ETSI TR 126 989 V17.0.0 (2022-05)

LTE; 5G; Mission Critical Push To Talk (MCPTT); Media, codecs and Multimedia Broadcast/Multicast Service (MBMS) enhancements for MCPTT over LTE (3GPP TR 26.989 version 17.0.0 Release 17)

RTR/TSGS-0426989vh00

General Information

• Status: Not Published
• Technical Committee: 3GPP SA 4 - Codec
• Current Stage: 12 - Completion
• Completion Date: 04-May-2022

Standards Content (Sample)

TECHNICAL REPORT
LTE;
5G;
Mission Critical Push To Talk (MCPTT);
Media, codecs and Multimedia Broadcast/Multicast Service
(MBMS) enhancements for MCPTT over LTE
(3GPP TR 26.989 version 17.0.0 Release 17)

3GPP TR 26.989 version 17.0.0 Release 17 1 ETSI TR 126 989 V17.0.0 (2022-05)

Reference
RTR/TSGS-0426989vh00
Keywords
5G,LTE
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: [phone]  Fax: [phone]

Siret N° 348 623 562 00017 - APE 7112B
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° w061004871

Important notice
The present document can be downloaded from:
http://www.etsi.org/standards-search
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any
existing or perceived difference in contents between such versions and/or in print, the prevailing version of an ETSI
deliverable is the one made publicly available in PDF format at www.etsi.org/deliver.
Users of the present document should be aware that the document may be subject to revision or change of status.
Information on the current status of this and other ETSI documents is available at
https://portal.etsi.org/TB/ETSIDeliverableStatus.aspx
If you find errors in the present document, please send your comment to one of the following services:
https://portal.etsi.org/People/CommiteeSupportStaff.aspx
If you find a security vulnerability in the present document, please report it through our
Coordinated Vulnerability Disclosure Program:
https://www.etsi.org/standards/coordinated-vulnerability-disclosure
Notice of disclaimer & limitation of liability
The information provided in the present deliverable is directed solely to professionals who have the appropriate degree of
experience to understand and interpret its content in accordance with generally accepted engineering or
other professional standard and applicable regulations.
No recommendation as to products and services or vendors is made or should be implied.
No representation or warranty is made that this deliverable is technically accurate or sufficient or conforms to any law
rule and/or regulation and further, no representation or warranty is made of merchantability or fitness
and/or governmental
for any particular purpose or against infringement of intellectual property rights.
In no event shall ETSI be held liable for loss of profits or any other incidental or consequential damages.

Any software contained in this deliverable is provided "AS IS" with no warranties, express or implied, including but not
limited to, the warranties of merchantability, fitness for a particular purpose and non-infringement of intellectual property
rights and ETSI shall not be held liable in any event for any damages whatsoever (including, without limitation, damages
for loss of profits, business interruption, loss of information, or any other pecuniary loss) arising out of or related to the use
of or inability to use the software.
Copyright Notification
No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm except as authorized by written permission of ETSI.
The content of the PDF version shall not be modified without the written authorization of ETSI.
The copyright and the foregoing restriction extend to reproduction in all media.

© ETSI 2022.
All rights reserved.
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 2 ETSI TR 126 989 V17.0.0 (2022-05)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The declarations
pertaining to these essential IPRs, if any, are publicly available for ETSI members and non-members, and can be
found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to
ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the
ETSI Web server (https://ipr.etsi.org/).
Pursuant to the ETSI Directives including the ETSI IPR Policy, no investigation regarding the essentiality of IPRs,
including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not
referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become,
essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
DECT™, PLUGTESTS™, UMTS™ and the ETSI logo are trademarks of ETSI registered for the benefit of its

