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<div class="div">
<h3>Features used during call </h3>

<p>All Nokia handover types can be used to transfer traffic
between the bands. Which is the most suitable in each case depends on the
network structure. The suggested handover types are:</p>


<ul>
<li><p>The Umbrella Handover may be used for
transferring traffic from the GSM 900/800 to the 1800/1900 band, as this only
takes into account the performance in the target cell. If it meets the specified
criteria (level threshold of the target cell), the handover is made. </p>
</li>
<li><p>Negative Power Budget Handover can
also be used to transfer traffic from the GSM 900/800 to the 1800/1900 layer.
If the Fast Moving Mobile algorithm is used to direct traffic from the GSM
900/800 layer to the micro cells, the umbrella HO algorithm cannot be used
and the negative power budget HO is the only possible solution.</p>
</li>
<li><p>Once the call is in the GSM1800/1900
band, it should be kept there, if possible. This is best accomplished by normal
power budget handovers (that is, the call is kept in the strongest cell).
The same method is used in the GSM 900/800 band.</p>
</li>
<li><p>The call may be returned to the GSM
900/800 layer by RX level/quality/interference (RR HO) handovers. Prioritisation
can be used with RR HOs to give a higher priority for the GSM 1800/1900 or
micro cells.</p>
</li>
<li><p>The MS Speed Detection or a Fast Moving
Mobile algorithm can be used to direct slow moving traffic to the micro cells
and to keep the fast moving mobiles in the macro layer. </p>
</li>
</ul>


<p>By balancing the parameters of the handovers between each
band it should be possible to balance the traffic load on each band.</p>


<a name="nov2221627914" shape="rect"></a>
<div class="topic">
<h4>PBGT
Handover</h4>

<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=id016179#id016179" 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=id016179#id016179');return false" shape="rect" target="_blank">PBGT</a> handovers are normally used to
keep the calls inside one layer. The idea is to keep the mobile in the strongest
cell. The following equations must be fulfilled when selecting the new cell
in the HO procedure.</p>


<a name="dec321540372" shape="rect"></a>
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<img alt="urn:mars:dn02251283:1:en:global:cgm_fixed:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn02251283&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /></div>


<p>where</p>


<p>Pa = (MsTxPWEMaxCell(n) -maxPwrMs)</p>


<a name="dec32154343" shape="rect"></a>
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<p>where</p>


<p>PBGT(n) = (MsTxPwrMax - AV_RXLEV_DL_HO - (BsTxPwrMax -
BS_TXPWR)) - (MsTxPwrMaxCell(n) - AV_RXLEV_NCELL(n))</p>


<p> = (AV_RXLEV_NCELL(n) - (MsTxPwrMax - MsTxPwrMaxCell(n)))
- (AV_RXLEV_DL_HO + (BsTxPwrMax - BS_TXPWR))</p>


<p>PBGT ping pong is avoided in a standard network by using
a positive margin, but a negative margin can be used for a special multi layer
configuration, for example when moving the traffic from the GSM 900/800 layer
to the GSM 1800/1900 layer. The PBGT handover must be disabled from the GSM
1800/1900 layer back to the GSM 900/800 layer in this case (high PBGT margin).</p>
</div>


<a name="nov22216273815" shape="rect"></a>
<div class="topic">
<h4>Radio
Reason Handovers</h4>

<p>The level and quality handovers are normally used as safety
handovers to transfer traffic back from the GSM 1800/1900 or micro layer to
the GSM 900/800 layer in a bad quality/level situation.</p>


<p>The parameter <span class="parameter-sem">Enable HO Margin Lev
Qual</span> set to Yes allows us to use Equation 7 instead of Equation 6 in
the target cell evaluation.</p>


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<p>The level and quality handovers are performed if the target
cell has a level exceeding the level of the source cell of <span class="parameter-sem">Ho
Margin Lev/Qual</span> dBm. Normally, the margin for quality handovers has
been set to 0 or to a negative value to favour handover to call drop.</p>


<p>The level and quality handovers target all kinds of cell,
without any relation to the cell layer. Prioritisation can, however, be used
with RR handovers to give a higher priority for a certain layer or cells.</p>
</div>


<a name="nov2221628716" shape="rect"></a>
<div class="topic">
<h4>Umbrella
Handover</h4>

