If the UE requests a service setup or channel reconfiguration in an area covered by multiple frequencies, the RNC sets up the service on a carrier with a light load to achieve load balancing among the cells on the different frequencies.
"Inter-frequency DRD for load balancing" is called "DRD for load balancing" for short in this section.
Overview of DRD for Load Balancing
Load balancing considers two resources, power, and code.
The availability of DRD for load balancing is specified by the associated parameters as follows:
The availability of power-based DRD for load balancing for DCH service is specified by the LdbDRDSwitchDCH parameter.
The availability of power-based DRD for load balancing for HSDPA service is specified by the LdbDRDSwitchHSDPA parameter.
The availability of code-based DRD for load balancing is specified by the CodeBalancingDrdSwitch parameter.
In practice, it is recommended that only either a power-based DRD for load balancing or a code-based DRD for load balancing is activated. If both are activated, power-based DRD for load balancing takes precedence over code-based DRD for load balancing.
Code-based DRD for load balancing is applicable to only R99 services because HSDPA services use reserved codes.
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Power-Based DRD for Load Balancing
This section describes the procedure of DRD for load balancing when DRD for service steering is disabled.
The following two algorithms are available for power-based load balancing. If power-based DRD for load balancing is enabled, one of them can be used. The algorithm used is specified by the LdbDRDchoice parameter.
Algorithm 1: DRD for load balancing is performed according to the cell measurement values about the DL non-HSDPA power and DL HS-DSCH GBP.
− For DCH service, the RNC sets up the service on a carrier with a light load of non-HSPA power to achieve load balancing among the cells at the different frequencies.
− For HSDPA service, the RNC sets up the service on a carrier with a light load of HS-DSCH GPB to achieve load balancing among the cells at different frequencies.
Algorithm 2: DRD for load balancing is performed according to the DCH ENU and HSDPA user number.
− For DCH service, the RNC sets up the service on a carrier with a light load of DCH ENU to achieve load balancing among the cells on different frequencies.
− For HSDPA service, the RNC sets up the service on a carrier with a light load of HSDPA user to achieve load balancing among the cells on different frequencies.
As shown in Figure 6-13:
Cell B has a lighter load of non-HSDPA power than cell A. If the UE requests a DCH service in cell A, preferably, the RNC selects cell B for the UE to access.
Cell A has a lighter load of HS-DSCH GBP than cell B. If the UE requests an HSDPA service in cell B, preferably, the RNC selects cell A for the UE to access.
Figure 6-13 Power-based DRD for load balancing
Cell A Cell B
Load of HS-DSCH GBP Load of non-HSDPA power
Load DCH service HSDPA service
Figure 6-14 shows the procedure of power-based DRD for load balancing.
Figure 6-14 Procedure of power-based DRD for load balancing
Receive a service request
Does power of the current cell meet DRD condition 1?
Are there multiple such cells available?
Select the cell meeting the DRD conditions as
the target cell
Select the cell with the lightest power load as
the target cell
Select the current cell as
the target cell
Is the request an HSPA one?
Initiate an inter-RAT DRD
Initiate a blind handover
Does power of a neighboring cell meet DRD
condition 2?
HSPA falls back to DCH
No
The procedure of power-based DRD for load balancing is as follows:
1. The RNC determines the candidate cells to which blind handovers can be performed.
A candidate cell must meet the following conditions:
− The frequency of the candidate cell is within the band supported by the UE.
− The quality of the candidate cell meets the requirements of inter-frequency DRD.
− The candidate cell supports the requested service.
2. If the current cell is such a candidate cell, the RNC goes to step 3. Otherwise, the RNC selects a cell with the lightest load from the candidate cells as the target cell and then
Issue Error! Unknown Error! Unknown document property 15
− For algorithm 1, condition 1 is as follows:
a. For DCH bearer
ThdAMR cutcell, Pnon H cutcell ,
Thdnon Hb. For HSDPA bearer
Thdtotal cutcell, PGBP cutcell,
ThdH− For algorithm 2, condition 1 is as follows:
a. For DCH bearer
ThdAMR cutcell, PD ENU cutcell ,
Thdnon Hb. For HSDPA bearer
ThdH ue cutcell , PH ue cutcell ,
/ThdH ue cutcell , ThdHHere:
non H
Thd is specified by LdbDRDLoadRemainThdDCH.
Thd is specified by LdbDRDLoadRemainThdHSDPA. H
If... Then...
Condition 1 is met The service tries admission to the current cell. Go to step 5.
Condition 1 is not met Go to step 4.