Members. 3GPP™ and LTE™ are trademarks of ETSI registered for the benefit of its Members and of the 3GPP
Organizational Partners. oneM2M™ logo is a trademark of ETSI registered for the benefit of its Members and of the ®
oneM2M Partners. GSM and the GSM logo are trademarks registered and owned by the GSM Association.
Legal Notice
This Technical Report (TR) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities. These shall be
interpreted as being references to the corresponding ETSI deliverables.
The cross reference between 3GPP and ETSI identities can be found under http://webapp.etsi.org/key/queryform.asp.
Modal verbs terminology
In the present document "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be
interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 3 ETSI TR 126 989 V17.0.0 (2022-05)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Abbreviations . 7
4 Reference Model . 7
5 Key Issues for Supporting MCPTT . 8
5.1 Key Issue#1: Codec for MCPTT . 8
5.1.1 Review of Codec Alternatives and their Relative Perceptual Performance . 8
5.1.1.1 Overview of the 3GPP Codec Comparison . 8
5.1.1.2 Narrowband Comparison vs AMR . 8
5.1.1.3 Wideband Comparison vs AMR-WB . 12
5.1.1.4 Super-wideband EVS and Relationships to Other Bandwidths . 16
5.1.1.5 Comparison of the 3GPP Codecs to TETRA . 17
5.1.1.6 Comparison of Performance over MCPTT Bearers . 20
5.1.1.6.1 "HD-Voice" AMR-WB performance over 3GPP networks . 20
5.1.1.6.2 MCPTT Bearers. 21
5.1.1.6.3 AMR-WB and EVS Performance over the MCPTT Bearers . 23
5.1.1.6.3.1 EVS Speech Quality . 23
5.1.1.6.3.2 Unicast bearer . 28
5.1.1.6.3.3 MBMS bearer . 28
5.1.1.6.3.4 LTE-D bearer . 31
5.1.1.6.4 Conclusions . 37
5.1.1.7 Listening effort evaluation of AMR-WB and EVS under impaired channels . 38
5.1.1.7.1 Test setup . 38
5.1.1.7.2 Test results . 38
5.1.2 Review of the Codec Alternatives and their Relative Speech Intelligibility in Clean and Low SNRs . 41
5.1.2.1 Speech Intelligibility . 41
5.1.2.1.1 MCPTT bearers – speech intelligibility . 48
5.1.2.1.2 Conclusions . 53
5.1.3 Review of Codec Alternatives and their Relative Complexity . 54
5.1.4 Recommended requirements . 55
5.1.5 GAP Analysis and Evaluation . 56
5.1.5.1 Requirements on Audio/Voice Quality . 56
5.1.5.2 Discrete/Ambient Listening and Remotely Initiated Monitoring . 56
5.1.5.3 Noise Reduction . 56
5.1.5.4 Common Codec Constraints of MCPTT . 56
5.1.5.5 Requirements on Transcoding Functions in the Network . 57
5.1.6 Criteria with respect to MCPTT codec selection . 58
5.1.7 Solution . 59
5.2 Key Issue#2: User Experience . 59
5.2.1 Description . 59
5.2.2 Recommended requirements . 59
5.2.3 GAP Analysis and Evaluation . 59
5.2.3.1 Longer e2e delay over BC bearer issue . 59
5.2.3.2 Mobility issue . 60
5.2.3.2.1 BC handoff to UC . 60
5.2.3.2.2 UC handoff to BC . 61
5.2.4 Assumptions . 61
5.2.5 Solution . 61
5.2.5.1 Transport delay difference adjustment . 61
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 4 ETSI TR 126 989 V17.0.0 (2022-05)
5.2.5.2 RTP payload treatment . 61
5.3 Key Issue#3: MCPTT over MBMS support . 62
5.3.1 Description . 62
5.3.2 Deployment Considerations . 64
5.3.3 Realization (Stage 3) Considerations (On-Network) . 64
5.3.4 Media Handling . 64
5.3.5 QoE for MCPTT over MBMS . 65
5.3.5.1 QoE for both MNO and MCPTT service provider . 65
5.3.6 eNB Scheduling on the MBMS Bearer . 65
5.3.7 Needed information to describe an MCPTT User Plane . 65
6 Conclusion . 65
Annex A:  Simulation Models and Parameters . 67
A.1 MBMS Bearer Simulation Model . 67
A.1.1 Coverage. 67
A.1.2 Error Traces . 68
A.1.3 eNB Scheduling . 71
A.2 Correlation between Subjective MOS and P.OLQA . 72
Annex B: Change history . 73
History . 74

