134170437 directed-retry-decision-libre

Directed Retry Decision
RAN12.0
Feature Parameter Description
Issue 03
Date 2010-12-20
HUAWEI TECHNOLOGIES CO., LTD.

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WCDMA RAN
Directed Retry Decision Contents
Issue 03 (2010-12-20) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
ii
Contents
1 Introduction................................................................................................................................1-1
1.1 Scope ............................................................................................................................................ 1-1
1.2 Intended Audience ........................................................................................................................ 1-1
1.3 Change History.............................................................................................................................. 1-1
2 Overview of DRD.......................................................................................................................2-1
3 RRC DRD.....................................................................................................................................3-1
4 Non-periodic DRD.....................................................................................................................4-1
4.1 Overview ....................................................................................................................................... 4-1
4.1.1 Blind-handover-based Non-periodic DRD............................................................................ 4-1
4.1.2 Measurement-based Non-periodic DRD .............................................................................. 4-1
4.2 Inter-Frequency DRD Procedure .................................................................................................. 4-2
4.3 DRD for Technological Satisfaction............................................................................................... 4-3
4.3.1 Overview............................................................................................................................... 4-3
4.3.2 Priority Sequence of HSPA+ Technologies .......................................................................... 4-4
4.3.3 Procedure of DRD for Technological Satisfaction ................................................................ 4-4
4.4 Inter-Frequency DRD for Service Steering ................................................................................... 4-5
4.4.1 Cell Service Priorities ........................................................................................................... 4-5
4.4.2 Procedure of DRD for Service Steering................................................................................ 4-6
4.5 Inter-Frequency DRD for Load Balancing..................................................................................... 4-8
4.5.1 Overview of DRD for Load Balancing................................................................................... 4-8
4.5.2 Power-Based DRD for Load Balancing................................................................................ 4-8
4.5.3 Code-Based DRD for Load Balancing................................................................................ 4-12
4.6 Inter-RAT DRD ............................................................................................................................ 4-14
4.7 MBDR.......................................................................................................................................... 4-15
4.7.1 Overview of the MBDR Algorithm....................................................................................... 4-15
4.7.2 MBDR Algorithm Switches ................................................................................................. 4-15
4.7.3 Procedure for the MBDR Algorithm.................................................................................... 4-15
5 Periodic DRD..............................................................................................................................5-1
5.1 Overview ....................................................................................................................................... 5-1
5.1.1 Switches for Periodic DRD ................................................................................................... 5-1
5.1.2 Triggering of Periodic DRD................................................................................................... 5-1
5.2 Periodic DRD Procedure............................................................................................................... 5-2
5.2.1 Blind-Handover-Based Periodic DRD .................................................................................. 5-2
5.2.2 Measurement-Based Periodic DRD ..................................................................................... 5-3
6 Parameters .................................................................................................................................6-1
7 Counters......................................................................................................................................7-1

WCDMA RAN
Directed Retry Decision Contents
iii
8 Glossary ......................................................................................................................................8-1
9 Reference Documents .............................................................................................................9-1

WCDMA RAN
Directed Retry Decision 1 Introduction
1-1
1 Introduction
1.1 Scope
This document describes Directed Retry Decision (DRD). It covers both the RRC DRD and the RAB
DRD, and furthermore provides parameter descriptions.
1.2 Intended Audience
This document is intended for:
 Personnel who are familiar with WCDMA basics
 Personnel who need to understand DRD
 Personnel who work with Huawei products
1.3 Change History
This section provides information on the changes in different document versions.
There are two types of changes, which are defined as follows:
 Feature change: refers to the change in the DRD feature.
 Editorial change: refers to the change in wording or the addition of the information that was not
described in the earlier version.
Document Issues
The document issues are as follows:
 03 (2010-12-20)
 02 (2010-06-20)
 01 (2010-03-30)
 Draft (2009-12-05)
03 (2010-12-20)
This is the document for the third commercial release of RAN12.0.
Compared with issue 02 (2010-06-20) of RAN12.0, this issue optimizes the description.
02 (2010-06-20)
This is the document for the second commercial release of RAN12.0.
Compared with issue 01 (2010-03-30) of RAN12.0, this issue corrects the error in 4.6 “Inter-RAT DRD.”
01 (2010-03-30)
This is the document for the first commercial release of RAN12.0.
Compared with issue Draft (2009-12-05) of RAN12.0, this issue incorporates the changes described in
the following table.

WCDMA RAN
Directed Retry Decision 1 Introduction
1-2
Change Type Change Description Parameter Change
Feature change The description about
measurement-based
non-periodic DRD
(MBDR) is added. For
details, see “4.7 MBDR.”
The added parameters are listed as follows:
 InterFreqActiveType
 InterRatActiveType
 UlNonCtrlThdForAMR
 UlNonCtrlThdForNonAMR
 UlNonCtrlThdForOther
 DlConvAMRThd
 DlConvNonAMRThd
 DlOtherThd
 InterFreqUlMbdrTrigThreshold
 InterFreqDlMbdrTrigThreshold
 InterRatUlMbdrTrigThreshold
 InterRatDlMbdrTrigThreshold
 UserPercentage
 MBDRPrio
 MaxAttNum
 MBDRFlag
 InterFreqReportMode
 TrigTime2C
 InterFreqMeasQuantity
 HOThdEcN0
 HOThdRscp
 InterRatReportMode
 InterRATPeriodReportInterval
 InterRATHOThd
 TrigTime3C
Editorial change None. None.
Draft (2009-12-05)
This is the draft of the document for RAN12.0.
This is a new document. The description about RRC DRD and non-periodic DRD is separated from the
Load Control Feature Parameter Description; the description about periodic DRD is newly added.

WCDMA RAN
Directed Retry Decision 2 Overview of DRD
2-1
2 Overview of DRD
Directed Retry Decision (DRD) is used to select a suitable cell for a UE to access. Different types of DRD
can be adopted during different phases of service processing. In this way, the system capacity can be
maximized, and better services can be provided.
Figure 2-1 shows the different types of DRD.
Figure 2-1 Types of DRD
RAB DRD is performed during the RAB phase, which starts from RAB setup processing and ends in
RAB release. There are two types of RAB DRD, non-periodic DRD and periodic DRD, as shown in
Figure 2-1.
DRD Type Application
Scenario
Description
RRC DRD During RRC
setup
RRC DRD is used to select a suitable inter-frequency neighboring
cell for a UE to set up an RRC connection in either of the following
situations:
 The RRC connection setup fails in the cell that the UE tries to
access.
 The cell that the UE tries to access does not support signaling
radio bearer (SRB) over HSPA when SRB over HSPA is selected
as the bearer scheme.
RRC DRD is based on blind handover.

WCDMA RAN
Directed Retry Decision 2 Overview of DRD
2-2
DRD Type Application
Scenario
Description
Non-periodic
DRD
During RAB
setup, RAB
modification, or
DCCC channel
reconfiguration
Non-periodic DRD can be performed based on blind handover or
measurement.
 Blind-handover-based non-periodic DRD is used to select a
suitable cell for a UE to access according to the HSPA+
technological satisfaction, service priority, and cell load. It
enables the UE to be served with the best technological
satisfaction and implements load balancing and service steering.
 Measurement-based non-periodic DRD, that is, Measurement
Based Directed Retry (MBDR) is used to select a signal qualified
cell for a UE according to the measurement result. Compared
with blind-handover-based non-periodic DRD, MBDR can
increase the DRD success rate when the current cell and the
DRD target cell cover different areas.
NOTE:
Blind-handover-based non-periodic DRD cannot work with MBDR. When
MBDR is enabled, this type of DRD is disabled automatically.
Periodic
DRD
After RAB setup
or after the
bearer scheme is
changed
Periodic DRD is triggered by the HSPA/HSPA+ retry or cell service
priority. It can be performed to select a suitable cell when the RNC
determines that the UE can be served by a better HSPA/HSPA+
technology or when a neighboring cell has a higher service priority
than the current cell. Note that only measurement-based periodic
DRD can be triggered by cell service priority.
After periodic DRD is triggered, it can be performed through either
of the following two ways:
 Blind-handover-based periodic DRD: It mainly applies to the
inter-frequency same-coverage scenarios. It selects the target
cell that support blind handover and does not consider the signal
quality of the target cell.
 Measurement-based periodic DRD: It applies to both the
inter-frequency different-coverage scenarios and the
inter-frequency same-coverage scenarios. It selects the target
cell according to the signal measurement results. Only the cell
that meets the specified signal conditions can be selected as the
target cell.
NOTE:
Blind-handover-based periodic DRD cannot work with measurement-based
periodic DRD. When the latter is enabled, the former is disabled
automatically.

WCDMA RAN
Directed Retry Decision 3 RRC DRD
3-1
3 RRC DRD
RRC DRD is performed during RRC connection setup. When a UE fails to access the current cell, the
RNC performs RRC DRD. The purpose is to instruct the UE to set up an RRC connection in a suitable
inter-frequency neighboring cell.
The DR_ RRC_DRD_SWITCH subparameter of the DrSwitch parameter determines whether RRC
DRD is enabled.
The RRC DRD procedure is as follows:
1. The RNC selects the intra-band inter-frequency neighboring cells of the current cell. These
neighboring cells are suitable for blind handovers. Whether the neighboring cells support blind
handover is specified by the parameter BlindHoFlag.
2. The RNC generates a list of candidate DRD-supportive inter-frequency cells according to the
following condition
(CPICH_EcNo)RACH > DRD_EcNOnbcell
Here:
− (CPICH_EcNo)RACH is the cached CPICH Ec/N0 value included in the RACH measurement report.
Note that this value is of the current cell.
− DRD_EcNOnbcell is the DRD threshold (DRDEcN0Threshhold) of the neighboring cell.
3. The RNC selects a target cell from the candidate cells for UE access. If the candidate cell list is
empty, the RRC DRD fails. The RNC performs RRC redirection. If the candidate cell list contains
more than one cell, the UE tries a cell randomly.
− If the admission is successful, the RNC continues the RRC connection setup procedure.
− If the admission to a cell fails, the UE tries admission to another cell in the candidate cell list until an
admission is successful or all admission attempts fail.
If all the admission attempts fail, then
− The RNC makes an RRC redirection decision when the function of RRC redirection after DRD failure
is enabled.
− The RRC connection setup fails when the function of RRC redirection after DRD failure is disabled.
For information about RRC redirection after DRD failure, see the Load Control Feature Parameter
Description.

