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<div class="div">
<h1>Radio Channel Allocation</h1>

<p>Radio channel allocation is used in the BSC to search and
allocate available free radio environment resources (SDCCHs, TCHs). The BSC
allocates radio resources so that it takes interference, the load of the cell
and rotation of resources into account.</p>


<p>The network operator can define the minimum C/N ratio on
a cell-by-cell basis. The channel allocation algorithm uses this ratio in
order to allocate the most suitable time slot. The following example illustrates
how this works:</p>


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<p>Table: Radio channel allocation</p>


<table border="1">
<tbody>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>CNThreshold </p>
</td>
<td colspan="1" rowspan="1"><p>20 dB</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>Uplink signal level</p>
</td>
<td colspan="1" rowspan="1"><p>-78 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>Interference band 0</p>
</td>
<td colspan="1" rowspan="1"><p>-110 ... -105 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>Interference band 1</p>
</td>
<td colspan="1" rowspan="1"><p>-104 ... -100 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>Interference band 2</p>
</td>
<td colspan="1" rowspan="1"><p>- 99 ... - 95 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>Interference band 3</p>
</td>
<td colspan="1" rowspan="1"><p>- 94 ... - 90 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>Interference band 4</p>
</td>
<td colspan="1" rowspan="1"><p>- 89 ... - 47 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>Maximum interference level</p>
</td>
<td colspan="1" rowspan="1"><p>-78 dBm - 20 dB = -98 dBm</p>
</td>
</tr>
</tbody>
</table>
</div>


<p>The BSC allocates a radio channel with an interference
band of 1 if available. If not, the BSC can allocate a channel with an interference
band of 0, 2, 3 or 4.</p>


<p>The network operator can define with a BTS level parameter
that traffic channels in the cell are allocated primarily from the BCCH TRX
or that TCHs are allocated primarily outside the BCCH TRX of the BTS.</p>


<p>The actual channel search depends, in addition to the requirements
included in the resource request, also on the available resources in the BTS.
The four main principles are followed in the single slot TCH allocation procedures:</p>


<ul>
<li><p>Efficiency of the search procedure:
a quick pre-selection of a resource can be performed by maintaining the general
information concerning the number of available resources and their distribution
between the TRXs of a specific BTS.</p>
</li>
<li><p>Rotation of allocable resources: successive
allocations of certain type of channels are directed to separate TRXs inside
the BTS, to separate TSLs inside the TRX, and to separate subchannels inside
the TSL.</p>
</li>
<li><p>Availability of different channel rates:
channels in permanent rate TSLs are allocated primarily so that allocation
of a channel of one rate type does not restrict the availability of the resources
of the other channel rate type. Dual rate resources for HR traffic are allocated
primarily from a half occupied DR TSL so that as many dual rate time slots
as possible can be maintained available also for FR traffic.</p>
</li>
<li><p>Attempt to avoid a collision between
HSCSD and speech calls: when the overall traffic load in the BTS is high,
TCHs for single slot allocations are selected from the ends of a TRX thus
saving gaps of successive idle TSLs for possible HSCSD calls.</p>
</li>
</ul>


<p>In multislot allocation for High Speed Circuit Switched
Data (HSCSD), call requests multiple TCH/Fs in a TRX can be allocated. HSCSD
call configurations of up to four TCH/Fs are possible.</p>
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