Vo lte(eran8.1 03)

eRAN
VoLTE Feature Parameter
Description
Issue 03
Date 2015-06-30
HUAWEI TECHNOLOGIES CO., LTD.

Copyright © Huawei Technologies Co., Ltd. 2015. All rights reserved.
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Huawei Technologies Co., Ltd.
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Email: support@huawei.com
Issue 03 (2015-06-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
i

Contents
1 About This Document.................................................................................................................. 1
1.1 Scope.............................................................................................................................................................................. 1
1.2 Intended Audience..........................................................................................................................................................2
1.3 Change History...............................................................................................................................................................2
1.4 Differences Between eNodeB Types..............................................................................................................................6
2 Overview......................................................................................................................................... 8
2.1 Background.....................................................................................................................................................................8
2.2 Introduction.................................................................................................................................................................... 9
2.3 Benefits.........................................................................................................................................................................10
2.4 Architecture.................................................................................................................................................................. 10
3 Basic VoLTE Functions...............................................................................................................14
3.1 Speech Codec Scheme and Traffic Model....................................................................................................................15
3.2 VoLTE Voice Policy Selection......................................................................................................................................16
3.2.1 Common Scenarios....................................................................................................................................................16
3.2.1.1 General Principles for Voice Policy Selection........................................................................................................16
3.2.1.2 VoLTE Mobility Capability Decision.....................................................................................................................18
3.2.2 VoLTE-Prohibited Scenario.......................................................................................................................................19
3.3 Radio Bearer Management........................................................................................................................................... 21
3.3.1 Radio Bearer Setup....................................................................................................................................................21
3.3.2 Radio Bearer QoS Management................................................................................................................................23
3.4 Admission and Congestion Control..............................................................................................................................24
3.4.1 Overview................................................................................................................................................................... 24
3.4.2 Load Monitoring........................................................................................................................................................24
3.4.3 Admission Control.....................................................................................................................................................25
3.4.4 Congestion Control....................................................................................................................................................25
3.5 Dynamic Scheduling and Power Control..................................................................................................................... 26
3.5.1 Dynamic Scheduling..................................................................................................................................................26
3.5.2 Power Control in Dynamic Scheduling.....................................................................................................................27
4 Enhanced VoLTE Features.........................................................................................................28
4.1 Capacity Enhancement................................................................................................................................................. 29
4.1.1 Semi-Persistent Scheduling and Power Control........................................................................................................29
4.1.1.1 Semi-Persistent Scheduling.................................................................................................................................... 29
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VoLTE Feature Parameter Description Contents
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4.1.1.2 Power Control in Semi-Persistent Scheduling........................................................................................................32
4.1.2 ROHC........................................................................................................................................................................ 33
4.2 Coverage Improvement................................................................................................................................................ 34
4.2.1 TTI Bundling............................................................................................................................................................. 34
4.2.1.1 Overview................................................................................................................................................................ 34
4.2.1.2 Principles................................................................................................................................................................ 34
4.2.2 ROHC........................................................................................................................................................................ 36
4.2.3 Uplink RLC Segmentation Enhancement..................................................................................................................37
4.3 Quality Improvement....................................................................................................................................................38
4.3.1 Voice Characteristic Awareness Scheduling..............................................................................................................38
4.3.2 Uplink Compensation Scheduling.............................................................................................................................39
4.3.3 Voice-Specific AMC..................................................................................................................................................41
4.4 Power Saving................................................................................................................................................................41
4.5 Mobility Management.................................................................................................................................................. 42
4.5.1 Overview................................................................................................................................................................... 42
4.5.2 Intra-Frequency Handover.........................................................................................................................................43
4.5.3 Inter-Frequency Handover.........................................................................................................................................43
4.5.4 Inter-RAT Handover.................................................................................................................................................. 45
4.5.4.1 Handover Type........................................................................................................................................................45
4.5.4.2 Handover Mode...................................................................................................................................................... 47
5 Special Processing by Other Features......................................................................................48
6 Related Features...........................................................................................................................51
6.1 LOFD-001016 VoIP Semi-persistent Scheduling.........................................................................................................52