WCDMA RAN
Directed Retry Decision 4 Non-periodic DRD
4-1
4 Non-periodic DRD
This section involves the following features:
 WRFD-02040001 Intra System Direct Retry
 WRFD-02040002 Inter System Direct Retry
 WRFD-01061112 HSDPA DRD
 WRFD-020402 Measurement based Direct Retry
4.1 Overview
Non-periodic DRD is used to select a suitable cell for UE access. It can be performed during RAB setup,
RAB modification, or DCCC channel reconfiguration.
Non-periodic DRD can be performed based on measurement or blind handover. Blind-handover-based
non-periodic DRD and measurement-based non-periodic DRD (that is, MBDR) can not be used
simultaneously. When the MBDR algorithm is enabled, other non-periodic DRD algorithms are
automatically disabled.
4.1.1 Blind-handover-based Non-periodic DRD
Blind-handover-based non-periodic DRD involves inter-frequency DRD (WRFD-02040001 Intra System
Direct Retry) and inter-RAT DRD (WRFD-02040002 Inter System Direct Retry).
The following parameters determine whether to enable blind-handover-based non-periodic DRD:
 For a single service, blind-handover-based non-periodic DRD is enabled by the
DR_RAB_SING_DRD_SWITCH subparameter of the DrSwitch parameter.
 For a service combination, blind-handover-based non-periodic DRD is enabled by the
DR_RAB_COMB_DRD_SWITCH subparameter of the DrSwitch parameter.
Note that if the measurement-based periodic DRD switch BasedOnMeasHRetryDRDSwitch is set to
ON, blind-handover-based non-periodic DRD is also controlled by the BlindDrdExceptHRetrySwitch
parameter.
For example, when the DR_RAB_SING_DRD_SWITCH subparameter of the DrSwitch parameter is set
to ON and the BasedOnMeasHRetryDRDSwitch parameter is set to ON, blind-handover-based
non-periodic DRD for a single service is enabled only if the BlindDrdExceptHRetrySwitch parameter is
set to ON.
For detailed information about blind-handover-based non-periodic DRD, see the following sections:
 4.2 Inter-Frequency DRD Procedure
 4.3 DRD for Technological Satisfaction
 4.4 Inter-Frequency DRD for Service Steering
 4.5 Inter-Frequency DRD for Load Balancing
 4.6 Inter-RAT DRD
4.1.2 Measurement-based Non-periodic DRD
Measurement-based non-periodic DRD (MBDR) is a feature introduced in RAN12.0. It can increase the
success rate of DRD, reduce the service drops caused by DRD with blind handover, and improve the
network performance.

WCDMA RAN
4-2
After an RRC connection is set up, the RNC decides whether to establish the requested service in an
inter-frequency or inter-RAT cell based on the current cell load and the type of service to be established.
If the RNC decides to establish the service in such a neighboring cell, the RNC sends an inter-frequency
or inter-RAT measurement control message to the UE, instructing the UE to measure the signal quality
of neighboring cells. If the signal quality of a neighboring cell meets the specified requirements, the RNC
establishes the service in this cell. Otherwise, the RNC attempts to establish the service in the current
cell.
For a type of service, whether MBDR can be performed can be set through the parameters
InterFreqActiveType and InterRatActiveTyp.
For detailed information about blind-handover-based non-periodic DRD, see 4.7 MBDR.
4.2 Inter-Frequency DRD Procedure
An inter-frequency DRD procedure consists of DRD for technological satisfaction, DRD for service
steering, and DRD for load balancing. The RNC performs these DRDs in sequence, as shown in Figure
4-1.
Figure 4-1 Performing DRDs in sequence
DRD for technological
satisfaction
DRD for service steering
DRD for load balancing
Sequence of performing DRDs
If one of the DRD function is disabled, the RNC does not consider the conditions based on which this
type of DRD is performed. For example, if DRD for load balancing is disabled, the RNC does not
consider the cell load when selecting a cell based on inter-frequency DRD.
DRD for technological satisfaction is efficient, but it is applicable only to UEs requesting HSPA+ services.
DRD for service steering and DRD for load balancing are controlled by the related parameters.
If all the DRD functions are enabled, the RNC performs the following steps:
1. The RNC determines the candidate cells to which a blind handover can be performed. Whether the
neighboring cells support blind handover is specified by the parameter BlindHoFlag. A candidate
cell must meet the following conditions:
− The candidate cell supports the requested service.
− The frequency of the candidate cell is within the band supported by the UE.
− The current cell meets the quality requirements of inter-frequency DRD. For details, see 3 "RRC
DRD."
2. The RNC selects a target cell from the candidate cells for UE access as follows:
(1) The RNC selects a cell with the highest technological satisfaction.
(2) If multiple cells have the highest technological satisfaction or the requested service is not an
HSPA+ one, the RNC selects a cell based on DRD for service steering as described in section 4.4
“Inter-Frequency DRD for Service Steering.“

WCDMA RAN
4-3
(3) If multiple cells have the highest service priority, the RNC selects a cell based on DRD for load
balancing as described in section 4.4 "Inter-Frequency DRD for Service Steering."
3. The CAC algorithm makes an admission decision based on the resource status of the cell.
− If the admission attempt is successful, the RNC initiates an inter-frequency blind handover to the cell.
− If the admission attempt fails, the RNC removes the cell from the candidate cells and then checks
whether all candidate cells are tried.
a. If there is any candidate cell that has not been tried, the algorithm goes back to step 2 to try this
cell.
b. If all candidate cells haven been tried, then:
− If 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 retry admission based on R99 service priorities.
− If the service request is a DCH one, the RNC initiates an inter-RAT DRD.
For UEs requesting the non-HSPA+ services, If both DRD for service steering and DRD for load
balancing are disabled, the RNC performs the following steps:
1. The UE attempts to access the current cell when its service priority is not 0. If the service priority of
the current cell is 0, the UE attempts to access a neighboring cell with the highest priority of blind
handover. The blind handover priority of the cell is specified by the parameter BlindHOPrio.
2. The CAC algorithm makes an admission decision based on the cell status. For details about the CAC
procedure, see the Call Admission Control Feature Parameter Description.
− If the admission attempt is successful, the RNC admits the service request.
− If the admission attempt fails, the UE attempts to access another candidate cell randomly.
3. If any request for access to a candidate cell is rejected, then:
− If 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 retry admission based on R99 service priorities.
− If the service request is a DCH one, the RNC initiates an inter-RAT DRD. For details about inter-RAT
DRD, see section 4.6 "Inter-RAT DRD."
4.3 DRD for Technological Satisfaction
4.3.1 Overview
DRD for technical satisfaction is used to select a suitable cell and HSPA+ technologies for a UE based
on the HSPA+ technologies supported by the UE and attributes of the requested service such as the
bearer channel, service type, and service rate.
DRD for technical satisfaction consists of the following phases:
1. The RNC determines the HSPA+ technologies that can be configured for the UE, based on the
HSPA+ technologies supported by the UE and attributes of the requested service, as described in
the Radio Bearers Feature Parameter Description.
2. The RNC determines the HSPA+ technical satisfaction of each candidate cell based on the priorities
of HSPA+ technologies and the intersection of the HSPA+ technologies that can be configured for
the UE and supported by the cell.
3. The RNC selects a suitable cell for the UE based on the priority sequence of HSPA+ technologies. In
addition, the RNC determines the HSPA+ technologies for the UE, which are the intersection of the
HSPA+ technologies that can be configured for the UE and supported by this cell.

WCDMA RAN
4-4
4.3.2 Priority Sequence of HSPA+ Technologies
From a UE perspective, the technical satisfaction of a cell is determined by the intersection of the HSPA+
technologies that can be configured for the UE and supported by the cell. If the HSPA+ technologies in
the intersection have a high priority, the cell has high technical satisfaction.
The HSPA+ technologies comprise DC-HSDPA, enhanced layer 2 (L2), MIMO, 64QAM, DTX+DRX, UL
16QAM, and HS-SCCH Less Operation. The priority sequences of the technologies in a cell supporting
HSPA+ are as follows:
 When MIMO64QAMorDCHSDPASwitch is set to DC-HSDPA and MIMOor64QAMSwitch to MIMO,
the priority sequence is DC-HSDPA (with downlink 64QAM activated in at least one cell) >
MIMO+64QAM > DC-HSDPA (with downlink 16QAM activated in at least one cell) > MIMO+DL
16QAM > DL 64QAM > DL enhanced L2 > UL 16QAM > UL enhanced L2 > DTX+DRX > HS-SCCH
Less Operation.
 When MIMO64QAMorDCHSDPASwitch is set to DC-HSDPA and MIMOor64QAMSwitch to 64QAM,
the priority sequence is DC-HSDPA (with downlink 64QAM activated in at least one cell) >
MIMO+64QAM > DC-HSDPA (with downlink 16QAM activated in at least one cell) > DL 64QAM >
MIMO+DL 16QAM > DL enhanced L2 > UL 16QAM > UL enhanced L2 > DTX+DRX > HS-SCCH Less
Operation.
 When MIMO64QAMorDCHSDPASwitch is set to MIMO_64QAM and MIMOor64QAMSwitch to
MIMO, the priority sequence is MIMO+64QAM > DC-HSDPA (with downlink 64QAM activated in at
least one cell) > MIMO+DL 16QAM > DL 64QAM > DC-HSDPA (with downlink 16QAM activated in at
least one cell) > DL enhanced L2 > UL 16QAM > UL enhanced L2 > DTX+DRX > HS-SCCH Less
Operation.
 When MIMO64QAMorDCHSDPASwitch is set to MIMO_64QAM and MIMOor64QAMSwitch to
64QAM, the priority sequence is MIMO+64QAM > DC-HSDPA (with downlink 64QAM activated in at
least one cell) > DL 64QAM > MIMO+DL 16QAM > DC-HSDPA (with downlink 16QAM activated in at
least one cell) > DL enhanced L2 > UL 16QAM > UL enhanced L2 > DTX+DRX > HS-SCCH Less
Operation.
4.3.3 Procedure of DRD for Technological Satisfaction
The procedure for performing DRD for technological satisfaction is as follows:
1. The RNC determines the candidate cells to which blind handovers can be performed. Whether the
neighboring cells support blind handover is specified by the parameter BlindHoFlag. A candidate
cell must meet the following conditions:
DRD."
2. The RNC selects a cell with the highest technical satisfaction as the target cell. If multiple cells have
the highest technical satisfaction, the RNC selects a suitable cell based on DRD for service steering.
Then, if multiple cells have the highest service priority, the RNC selects a suitable cell based on DRD
for load balancing.
The RNC also determines the HSPA technologies for the UE in this step.
If the UE requires the DC-HSPA technology, the RNC searches for a DC-HSPA cell group based on the target cell. If
multiple DC-HSPA cell groups have the highest technical satisfaction, the RNC selects a suitable cell group based on
DRD for service steering. Then, if multiple cell groups have the highest service priority, the RNC selects a suitable cell
group based on DRD for load balancing.

