RAN
Load Control Parameter Description
Issue 01
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About This Document
Author
Prepared by Wu Xianbin Date 2008-10-26
Edited by Cheng Xiaoli Date 2008-12-09
Reviewed by Zeng Yongmei Date 2008-12-10
Translated by Wang Xiaofen Date 2008-12-20
Tested by Zhang Shasha Date 2009-01-10
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Contents
1 Change History ... 1
2 Load Control Introduction ... 1
3 Load Control Algorithm Overview ... 1
3.1 Load Control Workflow ... 1
3.2 Algorithm Introduction ... 2
3.3 Priorities Involved in Load Control ... 4
3.3.1 User Priority ... 4
3.3.2 RAB Integrated Priority ... 5
3.3.3 User Integrated Priority ... 5
4 Load Measurement Algorithm ... 1
4.1 Measurement Quantities and Procedure ... 1
4.1.1 Major Measurement Quantities ... 1
4.1.2 LDM Procedure ... 2
4.2 Load Measurement Filtering ... 2
4.2.1 Filtering on the NodeB Side ... 2
4.2.2 Smooth Window Filtering on the RNC Side ... 3
4.2.3 Reporting Period ... 4
4.2.4 Provided Bit Rate ... 4
4.3 Auto-Adaptive Background Noise Algorithm ... 5
5 Potential User Control Algorithm ... 1
6 Intelligent Access Control Algorithm ... 1
6.1 IAC Overview ... 1
6.2 IAC During RRC Connection Setup ... 3
6.2.1 RRC Redirection for Service Steering ... 5
6.2.2 RRC DRD ... 6
6.2.3 RRC Redirection After DRD Failure ... 6
6.3 Rate Negotiation ... 7
6.3.1 PS MBR Negotiation ... 7
6.3.2 PS GBR Negotiation ... 7
6.3.4 Target Rate Negotiation ... 8
6.4 RAB DRD ... 9
6.4.1 RAB DRD Overview ... 9
6.4.2 Inter-Frequency DRD for Service Steering ... 10
6.4.3 Inter-Frequency DRD for Load Balancing ... 12
6.4.4 Inter-Frequency DRD... 19
6.4.5 Inter-RAT DRD ... 22
6.5 Preemption ... 24
6.6 Queuing ... 26
6.7 Low-Rate Access of the PS BE Service ... 27
6.8 IAC for Emergency Calls ... 29
6.8.1 RRC Connection Setup Process of Emergency Calls... 29
6.8.2 RAB Process of Emergency Calls ... 30
7 Call Admission Control Algorithm ... 1
7.1 CAC Overview ... 1
7.2 CAC Based on Code Resource ... 3
7.3 CAC Based on Power Resource ... 3
7.3.1 Overview ... 3
7.3.2 Admission Decision for RRC Connection Setup Request ... 5
7.3.3 Power-Based Admission Algorithm 1 ... 5
7.3.4 Power-Based Admission Algorithm 2 ... 13
7.3.5 Power-Based Admission Algorithm 3 ... 15
7.4 CAC Based on NodeB Credit Resource ... 15
7.4.1 NodeB Credit ... 15
7.4.2 Procedure of Admission Decision Based on NodeB Credit ... 17
7.5 CAC Based on Iub Resource ... 18
7.6 CAC Based on the Number of HSPA Users ... 18
7.6.1 CAC of HSDPA Users ... 18
7.6.2 CAC of HSUPA Users ... 18
8 Intra-Frequency Load Balancing Algorithm ... 1
9 Load Reshuffling Algorithm ... 1
9.1 Basic Congestion Triggering ... 1
9.1.1 Power Resource ... 1
9.1.2 Code Resource ... 2
9.1.3 Iub Resource ... 3
9.1.4 NodeB Credit Resource ... 3
9.2 LDR Procedure ... 4
9.3 LDR Actions... 7
9.3.1 Inter-Frequency Load Handover ... 7
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9.3.3 QoS Renegotiation for Uncontrollable Real-Time Services ... 9
9.3.4 Inter-RAT Handover in the CS Domain ... 10
9.3.5 Inter-RAT Handover in the PS Domain ... 10
9.3.6 AMR Rate Reduction ... 11
9.3.7 Code Reshuffling ... 11
9.3.8 MBMS Power Reduction ... 12
9.3.9 UL and DL LDR Action Combination of a UE ... 13
10 Overload Control Algorithm ... 1
10.1 OLC Triggering ... 1
10.2 General OLC Procedure ... 2
10.3 OLC Actions... 4
10.3.1 Performing TF Control of BE Services ... 4
10.3.2 Switching BE Services to Common Channels ... 6
10.3.3 Adjusting the Maximum FACH TX Power ... 7
10.3.4 Releasing Some RABs ... 7
11 Dynamic Power Sharing Among Carriers ... 1
11.1 Introduction ... 1
11.2 Power Sharing Mode ... 1
12 Load Control Parameters ... 1
12.1 Description ... 1
12.2 Values and Ranges ... 27
1
Change History
The change history provides information on the changes in different document versions.
Document and Product Versions
Document Version RAN Version
01 (2009-03-30) 11.0
Draft (2009-03-10) 11.0
Draft (2009-01-15) 11.0
This document is based on the BSC6810 and 3900 series NodeBs.
The available time of each feature is subject to the RAN product roadmap.
There are two types of changes, which are defined as follows:
Feature change: refers to the change in the load control feature.
Editorial change: refers to the change in the information that was inappropriately described or the addition of the information that was not described in the earlier version.
01 (2009-03-30)
This is the document for the first commercial release of RAN11.0.
Compared with issue draft (2009-03-10) of RAN11.0, this issue incorporates the following changes:
Change Type Change Description Parameter Change
Feature change The description of Control RTWP Anti-interfence algorithm is added. For details, see 7.3 "CAC Based on Power Resource" and 10.3 "OLC Actions."
The added parameter is as follows: RsvdPara1.
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Draft (2009-03-10)
This is the second draft of the document for RAN11.0.
Compared with issue draft(2009-01-15) of RAN11.0, draft (2009-03-10) incorporates the following changes:
Change Type Change Description Parameter Change
Feature change None. None.
Editorial change
The description of dynamic cell shutdown algorithm is moved to Green BTS Description.
The corresponding parameters as follows are move to Green BTS Description: StartTime1 EndTime1 StartTime2 EndTime2 StartTime3 EndTime3 DynShutdownSwitch TotalUserNumThd HsdpaUserNumThd HsupaUserNumThd NCellLdrRemainThd DynCellShutdownProtectTimerlen DynCellOpenJudgeTimerlen
Draft (2009-01-15)
This is the initial draft of the document for RAN11.0.
Compared with issue 03 (2008-12-30) of RAN10.0, draft (2009-01-15) incorporates the following changes:
Change Type Change Description Parameter Change
Feature change Some parameters are added to section 4.1 "Measurement Quantities and Procedure."
