VoLTE Feature Parameter
Description
Issue 01
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Contents
1 About This Document... 1
1.1 Scope... 1
1.2 Intended Audience...2
1.3 Change History... 3
1.4 Differences Between eNodeB Types... 9
2 Overview... 11
2.1 Background...11
2.2 Introduction... 12
2.3 Benefits...13
2.4 Architecture... 13
3 Basic VoLTE Functions...18
3.1 Speech Codec Scheme and Traffic Model...19
3.2 VoLTE Voice Policy Selection...20
3.2.1 Common Scenarios...20
3.2.1.1 General Principles for Voice Policy Selection...20
3.2.1.2 VoLTE Mobility Capability Decision... 22
3.2.2 VoLTE-Prohibited Scenario...23
3.3 Radio Bearer Management... 25
3.3.1 Radio Bearer Setup...25
3.3.2 Radio Bearer QoS Management... 27
3.4 Admission and Congestion Control...28
3.4.1 Overview... 28
3.4.2 Load Monitoring...28
3.4.3 Admission Control...29
3.4.4 Congestion Control...29
3.5 Dynamic Scheduling and Power Control... 30
3.5.1 Dynamic Scheduling...30
3.5.2 Power Control in Dynamic Scheduling... 31
4 Enhanced VoLTE Features...32
4.1 Capacity Enhancement... 33
4.1.1 Semi-Persistent Scheduling and Power Control...33
4.1.1.2 Power Control in Semi-Persistent Scheduling...37
4.1.2 ROHC... 38
4.2 Coverage Improvement... 39
4.2.1 LOFD-001048 TTI Bundling... 39
4.2.1.1 Overview... 39
4.2.1.2 Principles... 39
4.2.2 LOFD-001017 RObust Header Compression (ROHC)...42
4.2.3 Uplink RLC Segmentation Enhancement...42
4.2.4 LOFD-111207 VoLTE Rate Control...43
4.2.4.1 Introduction... 43
4.2.4.2 Principles... 43
4.2.5 LOFD-081219 Inter-eNodeB VoLTE CoMP...46
4.3 Quality Improvement...47
4.3.1 LOFD-081229 Voice Characteristic Awareness Scheduling... 47
4.3.2 LBFD-081105 Uplink Compensation Scheduling...49
4.3.3 LBFD-081106 Voice-Specific AMC... 50
4.3.4 Preferential Access for Voice Service...51
4.3.4.1 Overview... 51
4.3.4.2 UE Identification... 51
4.3.4.3 UE Access Processing... 51
4.3.5 Uplink PUSCH RB Reservation for Voice UEs... 52
4.3.6 Uplink Voice Mute Recovery... 52
4.4 Power Saving...53 4.5 Mobility Management... 54 4.5.1 Overview... 54 4.5.2 Intra-Frequency Handover...54 4.5.3 Inter-Frequency Handover...55 4.5.4 Inter-RAT Handover... 56 4.5.4.1 Handover Type...56 4.5.4.2 Handover Mode... 58
5 Special Processing by Other Features...60
6 Related Features...63
6.1 Features Related to LBFD-081104 UL Compensation Scheduling...64
6.2 Features Related to LBFD-081105 Voice-Specific AMC... 64
6.3 Features Related to LOFD-001016 VoIP Semi-persistent Scheduling...65
6.4 Features Related to LOFD-001048 TTI Bundling... 67
6.5 Features Related to LOFD-081229 Voice Characteristic Awareness Scheduling... 70
6.6 Features Related to LOFD-111207 VoLTE Rate Control... 71
6.7 Features Related to Uplink RLC Segmentation Enhancement...71
6.8 Features Related to Preferential Access for Voice Service...72
7.1 LBFD-081104 UL Compensation Scheduling... 75
7.2 LBFD-081105 Voice-Specific AMC... 75
7.3 LOFD-001016 VoIP Semi-persistent Scheduling...76
7.4 LOFD-001048 TTI Bundling... 77
7.5 LOFD-081229 Voice Characteristic Awareness Scheduling... 77
7.6 LOFD-111207 VoLTE Rate Control...78
7.7 Uplink RLC Segmentation Enhancement...79
7.8 Preferential Access for Voice Service...79
7.9 Uplink PUSCH RB Reservation for Voice UEs... 79
7.10 Uplink Voice Mute Recovery... 80
8 Voice Service Performance Evaluation... 81
8.1 QoS Requirements...81 8.2 Quality Evaluation...81 8.2.1 Subjective Evaluation... 81 8.2.2 Objective Evaluation... 82 8.2.3 Measurement-based Evaluation...82 8.3 Capacity Evaluation...84 8.4 Performance Evaluation... 85
9 Engineering Guidelines... 86
9.1 Basic Functions...869.1.1 When to Use Basic Functions...86
9.1.2 Required Information... 87
9.1.3 Deployment... 87
9.1.3.1 Requirements... 87
9.1.3.2 Precautions...87
9.1.3.3 Hardware Adjustment...87
9.1.3.4 Data Preparation and Feature Activation...87
9.1.3.4.1 Data Preparation... 87
9.1.3.4.2 Using the CME... 90
9.1.3.4.3 Using MML Commands...90
9.1.3.4.4 MML Command Examples... 91
9.1.3.5 Activation Observation...91
9.1.3.6 Reconfiguration... 93
9.1.3.7 Deactivation...93
9.1.3.7.1 Using the CME... 94
9.1.3.7.2 Using MML Commands...94 9.1.3.7.3 MML Command Examples... 94 9.1.4 Performance Monitoring...94 9.1.4.1 Voice KPIs... 94 9.1.4.2 Voice QoS... 98 9.1.4.3 Voice Quality... 100 9.1.4.4 Voice Capacity... 105
9.1.5 Parameter Optimization...107
9.1.6 Troubleshooting... 107
9.2 Capacity Enhancement... 108
9.2.1 When to Use Semi-Persistent Scheduling and Deploy Power Control... 108
9.2.2 Required Information... 108
9.2.3 Deployment... 108
9.2.3.1 Requirements... 109
9.2.3.2 Precautions...109
9.2.3.3 Hardware Adjustment...109
9.2.3.4 Data Preparation and Feature Activation...109
9.2.3.4.1 Data Preparation... 109
9.2.3.4.2 Using the CME... 113
9.2.3.4.3 Using MML Commands... 113
9.2.3.4.4 MML Command Examples... 113
9.2.3.5 Activation Observation... 114
9.2.3.6 Reconfiguration... 117
9.2.3.7 Deactivation... 117
9.2.3.7.1 Using the CME... 117
9.2.3.7.2 Using MML Commands... 117 9.2.3.7.3 MML Command Examples... 118 9.2.4 Performance Monitoring...118 9.2.5 Parameter Optimization... 118 9.2.6 Troubleshooting... 118 9.3 Coverage Improvement...118
9.3.1 When to Use TTI Bundling... 119
9.3.2 Required Information...119
9.3.3 Deployment...119
9.3.3.1 Requirements... 119
9.3.3.2 Precautions...120
9.3.3.3 Hardware Adjustment...120
9.3.3.4 Data Preparation and Feature Activation...120
9.3.3.4.1 Data Preparation... 120
9.3.3.4.2 Using the CME... 128
9.3.3.4.3 Using MML Commands...128
9.3.3.4.4 MML Command Examples... 129
9.3.3.5 Activation Observation...129
9.3.3.6 Reconfiguration... 132
9.3.3.7 Deactivation...133
9.3.3.7.1 Using the CME... 133
9.3.3.7.2 Using MML Commands...133
9.3.3.7.3 MML Command Examples... 133
9.3.5 Parameter Optimization...133
9.3.6 Troubleshooting... 133
9.4 Voice Characteristic Awareness Scheduling...133
9.4.1 When to Use Voice Characteristic Awareness Scheduling... 133
9.4.2 Required Information... 134
9.4.3 Deployment... 135
9.4.3.1 Requirements... 135
9.4.3.2 Precautions...136
9.4.3.3 Hardware Adjustment...136
9.4.3.4 Data Preparation and Feature Activation...136
9.4.3.4.1 Data Preparation... 136
9.4.3.4.2 Using the CME... 142
9.4.3.4.3 Using MML Commands...142
9.4.3.4.4 MML Command Examples... 143
9.4.3.5 Activation Observation...143
9.4.3.6 Reconfiguration... 149
9.4.3.7 Deactivation...149
9.4.3.7.1 Using the CME... 149
9.4.3.7.2 Using MML Commands...149 9.4.3.7.3 MML Command Examples... 150 9.4.4 Performance Monitoring...150 9.4.5 Parameter Optimization...152 9.4.6 Troubleshooting... 152
10 Parameters...153
11 Counters... 263
12 Glossary...304
13 Reference Documents... 305
1
About This Document
1.1 Scope
This document describes Voice over LTE (VoLTE), including its technical principles, related features, network impact, and engineering guidelines. VoLTE is based on IP multimedia subsystem (IMS).
