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<h2>Forced HR mode</h2>

<p>During low traffic hours it is useful to prefer full rate (FR) mode
as FR channels provide better subjective speech quality. In this situation
the existing cell load based rate selection between FR and half rate (HR)
method is sufficient.</p>


<p>However, the most advantage of DFCA can be taken when the interfering
and interfered traffic channels are of the same type. This may lead to a decision
to use HR channels even if there are still sufficient hardware resources available
for FR use in the cell. This is called Forced HR mode.</p>


<p>Forced HR mode is a method for channel rate selection between FR and
HR, based on the average of the estimated incoming DL C/Is of DFCA allocations
in a cell. The average DL C/I provides a good benchmark of the load of DFCA
frequencies and thus, it can be used to trigger HR allocation. When HR allocation
is triggered in the cell because of forced HR mode, it is triggered also in
the interfering neighbour cells. Forced HR mode provides better HR performance
and improves the C/I situation in the cell and its BIM neighbours.</p>


<p>Note that in order to use Forced HR mode, the traffic channels should
be Dual Rate TCHs.</p>


<p>DFCA algorithm calculates the C/I over the averaging period and if the
C/I is below the threshold, the forced HR mode is triggered. The forced HR
mode ends when the average C/I reaches the threshold + defined forced HR mode
hysteresis.</p>


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