WCDMA RAN
4-5
3. The CAC algorithm makes an admission decision based on the resource status of the cell or cell
group.
− If the admission attempt is successful, the RNC initiates an inter-frequency blind handover to the cell
or cell group.
− If the admission attempt fails, the RNC removes the cell or cell group from the candidate cells and
then checks whether all candidate cells are tried.
a. If there is any candidate cell that has not been tried, the algorithm goes back to step 2 to try this
cell.
b. If all candidate cells have been tried and the service request is an HSPA one, the HSPA request
falls back to a DCH one to retry admission based on R99 service priorities according to the DRD for
service steering and load balancing.
4.4 Inter-Frequency DRD for Service Steering
This section describes the features WRFD-02040004 Traffic Steering and Load Sharing During RAB
Setup.
If the UE requests a service in an area covered by multiple frequencies, the RNC selects the cell with the
highest service priority for UE access, based on the service type of RAB and the definitions of service
priorities in the cells.
The availability of DRD for service steering is specified by the ServiceDiffDrdSwitch parameter.
Inter-Frequency DRD for service steering can also be called Inter-Frequency DRD for traffic steering.
"Inter-frequency DRD for service steering" is called "DRD for service steering" for short in this section.
4.4.1 Cell Service Priorities
A cell service priority is a service-specific priority of a cell among cells under the same coverage. Cell
service priorities help achieve traffic absorption in a hierarchical way.
The service priorities of a cell are set as follows:
1. Run the ADD USPG command to add a service priority group, which is identified by SpgId. This
group includes the service priorities of a cell.
2. Run the ADD UCELLSETUP, MOD UCELLSETUP, or ADD UCELLQUICKSETUP command to
assign the SPG identity to the cell, that is, set the service priorities for the cell.
The SPG to which a cell belongs is independent of DRD for service steering. For example, if the priority of a service is set
to 0 in an SPG, the establishment of this service is impossible in the cells belonging to the SPG, regardless of whether
DRD for service steering is activated or not.
When selecting a target cell for RAB processing, the RNC selects a cell with a high priority, that is, a cell
that has a small value of service priority.
The service priority of a DC-HSDPA cell group is determined by the highest service priority of the two
cells in the group.
Assume that the service priority groups given in the following table are defined on an RNC.

WCDMA RAN
4-6
Cell SPG
Identity
Service Priority
of R99 RT Service
Service Priority
of R99 NRT
Service
Service Priority
of HSDPA
Service
Service Priority
of HSUPA
Service
Service
Priority of
Other
Services
A 1 2 1 1 1 0
B 2 1 2 0 0 0
As shown in the following figure, cell B has a higher service priority of the R99 RT service than cell A. If
the UE requests an R99 RT service in cell A, preferably the RNC selects cell B for the UE to access.
Figure 4-2 Example of DRD for service steering
If the requested service is a combination of multiple services, the RAB with the highest priority is used when a cell is
selected for RAB processing. In addition, the target cell must support all these services.
4.4.2 Procedure of DRD for Service Steering
This section describes the procedure of DRD for service steering when DRD for load balancing is disabled.

WCDMA RAN
4-7
Figure 4-3 Procedure of DRD for service steering
The procedure of DRD for service steering is as follows:
1. The RNC determines the candidate cells to which blind handovers can be performed and sorts the
candidate cells in descending order according to service priority.
A candidate cell must meet the following conditions:
− The candidate cell supports blind handover. Whether the neighboring cells support blind handover is
specified by the parameter BlindHoFlag.
DRD."
2. The RNC selects a target cell from the candidate cells in order of service priority for the UE to access.
If there is more than one cell with the same service priority,
− When the cell, in which the UE requests the service, is one of the candidate cells with the same
service priority, preferably, the RNC selects this cell for admission decision.
− Otherwise, the RNC randomly selects a cell as the target cell.
3. The CAC algorithm makes an admission decision based on the status of the target cell.
 If the admission attempt is successful, the RNC accepts the service request.
 If the admission attempt fails, the RNC removes the cell from the candidate cells and then checks
− If there are any cells where no admission decision has been made, the algorithm goes back to step 2.
− If admission decisions have been made in all the candidate cells, then:
a. If 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. If the service request is a DCH one, the RNC initiates an inter-RAT DRD.
In the case of DC-HSDPA services, if multiple DC-HSDPA cell groups have the highest technical
satisfaction, the RNC selects a cell group with the highest service priority.

WCDMA RAN
4-8
The service priority of a DC-HSDPA cell group is determined by the highest service priority of the two
cells.
4.5 Inter-Frequency DRD for Load Balancing
This section involves the feature WRFD-02040004 Traffic Steering and Load Sharing During RAB Setup.
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 also can be called Inter-Frequency DRD for load sharing.
"Inter-frequency DRD for load balancing" is called "DRD for load balancing" for short in this section.
This section describes the procedure of DRD for load balancing when DRD for service steering is disabled.
4.5.1 Overview of DRD for Load Balancing
DRD for 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 be 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.
4.5.2 Power-Based DRD for Load Balancing
In the Case of Non-DC-HSDPA Services
The following two algorithms are available for power-based load balancing. 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-HSDPA 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 GBP to
achieve load balancing among the cells at different frequencies.
 Algorithm 2: DRD for load balancing is performed according to the DCH equivalent number of users
(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.

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Figure 4-4 shows the procedure of power-based DRD for load balancing.
Figure 4-4 Procedure of power-based DRD for load balancing
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. Note that the selection of target cell is also based
on the resources of the DC-HSDPA cell group when the cell group is involved.
DRD."
2. If the current cell meets the preceding conditions, the RNC proceeds to step 3. Otherwise, the RNC
selects the cell with lowest load from the candidate cell list and goes to step 5.
3. The RNC determines whether the current cell meets the following condition (condition 1).
− For algorithm 1, condition 1 is as follows:

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4-10
a. For DCH service
(ThdAMR,cutcell - Pnon-H,cutcell) > Thdnon-H
Here,
ThdAMR,cutcell is specified by DlConvAMRThd.
Pnon-H,cutcell is the Non-HSDPA power load of the current cell.
Thdnon-H is specified by LdbDRDLoadRemainThdDCH.
b. For HSDPA service
(Thdtotal,cutcell - PGBP,cutcell) > ThdH
Here,
Thdtotal,cutcell is specified by DlCellTotalThd.
PGBP,cutcell is the HS-DSCH GBP load of the current cell.
ThdH is specified by LdbDRDLoadRemainThdHSDPA.
− For algorithm 2, condition 1 is as follows:
a. For DCH service
(ThdAMR,cutcell - PD-enu,cutcell) > Thdnon-H
Here, PD-enu,cutcell is DCH ENU load of the current cell.
b. For HSDPA service
(ThdH-ue,cutcell - PH-ue,,cutcell) / ThdH-ue,cutcell > ThdH
Here,
ThdH-ue,cutcell is specified by MaxHsdpaUserNum.
PH-ue,,cutcell is the total number of HSDPA users of the current cell.
If... Then...
Condition 1 is met For non-DC-HSDPA services:
 If the current cell does not support DC-HSDPA, the service tries
admission to the current cell. Goes to step 5.
 If the DC-HSDPA cell group is selected, the cell with the lowest load is
selected. Goes to step 5.
Condition 1 is not met Goes to step 4.
4. The RNC selects a target cell for the UE to access.
The RNC determines whether any inter-frequency neighboring cell meets the following condition
(condition 2):
 For algorithm 1, condition 2 is as follows:
− For DCH service
(ThdAMR,nbcell - Pnon-H,nbcell) - (ThdAMR,cutcell - Pnon-H,cutcell) > ThdD,loadoffset
(Thdtotal,cutcell - Pload,cutcell) - (Thdtotal,nbcell - Pload,nbcell) < Thdtotal,loadoffset
Here,
ThdAMR,nbcell is specified by DlConvAMRThd.
Pnon-H,nbcell is the Non-HSDPA power load of the neighboring cell.

