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<h1>Channel Finder (CF)</h1>

<p>It is important that indoor and outdoor networks perform
properly together beyond the initial planning and integration phase, maintaining
this performance during the expansion and maintenance phases. Due to the fact
that the Automatic Picocell Planning (APP) method produces a frequency plan
that is separate from the plan for the outdoor network, a method is needed
to cope with changes on one or the other sides. Since the initial frequency
allocation by the APP is done by adapting indoor GSM to the surrounding outdoor
environment, the basic principle is to make Nokia InSite BTSs adapt themselves
to external changes during the later phases of network evolution.</p>


<p>There are three cases where an indoor network may require
re-tuning:</p>


<ul>
<li><p>The outdoor GSM frequency plan changes.</p>
</li>
<li><p>A new outdoor cell is introduced nearby.</p>
</li>
<li><p>Performance statistics indicate indoor
quality is decreasing due to interference.</p>
</li>
</ul>


<p>The Channel Finder (CF) handles the first two cases in
the Nokia NMS/2000 before any conflicts between indoor and outdoor networks
emerge. The NMS/2000 compares the new plan and the old plan, uses the radio
measurement data produced by the APP, and finally determines new frequency
channels for indoor base stations if necessary. The new frequencies are activated
in the indoor network at the same time as changes take place in the outdoor
network.</p>


<p>Naturally, the first two cases do not require any indoor
vs. outdoor adaptation if the operator has dedicated frequency channels for
indoor use only.</p>


<p>The last case listed above requires special attention.
Nokia has developed a Channel Finder for this purpose. With the help of the
Channel Finder, a better frequency can be found for a cell suffering from
external, outdoor originated interference.</p>


<p>The choice of this optimum channel is based on an analysis
of signal levels from the surrounding cells. These measurements are provided
as part of the standard GSM functionality by the mobile stations of ordinary
subscribers while engaged in a call. The channel with least interference is
found by establishing the level of interference for each channel used by the
operator, thus enabling easy comparison of interference levels from different
cells.</p>


<p>When a mobile enters active mode, that is, when a call
is started, the BSC informs the mobile of the BCCH frequencies that it should
measure during the call. This is achieved by using the 'Double BA List' feature
of the BSC. The maximum number of channels that can be measured at one time
is 32. In addition to the level of the serving cell, the mobile reports the
six strongest BCCH channels of the neighbouring cells. The existing software
release supports a maximum of 255 different BCCH Allocation (BA) lists per
BSC. The maximum rate at which the mobile is able to report its signal level
measurements is twice per second. This means that during a 90-second call,
approximately 180 measurement reports are being obtained, and thus a measurement
period of one busy hour is adequate.</p>


<p>The measurement results are transferred automatically to
the NMS/2000 where they are analysed. Finally, a new interference free channel
is proposed for the cell under examination.</p>


<p>This method can be applied to several cells simultaneously,
which makes it possible to analyse and optimise large areas during a day.
The Channel Finder Measurement can be applied regardless of the original planning
method, the APP or a dedicated planning tool, making it feasible not only
for Nokia InSite Base Stations but also for traditional indoor solutions as
well as microcellular networks.</p>
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