This document covers the following features:
l LOFD-001016 VoIP Semi-persistent Scheduling l LOFD-001048 TTI Bundling
l LOFD-081229 Voice Characteristic Awareness Scheduling l LBFD-081104 UL Compensation Scheduling
l LBFD-081105 Voice-Specific AMC l LOFD-111207 VoLTE Rate Control
For the technical principles of and engineering guidelines for the VoLTE-related features and functions listed in Table 1-1, see the corresponding feature parameter descriptions.
Table 1-1 VoLTE-related functions and features
Feature/Function Document
LBFD-002023 Admission Control Admission and Congestion Control Feature Parameter Description
LBFD-002024 Congestion Control Admission and Congestion Control Feature Parameter Description
LOFD-00101502 Dynamic Scheduling
Scheduling Feature Parameter Description Power control in dynamic scheduling Power Control Feature Parameter Description
Feature/Function Document LOFD-001017 RObust Header
Compression (ROHC)
ROHC Feature Parameter Description LOFD-001109 DL Non-GBR Packet
Bundling
Scheduling Feature Parameter Description Intra-frequency handover Intra-RAT Mobility Management in Connected
Mode Feature Parameter Description
Inter-frequency handover Intra-RAT Mobility Management in Connected Mode Feature Parameter Description
Inter-RAT handover For details about SRVCC, see SRVCC Feature
Parameter Description.
For details about PS handovers, see Inter-RAT Mobility Management in Connected Mode Feature Parameter Description.
LBFD-002017 DRX DRX and Signaling Control Feature Parameter
Description LOFD-081219 Inter-eNodeB VoLTE
CoMP
UL CoMP Feature Parameter Description
This document applies to the following types of eNodeBs.
eNodeB Type Model
Macro 3900 series eNodeB
Micro base station
BTS3202E BTS3911E
LampSite DBS3900 LampSite
Any managed objects (MOs), parameters, alarms, or counters described herein correspond to the software release delivered with this document. Any future updates will be described in the product documentation delivered with future software releases.
This document applies only to LTE FDD. Any "LTE" in this document refers to LTE FDD, and "eNodeB" refers to LTE FDD eNodeB.
1.2 Intended Audience
This document is intended for personnel who: l Need to understand the features described herein l Work with Huawei products
1.3 Change History
This section provides information about the changes in different document versions. There are two types of changes:
l Feature change
Changes in features and parameters of a specified version as well as the affected entities l Editorial change
Changes in wording or addition of information and any related parameters affected by editorial changes. Editorial change does not specify the affected entities.
eRAN 11.1 01 (2016-03-07)
This issue includes the following changes. Change
Type Change Description ParameterChange AffectedEntity
Feature change
The eNodeB supports configuration of the
CellHoParaCfg.HoMrDelayTimer Qci1 parameter for QCI 1. Revised the following sections:
3.3.1 Radio Bearer Setup 9.1 Basic Functions Added the following parameters: CellHoParaCf g.HoMrDelayT imerQci1 Macro, micro, and LampSite eNodeBs Editorial change None None
-eRAN11.1 Draft A (2015-12-30)
Compared with Issue 03 (2015-06-30) of eRAN8.1, Draft A (2015-12-30) of eRAN11.1 includes the following changes.
Change
Type Change Description ParameterChange AffectedEntity
Feature change
Modified the Independent
Configurations for the UE Inactivity Timer for Voice Services function to support the configuration of the UE inactivity timer by QCI. Revised the following sections: 4.3.1 LOFD-081229 Voice Characteristic Awareness Scheduling 7.5 LOFD-081229 Voice Characteristic Awareness Scheduling 9.4 Voice Characteristic Awareness Scheduling Added the following parameters: GlobalProcSwi tch.QciParaEff ectFlag QciPara.UeIna ctiveTimerPri QciPara.UeIna ctivityTimerDy nDrxQci QciPara.UeIna ctiveTimerFor Qci Macro, micro, and LampSite eNodeBs
Added optimization of cooperation between semi-persistent scheduling and DRX. Revised the following sections:
4.1.1.2 Power Control in Semi-Persistent Scheduling
7.3 LOFD-001016 VoIP Semi-persistent Scheduling 9.2 Capacity Enhancement Added the following parameter: Added the SpsAndDrxOp tSwitch option to the CellUlSchAlgo .UlEnhencedVo ipSchSw parameter. Macro, micro, and LampSite eNodeBs
Added the uplink voice mute recovery function. Added the following sections:
4.3.6 Uplink Voice Mute Recovery 7.10 Uplink Voice Mute Recovery
Revised the following section:
9.4 Voice Characteristic Awareness Scheduling Added the following parameter: Added the UlCallMuteRe coverSwitch(U lCallMuteReco verSwitch) option to the CellUlschAlgo. UlEnhencedVoi pSchSw parameter. Macro, micro, and LampSite eNodeBs
Change
Type Change Description ParameterChange AffectedEntity
Deleted the Power Control in Downlink Semi-Persistent Scheduling function. Revised the following sections:
4.1.1.2 Power Control in Semi-Persistent Scheduling 9.2 Capacity Enhancement Deleted the following parameter: Deleted the PdschSpsPcSw itch option from the CellAlgoSwitc h.DlPcAlgoSwi tch parameter. Macro, micro, and LampSite eNodeBs
Enabled dynamic scheduling to use the HARQ processes reserved for semi-persistent scheduling. Revised the following section:
4.1.1.1 LOFD-001016 VoIP Semi-persistent Scheduling Added the following parameter: Added the DlSpsRevHarq UseSwitch(DlS psRevHarqUse Switch) option to the CellDlschAlgo. DlEnhancedVo ipSchSw parameter. Macro, micro, and LampSite eNodeBs
Allowed the semi-persistent scheduling interval to be set to 20 ms or 40 ms.
