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<h1>Intelligent BTS Shutdown Due to Mains Break</h1>

<p>To provide protection against mains break, a BTS site may
be equipped with battery back up. The aim is to maintain service as long as
possible. To achieve this, it is reasonable to reduce capacity on certain
sites in order to save battery and maintain only the essential BTS functions.</p>


<p>This feature provides means to control the behaviour of
the site equipped with battery back up in case of mains break. As the power
consumption depends on the equipment supplied by the back-up batteries, shutting
down a part of the site prolongs the remaining service time.</p>


<p>On a BTS site basis, the operator can define the service
level of the site to be maintained while battery back up is in use. Also the
operator can define two timers to allow executing the shutdown procedure in
several phases. Three service level options are available:</p>


<ol class="type-odd">
<li type="1"><p>Full service. Service is maintained
on full level as long as batteries last.</p>
</li>
<li type="1"><p>BCCH back up. Only BCCH TRX(s) are
maintained to offer minimum service, other TRXs are switched off. Non BCCH-TRXs
are switched off after the first timer expires. Timer two has no meaning in
this case.</p>
</li>
<li type="1"><p>Transmission back up. Only the BTS
transmission equipment power is supplied. TRXs are switched off and the BCCH
transmission is stopped. This secures the functionality of a transmission
chain. Non BCCH-TRXs are switched off after the first timer expires. Then
the timer two starts, and after it expires, the BCCH TRX is switched off and
only transmission equipment is left powered to maintain transmission links
for chain configuration.</p>
</li>
</ol>


<p>When a mains break takes place, the BTS sends an alarm
to the BSC, which performs forced handovers for all the calls on the TRXs
to be shut down. The calls are handed over to a TRX, which will remain powered,
or to adjacent cells. If all the necessary handovers cannot be made during
the defined maximum time, the calls are released. Finally the BSC orders the
BTS site to power down the TRXs.</p>


<p>When the mains power restores, the BSC takes the BTS automatically
back in full service.</p>


<p>Third party BBU equipment can also be used together with
intelligent shutdown. It is possible to designate an external alarm line,
which is used to indicate a mains break to the BTS. This alarm is then sent
to the BSC as a mains break down alarm which then triggers the shutdown procedure.</p>
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