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<div class="div">
<h2>Cell selection and re-selection</h2>

<p>MS cell selection at the packet transfer is controlled
by the following cell re-selection criteria:</p>


<ul>
<li><p>Path loss criterion (C1)</p>
</li>
<li><p>Signal Strength threshold criterion
(C31)</p>
</li>
<li><p>Cell ranking (C32)</p>
</li>
<li><p>Cell reselection criteria (C2)</p>
</li>
</ul>


<p>C31/C32 are introduced as a complement to the current GSM
cell re-selection criteria. This gives the possibility to optimise the cell
re-selection for (E)GPRS without affecting the circuit switched cell re-selection
behaviour. This allows more flexibility in using cell resources, allowing,
for example, some cells to be packet free, should this be of interest.</p>


<p>In a multi-vendor environment, there is a requirement that
all vendors should support broadcasting of the C31/C32 parameters.</p>


<p>The C31/32 functionality can only be used if <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=id08956#id08956" 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=id08956#id08956');return false" shape="rect" target="_blank">PBCCH</a>
is allocated to the cell, otherwise the circuit switched signalling channels
are used and, consequently, C1 and C2.</p>


<a name="dec1121231623" shape="rect"></a>
<div class="topic">
<h3>MS
cell re-selection algorithm</h3>

<p>The MS makes the cell re-selection if the path loss criterion
(C1) for the serving cell falls below zero.</p>


<p>The MS can make the cell re-selection also when it finds
a non-serving cell that is more suitable than the serving cell. The MS selects
the cell having the highest C32 value among those that have the highest priority
class among those that fulfill the criterion C31 &gt;= 0. The priority classes
may correspond to different HCS layers. If none of the cells fulfills the
C31&gt;=0 criterion, the MS must select the cell having the highest C32 value.</p>


<p>If the <em>c32Qual</em> parameter is set,
positive <em>gprsReselectOffset</em> values are only applied
to the neighbour cell with the highest RLA_P value of those cells for which
C32 is compared above.</p>


<p>When the MS is in ready state, time defined by the <em>gprsCellReselHysteresis</em> value is subtracted from the C32
value for the neighbour cells. If the parameter <em>c31Hysteresis</em>
is set, the GPRS_CELL_RESELECT_HYSTERESIS is subtracted also from C31 neighbour
cells. When the new cell is from a different routing area, the <em>raReselectHysteresis</em>
parameter value is subtracted from C32 for the neighbour cells. In case a
cell re-selection occurred within the previous 15 seconds, 5 dBs are subtracted
from C32 for the neighbour cells.</p>


<a name="dec11210192814" shape="rect"></a>
<div>
<table border="1">
<thead>
<tr align="left" char="" charoff="50" valign="bottom">
<th colspan="1" rowspan="1" valign="top"><p>Q3 parameter name</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Range</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>MML value</p>


<p></p>
</th>
</tr>
</thead>
<tbody>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>gprsRxLevAccessMin</p>
</td>
<td colspan="1" rowspan="1"><p>-110…-47 dBm</p>
</td>
<td colspan="1" rowspan="1"><p>-105</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>gprsMsTxpwrMaxCCH</p>
</td>
<td colspan="1" rowspan="1"><p>5 .. 43 dBm with 2 dBm step for GSM 850 and 900</p>


<p>0 .. 36 dBm with 2 dBm step for GSM 1800</p>


<p>0 .. 32 dBm with 2 dBm step and 33 dBm for GSM 1900</p>
</td>
<td colspan="1" rowspan="1"><p>33 dBm for GSM 850 and 900.30 dBm for GSM 1800 and 1900.</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><em>hcsThreshold</em></p>
</td>
<td colspan="1" rowspan="1"><p>-110, -108, … , -48 dB with 2 dB step</p>
</td>
<td colspan="1" rowspan="1"><p>N (not used)</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><em>gprsTemporaryOffset</em></p>
</td>
<td colspan="1" rowspan="1"><p>0 .. 70 dB with a step size of 10 dB</p>
</td>
<td colspan="1" rowspan="1"><p>0</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><em>gprsPenaltyTime</em></p>
</td>
<td colspan="1" rowspan="1"><p>10 .. 320 (s) with a step size of 10 s</p>
</td>
<td colspan="1" rowspan="1"><p>10</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><em>hcsPriorityClass</em></p>
</td>
<td colspan="1" rowspan="1"><p>0 to 7</p>
</td>
<td colspan="1" rowspan="1"><p>7</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><em>gprsReselectOffset</em></p>
</td>
<td colspan="1" rowspan="1"><p>-52, -48,..., -12, -10,..., 12, 16, ...,48 (dB)</p>
</td>
<td colspan="1" rowspan="1"><p>0</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><em>gprsCellReselHysteresis</em></p>
</td>
<td colspan="1" rowspan="1"><p>0, 2, 4, 6, 8, 10, 12, 14 dB</p>
</td>
<td colspan="1" rowspan="1"><p>4</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><em>c31Hysteresis</em></p>
</td>
<td colspan="1" rowspan="1"><p>Y/N</p>
</td>
<td colspan="1" rowspan="1"><p>N</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><em>c32Qual</em></p>
</td>
<td colspan="1" rowspan="1"><p>Y/N</p>
</td>
<td colspan="1" rowspan="1"><p>N</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><em>raReselectHysteresis</em></p>
</td>
<td colspan="1" rowspan="1"><p>0, 2, 4, 6, 8, 10, 12, 14 dB</p>
</td>
<td colspan="1" rowspan="1"><p>4</p>
</td>
</tr>
</tbody>
</table>
</div>
</div>