6.2 LOFD-001048 TTI Bundling....................................................................................................................................... 53
6.3 Uplink RLC Segmentation Enhancement.....................................................................................................................54
6.4 LOFD-081229 Voice Characteristic Awareness Scheduling........................................................................................54
6.5 LBFD-081104 UL Compensation Scheduling............................................................................................................. 55
6.6 LBFD-081105 Voice-Specific AMC............................................................................................................................ 55
6.7 Other Features...............................................................................................................................................................55
7 Network Impact........................................................................................................................... 58
7.1 LOFD-001016 VoIP Semi-persistent Scheduling.........................................................................................................59
7.2 LOFD-001048 TTI Bundling....................................................................................................................................... 59
7.3 Uplink RLC Segmentation Enhancement.....................................................................................................................60
7.4 LOFD-081229 Voice Characteristic Awareness Scheduling........................................................................................60
7.5 LBFD-081104 UL Compensation Scheduling............................................................................................................. 61
7.6 LBFD-081105 Voice-Specific AMC............................................................................................................................ 61
7.7 Other Features...............................................................................................................................................................62
8 Voice Service Performance Evaluation................................................................................... 64
8.1 QoS Requirements........................................................................................................................................................64
8.2 Quality Evaluation........................................................................................................................................................64
8.2.1 Subjective Evaluation................................................................................................................................................64
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8.2.2 Objective Evaluation................................................................................................................................................. 65
8.2.3 Measurement-based Evaluation.................................................................................................................................65
8.3 Capacity Evaluation......................................................................................................................................................67
8.4 Performance Evaluation............................................................................................................................................... 68
9 Engineering Guidelines............................................................................................................. 69
9.1 Overview...................................................................................................................................................................... 69
9.2 Basic Functions.............................................................................................................................................................70
9.2.1 When to Use Basic Functions....................................................................................................................................70
9.2.2 Required Information................................................................................................................................................ 71
9.2.3 Deployment............................................................................................................................................................... 71
9.2.3.1 Requirements..........................................................................................................................................................71
9.2.3.2 Data Preparation..................................................................................................................................................... 71
9.2.3.3 Precautions..............................................................................................................................................................73
9.2.3.4 Hardware Adjustment.............................................................................................................................................73
9.2.3.5 Initial Configuration............................................................................................................................................... 73
9.2.3.6 Activation Observation...........................................................................................................................................76
9.2.3.7 Reconfiguration...................................................................................................................................................... 78
9.2.3.8 Deactivation............................................................................................................................................................78
9.2.4 Performance Monitoring............................................................................................................................................79
9.2.4.1 Voice KPIs.............................................................................................................................................................. 79
9.2.4.2 Voice QoS............................................................................................................................................................... 83
9.2.4.3 Voice Quality.......................................................................................................................................................... 84
9.2.4.4 Voice Capacity........................................................................................................................................................87
9.2.5 Parameter Optimization.............................................................................................................................................89
9.2.6 Troubleshooting.........................................................................................................................................................90
9.3 Semi-Persistent Scheduling.......................................................................................................................................... 90
9.3.1 When to Use Semi-Persistent Scheduling and Deploy Power Control..................................................................... 90
9.3.2 Required Information................................................................................................................................................ 91
9.3.3 Deployment of Semi-Persistent Scheduling..............................................................................................................91
9.3.3.1 Requirements..........................................................................................................................................................91
9.3.3.2 Data Preparation..................................................................................................................................................... 92
9.3.3.3 Precautions..............................................................................................................................................................93
9.3.3.4 Hardware Adjustment.............................................................................................................................................93
9.3.3.5 Initial Configuration............................................................................................................................................... 93
9.3.3.6 Activation Observation...........................................................................................................................................96
9.3.3.7 Reconfiguration...................................................................................................................................................... 99
9.3.3.8 Deactivation............................................................................................................................................................99
9.3.4 Performance Monitoring..........................................................................................................................................100
9.3.5 Parameter Optimization...........................................................................................................................................100
