In-Building Cellular Systems Move Wireless Service Inside

June 1, 2007
More building owners and enterprises are purchasing their own in-building systems to provide multi-carrier coverage that serves everyone in the building

By John Spindler

Most people now use a cell phone as their primary contact device, so they're not very happy when they don't get coverage inside a building. In-building cellular systems can eliminate indoor coverage problems.

The cellular network was designed to provide outdoor - not indoor - coverage. While some buildings get good coverage from external cell towers, many others have spotty coverage because concrete, steel, and other building materials block cellular radio signals, or because the nearest external cell tower is just too far away. Even in buildings where there is adequate coverage near windows in exterior offices, the cellular signal often weakens as callers move toward the interior of the structure.

To remedy this problem, buildings are deploying in-building cellular systems. An in-building system consists of a carrier signal source and a distributed antenna system (DAS) that propagates the signal throughout the structure. The carrier signal source is either a base station deployed in the building's telecommunications room or a rooftop antenna that captures an external signal and brings it inside the building. If the system supports more than one carrier's service, there must be a base station or antenna for each carrier. The DAS takes the carrier signal and transmits it to a system of remote antennas throughout the building.

In the past, in-building systems were primarily deployed by wireless carriers in response to customer demands for coverage. Carriers often deploy a DAS in exchange for renewal or extension of a corporate service contract. Sometimes, the carrier and the building owner split the cost of the DAS. In many cases, however, these carrier-supplied systems are specific to just the one carrier, leaving company visitors or contractors not on that carrier's service out in the cold. Today, more and more building owners and enterprises are purchasing their own in-building systems to provide multi-carrier coverage that serves everyone in the building.

In-building systems generally fall into two categories: passive and active systems. Passive systems use thick, inflexible coaxial cable to distribute signals. These cables carry radio signals to remote antennas without amplification along the way; however, these systems are relatively expensive to install. Also, given the characteristics of copper, the radio signal grows weaker as it moves along the cable, so antennas farther from the beginning of the cable (the signal source) will output less power than those that are closer to the beginning of the cable.

In contrast, active in-building systems use a series of electronic hubs to amplify the radio signal so that every antenna in the system produces the same signal strength. Active systems are less expensive to deploy because they use more flexible, less expensive fiber, Cat-5, and CATV cable to link hubs and antennas.

In either case, today's in-building cellular systems can deliver "four bars" of coverage throughout any facility, including underground garages and interior conference rooms, ensuring that cell phone users can make calls or check e-mail wherever they are.

John Spindler is vice president of marketing at San Jose, CA-based LGC Wireless (

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