Revised the following section:
4.1.1.1 LOFD-001016 VoIP Semi-persistent Scheduling Added the following parameters: l CellUlschAl go.UlSpsInt erval l CellDlschAl go.DlSpsInt erval Macro, micro, and LampSite eNodeBs
Supported the configuration of the target SINR in TTI bundling. Revised the following section:
4.2.1 LOFD-001048 TTI Bundling
Added the following parameter: CellTtiBundlin gAlgo.SinrThd ToTrigTtib Macro, micro, and LampSite eNodeBs
Change
Type Change Description ParameterChange AffectedEntity
Added the VoLTE Rate Control feature. Added the following sections:
l 4.2.4 LOFD-111207 VoLTE Rate Control
l 6.6 Features Related to LOFD-111207 VoLTE Rate Control
l 7.6 LOFD-111207 VoLTE Rate Control
Revised the following sections: l 1.1 Scope l 1.4 Differences Between eNodeB Types l 2.4 Architecture l 4.2 Coverage Improvement l 9.3 Coverage Improvement Added the following parameters: l CellAlgoSw itch.UlAmrc Mode l VoiceAmrC ontrol.High AmrCoding Mode l VoiceAmrC ontrol.Low AmrCoding Mode l VoiceAmrC ontrol.PlrT hdForDecre asingAmr l VoiceAmrC ontrol.PlrT hdForIncre asingAmr l VoiceAmrC ontrol.RsnT hdForDecre asingAmr l VoiceAmrC ontrol.RsnT hdForIncre asingAmr l CellAlgoSw itch.AmrcAl goSwitch l Added the UL_AMRC _SWITCH_ OFF option to the UeCompat Opt.BlkLst CtrlSwitch parameter. l Added the UL_AMRC _SWITCH_ ON option Macro, micro, and LampSite eNodeBs
Change
Type Change Description ParameterChange AffectedEntity
to the UeCompat Opt.WhiteL stCtrlSwitch parameter. Supported end-to-end voice quality
evaluation. Revised the following sections: l 8.2.3 Measurement-based Evaluation l 9.1 Basic Functions Added the following parameter: EnodebAlgoS witch.E2EVQI AlgoSwitch VQMAlgo.VQ MAlgoPeriod Macro, micro, and LampSite eNodeBs
Optimized downlink semi-persistent scheduling AMC and revised the following sections: l 4.1.1.1 LOFD-001016 VoIP Semi-persistent Scheduling l 9.2 Capacity Enhancement Added the following parameters: CellDlschAlgo. DlSpsMcsDecr easeIblerThd CellAlgoSwitc h.CqiAdjAlgoS witch Macro, micro, and LampSite eNodeBs
Supported load-based scheduling and updated the following sections: l 4.1.1.1 LOFD-001016 VoIP Semi-persistent Scheduling l 9.2 Capacity Enhancement Changed the following parameters: CellUlSchAlgo .UlEnhencedVo ipSchSw CellDlSchAlgo .DlEnhancedV oipSchSw Macro, micro, and LampSite eNodeBs
Supported downlink voice packet bundling and revised the following sections: l 3.5.1 Dynamic Scheduling l 9.1.3 Deployment Added the following parameter: Added the DlVoipBundlin gSwitch option to the CellAlgoSwitc h.DlSchSwitch parameter. Macro, micro, and LampSite eNodeBs
Change
Type Change Description ParameterChange AffectedEntity
Optimized uplink dynamic scheduling and revised the following sections: l 4.3.2 LBFD-081105 Uplink Compensation Scheduling l 9.4 Voice Characteristic Awareness Scheduling Added the following parameters: CellUlschAlgo. UlCompenSch PeriodinSpurt CellUlschAlgo. UlCompenSch PeriodinSilenc e Added the UlVoipServSta teEnhancedSw option to the CellUlschAlgo. UlEnhencedVoi pSchSw parameter. Macro, micro, and LampSite eNodeBs
Added the preferential access for voice service function and added the following sections:
l 4.3.4 Preferential Access for Voice Service
l 6.8 Features Related to Preferential Access for Voice Service
l 7.8 Preferential Access for Voice Service
Revised the following sections: l 1.1 Scope l 2.4 Architecture l 9.4 Voice Characteristic Awareness Scheduling Added the following parameters: Added the VoltePrefAdmi ssionSwitch option to the CellAlgoSwitc h.RacAlgoSwit ch parameter. CellRacThd.Vo lteReservedNu mber CellRacThd.Vo ltePrefAdmissi onTimer Macro, micro, and LampSite eNodeBs
Added the AC Barring Skip feature and revised 5 Special Processing by Other Features.
None Macro, micro,
and LampSite eNodeBs
Change
Type Change Description ParameterChange AffectedEntity
Added uplink PUSCH PRB
reservation for voice UEs and added the following sections:
l 4.3.5 Uplink PUSCH RB Reservation for Voice UEs
l 7.9 Uplink PUSCH RB Reservation for Voice UEs
Revised the following section:
9.4 Voice Characteristic Awareness Scheduling Added the following parameters: CellAlgoSwitc h.UlSchExtSwi tch CellUlschAlgo. UlVoipRsvRbSt art CellUlschAlgo. UlVoipRsvRbN um Macro, micro, and LampSite eNodeBs Supported independent
configurations for the UE inactivity timer for voice services and Revised the following sections:
4.3.1 LOFD-081229 Voice Characteristic Awareness Scheduling Added the following parameters: RrcConnState Timer.UeInact TimerDynDrx Qci1 Macro, micro, and LampSite eNodeBs
Supported VoLTE and data service delay scheduling. Revised the following sections: 4.3.1 LOFD-081229 Voice Characteristic Awareness Scheduling 7.5 LOFD-081229 Voice Characteristic Awareness Scheduling 9.4 Voice Characteristic Awareness Scheduling Changed the following parameter: Added the VOIP_AND_D ATA_DELAYS CH option to the CELLULSCH ALGO.UlDela ySchStrategy parameter. Macro, micro, and LampSite eNodeBs
Added the new micro eNodeB type BTS3911E.
None Micro
Editorial change
Revised 9 Engineering Guidelines. None
-1.4 Differences Between eNodeB Types
Feature Support by Macro, Micro, and LampSite eNodeBs
VoLTE services are implemented on the basis of multiple features and functions. The following table lists the differences of VoIP-related features between eNodeB types. For
details about other features and functions, see the corresponding feature parameter descriptions.
Feature ID Feature Name Suppor
ted by Macro eNode Bs Supported by Micro eNodeBs Supported by LampSite eNodeBs
LOFD-001016 VoIP Semi-persistent Scheduling
Yes Yes Yes
LOFD-001048 TTI Bundling Yes Yes Yes
LOFD-081229 Voice Characteristic Awareness Scheduling
Yes Yes Yes
LBFD-081105 UL Compensation
Scheduling
Yes Yes Yes
LBFD-081105 Voice-Specific AMC Yes Yes Yes
LOFD-111207 VoLTE Rate Control Yes Yes Yes
Function Implementation in Macro, Micro, and LampSite eNodeBs
Function Difference
High speed mobility
Micro and LampSite eNodeBs do not support high speed mobility. The dynamic scheduling policies for high speed mobility described herein apply only to macro eNodeBs. For details, see 3.5.1 Dynamic Scheduling.
1.4 MHz bandwidth
Micro and LampSite eNodeBs do not support 1.4 MHz bandwidth. The dynamic scheduling policies for 1.4 MHz bandwidth described herein apply only to macro eNodeBs. For details, see 3.5.1 Dynamic Scheduling.
2
Overview
2.1 Background
The LTE voice solution is as follows:
l Voice solution based on dual-standby UEs
A dual-standby UE is capable of receiving or sending signals in both E-UTRAN and GERAN or UTRAN. Dual-standby UEs automatically select GERAN or UTRAN to perform voice services and select UTRAN to perform data services. That is, the E-UTRAN provides dual-standby UEs with only data services.
l Voice solution based on CSFB
In the initial phase of LTE network deployment, CSFB is a transitional solution to provide voice services for LTE users if the IMS is not yet deployed. Figure 2-1 shows the voice solution based on CSFB.
Figure 2-1 Voice solution based on CSFB
With the CSFB solution, when a UE initiates a CS service in the E-UTRAN, the MME instructs the UE to fall back to the legacy CS domain of the GERAN or UTRAN before
the UE performs the service. For details about CSFB, see CS Fallback Feature Parameter Description.
l Voice solution based on IMS
This solution is used in the mature stage of the LTE network when the IMS is deployed, as shown in Figure 2-2. With this solution, UEs can directly perform voice services in an LTE network. This solution is also termed as the Voice over LTE (VoLTE) solution. When LTE coverage has not been complete, UEs may move out of LTE coverage and their voice services may be discontinued. Huawei uses the following methods to ensure voice service continuity:
– If the PS domain of the UTRAN/GERAN does not support VoIP services, VoIP services are handed over to the CS domain of the UTRAN/GERAN through single radio voice call continuity (SRVCC). For details about SRVCC, see SRVCC Feature Parameter Description.