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ThdD,loadoffset is specified by LdbDRDOffsetDCH.
Pload,cutcell is the sum of the non-HSDPA power and the GBP load of the current cell.
Thdtotal,nbcell is specified by DlCellTotalThd.
Pload,nbcell is the sum of the non-HSDPA power and the GBP load of the neighboring cell.
Thdtotal,loadoffset is specified by LdbDRDTotalPwrProThd.
For HSDPA service
(Thdtotal,nbcell - PGBP,nbcell) - (Thdtotal,cutcell - PGBP,cutcell) > ThdH,loadoffset
(Thdtotal,cutcell - Pload,cutcell) - (Thdtotal,nbcell - Pload,nbcell) < Thdtotal,loadoffset
Here,
PGBP,nbcell is the HS-DSCH GBP load of the neighboring cell.
ThdH,loadoffset is specified by LdbDRDOffsetHSDPA.
 For algorithm 2, condition 2 is as follows:
− For a DCH service
(ThdAMR,nbcell – PD-enu,nbcell) - (ThdAMR,cutcell – PD-enu,cutcell) > ThdD,loadoffset
Here, PD-enu,nbcell is the DCH ENU load of the neighboring cell.
− For an HSDPA service
(ThdH-ue,nbcell – PH-ue,nbcell) / ThdH-ue,nbcell - (ThdH-ue,cutcell – PH-ue,cutcell) / ThdH-ue,cutcell > ThdH,loadoffset
Here,
ThdH-ue,nbcell is specified by MaxHsdpaUserNum.
PH-ue,nbcell is the total number of HSDPA users of the neighboring cell.
Then, the RNC selects the target cell as follows:
 If there is only one inter-frequency neighboring cell that meets the condition 2, 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.
 If the admission attempt is successful, the RNC admits the service request.
 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.

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In the Case of DC-HSDPA Services
If multiple DC-HSDPA cell groups are available after DRD for technical satisfaction and DRD for service
steering, the RNC performs DRD for load balancing.
DRD for load balancing in the case of DC-HSDPA services is similar to that in the case of
non-DC-HSDPA services. The difference is that the former considers cell groups (not individual cells),
calculates the load factors of cell groups, and finally selects a suitable cell group.
After the RNC selects a suitable DC-HSDPA cell group, it determines the primary cell based on the
technical satisfaction and service priorities of the two cells. If the two cells have the same technical
satisfaction and service priority, the RNC performs the following operations:
 If the uplink load balancing switch ULLdbDRDSwitchDcHSDPA is turned off, the RNC selects either
of the two cells as the primary cell.
 If this switch is turned on, the RNC determines the primary cell based on uplink load balancing.
The uplink load balancing mechanism is introduced to prevent RNC from selecting the same cell as the
primary cell for multiple UEs requesting DC-HSDPA services.
The uplink load balancing between the two cells is performed based on the uplink ENU:
During Uplink load balancing, if the serving cell is not in the target DC-HSDPA cell group, the RNC
selects a primary cell with lower load. Otherwise, the RNC checks whether the UL load margin of the
serving cell is higher than the value of ULLdbDRDLoadRemainThdDCHSDPA:
 If the condition is met, the RNC selects the serving cell as the primary cell.
 If the condition is not met, the RNC calculates the difference between the UL load margin of the
serving cell and that of the target cell. Then,
− If the difference is greater than the value of ULLdbDRDOffsetDcHSDPA, the RNC selects the target
cell as the primary cell.
− Otherwise, the RNC selects the serving cell as the primary cell.
4.5.3 Code-Based DRD for Load Balancing
The procedure of code-based DRD for load balancing is similar to that of power-based DRD for load
balancing. The difference is that the RNC considers code resources when selecting a target cell.
The following figure shows the procedure for selecting a target cell based on code resource.

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Figure 4-5 Procedure of code-based DRD for load balancing
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 as follows:
− 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.

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− 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.
4.6 Inter-RAT DRD
When all admission attempts for inter-frequency DRD during RAB processing fail, the RNC determines
whether to initiate an inter-RAT DRD.
The following figure shows the inter-RAT DRD procedure.
Figure 4-6 Inter-RAT DRD procedure
The inter-RAT DRD procedure is as follows:
1. If the current cell is configured with any neighboring GSM cell suitable for blind handover, and if the
"service handover" IE that is contained in the RAB assignment signaling assigned by the CN is set to
"handover to GSM should be performed" or "handover to GSM should not be performed" , then the
RNC performs step 2. Otherwise, the service request undergoes preemption and queuing.
Whether the neighboring cells support blind handover is specified by the parameter BlindHoFlag.
2. The RNC generates a list of candidate DRD-supportive inter-RAT cells that fulfill the quality
requirement. For details, see 3 "RRC DRD". If the candidate cell list does not include any cell, the
service request undergoes preemption and queuing.
3. The RNC selects target GSM cells for the service request according to the blind handover priority.
The blind handover priority of the cell is specified by the parameter BlindHOPrio.
4. If all admission attempts fail or the number of inter-RAT handover retries exceeds the value of
DRMaxGSMNum, the service request undergoes preemption and queuing.

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The Inter-RAT DRD is not applicable to RABs of combined services, R99 PS services, and HSPA services.
4.7 MBDR
This section describes the feature WRFD-020402 Measurement based Direct Retry.
4.7.1 Overview of the MBDR Algorithm
When an RAB is set up, the DRD algorithm uses the blind handover procedure to achieve load balancing
and service steering. In this situation, if the current cell and the DRD target cell cover different areas, the
UE DRD may fail.
After the Measurement Based Directed Retry (MBDR) function is implemented, inter-frequency or
inter-RAT measurement is performed. This ensures good signal quality of the DRD target cell. With this
function, the success rate of inter-frequency or inter-RAT DRD can be ensured even if the current cell
and the DRD target cell cover different areas. The UE access delay, however, is increased.
Note that the MBDR algorithm cannot be used with other non-periodic DRD algorithms simultaneously.
When the MBDR algorithm is enabled, other non-periodic DRD algorithms are automatically disabled.
4.7.2 MBDR Algorithm Switches
The MBDR algorithm switches are InterFreqActiveType and InterRatActiveType. They specify
whether a type of service can use MBDR.
 The following types of service support inter-frequency MBDR:
− CS AMR
− CS non-AMR
− PS R99
− PS HSPA
 Only CS AMR services support inter-RAT MBDR.
4.7.3 Procedure for the MBDR Algorithm
Overview
After an RRC connection setup, the RNC determines whether to establish services in inter-frequency or
inter-RAT cells based on the current cell load and the type of services to be established. If required, the
RNC sends the UE an inter-frequency or inter-RAT measurement control message, instructing the UE to
measure the signal quality of the target cell. If the signal quality of the target cell meets the specified
requirements, the RNC establishes services in the target cell. Otherwise, the RNC attempts to establish
services in the current cell.
The procedure for the inter-frequency MBDR algorithm is as follows:
1. After an RRC connection setup, the MBDR algorithm triggers the measurement of an inter-frequency
MBDR cell if the corresponding MBDR algorithm switch is turned on and the current cell load
exceeds the MBDR congestion decision threshold.
2. The RNC sends the UE an inter-frequency measurement control message, instructing the UE to
measure the signal quality of the inter-frequency MBDR cell. If the signal quality of the
inter-frequency MBDR cell meets the specified requirements, the RNC establishes services in this
cell.
If several inter-frequency MBDR cells are qualified, the RNC prioritizes these cells and establishes
services in the cell with the highest priority.

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3. If services are established successfully, the RAB is set up successfully. Otherwise, the RNC attempts
to establish services in the cell with the second highest priority.
The procedure for the inter-RAT MBDR algorithm is similar to that for the inter-frequency MBDR
algorithm.
Trigger Conditions of MBDR
After an RRC connection setup, if the MBDR algorithm switch for the service type to which this RAB
belongs is turned on, the RNC triggers MBDR when either of the following conditions is met:
 The uplink admission control switch NBMUlCacAlgoSelSwitch is not set to ALGORITHM_OFF, and
the cell is in the MBDR congestion state, that is, the formula {Uplink admission threshold × MBDR
congestion decision threshold ≤ Current cell load factor ≤ Uplink admission threshold } is fulfilled.
 The downlink admission control switch NBMDlCacAlgoSelSwitch is not set to ALGORITHM_OFF,
and the cell is in the MBDR congestion state, that is, the formula {Downlink admission threshold ×
MBDR congestion decision threshold ≤ Current cell load factor ≤ Downlink admission threshold } is
fulfilled.
In the above two formulas:
 The uplink admission threshold is specified by the UlNonCtrlThdForAMR,
UlNonCtrlThdForNonAMR, or UlNonCtrlThdForOther parameter. The downlink admission
threshold is specified by the DlConvAMRThd, DlConvNonAMRThd, or DlOtherThd parameter.
 The MBDR congestion decision threshold is specified by the InterFreqUlMbdrTrigThreshold,
InterFreqDlMbdrTrigThreshold, InterRatUlMbdrTrigThreshold, or InterRatDlMbdrTrigThreshold
parameter.
 The current cell load factor indicates the percentage of the used cell capacity to the total cell capacity.
The current cell load factor in both uplink and downlink is calculated by the RNC according to the cell
load measurement results reported by the NodeB. For details, see the Load Control Parameter
Description.
In the case of inter-RAT MBDR, the RNC triggers MBDR for only a certain percentage of UEs that meet
the trigger conditions. This percentage is specified by the UserPercentage parameter.
MBDR Target Cell Selection
After MBDR is triggered, the RNC starts target cell selection.
If the current cell has only one MBDR neighboring cell, the RNC sends the UE a measurement request,
instructing the UE to measure the signal quality of this neighboring cell. If the measured signal quality
meets the specified requirements, the RNC establishes services in this neighboring cell. If service
establishment fails, the RNC establishes services in the current cell.
If the current cell has more than one MBDR neighboring cell, the following procedure is triggered:
1. The RNC sends the UE a measurement request, instructing the UE to measure the signal quality of
all the MBDR neighboring cells.
2. According to the measurement results, the RNC selects the neighboring cells that meet the specified
requirements as target cells. Note that the neighboring cell in the MBDR congestion state can not be
selected as target cell.
− If only one neighboring cell meets the specified requirements, the RNC establishes services in this
neighboring cell.
− If more than one neighboring cell meets the specified requirements, the RNC prioritizes these cells
based on the value of the MBDRPrio parameter and then establishes services in the cell with the
highest priority. If these cells have the same priority, the RNC randomly selects one of them and then
establishes services in this cell. A smaller value of MBDRPrio indicates a higher priority.

