The DHA feature optimizes the usage of capacity when the
cell load is high, whilst offering the best possible speech quality when the
cell load is low. This is achieved by allocating FR or HR TCHs in accordance
with the cell load, at the time when a new TCH shall be selected due to
assignment and most types of handovers. At high cell load HR TCHs have
precedence and at low cell load FR TCHs have precedence.
The feature is invoked
if the parameter DHA is ON.
The parameter is set on cell
level. The feature is not invoked at immediate assignment if using a TCH. Then
it is the setting of the parameter CHAP that controls whether
FR and/or HR may be used
To
trigger the functionality it must also be checked that the DL signal strength
measured by the MS is not too low. If the signal strength is below DHASSTHRASS
(if during assignment) or DHASSTHRHO (if during handover) then
dynamic HR allocation evaluation will not be performed. This signal strength
check can be activated and deactivated using the parameter DHASS.
The
thresholds for when allocation of HR TCHs is triggered are given by the
parameters DTHAMR and DTHNAMR
and are set per cell. These parameters are percentage values and are compared
to the number of idle TCH BPCs divided by the total number of de-blocked TCH
BPCs. The two parameters indicate that AMR and non AMR DR capable MSs may,
depending on the cell load, be treated differently in the allocation of TCHs.
If using the feature Speech Quality Priority, and turning the parameter DHPR
ON, it is also possible to set these two parameters differently for different
priority levels. By doing that it is for example possible to start allocating
HR to low priority users at moderate cell load, and let high priority users get
FR until the load in the cell is very high.
In
general the following cases occur:
§ If
the MS and the cell support AMR/HR and the number of idle TCH BPCs divided by
the total number of de-blocked TCH BPCs is equal to or above the value of DTHAMR
set for the specific priority level that the MS is assigned, then FR TCHs will
have precedence over HR TCHs at channel allocation. If the number of idle TCH
BPCs divided by the total number of de-blocked TCH BPCs is less than DTHAMR ,
but higher than DTHNAMR, then AMR/HR TCHs will
have precedence over FR TCHs. If the number of idle TCH BPCs divided by the
total number of de-blocked TCH BPCs is less than both DTHAMR
and DTHNAMR,
then HR TCHs will have precedence over FR TCHs (both AMR/HR and HR will have
precedence, and in this order).
§ If
the MS or the cell do not support AMR/HR and the number of idle TCH BPCs
divided by the total number of de-blocked TCH BPCs is equal or above DTHNAMR
set for the specific priority level that the MS is assigned, then FR TCHs will
have precedence over HR TCHs. If the number of idle TCH BPCs divided by the
total number of de-blocked TCH BPCs is less than DTHNAMR,
then HR TCHs will have precedence over FR TCHs (only HR SPV1).
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