– If the PS domain of the UTRAN/GERAN supports VoIP services, VoIP services are handed over to the UTRAN/GERAN through PS handovers. For details about PS handovers, see Inter-RAT Mobility Management in Connected Mode Feature Parameter Description.
Figure 2-2 Voice solution based on IMS
2.2 Introduction
VoLTE is the voice service supported by the IP transmission network between UEs in the E-UTRAN and the IMS. That is, with VoLTE, UEs in the LTE network can perform voice services directly.
Emergency services are not described in this document. For details about emergency services, see Emergency Call Feature Parameter Description.
2.3 Benefits
VoLTE provides UEs in the E-UTRAN with voice services, without the need of falling back to GERAN or UTRAN. VoLTE features the following characteristics:
l Higher spectral efficiency
l Better user experience, such as lower access delay and better voice quality
2.4 Architecture
Network Architecture
Figure 2-3 illustrates the LTE/SAE architecture in non-roaming scenarios. SAE is short for System Architecture Evolution. For details about the architectures in roaming and non-roaming scenarios, see section 4.2 "Architecture reference model" in 3GPP TS 23.401. Figure 2-3 LTE/SAE architecture in non-roaming scenarios
MME: mobility management entity S-GW: serving gateway SGSN: serving GPRS support node HSS: home subscriber server PCRF: policy and charging rule function PDN Gateway: packet data network
gateway
IP multimedia subsystem (IMS) includes multiple network elements (NEs). These NEs perform voice session control and multimedia negotiation between the calling and called UEs.
Function Architecture
Table 2-1 Basic VoLTE functions
Function Description
Speech codec scheme and traffic model
During a VoLTE call, the UE and the IMS negotiate a speech codec scheme. The commonly used codec scheme is Adaptive Multirate (AMR). For details about its voice traffic model, see
3.1 Speech Codec Scheme and Traffic Model. VoLTE voice policy
selection
During the attach procedure, the UE negotiates with the MME and selects VoLTE as the voice policy. For details about voice policy selection, see 3.2 VoLTE Voice Policy Selection. Radio bearer
management
Radio bearers with QoS class identifiers (QCIs) of 1 and 5 are set up between the calling and called UEs to carry
conversational voice and signaling, respectively. For details about radio bearer management, see 3.3 Radio Bearer Management.
Admission and congestion control
The eNodeB performs admission and congestion control for conversational voice (QCI 1) and signaling (QCI 5). For details about admission and congestion control, see 3.4 Admission and Congestion Control.
Dynamic scheduling and power control
By default, the eNodeB performs dynamic scheduling and uses power control policies that are suitable for dynamic scheduling. For details about dynamic scheduling and power control, see
3.5 Dynamic Scheduling and Power Control.
UEs can perform VoLTE services after the preceding functions are enabled. Table 2-2
describes the features that help improve VoLTE performance such as capacity, coverage, and voice quality.
Table 2-2 Enhanced VoLTE features/functions
Category Feature/Function Name Description Capacity enhanceme nt Semi-persistent scheduling and power control
The eNodeB performs semi-persistent scheduling and uses suitable power control policies for UEs during talk spurts.
The eNodeB can adaptively select dynamic scheduling and semi-persistent scheduling based on load in both uplink and downlink. This feature applies only to voice services. For details about semi-persistent scheduling and power control, see 4.1.1 Semi-Persistent Scheduling and Power Control.
The eNodeB performs dynamic scheduling and uses suitable power control policies for UEs at voice service setup and during silent periods.
Category Feature/Function
Name Description
Robust header compression (ROHC)
ROHC compresses the headers of voice packets to reduce air interface overheads.
This feature applies only to voice services. For details about how ROHC works for VoLTE, see
4.1.2 ROHC. Coverage
improveme nt
Transmission time interval (TTI) bundling
Multiple TTIs are bound together for UEs with poor signal quality to transmit the same data. This increases the once-off transmission success rate.
This feature applies only to uplink voice services. For details, see 4.2.1 LOFD-001048 TTI Bundling.
Robust header compression (ROHC)
ROHC compresses the headers of voice packets to reduce air interface overheads and increase the once-off transmission success rate.
This feature applies only to voice services. For details about how ROHC works for VoLTE, see
4.2.2 LOFD-001017 RObust Header Compression (ROHC).
Uplink RLC segmentation enhancement
This feature restricts the transport block size (TBS) in UL dynamic scheduling to control the number of uplink RLC segments for VoLTE packets. This restriction improves voice quality when channel quality is poor. For details about this feature, see 4.2.3 Uplink RLC
Segmentation Enhancement.
VoLTE Rate Control This feature performs AMR-NB/AMR-WB rate adjustment on uplink voice services based on the quality of uplink channels. For details about this feature, see 4.2.4 LOFD-111207 VoLTE Rate Control.
Category Feature/Function Name Description Quality improveme nt Voice characteristic awareness scheduling
During uplink dynamic scheduling, the eNodeB adjusts the scheduling priorities of UEs based on their waiting time and estimates the voice volume to be dynamically scheduled in the uplink. An independent inactivity timer is configured for voice services. The purpose is to improve voice quality, decrease the service drop rate, and increase the proportion of satisfied voice service users.
This feature applies only to voice services. For details about how UL delay-based dynamic scheduling, UL VoLTE volume estimation for dynamic scheduling, and independent
configuration for voice inactivity timer work for VoLTE, see 4.3.1 LOFD-081229 Voice Characteristic Awareness Scheduling. Uplink compensation
scheduling
For each voice user, the eNodeB measures the duration in which the user is not scheduled in the uplink. If the duration reaches a threshold, the eNodeB performs uplink compensation scheduling for the UE. The purpose is to ensure that uplink voice packets can be timely
transmitted, shorten their waiting time, and reduce the number of packets discarded because of the expiry of PDCP Discard Timer. This feature applies only to voice services. For details, see 4.3.2 LBFD-081105 Uplink Compensation Scheduling.
Voice-specific AMC The eNodeB sets a target IBLER for uplink voice services.
This feature applies only to voice services. For details, see 4.3.3 LBFD-081106 Voice-Specific AMC.
Preferential access for voice service
The eNodeB reserves user number resources to ensure that UEs performing voice services preferentially access the network in cell user number congestion scenarios.
This function applies only to voice services. For details, see 4.3.4 Preferential Access for Voice Service.
Power saving
Discontinuous reception (DRX)
With DRX, UEs enter the sleep state when data is not transmitted, saving UE power.
For details about how DRX works for VoLTE, see 4.4 Power Saving.
Category Feature/Function
Name Description
Mobility managemen t
Intra-frequency handover The eNodeB performs intra-frequency, inter-frequency, or inter-RAT handovers to transfer UEs performing voice services to appropriate neighboring cells to maintain voice continuity. For details about how mobility management works for VoLTE, see 4.5 Mobility
Management. Inter-frequency handover
Inter-RAT handover
Voice service performance can be evaluated on various dimensions. For details about voice service performance evaluation, see 8 Voice Service Performance Evaluation.
3
Basic VoLTE Functions
The ENodeBAlgoSwitch.EutranVoipSupportSwitch parameter specifies whether to enable VoLTE.l When this parameter is set to ON(On) on an eNodeB, this eNodeB supports VoLTE and allows the establishment, access, incoming handover, and reestablishment of the dedicated bearer with a QCI of 1.
l When this parameter is set to OFF(Off) on an eNodeB, this eNodeB does not support VoLTE and does not allow the establishment, access, incoming handover, and
3.1 Speech Codec Scheme and Traffic Model
The speech codec scheme is classified into AMR and G.7 series. VoLTE uses the AMR-based speech codec scheme.
AMR
Adaptive Multi Rate (AMR) is an audio data compression scheme optimized for speech coding and is now widely used in GERAN and UTRAN. AMR is classified into adaptive multirate wideband (AMR-WB) and adaptive multirate narrowband (AMR-NB).
l AMR-NB has eight speech coding rates. They are 12.2 kbit/s, 10.2 kbit/s, 7.95 kbit/s, 7.4 kbit/s, 6.7 kbit/s, 5.9 kbit/s, 5.15 kbit/s, and 4.75 kbit/s.
l AMR-WB has nine speech coding rates. They are 23.85 kbit/s, 23.05 kbit/s, 19.85 kbit/s, 18.25 kbit/s, 15.85 kbit/s, 14.25 kbit/s, 12.65 kbit/s, 8.85 kbit/s, and 6.6 kbit/s.