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3. If services fail to be established in the cell with the highest priority, the RNC attempts to establish
services in the cell with the second highest priority. If service establishment still fails, the RNC tries
the neighboring cell with the third highest priority. By this analogy, the RNC establishes services in
the current cell only after the number of attempts exceeds the value of the MaxAttNum parameter or
after the RNC tries all the target cells.
MBDR neighboring cells are specified by the MBDRFlag parameter.
Measurement Control Items
After MBDR is triggered, the RNC sends the UE a measurement control message, instructing the UE to
measure the signal quality of the target cell. After measurement, the UE reports the measurement results
to the RNC.
The parameters associated with measurement control items, for example, the measurement report
mode and trigger threshold, can be configured by running the ADD CELLMBDRINTERFREQ or ADD
CELLMBDRINTERRAT command.
In the case of inter-frequency MBDR, you can:
 Set the InterFreqReportMode parameter to PERIODICAL_REPORTING or EVENT_TRIGGER.
− If the InterFreqReportMode parameter is set to PERIODICAL_REPORTING, the UE reports
measurement results to the RNC at an interval of PrdReportInterval. Then, the RNC determines
whether the signal quality of this inter-frequency cell meets the specified requirements according to
the measurement results and the tigger conditions.
− If the InterFreqReportMode parameter is set to EVENT_TRIGGER, the UE sends the RNC a
measurement report (indicating that the signal quality of the inter-frequency cell meets the
inter-frequency handover requirements) when the signal quality of the inter-frequency cell is higher
than the trigger threshold for the period specified by TrigTime2C.
 Set the InterFreqMeasQuantity parameter to Ec/No, RSCP, or BOTH.
The InterFreqMeasQuantity parameter cannot be set to BOTH if the InterFreqReportMode parameter is set to
EVENT_TRIGGER.
− If the InterFreqMeasQuantity parameter is set to Ec/No, the Ec/No value of the target cell must
reach the inter-frequency handover trigger threshold, which is specified by the HOThdEcN0
parameter.
− If the InterFreqMeasQuantity parameter is set to RSCP, the RSCP value of the target cell must
reach the inter-frequency handover trigger threshold, which is specified by the HOThdRscp
parameter.
− If the InterFreqMeasQuantity parameter is set to BOTH, both the Ec/No and RSCP values of the
target cell must reach the corresponding inter-frequency handover trigger threshold.
In the case of inter-RAT MBDR, you can set the InterRatReportMode parameter to
PERIODICAL_REPORTING or EVENT_TRIGGER.
 If the InterRatReportMode parameter is set to PERIODICAL_REPORTING, the UE reports
measurement results to the RNC at an interval of InterRATPeriodReportInterval. Then, the RNC
compares the measurement results with InterRATHOThd to determine whether the signal quality of
this inter-RAT cell meets the specified requirements.
 If the InterRatReportMode parameter is set to EVENT_TRIGGER, the UE sends the RNC a
measurement report (indicating that the signal quality of the inter-RAT cell meets the inter-RAT
handover requirements) when the signal quality of the inter-RAT cell is higher than the trigger
threshold for the period specified by TrigTime3C.

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The measurement mechanism for inter-frequency or inter-RAT MBDR is the same as that for handover.
For details about the measurement mechanism, see the Handover Parameter Description.

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5-1
5 Periodic DRD
5.1 Overview
5.1.1 Switches for Periodic DRD
The DR_RAB_SING_DRD_SWITCH and DR_RAB_COMB_DRD_SWITCH subparameters of the
DrSwitch parameter determine whether to enable RAB DRD for a single service and a service
combination respectively. The BasedOnMeasHRetryDRDSwitch parameter further determines
whether to enable blind-handover-based non-periodic DRD, blind-handover-based periodic DRD, or
measurement-based periodic DRD.
When the subparameter DR_RAB_SING_DRD_SWITCH or DR_RAB_COMB_DRD_SWITCH is set to
ON, the functions of the BasedOnMeasHRetryDRDSwitch parameter are as follows:
 When the BasedOnMeasHRetryDRDSwitch parameter is set to ON:
− Measurement-based periodic DRD is enabled.
− Blind-handover-based periodic DRD is disabled.
− Blind-handover-based non-periodic DRD is further controlled by the BlindDrdExceptHRetrySwitch
parameter.
 When the BasedOnMeasHRetryDRDSwitch parameter is set to OFF:
− Measurement-based periodic DRD is disabled.
− Blind-handover-based periodic DRD is enabled if the ChannelRetryTimerLen parameter is not set
to 0.
− Blind-handover-based non-periodic DRD is enabled.
5.1.2 Triggering of Periodic DRD
Periodic DRD is triggered by the HSPA/HSPA+ retry. The HSPA/HSPA+ retry can be performed after the
bearer scheme of a service is changed, for example, after RAB setup, RAB modification, soft handover,
hard handover, or best cell change.
After the bearer scheme of a service is changed, the RNC determines whether the UE can be served by
a better HSPA/HSPA+ technology by considering the technological satisfaction. If a better HSPA/HSPA+
technology can be used, the HSPA/HSPA+ retry is performed and consequently periodic DRD is
triggered. In this way, a suitable cell can be selected to serve the UE with a better HSPA/HSPA+
technology.
Measurement-based periodic DRD can also be triggered when a neighboring cell has a higher service
priority than the current cell. In this way, service steering is achieved.
In different situations, HSPA/HSPA+ technologies that can trigger HSPA/HSPA+ retry and consequently
periodic DRD are different. The conditions on which an HSPA/HSPA+ technology can trigger
HSPA/HSPA+ retry and consequently periodic DRD are as follows:
 The HSPA+ technology must be selected through RetryCapability parameter.
This condition does not apply to the HSPA technologies.
 The HSPA/HSPA+ technology must be supported by periodic DRD.
Note that different types of periodic DRD support different HSPA/HSPA+ technologies.

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− For blind-handover-based periodic DRD, the supported HSPA/HSPA+ technologies are HSUPA,
HSDPA, 64QAM, MIMO, and DC-HSDPA.
− For measurement-based periodic DRD, the supported HSPA/HSPA+ technologies are HSDPA,
HSUPA, uplink enhanced L2, uplink 16QAM, downlink enhanced L2, CPC, 64QAM, DC-HSDPA, and
MIMO.
The reason why measurement-based periodic DRD supports more HSPA+ technologies than
blind-handover-based periodic DRD is as follows: When measurement-based periodic DRD is enabled,
non-periodic DRD may not be applied. In such a case, the HSPA+ technologies that are supported by
non-periodic DRD can be supported by measurement-based periodic DRD. In this way, the function of
non-periodic DRD can be indirectly implemented through measurement-based periodic DRD.
When measurement-based periodic DRD is enabled, whether non-periodic DRD can be applied is further determined by
the BlindDrdExceptHRetrySwitch parameter. For details, see 4 “Non-periodic DRD.”
5.2 Periodic DRD Procedure
5.2.1 Blind-Handover-Based Periodic DRD
Blind-handover-based periodic DRD applies to the inter-frequency same-coverage scenarios. It is
performed at regular intervals. The interval is specified by the ChannelRetryTimerLen parameter.
Figure 5-1 shows the procedure of blind-handover-based periodic DRD.
Figure 5-1 Procedure of blind-handover-based periodic DRD
The procedure of blind-handover-based periodic DRD is as follows:
1. The RNC decides whether candidate cells that the UE can retry accessing exist. The candidate cells
are selected from the same-coverage neighboring cells of the current best cell. A candidate cell must
meet the following conditions:

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− The frequency of the cell is within the band supported by the UE.
− The cell supports the requested service.
− The cell is not overloaded.
− The HSPA+ technological satisfaction of the cell is higher than that of the current cell.
If such candidate cells do not exist, the procedure of blind-handover-based periodic DRD fails. In such
a case, the RNC waits for the next DRD period.
If such candidate cells exist, the following step is performed.
2. The RNC sequences the candidate cells according to the HSPA+ technological satisfaction.
3. The RNC selects a target cell for UE access according to the sequence from the highest to the
lowest.
 If the admission attempt fails, the RNC removes the cell from the candidate cells and then checks
− If admission decisions fail in all the candidate cells, the procedure of blind-handover-based periodic
DRD fails. In such a case, the RNC waits for the next DRD period.
5.2.2 Measurement-Based Periodic DRD
In a multi-band network, the cells that operate on different frequency bands have different coverage
areas. When a UE needs to perform an inter-frequency handover in a multi-band network, it normally
does not perform a blind handover as the success rate of the blind handover is relatively low. Instead,
the UE performs handover decision according to the signal of each inter-frequency cell.
Measurement-based periodic DRD is introduced to select a signal-qualified cell for the UE to access.
Measurement-based periodic DRD applies to both the inter-frequency same-coverage scenarios and the
inter-frequency different-coverage scenarios. It can increase the DRD success rate in both the
same-coverage scenarios and the different-coverage scenarios.
Figure 5-2 shows the procedure of measurement-based periodic DRD.

