LDR actions include inter-frequency load handover, BE rate reduction, QoS renegotiation for uncontrollable real-time services, inter-RAT handover in the CS domain, inter-RAT handover in the PS domain, AMR rate reduction, code reshuffling, and MBMS power reduction.
9.3.1 Inter-Frequency Load Handover
The inter-frequency load handover algorithm is restricted by the inter frequency hard handover algorithm switch. Inter-frequency load handover can be performed only when the inter frequency hard handover algorithm is enabled.
The LDR algorithm performs the following steps:
1. The algorithm checks whether cells for inter-frequency blind handover are available. If available, the algorithm goes to the next step. Otherwise, the action fails, and the algorithm takes the next action.
2. The algorithm selects the target cell according to the type of resource that causes the basic congestion:
− If the basic congestion is caused by power resource:
The algorithm checks whether the load margin of the target cell is higher than both UlInterFreqHoCellLoadSpaceThd and DlInterFreqHoCellLoadSpaceThd and whether the load of the target cell is normal.
If the margin is not higher than the threshold, the action fails, and the algorithm takes the next action.
If there is more than one cell meeting the requirements, the first one is selected as the blind handover target cell.
− If the basic congestion is caused by code resource:
Whether there are blind handover target cells meeting the requirements is decided by the following conditions:
a. The minimum SF of the target cell is not greater than that of the current cell.
b. The difference of code usage between the current cell and the target cell is greater than LdrCodeUsedSpaceThd.
c. The state of target cell is normal.
If there is no such cell, this action fails and the algorithm takes the next action. If there is more than one cell meeting the requirements, the first cell is selected as the blind handover target cell.
The load margin refers to the difference between the load of the target cell and the basic congestion triggering threshold of the target cell, but not the difference between the load of the target cell and the load of the current cell.
3. The algorithm selects the UEs to be handed over according to the setting of NbmLdcBHOUeSelSwitch:
− If NbmLdcBHOUeSelSwitch is set to NBM_LDC_MATCH_UE_ONLY, the algorithm performs the following steps:
a. Selects the UEs whose service types are supported by the target cell as candidate UEs.
b. Sorts the candidate UEs whose rates are not higher than the handover bandwidth thresholds, based on the integrated priority.
c. Selects the UE with the lowest integrated priority for handover.
− If NbmLdcBHOUeSelSwitch is set to NBM_LDC_MATCH_UE_FIRST, the algorithm performs the following steps:
a. Selects the UEs whose service types are supported by the target cell as candidate UEs.
b. Sorts the candidate UEs whose rates are not higher than the handover bandwidth thresholds, based on the integrated priority.
c. Selects the UE with the lowest integrated priority for handover.
If the rates of all the candidate UEs are higher than the handover bandwidth thresholds, the algorithm performs the following steps:
a. Selects the UEs whose service types are not supported by the target cells as candidate UEs.
b. Sorts the UEs whose rates are not higher than the handover bandwidth threshold, based on the integrated priority.
c. Selects the UE with the lowest integrated priority for handover.
− If NbmLdcBHOUeSelSwitch is set to NBM_LDC_ALL_UE, the algorithm performs the following steps:
Issue Error! Unknown Error! Unknown document property 9 a. From the current cell, selects the UEs whose rates are not higher than the handover bandwidth thresholds, and then sorts them by integrated priority.
b. Selects the UE with the lowest integrated priority for handover.
If multiple UEs have the same lowest integrated priority, the algorithm selects the one with the lowest rate for handover.
The UL and DL handover bandwidth thresholds are specified by UlInterFreqHoBWThd and DlInterFreqHoBWThd respectively. Both the thresholds are considered in the selection of the target UE.
4. After selecting the target cell and the UE, the algorithm takes handover actions according to the status of the UE and the measurement of the signal quality.
9.3.2 BE Rate Reduction
The BE rate reduction algorithm is controlled by the DCCC algorithm switch. BE rate reduction can only be performed when the DCCC algorithm is enabled.
Different from the TF restriction to the OLC algorithm, the BE rate reduction is implemented by bandwidth reconfiguration. The bandwidth reconfiguration requires signaling interaction on the Uu interface. This procedure is relatively long.
In the same environment, different rates have different downlink transmit powers. The higher the rate, the greater the downlink transmit power. Therefore, the load can be reduced by bandwidth reconfiguration.
For HSUPA services, the consumption of CEs is based on the bit rate. The higher the rate, the more the consumption of CEs. Therefore, the consumption of CEs can be reduced by
bandwidth reconfiguration.
The LDR algorithm operates as follows:
1. Based on the integrated priority, the algorithm sorts the RABs in descending order.
2. The algorithm selects the RABs with the lowest integrated priorities and with the current rate higher than the GBR specified through the SET USERGBR command for related to the BE services. If the integrated priorities of some RABs are identical, the RAB with the highest rate is selected. The number of selected RABs is specified by the UlLdrBERateReductionRabNum or DlLdrBERateReductionRabNum parameter.
3. If services can be selected, the action is successful. If services cannot be selected, the action fails. The algorithm takes the next action.
