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PowerPoint PresentationWCDMA Load Congestion Control
By Ahmad Allam
The WCDMA system is a self interference system. As the load of the WCDMA system increases, the interference rises. A relatively high interference may affect the coverage and Quality of Service (QoS) of established services. Therefore, capacity, coverage and QoS of the WCDMA system are mutually affected. The purpose of load control is to maximize the system capacity while ensuring coverage and QoS.
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
LCC (Load Congestion Control)
Load%
THLDR
THOLC
100%
Basic congestion state: LDR will be used
LCC (Load Congestion Control) consist of LDR (Load Reshuffling) and OLC (OverLoad Control).
In basic congestion state, LDR will be used to optimize resource distribution, the main rules is not to affect the feeling of users as possible as we can.
In overload state, OLC will be used to release overload state quickly, keep system stability and the service of high priority users.
LDR (Load Reshuffling)
Reasons
When the cell is in basic congestion state, new coming calls could be easily rejected by system
Purpose
Triggering of LDR
Power resources, code resource, Iub resources or Iub bandwidth, NodeB Credit resource
Parameters for LDR Algorithm Switch
NBMLdcAlgoSwitch (Cell algorithm switch)
Default status: OFF
Most of the LDR actions (except inter-frequency load handover) affect QoS
Set LDR Algorithm Switch through ADD CELLALGOSWITCH, query it through LST CELLALGOSWITCH, and modify it through MOD CELLALGOSWITCH.
Parameters for LDR Action Sequence
UL (DL) LDRFIRSTACTION (UL/DL LDR First action) ~
UL (DL) LDRSIXTHACTION (UL/DL LDR Sixth action)
Value range: NOACT, INTERFREQLDHO, BERATERED, QOSRENEGO, CSINTERRATLDHO, PSINTERRATLDHO, AMRRATERED, MBMSDECPOWER, CODEADJ
Default value: UlLdrFirstAction or DlLdrFirstAction is CODEADJ, UlLdrSecondAction or DlLdrSecondAction is INTERFREQLDHO UlLdrThirdAction or DlLdrThirdAction is BERATEREDthe other is NOACT
Set the following parameters through ADD CELLLDR, query it through LST CELLLDR, and modify it through MOD CELLLDR.
This set of parameters determines the action sequence for the uplink/downlink LDR.
NOACT: NO ACTION
QOSRENEGO: UNCONTROLLED REAL-TIME TRAFF QOS RE-NEGOTIATION
CSINTERRATLDHO: CS DOMAIN INTER-RAT LOAD HANDOVER
PSINTERRATLDHO: PS DOMAIN INTER-RAT LOAD HANDOVER
AMRRATERED: AMR TRAFF RATE REDUCTION
Parameters for LDR Algorithm Priority
Priority for load reshuffling
Default status:
LdrFirstPri = IUBLDR
LdrSecondPri = CREDITLDR
LdrThirdPri = CODELDR
LdrFourthPri = UULDR
Set LDR Algorithm Switch through SET LDCALGOPARA, query it through LST LDCALGOPARA, and modify it through MOD LDCALGOPARA.
Triggering conditions of all types of resources congestion are monitored simultaneously, however LDR can handle only one type of resource congestion at a time. If there is only one type of congestion occurred it will be handled by LDR regardless of the priority settings.
If more than one resource congestion are triggered at the same time, they are to be released in the resource order priority for load reshuffling.
LDR Procedure
Wait for congestion indication
Sequence of
N
Inter-system
handover
Wait for congestion indication
Sequence of
N
Inter-system
handover
LDR Actions intended for different resources
Every type of resource congestion has its own triggering conditions and a specified set of solving actions.
As shown, there is no action that can solve all types of resources congestion.
LDR Actions
LDR Actions - Code Reshuffling
Cell load is decreased under basic congestion trigger threshold
Sufficient code resources can be reserved for subsequent service
When code resources are in basic congestion state, sufficient code resources can be reserved for subsequent service access through code reshuffling.
The LDR algorithm is implemented as follows:
Select a subtree. Ensure that the number of users in the subtree is not higher than Max user number of code adjust.
Treat each user in the subtree as a new user and allocate code resources to each user.
Initiate the reconfiguration procedure for each user in the subtree and reconfigure the channel codes of the users to the newly-allocated code resources.
The reconfiguration procedure on the air interface is implemented through the PHYSICAL CHANNEL RECONFIGURATION message and that on the Iub interface through the RL RECONFIGURATION message.
LDR Actions - BE Rate Reduction
Candidate RABs
The data rate of BE service is larger than GBR
Target RABs
Rank the candidate RABs by the integrate priority, the low priority RABs reduce BE rate first
Result
Cell load is decreased under basic congestion trigger threshold
The BE service rate of low priority RABs is limited in GBR
BE rate reduction is implemented by reconfiguring the bandwidth. 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 reconfiguring the bandwidth.
The LDR algorithm is implemented as follows:
Based on the integrate priority, the LDR sorts the RABs in descending order. The top RABs related to the BE services whose current rate is higher than its GBR are selected. The number of RABs to select is determined by UL/DL LDR-BE rate reduction RAB number.
The bandwidth of the selected services is reduced to the specified rate.
If services can be selected, the action is successful. If services cannot be selected, the action fails. The LDR takes the next action.
The reconfiguration is completed as indicated by the RB RECONFIGURATION message on the Uu interface and through the RL RECONFIGURATION message on the Iub interface.
The BE rate reduction algorithm is controlled by the DCCC algorithm switch. BE rate reduction can be performed only when the DCCC algorithm is enabled.
Parameters for Triggering Code Reshuffling
CELLLDRSFRESTHD (Cell LDR SF reserved threshold)
Value Range:0, 1, 2, 3, 4, 5, 6, 7
Physical value Range: SF4, SF8, SF16, SF32, SF128, SF256
Recommended value: SF8
Set the following parameters through ADD CELLLDR, query it through LST CELLLDR, and modify it through MOD CELLLDR.
CELLLDRSFRESTHD (Cell LDR SF reserved threshold):
The code adjusting could be done only when the minimum available SF of a cell is larger than this threshold.
Parameters for LDR Code Reshuffling
MAXUSERNUMCODEADJ (Max user number of code adjust)
Value range: 1 to 3
Recommended value: 1
Value range: FALSE, TRUE
Number of users selected in a code adjust.
LDRCODEPRIUSEIND (LDR code priority indicator):
"FALSE" denotes not considering the priority of code when code adjust; "TRUE" denotes considering the priority of code when code adjust.
Parameters for Triggering of Power Resource LDR(1)
ULLDRTRIGTHD (UL LDR trigger threshold)
Value range: 0 to 100%
Recommended value: 55, namely 55%
ULLDRRELTHD (UL LDR release threshold)
Set the following parameters through ADD CELLLDM, query it through LST CELLLDM, and modify it through MOD CELLLDM.
Parameters for Triggering of Power Resource LDR (2)
DLLDRTRIGTHD (DL LDR trigger threshold)
DLLDRRELTHD (DL LDR release threshold)
Thank You

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