ETSI
3GPP TR 26.989 version 17.0.0 Release 17 5 ETSI TR 126 989 V17.0.0 (2022-05)
Foreword
rd
This Technical Report has been produced by the 3 Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 6 ETSI TR 126 989 V17.0.0 (2022-05)
1 Scope
The present document covers the enhancement required to support MCPTT.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 22.179: "Mission Critical Push To Talk (MCPTT) over LTE; Stage 1"
[3] 3GPP TR 26.952: "Codec for Enhanced Voice Services (EVS);Performance Characterization".
[4] 3GPP TS 26.114: "IP Multimedia Subsystem (IMS); Multimedia Telephony; Media handling and
interaction".
[5] ITU-T Technical Paper - GSTP-GVBR, Performance of ITU-T G.718 (http://www.itu.int/pub/T-
TUT) (http://www.itu.int/pub/publications.aspx-lang=en&parent=T-TUT-ASC-2010).
[6] ETSI EN 300 395-2: "Terrestrial Trunked Radio (TETRA) Speech codec for full-rate traffic
channel Part 2: TETRA codec", version 1.3.1 (25 January 2005).
[7] 3GPP TR 26 975: "Performance characterization of the Adaptive Multi-Rate (AMR) speech
codec".
[8] 3GPP TR 46.055: "Performance characterization of the GSM Enhanced Full Rate (EFR) speech
codec".
[9] (void)
[10] IETF RFC 3550: "RTP: A Transport Protocol for Real-Time Applications".
[11] 3GPP TS 26.346: "Multimedia Broadcast/Multicast Service (MBMS); Protocols and codecs".
[12] 3GPP TS 23.468: "Group Communication System Enablers for LTE (GCSE_LTE); Stage 2".
[13] 3GPP TR 26 976: "Performance characterization of the Adaptive Multi-Rate Wideband (AMR-
WB) speech codec".
[14] 3GPP TS 22.076: "Noise suppression for the AMR codec; Service description; Stage 1".
[15] 3GPP TS 26.131: "Terminal acoustic characteristics for telephony; Requirements".
[16] NTIA Report 15-520: "Speech Codec Intelligibility Testing in Support of Mission-Critical Voice
Applications for LTE", S.D. Voran & A.A. Catellier September 2015.
[17] (void)
[18] (void)
[19] 3GPP TS 36.300: "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2".
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 7 ETSI TR 126 989 V17.0.0 (2022-05)
[20] 3GPP TR 26.947: "Multimedia Broadcast/Multicast Service (MBMS); Selection and
characterisation of application layer Forward Error Correction (FEC)".
[21] (void)
[22] (void)
[23] (void)
[24] ITU-T Recommendation P.800 (08/1996): "Methods for subjective determination of transmission
quality".
[25] 3GPP TS 26.442: "Codec for Enhanced Voice Services (EVS); ANSI C code (fixed-point)".
[26] 3GPP TS 26.448: "Codec for Enhanced Voice Services (EVS); Jitter buffer management".
[27] ITU-T Recommendation P.807 (02/2016): "Subjective test methodology for assessing speech
intelligibility".
3 Abbreviations
For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply.
An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any,
in 3GPP TR 21.905 [1].
ADP Associated Delivery Procedures
AS Application Server
BC Broadcast
BM-SC Broadcast-Multicast - Service Centre
GCS Group Communication Service
MCPTT Mission Critical Push-To-Talk
MBMS Multimedia Broadcast/Multicast Service
MBSFN Multimedia Broadcast Single Frequency Network
MOS Mean Opinion Score