9.3.6 Troubleshooting.......................................................................................................................................................101
9.4 TTI Bundling.............................................................................................................................................................. 101
9.4.1 When to Deploy TTI Bundling................................................................................................................................101
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9.4.2 Required Information.............................................................................................................................................. 101
9.4.3 Deployment of TTI Bundling..................................................................................................................................101
9.4.3.1 Requirements........................................................................................................................................................101
9.4.3.2 Data Preparation................................................................................................................................................... 102
9.4.3.3 Precautions............................................................................................................................................................104
9.4.3.4 Hardware Adjustment...........................................................................................................................................104
9.4.3.5 Initial Configuration............................................................................................................................................. 104
9.4.3.6 Activation Observation.........................................................................................................................................106
9.4.3.7 Reconfiguration.................................................................................................................................................... 108
9.4.3.8 Deactivation..........................................................................................................................................................108
9.5 UL RLC Segmentation Enhancement........................................................................................................................ 109
9.5.1 When to Use Uplink RLC Segmentation Enhancement..........................................................................................110
9.5.2 Required Information...............................................................................................................................................110
9.5.3 Deployment..............................................................................................................................................................110
9.5.3.1 Requirements........................................................................................................................................................ 110
9.5.3.3 Precautions............................................................................................................................................................111
9.5.3.4 Hardware Adjustment........................................................................................................................................... 111
9.5.3.5 Initial Configuration..............................................................................................................................................111
9.5.3.8 Deactivation..........................................................................................................................................................115
9.5.6 Troubleshooting....................................................................................................................................................... 116
9.6 Voice Characteristic Awareness Scheduling...............................................................................................................116
9.6.1 When to Use Voice Characteristic Awareness Scheduling......................................................................................116
9.6.2 Required Information...............................................................................................................................................116
9.6.3 Deployment..............................................................................................................................................................116
9.6.3.1 Requirements........................................................................................................................................................ 116
9.6.3.3 Precautions............................................................................................................................................................118
9.6.3.8 Deactivation..........................................................................................................................................................121
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9.7 Uplink Compensation Scheduling..............................................................................................................................123
9.7.1 When to Use Uplink Compensation Scheduling..................................................................................................... 123
9.7.3 Deployment............................................................................................................................................................. 123
9.7.3.1 Requirements........................................................................................................................................................123
9.7.3.3 Precautions............................................................................................................................................................124
9.7.3.8 Deactivation..........................................................................................................................................................128
9.8 Voice-Specific AMC...................................................................................................................................................129
9.8.1 When to Use Voice-Specific AMC..........................................................................................................................129
9.8.3 Deployment............................................................................................................................................................. 129
9.8.3.1 Requirements........................................................................................................................................................129
9.8.3.3 Precautions............................................................................................................................................................130
9.8.3.8 Deactivation..........................................................................................................................................................134
10 Parameters.................................................................................................................................136
11 Counters.................................................................................................................................... 215
12 Glossary.....................................................................................................................................247
13 Reference Documents.............................................................................................................248
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1About 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
This document applies to the following types of eNodeBs.
eNodeB Type Model
Macro 3900 series eNodeB
Micro base
station
BTS3202E
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.
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VoLTE Feature Parameter Description 1 About This Document
1

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.
eRAN8.1 03 (2015-06-30)
This issue includes the following changes.
Change
Type
Change Description Parameter
Change
Affected
Entity
Feature
change
None None Macro, micro,
and LampSite
eNodeBs
Editorial
change
Revised the following sections:
4.1.1 Semi-Persistent Scheduling
and Power Control
4.3.1 Voice Characteristic
Awareness Scheduling
4.3.2 Uplink Compensation
Scheduling
None -
eRAN8.1 02 (2015-04-30)
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Change
Type
Change
Affected
Entity
Feature
change
Changed the optional feature Voice-
Specific AMC to a basic feature, and
changed the feature ID from
LOFD-081230 to LBFD-081105.
None Macro, micro,
and LampSite
eNodeBs
Editorial
change
Revised the following sections:
3.2.1.2 VoLTE Mobility Capability
Decision
3.2.2 VoLTE-Prohibited Scenario
9.2.3.1 Requirements
9.2.6 Troubleshooting
None -
eRAN8.1 01 (2015-03-23)
Change
Type
Change
Affected
Entity
Feature
change
Modified the LOFD-081229 Voice
Characteristic Awareness Scheduling
feature to add independent
configurations for the UE inactivity
timer for voice services. For details,
see the following sections:
2.4 Architecture
4.3.1 Voice Characteristic
7.4 LOFD-081229 Voice
Characteristic Awareness
Scheduling
Added the
following
parameter:
CELLALGOS
WITCH.UEIn
activeTimerQC
I1Switch
Macro, micro,
and LampSite
eNodeBs
Editorial
change
Added network impact descriptions.