4. The bandwidth of the selected services is reduced to the specified rate. For details about the rate reduction procedure, see the Rate Control Parameter Description.
5. The reconfiguration is completed as indicated by the RADIO BEARER RECONFIGURATION message on the Uu interface and through the synchronized radio link reconfiguration procedure on the Iub interface.
When admission control of Power/NodeB Credit is disabled, it is not recommended that the BE Rate Reduction be configured as an LDR action in order to avoid ping-pong effect.
9.3.3 QoS Renegotiation for Uncontrollable Real-Time Services
Uncontrollable real-time services refer to PS streaming services.
The QoS renegotiation algorithm for uncontrollable real-time services is set by the
DRA_IU_QOS_RENEG_SWITCH subparameter of the DraSwitch parameter. The QoS renegotiation can be performed only when the DRA_IU_QOS_RENEG_SWITCH is on.
The load can be reduced by adjusting the rates of real-time services through QoS
renegotiation. In 3GPP R5, the RNC initiates the RAB renegotiation procedure through the RAB MODIFY REQUEST message on the Iu interface.
Upon reception of the RAB MODIFY REQUEST message, the Core Network (CN) sends the RAB ASSIGNMENT REQUEST message to the RNC for RAB parameter reconfiguration.
Based on this function, the RNC can adjust the rate of real-time services to reduce the load of the current cell.
The LDR algorithm operates as follows:
1. Based on the integrated priority, the algorithm sorts the RABs for real-time services in the PS domain in descending order.
2. The algorithm selects the RABs with the lowest integrated priorities for QoS renegotiation. The number of selected RABs is specified by the UlLdrPsRTQosRenegRabNum or DlLdrPsRTQosRenegRabNum parameter.
3. The algorithm performs QoS renegotiation for the selected services. The GBR during the service setup is the minimum rate of the service after the QoS renegotiation.
4. The RNC initiates the RAB MODIFY REQUEST message to the CN for the QoS renegotiation.
5. If the RNC cannot find an appropriate service for the QoS renegotiation, the action fails.
The algorithm takes the next action.
9.3.4 Inter-RAT Handover in the CS Domain
The action is restricted by the CS inter-RAT handover algorithm switch. This action can only be performed when the CS inter-RAT handover algorithm is enabled.
The size and coverage mode of a 2G cell are different from those of a 3G cell. Therefore, inter-RAT blind handover is not considered.
Inter-RAT handover in the CS domain involves the following actions:
Inter-RAT Should Be Load Handover in the CS Domain The LDR algorithm operates as follows:
1. Based on the integrated priority, the algorithm sorts the UEs with the "service handover"
IE set to "handover to GSM should be performed" in the CS domain in descending order.
2. The algorithm selects the UEs with the lowest integrated priorities. The number of selected UEs is specified by the UlCSInterRatShouldBeHOUeNum or DlCSInterRatShouldBeHOUeNum parameter.
3. For the selected UEs, the LDR module sends the load handover command to the inter-RAT handover module to ask the UEs to be handed over to the 2G system.
4. The handover module decides to trigger the inter-RAT handover, depending on the capability of the UE to support the compressed mode.
5. If a UE that satisfies the handover criteria is not found, the algorithm takes the next action.
Inter-RAT Should Not Be Load Handover in the CS Domain
Issue Error! Unknown Error! Unknown document property 11 The algorithm for this action is the same as that for the action "Inter-RAT Should Be Load Handover in the CS Domain". The difference is that this action only involves CS users with the "service handover" IE set to "handover to GSM should not be performed".
The number of selected UEs is specified by the UlCSInterRatShouldNotHOUeNum or DlCSInterRatShouldNotHOUeNum parameter.
9.3.5 Inter-RAT Handover in the PS Domain
The action is restricted by the PS inter-RAT handover algorithm switch. This action can only be performed when the PS inter-RAT handover algorithm is enabled.
Inter-RAT handover in the PS domain involves the following actions:
Inter-RAT Should Be Load Handover in the PS Domain
The algorithm for this action is the same as that for the action "Inter-RAT Should Be Load Handover in the CS Domain". The difference is that this action involves only PS users with the "service handover" IE set to "handover to GSM should be performed".
The number of controlled UEs is determined by the UlPSInterRatShouldBeHOUeNum or DlPSInterRatShouldBeHOUeNum parameter.
Inter-RAT Should Not Be Load Handover in the PS Domain
The algorithm for this action is the same as that for the action "Inter-RAT Should Not Be Load Handover in the CS Domain". The difference is that this action involves only PS users with the "service handover" IE set to "handover to GSM should not be performed".
The number of controlled UEs is specified by the UlPSInterRatShouldNotHOUeNum or DlPSInterRatShouldNotHOUeNum parameter.
HSPA services can be selected only when HsdpaCMPermissionInd is set to TRUE and HsupaCMPermissionInd is not set to Limited.
For details about the two parameters, see the Handover Parameter Description.
9.3.6 AMR Rate Reduction
The action is restricted by the AMRC algorithm switch. This action can only be performed when the AMRC algorithm is enabled.
