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C
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ORDLESS
HONE
call traffic and/or high user density, the interference will be noticeable not
only to the system itself but also to the users.
The user will randomly experience very short and disturbing periods of
silence or clicks. Also dropped and/or unanswered voice calls may be
the result. Data (alarm or messaging) is not as sensitive to the interfer-
ence since retransmissions will be made, however delays may be expe-
rienced due to these retransmission
5.5
Un synchronized Systems
If two systems operating in the same cell/coverage area are synchro-
nized with each other they will dynamically share the available 120 chan-
nels capacity. However, if the two systems are un synchronized, each
call and/or dummy bearer in any of the two systems will steal two chan-
nels from the dynamically shared resources. If more un synchronized
systems are installed, the issue will grow.
A multiple base station system (including repeaters to these systems)
has all base stations synchronized to a central clock i.e. a base stations
in such system will not disturb other base stations in the same synchro-
nized system. If two of these systems (un synchronized) or one residen-
tial base station are installed within the coverage of the system, the
theoretical capacity in the shared radio resource will obviously decrease.
In practice and to some extent, reuse of the channels will be done
depending on the position of portable devices and base stations.
Imagine that you have one system and that you add another one. Then
think about what will happen when additional residential base stations
are installed instead of one multiple base station system or a combina-
tion of these in one single coverage area? Add to this the normal radio
environment conditions like sliding collisions, interference from for
example reflections, portable devices in the outer part of the coverage
area with low field strength, also hearing high field strength from
neighbor base stations, etc. All in all it creates load on the base stations
and the radio environment will sooner or later be drained out of free
bearers.
It is obvious that if many DECT systems are placed within the same
coverage area an increased disturbance will be experienced.
The disturbances described above are normally not a problem since
DECT as a standard is designed for coexistence with multiple systems
and that any portable device or base station that experiences a distur-
bance or error on the slot will communicate to the other part (portable
device/base station) that they should switch to another non-disturbed
slot. However a hand over from one slot to the other does take some
time and the more system disturbances experienced the harder it will be
to find a stable and non-disturbed slot.
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