The added parameters are as follows:
UlBasicCommMeasFilterCoeff DlBasicCommMeasFilterCoeff PucAvgFilterLen UlCacAvgFilterLen DlCacAvgFilterLen LdbAvgFilterLen UlLdrAvgFilterLen DlLdrAvgFilterLen UlOlcAvgFilterLen DlOlcAvgFilterLen HsdpaNeedPwrFilterLen ChoiceRprtUnitForHsdpaPwrMeas TenMsecForHsdpaPwrMeas MinForHsdpaPwrMeas ChoiceRprtUnitForHsdpaRateMeas TenMsecForHsdpaPrvidRateMeas MinForHsdpaPrvidRateMeas ChoiceRprtUnitForHsupaRateMeas TenMsecForHsupaPrvidRateMeas MinForHsupaPrvidRateMeas HsdpaPrvidBitRateFilterLen HsupaPrvidBitRateFilterLen The description of RRC redirection for service steering is added. For details, see 6.2.1 "RRC Redirection for Service Steering."
The added parameters are as follows:
RedirSwitch RedirFactorOfNorm RedirFactorOfLDR RedirBandIn ReDirUARFCNUplinkInd ReDirUARFCNUplink ReDirUARFCNDownlink
The description of initial rate negotiation for BE services is optimized. For details, see 6.3.3 "Initial Rate
Negotiation."
The added parameters are as follows:
EcN0EffectTime EcN0Ths
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Change Type Change Description Parameter Change
The description of low-rate access is added. For details, see 6.1 "IAC Overview" and 6.7 "Low-Rate Access of the PS BE Service."
The added parameters are as follows:
PSBELowRateAccessSwitch ZeroRateUpFailToRelTimerLen
The description of an OLC action, that is, the adjustment of maximum FACH transmit power, is added. For details, see 10.3.3 "Adjusting the Maximum FACH TX Power."
The added parameter is as follows:
FACHPwrReduceValue
The description of dynamic cell shutdown algorithm is added.
The added parameters are as follows:
StartTime1 EndTime1 StartTime2 EndTime2 StartTime3 EndTime3 DynShutdownSwitch TotalUserNumThd HsdpaUserNumThd HsupaUserNumThd NCellLdrRemainThd DynCellShutdownProtectTimerlen DynCellOpenJudgeTimerlen
The description of dynamic power sharing among carriers is added. For details, see 11 "Dynamic Power Sharing Among Carriers."
The added parameters are as follows:
SLOCELL DLOCELL MAXSHRTO SHMGN Editorial change
The title of the document is changed from Load Control Description to Load Control Parameter Description. Parameter names are replaced with parameter IDs.
2
Load Control Introduction
The WCDMA system is a self-interfering system. As the load of the system increases, the interference rises. A relatively high interference can affect the coverage and QoS of
established services. Therefore, the capacity, coverage, and QoS of the WCDMA system are mutually affected.
Through the control of key resources, such as power, downlink channelization codes, channel elements (CEs), Iub transmission resources, which directly affect user experience, load control aims to maximize the system capacity while ensuring coverage and QoS.
In addition, load control provides differentiated services for users with different priorities. For example, when the system resources are insufficient, procedures such as direct admission, preemption, redirection can be performed to ensure the successful access of emergency calls to the network.
Intended Audience
This document is intended for:
System operators who need a general understanding of load control.
Personnel working on Huawei products or systems.
Impact
Impact on System Performance
This feature has no impact on system performance.
Impact on Other Features
This feature has no impact on other features.
Network Elements Involved
Table 2-1 lists the Network Elements (NEs) involved in load control.
Table 2-1 NEs involved in load control
UE NodeB RNC MSC Server MGW SGSN GGSN HLR
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UE NodeB RNC MSC Server MGW SGSN GGSN HLR
NOTE:
– : not involved √: involved
UE = User Equipment, RNC = Radio Network Controller, MSC Server = Mobile Service Switching Center Server, MGW = Media Gateway, SGSN = Serving GPRS Support Node, GGSN = Gateway GPRS Support Node, HLR = Home Location Register
3
Load Control Algorithm Overview
This chapter consists of the following sections:
Load Control Workflow
Algorithm Introduction
Priorities Involved in Load Control
3.1 Load Control Workflow
Depending on the actual phase of UE access, different load control algorithms are used, as shown in the following figure.
Figure 3-1 Load Control algorithms in different UE access phases
The load control algorithms are applied to the different UE access phases as follows:
Before UE access: Potential User Control (PUC)
During UE access: Intelligent Access Control (IAC) and Call Admission Control (CAC) After UE access: intra-frequency Load Balancing (LDB), Load Reshuffling (LDR), and
Overload Control (OLC)
In addition, functional load control algorithms vary depending on the load levels of the cell, as shown in the following figure.
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Figure 3-2 Load control algorithms used on different cell load levels
Start PUC: enable UEs in idle mode to camp on cells with light load Start IAC: increase the access rate in cells with
heavy load by some actions while ensuring the QoS
Start LDR: check and relieve basic congestion in cells NodeB TX
power (noise)
Cell load (number of subscribers)
Start OLC: check and relieve overload congestion in cells
Icons for different load levels
Load control is unneeded
3.2 Algorithm Introduction
The load control algorithms are built into the RNC.The input of load control comes from the measurement information of the NodeB.
Figure 3-3 Load control algorithm in the WCDMA system
Load control has the following algorithms:
The function of PUC is to balance traffic load between inter-frequency cells. The RNC uses PUC to modify cell selection and reselection parameters, and broadcasts them through system information. In this way, UEs are led to cells with a light load. The UEs can be in idle mode, CELL_FACH state, CELL_PCH state, or URA_PCH state.
Intelligent Access Control (IAC)
The function of IAC is to increase the access success rate with the current QoS
guaranteed through rate negotiation, queuing, preemption, and Directed Retry Decision (DRD).
Call Admission Control (CAC)
The function of CAC is to decide whether to accept resource requests from UEs, such as access, reconfiguration, and handover requests, depending on the resource status of the cell.
Intra-frequency Load Balancing (LDB)
The function of intra-frequency LDB is to balance the cell load between neighboring intra-frequency cells to provide better resource usage.
Load Reshuffling (LDR)
The function of LDR is to reduce the cell load when the available resources for a cell reach the specified alarm threshold. The purpose of LDR is to increase the access success rate by taking the following actions:
− Inter-frequency load handover
− Code reshuffling
− BE service rate reduction
− AMR voice service rate reduction
− QoS renegotiation for uncontrollable real-time services
− CS inter-RAT load handover
− PS inter-RAT load handover
− MBMS power reduction
Overload Control (OLC)
The function of OLC is to reduce the cell load rapidly when the cell is overloaded. The purpose of OLC is to ensure the system stability and the QoS of most UEs in the following ways:
− Restricting the Transport Format (TF) of the BE service
− Switching BE services to common channels
− Adjusting the maximum transmit power of FACHs
− Releasing some RABs
Dynamic power sharing among carriers
In dynamic power sharing among carriers, a carrier that carries the HSPA service can dynamically use the idle power resource of another carrier, thus improving the power usage and the cell HSPA service rate.
