Designing and installing fiber-
optic cabling to support
distributed antenna systems
Examining the similarities and differences
between distributed antenna systems
and fiber-to-the-antenna systems.
BY ERIC R. PEARSON, CFOS/C/S/T/I, Pearson Technologies Inc.
A distributed antenna system (DAS) is
a wireless communication system that
replaces the single, high-output-power,
cell-phone antenna with multiple, re-duced-power antennas. It is, in effect,
a mirror of the cell phone network, but
with a reduced coverage area.
Distributed antenna systems are implemented in confined areas, such as
campuses, sports stadium, and areas
with small concentrations that require
high capacity and may have dead zones
or zones of low signal strength.
There are four basic reasons for DAS
use: 1) Insufficient signal strength; 2)
Insufficient bandwidth; 3) Adding value;
4) Legal requirement.
The two causes of insufficient signal strength are the signal absorbing or
blocking materials in and within buildings, and dense buildings blocking the
In indoor locations, modern building materials block or degrade wireless
communications signals creating “dead
zones” (not be confused with optical
time-domain reflectometer dead zones).
This situation exists in many modern office buildings, tunnels, mass transit systems, and event and sports arenas. In
this situation, a DAS extends communication capability with multiple antennas
placed in locations in which the wireless
signal is weak.
In indoor locations, high building-den-sity can interfere with wireless signals. A
DAS distributes the signal unreachable
by the cell phone tower. Outdoor arenas
and sports venues have high bandwidth
requirements. By dividing the coverage
area into areas of reduced size served by
individual antennas, a DAS enables increased bandwidth per user.
In some indoor and outdoor locations, such as event arenas, the signal
strength may be sufficient but the bandwidth is not. In this situation, multiple
antennas segment the bandwidth by localized regions. By reducing the number
of users per antenna, a DAS multiplies
the effective bandwidth per user by the
number of antennas.
Because an estimated 80 percent of
all cell phone traffic begins or ends inside
buildings, in-building cell phone access is
important. Some wireless carriers install
DAS inside certain buildings to enhance
their service offering. In addition, some
building owners add value to their real
estate assets by installing a DAS. A side
benefit is increased cell phone battery
life, as the phone can use reduced power
to maintain a connection.
Some municipalities require new
buildings to provide reliable wireless
service. This service is for emergency
services personnel, including police, fire,
EMTs and 911 location service.
Distributed antenna systems are variously known as small cells, microcells
and femtocells. The designation depends
on the coverage radius.
All DAS start with one of two inputs:
a connection to a carrier via fiber-optic
cable; or an antenna, called a donor antenna, that receives from and transmits
to the cell phone system.
This antenna is located such that
there is no communication interference or blockage. Typically, this location is outdoors and above the tree line.
Typically, this antenna receives multiple
frequencies to increase capacity and enable emergency communications.
This antenna connects to one of two
types of equipment: a bidirectional amplifier or a repeater, usually located in
an equipment room known as the “head