NTIA National Telecommunications & Information Administration
TETRA TErrestrial Trunked Radio
SC-PTM Single Cell-Point To Multipoint
SWB Super Wide Band
UC Unicast
4 Reference Model
Figure 1 shows a reference model of MCPTT support over UC and BC. The GCS AS interacts with UE over GC1
interface for application signalling. The GCS AS determines whether to deliver the audio over UC or BC. GCS AS
interacts with BM-SC over MB2 interface to deliver audio to BM-SC. The BM-SC delivers the audio over broadcast
channel to the UE via SGi-mb interface. The GCS AS interacts with P-GW over SGi interface to deliver audio to the
UE. The red line represents the audio delivered over UC channel. The green line represents the audio delivered over
BC channel.
NOTE: The UE interacts with the BM-SC using HTTP method via SGi interface for MBMS Associated Delivery
Procedure. Whether the ADP procedure applies to the MCPTT is TBD.
ETSI
MB2-U
MB2-C
3GPP TR 26.989 version 17.0.0 Release 17 8 ETSI TR 126 989 V17.0.0 (2022-05)
GCS AS
GC1
Gx Rx
PCRF
S/P-
SGi
GW
UE eNB
MBMS
SGi-mb
-GW BM-SC
SGmb
Figure 1: MCPTT support Reference Model
5 Key Issues for Supporting MCPTT
5.1 Key Issue#1: Codec for MCPTT
5.1.1 Review of Codec Alternatives and their Relative Perceptual
Performance
5.1.1.1 Overview of the 3GPP Codec Comparison
The EVS Selection and Characterization Phase Test Results provided in the main body and Annex D of TR 26.952 [3]
give a detailed assessment of the performance of the EVS Codec in realistic scenarios compared to both AMR and
AMR-WB. A summary of this comparison is provided in the next two subclauses.
In the fourth subclause the relative performance of different audio bandwidths coded with AMR, AMR-WB and EVS is
provided showing that the SWB modes of EVS outperform the WB and NB Primary modes of EVS, AMR-WB and
AMR.
In the fifth subclause, a review of the TETRA codec performance in comparison to the 3GPP Codecs is provided.
This version of the document includes a review of codec alternatives and their relative intelligibility in high noise
conditions, e.g., at SNRs in the range of -30 dB to 5 dB. The NTIA report [16] covered six noise types for an
intelligibility study that included a range of public safety and civilian environments. Results of intelligibility testing for
additional public safety specific high noise background conditions are not included in this document.
5.1.1.2 Narrowband Comparison vs AMR
For Narrowband (NB) signals, four experiments were conducted in the EVS Selection and four in the EVS
Characterization. Taken together, these results provide a complete picture of the performance of EVS with respect to
AMR but the highlights are provided in Figures 2 to 6 below.
It can be seen that EVS always significantly out-performs AMR in terms of intrinsic audio quality for both speech and
Mixed/Music signals. EVS is also significantly more robust to frame erasures; both randomly distributed or according
to the Delay and Error profiles from TS 26.114 [4] using the EVS JBM.
ETSI
SGi
3GPP TR 26.989 version 17.0.0 Release 17 9 ETSI TR 126 989 V17.0.0 (2022-05)

