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<h2>WCDMA compressed mode</h2>

<p>Compressed mode is a radio path feature that allows a single
3G user equipment (UE) to make measurements from either another <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=id010817#id010817" 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=id010817#id010817');return false" shape="rect" target="_blank">FDD</a>
frequency or from the roaming partner's GSM network. The compressed mode functionality
halts the transmission and reception of the ongoing WCDMA call to perform
measurements on the other frequencies or system for a short period of time.
The intention is not to lose any user data but to compress the data transmission
in the time domain.</p>


<p>The compressed mode feature is obligatory if inter-frequency
or inter-system handovers are needed. Compressed mode itself does not give
any benefit for the network operation. The advantage of it comes from inter-system
and inter-frequency handovers. </p>


<p>Compressed mode is described in figure <em>WCDMA
compressed mode</em>.</p>


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<img alt="urn:mars:dn02249925:1:en:global:cgm_fixed:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn02249925&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: WCDMA compressed mode</p>
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<p>The frame compression can be achieved with the following
methods:</p>


<ul>
<li><p>Higher layer scheduling which means
that <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=id010069#id010069" 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=id010069#id010069');return false" shape="rect" target="_blank">DCH</a> user data rate transmitted in the channel is
reduced. Lower bit rate transport format combination set is constructed.</p>
</li>
<li><p>Halving the spreading factor which
doubles temporarily the physical channel data rate in the radio channel.</p>
</li>
</ul>


<p>In practice, compressed mode takes place when inter-system
handover measurement has to be performed. The RNC detects the possibility
for a handover based on neighbour cell definitions, channel allocations, cell
layers and possible other control parameters and orders the UE to measure
certain frequency. The handover decision is based on measurement reports from
the UE and control parameters of the radio network.</p>


<p>Depending on the UE capabilities, the RNC commands the
UE and the BTS to enter in compressed mode and provides downlink and/or uplink
compressed mode parameters.</p>


<p>In RAN 1.5, the gap length (TGL) is always 7 slots. Single
or double frame pattern can be used according to the possibilities that the
compressed mode method allows. An example of the single and double frame pattern
is shown in the following figures:</p>


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<img alt="urn:mars:dn02249901:1:en:global:cgm_fixed:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn02249901&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Single frame gap. 7 slot gap. Variable number of normal frames between
compressed frames. In the figure, there are 0 normal frames between compressed
frames.</p>
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<a name="dec121319393" shape="rect"></a>
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<img alt="urn:mars:dn02249882:1:en:global:cgm_fixed:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn02249882&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Double frame gap. 7 slot gap. Variable number of normal frames between
compressed frames.</p>
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<p><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=ned_12#ned_12" onclick="sync(this);return true" shape="rect">Effect of compressed mode on WCDMA coverage and capacity</a></p>


<p><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=ned_13#ned_13" onclick="sync(this);return true" shape="rect">Capacity reduction</a></p>


<p><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=ned_14#ned_14" onclick="sync(this);return true" shape="rect">Coverage reduction</a></p>


<p><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=ned_15#ned_15" onclick="sync(this);return true" shape="rect">Handover delay</a></p>
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