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<h2>Operation and architecture BSS Synchronisation</h2>

<p>Nokia BSS Synchronisation utilises the Global Positioning System (GPS)
time reference for synchronising all the BTS site clocks along the network
to the same global reference.</p>


<p>The accuracy, stability, and reliability of synchronisation are critical
as they determine the efficiency of the whole solution. The implementation
based on GPS time reference ensures very high accuracy.</p>


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<h3>Location Measurement Unit (LMU)</h3>

<p>The LMU has been developed to support both positioning and synchronisation
functionalities. It includes a GPS receiver and an interface to provide the
GPS reference clock to the BTSs.</p>


<p>An LMU with a GPS antenna is placed at every BTS site in the synchronisation
area. Each LMU receives the reference clock signal from the GPS system and
supplies the BTS site with a consistent frame clock adjusted by FN Offset
and TSL Offset.</p>
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<h3>BTS</h3>

<p>The LMU is the master clock for all the BTSs on the site. The BCF next
to the LMU is called the master clock BCF. It passes the input from the LMU
signals straight through to the following BTS in the chain, and uses the LMU
signal as a reference for its internal clocks. The figure below shows how
synchronisation is arranged at a BTS site.</p>


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<h3>BSC</h3>

<p>The BSC controls the synchronisation recovery functionality and supplies
the LMUs with the values for <span class="parameter-sem">FN Offset</span> and <span class="parameter-sem">TSL Offset</span>.</p>


<p>Furthermore, the BSC keeps track of the synchronisation status of the
network. The operator can query this status with the command <span class="parameter-sem">EFL</span>.</p>
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