For details, see the following
sections:
7.1 LOFD-001016 VoIP Semi-
persistent Scheduling
7.2 LOFD-001048 TTI Bundling
None -
eRAN8.1 Draft A (2015-01-15)
Compared with Issue 05 (2014-11-13) of eRAN7.0, Draft A (2015-01-15) of eRAN8.1
includes the following changes.
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3

Change
Type
Change
Affected
Entity
Feature
change
Modified the voice quality
monitoring mechanism as follows:
l The voice quality threshold
becomes configurable.
l The downlink voice quality
evaluation is changed from E-
Model to VQI-Model.
For details, see 8.2.3 Measurement-
based Evaluation.
Added the
following
parameters:
l VQMAlgo.
VqiExcellen
tThd
l VQMAlgo.
VqiPoorThd
l VQMAlgo.
VqiGoodTh
d
l VQMAlgo.
VqiBadThd
Macro, micro,
and LampSite
eNodeBs
Added policy control for
measurements (such as ANR
measurement) by UEs performing
voice services.
For details, see 5 Special Processing
by Other Features.
Added the
GlobalProcSwi
tch.VoipWithG
apMode
parameter.
Macro, micro,
and LampSite
eNodeBs
Added the descriptions of the
relationship between LOFD-001016
VoIP Semi-persistent Scheduling and
LAOFD-0010014 DL 2x2 MIMO
based on TM9. For details, see 4.1.1
Semi-Persistent Scheduling and
Power Control.
None Macro, micro,
and LampSite
eNodeBs
Modified the relationship between
LOFD-001048 TTI Bundling and
LAOFD-001001 LTE-A
Introduction. For details, see 4.2.1
TTI Bundling.
None Macro, micro,
and LampSite
eNodeBs
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Change
Type
Change
Affected
Entity
Modified the functions of TTI
bundling:
l Enabled the configuration of
applicable services of TTI
bundling. The applicable services
include VoLTE or a combination
of VoLTE and data.
l Added five key parameters to
TTI bundling.
For details, see 4.2.1 TTI Bundling.
Added the
following
parameter:
l CellAlgoSw
itch.TtiBun
dlingTrigge
rStrategy
l CellAlgoSw
itch.
StatisticNu
mThdForTt
ibTrig
l CellAlgoSw
itch.
StatisticNu
mThdForTt
ibExit
l CellAlgoSw
itch.
HystToExit
TtiBundling
l CellAlgoSw
itch.
TtiBundling
RlcMaxSeg
Num
l CellAlgoSw
itch.
TtiBundling
HarqMaxT
xNum
Macro, micro,
and LampSite
eNodeBs
Added LOFD-081229 Voice
Scheduling. For details, see 4.3.1
Voice Characteristic Awareness
Scheduling and 9.6 Voice
Scheduling.
l Added the
CellAlgoSw
itch.UlDela
ySchStrateg
y parameter.
l Added the
UlVoLTED
ataSizeEstS
witch option
to the
CellAlgoSw
itch.UlEnhe
ncedVoipSc
hSw
parameter.
Macro, micro,
and LampSite
eNodeBs
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Change
Type
Change
Affected
Entity
Added LBFD-081104 UL
Compensation Scheduling. For
details, see 4.3.2 Uplink
Compensation Scheduling and 9.7
Uplink Compensation Scheduling.
Added the
UlVoipSchOpt
Switch option
to the
CellAlgoSwitc
h.UlEnhenced
VoipSchSw
parameter.
Macro, micro,
and LampSite
eNodeBs
Added LOFD-081230 Voice-
Specific AMC. For details, see 4.3.3
Voice-Specific AMC and 9.8 Voice-
Specific AMC.
Added the
CellAlgoSwitc
h.SinrAdjTarge
tIblerforVoLTE
parameter.