<p>The umbrella handover can be used to transfer mobiles from
the 900/800 layer to the 1800/1900 layer when the level in the target cell,
that is, 1800/1900, meets a specified criterion, usually higher than -85 dBm
to -90 dBm. This algorithm introduces a simple way to "suck" the traffic towards
the 1800/1900 layer. </p>


<p>The implementation of this algorithm does not require the
usage of the parameter <span class="parameter-sem">Adjacent Cell Layer</span>. In
that case the Power Budget handover from the GSM 1800/1900 layer to the GSM
900/800 layer should be manually prevented by setting the PB margin to –63
dB.</p>


<p>If <span class="parameter-sem">Adjacent Cell Layer</span> is used,
it is reasonable to define the 1800/1900 layer as a lower layer for the 900/800
layer. Thus, all Power Budget handovers are automatically prevented between
the upper-lower layers.</p>
</div>


<a name="nov22216333817" shape="rect"></a>
<div class="topic">
<h4>Fast
Moving MS Handling and MS Speed Detection</h4>

<p>The Fast Moving MS Handling feature is an optional feature
and includes the <span class="parameter-sem">Adjacent Cell Layer</span> parameter.
An adjacent cell can be of the SAME, UPPER, or LOWER layer, depending on the
source cell.</p>


<p>The Fast Moving MS handover algorithm allows you to direct
a mobile to the right layer regarding its speed, that is, the fast mobile
uses the upper layer cell (large coverage area cell), while the slow mobile
uses the lower layer cell, supposed to be the capacity-oriented one. This
algorithm is mostly used in micro cellular networks. In a dual band configuration,
the 1800/1900 cell provides the capacity but its range is not similar to a
micro cell and thus it has to be used carefully. Normally, the GSM 1800/1900
cell can be defined as the same-layer cell as the GSM 900/800 cell to avoid
an unwanted micro cell handover when going to the 1800/1900 macro layer.</p>


<p>The Fast Moving MS Handling in Macrocell has a lower layer
cell target and is accomplished according to the following equations.</p>


<p>In each SACCH, the measurements for lower layer cells are
monitored (every 480 ms).</p>


<ul>
<li><p>If Equation 8 is verified, the counter
is increased by 2.</p>
</li>
<li><p>If the measurement is missing or does
not verify Equation 8, the counter is decreased by 1.</p>
</li>
</ul>


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<ul>
<li><p>The handover is triggered when the
counter of the target cell meets the Fast Moving Threshold (FMT). All lower
level cells are target cells.</p>
</li>
</ul>


<p>Concerning the speed measurements in the BTS, a handover
is triggered to</p>


<ul>
<li><p>The upper layer cell if the mobile
reaches the upper speed level</p>
</li>
<li><p>The lower layer cell if the mobile
speed is below the lower speed level.  </p>
</li>
</ul>


<p>Nx and Px are used to tune the handover processing time.
Px sets the number of measurements that have to meet the criterion, Nx sets
the number of measurements to be checked (Nx  ≥ Px. </p>


<p>When the handover is triggered on the speed reason, the
target cell is selected according to Equation 9.</p>


<a name="dec321650112" shape="rect"></a>
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<img alt="urn:mars:dn02251326:1:en:global:cgm_fixed:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn02251326&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /></div>


<p>When the speed measurements are not taken into account,
the umbrella handover is triggered as soon as one target cell meets the equation
criterion.</p>


<a name="nov22217282927" shape="rect"></a>
<dl class="note-notification">
<dt class="note-caption">Note</dt>
<dd>The speed measurement in the BTS does not work if the MS
is using frequency hopping.</dd>
</dl>
</div>


<a name="nov22216372418" shape="rect"></a>
<div class="topic">
<h4>Handover
priorities and load management</h4>

<p>When several layers of cells exist in the network, it is
necessary to balance the load between the layers to achieve the maximum capacity.
By using the features Adjacent Cell Priorities and Load Factors it is possible
to direct the mobiles to a particular band (or cell) based on the priority
factor of the handover candidate cells and the traffic load in those cells.</p>


<p>The target cell priority can be set in each cell for each
adjacent cell. A load threshold can be defined to dynamically change this
priority according to the traffic load of the cell. The use of this load management
is an intra-BSC feature.</p>


<p>The table <em>HO priority and load factor
parameters</em> describes the parameters of each adjacent cell associated
with this feature and the feature’s functionality.</p>


