One option is to conduct an RF survey of the building or campus to document it. These RF environments are dynamic, with changes constantly being made to them. But a survey will provide an understanding of what your coverage is today.
CI&M: A DAS provides some particular benefits in the realm of emergency services, first responders, public safety—doesn’t it?
Dixon: It does. A DAS can provide a signal to support first responders, which is a requirement growing among many municipalities. There is an important distinction to be made, though. If you have public safety on DAS, that capability is not there for the direct benefit of the users within the building. Having public safety over the DAS is to ensure that fire and police personnel can communicate back to their headquarters. Often, the time that elapses between a fire alarm sounding and the arrival of fire-department personnel is very short, but the time between their arrival at the site and their entry into the building can be much longer because of their need to establish communication. Having public safety over DAS can shorten the time between the arrival of first responders and their entry into the building.
CI&M: Any other advantage to DAS that I or other potential users might not be thinking about?
Dixon: It provides a clean, consistent signal that extends the battery life of your mobile device. DAS allows for the extension of coverage into a stairwell, parking garage or elevator—areas you’d not reach with the macro network. Mobile-device users can reach the network from anywhere.
CI&M: And is there anything I didn’t ask you about that would be worthwhile to discuss?
Dixon: DAS is an additional cost of doing business for carriers. It adds to their asset base. For the enterprise it is completely different, providing service to people inside a building. A change is coming in the marketplace. By our own internal estimates [as opposed to hard scientific data], we believe 7 out of 10 opportunities presented to carriers do not get funded. That means 70 percent of venues who have gone to their carriers with a wireless problem, came away with the same wireless problem. They can either live with that problem or fix it themselves. We believe that the users who are choosing to fix these problems themselves, through DAS, are on a growth path.
Patrick McLaughlin is our chief editor.
Distributed antenna systems and the Super Bowl champion Giants
Fans of the National Football League’s New York Giants who were present at Lucas Oil Stadium for the team’s victory over the New England Patriots in Super Bowl XLVI took advantage of the distributed antenna system (DAS) at the host site, Lucas Oil Stadium in Indianapolis, as they celebrated their team’s victory with text messages, phone calls, Tweets and Facebook status updates.
Shortly before the big game, Corning MobileAccess announced that its portfolio of DAS was delivering pervasive wireless coverage at major Indianapolis venues just in time for the event. “From arrival, to hotel stay, to pregame events, and game time, mobile users can enjoy fast, uninterrupted access to voice and data,” Corning said, “allowing them to coordinate with friends, share photos, or check out NFL analysis and pregame video with their smartphones.” The DAS deployment included Lucas Oil Stadium, Indianapolis International Airport, eight area hotels, two medical centers, the Indiana Convention Center and the Indianapolis Colts training facility.
Corning Cable Systems’ senior vice president of wireless networks and new business development, Mike Genovese, stated, “While large sites are great for events, the structures themselves and the massive amount of people within them trying to access cellular networks simultaneously can result in dropped calls and slower data access. Our solutions distribute cell signals throughout these locations, so that Indianapolis visitors and residents can effortlessly connect via their mobile devices.”
The company added that Corning MobileAccess DAS had been used to outfit four previous Super Bowl sites, in Houston, Jacksonville, Detroit and Glendale, AZ (where the Giants also defeated the Patriots, for those of us who hold grudges against such things). -Ed.