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Figure 5-2 Procedure of measurement-based periodic DRD
The procedure of measurement-based periodic DRD is as follows:
1. Based on HSPA+ technological satisfaction and cell service priority, the RNC decides whether
candidate cells that the UE can retry accessing exist. The candidate cells are selected from the best
cell and its neighboring cells.
A candidate cell must meet the following conditions:
− The frequency of the cell is within the band supported by the UE.
− The cell supports the requested service.
− The DrdOrLdrFlag parameter of the cell is set to True, indicating that the cell can be measured.
− The HSPA+ technological satisfaction of the cell is higher than that of the current cell, or the service
priority of the cell is higher than or equal to that of the current cell.
For details about the HSPA+ technological satisfaction and cell service priority, see the Load Control
Feature Parameter Description.
If such candidate cells exist, the following step is performed.
2. The RNC starts the timer for periodic DRD. The length of the timer is specified by the
HRetryTimerLength parameter.
− If there is only one candidate cell and it is the current cell, the UE retries higher HSPA+ technologies
in the current cell when the timer expires.
− In other situations, the RNC issues a measurement control message, requesting the UE to measure
the signal quality of all candidate cells.
3. The UE measures the RSCP and Ec/No of the candidate cells and periodically reports the
measurement results to the RNC. The reporting period is specified by the PrdReportInterval
parameter.

WCDMA RAN
5-5
4. Based on the received measurement results, the RNC selects the candidate target cells.
A candidate target cell must meet the following conditions:
− The cell is not overloaded.
− The measured RSCP is higher than the RSCP threshold that is specified by the TargetFreqThdRscp
parameter.
− The measured Ec/No is higher than the Ec/No threshold that is specified by the TargetFreqThdEcN0
parameter.
If such candidate target cells do not exist, the procedure of measurement-based periodic DRD fails. In
such a case, the RNC waits for the DRD timer to expire.
If such candidate target cells exist, the following step is performed.
5. The RNC sequences the candidate target cells according to the HSPA+ technological satisfaction
and cell service priority.
6. The RNC selects a candidate target cell for UE access according to the sequence from the highest to
the lowest.
7. The CAC algorithm makes an admission decision based on the status of the candidate target cell.
 If the admission attempt fails, the RNC removes the cell from the candidate target cells and then
checks whether all candidate target cells are tried.
− If admission decisions fail in all the candidate target cells, the procedure of measurement-based
periodic DRD fails. In such a case, the RNC waits for the DRD timer to expire.
If the measurement or retry fails during the procedure of measurement-based periodic DRD, a failure
penalty timer is started when the DRD timer expires. During the penalty time, such a procedure cannot
be performed and the UE can retry accessing only the current cell. The length of the penalty timer is
specified by multiplying the value of the HRetryTimerLength parameter by the value of the
DrdFaiPenaltyPeriodNum parameter.

WCDMA RAN
Directed Retry Decision 6 Parameters
6-1
6 Parameters
Table 6-1 Parameter description
Parameter ID NE MML Command Description
BasedOnMeasH
RetryDRDSwitc
h
BSC6
900
SET
UDRD(Optional)
Meaning: Controls the validity of the measurement-based
DRD algorithm. Assume that the DRD algorithm is enabled. If
the switch is on, the RNC uses the DRD algorithm based on
the measurement (for measuring the signals in the
neighboring cell of the best cell). You can run the "SET
UMCDRD" command to configure the related parameters. If
the switch is off, the RNC implements the DRD algorithm
based on blind handovers. Note: When the
measurement-based DRD algorithm is used, you need to
measure the signal quality of the target cell before a DRD
retry. This cell can act as the actual target cell only when its
signal quality meets the preset threshold. The
measurement-based DRD is performed only for the periodic
retry flow.
GUI Value Range: OFF, ON
Actual Value Range: OFF, ON
Unit: None
Default Value: OFF
BlindDrdExcept
HRetrySwitch
BSC6
900
ADD
UCELLMCDRD(Op
tional)
MOD
UCELLMCDRD(Op
tional)
Meaning: When the measurement-based DRD is performed,
this parameter is used to determine whether the DRD retry
for blind handover is performed in aperiodic mode. The
aperiodic retry includes the setup of the RAB, modification of
the RAB, and DCCC channel handover.
If this parameter is set to "ON", the DRD retry for blind
handover is performed in aperiodic mode.
If this switch is set to "OFF", the DRD retry for blind handover
is not performed in aperiodic mode.
GUI Value Range: OFF, ON
Actual Value Range: OFF, ON
Unit: None
Default Value: OFF
ChannelRetryTi
merLen
BSC6
900
SET
UCOIFTIMER(Opti
onal)
Meaning: This parameter specifies the value of the channel
retry timer. The timer will start when traffic is set up or
reconfigured and some higher technique is not configured by
some reason except for the capability of UE or cell. Channel
retry will be performed after this timer expires.
GUI Value Range: 0~180
Actual Value Range: 0~180
Unit: s
Default Value: 5

WCDMA RAN
6-2
CodeBalancing
DrdCodeRateTh
d
BSC6
900
ADD
UCELLDRD(Option
al)
MOD
UCELLDRD(Option
al)
Meaning: One of the triggering conditions of code balancing
DRD. The other condition is the minimum spreading factor.
Code balancing DRD is applied only when the code
occupancy in the best cell is not lower than the value of this
parameter.
Unit: %
Default Value: 13
CodeBalancing
DrdMinSFThd
BSC6
900
ADD
UCELLDRD(Option
al)
MOD
UCELLDRD(Option
al)
Meaning: One of the triggering conditions of code balancing
DRD. The other condition is the code occupancy threshold.
Code balancing DRD is applied only when the minimum
spreading factor in the best cell is not lower than the value of
this parameter.
GUI Value Range: SF4, SF8, SF16, SF32, SF64, SF128,
SF256
Actual Value Range: SF4, SF8, SF16, SF32, SF64, SF128,
SF256
Unit: None
Default Value: SF8
CodeBalancing
DrdSwitch
BSC6
900
ADD
UCELLDRD(Option
al)
MOD
UCELLDRD(Option
al)
Meaning: Whether to apply the code balancing DRD
algorithm. The "DR_RAB_SING_DRD_SWITCH" parameter
in "SET UCORRMALGOSWITCH" needs to be enabled. For
combination services, the
"DR_RAB_COMB_DRD_SWITCH" parameter needs to be
enabled.
GUI Value Range: ON, OFF
Actual Value Range: ON, OFF
Unit: None
Default Value: OFF
ConnectFailRrc
RedirSwitch
BSC6
900
SET
UDRD(Optional)
Meaning: RRC redirection switch used in the case of
admission failure. It is valid only when the
"DR_RRC_DRD_SWITCH" parameter is set to ON.
- OFF indicates that the RRC redirection is not allowed.
- Only_To_Inter_Frequency indicates that only RRC
redirection to inter-frequency cells is allowed.
- Allowed_To_Inter_RAT indicates that both RRC redirection
to inter-frequency cells and redirection to inter-RAT cells are
allowed.
GUI Value Range: OFF, Only_To_Inter_Frequency,
Allowed_To_Inter_RAT
Actual Value Range: OFF, Only_To_Inter_Frequency,
Allowed_To_Inter_RAT
Unit: None
Default Value: Only_To_Inter_Frequency

WCDMA RAN
6-3
DeltaCodeOccu
piedRate
BSC6
900
SET
UDRD(Optional)
Meaning: Threshold of code occupancy offset between the
current cell and the target cell when code balancing DRD is
applied. Only when the cell code occupancy offset reaches
this threshold can a neighboring cell be selected to be a
candidate cell for DRD.
Unit: %
Default Value: 7
DlCellTotalThd BSC6
900
ADD
UCELLCAC(Option
al)
MOD
UCELLCAC(Option
al)
Meaning: Admission threshold of the total cell downlink
power. If the value is too high, too many users will be
admitted. However, the throughput of a single user is easy to
be limited. If the value is too low, cell capacity will be wasted.
Actual Value Range: 0~1, step:0.01
Unit: %
Default Value: 90
DlConvAMRThd BSC6
900
ADD
UCELLCAC(Option
al)
MOD
UCELLCAC(Option
al)
Meaning: The percentage of the conversational AMR service
threshold to the 100% downlink load. It is applicable to
algorithm 1 and algorithm 2. The parameter is used for
controlling the AMR service admission. That is, when an
AMR service is accessing, the RNC evaluates the
measurement value of the downlink load after the service is
accessed. If the DL load of a cell is higher than this threshold
after the access of an AMR speech service, this service will
be rejected. If the DL load of a cell will not be higher than this
threshold, this service will be admitted.
The DL load factor thresholds include parameters of [DL
threshold of Conv non_AMR service], [DL handover access
threshold] and [DL threshold of other services]. The four
parameters can be used to limit the proportion between the
conversational service, handover user and other services in
a specific cell, and to guarantee the access priority of the
conversational AMR service.
Unit: %
Default Value: 80

WCDMA RAN
6-4
DlConvNonAMR
Thd
BSC6
900
ADD
UCELLCAC(Option
al)
MOD
UCELLCAC(Option
al)
Meaning: The percentage of the conversational non-AMR
service threshold to the 100% downlink load. It is applicable
to algorithm 1 and algorithm 2. The parameter is used for
controlling the non-AMR service admission. That is, when a
non-AMR service is accessing, the RNC evaluates the
measurement value of the downlink load after the service is
accessed. If the DL load of a cell is higher than this threshold
after the access of a non-AMR speech service, this service
will be rejected. If the DL load of a cell will not be higher than
this threshold, this service will be admitted.
a specific cell, and to guarantee the access priority of the
conversational non-AMR service.
Unit: %
Default Value: 80
DlOtherThd BSC6
900
ADD
UCELLCAC(Option
al)
MOD
UCELLCAC(Option
al)
Meaning: The percentage of other service thresholds to the
100% downlink load. The services refer to other admissions
except the conversational AMR service, conversational
non-AMR service, and handover scenarios. It is applicable to
algorithm 1 and algorithm 2. The parameter is used for
controlling other service admissions. That is, when a service
is accessing, the RNC evaluates the measurement value of
the downlink load after the service is accessed. If the DL load
of a cell is higher than this threshold after the access of a
service, this service will be rejected. If the DL load of a cell
will not be higher than this threshold, this service will be
admitted.
a specific cell, and to guarantee the access priority of other
services.
Unit: %
Default Value: 75