In the WCDMA system, voice services work in eight AMR modes. Each mode has its own rate. Therefore, mode control is functionally equivalent to rate control.
LDR Algorithm for AMR Rate Control in the Downlink
The LDR algorithm operates in the downlink as follows:
1. Based on the integrated priority, the algorithm sorts the RABs in descending order.
2. The algorithm selects the RABs with the lowest integrated priorities and with the rates higher than the GBR for AMR services (conversational). The number of selected RABs is specified by the DlLdrAMRRateReductionRabNum parameter.
3. The RNC sends the Rate Control request message through the Iu interface to the CN to adjust the AMR rate to the GBR.
4. If the RNC cannot find an appropriate RAB for the AMR rate reduction, the action fails.
The algorithm takes the next action.
LDR Algorithm for AMR Rate Control in the Uplink
In the uplink, the LDR algorithm operates as follows:
1. Based on the integrated priority, the algorithm sorts the RABs in descending order.
2. The algorithm selects the RABs with the lowest integrated priorities and with the rates higher than the GBR for AMR services (conversational). The number of selected RABs is determined by the UlLdrAMRRateReductionRabNum parameter.
3. The RNC sends the TFC CONTROL command to the UE to adjust the AMR rate to the GBR.
4. If the RNC cannot find an appropriate RAB for the AMR rate reduction, the action fails.
The algorithm takes the next action.
9.3.7 Code Reshuffling
When the cell is in the basic congestion state caused by code resource, code reshuffling can be performed to reserve sufficient code resources for subsequent services. Code subtree
adjustment refers to the switching of users from one code subtree to another. It is used for code tree defragmentation, so as to release smaller codes first.
The algorithm operates as follows:
1. Initializes SF_Cur to CellLdrSfResThd.
2. Traverses all the subtrees with this SF_Cur at the root node except the subtrees occupied by common channels and HSDPA channels, and takes the subtrees in which the number of users is not larger than the value of MaxUserNumCodeAdj as candidates for code reshuffling.
− If such candidates are available, the algorithm goes to step 3.
− If no such candidate is available, subtree selection fails. This procedure ends.
3. Selects a subtree from the candidates according to the setting of LdrCodePriUseInd.
− If this parameter is set to TRUE, the algorithm selects the subtree with the largest code number from the candidates.
− If this parameter is set to FALSE, the algorithm selects the subtree with the smallest number of users from the candidates. In the case that multiple subtrees have the same number of users, the algorithm selects the subtree with the largest code number.
4. Treats each user in the subtree as a new user and allocates code resources to each user.
5. Initiates the reconfiguration procedure for each user in the subtree and reconfigures the channelization codes of the users to the newly allocated code resources.
The reconfiguration procedure on the UU interface is implemented through the PHYSICAL CHANNEL RECONFIGURATION message and that on the Iub interface through the RL RECONFIGURATION message.
Figure 9-28 shows an example of code reshuffling. In this example, CellLdrSfResThd is set to SF8, and MaxUserNumCodeAdj is set to 1.
Issue Error! Unknown Error! Unknown document property 13 Figure 9-28 Code reshuffling
9.3.8 MBMS Power Reduction
The downlink power load can be reduced by lowering power on MBMS traffic channels.
The algorithm operates as follows:
1. Based on the integrated priority, the algorithm sorts the RABs in descending order.
2. The algorithm selects a RAB with the lowest integrated priority and with the current power higher than the minimum transmit power of the corresponding MTCH. That is, it selects a RAB of which the ARP value is higher than MbmsDecPowerRabThd.
3. The algorithm triggers a reconfiguration procedure to set the power to the minimum transmit power of the FACH onto which the MTCH is mapped.
The reconfiguration procedure on the Iub interface is implemented through the COMMON TRANSPORT CHANNEL RECONFIGURATION REQUEST message.
9.3.9 UL and DL LDR Action Combination of a UE
LDR actions in the uplink and the downlink are independent. Sometimes, the actions in both directions are applied to the same UE. In this situation, the actions are combined as follows:
If the actions in the two directions are identical, the actions are combined. For example, if BE rate reduction actions in both the uplink and the downlink need to be applied to the same UE, then only a single RADIO BEARER RECONFIGURATION message is sent out.
If the actions in the two directions are different and if one direction requires inter-frequency handover, the UE undergoes the inter-inter-frequency handover. The other action is not taken.
If the actions in the two directions are different and if one direction requires the inter-RAT handover, the UE undergoes the inter-inter-RAT handover. The other action is not taken.
If the action in one direction requires inter-frequency handover, and the action in the other direction requires inter-RAT handover, the UE undergoes the UL LDR action. The DL LDR action is not taken.
10 Overload Control Algorithm
After the UE access is allowed, the power consumed by a single link is adjusted by the single link power control algorithm. The power varies with all kinds of factors such as the mobility of the UE and the changes in the environment. In some situations, the total power load of the cell can be higher than the target load. To ensure the system stability, Overload Control (OLC) must be performed.
This chapter consists of the following sections:
OLC Triggering
General OLC Procedure
OLC Actions