NOTE
AMR-NB herein corresponds to AMR in the protocol.
Figure 3-1 shows the voice service traffic model when AMR is used as the codec scheme for VoLTE services. Whether AMR-WB or AMR-NB is used is negotiated between the UEs and the IMS.
Figure 3-1 Voice traffic model
There are two VoLTE traffic states: l Talk spurts
During talk spurts, the uplink of UEs transmits voice packets or the downlink of UEs receives voice packets. Voice packets are transmitted at intervals of 20 ms, and the packet size is determined by the speech coding rate.
l Silent period
During silent periods, the UE transmits silence insertion descriptor (SID) frames or receives SID frames at intervals of 160 ms. For different AMR speech codec rates, the SID frame sizes are all 56 bits.
The differences between talk spurts and silent period are as follows: l The size of voice frames is greater than the size of SID frames.
l The interval between neighboring voice frames is different from the interval between SID frames.
The eNodeB distinguishes between voice frames and SID frames based on the preceding differences.
G.7 Series
The widely used G.7 series standards include G.711, G.729, and G.726.
l G.711
G.711, also known as pulse code modulation (PCM), is primarily used in fixed-line telephony. It supports a coding rate of 64 kbit/s.
l G.729
G.729, known for the high voice quality and low delay, is widely used in various domains of data communications. It supports a coding rate of 8 kbit/s.
l G.726
G.726 supports coding rates of 16 kbit/s to 40 kbit/s. The most commonly used rate is 32 kbit/s. In actual application, voice packets are sent at intervals of 20 ms.
3.2 VoLTE Voice Policy Selection
UE capability and configurations on the MME determine whether a UE uses VoLTE. However, VoLTE may be inappropriate for certain sites or regions. This case is termed as VoLTE-prohibited scenario.
This section describes voice policy selection for UEs in common and VoLTE-prohibited scenarios.
3.2.1 Common Scenarios
3.2.1.1 General Principles for Voice Policy Selection
During the UE attach and tracking area update (TAU) period, the MME selects a voice policy based on the UE capability and configuration on the MME side. The MME then sends the UE the voice policy contained in the Attach Accept and TAU Accept messages. During voice policy selection, the MME selects a voice policy based on the following principles: l If the UE supports only CSFB, the corresponding voice policy is CS Voice only. l If the UE supports only VoLTE, the corresponding voice policy is IMS PS Voice only,
that is, VoLTE.
l If the UE supports both CSFB and VoLTE, the voice policy used before negotiation with the MME is one of the following voice policies specified by operators during UE registration:
– CS Voice only That is, CSFB. – IMS PS Voice only
– Prefer CS Voice with IMS PS Voice as secondary That is, CSFB takes precedence over VoLTE.
For details about the voice policy negotiation procedures between the UE and MME when this policy is used, see Annex A.2 in 3GPP TS 23.221 V9.4.0.
– Prefer IMS PS Voice with CS Voice as secondary That is, VoLTE takes precedence over CSFB.
Figure 3-2 and Figure 3-3 show the voice policy negotiation procedures between the UE and MME when this policy is used. For details about the voice service policy negotiation, see Annex A.2 in 3GPP TS 23.221 V9.4.0.
Figure 3-3 Procedures for voice policy selection (combined attach)
3GPP Release 11 introduced VoLTE mobility capability decision, which further helps the MME in selecting a VoLTE policy.
3.2.1.2 VoLTE Mobility Capability Decision
Figure 3-4 Signaling procedure of VoLTE mobility capability decision
1. During the UE attach period, the MME sends the UE Radio Capability Match Request message to the eNodeB to query whether the UE has the VoLTE mobility capability. 2. If the eNodeB does not receive the UE radio capability message from the UE, the
eNodeB sends a UE Capability Enquiry message to the UE.
3. The UE reports its radio capability through the UE Capability Information message. For details, see section 5.6.3 "UE Capability Transfer" in 3GPP TS 36.331 R10.
4. If the eNodeB determines that the UE can ensure mobility after the UE performs VoLTE services, the eNodeB replies the MME with the decision result through the UE Radio Capability Match Response message.
The SupportS1UeCapMatchMsg option of the GlobalProcSwitch.ProtocolSupportSwitch parameter specifies whether the eNodeB supports the VoLTE mobility decision.
l When the SupportS1UeCapMatchMsg(SupportS1UeCapMatchMsg) option is selected, the UE can ensure mobility after the performing VoLTE services if the UE meets any of the following conditions:
– The UE supports UTRAN and SRVCC from E-UTRAN to UTRAN. – The UE supports GERAN and SRVCC from E-UTRAN to GERAN.
– The UE supports the PS domain of UTRAN-FDD (VoHSPA), SRVCC from the PS domain to the CS domain of UTRAN-FDD, and SRVCC from the PS domain of UTRAN-FDD to the CS domain of GERAN.
– The UE supports the PS domain of UTRAN-TDD (VoHSPA), SRVCC from the PS domain to the CS domain of UTRAN-TDD, and SRVCC from the PS domain of UTRAN-TDD to the CS domain of GERAN.
l When the SupportS1UeCapMatchMsg option is deselected, the eNodeB does not perform VoLTE mobility capability decision. In this case, the eNodeB replies ERROR INDICATION when receiving the UE RADIO CAPABILTY MATCH REQUEST message. If the UE uses VoLTE but does not support SRVCC, VoLTE mobility cannot be ensured.
NOTE
The UE RADIO CAPABILTY MATCH REQUEST message is introduced in 3GPP Release 11. The MME informs the eNodeB of the MME's SRVCC capability in the Initial UE Context Setup message.
l After the eNodeB obtains the MME's SRVCC capability, it also considers the MME's capability while determining the preceding conditions. Otherwise, the eNodeB replies to the eNodeB that the VoLTE mobility cannot be ensured.
l If the eNodeB is not informed of the MME's SRVCC capability, for example, the UE RADIO CAPABILTY MATCH REQUEST message arrives at the eNodeB earlier than the Initial UE Context Setup message, the eNodeB does not consider the MME's capability while determining UE voice service continuity.
3.2.2 VoLTE-Prohibited Scenario
The E-UTRAN supports VoLTE after the IMS is deployed. However, a non-VoLTE solution (such as CSFB) is used in the following scenarios because VoLTE is not appropriate for these scenarios:
l Transmission delay is large.
Voice services have high requirements on end-to-end delay. Figure 3-5 shows the relationship between end-to-end delay and perceived voice quality, as per ITU-T Recommendation G.114. As shown in the figure, the end-to-end delay threshold to achieve very satisfied user experience is 200 ms, and that to achieve satisfied user experience is 275 ms. That is, VoLTE users become dissatisfied on voice quality when the end-to-end delay exceeds 275 ms. The recommended packet delay budget for the Uu interface is 80 ms, as per Table 6.1.7: Standardized QCI characteristics in section 6.1.7.2 "Standardized QCI characteristics" of 3GPP TS 23.203. The delay budget between the EPC and eNodeB is 20 ms. If the transmission delay between the EPC and eNodeB is greater than 20 ms, voice quality may not be guaranteed after VoLTE is deployed on the eNodeB.
Figure 3-5 Relationship between delay and voice quality
l Voice services are not allowed on certain frequency bands.
Certain operators expect that some frequency bands such as LTE TDD bands do not serve voice service but serve only data services.
MMEs are required in the preceding scenarios to prohibit VoLTE in certain areas. Operators can allocate dedicated tracking area identities (TAIs) to regions. After setting dedicated TAIs on the MME, areas in such scenarios use CSFB instead of VoLTE. During the Attach and tracking area update (TAU), UEs negotiate or re-negotiate with the MME about voice policies. Voice policy negotiation between the UE and the MME is transparent to the eNodeB.
