This section describes briefly the CAC mechanisms on downlink radio resources i.e.
power and OVSF code tree.
Starting UA06, two modes of operation are available :
- when “fair sharing” is not enabled, the call admission control is resource oriented
i.e. resources are more or less managed independently for R99 and HSDPA
- when “fair sharing” is enabled, the call admission is service oriented meaning
resources and CAC are managed as one pool whatever is the pipe used
(dedicated or shared)
CAC OF HSDPA RADIO RESOURCES CAC
When fair sharing is disabled, the basic Call Admission Control for HSDPA and EDCH
are based on a number of users and there is no radio resource based CAC for
call admission. When the call is admitted, the resources granted for the UE are
managed by the scheduler based on the current radio resources availability.
DL POWER FOR HSDPA
When fair sharing is not enabled, the main principle is to make HSDPA use the remaining power
which is not used currently used by R99.
As stated above, there is a minimum Power for HSDPA which can be reserved.
For the maximum HSDPA power, the RNC has the means to limit the HSDPA power used to
the whole remaining power minus a margin. This margin could be also null, in this case the
NBAP IE will not be sent to the Node B.
OVSF CODE TREE
In the current release, one downlink scrambling code (i.e. one OVSF code tree) is
managed per cell. In this OVSF tree, some codes are reserved :
- codes for common control channels
- codes for OCNS
- a sub-tree is allocated to the Node B for HSDPA usage.
The rest of the OVSF tree is used by calls handled over R99 resources. For each
allocation, the OVSF tree will be run from up to down (filling the gaps when any),
which avoids to block too many branches
If a free code is found, the resource is granted to the call and the OVSF code CAC is
successful, otherwise the call is rejected and the CAC on OVSF code is declared
failed.
Please note that up to UA4.2, the number of codes reserved for HSDPA was static.
Starting UA05, thanks to Dynamic DL OVSF code tree management feature, the
sharing of the OVSF tree is dynamic and adjusted in function of the traffic on HSDPA
and R99 resources with a priority to R99 calls: in case the occupancy is higher than a
threshold for R99 resources, a part of the sub-tree is preempted back by for R99 calls.
There is a dual mechanism which allows to give back codes to HSDPA when not used
by R99.