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<div class="div">
<h1>FER Measurement </h1>

<p>The FER Measurement provides an ability to report the UL
FER from the BTS to the BSC. This provides a more realistic measure of the
voice quality in the system and enables to perform handovers and power control
based in the FER rather than BER-based RxQuality. This feature can then provide
more capacity and better quality.</p>


<p>Additionally, the DL FER is estimated using the correlation
between the UL FER and UL BER values and applying these to the DL BER values.
Both UL FER values and estimated DL FEP (Frame Erasure Probability) values
are available in the new FER measurement. In addition to handover and power
control algorithms, the feature provides also significant improvements to
network quality statistics.</p>


<p>Frame Erasure Rate is the best available indicator in a
GSM system to assess the Voice Quality provided in a network. It represents
the percentage of frames being dropped due to high number of not corrected
bit errors in the frame.</p>


<p>The BER figure currently reported to the system is not
a good indication of the quality of the network, especially when efficiency
of the error correction mechanism changes due to the functionality introduced
in the network such as frequency hopping or dynamic channel coding.  Hopping
spreads out the fading and interference problems allowing effectively the
decoding mechanism to restore the original information via the Error Correction
process. Not only the correlation between the BER and FER will change when
Frequency Hopping is in use, but different frequency hopping schemes (depending
in the reuse and number of frequencies to hop over) will have a different
BER to FER correlation. The figure below shows this effect measured in a real
operational network for the DL path. The area of interest is the one showing
the correlation of RXQUAL 4 to 6 and the voice quality degradation (FER&gt;5%).</p>


<p>There are 7 classes defined for the FER measurement. The
class boundaries B1..B7 (FER %) and averaging window size (SACCH frames) are
defined in the measurement set-up. B0 and B8 are fixed. Class0 is between
boundary 0 (B0) and boundary 1 (B1) etc. Occurrences give the number of records
where the setting is met. If there is more than one line, different settings
are used in the area.</p>


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<p>Table: Boundaries used in the selected area for defining the classes</p>


<table border="1">
<thead>
<tr align="left" char="" charoff="50" valign="bottom">
<th colspan="1" rowspan="1" valign="top"><p>B0</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>B1</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>B2</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>B3</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>B4</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>B5</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>B7</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>B8</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Ave Win Size</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>OCCURENCES</p>
</th>
</tr>
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<td colspan="1" rowspan="1"><p>0</p>
</td>
<td colspan="1" rowspan="1"><p>2%</p>
</td>
<td colspan="1" rowspan="1"><p>4%</p>
</td>
<td colspan="1" rowspan="1"><p>6%</p>
</td>
<td colspan="1" rowspan="1"><p>8%</p>
</td>
<td colspan="1" rowspan="1"><p>10%</p>
</td>
<td colspan="1" rowspan="1"><p>12%</p>
</td>
<td colspan="1" rowspan="1"><p>14%</p>
</td>
<td colspan="1" rowspan="1"><p>2</p>
</td>
<td colspan="1" rowspan="1"><p>31</p>
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<a name="apr1541859819" shape="rect"></a>
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<img alt="urn:mars:dn0468745:1:en:global:tiff:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn0468745&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: RX Quality / FER Correlation for hopping and non-hopping cases</p>
</div>


<p>The Channel Coding algorithm in use has a direct impact
in the Error Correction performance. Depending how robust the channel coding
is, its associated performance will vary. A clear example of this will take
place when different coding schemes are implemented simultaneously in AMR
networks. Again the correlation between the BER and FER will change, and this
time it will potentially do it dynamically according to the conditions.</p>
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