Each load control algorithm involves three factors: measuring, triggering, and controlling. Valid measurement is a prerequisite for effective control.
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Table 3-2 Resources used by different load control algorithms
Load Control Algorithm Resources
Power Code NodeB
Credits Iub Bandwidth
CAC √ √ √ √ IAC √ √ √ √ PUC √ - - - LDB √ - - - LDR √ √ √ √ OLC √ - - √
Dynamic power sharing among carriers
√ - - -
NOTE
–: not considered √: considered
3.3 Priorities Involved in Load Control
The priorities involved in load control are user priority, Radio Access Bearer (RAB) integrated priority, and user integrated priority.
3.3.1 User Priority
There are three levels of user priority (1, 2, and 3), which are denoted as gold (high priority), silver (middle priority) and copper (low priority) users. The relation between user priority and Allocation Retention Priority (ARP) can be set through SET USERPRIORITY command; the typical relation is shown in the following table.
Table 3-3 Typical relation between user priority and ARP
ARP 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
User Priority
ERROR 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3
ARP 15 is always the lowest priority and is not configurable. It corresponds to user priority 3 (copper). If ARP is not received in messages from the Iu interface, the user priority is regarded as copper.
The levels of user priority are mainly used to provide different QoS for different users, for example, setting different Guaranteed Bit Rate (GBR) values for BE services according to different priority levels.
The GBR of BE services are configurable. According to the traffic class, priority level, and carrier type (DCH or HSPA), the different values of GBR are configured through the SET
USERGBR command.
Changes in the mapping between ARP and user priority have an influence on the following features:
High Speed Downlink Packet Access (HSDPA) High Speed Uplink Packet Access (HSUPA)
Adaptive Multi Rate (AMR)
Adaptive Multi-Rate – Wideband (AMR-WB)
Iub overbooking
Load control
3.3.2 RAB Integrated Priority
RAB integrated priority is mainly used in load control algorithms.
The values of RAB integrated priority are set according to the integrated priority configuration reference parameter (PriorityReference):
If the integrated priority configuration reference parameter is set to Traffic Class, the
integrated priority abides by the following rules:
− Traffic classes: conversational -> streaming -> interactive -> background =>
− Services of the same class: priority based on Allocation/Retention Priority (ARP) values, that is, ARP1 -> ARP2 -> ARP3 -> ... -> ARP14 =>
− Only for the interactive service of the same ARP value: priority based on Traffic Handling Priority (THP), that is, THP1 -> THP2 -> THP3 -> ... -> THP14 =>
− Services of the same ARP, traffic class and THP (only for interactive services): High Speed Packet Access (HSPA) or Dedicated Channel (DCH) service preferred depending on the carrier type priority indicator parameter (CarrierTypePriorInd).
If the integrated priority configuration reference parameter is set to ARP, the integrated priority abides by the following rules:
− ARP: ARP1 -> ARP2 -> ARP3 -> ... -> ARP14 =>
− Services of the same ARP: priority based on traffic classes, that is, conversational -> streaming -> interactive -> background =>
− Only for the interactive service of the same ARP value: priority based on Traffic Handling Priority (THP), that is, THP1 -> THP2 -> THP3 -> ... -> THP14 =>
− Services of the same ARP, traffic class and THP (only for interactive services): HSPA or DCH service preferred depending on the carrier type priority indicator parameter.
ARP and THP are carried in the RAB ASSIGNMENT REQUEST message, and they are not configurable on the RNC LMT.
3.3.3 User Integrated Priority
For multiple-RAB users, the integrated priority of the user is based on the service of the highest priority. User integrated priority is used in user-specific load control. For example, the
Issue Error! Unknown Error! Unknown document property 6 selection of R99 users during preemption, the selection of users during inter-frequency load handover for LDR, and the selection of users during switching of BE services to common channels are performed according to the user integrated priority.
4
Load Measurement Algorithm
The load control algorithms, such as OLC and CAC, use load measurement values in the uplink and the downlink. A common Load Measurement (LDM) algorithm is required to control load measurement in the uplink and the downlink, which makes the algorithm relatively independent.
The NodeB and the RNC perform measurements and filtering. The statistics obtained after the measurements and filtering serve as the data input for the load control algorithms.
This chapter consists of the following sections:
Measurement Quantities and Procedure Load Measurement Filtering
Auto-Adaptive Background Noise Algorithm
4.1 Measurement Quantities and Procedure
4.1.1 Major Measurement Quantities
The major measurement quantities of the LDM are as follows:
Uplink Received Total Wideband Power (RTWP) Downlink Transmitted Carrier Power (TCP)
Non-HSPA power: TCP excluding the power used for transmission on PDSCH, HS-SCCH, E-AGCH, E-RGCH, and E-HICH
Here:
− HS-PDSCH: High Speed Physical Downlink Shared Channel
− HS-SCCH: High Speed Shared Control Channel
− E-AGCH: Enhanced Dedicated Channel (E-DCH) Absolute Grant Channel
− E-RGCH: E-DCH Relative Grant Channel
− E-HICH: E-DCH HARQ Acknowledgement Indicator Channel
Provided Bit Rate (PBR) on HS-DSCH
PBR on E-DCH
Power Requirement for GBR (GBP) on HS-DSCH: minimum power required to ensure the GBR on HS-DSCH
Issue Error! Unknown Error! Unknown document property 2 Received Scheduled E-DCH Power Share (RSEPS): power of the E-DCH scheduling
service
4.1.2 LDM Procedure
The following figure shows the LDM procedure.
Figure 4-4 LDM procedure
The NodeB measures the major measurement quantities and then obtains original
measurement values. After layer 3 filtering on the NodeB side, the NodeB reports the cell measurement values to the RNC.
The RNC performs smooth filtering on the measurement values reported from the NodeB and then obtains the measurement values, which further serve as data input for the load control algorithms.
4.2 Load Measurement Filtering
4.2.1 Filtering on the NodeB Side
The Provided Bit Rate (PBR) measurement, however, does not use alpha filtering on the NodeB side. The following figure shows the measurement model at the physical layer that is compliant with 3GPP 25.302.
Figure 4-5 Measurement model at the physical layer Layer 1 filtering Layer 3 filtering Measurement evaluation A B C C’ Parameters Parameters D In Figure 4-5:
A is the sampling value of the measurement. B is the measurement value after layer 1 filtering. C is the measurement value after layer 3 filtering.
C' is another measurement value (if any) for measurement evaluation.
D is the reported measurement value after measurement evaluation on the conditions of periodic measurement and event-triggered measurement.
Layer 1 filtering is not standardized by protocols and it depends on vendor equipment. Layer 3 filtering is standardized. The filtering effect is controlled by a higher layer. The alpha filtering that applies to layer 3 filtering is calculated according to the following formula:
Here:
Fn is the new post-filtering measurement value. Fn-1 is the last post-filtering measurement value.