You can turn off the ENodeBAlgoSwitch.EutranVoipSupportSwitch switch for eNodeBs with dedicated TAIs working in the preceding scenarios. For eNodeBs with non-dedicated TAIs, you can select the VoipHoControlSwitch option of the
ENodeBAlgoSwitch.HoAlgoSwitch parameter and configure the VoLTE handover blacklist in the EUTRANVOIPHOBLKLIST MO. This prevents UEs performing voice services from being handed over to these eNodeBs or reestablished on the eNodeBs.
After the ENodeBAlgoSwitch.EutranVoipSupportSwitch switch is turned off and VoLTE is disabled for a specific tracking area on the MME, the statistics about VoLTE-related KPIs such as E-RAB Setup Success Rate (VoIP) become 0.
The following is an example.
The MCC and MNC of a network are 001 and 02, respectively. In this network, tracking area code (TAC) 1 corresponds to eNodeB A, and the other TACs correspond to eNodeBs B to Z. CSFB is to be used in the area that is labeled TAC 1.
The configurations are as follows:
2. On eNodeB A, run the following command:
MOD ENODEBALGOSWITCH:EutranVoipSupportSwitch=OFF;
3. (Optional) On eNodeBs B to Z, perform the following command: MOD ENODEBALGOSWITCH:EutranVoipSupportSwitch=ON;
4. On eNodeBs B to Z, run the following command:
MOD ENODEBALGOSWITCH:HoAlgoSwitch=VoipHoControlSwitch-1; 5. On eNodeBs B to Z, run the following command:
ADD EUTRANVOIPHOBLKLIST: Mcc="001", Mnc="02", Tac=TAC1;
NOTE
In the preceding VoLTE-prohibited scenarios, when a UE performing voice services triggers an intra-RAT intra-frequency or inter-frequency handover, the eNodeB determines whether to filter out cells in the VoLTE handover blacklist (specified by the EutranVoipHoBlkList MO) depending on the settings of the VoipHoControlSwitch option in the ENodeBAlgoSwitch.HoAlgoSwitch parameter.
According to current 3GPP specifications, voice policies can be configured only on a TAC basis on the MME. The ENodeBAlgoSwitch.EutranVoipSupportSwitch parameter and the VoipHoControlSwitch option of the ENodeBAlgoSwitch.HoAlgoSwitch parameter are added to the eNodeB side to
accommodate the TAC-based voice policy configurations on the MME side.
For details about the VoLTE handover blacklist and target cell selection procedures for VoLTE handovers, see Intra-RAT Mobility Management in Connected Mode Feature Parameter Description.
l Voice services are not allowed on certain frequencies.
The EutranInterNFreq.VolteHoTargetInd parameter is set to
NOT_ALLOWED(NOT_ALLOWED) for frequencies that do not support voice services. The eNodeB filters such frequencies during measurement or blind handover in inter-frequency handovers for VoLTE services.
3.3 Radio Bearer Management
3.3.1 Radio Bearer Setup
From the perspective of eNodeBs, voice session setup includes the following procedures: RRC connection setup, QCI 5 radio bearer setup, and QCI 1 radio bearer setup. Figure 3-6
Figure 3-6 Voice session setup process
The process is as follows:
1. In the RRC connection setup procedure, a radio connection is set up between a UE and an eNodeB so that the UE can send service requests and data packets to upper-layer NEs. 2. In the EPS bearer setup (QCI 5) procedure, a QCI 5 radio bearer is set up for signaling
exchange between the UE and the IMS.
3. After the QCI 5 radio bearer is set up, the calling UE and the IMS perform Session Initiation Protocol (SIP) negotiation on the speech codec scheme, IP address, port number, called UE's information, and other information.
4. In the EPS bearer establishment (QCI 1) procedure, a QCI 1 radio bearer is set up to carry voice packets.
NOTE
If VoLTE is determined as the voice solution for a UE according to negotiation with the MME, a QCI 5 radio bearer is set up when the UE enters RRC_CONNECTED mode, irrespective of whether the UE is performing a voice service or not.
When ENodeBAlgoSwitch.EutranVoipSupportSwitch is set to OFF(Off), the eNodeB cannot set up QCI 1 radio bearers (the eNodeB sends to the EPC a message containing the cause value "Not supported QCI Value") but can set up QCI 5 radio bearers.
If the UE initiates a conversational video service, a radio bearer (QCI 2) is also set up in the preceding procedures.
eNodeBs provide the following QCI 1-specific timer settings:
ENodeBConnStateTimer.S1MsgWaitingTimerQci1, ENodeBConnStateTimer.X2MessageWaitingTimerQci1, ENodeBConnStateTimer.UuMessageWaitingTimerQci1,
RrcConnStateTimer.UeInactiveTimerQci1, and CellQciPara.TrafficRelDelay. For details about these
parameters, see Connection Management Feature Parameter Description.
The eNodeB supports configuration of the CellHoParaCfg.HoMrDelayTimerQci1 parameter for QCI 1. After bearers for QCI 1 are successfully set up, the eNodeB returns an E-RAB SETUP RESPONSE message to start the timer specified by CellHoParaCfg.HoMrDelayTimerQci1. The eNodeB does not process inter-eNodeB handover measurement reports (MRs) until the timer stops. The eNodeB stops the timer when it receives an UPLINK NAS TRANSPORT message or the timer expires. The purpose of this timer is to ensure that the UPLINK NAS TRANSPORT message for a dedicated bearer is
successfully sent to the EPC and to prevent the EPC from releasing the voice bearer due to not receiving the NAS response message.
3.3.2 Radio Bearer QoS Management
Radio bearer QoS management for voice services complies with the Policy and Charging Control architecture defined in 3GPP specifications.
Figure 3-7 shows the architecture of radio bearer QoS management for voice services.
The dedicated bearers for voice services perform QoS parameter control based on the dynamic PCC rule as follows:
1. The IMS (P-CSCF) sends QCI information to the PCRF over the Rx interface. 2. Based on the received QCI information and subscription information, the PCRF
generates a QoS rule (including the following key QoS parameters: QCI, ARP, GBR, and MBR) and sends the rule to the P-GW over the Gx interface.
3. Based on the QoS rule sent from the PCRF, the P-GW instructs the S-GW, MME, and eNodeB to set up EPS bearers. Services of different QoS requirements are carried by radio bearers with different QCIs. According to 3GPP specifications, the QCIs for conversational voice, conversational video, and IMS signaling are 1, 2, and 5,
respectively. Table 3-1 lists their QoS parameters. QoS parameters are set in QciPara MOs, and the Radio Link Control (RLC) modes for setting up conversational voice, conversational video, and IMS signaling E-RABs are specified by the
RlcPdcpParaGroup.RlcMode parameter. For details, see 3GPP 23.203.
Table 3-1 QoS parameters for conversational voice, conversational video, and IMS signaling
QC
I ResourceType Priority Delay Packet LossRate Service Type
1 GBR 2 100 ms 10-2 Conversational
voice
2 GBR 4 150 ms 10-3 Conversational
video
5 Non-GBR 1 100 ms 10-6 IMS signaling
NOTE
A smaller priority value indicates a higher priority.
For details about QCIs and RLC modes, see QoS Management Feature Parameter Description.
3.4 Admission and Congestion Control
3.4.1 Overview
This section describes how the basic features LBFD-002023 Admission Control and LBFD-002024 Congestion Control work for VoLTE. For details about the two features, see Admission and Congestion Control Feature Parameter Description.
The eNodeB performs admission and congestion control for conversational voice (QCI of 1) and IMS signaling (QCI of 5) separately.
3.4.2 Load Monitoring
Load monitoring provides decision references for admission and congestion control. The eNodeB monitors various resources in a cell to obtain the usage of physical resource blocks
(PRBs), QoS satisfaction rates of GBR services, and resource insufficiency indicators. In this way, the eNodeB can know the current status of a cell.