(a) (b)
(c) (d)
Figure 2: EVS NB vs AMR – Speech - Random Frame Erasures - Selection
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 10 ETSI TR 126 989 V17.0.0 (2022-05)

(a) (b)
(c) (d)
Figure 3: EVS NB vs AMR – Speech - Random Frame Erasures - Characterization

ETSI
3GPP TR 26.989 version 17.0.0 Release 17 11 ETSI TR 126 989 V17.0.0 (2022-05)

(a) (b)
Figure 4: EVS NB vs AMR – Speech - TS 26.114 Delay & Error Profiles

(a) (b)
Figure 5: EVS NB vs AMR – Music & Mixed Content - Random Frame Erasures

ETSI
3GPP TR 26.989 version 17.0.0 Release 17 12 ETSI TR 126 989 V17.0.0 (2022-05)

(a) (b)
Figure 6: EVS NB vs AMR – Music & Mixed Content - TS 26.114 Delay & Error Profiles

5.1.1.3 Wideband Comparison vs AMR-WB
For Wideband (WB) signals, seven experiments were conducted during the EVS Selection and five experiments during
Characterization; focused on determining the performance of the EVS Wideband Primary Modes of operation. Taken
together these experiments provide unique information about the performance of EVS with respect to AMR-WB but the
highlights are provided below in Figures 7 to 10.
As in the case of AMR and NB, it can be seen that EVS always significantly out-performs AMR-WB or AMR-
WB/G.718IO in terms of intrinsic audio quality for both speech and Mixed/Music signals. EVS is also significantly
more robust to input level and frame erasures; both randomly distributed or using the EVS JBM in conjunction with the
packet delay and error profiles taken from either TS 26.114 or the new profiles defined for LTE.
What is less clear from the frame erasure plots is that AMR-WB, in its basic form, performs significantly less well than
these curves would suggest. Work in ITU-T as part of the G.718 exercise led to significant improvements to the packet
loss concealment of AMR-WB (G.722.2) and these improvements are shown in Figures 11 & 12 (FER and BFER);
taken from the Characterization Report of Recommendation ITU-T G.718 [5]. The enhancements achieved during the
development of G.718 formed part of the justification of the EVS work item and thus it can be assumed that EVS will
perform even better than suggested by Figures 8, 9 and 10.
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 13 ETSI TR 126 989 V17.0.0 (2022-05)

(a) (b)
Figure 7: EVS WB vs AMR-WB – Speech – Clean Channel & Levels

(a) (b)
Figure 8: EVS WB vs AMR-WB – Speech - Random Frame Erasures

ETSI
3GPP TR 26.989 version 17.0.0 Release 17 14 ETSI TR 126 989 V17.0.0 (2022-05)

(a) (b)
Figure 9: EVS WB vs AMR-WB – Speech - TS 26.114 Delay & Error Profiles

(a) (b)
Figure 10: EVS WB vs AMR-WB – Speech – New EVS JBM Delay & Error Profiles

ETSI
3GPP TR 26.989 version 17.0.0 Release 17 15 ETSI TR 126 989 V17.0.0 (2022-05)

Figure 11: AMR-WB (G.722.2) vs G.718IO – Speech (American English) Figure 27 of [3]
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 16 ETSI TR 126 989 V17.0.0 (2022-05)

Figure 12: AMR-WB (G.722.2) vs G.718IO – Speech (French) Figure 28 of [3]
5.1.1.4 Super-wideband EVS and Relationships to Other Bandwidths
Three mixed bandwidth tests were performed during the EVS Characterization and the results are shown in Figure 13.
It is clear from Figure 13 that the Super-wideband (SWB) modes of EVS outperform the WB modes, which themselves
outperform the NB modes. On the whole it is clear that these trends hold across input types and bit rates. The EVS
codec can also be seen to scale well with bit rate within each bandwidth and asymptotically approaches the Direct
Source (DS) in the case of SWB and progressively lower value in the cases of the reduced bandwidth signals; WB and
NB.
These mixed bandwidth test results also reinforce the performance advantages of EVS compared to AMR and AMR-
WB.
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 17 ETSI TR 126 989 V17.0.0 (2022-05)

(a) Clean (b) Car Noise
(c) Music & Mixed Content - Chinese (d) Music & Mixed Content - US English