Mn is the new measurement value from the physical layer.
α = (1/2)k/2
, where k is specified by the UlBasicCommMeasFilterCoeff or
DlBasicCommMeasFilterCoeff parameter.
4.2.2 Smooth Window Filtering on the RNC Side
After the RNC receives the measurement report, it filters the measurement value with the smooth window.
Assuming that the reported measurement value is Qn and that the size of the smooth window
is N, the filtered measurement value is
Delay susceptibilities of PUC, CAC, LDR, and OLC to common measurement are different. The LDM algorithm must apply different smooth filter coefficients and measurement periods to those algorithms; thus, they can get expected filtered values.
The following table lists the smooth window length parameters for setting different algorithms.
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Algorithm Smooth Window Length Parameter
PUC PucAvgFilterLen CAC UlCacAvgFilterLen DlCacAvgFilterLen LDB LdbAvgFilterLen LDR UlLdrAvgFilterLen DlLdrAvgFilterLen OLC UlOlcAvgFilterLen DlOlcAvgFilterLen
GBP measurements have the same smooth window length in all related algorithms. The filter length for GBP measurement is specified by the HsdpaNeedPwrFilterLen parameter.
4.2.3 Reporting Period
The NodeB periodically reports each measurement quantity to the RNC. The following table lists the reporting period parameters for setting different measurement quantities.
Measurement Reporting Period Parameter
RTWP ChoiceRprtUnitForUlBasicMeas TenMsecForUlBasicMeas MinForUlBasicMeas ChoiceRprtUnitForDlBasicMeas TenMsecForDlBasicMeas MinForDlBasicMeas RSEPS TCP Non-HSDPA power GBP ChoiceRprtUnitForHsdpaPwrMeas TenMsecForHsdpaPwrMeas MinForHsdpaPwrMeas
4.2.4 Provided Bit Rate
The Provided Bit Rate (PBR) measurement quantity is also reported by the NodeB to the RNC. Different from other power measurement quantities, PBR does not undergo alpha filtering on the NodeB side.
For details about PBR, see the 3GPP 25.321.
Measurement Reporting Period Parameter HS-DSCH PBR ChoiceRprtUnitForHsdpaRateMeas TenMsecForHsdpaPrvidRateMeas MinForHsdpaPrvidRateMeas E-DCH PBR ChoiceRprtUnitForHsupaRateMeas TenMsecForHsupaPrvidRateMeas MinForHsupaPrvidRateMeas
On the RNC side, the length of the PBR smooth filter window is specified by the
HsdpaPrvidBitRateFilterLen / HsupaPrvidBitRateFilterLen parameter.
4.3 Auto-Adaptive Background Noise Algorithm
Uplink (UL) background noise is sensitive to environmental conditions. Therefore, the LDM algorithm incorporates an auto-adaptive update algorithm to restrict the background noise within a specified range, as described here:
If the temperature in the equipment room is constant, the background noise changes slightly. In this case, the background noise requires no more adjustment after initial correction.
If the temperature in the equipment room varies with the ambient temperature, the
background noise changes greatly. In this case, the background noise requires auto-adaptive upgrade.
Figure 4-6 shows the procedure of auto-adaptive background noise upgrade, which is enabled by the BGNSwitch parameter.
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Figure 4-6 Procedure of auto-adaptive background noise upgrade
Initialize the counter and filter used for auto-adaptive background noise upgrade
Receive the RTWP measurement value (Mn)
BgnStartTime < Current time
< BgnEndTime?
Equivalent user quantity >
BGNEqUserNumThd?
|Mn – Fn-1| <
BgnAbnormalThd?
Set the counter to 0
Keep the current background noise unchanged and set the initial value of the filter to the current background noise
Set the counter to 0 Increment the counter by one Calculate Fn according to the Alpha filter formula
Does the counter reach the counting threshold?
|Fn - BackgroundNoise| < BgnAbnormalThd?
|Fn – Current background noise| > BgnUpdateThd?
Set the current background noise to Fn, and set the counter to 0 No No No No No No Yes Yes Yes Yes Yes Yes
The Alpha filter formula is: Fn = (1 - α) x Fn-1 + α x Mn (n≥1). For details about this formula, see
4.2.1 "Filtering on the NodeB Side."
Counting threshold = (Duration of background noise)/(RTWP reporting period). The duration of background noise is used in auto-adaptive upgrade decision and is set through BGNAdjustTimeLen. For the setting of RTWP reporting period, see 4.2.3 "Reporting Period."
In the case that BGNSwitch is set to ON, the procedure of auto-adaptive background noise upgrade is as follows:
1. The RNC initializes the counter and filter that are used for auto-adaptive upgrade and sets the initial value (F0) of the filter to BackgroundNoise.
2. The RNC receives the latest RTWP measurement value (Mn) from the physical layer.
3. The RNC determines whether the current time is within the effective period of the algorithm, that is, whether the current time is later than BgnStartTime and earlier than
BgnEndTime. If the current time is within the effective period, the RNC performs the
next step. Otherwise, the RNC waits for the next RTWP measurement value.
4. The RNC determines whether the current Equivalent Number of Users (ENU) in the cell is greater than the value of BGNEqUserNumThd:
− If the current ENU is greater than this threshold value, the RNC infers that Mn
includes other noises in addition to the background noise, and therefore it does not feed Mn to the filter. In addition, the RNC sets the counter to zero, keeps the current
background noise unchanged, sets the initial value of the filter to the current background noise, and waits for the next RTWP measurement value.
− If the current ENU in the cell is smaller than or equal to the threshold value, the RNC feeds Mn to the filter and performs the next step.
5. The RNC determines whether |Mn – Fn-1| is smaller than the value of BgnAbnormalThd.
If it is smaller than this threshold value, the RNC increments the counter by one, calculates Fn according to the Alpha filter formula, and performs the next step.
Otherwise, the RNC waits for the next RTWP measurement value.
6. The RNC determines whether the counter reaches the counting threshold. If it reaches the counting threshold, the RNC performs the next step. Otherwise, the RNC waits for the next RTWP measurement value.
7. The RNC determines whether |Fn - BackgroundNoise| is smaller than the value of BgnAbnormalThd. The purpose is to prevent burst interference and RTWP spike. If it
is smaller than the value of BgnAbnormalThd, the RNC performs the next step. Otherwise, the RNC sets the counter to zero and waits for the next RTWP measurement value.
8. The RNC determines whether |Fn - current background noise| is greater than the value of BgnUpdateThd. The purpose is to prevent frequent background noise upgrades on the
Iub interface. If it is greater than the value of BgnUpdateThd, the RNC sets the current background noise to Fn, sets the counter to zero, and waits for the next RTWP
measurement value. Otherwise, the RNC sets the counter to zero and waits for the next RTWP measurement value.
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5
Potential User Control Algorithm
In the WCDMA system, the mobility management of the UE in idle or connected mode is implemented by cell selection and reselection. The Potential User Control (PUC) algorithm controls the cell selection and cell reselection of the potential UE and prevents an idle UE from camping on a heavily loaded cell.