Macro, micro,
and LampSite
eNodeBs
Editorial
change
Modified the document structure to
enhance readability.
None -
Added 8.2.2 Objective Evaluation. None -
Added counters to measure handover
success rates for VoLTE services.
For details, see 9.2.4.1 Voice KPIs.
None -
Added 4.3.1 Voice Characteristic
Awareness Scheduling, which
incorporates the description of
uplink delay-based dynamic
scheduling.
None -
1.4 Differences Between eNodeB Types
Feature Support by Macro, Micro, and LampSite eNodeBs
VoIP 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
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Feature ID Feature Name Suppor
ted by
Macro
eNode
Bs
Supported
by Micro
eNodeBs
Supported by
LampSite
eNodeBs
LOFD-081229 Voice Characteristic
Yes Yes Yes
LBFD-081105 UL Compensation
Scheduling
Yes Yes Yes
LBFD-081105 Voice-Specific AMC 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.
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2Overview
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 E-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
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VoLTE Feature Parameter Description 2 Overview
8

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
– 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
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.
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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 describes the basic functions of VoLTE.
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Table 2-1 Basic VoLTE functions
Function Description
Speech codec scheme
and traffic model
During a VoLTE call, the UEs negotiate a speech codec scheme
with the IMS. 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.
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.
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Name
Description
Robust header
compression (ROHC)
ROHC compresses the headers of voice packets
to reduce air interface overheads.
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 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.
details about how ROHC works for VoLTE, see
4.2.2 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.
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.
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 Voice Characteristic
Awareness Scheduling.
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Name
Description
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.
details, see 4.3.2 Uplink Compensation
Scheduling.
Voice-specific AMC The eNodeB sets a target IBLER for uplink
voice services.
details, see 4.3.3 Voice-Specific AMC.
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.
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.
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3Basic 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
reestablishment of the dedicated bearer with a QCI of 1.
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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.
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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
That is, VoLTE.
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– 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 3-2 Procedures for voice policy selection (non-combined attach)
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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.
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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.
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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
handing 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:
1. On the MME, configure CSFB for TAC1.
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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. ENODEBALGOSWITCH.EutranVoipSupportSwitch and
ENODEBALGOSWITCH.HoAlgoSwitch.VoipHoControlSwitch parameters for the eNodeB are used
to support the configuration of TAC-based voice policies 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.
When the ENodeBAlgoSwitch.EutranVoipSupportSwitch switch is turned on, dedicated bearer for
services with QCI of 1 can be set up for the eNodeB. When this switch is turned off, dedicated bearer for
services with QCI of 1 is not allowed to be set up for the eNodeB.
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
shows the process of setting up a voice session between the calling and called UEs.
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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.
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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 CellStandardQci.TrafficRelDelay. For details about
these parameters, see Connection Management Feature Parameter Description.
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.
Figure 3-7 Architecture of radio bearer QoS management
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.
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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
StandardQci 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
Resource
Type
Priorit
y
Delay Packet Loss
Rate
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.
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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
The admission control of GBR services with a QCI of 1is performed based on load-based
decisions.
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.
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.
N/A
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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 CellAlgoSwitch.UlschStrategy parameter is set to ULSCH_STRATEGY_EPF.
l The CellAlgoSwitch.UlschStrategy 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 1) is lower than the priorities of data retransmitted using
HARQ, signaling radio bearer 1 (SRB1), SRB2, and IMS signaling (QCI 5), but higher than
the priorities of other initially transmitted data.
It is recommended that the UlLast2RetransSchOptSwitch option of the
CELLALGOSWITCH.UlSchSwitch 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.
Uplink voice preallocation is introduced to reduce the delay of voice services. When the
number of UEs in a cell exceeds 50, the eNodeB preallocates uplink resources only to 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
CellAlgoSwitch.UlEnhencedVoipSchSw parameter.
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
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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 depends on the value for the
VoipTbsBasedMcsSelSwitch option of the CellAlgoSwitch.DlSchSwitch parameter.
l When this option is selected, the eNodeB checks the number of online VoIP 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 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.
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.
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4Enhanced VoLTE Features
Operators can enable features described in this chapter to improve VoLTE performance such
as capacity and coverage.
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28

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 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.
