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A Distributed Antenna System, or DAS, is a
network of spatially separated antenna
nodes connected to a common source via a
transport medium that provides wireless
service within a geographic area or
structure.
The idea is to split the transmitted power
among several antenna elements, separated
in space so as to provide coverage over
the same area as a single antenna but with
reduced total power and improved
reliability (see Figure one the right). A
single antenna radiating at high power is
replaced by a group of low-power antennas
to cover the same area.
The idea works because less power is
wasted in overcoming penetration and
shadowing losses, and because a
line-of-sight channel is present more
frequently, leading to reduced fade depths
and reduced delay spread.
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Conventional antenna (top)
and distributed antenna system
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WinProp supports the definition of DAS.
Antennas belonging to DAS are defined in
the same way than conventional antennas,
i.e. location, carrier frequency, and
transmit power of the antennas are defined
as usual. The only difference to
traditional antennas is that the so called
Signal Group has to be set to the
same ID for all antennas belonging to a
DAS. For conventional antennas the Signal
Group ID is set to individual.
Generally all antennas of a DAS must have
the same carrier. Depending on the
assigned Signal Group ID the
signals from different antennas are
combined constructively or interfere each
other.
Selection of Signal Group
in transmitter dialog
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In this section a simple example is
presented for the better understanding of
the DAS feature in WinProp. In the
following Figures a simple scenario with
three antennas is shown. All antennas use
the same carrier - otherwise there would
be no co-channel interference in the
scenario.
In
the first figure all antennas operate on
the same carrier and no DAS is available.
Because of that the signals from all 3
antennas interfere with each other
(co-channel interference). Thus there is a
large hole in the coverage (white area).
In this area the SNIR is below 1 dB.
SNIR for conventional
network
The figure below shows a
second configuration where again all
antennas operate on the same carrier, but
with sites 2 and 3 forming a DAS. Thus the
antennas of sites 2 and 3 do not interfere
with each other. Because of that the
signals of both antennas are superposed
constructively. This leads to a larger
covered area.
SNIR if sites 2 and 3 form
a DAS
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