Making the call: Distributed antenna systems and in-building wireless

Distributed antenna systems and in-building wireless solutions are two options to improve wireless cellular coverage within an enterprise facility.

Since the early days of cellular phones, wireless operators have struggled with in-building wireless coverage.

Steel-framed office towers and concrete warehouses interfere with and block wireless signals, creating a communications problem for enterprises whose employees rely on cellular devices in the office.

Wireless operators offer quick-fix solutions like cell repeaters, but these devices are single-carrier solutions. Most enterprises need more pervasive wireless coverage from multiple mobile operators. Enterprises have two options when cell repeaters are inadequate. They can convince one or more operators to install a distributed antenna system within an enterprise facility or they can take a do-it-yourself approach with an in-building wireless system that piggybacks on existing enterprise network infrastructure.

Distributed antenna systems: A cell tower inside your building

A distributed antenna system (DAS) solves the problem of poor coverage by linking an array of antenna modules to a central controller, which then connects to the wireless operator’s base station. Unlike a cellular repeater, which collects in-building wireless signals to rebroadcast outdoors, a DAS includes all of the components of a cellular tower.

“A DAS is essentially an in-building cell site, with its own wired backhaul to the operator network. In some cases, a DAS will connect to another cell site wirelessly, but the goal is to take pressure off of the operator network, not add to it,” said Peter Jarich, research director for wireless infrastructure at Current Analysis.

Distributed antenna systems are transparent to mobile devices, providing both voice and data services to mobile devices like any tower on the cellular network. DAS units are also largely vendor neutral, allowing any number of operators to support multiple wireless services, such as 2G, 3G and 4G, on a single DAS platform.  

“Like cellular towers, we partner with other operators to share space on a DAS. After we deploy a system, we actually turn it over to the tower folks to let others tap into it,” said Jim Parker, senior manager for the Antenna Solutions Group at AT&T Services  Inc.

Because distributed antenna systems operate onspectrum licensed to wireless operators, an enterprise cannot undertake a DAS deployment without involving the operators. In fact, wireless operators initiate the majority of DAS deployments, Jarich said. Wireless operators use both their own proactive traffic monitoring and customer feedback to determine locations to deploy distributed antenna systems, according to Parker. Densely populated spaces, such as shopping malls, medical centers and high-rise buildings, are likely candidates for DAS deployments. In such cases, the wireless operator will bear the costs of installing the system, as well as ongoing maintenance expenses.  

When Parker’s team identifies a location that can benefit from a DAS, it engages the site's owner or manager to work out an agreement for the space needed to house the DAS components. Deployment is the most expensive stage of a DAS project because installing antenna modules, stringing fiber optical or coaxial cable between antenna modules and the controller, and installing a base station are all very labor intensive processes.

In many deployments, a carrier will install a separate wireless LAN infrastructure for hotspot access alongside the DAS solution, said Parker. A Wi-Fi hotspot deployment in parallel to a DAS enables operators such as AT&T to offload wireless data traffic from its stressed cellular networks, saving the spectrum for voice traffic. Many of the operator’s smartphone offerings, including the iPhone and BlackBerry devices, are pre-programmed to switch to Wi-Fi whenever they are in range of AT&T’s global Wi-Fi network, completely transparent to the user.

While a distributed antenna system may sound like the perfect solution for your cellular coverage woes, there is no guarantee that a wireless operator will agree to install one for your enterprise facility. DAS solutions are an expensive proposition, both in terms of equipment, installation and ongoing maintenance costs. The carriers will only agree to take on these costs if the deployment fits within their network plans, covering a large number of their subscribers or filling an obvious gap in their service. Likewise, a DAS solution is ultimately owned and managed by the wireless operator and not the building management or tenants, which means a building owner cannot relocate or add to the antenna arrays.

Enterprise-ready, in-building wireless solutions

If mobile operators refuse to deploy a DAS within an enterprise facility, the IT organization has an alternative. Some vendors offer distributed antenna system products that use Ethernet cabling instead of expensive fiber, but DAS vendor MobileAccess goes one step further with MobileAccessVE, a new, enterprise-friendly, in-building wireless solution. Rather than stringing fiber optic or coax cabling through the facility, network engineers can connect the components of MobileAccessVE with the Ethernet links of an existing enterprise wireless LAN network.

An in-building wireless system consists of a series of access pods deployed throughout the building, which connect to a central control unit over Ethernet. Typically installed between a wireless LAN access point and the wiring closet, the access pods tap both the network link and Power over Ethernet (PoE) sources to operate, offering wireless cellular services which do not interfere with the enterprise wireless LAN. The central control unit can operate like a distributed cellular repeater, using an external antenna to communicate to a nearby cell tower, or it can operate like a DAS and use a wired backhaul provided by the mobile operator. Depending on configuration, deploying an in-building wireless solution may still require some guidance from the carrier. Unlike a DAS, however, the enterprise has more flexibility in deploying additional access nodes or moving equipment around as needed.

As enterprises move toward ubiquitous Wi-Fi access throughout their campuses, network administrators can simultaneously extend pervasive coverage to the cellular networks to every location where a wireless LAN access point has an Ethernet backhaul link.

While distributed antenna systems can work with an unlimited number of carriers and licensed spectrums, the MobileAccessVE in-building wireless system only has the capacity to support two mobile operators at a time.

Next Steps

Distributed antenna systems and WLAN can be a network management burden.

Learn how large venues can streamline wireless management with DAS.

This was first published in June 2011

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