The PUC algorithm is only valid for inter-frequency cells. Figure 5-7 shows the PUC procedure.
Figure 5-7 PUC procedure
Adjust the parameters of the current cell and neighboring cells
according to the load
Yes No
Update and broadcast the system information of the current cell and
neighboring cells Periodically monitor the load of the
current cell and neighboring cells
Are these parameters changed?
The PUC algorithm is enabled only when the PUC subparameter of the NBMLdcAlgoSwitch parameter is set to 1.
The RNC periodically monitors the downlink load of the cell.
If the cell load is higher than the upper threshold (SpucHeavy) plus the load level
division hysteresis (SpucHyst), the cell load is considered heavy.
If the cell load is lower than the lower threshold (SpucLight) minus SpucHyst, the cell load is considered light.
Figure 5-8 Cell load states
PUC takes effect only in downlink.
Based on the cell load, the PUC works as follows:
If the cell load becomes heavy, the PUC modifies cell selection and reselection
parameters and broadcasts them through system information. In this way, the PUC leads UEs to the neighboring cells with light load.
If the cell load becomes normal, the PUC uses the cell selection and reselection parameters configured on the RNC LMT.
If the cell load becomes light, the PUC modifies cell selection and reselection parameters and broadcasts them through system information. In this way, the PUC leads UEs to this cell.
Table 5-4 describes PUC-related variables and their impacts on UEs.
Table 5-4 PUC-related variables and their impacts on UEs
Item Description
Implementation The variables related to cell selection and reselection are Qoffset1(s,n) (load level offset), Qoffset2(s,n) (load level offset), and Sintersearch (start threshold for inter-frequency cell reselection).
The NodeB periodically reports the transmit power of the cell, and the PUC periodically triggers the following activities:
Assessing the cell load level based on the non-HSPA power and
HS-DSCH GBP
Setting Sintersearch, Qoffset1(s,n), and Qoffset2(s,n) based on the cell
load level
Issue Error! Unknown Error! Unknown document property 3
Item Description
Adjustment Based on the characteristics of inter-frequency cell selection and reselection, the UE makes the corresponding adjustments:
Sintersearch
- When this value is increased by the serving cell, the UE starts
inter-frequency cell reselection ahead of schedule.
- When this value is decreased by the serving cell, the UE delays
inter-frequency cell reselection.
Qoffset1(s,n): applies to R (reselection) rule with CPICH RSCP
- When this value is increased by the serving cell, the UE has a
lower probability of selecting a neighboring cell.
- When this value is decreased by the serving cell, the UE has a
higher probability of selecting a neighboring cell.
Qoffset2(s,n): applies to R (reselection) rule with CPICH Ec/I0
- When this value is increased by the serving cell, the UE has a
lower probability of selecting a neighboring cell.
- When this value is decreased by the serving cell, the UE has a
higher probability of selecting a neighboring cell.
Depending on the load status of the current cell, the cell reselection parameters are adjusted. The setting of Sintersearch affects the current cell. Its value is related to the load of the current cell. Table 5-5 describes the changes of Sintersearch.
Table 5-5 Changes of Sintersearch according to the load state Load State of the
Current Cell Sintersearch Change of Sintersearch
Light S'intersearch = Sintersearch + OffSinterLight
Normal S'intersearch = Sintersearch →
Heavy S'intersearch = Sintersearch + OffSinterHeavy →: indicates that the parameter value remains unchanged.
: indicates that the parameter value increases. : indicates that the parameter value decreases.
The configuration of Qoffset1 and Qoffset2 affects the neighboring cells. Their values are related to the load of the current cell and the load of the neighboring cells. Table 5-6 describes the changes of Qoffset1 and Qoffset2.
Table 5-6 Changes of Qoffset1 and Qoffset2 according to the load state Load State of the Neighboring Cells Load State of the Current Cell Q'offset1 Change of
Q'offset1 Q'offset2 Change of Q'offset2
Light Light Q'offset1 = Qoffset1 → Q'offset2 = Qoffset2 →
Light Normal Q'offset1 = Qoffset1 → Q'offset2 = Qoffset2 →
Light Heavy Q'offset1 = Qoffset1 +
OffQoffset1Light
Q'offset2 = Qoffset2 +
OffQoffset2Light
Normal Light Q'offset1 = Qoffset1 → Q'offset2 = Qoffset2 →
Normal Normal Q'offset1 = Qoffset1 → Q'offset2 = Qoffset2 →
Normal Heavy Q'offset1 = Qoffset1 +
OffQoffset1Light
Q'offset2 = Qoffset2 +
OffQoffset2Light
Heavy Light Q'offset1 = Qoffset1 +
OffQoffset1Heavy
→ Q'offset2 = Qoffset2 +
OffQoffset2Heavy
→
Heavy Normal Q'offset1 = Qoffset1 +
OffQoffset1Heavy
Q'offset2 = Qoffset2 +
OffQoffset2Heavy
Heavy Heavy Q'offset1 = Qoffset1 → Q'offset2 = Qoffset2 →
The prerequisite for the changes of the preceding parameters is that these parameters take their default values.
Issue Error! Unknown Error! Unknown document property 1
6
Intelligent Access Control Algorithm
The access of a service to the network consists of setup of an RRC connection and a RAB. The Intelligent Access Control (IAC) algorithm is used to improve the access success rate.
This chapter consists of the following sections:
IAC Overview
IAC During RRC Connection Setup Rate Negotiation
RAB DRD
Preemption Queuing
Low-Rate Access of the PS BE Service
IAC for Emergency Calls
6.1 IAC Overview
Figure 6-9 Service access control procedure
Admission algorithm
Fails or not supported
Fails Target cell selected Fails Succeeds RAB processing RRC connection processing Rate negotiation PS domain: maximum rate PS and CS domains: initial rate Code admission Power admission Credit admission Iub resource admission Fails RRC connection request Admission algorithm DRD Redirection
RAB setup request
HSPA user number admission Succeeds PS domain: GBR of PS RT service Service request accepted Preemption Queuing
Fails or not supported Succeeds Succeeds Succeeds Fails No Yes Service steering DRD Load balancing DRD Is there any inter-frequency cell not tried? Service request denied Target Rate Negotiation Service-based RRC redirection Lead UE to another cell
Access from another cell
Access from current cell
Succeeds
Low-rate access
Fails or not supported Succeeds
Inter-frequency DRD algorithm
Inter-RAT DRD
Fails or not supported
Lead UE to the inter-RAT cell
Succeeds
As shown in Figure 6-9, the procedure of service access includes the procedures for RRC connection setup and RAB setup. The successful setup of the RRC connection is one of the prerequisites for the RAB setup.
During the RRC connection processing, the RNC first performs RRC redirection for
service steering:
− If the RNC decides UE access from the current cell, it then makes a resource-based admission decision through the CAC algorithm. If the resource-based admission fails, the RNC performs DRD and redirection.