Conversational Voice (QCI 1)
For the method of calculating the QoS satisfaction rate of QCI 1, see Admission and Congestion Control Feature Parameter Description.
IMS Signaling (QCI 5)
QCI 5 indicates non-GBR services. There is no need to calculate their QoS satisfaction rates.
3.4.3 Admission Control
Admission control determines whether to admit a GBR service (new service or handover service) based on the cell load reported by the load monitoring module. The cell load is represented by the PRB usage, QoS satisfaction rates of GBR services, and resource insufficiency indicators. For details, see Admission and Congestion Control Feature Parameter Description.
Conversational Voice (QCI 1)
The admission control of GBR services with a QCI of 1is performed based on load-based decisions.
IMS Signaling (QCI 5)
Admission control for non-GBR services (QCI 5) is not based on load. If SRS and PUCCH resources are successfully allocated, non-GBR services (QCI 5) are directly admitted.
NOTE
The allocation of SRS resources needs to be considered during admission control of non-GBR services (QCI 5) only when the eNodeB is configured with the LBBPc. The services can be admitted only after SRS resources are successfully allocated.
Even if the PreemptionSwitch option under the CellAlgoSwitch.RacAlgoSwitch parameter is selected, IMS signaling (QCI 5) cannot be preempted.
3.4.4 Congestion Control
When the network is congested, the eNodeB preferentially releases low-priority GBR services to free up resources for other services. For details, see Admission and Congestion Control Feature Parameter Description.
Conversational Voice (QCI 1)
The eNodeB monitors PRB usage and QoS satisfaction rate to evaluate load status. When the eNodeB determines that a cell is congested, the eNodeB rejects service access requests and triggers congestion control to decrease load. The congestion threshold is specified the CellRacThd.Qci1CongThd parameter. For details about how to set this parameter, see Admission and Congestion Control Feature Parameter Description.
IMS Signaling (QCI 5)
N/A
3.5 Dynamic Scheduling and Power Control
3.5.1 Dynamic Scheduling
This section describes how the optional feature LOFD-00101502 Dynamic Scheduling works for VoLTE. For details about the principles and engineering guidelines of dynamic scheduling, see Scheduling Feature Parameter Description.
Overview
Voice services have demanding requirements on delay. Therefore, the Huawei scheduler optimizes the handling of voice service priorities to ensure voice service QoS. When VoLTE is deployed, it is recommended that the enhanced proportional fair (EPF) scheduling policy be used in the uplink and downlink. That is:
l The CellUlschAlgo.UlschStrategy parameter is set to ULSCH_STRATEGY_EPF. l The CellDlschAlgo.DlschStrategy parameter is set to DLSCH_PRI_TYPE_EPF. On commercial LTE networks, the EPF scheduling policy is used in the uplink and downlink by default.
For details about dynamic scheduling for voice services, see Scheduling Feature Parameter Description.
Uplink Dynamic Scheduling
When uplink dynamic scheduling uses the enhanced proportional fair (EPF) algorithm, the priority of conversational voice (QCI of 1) is lower than the priorities of data retransmitted using HARQ, signaling radio bearer 1 (SRB1), SRB2, and IMS signaling (QCI of 5), but higher than the priorities of other initially transmitted data.
It is recommended that the UlVoipRblerControlSwitch option of the
CELLULSCHALGO.UlEnhencedVoipSchSw parameter be selected when dynamic
scheduling is used and there are voice services. Selecting this option decreases the packet loss rate of voice services and improves user experience on voice services. For cells where this switch is turned on, the eNodeB determines whether to use the adaptive retransmission for prioritized RBs for the last two retransmissions based on the number of retransmissions and transmit power of UEs with voice services.
Uplink voice preallocation is introduced to reduce the delay of voice services. When the number of UEs in a cell exceeds 50, the eNodeB can preallocate available uplink resources to only UEs performing voice services. When the number of UEs in a cell is less than or equal to 50, the eNodeB retains the existing uplink preallocation or uplink smart preallocation
mechanism for all UEs. For details, see Scheduling Feature Parameter Description. Uplink voice preallocation is controlled by the UlVoipPreAllocationSwtich option of the
Downlink Dynamic Scheduling
When dynamic scheduling is used, the scheduling priority is related to whether the LOFD-001109 DL Non-GBR Packet Bundling feature is enabled:
l If the LOFD-001109 DL Non-GBR Packet Bundling feature is not enabled: When the EPF downlink scheduling algorithm is used, the priority for scheduling voice packets (QCI of 1) is lower than that for scheduling common control messages, user-level control messages, IMS signaling (QCI of 5), HARQ retransmission data, and RLC AM status report. However, the priority for scheduling voice packets (QCI of 1) is higher than that for scheduling initial transmission data.
l If the LOFD-001109 DL Non-GBR Packet Bundling feature is enabled: The priority for scheduling voice packets (QCI of 1) is no longer higher than that for scheduling initial transmission data. Instead, the eNodeB sorts overall priorities.
When dynamic scheduling is used, the MCS selection policy is related to the value of the VoipTbsBasedMcsSelSwitch option of the CellAlgoSwitch.DlSchSwitch parameter. l When this option is selected, the eNodeB checks the number of online VoLTE
subscribers and IBLER and then determines whether to apply the TBS-based MCS selection function to voice services. TBS is short for transport block size. If the function takes effect on voice services, the eNodeB makes decisions based on the packet size during a voice call to select a relatively low MCS while ensuring that the number of RBs remains unchanged. In this way, HARQ retransmission and user delay are reduced. l When this option is deselected, the eNodeB determines the MCS for voice services based
on the downlink CQI adjustment algorithm. For details about the downlink CQI adjustment algorithm, see Scheduling Feature Parameter Description.
When dynamic scheduling is used for voice services, it is recommended that the
DlRetxTbsIndexAdjOptSwitch option of the CellAlgoSwitch.CqiAdjAlgoSwitch parameter be turned on to reduce the voice packet loss rate and improve voice user experience. For details about this switch, see Scheduling Feature Parameter Description.
When dynamic scheduling is used, you can select the DlVoipBundlingSwitch option of the CellAlgoSwitch.DlSchSwitch parameter to enable active packet bundling for downlink VoLTE services. In this way, two or more voice packets can be bundled for scheduling, which saves PDCCH CCE resources for downlink VoLTE services.
3.5.2 Power Control in Dynamic Scheduling
Power control policies for voice services in dynamic scheduling are the same as those for data services. For details about voice service power control policies when dynamic scheduling is used for voice services, see Power Control Feature Parameter Description.
4
Enhanced VoLTE Features
Operators can enable features described in this chapter to improve VoLTE performance such as capacity and coverage.4.1 Capacity Enhancement
The following features can be enabled to increase capacity for voice services: l Semi-persistent scheduling and power control
When the capacity is low due to high PDCCH overheads, these features can be used to reduce PDCCH overheads and therefore increase the maximum number of VoLTE users or the throughput of data services (provided that the number of VoLTE users remains unchanged).
l Uplink delay-based dynamic scheduling
When there are too many VoLTE users, this feature can be used to improve the performance of cell edge users (CEUs) by sacrificing the performance of cell center users (CCUs) and increase the proportion of satisfied VoLTE users.
l ROHC
By compressing the headers of voice packets, this feature reduces air interface overheads and increase the maximum number of VoLTE users or the throughput of data services (provided that the number of VoLTE users remains unchanged).
4.1.1 Semi-Persistent Scheduling and Power Control
4.1.1.1 LOFD-001016 VoIP Semi-persistent Scheduling
This section describes the LOFD-001016 VoIP Semi-persistent Scheduling feature.
Introduction
When dynamic scheduling is used for voice services, time-frequency resource or MCS is updated through the PDCCH every 20 ms. This consumes a large number of PDCCH resources. Figure 4-1 shows the resource allocation for dynamic scheduling.