Figure 4-1 Resource allocation for dynamic scheduling
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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 delivering the the PDCCH message, the eNodeB transmits voice packets in an interval
of 20 ms.
Figure 4-2 Resource allocation for semi-persistent scheduling
The eNodeB configures semi-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.
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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
– The SpsSchSwitch option of the CELLALGOSWITCH.DlSchSwitch parameter.
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.
eNodeBs use dynamic scheduling in the following scenarios during talk spurts:
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)
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l Wideband signal to interference plus noise ratio (SINR)
After semi-persistent scheduling is activated, the UE periodically sends data and the eNodeB
periodically receives data using the semi-persistently allocated resources. In addition, 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.
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 CellAlgoSwitch.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 semi-persistent scheduling
exceeds the value of CellAlgoSwitch.SpsRelThd, the eNodeB automatically releases semi-
persistently allocated resources.
Downlink Semi-Persistent Scheduling
Downlink data transmitted in semi-persistent scheduling mode has a lower priority than
common control (such as broadcast and paging) information but a higher priority than UE-
specific control information and user-plane data. The eNodeB periodically sends data and the
UE periodically receives data using the semi-persistently allocated resources.
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 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.
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.
When the eNodeB configures semi-persistent scheduling for UEs, the PUCCH requires
available semi-persistent code channel for HARQ. Otherwise, the eNodeB does not configure
semi-persistent scheduling for UEs.
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.
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Power Control in Uplink Semi-Persistent Scheduling
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.
Power Control in Downlink Semi-Persistent Scheduling
When semi-persistent scheduling is used for VoLTE in the downlink, power control for the
PDSCH can be enabled or disabled by setting the PdschSpsPcSwitch option of the
CellAlgoSwitch.DlPcAlgoSwitch parameter.
l If the PdschSpsPcSwitch option is selected, the eNodeB periodically adjusts the
PDSCH transmit power for UEs based on the measured IBLER.
l If the PdschSpsPcSwitch option is deselected, power control for the PDSCH in semi-
persistent scheduling is not used. Instead, the eNodeB transmit power is evenly shared
by each RB.
4.1.2 ROHC
This section describes how the optional feature LOFD-001017 RObust Header Compression
(ROHC) works for VoLTE. For details about this feature, see ROHC Feature Parameter
Description.
ROHC provides an efficient header compression mechanism for data packets transmitted on
radio links to solve the problems of high bit error rates (BERs) and long round trip time
(RTT). ROHC helps reduce header overheads, lower the packet loss rate, and shorten
response time.
In the current version, ROHC is used to compress the headers of only voice packets (QCI of 1
and PTT QCI services), as shown in Figure 4-4. ROHC reduces the packet size and physical
resource block (PRB) overheads. When PRBs are insufficient, ROHC helps increase system
capacity.
Figure 4-4 ROHC for VoLTE
After deploying VoLTE, operators can enable or disable ROHC by setting the
PdcpRohcPara.RohcSwitch parameter. ROHC is an extensible framework consisting of
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different profiles for data streams compliant with different protocols. Profiles define the
compression modes for streams with different types of protocol headers. Voice services use
profiles 0x0001 and 0x0002.
The ROHC compression efficiency varies with the ROHC operating mode and variations in
the dynamic part of packet headers at the application layer. A header can be compressed to a
size as small as 1 byte, which efficiently reduces the voice packet size.
4.2 Coverage Improvement
Operators can enable the following features to improve voice service coverage in poor
coverage scenarios:
l TTI Bundling
l ROHC
l Uplink RLC segmentation enhancement
4.2.1 TTI Bundling
This section describes the principles of the optional feature LOFD-001048 TTI Bundling and
how this feature works for VoLTE.
4.2.1.1 Overview
TTI bundling enables a data block to be transmitted in four consecutive TTIs, which are
bound together and treated as the same resource. Different HARQ redundancy versions of the
same data block are transmitted in different TTIs. TTI bundling makes full use of HARQ
combining gains and reduces the number of retransmissions and RTT.
When the UE's channel quality is poor and transmit power is limited, TTI bundling increases
the cell edge coverage of the PUSCH by about 1 dB. The gains produced by this feature can
be observed when voice quality is maintained at a certain level, for example, when the mean
opinion score (MOS) is 3.
