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<td align="center" colspan="1" rowspan="1" width="20%"><a href="NED?action=retrieve&amp;identifier=dn04177859&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=ned_1#ned_1" onclick="sync(this);return true" shape="rect">Functionality of Dynamic Frequency and Channel Allocation
(DFCA)</a></td>
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<h2>Automatic recovery</h2>

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<h3>Loss of BSS synchronisation</h3>

<p>DFCA hopping requires that the network is working in BSS synchronisation.
The synchronisation is implemented in each BCF with a clock synchronisation
signal from the LMU unit. If a base station site temporarily loses BSS synchronisation,
the BSC automatically switches the BCF from synchronised to unsynchronised
mode.</p>


<p>During the unsynchronised DFCA operation, the DFCA algorithm is suspended
and the conventional channel allocation procedure is also used in the DFCA
TRXs. The DFCA TRXs change to unsynchronised random frequency hopping operation
with the unsynchronised mode DFCA MA list. The BSC automatically determines
the hopping sequence number (HSN) and the MAIO values for the DFCA TRXs.</p>


<p>When the synchronisation status of a BCF changes back to synchronised,
normal DFCA operation is restored for the DFCA TRXs.</p>


<p>For more information, see <a href="NED?action=retrieve&amp;identifier=dn04122203&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=dec331522341#dec331522341" onclick="sync(this);return true" shape="rect">BSS
Synchronisation</a>.</p>
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<h3>Loss of inter-BSC connection</h3>

<p>Efficient DFCA operation in a BTS requires that there are no detected
problems in connections to the neighbour BSCs controlling DFCA cells that
cause interference to the BTS. If such connection failures take place during
DFCA operation, it leads to similar recovery actions as when the synchronisation
of a BTS is lost.</p>


<p>If the C/I value of any of the cells in the neighbour BSC is low enough,
the communication fault may cause excessive uncontrolled interference in the
DFCA TRXs of the cell, because the DFCA algorithm is operating without up-to-date
knowledge on some of its interfering cells. However, short inter-BSC communication
breaks do not require immediate recovery actions.</p>


<p>When the BSC is informed on the return of inter-BSC communication to
a remote BSC, DFCA returns to normal operation.</p>
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