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INTELLIGENT BUILDINGS
Key Considerations for DAS Deployment
John Spindler
Vice President
Zinwave
D istributed Antenna Systems (DAS) bring commercial
cellular and public safety radio signals indoors, so
building occupants can enjoy strong and uninterrupt-
ed service. Wireless access is increasingly being considered a
standard utility like water and power, so building owners and
managers should consider deploying a DAS when in-building
wireless signals are weak.
DAS installation costs can amount
to fifty or sixty percent of the total
cost of distributed antenna system
deployment, so it’s important to select
systems that minimize total cost of
ownership (TCO). There are three key
aspects to consider regarding TCO:
architecture, future-proofing and
facilities use.
Architecture
DAS systems typically consist of a main
hub or head-end (fed by an RF source
such as a repeater or base station)
connected via cabling to either one
or more secondary/intermediate
hubs, which in turn distribute the
signal to one or more remote units.
Alternatively, the head end may be
directly connected to the remote units
without an intermediate stage. The
remote unit is the last point of amplification in the system.
But there are different DAS architectures, and not all of them
deliver low TCO. For example, some systems use heavy coaxial ca-
bling or a combination of coax and fiber (known as hybrid fiber/
coax systems). Coax cabling, usually half an inch in diameter, is
more costly and difficult to install than fiber.
The architectural difference between hybrid fiber/coax DAS
systems and all-fiber DAS systems is that with hybrid fiber/coax
solutions, the remote unit is placed in a wiring closet or IDF, and amplifier, it allows you to spread the amp’s power across multiple
the ‘last mile’ of cabling is coaxial cabling used to feed passive
antennas. With an all-fiber DAS, the remote and antenna are co-lo-
cated (usually in the ceiling) and there is no use of coax cabling
infrastructure. With coax, there is signal loss which can vary de-
pending on the length of the coax, and both coverage and overall
performance can be affected. With an all fiber infrastructure where
32 Realcomm
the remote (the last point of signal amplification) and antenna are
co-located, there is no signal loss in the system and the coverage
area is consistent out of each and every antenna point.
Future-proofing
Regardless of the architecture, the challenge with most DAS
systems is that they frequently must
be upgraded with new equipment
every time a new frequency is added.
Cellular carriers add new frequen-
cies every couple of years (and even
public safety systems will soon be
moving to 700 MHz frequencies), and
this means adding new hardware
and amplifiers to a conventional DAS.
This is because conventional DAS
solutions use a separate amplifier to
support each frequency, so they have
to ‘stack’ amplifiers in order to support
more than one frequency. (Today’s
demands typically require support of
as many as eight frequencies.) When it
becomes necessary to add a frequen-
cy to the system, yet another amplifier
must be added to the stack.
To add that additional amplifier to
a conventional DAS, you may need
to add another card or blade into
the head end, the intermediate hub (if one is being used), and
in the remote unit, assuming the remote is a chassis which is
closet-mounted and can accept cards or blades. With a self-con-
tained ceiling-mounted remote (typically found in an all-fiber
DAS), you would have to insert an add-on module, or you would
add a second remote. That second remote would have to be
daisy-chained off the primary remote, and if that’s not possible
then you would end up deploying a whole new second layer of
equipment simply to support one additional frequency. And this
may be the case in any event if there is no additional space (card
slots) in the head-end, intermediate hub, or remote chassis.
A truly wideband DAS is different: it uses a single amplifier that
covers every frequency. Because of the high-power nature of this
frequencies (and carriers using those frequencies) while being