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<div class="div">
<h3>Features used in idle mode</h3>

<p>The C1 and C2 criteria can be used to force a dual band
MS to camp on a specific cell when the mobile is in the idle mode. The C2
parameter can be used, for example, to force the dual band mobiles to favour
the GSM 1800/1900 cells in idle mode, even though they may have a lower signal
level than the GSM 900/800 cells. This simply gives a fixed signal level offset
to the GSM 1800/1900 signal level received by the mobile when it decides which
cell to camp on. </p>


<p>The problem with using C2 is that the offset is fixed.
This may result in the mobile camping on a barely acceptable GSM 1800/1900
carrier even though a far better, and possibly empty, GSM 900/800 carrier
exists. This results in less than optimum call quality. This kind of problem
can be partly avoided by setting a high enough value for the minimum access
level for the cell.</p>


<p><a href="NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id011433#id011433" onclick="openSmallPopup(event,'NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id011433#id011433');return false" shape="rect" target="_blank">Localised Service Area (LSA)</a> is in
the process of standardisation as part of GSM phase 2+, which will allow cells
to be given a different priority for different users in idle mode.</p>


<p>The C1 and C2 equations are presented in ETSI TS 05.08
and the use is explained in ETSI TS 03.22.</p>


<p>It is important to remember that C2 use requires a PHASE
2 mobile support, which all the dual band MSs have.</p>


<a name="nov2221545312" shape="rect"></a>
<div class="topic">
<h4>C1
and C2 equations</h4>

<a name="dec32143834" shape="rect"></a>
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<p>where</p>


<p>A= Average received LEVEL - RXLEV_ACCESS_MIN</p>


<p>B= MS_TXPWR_MAX_CCH - P</p>


<p>and</p>


<p>RXLEVEL_ACCESS_MIN is the minimum downlink received level
required to access the cell (BTS parameter).</p>


<p>MS_TXPWR_MAX_CCH is the maximum TX power level the MS may
have in the cell (BTS parameter).</p>


<p>P is the maximum RF output power of the MS (fixed for each
MS). </p>


<p>All values are expressed in dBm. The path loss value criterion
is satisfied when C1 &gt; 0 (GSM 03.22). </p>


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<a name="dec32156376" shape="rect"></a>
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<p>where</p>


<p>H(x) = 0 for x &lt; 0, that is, Penalty_Time &lt;T</p>


<p>H(x) = 1 for x ≥ 0, that is, Penalty_Time ≥ T</p>


<p>T is a timer started from 0 when the cell appears on the
list of the 6 strongest BCCH frequencies of the MS.</p>
</div>


<a name="nov2221546343" shape="rect"></a>
<div class="topic">
<h4>How
to use C1 and C2 in Dual Band environment</h4>

<p>All the parameters involved in these equations are cell-specific
and they are sent within the Sys_info messages on the <a href="NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id04445#id04445" onclick="openSmallPopup(event,'NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id04445#id04445');return false" shape="rect" target="_blank">BCCH</a>.</p>


<p>The MS uses the C1 criterion in order to camp on the cells
according to the received power levels and minimum access levels of the cells.
By using the C2 criterion, the MS camps again in another cell set, where it
starts a call set-up.</p>


<p>The method proposed here to set the C2 parameter is based
on the difference in a cell of the following values:</p>


<ul>
<li><p>GSM parameter <span class="parameter-sem">RXLEV_ACCESS_MIN</span></p>
</li>
<li><p>Propagation behaviour</p>
</li>
<li><p><a href="NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id013657#id013657" onclick="openSmallPopup(event,'NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id013657#id013657');return false" shape="rect" target="_blank">EIRP</a>.</p>
</li>
</ul>


<p><span class="parameter-sem">Cell Reselect Offset</span> is used
to give a higher priority to the chosen cell (GSM 1800/1900, micro, and so
on). To ensure the camping to the “right” cell, the cell reselect offset value
should be set higher than the difference in RxLev_Access_Min, Propagation,
and EIRP between the cells (="delta" offset) to camp in.</p>


<p>The <em>"delta" offset</em> is calculated
as follows:</p>


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<p>where</p>


<p>Propagation is normally set to 10 dB in favour of 900/800
MHz cells. Another value can be used on the propagation difference measurements.</p>


<p><span class="parameter-sem">Temporary Offset</span> and <span class="parameter-sem">Penalty
Time</span></p>


<p><span class="parameter-sem">Penalty Time</span> is used when the
micro cells are present to ensure that only slow moving mobiles would camp
in the micro layer. It means that, during the penalty time, the micro cell
has a lower priority to be selected to get enough measurement results (to
see if the MS is moving slow or fast). After the penalty time, the micro cell
is selected if the MS is slow moving. The proposed value is 20 seconds.</p>