The resources include power resource, code resource, Iub resource, credit resource, and number of HSPA users.
− If the RNC decides UE access from another cell, it then sends an RRC connection reject message to the UE. The message carries the information about the cell and instructs the UE to set up an RRC connection to the cell.
During the RAB processing, the RNC performs the following steps:
1. Performs inter-frequency DRD to select a suitable cell for service steering or load balancing.
Issue Error! Unknown Error! Unknown document property 3 2. Performs rate negotiation according to the service requested by the UE.
3. Makes cell resource–based admission decision. If the admission is successful, UE access is granted. Otherwise, the RNC performs the next step.
4. Selects a suitable cell, according to the inter-frequency DRD algorithm, from the cells where no admission attempt has been made, and then goes to 2. If the attempt fails, the RNC performs the next step.
5. selects a suitable cell, according to the inter-RAT DRD algorithm. If the inter-RAT access is successful, UE access in the inter-RAT cell. If the inter-RAT DRD fails or is not supported, the RNC performs the next step.
6. Makes a preemption attempt. If the preemption is successful, UE access is granted. If the preemption fails or is not supported, the RNC performs the next step.
7. Makes a queuing attempt. If the queuing is successful, UE access is granted. If the queuing fails or is not supported, the RNC performs the next step.
8. Performs low-rate access. If the low-rate access is successful, UE access is granted. If the low-rate access is unsuccessful, the RNC performs the next step.
9. Rejects UE access.
After the admission attempts of an HSPA service request fail in all candidate cells, the service falls back to the DCH. Then, the service reattempts to access the network.
Table 6-7 IAC procedure supported by services Service
Type Low-Rate Access Rate Negotiation Preemption Queuing DRD
M B R N egot iat ion G B R N egoti at io n Ini ti al R at e N egoti at io n T arget R at e N egoti at io n Int er - Freq uen cy Int er -R A T DCH √ √ √ √ √ √ √ √ √ HSUPA - √ √ √ √ √ √ √ – HSDPA - √ √ – – √ √ √ –
In the previous table, MBR stands for maximum bit rate.
For details about CAC, see 7 "Call Admission Control Algorithm."
6.2 IAC During RRC Connection Setup
Before a new service is admitted to the network, an RRC connection must be set up.
During the RRC connection setup, the RRC redirection for service steering algorithm is used for service steering and load sharing between inter-frequency or inter-RAT cells.
When the resources of a cell for UE access are insufficient, the RNC instructs the UE to an inter-frequency or inter-RAT cell through DRD or redirection to increase the access rate.
Figure 6-10 RRC connection setup procedure RRC DRD and redirection UE RNC 1. RRC CONNECTION REQUEST No 2. RRC CONNECTION SETUP
3. RRC CONNECTION SETUP COMPLETE 2. RRC CONNECTION REJECT
Yes
No Yes
RRC redirection
Does the resource request succeed?
Is any candidate cell available? Is the switch of RRC redirection for service
steering ON?
Yes No
May the UE accesses the network from
the current cell?
Yes
No
After receiving an RRC CONNECTION REQUEST message from the UE, the RNC uses the RRC redirection algorithm for service steering to decide whether the UE may access the network from the current cell:
If the UE needs to access the network from another cell according to the decision, the
RNC sends an RRC CONNECTION REJECT message to the UE. The message carries the information about this cell.
If the UE attempts to access the network from the current cell according to the decision,
the RNC uses the CAC algorithm to decide whether an RRC connection can be set up between the UE and the current cell.
Issue Error! Unknown Error! Unknown document property 5 − If the RRC connection can be set up between the UE and the current cell, the RNC sends an RRC CONNECTION SETUP message to the UE. For details about CAC, see 7 "Call Admission Control Algorithm."
− If no RRC connection can be set up between the UE and the current cell, the RNC attempts to set up an RRC connection through RRC DRD or RRC redirection.
6.2.1 RRC Redirection for Service Steering
This algorithm is not applicable to combined services.
The switch of RRC redirection for service steering can be set through the DR_ RRC_DRD_SWITCH subparameter of the DrSwitch parameter.
During the RRC connection setup, the RNC implements service steering between inter-frequency or inter-RAT cells according to the cause of RRC connection setup. In addition, the RNC considers the load of the cell for access and the redirection factors to control the degree of load balancing.
The procedure of RRC redirection for service steering is as follows:
1. The RNC obtains the information about the service requested by the UE and the capability of the UE.
2. If the switch of RRC redirection for service steering is on, the RNC determines the service type requested by the UE. If the switch is off or the RNC fails to determine the service type, the RNC handles the RRC connection setup request of the UE in the current cell.
3. If the RNC succeeds in determining the service type requested by the UE and the switch of RRC direction for service steering (RedirSwitch) is set to
ONLY_TO_INTER_FREQUENCY or ONLY_TO_INTER_RAT, the RNC performs
the next step. Otherwise, the RNC handles the RRC connection setup request of the UE in the current cell.
4. Based on the cell load and the redirection factors, the RNC decides whether to perform RRC redirection for service steering.
− If the cell is normal, the RNC generates a random number between 0 and 1 and compares it with the corresponding unconditional redirection factor
(RedirFactorOfNorm). If the random number is smaller than this factor, the RNC performs the next step. Otherwise, the RNC handles the RRC connection setup request of the UE in the current cell.
− If the cell is in the basic congestion or overload state, the RNC generates a random number between 0 and 1 and compares it with the corresponding LDR-triggered redirection factor (RedirFactorOfLDR). If the random number is smaller than this factor, the RNC performs the next step. Otherwise, the RNC handles the RRC connection setup request of the UE in the current cell.
5. Based on the setting of RedirSwitch, the RNC takes the corresponding actions:
− If RedirSwitch is set to ONLY_TO_INTER_FREQUENCY, the RNC sends an RRC CONNECTION REJECT message to the UE, redirecting the UE to the destination frequency carried in the message.
The frequency information carried in the message can be set through the parameters RedirBandInd,
ReDirUARFCNUplinkInd, ReDirUARFCNUplink, and ReDirUARFCNDownlink. − If RedirSwitch is set to ONLY_TO_INTER_RAT, the RNC sends an RRC
CONNECTION REJECT message to the UE. The message carries the information about inter-RAT neighboring cells.
6.2.2 RRC DRD
If the DR_ RRC_DRD_SWITCH subparameter of the DrSwitch parameter is set to 0, the RNC performs RRC redirection without performing RRC DRD. Otherwise, the RNC performs the following steps:
1. The RNC selects intra-band inter-frequency neighboring cells of the current cell. These neighboring cells are suitable for blind handovers.
2. The RNC generates a list of candidate DRD-supportive inter-frequency cells. The quality of the candidate cell meets the requirements of inter-frequency DRD:
Here:
− is the cached CPICH Ec/N0 value included in the RACH
measurement report.
− is the DRD threshold (DRDEcN0Threshhold).
3. The RNC selects a target cell from the candidate cells for UE access. If the candidate cell list contains more than one cell, the UE tries a cell randomly.