Huawei introduces the VoLTE semi-persistent scheduling feature for small-packet services that are periodically transmitted such as VoLTE. Before entering talk spurts, the eNodeB allocates fixed resources to UEs through the PDCCH message. Before exiting talk spurts or releasing resources, the UEs do not need to apply for resource allocation from the PDCCH again, thereby saving PDCCH resources. Figure 4-2 shows the resource allocation for semi-persistent scheduling.
After the PDCCH message is sent, voice packets are sent at the intervals specified by CellUlschAlgo.UlSpsInterval and CellDlschAlgo.DlSpsInterval. If the semi-persistent scheduling intervals are small, the scheduling delay of voice packets is small, which means that users performing voice services can enjoy higher voice quality.
NOTE
CellUlschAlgo.UlSpsInterval and CellUlschAlgo.DlSpsInterval cannot be set to
ADAPTIVE(ADAPTIVE) in LTE FDD mode. Otherwise, the actual semi-persistent scheduling
intervals are 20 ms.
Figure 4-2 Resource allocation for semi-persistent scheduling
The eNodeB configures persistent scheduling parameters for UEs supporting semi-persistent scheduling in the RRC Connection Reconfiguration message during DRB setup for QCI of 1. The eNodeB activates UL or DL semi-persistent scheduling for UEs when UEs meet the UL or DL semi-persistent scheduling activation conditions. The eNodeB instructs UEs to activate UL or DL semi-persistent scheduling through the PDCCH Order notification. For details about the PDCCH Order format, see section 9.2 "PDCCH/EPDCCH validation for semi-persistent scheduling" in 3GPP TS 36.213 V12.3.0.
Effect Period
Figure 4-3 Semi-persistent scheduling effect period
In talk spurt, uplink or downlink semi-persistent scheduling takes effect when all the following conditions are met:
l The following options are selected:
– The SpsSchSwitch option of the CELLALGOSWITCH.UlSchSwitch parameter in the uplink
– The SpsSchSwitch option of the CELLALGOSWITCH.DlSchSwitch parameter in the downlink.
l The UE supports semi-persistent scheduling.
l The UE performing voice services is in uplink or downlink talk spurts.
l The uplink or downlink for the UE has only one dedicated bearer for services with QCI of 1. For the uplink, there is no data transmission on the data bearer.
l RLC segmentation is not performed in the uplink or downlink for the UE.
l When ROHC is enabled, the uplink or downlink ROHC is in the stable compression state, that is, the size of the ROHC header is relatively stable.
During talk spurts, eNodeBs use dynamic scheduling in the following scenarios:
l Transmission of large packets, such as channel-associated signaling or uncompressed packets generated when the ROHC feature updates contexts
l Downlink semi-persistent retransmission l Uplink semi-persistent adaptive retransmission
NOTE
When the UE uses semi-persistent scheduling, the highest MCS index is only 15.
Uplink Semi-Persistent Scheduling
During semi-persistent scheduling, the eNodeB determines the modulation and coding scheme (MCS) and the number of PRBs based on the following items:
l Voice packet size (ROHC disabled) or size of compressed voice packets (ROHC enabled)
l Wideband signal to interference plus noise ratio (SINR)
After uplink semi-persistent scheduling is activated, the UE periodically sends data and the eNodeB periodically receives data using the uplink semi-persistently allocated resources. In addition, the eNodeB checks whether the MCS allocated in uplink semi-persistent scheduling matches the current channel status. If the MCS does not match the current channel status, the eNodeB activates semi-persistent scheduling again.
After the eNodeB triggers a UE to enter uplink semi-persistent scheduling, the
logicalChannelSR-Mask-r9 IE in the RRC Reconfiguration message instructs the UE not to send scheduling requests over the radio bearers for QCI of 1. This reduces UE power consumption. The CellULSchAlgo.SrMaskSwitch parameter controls this function. It is recommended that both this function and uplink semi-persistent scheduling be enabled. This function takes effect only on UEs that comply with 3GPP Release 9 or later.
When the number of empty packets received by the eNodeB in uplink semi-persistent scheduling exceeds the value of CellUlschAlgo.SpsRelThd, the eNodeB automatically releases semi-persistently allocated resources.
Downlink Semi-Persistent Scheduling
During semi-persistent scheduling, the eNodeB determines the MCS and the number of PRBs based on the following items:
l Voice packet size (ROHC disabled) or size of compressed voice packets (ROHC enabled)
l Wideband CQI
The UE and eNodeB then receive and send data on the allocated resources.
After downlink semi-persistent scheduling is activated, the eNodeB checks whether the MCS allocated in semi-persistent scheduling matches the current channel status. If the MCS does not match the current channel status, the eNodeB activates semi-persistent scheduling again. There are two scenarios:
l If the periodically measured IBLER is greater than the
CellDlschAlgo.DlSpsMcsDecreaseIblerThd parameter value, the eNodeB lowers the MCS and activates downlink semi-persistent scheduling again.
l If the periodically measured IBLER is lower than 5%, the eNodeB increases the MCS and activates downlink semi-persistent scheduling again. The DlSpsMcsIncreaseSwitch option of the CellAlgoSwitch.CqiAdjAlgoSwitch parameter specifies whether to enable MCS index increase for semi-persistent scheduling.
According to 3GPP TS 36.321 and 3GPP TS 36.331, the eNodeB reserves HARQ processes for downlink semi-persistent scheduling while configuring semi-persistent scheduling for UEs. Before downlink semi-persistent scheduling is activated, reserved HARQ processes can be used for dynamic scheduling to increase the number of HARQ processes available for data services. This function is controlled by the
DlSpsRevHarqUseSwitch(DlSpsRevHarqUseSwitch) option of the CellDlschAlgo.DlEnhancedVoipSchSw parameter.
When the eNodeB configures downlink semi-persistent scheduling for UEs, the PUCCH requires available downlink semi-persistent code channels for HARQ feedback.
Load-based scheduling
For voice services, there are two scheduling modes, as compared in Table 4-1.
Table 4-1 Comparison between dynamic scheduling and semi-persistent scheduling Scheduling
Method Response toChannel
Condition Changes
Highest MCS
Index PDCCH ResourceConsumption
Dynamic scheduling Fast 28 Large
Semi-persistent scheduling
Slow 15 Small
For newly originated voice services, load-based scheduling allows the eNodeB to adaptively select dynamic or semi-persistent scheduling based on service load in both uplink and downlink.
l When the load is high, the eNodeB applies semi-persistent scheduling to avoid PDCCH overload and the impact on voice quality and capacity.
l When the load is low, the eNodeB applies dynamic scheduling to provide better experience on voice services and improve spectral efficiency.
Load-based scheduling in the uplink and downlink is controlled by different options: l The UlVoIPLoadBasedSchSwitch option of the
CellUlSchAlgo.UlEnhencedVoipSchSw parameter controls load-based scheduling in the uplink.
l The DlVoIPLoadBasedSchSwitch option of the
CellDlSchAlgo.DlEnhancedVoipSchSw parameter controls load-based scheduling in the downlink.
4.1.1.2 Power Control in Semi-Persistent Scheduling
This section describes voice service power control policies when semi-persistent scheduling is used for VoLTE. For details about power control, see Power Control Feature Parameter Description.
When semi-persistent scheduling is used for VoLTE in the downlink, power control is not performed. Instead, the eNodeB transmit power is evenly shared by each PRB.
When semi-persistent scheduling is used for VoLTE in the uplink, closed-loop power control for the physical uplink shared channel (PUSCH) can be enabled or disabled by setting the CloseLoopSpsSwitch option of the CellAlgoSwitch.UlPcAlgoSwitch parameter.
l If the CloseLoopSpsSwitch option is selected, the eNodeB adjusts transmit power for the PUSCH based on the measured IBLER of voice services.
l If the CloseLoopSpsSwitch option is deselected, the eNodeB uses open-loop (not closed-loop) power control for the PUSCH.
The SpsAndDrxOptSwitch option of the CellUlSchAlgo.UlEnhencedVoipSchSw parameter is used to control optimization of cooperation between semi-persistent scheduling and DRX.