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<h1>8-ary Phase Shift Keying</h1>

<p>While GSM uses only Gaussian Minimum Shift Keying (GMSK), <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> uses both 8-ary Phase Shift Keying (8PSK) and
GMSK. 8PSK is a linear, higher-order modulation. Introducing 8PSK in addition
to GMSK allows the data transmission rates to be tripled. An 8PSK signal carries
three bits per modulated symbol over the radio path, compared to a GMSK signal,
which carries only one bit per symbol.</p>


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<p>Table: 8PSK and GMSK comparison</p>


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<th colspan="1" rowspan="1" valign="top"><p>8PSK</p>
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<th colspan="1" rowspan="1" valign="top"><p>GMSK</p>
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<td colspan="1" rowspan="1"><p>Modulation</p>
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<td colspan="1" rowspan="1"><p>8PSK, 3 bit/sym</p>
</td>
<td colspan="1" rowspan="1"><p>GMSK, 1 bit/sym</p>
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<td colspan="1" rowspan="1"><p>Symbol rate</p>
</td>
<td colspan="1" rowspan="1"><p>270.833 ksps</p>
</td>
<td colspan="1" rowspan="1"><p>270.833 ksps</p>
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<td colspan="1" rowspan="1"><p>Payload/burst</p>
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<td colspan="1" rowspan="1"><p>346 bits</p>
</td>
<td colspan="1" rowspan="1"><p>116 bits</p>
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<td colspan="1" rowspan="1"><p>Gross rate/time slot</p>
</td>
<td colspan="1" rowspan="1"><p>69.6 kbit/s</p>
</td>
<td colspan="1" rowspan="1"><p>23.2 kbit/s</p>
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<p>Nokia uses standardized 3pi/8 offset rotation to reduce
amplitude variations with 8PSK modulation, as shown in the figure <em>8PSK
modulation scheme</em>. The standard GSM carrier symbol rate (270.833 ksps)
is the same as with 8PSK. The burst lengths are the same as the existing GMSK
Time Division Multiple Access (<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=id05343#id05343" 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=id05343#id05343');return false" shape="rect" target="_blank">TDMA</a>) structure,
and the same 200 kHz nominal frequency spacing between carriers is used. </p>


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<h2>Related
topics</h2>

<p><a href="NED?action=retrieve&amp;identifier=dn02242662&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 Nokia EDGE</a></p>
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