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<div class="div">
<h1>Circuit Switched Data Services</h1>

<p>This feature allows mobile subscribers to use wireless
data transmission connections through the mobile network. Computers and faxes
can be connected remotely to public data transmission network. The BSC passes
control information on channels to the BTS, which, in turn, takes care of
the transcoder. The RA1/RA1' function is used to convert the radio interface
rates (12 kbits/s, 6 kbits/s, 3.6 kbits/s) at the interface between the channel
encoder/decoder and rate adapter of the BTS and the CCITT V.110 80 bit frames
of intermediate rates 8 and 16 kbits/s on terrestrial links. This function
is needed for all bearer services and non-voice teleservices, transparent
and non-transparent.</p>


<p>The MSC controls the channel type to be used for data transmission.
The following data transmission speeds and types can be used:</p>


<p>600 bit/s, 1200 bit/s, 2400 bit/s, 4800 bit/s, 9600 bit/s,
14400 bit/s.</p>


<p>The following radio interface data rate can be used for
the non-transparent service:</p>


<p>12 kbit/s.</p>


<a name="mar44118517" shape="rect"></a>
<dl class="note-notification">
<dt class="note-caption">Note</dt>
<dd>Data channels over TCH/H are not supported.</dd>
</dl>


<p>At the top of this feature, a 14.4 kbit/s GSM data service
is built. The latest feature is available and provides an accelerated user
data rate of 14,4 kbit/s. To do this, change the puncturing scheme illustrated
in the following picture:</p>


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<img alt="urn:mars:dn0469659:1:en:global:tiff:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn0469659&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Puncturing scheme</p>
</div>


<p>The use of 14.4 kbit/s data service reduces cell coverage.
For example, if the current 9.6 kbit/s service has a 90 % coverage, the 14.4
kbit/s service will have a coverage of about 84-87 %. The current threshold
for power control represents the predicted border of the acceptable user data
performance for the speech or 9.6 kbit/s data. This is not adequate for 14.4
kbit/s user data since 14.4 kbit/s channel coding can stand a smaller number
of errors. To maintain the 14.4 kbit/s performance adequate, the RX_QUAL need
to be kept better and so the power increase has to be started with better
quality for 14.4 kbit/s calls than other calls. A new threshold parameter
is defined for triggering the downlink and uplink power increase for the 14.4
kbit/s connection. However, for an optimal performance, the channel coding
is changed between 14.4 kbit/s and 9.6 kbit/s channel codings by an automatic
link adaptation (ALA) procedure according to MS and BTS power levels. The
new parameter determines the MS and BTS power levels when the ALA is performed.
The ALA is applicable for non-transparent data connections.</p>


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<img alt="urn:mars:dn0469662:1:en:global:tiff:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn0469662&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Automatic Link Adaptation (ALA) procedure</p>
</div>


<p>14.4 kbit/s data service can be combined with the high
speed circuit switched data (HSCSD).</p>


<p>In the A interface, the 14.4 kbit/s data connection can
be switched to one of the new pools, which support the 14.4 kbit/s channel
coding.</p>
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