WCDMA RAN
6-5
DRDEcN0Thres
hhold
BSC6
900
ADD
U2GNCELL(Option
al)
MOD
U2GNCELL(Option
al)
Meaning: DRD Ec/No threshold for determining whether to
perform the blind handover. The DRD is permitted if Ec/No of
the current cell is greater than the DRD Ec/No threshold of a
inter-RAT/inter-frequency neighboring cell.
GUI Value Range: -24~0
Actual Value Range: -24~0
Unit: dB
Default Value: -18
DrdFaiPenaltyP
eriodNum
BSC6
900
ADD
UCELLMCDRD(Op
tional)
MOD
UCELLMCDRD(Op
tional)
Meaning: Number of retry periods in the interval between a
failure of a measurement-based DRD re-attempt and the
initiation of the next DRD re-attempt. If this parameter is set
to a great value, the probability of a user re-accessing a cell
with a high priority becomes low; If this parameter is set to a
small value, the probability of a user re-accessing a cell with
a high priority becomes high; however, the performance is
greatly affected. Note: The process of a
measurement-based DRD retry is as follows: At the
beginning, the RNC determines to enable the DRD retry;
then, it starts inter-frequency measurement control; next, the
RNC receives the measurement report from a UE; after that,
the RNC retries the access to a cell in the reported DRD cell
list. The process ends until the cell access succeeds.
Unit: None
Default Value: 10
DrdOrLdrFlag BSC6
900
ADD
UINTERFREQNCE
LL(Optional)
MOD
UINTERFREQNCE
LL(Optional)
Meaning: Specify the flags of the cells that the DRD
measurement or LDR measurement is performed.
The value "TRUE" indicates that the cell can be considered
as the measurement object in the DRD measurement
algorithm or LDR measurement algorithm. The value
"FALSE" indicates that the cell is invalid.
GUI Value Range: FALSE(Do not send), TRUE(Send)
Actual Value Range: FALSE, TRUE
Unit: None
Default Value: False
DRMaxGSMNu
m
BSC6
900
ADD
UCELLDRD(Option
al)
MOD
UCELLDRD(Option
al)
Meaning: Maximum number of inter-RAT RAB directed
retries. It decides the size of the candidate set for inter-RAT
DRD. The value 0 indicates that inter-RAT RAB DRD is not
applicable. This parameter can be cell-oriented.
Unit: None
Default Value: 2

WCDMA RAN
6-6
DrSwitch BSC6
900
SET
UCORRMALGOS
WITCH(Optional)
Meaning: Direct retry switch group.
1) DR_RRC_DRD_SWITCH(DRD switch for RRC
connection): When the switch is on, DRD and redirection is
performed for RRC connection if retry is required.
2) DR_RAB_SING_DRD_SWITCH(DRD switch for single
RAB): When the switch is on, DRD is performed for single
service if retry is required.
3) DR_RAB_COMB_DRD_SWITCH(DRD switch for
combine RAB): When the switch is on, DRD is performed for
combined services if retry is required.
GUI Value Range: DR_RRC_DRD_SWITCH,
DR_RAB_SING_DRD_SWITCH,
DR_RAB_COMB_DRD_SWITCH
Actual Value Range: DR_RRC_DRD_SWITCH,
DR_RAB_SING_DRD_SWITCH,
DR_RAB_COMB_DRD_SWITCH
Unit: None
Default Value: None
HOThdEcN0 BSC6
900
ADD
UCELLMBDRINTE
RFREQ(Optional)
MOD
UCELLMBDRINTE
RFREQ(Optional)
Meaning: Threshold of signal quality of the target frequency
for triggering inter-frequency(Ec/No) measurement.
If the mode is set to event mode, this parameter is used to
set measurement control on the event 2C.
If the mode is set to periodical mode, this parameter is used
to estimate the periodical reports and only if quality of the
target frequency is beyond the threshold, the DRD procedure
is triggered.
GUI Value Range: -24~0
Actual Value Range: -24~0
Unit: dB
Default Value: -16
HOThdRscp BSC6
900
ADD
UCELLMBDRINTE
RFREQ(Optional)
MOD
UCELLMBDRINTE
RFREQ(Optional)
Meaning: Threshold of signal quality of the target frequency
for triggering inter-frequency(RSCP) measurement.
If the mode is set to event mode, this parameter is used to
set measurement control on the event 2C.
If the mode is set to periodical mode, this parameter is used
to estimate the periodical reports and only if quality of the
target frequency is beyond the threshold, the DRD procedure
is triggered.
GUI Value Range: -115~-25
Actual Value Range: -115~-25
Unit: dB
Default Value: -92

WCDMA RAN
6-7
HRetryTimerLen
gth
BSC6
900
ADD
UCELLMCDRD(Op
tional)
MOD
UCELLMCDRD(Op
tional)
Meaning: Specifies the time length of the
measurement-based DRD periodic retry timer. After the
service is set up or the data reconfiguration is complete, and
if the service data can be carried by the neighboring cell
applied with an advanced technology or carried by the HCS
cell with a higher priority, you need to enable the
measurement-based DRD periodic retry timer, initiate an
inter-frequency measurement for the DRD inter-frequency
neighboring cell, and initiate the channel retry when the
inter-frequency measurement report from the UE is received.
When the timer expires, the channel retry can be initiated
only in this cell. If this parameter is set to a greater value, the
probability for subscribers to re-access the cell with a high
priority becomes low. If this parameter is set to a smaller
value, the probability for subscribers to re-access the cell
with a high priority becomes high.
Unit: s
Default Value: 10
InterFreqActiveT
ype
BSC6
900
ADD
UCELLMBDRINTE
RFREQ(Optional)
MOD
UCELLMBDRINTE
RFREQ(Optional)
Meaning: MBDR switch
GUI Value Range: CSAMR_INTERFREQ(CS AMR
inter-frequency switch), CSNONAMR_INTERFREQ(CS non
AMR inter-frequency switch), PSR99_INTERFREQ(PSR99
inter-frequency switch), PSHSPA_INTERFREQ(PSHSPA
inter-frequency switch)
Actual Value Range: CSAMR_INTERFREQ,
CSNONAMR_INTERFREQ, PSR99_INTERFREQ,
PSHSPA_INTERFREQ
Unit: None
Default Value: None
InterFreqDlMbdr
TrigThreshold
BSC6
900
ADD
UCELLMBDRINTE
RFREQ(Optional)
MOD
UCELLMBDRINTE
RFREQ(Optional)
Meaning: This parameter is the relative threshold of cell for
judging whether downlink MBDR algorithm of inter frequency
is in overload state. It represents the percentage of the cell
admission control threshold of downlink. The smaller this
parameter is, the earlier downlink MBDR algorithm of inter
frequency goes into overload state. When cell load is higher
than the product of downlink cell admission control threshold
and this parameter, and is lower than the downlink cell
admission control threshold, downlink MBDR algorithm of
inter frequency is in overload state.
Unit: None
Default Value: 80

WCDMA RAN
6-8
InterFreqMeasQ
uantity
BSC6
900
ADD
UCELLMBDRINTE
RFREQ(Optional)
MOD
UCELLMBDRINTE
RFREQ(Optional)
Meaning: Measurement quantity used in
measurement-based inter-frequency measurement in event
(2C) triggered or periodical reporting mode.
- CPICH: Common Pilot Channel
- Ec/No: Signal-to-Noise Ratio
- RSCP: Received Signal Code Power
- CPICH_Ec/No: to use the Ec/No measurement quantity for
event 2C or Inter-Frequency periodical measurement. The
physical unit is dB.
- CPICH_RSCP: to use the RSCP measurement quantity for
event 2C or Inter-Frequency periodical measurement. The
physical unit is dBm.
- BOTH:both quantities of the target cell must be satisfied
when performing the handover judgement.Valid when the
Inter-Frequency measurement chooses
PERIODICAL_REPORTING Mode. Recommended value
(default value): BOTH(PERIODICAL_REPORTING Mode),
CPICH_RSCP(EVENT_TRIGGER Mode)
GUI Value Range: CPICH_EC/NO, CPICH_RSCP, BOTH
Actual Value Range: CPICH_EC/NO, CPICH_RSCP, BOTH
Unit: None
Default Value: CPICH_EC/NO

WCDMA RAN
6-9
InterFreqReport
Mode
BSC6
900
ADD
UCELLINTERFRE
QHOCOV(Optional
)
MOD
UCELLINTERFRE
QHOCOV(Optional
)
Meaning: Inter-frequency measurement report mode.
If this parameter is set to PERIODICAL_REPORTING,
measurement reports are periodically reported. If this
parameter is set to EVENT_TRIGGER, measurement reports
are reported by triggering the event.
There are two inter-frequency handover report modes in the
RNC, namely, event-triggered report and periodical report.
The report mode is selected by setting the inter-frequency
report mode switch that is RNC-oriented.
Event-triggered report mode
In this mode, event 2B is used to decide whether to trigger
inter-frequency handover. This prevents the ping-pong
handover (The quality of the currently used frequency is
lower than the absolute threshold "used frequency quality
threshold", and the quality of the unused frequency is higher
than another absolute threshold "target frequency trigger
threshold"). Event 2B cannot change from event-triggered
mode to periodical mode. When event-triggered
measurement report mode is selected, Ec/No and RSCP are
both used as the measurement quantity for inter-frequency
measurement.The advantage of event-triggered report mode
is that the signaling transmission and processing load are
saved. Comparing the signal quality between intra-frequency
and inter-frequency handovers, the ping-pong effect in
handover is prevented to some extent. The disadvantage of
event-triggered report mode is that the event is reported only
once and cannot be changed to periodical mode. For the
cell-oriented algorithm parameters, each time when the best
cell is updated, the inter-frequency measurement parameters
should be updated accordingly.
Periodical report mode
In this mode, event 2D/2F is used to start and stop the
compressed mode, and to periodically report the
inter-frequency cell measurement result in compressed
mode. When the cell quality reported by the UE is higher
than the absolute threshold plus hysteresis, the triggering
delay timer is started. If the conditions are always met before
the timer expires, the inter-frequency handover is started
after the timer expires.
If the handover fails, the handover decision is performed,
according to the periodical inter-frequency measurement
report.
The advantage of the periodical measurement report mode is
that it can repeatedly perform direct retry on the same cell
when the handover fails, and that the following algorithms
can be flexibly developed. For the cell-oriented algorithm
parameters, the UE need not be informed through signaling
but the cell need be updated only when the handover
decision is performed in the RNC. The disadvantage of the
periodical measurement report mode is that it requires large
amount of signaling and increases the load on the air
interface and for signaling processing.
As for the impact on network performance,the two