<a name="nov1921849515" shape="rect"></a>
<div>
<p>Table: HO priority and load factor parameters</p>


<table border="1">
<thead>
<tr align="left" char="" charoff="50" valign="bottom">
<th colspan="1" rowspan="1" valign="top"><p>Parameter</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Value/Function</p>
</th>
</tr>
</thead>
<tbody>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><span class="parameter-sem">HO Priority Level</span></p>
</td>
<td colspan="1" rowspan="1"><p>0 to 7. Highest priority is 7.</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><span class="parameter-sem">HO Load Factor</span></p>
</td>
<td colspan="1" rowspan="1"><p>0 to 7. The amount by which Priority Level is reduced when
cell Load Threshold is exceeded.</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><span class="parameter-sem">Load Threshold</span></p>
</td>
<td colspan="1" rowspan="1"><p>0 to 100%. Threshold above which the attractiveness of
the cell is reduced.</p>
</td>
</tr>
</tbody>
</table>
</div>


<p>If the load in the target cell exceeds the Load Threshold
value, the priority of that cell as a handover candidate is reduced by the
HO Load Factor according to Equation 10. </p>


<a name="dec321652174" shape="rect"></a>
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<img alt="urn:mars:dn02251338:1:en:global:cgm_fixed:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn02251338&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /></div>


<p>For example, the coverage from the GSM 900 macro cell,
GSM 900 micro cell, and GSM 1800 macro cell is overlapping. The mobile is
served by the GSM 900 macro cell but has acceptable (from the RF point of
view) handover candidates to both the GSM 900 micro cell and the GSM 1800
macro cell.</p>


<a name="dec22183272" shape="rect"></a>
<div>
<img alt="urn:mars:dn02250518:1:en:global:cgm_fixed:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn02250518&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Handover candidates for GSM 900 macro cell </p>
</div>


<p>The cell parameters are given in the following table.</p>


<a name="nov19218582017" shape="rect"></a>
<div>
<p>Table: Example of handover priority and load factors</p>


<table border="1">
<thead>
<tr align="left" char="" charoff="50" valign="bottom">
<th colspan="1" rowspan="1" valign="top"><p>HO Candidate</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>HO Priority Level</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Load</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>HO Load Factor</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Load Threshold</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>New Priority</p>
</th>
</tr>
</thead>
<tbody>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>900 Micro</p>
</td>
<td colspan="1" rowspan="1"><p>2</p>
</td>
<td colspan="1" rowspan="1"><p>60%</p>
</td>
<td colspan="1" rowspan="1"><p>1</p>
</td>
<td colspan="1" rowspan="1"><p>70%</p>
</td>
<td colspan="1" rowspan="1"><p>2</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>1800 Macro</p>
</td>
<td colspan="1" rowspan="1"><p>4</p>
</td>
<td colspan="1" rowspan="1"><p>80%</p>
</td>
<td colspan="1" rowspan="1"><p>3</p>
</td>
<td colspan="1" rowspan="1"><p>70%</p>
</td>
<td colspan="1" rowspan="1"><p>1</p>
</td>
</tr>
</tbody>
</table>
</div>


<p>From the RF measurement point of view, the GSM 900 micro
cell would be the best candidate. The <span class="parameter-sem">HO Priority Level</span>
of the 1800 cell is, however, higher - it becomes the higher handover candidate.
But the 1800 cell is already overloaded, so its priority level is reduced
by the <span class="parameter-sem">HO Load Factor</span>. The highest priority is
given to the 900 micro cell which is chosen for the handover.</p>


<p>Load Management proceeds in the BSC for an MS entering
a target cell. To trigger a handover for load reasons in the serving cell
(Traffic Reason HO), the MSC support is needed.</p>


<p>Priorities and load factors are set on a cell adjacency
basis and can be set for a whole layer.</p>
</div>


<a name="nov2221640719" shape="rect"></a>
<div class="topic">
<h4>Advanced
Multilayer Handling</h4>

<p>Advanced Multilayer Handling can be used to balance the
load between the layers or to improve network quality. It includes, for example,
a traffic-reason handover triggered by traffic load to transfer the calls
from occupied cells to less occupied ones. Adjustable Power Budget margins
based on the traffic load can also be used.</p>
</div>
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