VoLTE(eRAN8.1_03)

eRAN

VoLTE Feature Parameter

Description

Issue 03

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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

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

8.2.2 Objective Evaluation... 65 8.2.3 Measurement-based Evaluation...65 8.3 Capacity Evaluation...67 8.4 Performance Evaluation... 68

9 Engineering Guidelines... 69

9.2.1 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

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 9.4.4 Performance Monitoring...109 9.4.5 Parameter Optimization...109 9.4.6 Troubleshooting... 109 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 9.5.3.2 Data Preparation... 110 9.5.3.3 Precautions...111 9.5.3.4 Hardware Adjustment... 111 9.5.3.5 Initial Configuration...111 9.5.3.6 Activation Observation... 113 9.5.3.7 Reconfiguration... 114 9.5.3.8 Deactivation... 115 9.5.4 Performance Monitoring...115 9.5.5 Parameter Optimization... 116 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 9.6.3.2 Data Preparation... 116 9.6.3.3 Precautions...118 9.6.3.4 Hardware Adjustment... 118 9.6.3.5 Initial Configuration... 118 9.6.3.6 Activation Observation...121 9.6.3.7 Reconfiguration... 121 9.6.3.8 Deactivation...121 9.6.4 Performance Monitoring...122 9.6.5 Parameter Optimization...123

9.6.6 Troubleshooting... 123

9.7 Uplink Compensation Scheduling... 123

9.7.1 When to Use Uplink Compensation Scheduling... 123

9.7.2 Required Information... 123 9.7.3 Deployment... 123 9.7.3.1 Requirements... 123 9.7.3.2 Data Preparation... 123 9.7.3.3 Precautions...124 9.7.3.4 Hardware Adjustment...124 9.7.3.5 Initial Configuration... 125 9.7.3.6 Activation Observation...127 9.7.3.7 Reconfiguration... 127 9.7.3.8 Deactivation...128 9.7.4 Performance Monitoring...128 9.7.5 Parameter Optimization...129 9.7.6 Troubleshooting... 129 9.8 Voice-Specific AMC...129

9.8.1 When to Use Voice-Specific AMC...129

9.8.2 Required Information... 129 9.8.3 Deployment... 129 9.8.3.1 Requirements... 129 9.8.3.2 Data Preparation... 129 9.8.3.3 Precautions...130 9.8.3.4 Hardware Adjustment...130 9.8.3.5 Initial Configuration... 130 9.8.3.6 Activation Observation...132 9.8.3.7 Reconfiguration... 134 9.8.3.8 Deactivation...134 9.8.4 Performance Monitoring...134 9.8.5 Parameter Optimization...135 9.8.6 Troubleshooting... 135

10 Parameters...136

11 Counters... 217

12 Glossary...249

13 Reference Documents... 250

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

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.

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 ParameterChange AffectedEntity

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)

This issue includes the following changes.

Change

Type Change Description ParameterChange AffectedEntity

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)

This issue includes the following changes.

Change

Type Change Description ParameterChange AffectedEntity

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 Awareness Scheduling 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.

Change

Type Change Description ParameterChange AffectedEntity

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-E-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

Change

Type Change Description ParameterChange AffectedEntity

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 parameters: l CellUlschAl go.TtiBundl ingTriggerS trategy l CellUlschAl go.Statistic NumThdFo rTtibTrig l CellUlschAl go.Statistic NumThdFo rTtibExit l CellUlschAl go.HystToE xitTtiBundli ng l CellUlschAl go.TtiBundl ingRlcMax SegNum l CellUlschAl go.TtiBundl ingHarqMa xTxNum Macro, micro, and LampSite eNodeBs

Added LOFD-081229 Voice Characteristic Awareness Scheduling. For details, see 4.3.1 Voice Characteristic Awareness Scheduling and 9.6 Voice Characteristic Awareness Scheduling. l Added the CELLULS CHALGO. UlDelaySch Strategy parameter. l Added the UlVoLTED ataSizeEstS witch option to the CELLULS CHALGO. UlEnhence dVoipSchSw parameter. Macro, micro, and LampSite eNodeBs

Change

Type Change Description ParameterChange AffectedEntity

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 CELLULSCH ALGO.UlEnhe ncedVoipSchS w 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 CELLULSCH ALGO.SinrAdj TargetIblerfor VoLTE 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

Feature ID Feature Name Suppor ted by Macro eNode Bs Supported by Micro eNodeBs Supported by LampSite eNodeBs

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

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 the 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:

– 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.