The TtiBundlingSwitch option of the CellAlgoSwitch.UlSchSwitch parameter determines
whether to enable TTI bundling. When this option is selected, the eNodeB determines
whether to activate TTI bundling based on the channel quality. After activating TTI bundling,
the eNodeB determines the number of PRBs and selects an MCS based on the channel quality
and the amount of data to be transmitted.
According to section 8.6.1 "Modulation order and redundancy version determination" in
3GPP TS 36.213 V10.1.0, when TTI bundling is enabled, the resource allocation size is
restricted to a maximum of three PRBs and the modulation scheme must be QPSK. Therefore,
the selected MCS index cannot be greater than 10. After TTI bundling is enabled, the
maximum available TBS is as large as 504 bits. Voice services are delay-sensitive. If higher-
layer data is not transmitted within the specified delay budget, voice quality deteriorates. To
prevent this, TTI bundling is disabled when a G.711-defined high speech codec rate is used.
4.2.1.2 Principles
Entry into the TTI Bundling State
In eRAN8.1, the CellAlgoSwitch.TtiBundlingTriggerStrategy parameter is introduced.
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34

l When the TtiBundlingTriggerStrategy parameter is set to
SERVICE_VOIP(SERVICE_VOIP), TTI bundling applies to only VoLTE. Under this
parameter setting, the conditions for entering the TTI bundling state are as follows:
– The TtiBundlingSwitch of the eNodeB is turned on.
– The UE supports TTI bundling.
– The UE has only one QCI 1 dedicated bearer and stays in the talk spurts state. In
addition, the UE does not have data to transmit on the data bearer.
– The UL power of the UE is limited, and the number of PRBs is less than or equal to
3.
– The measured SINR is less than the target SINR for multiple consecutive times.
The number of consecutive times is specified by the
CellAlgoSwitch.StatisticNumThdForTtibTrig.
If the UE meets all these conditions, the eNodeB sends the UE an RRC Connection
Reconfiguration message, instructing the UE to enter the TTI bundling state.
l When the TtiBundlingTriggerStrategy parameter is set to
SERVICE_MULTIAPP(SERVICE_MULTIAPP), TTI bundling can apply to VoLTE
or a combination of VoLTE and data. Under this parameter setting, the conditions for
entering the TTI bundling state are as follows:
– The TtiBundlingSwitch of the eNodeB is turned on.
– The UE supports TTI bundling.
– The UE has a QCI 1 dedicated bearer.
– The UL power of the UE is limited, and the number of PRBs is less than or equal to
3.
– The measured SINR is less than the target SINR for multiple consecutive times.
The number of consecutive times is specified by the
CellAlgoSwitch.StatisticNumThdForTtibTrig.
If the UE meets all these conditions, the eNodeB sends the UE an RRC Connection
Reconfiguration message, instructing the UE to enter the TTI bundling state.
The processing in versions earlier than eRAN8.1 is the same as that when the
TtiBundlingTriggerStrategy parameter is set to SERVICE_VOIP(SERVICE_VOIP) in
eRAN8.1.
Data Block Transmission
For the UE in the TTI bundling state, the eNodeB determines the number of PRBs and MCS
based on channel quality and the amount of data to transmit. Then, the eNodeB transmits data
blocks.
As shown in Figure 4-5 , the UE transmits identical data within four consecutive TTIs in a
bundle and performs HARQ retransmission also within four TTIs in a bundle. The
retransmission operates in synchronous non-adaptive mode. Four uplink subframes in PHICH
carry one ACK/NACK message. The HARQ retransmission interval is changed from 8 TTIs
(Normal HARQ RTT) to 16 TTIs (Bundle HARQ RTT).
Take the transmission of a data block as an example. Assume that the UE transmits the data
block in a bundle of TTIs, among which the last TTI is numbered N. The eNodeB sends an
ACK or NACK as feedback to the UE in the (N + 4)th TTI. Based on the feedback, the UE
determines whether a retransmission is required. If it is required, the UE retransmits the data
block in the (N + 13)th through (N + 16)th TTIs.