− If the admission is successful, the RNC initiates an RRC DRD procedure.
− If the admission to a cell fails, the UE tries admission to another cell in the candidate cell list. If all the admission attempts fail, the RNC makes an RRC redirection decision.
4. If the candidate cell list does not contain any cell, the RRC DRD fails. The RNC performs the next step, that is, RRC redirection.
6.2.3 RRC Redirection After DRD Failure
When the RRC DRD fails, the associated RRC connection fails to be set up if the DR_
RRC_DRD_SWITCH subparameter of the DrSwitch parameter is set to 0 or if the switch of
RRC redirection after DRD failure (ConnectFailRrcRedirSwitch) is set to OFF. Otherwise, the RNC performs the following steps when the RRC DRD fails:
1. The RNC selects all intra-band inter-frequency cells of the local cell.
2. The RNC selects candidate cells. The candidate cells are the cells selected in step 1 but exclude the cells that have carried out inter-frequency RRC DRD attempts.
3. If more than one candidate cell is available, the RNC selects a cell randomly and redirects the UE to the cell.
4. If no candidate cell is available,
− If the switch of RRC redirection after DRD failure is set to
Only_To_Inter_Frequency, the RRC connection setup fails.
− If the switch of RRC redirection after DRD failure is set to Allowed_To_Inter_RAT, then:
a.If a neighboring GSM cell is configured, the RNC redirects the UE to that GSM cell. b.If no neighboring GSM cell is configured, the RRC connection setup fails.
Issue Error! Unknown Error! Unknown document property 7
6.3 Rate Negotiation
Rate negotiation includes MBR negotiation, GBR negotiation, initial rate negotiation, and target rate negotiation.
For details about AMR and AMR-WB speech services in the CS domain, see the Rate Control Parameter Description.
6.3.1 PS MBR Negotiation
If the IE "Alternative RAB Parameter Values" is present in the RANAP RAB ASSIGNMENT REQUEST or the RELOCATION REQUEST message when a PS service is set up,
reconfigured, or admitted, then the RNC and the CN negotiate the rate according to the UE capability to obtain the MBR while ensuring a proper QoS.
For the PS streaming service, when PS_STREAM_IU_QOS_NEG_SWITCH is set to
1, the Iu QoS negotiation function is enabled for MBR negotiation.
For the PS BE service:
− When both PS_BE_IU_QOS_NEG_SWITCH and
PS_BE_STRICT_IU_QOS_NEG_SWITCH are set to 1, the Iu QoS negotiation
function is enabled, and the RNC determines the MBR of Iu QoS negotiation based on the information about UE capability, cell capability and other settings..
− When PS_BE_IU_QOS_NEG_SWITCH is set to 1 and
PS_BE_STRICT_IU_QOS_NEG_SWITCH is set to 0, the Iu QoS negotiation
function is enabled, and the RNC determines the MBR of Iu QoS negotiation based on the maximum rate supported by the UE rather than the cell capability and other settings.
6.3.2 PS GBR Negotiation
During the setup, reconfiguration, or handover of a real-time PS service, if the RAB assignment message carries multiple alternative GBRs and
PS_STREAM_IU_QOS_NEG_SWITCH is set to 1, the RNC selects the minimum rate as
the GBR of this RAB and sends it to the CN. If the IE "Type of Alternative Guaranteed Bit Rate Information" in the message is set to unspecified, the GBR is set to 8 kbit/s.
6.3.3 Initial Rate Negotiation
For a non-real-time service in the PS domain, the RNC selects an initial rate to allocate bandwidth for the service before the admission request based on cell resources in the following cases:
A service is set up.
The UE state changes from CELL_FACH to CELL_DCH.
The negotiation is based on the cell load information, which includes:
Uplink and downlink radio bearer status of the cell Minimum spreading factor (SF) supported
HSPA capability
Initial Rate Definition for DCH Services
DCCC
Switch PS BE Initial Rate Dynamic Configuration Switch
Actual Initial Rate
ON ON In the uplink, the initial rate is the smaller one of the MBR and 384 kbit/s.
In the downlink, the initial rate is dynamically set on the basis of Ec/N0. For the specific method, see the description following this table.
ON OFF In the uplink, the initial rate is the smaller one of the MBR and the initial rate of the uplink BE service.
In the downlink, the initial rate is the smaller one of the MBR and the initial rate of the downlink BE service.
OFF - MBR
The parameter corresponding to the DCCC switch is DCCC_SWITCH.
The parameter corresponding to the PS BE initial rate dynamic configuration switch is
PS_BE_INIT_RATE_DYNAMIC_CFG_SWITCH.
As described in the table, when the two switches are ON, the initial rate is dynamically set on the basis of Ec/N0 in the downlink. The specific method is as follows:
When receiving an RRC connection setup request, the RNC starts the timer
EcN0EffectTime.
Before the timer expires, the RNC dynamically sets the initial rate based on the P-CPICH Ec/N0 carried in the RRC CONNECTION REQUEST message:
− If the cell Ec/N0 is above the Ec/N0 threshold (EcN0Ths), the RNC sets the actual initial rate to the smaller one of the MBR and 384 kbit/s.
− If the cell Ec/N0 is below or at the Ec/N0 threshold (EcN0Ths) or the RRC
CONNECTION REQUEST message does not carry the information about Ec/N0, the RNC sets the actual initial rate to the smaller one of the MBR and the initial rate of the downlink BE service (DlBeTraffInitBitrate).
If the DCCC function is enabled and PS_RAB_Downsizing_Switch is set to 1, the RNC can decrease the rate through the RAB rate decrease function when the admission based on the initial rate fails.
Initial Rate Definition for HSUPA Services
For the HSUPA service, the initial rate is defined as follows:
If HSUPA_DCCC_SWITCH is set to 1, the actual initial rate is the initial rate of the HSUPA BE service (HsupaInitialRate).
Issue Error! Unknown Error! Unknown document property 9
6.3.4 Target Rate Negotiation
For a non-real-time service in the PS domain, if cell resource–based admission fails, the RNC selects a target rate to allocate bandwidth for the service based on cell resource in following cases:
Service setup
Soft handover
DCCC rate upsizing
If the cell has sufficient code and CE resources, the RNC sets the candidate target rate to the one that matches the cell resource surplus. Then, the RNC sets the target rate to the greater one of the candidate target rate and the GBR.
In the case of soft handover, the actual target rate is the candidate target rate set by the RNC.
In the case of DCCC rate upsizing, if the rate upsizing fails, the target rate is the greater one of the candidate target rate and the pre-upsizing DCCC rate.
6.4 RAB DRD
RAB DRD is used to select a suitable cell for the UE to try an access.
For a single service, RAB DRD can be enabled by the DR_RAB_SING_DRD_SWITCH subparameter of the DrSwitch parameter.
For combined services, RAB DRD can be enabled by the
DR_RAB_COMB_DRD_SWITCH subparameter of the DrSwitch parameter.