4. The RNC selects a target cell for UE access.
The RNC determines whether any inter-frequency neighboring cell meets the following condition (condition 2): Based on the bearer type (DCH or HSDPA) of the requested service, the RNC selects an appropriate condition as follow:
If algorithm 1 is used, condition 2 is as follows:
− For an HSDPA service
Thd
total nbcell, P
GBP nbcell, Thd
total cutcell, P
GBP cutcell, Thd
H loadoffset, Thd
total cutcell, P
load cutcell, Thd
total nbcell, P
load nbcell, Thd
total loadoffset,− For a DCH service
ThdAMR nbcell, Pnon H nbcell ,
ThdAMR cutcell, Pnon H cutcell ,
ThdD loadoffset, Thd
total cutcell, P
load cutcell, Thd
total nbcell, P
load nbcell, Thd
total loadoffset, If algorithm 2 is used, condition 2 is as follows:
− For an HSDPA service
, ,
,
, ,
,,
/ /
H ue nbcell H ue nbcell H ue nbcell H ue cutcell H ue cutcell H ue cutcell
H loadoffset
Thd P Thd Thd P Thd
Thd
− For a DCH service
ThdAMR nbcell, PD enu nbcell ,
ThdAMR cutcell, PD enu cutcell ,
ThdD loadoffset,The related variables are described as follows:
Current cell Inter-frequency
Neighboring Cell Description
, total cutcell
Thd Thdtotal nbcell, DL total power threshold
(DlCellTotalThd)
, GBP cutcell
P PGBP nbcell, HS-DSCH GBP
Total power load, which is the sum of the non-HSDPA power and the GBP
, non H cutcell
P Pnon H nbcell , Non-HSDPA power load
, AMR cutcell
Thd ThdAMR nbcell, DL threshold of conversational AMR
service (DlConvAMRThd)
Thd - Load balancing DRD offset for HSDPA
(LdbDRDOffsetHSDPA)
, D loadoffset
Thd - Load balancing DRD offset for DCH
(LdbDRDOffsetDCH)
, total loadoffset
Thd - Load balancing DRD total power protect
threshold (LdbDRDTotalPwrProThd)
Then, the RNC selects the target cell as follows:
If there is only one inter-frequency neighboring cell that meets the conditions of DRD for load balancing, the RNC selects this cell as the target cell. If there are multiple such cells:
− For a DCH service
a.If algorithm 1 is used, the RNC selects the cell with the lightest non-HSDPA load as the target cell.
b.If algorithm 2 is used, the RNC selects the cell with the lightest load of DCH ENU as the target cell.
− For an HSDPA service
a.If algorithm 1 is used, the RNC selects the cell with the lightest load of HS-DSCH required power as the target cell.
b.If algorithm 2 is used, the RNC selects the cell with the lightest load of HSDPA user as the target cell.
If there is no such cell, the RNC selects the current cell as the target cell.
5. The CAC algorithm makes an admission decision based on the status of the target cell.
If the admission attempt is successful, the RNC admits the service request.
Issue Error! Unknown Error! Unknown document property 17
If the admission attempt fails, the RNC checks whether admission decisions have been made in all candidate inter-frequency neighboring cells.
− If there is any cell where no admission decision is made, the algorithm goes back to step 2.
− If admission decisions have been made in all the candidate cells:
a.When the service request is an HSPA one, the HSPA request falls back to a DCH one. Then, the algorithm goes back to step 1 to make an admission decision based on R99 service priorities.
b.When the service request is a DCH one, the RNC initiates an inter-RAT DRD.
Code-Based DRD for Load Balancing
The procedure of DRD for load balancing based on code resource is similar to that based on power resource.
Figure 6-15 shows the procedure for selecting a target cell based on code resource.
Figure 6-15 Procedure of code-based DRD for load balancing Start
Is there a cell with the lightest code load?
Minimum SF of the current cell <
CodeBalancingDrdMinSFThd?
Yes
No
Yes
No
No
Yes
Yes
No
Select the current cell as the target cell Select the cell with the lightest code
load as the target cell Is the current cell in
candidate cells?
Code load of the current cell <
CodeBalancingDrdCodeRateThd?
Select the cell with the lightest code load from the cells with the same service priority
as the target cell
The procedure is as follows:
1. The RNC determines whether the minimum remaining SF of the current cell is smaller than the minimum SF threshold of DRD for code balancing (CodeBalancingDrdMinSFThd).
If the minimum SF is smaller than this threshold, the RNC tries the admission of the service request to the current cell.
If the minimum SF is not smaller than this threshold, the RNC goes to the next step.
2. The RNC determines whether the code load of the current cell is lower than the code occupation rate threshold of DRD for code balancing (CodeBalancingDrdCodeRateThd).
If the code load is lower than this threshold, the service tries the admission to the current cell.
If the code load is higher than or equal to this threshold, the RNC selects the cell with the lightest load or the current cell as the target cell. The RNC selects the cell as follows:
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− If the minimum SF supported by the cell with the lightest code load is the same as that supported by the current cell, and the difference between the code resource occupancies of the two is larger than or equal to the value of
DeltaCodeOccupiedRate, the RNC selects the cell with the lightest code load as the target cell. Otherwise, the RNC selects the current cell as the target cell.
− If the minimum SF supported by the cell with the lightest code load is smaller than the minimum SF supported by the current cell, the RNC selects the cell with the lightest code load as the target cell.