<a name="dec11212233820" shape="rect"></a>
<div class="topic">
<h3>C1
parameter</h3>

<p>The path loss criterion C1&gt;= 0 is used as a minimum signal
strength criterion for the cell selection for (E)GPRS in the same way as for
CSW in idle mode. </p>


<p>C1 = (A – Max(B,0))</p>


<p>where</p>


<p>A = Received Level Average (RLA_P) – <em>gprsRxLevAccessMin</em></p>


<p>B = <em>gprsMsTxpwrMaxCCH</em> – P (GSM900)</p>


<p><em>gprsRxLevAccessMin</em> = Minimum
received level at the (E)GPRS MS required for access to the system</p>


<p><em>gprsMsTxpwrMaxCCH</em> = Maximum TX
power level a (E)GPRS MS may use when accessing the system until otherwise
commanded</p>


<p>P = Maximum RF output power of the MS</p>


<p>All values are expressed in dBm. POWER_OFFSET is not used</p>
</div>


<a name="dec11212243221" shape="rect"></a>
<div class="topic">
<h3>C31
parameter</h3>

<p>The signal strength threshold criterion (C31) for hierarchical
cell structures (<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=id06598#id06598" 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=id06598#id06598');return false" shape="rect" target="_blank">HCS</a>) is used to decide whether the
cell is qualified for the prioritised hierarchical cell selection. RLA - Received
Link Average.</p>


<p>C31(s) = RLA(s) – <em>hcsThreshold</em>
(s) (serving cell)</p>


<p>C31(n) = RLA(n) – <em>hcsThreshold</em>
(n) – TO(n) * L(n) (neighbour cell)</p>


<p>where</p>


<p>HCS_THR = signal threshold for applying HCS re-selection</p>


<p>TO(n) = <em>gprsTemporaryOffset</em> (n)
* H(<em>gprsPenaltyTime</em> (n) – T(n)) </p>


<p>L(n) = 0, if <em>hcsPriorityClass</em>
(n) = PRIORITY_CLASS(s)</p>


<p>1, if <em>hcsPriorityClass</em> (n) ‡ <em>hcsPriorityClass</em> (s)</p>


<p>H(x) = 0, if x &lt; 0 </p>


<p>1, if x &gt;= 0</p>


<p><em>gprsTemporaryOffset</em> applies a
negative offset to C31/C32 for the duration of <em>gprsPenaltyTime</em>
after the timer T has started for that cell.</p>


<p>T is a timer implemented for each cell in the list of strongest
carriers. T shall be started from zero at the time the cell is placed by the
MS on the list of the strongest carriers, except when the previous serving
cell is placed on the list of the strongest carriers at the cell re-selection.
In this case, T shall be set to the value of PENALTY_TIME (that is, expired).</p>
</div>


<a name="dec11212282722" shape="rect"></a>
<div class="topic">
<h3>C32
parameter</h3>

<p>The cell ranking criterion (C32) is used to select cells
among those with the same priority.</p>


<p>C32(s) = C1(s) (serving cell)</p>


<p>C32(n) = C1(n) + <em>gprsReselectOffset</em>
(n) – TO(n) * (1 – L(n))  (neighbour cell)</p>


<p>where</p>


<p><em>gprsReselectOffset</em> applies an
offset and hysteresis value to each cell.</p>


<p>TO and L as in C31.</p>


<p><em>gprsReselectOffset</em> applies an
offset and hysteresis value to each cell.</p>
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