– 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 calling/called UEs in the E-UTRAN and the IMS. That is, with VoLTE, calling/called 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 describes the basic functions of VoLTE.

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, while the IMS may or may not take part in the negotiation. 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.

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 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 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.

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 Voice Characteristic Awareness Scheduling.

Category Feature/Function

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. This feature applies only to voice services. For details, see 4.3.2 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 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.

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

reestablishment of the dedicated bearer with a QCI of 1.

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

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. The AMR codec scheme to be used is negotiated between UEs, with the IMS involved. The eNodeB is transparent in the AMR codec scheme negotiation.

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

That is, VoLTE.

– 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. VoLTE Feature Parameter Description 3 Basic VoLTE Functions

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. Based on the reply, the MME then selects a voice policy for UEs as follows:

– If mobility can be ensured, VoLTE is used. – If mobility cannot be ensured, CSFB is used.

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.

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 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. 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 eNodeB's ENODEBALGOSWITCH.EutranVoipSupportSwitch and

ENODEBALGOSWITCH.HoAlgoSwitch.VoipHoControlSwitch 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

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 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. 2. Based on the received QCI information and subscription information, the PCRF

generates a QoS rule (including 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.

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 QCI and RLC mode, 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)

The QoS satisfaction rates for QCI 1 are calculated as follows:

l Downlink QoS satisfaction rate

Downlink QoS satisfaction rate for QCI 1 services = Sum of downlink QoS satisfaction rates of all VoIP services in the cell/Number of VoIP services in the cell

l Uplink QoS satisfaction rate

Uplink QoS satisfaction rate for QCI 1 services = Sum of uplink QoS satisfaction rates of all VoIP services in the cell/Number of VoIP services in the cell

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, admits 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.

The eNodeB directly admits non-GBR services without evaluating the QoS satisfaction rate. When PreemptionSwitch under the CellAlgoSwitch.RacAlgoSwitch parameter is turned on, 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 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 the 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 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 details, see Scheduling Feature Parameter Description. Uplink voice preallocation is controlled by the UlVoipPreAllocationSwtich option of the

CELLULSCHALGO.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 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 modulation and coding scheme (MCS) selection policy is related to the value for the VoipTbsBasedMcsSelSwitch option of the

CellAlgoSwitch.DlSchSwitch parameter.

l When this option is selected, the eNodeB checks the number of online 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. HARQ retransmission and user delay are reduced if the function takes effect on voice services.

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 service, 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.

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 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.

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.

The semi-persistent scheduling interval is 20 ms and applies only to services with QCI of 1 and PTT QCI services.

Effect Period

Figure 4-3 Semi-persistent scheduling effect period

The VoLTE voice status is classified into instantaneous state, talk spurt, and silent 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 default 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 to supplement semi-persistent scheduling 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)

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 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 semi-persistent scheduling exceeds the value of CellUlschAlgo.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 persistent code channel. 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.

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

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 controls 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 CELLULSCHALGO.TtiBundlingTriggerStrategy parameter is introduced. VoLTE Feature Parameter Description 4 Enhanced VoLTE Features

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 default 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

CellUlschAlgo.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

CellUlschAlgo.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. 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.

When the UE is in the TTI bundling state, the maximum number of uplink HARQ

retransmissions is specified by the CellUlschAlgo.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 specified by the CellUlschAlgo.TtiBundlingRlcMaxSegNum. 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

CellUlschAlgo.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.