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<h1>Clock Synchronisation between UltraSite Base Stations</h1>

<p>This feature enables synchronous handovers between base
stations. Furthermore, the sectors defined to different base stations can
use common hopping frequencies with RF-hopping, which increases the channel
capacity. The maximum site configuration is 9 Nokia UltraSite EDGE BTSs in
a chain or 1 Nokia Talk-family BTS + 5 Nokia UltraSite EDGE BTSs.</p>


<p>The Nokia UltraSite EDGE Base Station has an external clock
interface that can be used to synchronise the air interface between several
Nokia UltraSite EDGE Base Stations located on one site.</p>


<p>When several Nokia UltraSite EDGE Base Stations are synchronised,
the master base station (the master BTS) functions as the frame clock source
to the slave BTSs. The master BTS transmits the frame clock and frame number
signals to the external clock line while the other BTSs (slave BTSs) receive
these signals. The slave BTS uses the received frame clock signal as a reference
clock signal to adjust its main frequency source. The master BTS uses reference
clock signal derived from the Pulse Code Modulation (PCM) signal.</p>


<p>The synchronisation of Nokia Talk-family and Nokia UltraSite
EDGE BTSs facilitates the most efficient utilisation of Nokia Talk-family
and Nokia UltraSite EDGE co-sites. The Nokia Talk-family BTS acts as the clock
master when it and Nokia UltraSite EDGE BTS(s) are synchronised together.
If there are several Nokia Talk-family BTS cabinets synchronised to each other,
the Nokia UltraSite EDGE BTS cabinet must always be the last cabinet in the
synchronisation chain since it can compensate the timing difference between
these two base station models by delaying the internal timing.</p>


<p>In order to implement the synchronisation, the Nokia Talk-family
BTS must incorporate the new BCFB unit and new Abis-connector board ABSA.
In the initial phase, the synchronisation of BTSs facilitates synchronised
handovers and RF hopping between the sectors using the same frequency lists.
In other words, the handovers between cells residing under separate Base Control
Functions (BCFs) can be performed synchronously and sectors in different cabinets
can use common hopping frequencies with RF-hopping.</p>


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<h2>Physical
properties</h2>

<p>The maximum cable length for the total system is 100 meters.
Synchronisation chain between the BTSs is made using RS-485 connection for
the transferred clock signals.</p>
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<h2>Synchronisation
recovery</h2>

<p>If there is a failure in the synchronisation between the
base stations, the slave BTS generates an alarm, and the BSC blocks all TRXs
of the alarming BCF. When the fault disappears, cancellation to the alarm
is sent to the BSC. The BSC then unblocks the TRXs under the alarming BCF
object.</p>


<p>The Nokia NetAct sees both Nokia UltraSite EDGE and Nokia
Talk-family BTSs as separate entities. The alarms are managed independently.
External alarms and controls are compatible. The mains alarm from Nokia Talk-family
site support equipment can be connected to Nokia UltraSite BTS and vice versa.</p>
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