Product manual

Configuration directions, Base station planning - additional information
Technical Product Manual - DCT1800-GAP
TD 92093 (1/LZBNB 103 108 R4D) / 2006-03-09/ Ver.C
© 2006
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A DECT signal consists of frames of 420 bits transmitted every 10 ms. The bit length for DECT is
0.868 µs. Mutes
1
and clicks on the line will occur if the time difference between the various received
signals is of the order of 1 bit length. If this occurs, the receiver has difficulty in distinguishing between
the different transmitted bits. A direct consequence of this observation is, therefore, that the base
stations in a metal hall must be sited such that the time delay spread is minimised. This means in turn
that you must locate the base stations such that the number of reflections is minimised.
Bear in mind also, of course, that a signal becomes weaker, the further it travels. Signal strength and
distance are in a squared inverse ratio (if the distance is twice as far, the signal strength is four times
as weak).
Soft suppressor
In a metal hall the noise level is usually fairly high because of the machines and the reflections of the
noise from metal walls. In such a case the noise level will cause the soft suppression to be activated,
which will decrease the overall sound level by 12 dB. Not only the noise level but also the speech level
will be decreased. In these situations the use of a headset (with a noise cancelling microphone) is
recommended.
Locations for base stations
Bearing the time delay spread theory in mind, there are, of course, a number of general rules to
consider with regard to siting a base station.
• Install a base station in line of sight
2
. As a user, you must be able to see the base station as much
as possible when moving with your cordless phone.
• Here too provide some 10 metres of extra cable at the base station so that you can move the
base station if there is dissatisfaction with it or because the contents of the hall change. In many
cases (in the event of problems) moving a base station results in a large improvement. Before
installing a base station, therefore, always use a site survey tool to verify the location.
• It is possible to increase the number of base stations at those locations that are important to the
client, but bear in mind that the speech quality can deteriorate in other places in the hall because
the cordless phone has to carry out more handovers.
• Site the base station at a minimum height of 3 metres as otherwise it is highly possible that
something will be placed in front of the base station, and this prevents the materials and machines
in the hall reflecting the signal.
• Do not install the base station too close to a metal ceiling because in this way you will be
substantially increasing the distance between the base station and the user and because
accessibility for maintenance is made difficult. Bear in mind that in some cases, however, precisely
this course of action is recommended, but this again depends to a large extent on the dimensions
of the hall.
• Ensure that the distance between the base station antennas and a metal wall is at least 30
centimetres to avoid interference with the impedance of the antennas.
To return to the above figure for a moment: assume that a client wishes to obtain the best possible
quality in the hall (in every position). The best position from the principle of minimum time delay spread
is one of the corners (such as corner A). The signal from corner A and the reflected signal from the
1. Interruptions in your conversation
2. The base station ‘sees’ the user