The result is that the user’s tolerance of dropped calls inside a building is
very low.
Cell services to most buildings are provided by the closest outdoor cell
base station or tower. Several elementsaffect in-building cellular service
including building structure and materials, distance to the nearest cell tower
and location of the caller in the building. Users at the upper floors of a high-
rise building can have problems as their handsets continuously hunt between
multiple cell towers. Users in underground floors may have no coverage
at all. Technically, the solution to dropped cell calls is to essentially “extend”
a carrier’s cell service antenna into the building. This can be done in
different ways.
One method is to mount a small directional antenna on the building pointed
toward a particular service provider’s cellular antenna; this is typically referred
to as the “donor” cell site. The building antenna provides direct two-way com-
munications with the cell tower. An alternative, albeit probably more expen-
sive option, is to have a “land line” connect the building and the cell tower
such as a T-1 line or metro Ethernet connection between the two locations.
From the antenna on the building coaxial cable is run to amplifiers that are
usually located in the main telecommunications equipment room. Coaxial
cable is commonly used to transmit RF and is well suited for transmitting
RF between the outdoor building antenna and the building distribution ampli-
fier. Because coaxial cable may run from outdoors to indoors, the installation
requires proper grounding and lightning arrestors.
From the amplifier in the telecom room a distributed antenna system
(DAS) is installed throughout the building. The in-building distribution system
comprises a series of strategically located indoor “omni” antennas connected
through coaxial cable using signal splitters and couplers similar to a cable tele-
vision distribution system.
Additional equipment, such as inlineamplifiers and boosters, can be used
in the distribution system to address the loss of signal strength through the
coaxial cable. In a campus environment, the amplified signal from the
antenna can be transmitted over the campus backbone network to other
buildings.
Signal strength and antenna coverage of the distribution system will be
determined by building structure, power of the indoor antennas, frequency
band of the cellular carrier and loss of signal through the coaxial. All of these
factors can be accounted for in system design and engineering (Fig. 10.2).
The early DASs were based on a single cell carrier and the exclusive use of
coaxial cable. More recent systems handle multiple carriers and distribute the
signal using managed network hubs that provide the same signal strength at
every antenna.
118 Smart Building Systems for Architects, Owners, and Builders