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<div class="div">
<h1>Overview of Common BCCH</h1>

<p>Common <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=id04445#id04445" 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=id04445#id04445');return false" shape="rect" target="_blank">BCCH</a> allows the integration of resources
from different frequency bands into one cell. A common BCCH of a cell is configured
in only one of the bands of operation when resources across all bands are
co-located and synchronised.</p>


<a name="dec12197423" shape="rect"></a>
<div>
<img alt="urn:mars:dn02249964:1:en:global:cgm_fixed:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn02249964&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: GSM 900 / GSM 1800 Common BCCH configuration</p>
</div>


<p>The following frequency band combinations are supported:</p>


<ul>
<li><p>PGSM 900 / EGSM 900</p>
</li>
<li><p>PGSM 900 / <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=id012006#id012006" 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=id012006#id012006');return false" shape="rect" target="_blank">GSM 1800</a></p>
</li>
<li><p>PGSM 900 / EGSM 900 / GSM 1800</p>
</li>
<li><p>EGSM 900 / GSM 1800</p>
</li>
<li><p>GSM 800 / <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=id012007#id012007" 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=id012007#id012007');return false" shape="rect" target="_blank">GSM 1900</a>.</p>
</li>
</ul>


<p>The BCCH carrier is allowed in any of the supported frequency
bands, except that the common BCCH is allowed in the EGSM 900 frequency band
only if there is no PGSM 900 in use in the network.</p>


<p>Common BCCH is application software in the BSC.</p>


<a name="nov2521746269" shape="rect"></a>
<div class="topic">
<h2>Benefits
of Common BCCH</h2>

<p>The following are the benefits of using common BCCH control:</p>


<ul>
<li><p>improved trunking gain</p>
</li>
<li><p>optimised use of signalling channels
by sharing them between bands</p>
</li>
<li><p>the absence of a BCCH channel (in non-BCCH
frequency band) leads to a reduction of the overall interference and allows
more freedom in frequency allocation with improved quality</p>
</li>
<li><p>reduced number of cells in the network</p>
</li>
<li><p>reduced number of Location Area Codes</p>
</li>
<li><p>reduced number of neighbouring cells</p>
</li>
<li><p>multi-layer network simplified into
one-layer network</p>
</li>
<li><p>quality improvement due to decreased
number of handovers between frequency layers; calls directed to an appropriate
layer in call set-up</p>
</li>
</ul>
</div>


<a name="nov25217514611" shape="rect"></a>
<div class="topic">
<h2>Segment
and BTS object</h2>

<p>Common BCCH, Multi BCF, and <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=id010415#id010415" 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=id010415#id010415');return false" shape="rect" target="_blank">EDGE</a>
utilise an architecture and radio network object called segment (SEG). The
properties of a segment are the following:</p>


<ul>
<li><p>A segment is essentially the same as
a telecom cell.</p>
</li>
<li><p>A segment may consist of several <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=id03816#id03816" 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=id03816#id03816');return false" shape="rect" target="_blank">BTS</a>
objects.</p>
</li>
<li><p>BTSs of a segment are co-located and
synchronised.</p>
</li>
<li><p>The maximum number of BTSs in a segment
is 32.</p>
</li>
</ul>


<p>The BTS object in a segment must consist of <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=id04885#id04885" 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=id04885#id04885');return false" shape="rect" target="_blank">TRXs</a>
of the same</p>


<ul>
<li><p>frequency band (PGSM 900, EGSM 900,
GSM 1800, GSM 800, GSM 1900 separated).</p>
</li>
<li><p>base station site type (Talk-family
and UltraSite separated).</p>
</li>
<li><p>radio technology (GSM and GSM/EDGE
separated).</p>
</li>
</ul>


<p>The maximum number of TRXs in segment is 36.</p>


<a name="dec12196192" shape="rect"></a>
<div>
<img alt="urn:mars:dn02249976:1:en:global:cgm_fixed:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn02249976&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Segment and BTS object in Common BCCH </p>
</div>


<p>A typical BTS configuration in Common BCCH is shown in
the figure. When considering Common BCCH, segment-specific and BTS-specific
parameters should be taken into account. In many cases, BTS and frequency
band are the same but in some case they are different, for example PGSM 900
Talk-family and PGSM 900 UltraSite must be configured as separate BTSs. Segment-specific,
BTS-specific and frequency-band-specific parameters need to be considered
in this case.</p>


<p>The allocation of a dedicated channel (<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=id011274#id011274" 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=id011274#id011274');return false" shape="rect" target="_blank">SDCCH</a>
or <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=id04070#id04070" 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=id04070#id04070');return false" shape="rect" target="_blank">TCH</a>) inside a multiband segment (that is, with BTSs
from different frequency bands) is based on:</p>


<ul>
<li><p>the frequency capabilities of the mobile
station</p>
</li>
<li><p>the prevailing radio conditions of
the mobile station</p>
</li>
<li><p>the resource situation on each band.</p>
</li>
</ul>


<p>The second condition is evaluated for the secondary frequency
band using a BTS parameter called <span class="parameter-sem">Non BCCH Layer Offset</span>.</p>
</div>


<a name="nov2521814813" shape="rect"></a>
<div class="topic">
<h2>Mobile
frequency capability</h2>

<p>Different classes of mobiles can be defined according to
their frequency capabilities. The information of the frequency capabilities
of the mobile station is included in 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=id05986#id05986" 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=id05986#id05986');return false" shape="rect" target="_blank">Mobile Station Classmark
2</a> and <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=id05986#id05986" 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=id05986#id05986');return false" shape="rect" target="_blank">Mobile Station Classmark 3</a> Information
Elements. </p>


