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<h3>Mobile station synchronisation requirements</h3>

<p>GSM specification 45.008, section 10.2.2 requires that
for synchronisation purposes, the network shall ensure that each MS with an
active <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=id011257#id011257" 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=id011257#id011257');return false" shape="rect" target="_blank">TBF</a> in uplink or downlink receives
at least one block transmitted with a coding scheme and a modulation that
can be decoded by that MS every 360 millisecond interval  (78 TDMA frames).</p>


<p>There is no special implementation for this GSM specification
requirement in GPRS territories (EGENA = N). In EGPRS territories (EGENA =Y),
this GSM specification requirement is implemented as follows. </p>


<p>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=id014238#id014238" 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=id014238#id014238');return false" shape="rect" target="_blank">PCU</a> registers when each MS was expected
to successfully decode a downlink block. Then, in the scheduling phase, each
MS is checked. If an MS has not been decoding anything for a 17 block period,
the PCU sets the limit of the MCS/CS for GPRS in the next downlink block so
low that the MS can be expected to decode it. The block may be addressed to
other MSs too but the MCS/CS is limited according to the rules below.</p>


<ul>
<li><p>An EGPRS MS is expected to decode blocks
that are using an MCS/CS lower or equal to the one selected by link adaptation
for the MS’s downlink TBF. If an EGPRS MS only has an uplink TBF, (M)CS-1
or (M)CS-2 in the downlink is considered robust enough to be decoded correctly.</p>
</li>
<li><p>An GPRS MS is expected to decode blocks
that are using CS-1 or CS-2.</p>
</li>
<li><p>If a GPRS MS has not been decoding
anything for a 17 block period, the PCU sends a CS-1 or CS-2 coded block.
If possible, the turn is given to a GPRS downlink TBF. If only an EGPRS TBF
exists on the downlink connection, the PCU sends a CS-1 (dummy) control block.</p>
</li>
</ul>
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