<p><span class="parameter-sem">Temporary Offset</span> is used to
change the priority of the cell selection for the penalty time (for example,
micro cell).</p>


<p><em>Example of C2 strategy</em> </p>


<p>The following assumptions have been made:</p>


<ul>
<li><p>Three-layer network; macro 900, micro
900, macro 1800</p>
</li>
<li><p>The highest priority for slow moving
mobiles to the micro cell</p>
</li>
<li><p>The second priority to the 1800 cells
(fast moving mobiles).</p>
</li>
</ul>


<p>The following values have been selected for the sake of
understanding, although they may be extreme and require fine-tuning on an
existing network.</p>


<a name="nov1921310348" shape="rect"></a>
<div>
<p>Table: Example values for RXLEV_ACCESS_MIN</p>


<table border="1">
<tbody>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p></p>


 </td>
<td colspan="1" rowspan="1"><p>	RXLEV_ACCESS_MIN</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>	M900</p>
</td>
<td colspan="1" rowspan="1"><p>	-110 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>	M1800</p>
</td>
<td colspan="1" rowspan="1"><p>	-98 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>	π900</p>
</td>
<td colspan="1" rowspan="1"><p>	-95 dBm</p>
</td>
</tr>
</tbody>
</table>
</div>


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<p>Depending on the priority set for each layer, <span class="parameter-sem">Cell
Reselect Offset</span> can be calculated. To ensure the camping to the chosen
cell, <span class="parameter-sem">Cell Reselect Offset</span> should be set bigger
than "delta" offset between the candidate cells. The C2 parameter planning
could proceed according to the following steps:</p>


<ol class="type-odd">
<li type="1"><p>In this example, the 2nd priority is
given to the M1800 cell. The M1800 cell should be set to look at least 27
dB stronger than the M1900 cell that has the lowest priority. <span class="parameter-sem">Cell
Reselect Offset</span> can be set to 30 dB.</p>
</li>
<li type="1"><p>The 1st priority was set to the π900
cell. The π900 cell should be set to look at least 18 dB stronger than the
2nd priority cell M1800 and 35 dB stronger than the M900 cell (MAX (30dB +
18dB), 35dB). <span class="parameter-sem">Cell Reselect Offset</span> can be set
to 60 dB.</p>
</li>
<li type="1"><p>Because fast moving MSs are not to
be camped in the π900 cell, the <span class="parameter-sem">Penalty Time</span> and <span class="parameter-sem">Temporary Offset</span> parameters must be used. The penalty
time can be set to 20 seconds and temporary offset to 60 dB to cancel the
effect of the <span class="parameter-sem">Cell Reselect Offset</span> parameter of
the π900 cell during the penalty time.</p>
</li>
</ol>


<a name="nov1921315449" shape="rect"></a>
<div>
<p>Table: Example of the C2 parameters</p>


<table border="1">
<thead>
<tr align="left" char="" charoff="50" valign="bottom">
<th colspan="1" rowspan="1" valign="top"><p>Priority</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Cell types</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Cell reselect offset </p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Penalty time</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Temporary offset</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>RxLev</p>


<p>Access Min</p>
</th>
</tr>
</thead>
<tbody>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>highest</p>
</td>
<td colspan="1" rowspan="1"><p>π900</p>
</td>
<td colspan="1" rowspan="1"><p>60 dB</p>
</td>
<td colspan="1" rowspan="1"><p>20 s.</p>
</td>
<td colspan="1" rowspan="1"><p>60 dB</p>
</td>
<td colspan="1" rowspan="1"><p>- 95 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p></p>


 </td>
<td colspan="1" rowspan="1"><p>M1800</p>
</td>
<td colspan="1" rowspan="1"><p>30 dB</p>
</td>
<td colspan="1" rowspan="1"><p>20 s.</p>
</td>
<td colspan="1" rowspan="1"><p>0 dB</p>
</td>
<td colspan="1" rowspan="1"><p>- 98 dBm</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>lowest</p>
</td>
<td colspan="1" rowspan="1"><p>M900</p>
</td>
<td colspan="1" rowspan="1"><p>0 dB</p>
</td>
<td colspan="1" rowspan="1"><p>20 s.</p>
</td>
<td colspan="1" rowspan="1"><p>0 dB</p>
</td>
<td colspan="1" rowspan="1"><p>- 110 dBm</p>
</td>
</tr>
</tbody>
</table>
</div>


<p>During the penalty time, the highest priority is given
to the M1800 and the 2nd priority to the M900 layer. The micro cell layer
is not selected because of the high <span class="parameter-sem">Temporary Offset</span>
value to ensure that the fast moving MS stays in the macro cell layer. </p>


<p>After the penalty time, the micro cell layer has the highest
priority for slow moving mobiles. The second priority is given to the M1800
layer (fast moving mobiles).</p>
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