<p>The Mobile Station Classmark 2 Information includes information
on the possible EGSM 900 capability of 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=id03944#id03944" 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=id03944#id03944');return false" shape="rect" target="_blank">MS</a>.
The Mobile Station Classmark 3 Information Element defines all the frequency
bands supported by the MS and the MS power capabilities in each supported
frequency band.</p>


<p>The network receives the Mobile Station Classmark 2 IE
in the <span class="message-sem">Establish Indication</span> message.
The Mobile Station Classmark 3 IE is received in the<span class="message-sem">Classmark Change</span> message. The BSC receives both of these messages while
the related mobile station is on a dedicated signalling channel (SDCCH).</p>
</div>


<a name="nov2621234502" shape="rect"></a>
<div class="topic">
<h2>Intra-segment
resource usability estimation</h2>

<p>When the BSC has received both information about the MS
frequency band capability and about the downlink received BCCH signal level
(measurement report), it defines the usability of different resource types
of the segment. </p>


<p>The following formula is used for non-BCCH layer resource
usability estimation whenever a channel inside the segment has to be assigned
(in intra-segment SDCCH-SDCCH handovers, TCH allocations, or intra-segment
TCH-TCH handovers).</p>


<p>RXLEV_DL - <span class="parameter-sem">Non BCCH Layer Offset</span>
&gt;= <span class="parameter-sem">Non BCCH Layer Access Threshold</span></p>


<p>If the MS is on a BCCH layer channel, the RXLEV_DL is the
terminal received signal level on the channel. If the MS is using a non-BCCH
layer channel, the RXLEV_DL is the downlink signal level of the BCCH carrier
of the segment.</p>


<p>If the RX lev min access feature is in use, the resource usability is
determined with the following formula:</p>


<p>RXLEV_DL - <span class="parameter-sem">Non BCCH Layer Offset</span> &gt;= <span class="parameter-sem">C/N</span> + <span class="parameter-sem">DL Noise Level</span> +
110</p>


<p>where C/N is a user-defined BSC-level parameter separate
for each call type and <span class="parameter-sem">DL Noise Level</span> a user-defined
BTS-level parameter.</p>
</div>


<a name="nov2621236333" shape="rect"></a>
<div class="topic">
<h2>Inter-segment
resource usability estimation</h2>

<p>When the BSC has defined a need for an inter-segment (SDCCH-SDCCH
or TCH-TCH) handover based on the measurements of the serving channel, the
usability of the different resource types of each candidate segment is decided
using the BCCH measurement results for the segment and the values of parameter <span class="parameter-sem">Non BCCH Layer Offset</span> for different resource types
in the segment according to the criterion:</p>


<p>AV_RXLEV_NCELL(n) – <span class="parameter-sem">Non BCCH Layer
Offset</span> &gt;= RxLevMinCell(n)</p>


<p>RxLevMinCell(n) is the level which the signal level in
the adjacent segment must exceed in order for the handover to the adjacent
segment to become possible.</p>


<p>If the RX lev min access feature is in use, the resource usability is
determined with the following formula:</p>


<p>AV_RXLEV_NCELL(n) - <span class="parameter-sem">Non BCCH Layer Offset</span>
&gt;= <span class="parameter-sem">C/N</span> + <span class="parameter-sem">DL Noise Level</span>
+ 110</p>


<p>where C/N is a user-defined BSC-level parameter separate for each call
type and <span class="parameter-sem">DL Noise Level</span> a user-defined BTS-level
parameter.</p>


<p>In a handover between two BSCs, the radio link measurements
related to the target segment are available on the source side BSC only. It
is therefore not possible to use the radio link measurements to define the
usability of the non-BCCH layer resources on the target side. In this case
the decisions are based on the <span class="parameter-sem">Non BCCH Layer Offset</span>
parameter. If the non-BCCH layer is regarded as a layer with less coverage
(as indicated by the positive value of the <span class="parameter-sem">Non BCCH
Layer Offset</span> parameter), only BCCH frequency band resources are used
in channel allocation for external handovers.</p>


<p>For more information, see <em>Radio Channel Allocation</em> in BSC/TCSM
documentation.</p>
</div>


<a name="jan265108411" shape="rect"></a>
<div class="topic">
<h2>Related topics</h2>

<ul>
<li><p><a href="NED?action=retrieve&amp;identifier=dn03298544&amp;edition=5&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=feb2131184918#feb2131184918" onclick="sync(this);return true" shape="rect">System impact of Common
BCCH</a></p>
</li>
<li><p><a href="NED?action=retrieve&amp;identifier=dn02228416&amp;edition=5&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=ned_top#ned_top" onclick="sync(this);return true" shape="rect">Common
BCCH and handover</a></p>
</li>
<li><p><a href="NED?action=retrieve&amp;identifier=dn02228431&amp;edition=5&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=ned_top#ned_top" onclick="sync(this);return true" shape="rect">Common
BCCH and channel allocation</a></p>
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<li><p><a href="NED?action=retrieve&amp;identifier=dn02228397&amp;edition=4&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=ned_top#ned_top" onclick="sync(this);return true" shape="rect">SDCCH
dimensioning with Common BCCH</a></p>
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<li><p><a href="NED?action=retrieve&amp;identifier=dn02222043&amp;edition=5&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=ned_top#ned_top" onclick="sync(this);return true" shape="rect">Overview
of implementing Common BCCH </a></p>
</li>
</ul>
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