6.4.1 RAB DRD Overview
Through the RAB DRD procedure, the RNC selects a suitable cell for RAB processing during access control. RAB DRD is of two types: inter-frequency DRD and inter-RAT DRD. Inter-frequency DRD is further classified into Inter-frequency DRD for service steering and inter-frequency DRD for load balancing.
After receiving a Radio Access Network Application Part (RANAP) message RAB
ASSIGNMENT REQUEST, the RNC initiates a RAB DRD procedure to select a suitable cell for RAB processing during access control.
The basic procedure of RAB DRD is as follows:
1. The RNC performs inter-frequency DRD. According to the purposes of directed retry, Inter-frequency DRD is of the following types:
− Inter-frequency DRD for service steering
For details, see Inter-Frequency DRD for Service Steering.
− Inter-frequency DRD for load balancing
For details, see Inter-Frequency DRD for Load Balancing.
2. If all admission attempts of inter-frequency DRD fail, the RNC performs an inter-RAT DRD.
3. If all admission attempts of inter-RAT DRD fail, the RNC selects a suitable cell to perform preemption and queuing (for selection of the target cell for preemption or queuing, see Preemption).
For details about preemption and queuing, see Preemption and Queuing, respectively.
6.4.2 Inter-Frequency DRD for Service Steering
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" is called "DRD for service steering" for short in this section.
Cell Service Priorities Introduction
Cell service priorities refer to the priorities of cells under the same coverage accepting specific service types. These priorities help achieve traffic absorption in a hierarchical way.
The priorities of specific service types in cells are configurable. If a cell does not support a service type, the priority of this service type is set to 0 in this cell. The group of service priorities in each cell is specified by the service priority group identity (SpgId) parameter.
Service priority groups are configured on the LMT. In each group, priorities of R99 RT services, R99 NRT services, HSPA services, and other services are defined.
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.
Assume that the service priority groups given in the following table are defined on an RNC.
Cell Service Priority Group Identity
Service Priority
of R99 RT Service Service Priority of R99 NRT Service Service Priority of HSPA Service Service Priority of Other Service
A 1 2 1 1 0
B 2 1 2 0 0
As shown in Figure 6-11, cell B has a higher service priority of the R99 RT service than cell A. If the UE requests an RT service in cell A, preferably the RNC selects cell B for the UE to access.
Issue Error! Unknown Error! Unknown document property 11
Figure 6-11 Example of DRD for service steering
RT service Cell A
Cell B
Cell Service priority group identity
A 1
B 2
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.
Procedure of DRD for Service Steering
This section describes the procedure of DRD for service steering when DRD for load balancing is disabled.
Figure 6-12 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.
− The frequency of the candidate cell is within the band supported by the UE.
− The quality of the candidate cell meets the requirements of inter-frequency DRD. For details, see 6.2 "IAC During RRC Connection Setup."
− The candidate cell supports the requested service.
2. The RNC selects a target cell from the candidate cells in order of service priority for UE 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 whether all candidate cells are tried.
− 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.
6.4.3 Inter-Frequency DRD for Load Balancing
If the UE requests a service setup or channel reconfiguration in an area covered by multiple frequencies, the RNC sets up the service on a carrier with a light load to achieve load balancing among the cells on the different frequencies.
"Inter-frequency DRD for load balancing" is called "DRD for load balancing" for short in this section.
Overview of DRD for Load Balancing
Load balancing considers two resources, power, and code.
The availability of DRD for load balancing is specified by the associated parameters as follows:
The availability of power-based DRD for load balancing for DCH service is specified by
the LdbDRDSwitchDCH parameter.
The availability of power-based DRD for load balancing for HSDPA service is specified
by the LdbDRDSwitchHSDPA parameter.
The availability of code-based DRD for load balancing is specified by the
CodeBalancingDrdSwitch parameter.
In practice, it is recommended that only either a power-based DRD for load balancing or a code-based DRD for load balancing is activated. If both are activated, power-based DRD for load balancing takes precedence over code-based DRD for load balancing.
Code-based DRD for load balancing is applicable to only R99 services because HSDPA services use reserved codes.
Issue Error! Unknown Error! Unknown document property 13
Power-Based DRD for Load Balancing
This section describes the procedure of DRD for load balancing when DRD for service steering is disabled.
The following two algorithms are available for power-based load balancing. If power-based DRD for load balancing is enabled, one of them can be used. The algorithm used is specified by the LdbDRDchoice parameter.
Algorithm 1: DRD for load balancing is performed according to the cell measurement
values about the DL non-HSDPA power and DL HS-DSCH GBP.
− For DCH service, the RNC sets up the service on a carrier with a light load of non-HSPA power to achieve load balancing among the cells at the different frequencies.
− For HSDPA service, the RNC sets up the service on a carrier with a light load of HS-DSCH GPB to achieve load balancing among the cells at different frequencies.
Algorithm 2: DRD for load balancing is performed according to the DCH ENU and
HSDPA user number.
− For DCH service, the RNC sets up the service on a carrier with a light load of DCH ENU to achieve load balancing among the cells on different frequencies.
− For HSDPA service, the RNC sets up the service on a carrier with a light load of HSDPA user to achieve load balancing among the cells on different frequencies.
As shown in Figure 6-13:
Cell B has a lighter load of non-HSDPA power than cell A. If the UE requests a DCH service in cell A, preferably, the RNC selects cell B for the UE to access.
Cell A has a lighter load of HS-DSCH GBP than cell B. If the UE requests an HSDPA
service in cell B, preferably, the RNC selects cell A for the UE to access.
Figure 6-13 Power-based DRD for load balancing
Cell A Cell B
Load of HS-DSCH GBP Load of non-HSDPA power
Load
DCH service HSDPA service
Figure 6-14 Procedure of power-based DRD for load balancing
Receive a service request
Does power of the current cell meet DRD condition 1?
Are there multiple such cells available?
Select the cell meeting the DRD conditions as
the target cell
Select the cell with the lightest power load as
the target cell
Select the current cell as
the target cell
CAC successful? Are all candidate cells tried? Is the request an HSPA one? Initiate an inter-RAT DRD Initiate a blind handover Yes Yes Yes Yes Yes Yes No No No No No Does power of a neighboring cell meet DRD
condition 2? HSPA falls
back to DCH
No
The procedure of power-based DRD for load balancing is as follows:
1. The RNC determines the candidate cells to which blind handovers can be performed. A candidate cell must meet the following conditions:
− The frequency of the candidate cell is within the band supported by the UE.
− The quality of the candidate cell meets the requirements of inter-frequency DRD.
− The candidate cell supports the requested service.
2. If the current cell is such a candidate cell, the RNC goes to step 3. Otherwise, the RNC selects a cell with the lightest load from the candidate cells as the target cell and then goes to step 4.
3. The RNC determines whether the DL radio load of the current cell is lower than the threshold of power-based DRD for load balancing (condition 1). Based on the bearer type (DCH or HSDPA) of the requested service, the RNC selects an appropriate condition.