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When the UE is in the TTI bundling state, the maximum number of uplink HARQ
retransmissions is specified by the CellAlgoSwitch.TtiBundlingHarqMaxTxNum parameter.
Figure 4-5 TTI bundling
In the TTI bundling state, the number of RLC segments of a voice packet cannot be greater
than the value of the CellAlgoSwitch.TtiBundlingRlcMaxSegNum parameter. The number is
4 in Figure 4-6.
Figure 4-6 Collaboration between TTI bundling and RLC segmentation
When the UE is located at the cell edge, RLC segmentation in collaboration with TTI
bundling produces fewer RLC segments than pure RLC segmentation, reducing PDCCH
overheads.
Exit from TTI Bundling
When the measured SINR is greater than the sum of the target SINR and the
CellAlgoSwitch.HystToExitTtiBundling parameter value for multiple consecutive times, the
eNodeB instructs the UE to exit the TTI bundling state through an RRC Connection
Reconfiguration message. The number of consecutive times is specified by the
StatisticNumThdForTtibExit parameter.
The eNodeB does not instruct the UE to exit the TTI bundling state even when the UE has
data to transmit on the default bearer, needs to set up a new dedicated bearer, or stops the
voice service (QCI 1). The eNodeB instructs the UE to exit the TTI bundling state when the
UE meets the exit conditions, experiences handover or service drop, or needs to reestablish a
new connection.
4.2.2 ROHC
This section describes how the optional feature LOFD-001017 RObust Header Compression
(ROHC) works for VoLTE. For details about this feature, see ROHC Feature Parameter
Description.
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36

ROHC can compress the RTP, UDP, or IP header of a voice packet, thereby reducing the size
of the entire packet. ROHC results in a higher probability of correctly transmitting voice
packets with fewer segments and enhances the edge coverage for voice services.
4.2.3 Uplink RLC Segmentation Enhancement
This section describes how uplink RLC segmentation enhancement works for VoLTE.
The number of Uplink RLC segments is dependent on the TBS determined by UL scheduling.
The smaller the TBS, the large the number of uplink RLC segments. When channel quality is
poor and UL power is limited, a small TBS results in a large number of uplink RLC segments,
which causes:
l Long delay of voice packets
l Uplink voice packet loss (because voice packets wait in the UE buffer so long that the
packet discard timer expires)
l Large overhead of RLC and MAC headers
l Large consumption of control channel elements (CCEs) and resource blocks (RBs) by
UL dynamic scheduling of VoLTE services
Uplink RLC segmentation enhancement restricts the TBS in UL dynamic scheduling to
control the number of uplink RLC segments for voice packets. This restriction improves voice
quality when channel quality is poor.
The CellAlgoSwitch.UlVoipRlcMaxSegNum parameter is introduced to control the
maximum number of uplink RLC segments for UEs not in the TTI bundling state.
l When the number of uplink RLC segments is less than or equal to the value of the
CellAlgoSwitch.UlVoipRlcMaxSegNum parameter, the number is not restricted.
l When the number of uplink RLC segments is greater than the value of the
CellAlgoSwitch.UlVoipRlcMaxSegNum parameter, the number is restricted. Based on
the voice packet size and the configured maximum number of RLC segments, a
minimum TBS is guaranteed in UL dynamic scheduling so that the number of uplink
RLC segments decreases to this maximum number.
This function takes effect when all the following conditions are met:
l The CellAlgoSwitch.UlVoipRlcMaxSegNum parameter is set to a none-zero value.
l The GLOBALPROCSWITCH.LcgProfile parameter is set to LCG_PROFILE_0 or
LCG_PROFILE_2.
This function does not take effect when one of the following conditions is met:
l The CellAlgoSwitch.UlVoipRlcMaxSegNum parameter is set to 0.
l The GLOBALPROCSWITCH.LcgProfile parameter is set to LCG_PROFILE_1.
l The UE enters the TTI bundling state.
NOTE
This function applies only to services with QCI of 1.
When the CellAlgoSwitch.UlVoipRlcMaxSegNum parameter is set to the recommended value, this
function increases the MOS of VoIP users who do not support TTI bundling by about 0.3 in uplink weak
coverage areas.
eRAN
37

Vo lte(eran8.1 03)

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