WCDMA RAN
6-10
measurement report modes have both advantages and
disadvantages. Currently, the traditional periodical report
mode is preferred.
GUI Value Range: PERIODICAL_REPORTING(Periodical
reporting), EVENT_TRIGGER(Event trigger)
Actual Value Range: PERIODICAL_REPORTING,
EVENT_TRIGGER
Unit: None
Default Value: PERIODICAL_REPORTING
InterFreqUlMbdr
TrigThreshold
BSC6
900
ADD
UCELLMBDRINTE
RFREQ(Optional)
MOD
UCELLMBDRINTE
RFREQ(Optional)
judging whether uplink MBDR algorithm of inter frequency is
in overload state. It represents the percentage of the cell
admission control threshold of uplink. The smaller this
parameter is, the earlier uplink MBDR algorithm of inter
frequency goes into overload state. When cell load is higher
than the product of uplink cell admission control threshold
and this parameter, and is lower than the uplink cell
admission control threshold, uplink MBDR algorithm of inter
frequency is in overload state.
Unit: None
Default Value: 80

WCDMA RAN
6-11
InterRatActiveTy
pe
BSC6
900
ADD
UCELLMBDRINTE
RRAT(Optional)
MOD
UCELLMBDRINTE
RRAT(Optional)
Meaning: MBDR switch
GUI Value Range: CSAMR_INTERRAT(CS AMR inter-RAT
switch)
Actual Value Range: CSAMR_INTERRAT
Unit: None
Default Value: None
InterRatDlMbdrT
rigThreshold
BSC6
900
ADD
UCELLMBDRINTE
RRAT(Optional)
MOD
UCELLMBDRINTE
RRAT(Optional)
judging whether downlink MBDR algorithm of inter RAT is in
overload state. It represents the percentage of the cell
admission control threshold of downlink. The smaller this
parameter is, the earlier downlink MBDR algorithm of inter
RAT goes into overload state. When cell load is higher than
the product of downlink cell admission control threshold and
this parameter, and is lower than the downlink cell admission
control threshold, downlink MBDR algorithm of inter RAT is in
overload state.
Unit: None
Default Value: 80

WCDMA RAN
6-12
InterRATHOThd BSC6
900
ADD
UCELLMBDRINTE
RRAT(Optional)
MOD
UCELLMBDRINTE
RRAT(Optional)
Meaning: Quality requirement for the inter-RAT cell during an
inter-RAT handover with CS domain services.
This parameter is used to set measurement control on the
event 3C. The event 3C is triggered when the signal quality
of the target frequency is above this threshold. Note that the
value 0 indicates that the physical value is smaller than -110
dBm.
If the periodical report mode is used, the inter-RAT handover
decision thresholds are used for the assessment of inter-RAT
coverage handover, namely as Tother_RAT in the following
formulas. The inter-RAT handover decision thresholds are
the absolute thresholds (RSSI) of inter-RAT cell quality for
the inter-RAT handover decision.
If the quality of another RAT in the inter-RAT measurement
report meets the following condition:
Mother_RAT + CIO >= Tother_RAT + H/2
the system starts the trigger timer and implements the
handover decision after timeout. If the quality of the
preceding RAT meets the following condition before timeout:
Mother_RAT + CIO < Tother_RAT - H/2
The system stops the timer, and the RNC waits for another
inter-RAT measurement report.
In which,
Mother_RAT indicates the measurement result of the GSM
RSSI;
Tother_RAT indicates the inter-RAT handover decision
threshold;
Cell Individual Offset (CIO) indicates the offset of the
inter-RAT cell;
H represents the hysteresis. Hysteresis can reduce wrong
decisions caused by signal jitters.
The sensitivity of a GSM mobile phone is -102 dBm, so the
outdoor reception level should not be lower than -90 dBm,
considering a margin of 3 dB for compensation of fast fading,
5 dB for compensation of slow fading, 2 dB for compensation
of interference noise, and 2 dB for compensation of ambient
noise.
The values of inter-RAT handover decision thresholds vary
with the handover policy. To have UEs hand over only to the
GSM cells with high quality, you can set the inter-RAT
handover decision threshold to a comparatively high value,
for example -85 dBm.
Actual Value Range: lower than -110, -110~-48(Actual value
meets the condition: Actual Value = GUI Value - 111)
Unit: dBm
Default Value: 21

WCDMA RAN
6-13
InterRATPeriod
ReportInterval
BSC6
900
ADD
UCELLINTERRAT
HOCOV(Optional)
MOD
UCELLINTERRAT
HOCOV(Optional)
Meaning: Interval that the UE reports inter-RAT
measurement results to the RNC.
This parameter specifies the interval that the UE sends
inter-RAT measurement results to the RNC in periodical
reporting mode. It is not recommended that this parameter is
set to NON_PERIODIC_REPORT since the UE behavior
may be unknown.
The GSM RSSI measurement period is 480 ms. Therefore,
the inter-RAT periodical reporting interval should be longer
than 480 ms. If the periodical reporting interval is excessively
high, the handover decision time will be long, and handovers
will be slow.
The adjustment should be made according to the configured
GSM RSSI measurement compressed mode sequence.
According to the current configured GSM RSSI
measurement compressed mode sequence, the RSSI
measurement of eight GSM cells can be finished in 480 ms.
Therefore, the RSSI measurement of 16 GSM cells can be
finished in 1000 ms. According to 3GPP specifications, the
number of inter-RAT neighboring cells should not exceed 32.
Therefore, the parameter value can be set to 2000 ms if the
number of neighboring GSM cells exceeds 16.
The setting of this parameter has impact on the Uu signaling
traffic. If the period is too short and the reporting frequency is
too high, the RNC may have high load in processing
signaling. If the period is too long, the network cannot detect
the signal changes in time, which may delay the inter-RAT
handover and thus cause call drops.
GUI Value Range: NON_PERIODIC_REPORT(Non
periodical reporting), D250~1 D500~2 D1000~3 D2000~4
D3000~5 D4000~6 D6000~7 D8000~8 D12000~9
D16000~10 D20000~11 D24000~12 D28000~13
D32000~14 D64000
Actual Value Range: NON_PERIODIC_REPORT, 250, 500,
1000, 2000, 3000, 4000, 6000, 8000, 12000, 16000, 20000,
24000, 28000, 32000, 64000
Unit: ms
Default Value: D1000

WCDMA RAN
6-14
InterRatReportM
ode
BSC6
900
ADD
UCELLINTERRAT
HOCOV(Optional)
MOD
UCELLINTERRAT
HOCOV(Optional)
Meaning: Inter-RAT measurement reporting mode.
When PERIODICAL_REPORTING is selected, the periodical
reporting is used for inter-RAT measurement. When
EVENT_TRIGGER is selected, the event-triggered reporting
is used for inter-RAT measurement.
The RNC provides two inter-RAT measurement reporting
modes, event-triggered reporting and periodical reporting.
Event-triggered reporting
To avoid the ping-pong effect before and after the inter-RAT
handover, use event 3A (quality of the currently used
frequency is lower than the absolute threshold and the signal
level of the GSM cell is higher than another absolute
threshold) as the triggering event that determines the
inter-RAT handover. To improve the handover success rate,
the BSIC of the GSM cell whose event 3A needs to be
triggered must be decoded correctly by the UE. The reporting
mode of event 3A is not changed from event-triggered
reporting to periodical reporting. Therefore, no handover
re-attempt is made when the handover fails unless event 3A
is triggered in this cell again.
The advantage of event-triggered reporting is that the
signaling transmission and processing load are saved.
Comparing the signal quality between intra-frequency and
inter-frequency handovers, the ping-pong effect in handover
is prevented to some extent. The drawback of
event-triggered reporting is that the event is reported only
once and cannot be changed to periodical reporting. For the
cell-oriented algorithm parameters, each time when the best
cell is updated, the inter-frequency measurement parameters
should be updated accordingly.
Periodical reporting
When the quality of the GSM cell reported by the UE meets
the criteria for inter-RAT handover, the delay trigger timer is
started. If the quality of the GSM cell always meets the
criteria for inter-RAT handover before timeout, the inter-RAT
handover is triggered after the delay trigger timer expires.
For the GSM cell whose BSIC can be decoded correctly, a
shorter delay trigger time should be set to indicate the high
priority attribute of the GSM cell. For the GSM cell whose
BSIC is not verified, a longer delay trigger time should be set
to indicate the low priority attribute of the GSM cell. In this
manner, the BSIC can be decoded faster.
If the handover fails, the handover re-attempt is made again
according to the periodical inter-RAT measurement report.
The advantage of periodical reporting is that it can be used
for repeated handover re-attempts on the same cell when the
handover fails, and that subsequent algorithms can be
flexibly developed. In addition, for the cell-oriented algorithm
parameters, the RNC updates the parameters when making
internal handover decision and the system needs not to
inform the UEs of the parameter change through signaling
messages after the handovers. The drawback of periodical
reporting is that it requires large amount of signaling and

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