User guide

TD 92422GB
18 February 2010 / Ver. E
System Planning
Ascom IP-DECT System
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dummy bearer is due to that the portable device listens to one dummy bearer and uses the
information to lock-on to the system; synchronize, check base station identity, system
capabilities, status and paging information for incoming voice and data call set-ups as well
as for preparing handover, call setups etc.
This means that a base station is always transmitting information regardless of which type,
resedential or multiple base station system. Note: The dummy bearer is only transmitted in
the base station to portable device direction.
A.3 Single vs. Multiple Base Station System
In this section we differentiate single (resedential) and multiple (enterprise) base station
systems. The reason is that it should be understood that they work in similar way but that
they are designed to be used for different purposes.
Resedential base stations are designed to be installed in homes and small offices with a
natural distance between each cell. Multiple base station systems are on the other hand
designed to be used and installed in traffic intense areas which also means that they can
be installed very close to each other.
Resedential base station systems are not synchronized. There is no need for this since the
density of users and/or calls are normally low in the coverage area where these systems are
supposed to be used.
Multiple base station systems have an internal intra-system synchronization, which means
that all base stations are transmitting at the same time, as well as, listening at the same
synchronized time. This means that multiple base station systems know, in contrast to
resedential base stations, which slots that are free to be used and not. This enables a very
high call capacity, robustness and possibility to make intra-system handovers (i.e.
possibility to move from one base to another with an ongoing seamless voice
conversation).
A.4 Radio Interference
A DECT system is as described earlier, designed to work, also in busy and/or hostile radio
environments. This also applies to interference from other DECT systems operating in the
same frequency range. If interference is found on the traffic channel, that a base station or
portable device is listening to, it will communicate to the other part (portable device or
base station) that a switch of slot or a handover must be made.
Any interference will of course disturb and the actual package sent will be discarded, but it
will not be noticeable to the user in the speech since the packets are very small (10
milliseconds). If it is data traffic, the sent package will be discarded and a retransmission
will be made. This means that due to the excellent dynamic channel selection and
allocation in DECT, no user will notice any disturbances in the conversation.
Interferences exist everywhere, unless the system is installed in an isolated laboratory
environment. It may be due to other DECT systems running in the same coverage area or it
may be by reflections in the own radio environment, for example due to metal plates or
walls in the area. All DECT systems are robust to this, to a certain extent. However when
many unsynchronized systems are used in environments with a high 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 interference since retransmissions will be made, however delays
may be experienced due to these retransmission.