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<h3>Inter-system handover decision algorithm</h3>

<p>The measurement results of the GSM neighbour cell must
satisfy the following equation before the inter-system handover or cell change
to GSM/GPRS is possible:</p>


<ul>
<li><p>AVE_RXLEV_NCELL(n)  &gt;  AdjgRxLevMinHO
(n) + max( 0, AdjgTxPwrMaxTCH (n)  – P_MAX ) </p>
</li>
</ul>


<p>AVE_RXLEV_NCELL(n) is the averaged GSM carrier RSSI value
of the GSM neighbour cell (n). The RNC calculates the averaged value directly
from the measured dBm values, linear averaging is not used in this case. The
sliding averaging window is controlled with the parameter <span class="parameter-sem">GsmMeasAveWindow</span>.</p>


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<th colspan="1" rowspan="1" valign="top"><p>Parameter</p>
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<th colspan="1" rowspan="1" valign="top"><p>Setting</p>
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<td colspan="1" rowspan="1"><p><span class="parameter-sem">AdjgRxLevMinHo</span></p>
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<td colspan="1" rowspan="1"><p>-95 dBm</p>
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<td colspan="1" rowspan="1"><p><span class="parameter-sem">AdjgTxPwrMaxTCH</span></p>
</td>
<td colspan="1" rowspan="1"><p>33 dBm</p>
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<td colspan="1" rowspan="1"><p><span class="parameter-sem">GsmMeasAveWindow</span></p>
</td>
<td colspan="1" rowspan="1"><p>6 MeasReport</p>
</td>
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<p>The parameter <span class="parameter-sem">AdjgRxLevMinHO(n)</span>
determines the minimum required RSSI (dBm) level which the averaged <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=id013928#id013928" 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=id013928#id013928');return false" shape="rect" target="_blank">RSSI</a>
value of the GSM neighbour cell (n) must exceed before the inter-system handover
is possible. The neighbour cell parameter <span class="parameter-sem">AdjgTxPwrMaxTCH(n)</span>
indicates the maximum Tx power level (dBm) a UE may use in the GSM neighbour
cell (n). P_MAX indicates the maximum RF output power capability of the UE
(dBm).</p>


<p>The RNP parameter <span class="parameter-sem">GsmNcellSearchPeriod</span>
determines the period starting from inter-system measurement setup during
which an inter-system handover to GSM is not possible.</p>


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<td colspan="1" rowspan="1"><p><span class="parameter-sem">GsmNcellSearchPeriod</span></p>
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<td colspan="1" rowspan="1"><p>0 MeasReport</p>
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<p>After the GSM neighbour cell search period has expired,
the RNC evaluates the radio link properties of the best neighbour GSM cells
after every inter-system measurement report. The RNC performs the inter-system
handover to the best GSM neighbour (target) cell as soon as the best GSM neighbour
cell meets the required radio link properties.</p>


<p>If there are several neighbour GSM cells which meet the
required radio link properties at the same time, the RNC ranks the potential
target cells according to the priority levels and select the highest ranked
GSM neighbour cell to be the target cell. The priority order is controlled
with the RNP parameter <span class="parameter-sem">AdjgPriorityCoverage</span> which
is defined for each GSM neighbour cell.</p>


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<td colspan="1" rowspan="1"><p><span class="parameter-sem">AdjgPriorityCoverage</span></p>
</td>
<td colspan="1" rowspan="1"><p>0</p>
</td>
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</table>
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<p>The crucial principle is that high priority cells are considered
better than low priority cells: a cell is ranked higher than another cell
if it has a higher priority level even though its signal strength condition
is worse. Signal strength conditions have effect only between cells which
have the same priority level.</p>


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<h4>BSIC
verification</h4>

<p>When an inter-system (GSM) measurement is initially started,
the reporting quantity is GSM Carrier RSSI. The RNC selects the highest ranked
GSM neighbour cell which meet the required radio link properties to be the
target cell as descibed in <a href="NED?action=retrieve&amp;identifier=dn03530055&amp;edition=3&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=nov283162538#nov283162538" onclick="sync(this);return true" shape="rect">Inter-system handover decision algorithm</a>.
After the target cell selection, the RNC repeats the inter-system measurement
for the target GSM carrier. The RNC requests the BSIC verification before
the execution of inter-system handover so that the mobile station can synchronise
to the GSM cell before the handover execution, and also to verify the identification
of the GSM neighbour cell if two or more neighbour GSM cells have the same
BCCH Frequency.</p>
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<h4>Interactions
between handover causes</h4>

<p>The quality and coverage reason inter-system handovers
have priority over the other inter-system handover causes. The RNC supports
the following quality and coverage reason inter-system handovers:</p>


<ul>
<li><p>Inter-system handover due to Uplink
DCH quality</p>
</li>
<li><p>Inter-system handover due to UE Tx
power</p>
</li>
<li><p>Inter-system handover due to Downlink
DPCH power</p>
</li>
<li><p>Inter-system handover due to CPICH
RSCP</p>
</li>
<li><p>Inter-system handover due to CPICH
Ec/No.</p>
</li>
</ul>


<p>If two or more of the above indicated quality and/or coverage
causes are present simultaneously, the handover cause which has triggered
first has the highest priority.</p>
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