Figure 13: EVS vs AMR and AMR-WB – Bandwidth and Bitrate Differences

5.1.1.5 Comparison of the 3GPP Codecs to TETRA
The details of the TETRA codec may be found in ETSI EN 300 395-2 [6]. The bit rate of the TETRA codec is 4,567
kbps and it makes use of the ACELP paradigm and 30ms frames. At the time of its selection in 1993, the TETRA
ACELP codec represented the state-of-the-art in low bit rate speech codecs and it was well adapted to its specific
application and the TETRA 4:1 TDMA air interface.
According to the Characterization tests conducted during the standardization of the TETRA ACELP codec which are
also provided in [6]:
"For clean speech at a nominal input level of -22 dB the average Q value obtained for the TETRA codec is 13,0 dB
for the linear input condition and 16,5 dB for the IRS input condition. For comparison purposes the corresponding
values obtained for the Global System for Mobile communications (GSM) full-rate codec are 17,4 dB and 18,9 dB
respectively."
These differences in dBQ are reproduced below (from [6]) in Tables 1 & 2 for various input signals.
From Tables 1 & 2 it is clear that the TETRA codec is consistently inferior to the original GSM Full Rate Speech Codec
of the order of 2.4 - 4.4 dBQ.
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 18 ETSI TR 126 989 V17.0.0 (2022-05)
Table 1: TETRA vs GSM TCH-FS for A-Law IRS Input Signals
TETRA ACELP GSM TCH-FS
(Nominal Level) (Nominal Level)
(dBQ) (dBQ)
Quiet 16.5 18.9
Vehicle -10dB 4.1 5.2
Vehicle -20dB 9.5 10.5
Office -10dB 7.2 8.7
Office -20dB 11.4 11.7
Table 2: TETRA vs GSM TCH-FS for FLAT Input Signals
TETRA ACELP GSM TCH-FS
(Nominal Level) (Nominal Level)
(dBQ) (dBQ)
Quiet 13.0 17.4
Vehicle -10dB 6.5 10.0
Vehicle -20dB 9.3 14.7
Office -20dB 9.4 14.6
Since the selection of the TETRA speech coding standard in 1993, firstly SMG, and latterly 3GPP, has developed
several generations of codec upgrades for NB speech; firstly the Enhanced Full-Rate Codec (EFR), then the Adaptive
Multi-Rate codec (AMR) which included the EFR as the 12.2 kbps mode and most recently the EVS codec. Each of
these developments has provided clear and measurable quality improvements over the generation that went before.
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 19 ETSI TR 126 989 V17.0.0 (2022-05)

Figure 14: (Figure 5.4 from [7]): AMR Family of Curves for Experiment 1b (Clean Speech in Half Rate)

Examining the performance gains of GSM EFR (= AMR 12.2 - ETSI ETR 305 or GSM 06.55 [8]) over the GSM Full
Rate Codec it is clear that EFR significantly outperformed the GSM Full Rate Codec in all tests [8]:
"The EFR codec is better than the actual FR codec for clear speech, for all error conditions (EP1, EP2 andEP3)
and for tandeming under error EP1; it is equivalent to G.728 for its intrinsic quality, for background noise
conditions and talker dependency."
Considering GSM AMR (ETSI TR 126 975 [7]), from Figure 14 (Figure 5.4 of [7]) it can be seen that all of the AMR
coding modes are at least as good as the GSM Full Rate Codec for clean speech [7]. Data is somewhat lacking on noisy
speech performance with AMR in [7] but it can be reasonably expected that In noisy speech, the higher bit rates of
AMR would exceed the performance of GSM FR due to the increasing similarity with EFR but that the margin would
diminish at lower bit rates. However, all of the bit rates of the AMR modes exceed the 4.567 kbps of TETRA.
It can therefore be confidently concluded that the overall perceptual quality of the TETRA Codec will be inferior to that
of any mode of the AMR codec.
Such a conclusion is anecdotally supported by the adoption of the AMR 4.75 kbps codec as a codec upgrade to TETRA
during the development of the TETRA-2 feature set.
From the EVS Characterization results in TR 26.952 [3] (reproduced in subclause 5.1.1.2) the comparisons between
AMR & EVS show an improvement for the EVS codec over all of the coding modes of AMR.
It can therefore be confidently concluded that the perceptual quality of the TETRA Codec is going to be noticeably
inferior to any of the EVS NB codec modes. It is also clear from subclause 5.1.1.4 that AMR-WB and the WB, SWB
and FB modes of EVS are capable of significantly improving not only the quality, but also the intelligibility, of any
MCPTT system when compared to narrowband communication systems such as TETRA and P25. The increased
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 20 ETSI TR 126 989 V17.0.0 (2022-05)
intelligibility of the wider audio bandwidths are also available at bit rates approaching the lower bit rates of AMR with
the EVS codec i.e. EVS Wideband VBR (nominally 5.9 kbps) and 7.2 kbps compared to AMR 4.75, 5.9, 6.7 and 7.4
kbps. This feature of the EVS codec simultaneously satisfies the requirements for improved intelligibility and for radio
resource efficiency given in subclauses 5.14, 6.15.5 and 6.15.6 of [2].
5.1.1.6 Comparison of Performance over MCPTT Bearers
5.1.1.6.1 "HD-Voice" AMR-WB performance over 3GPP networks
The "HD Voice" reference describes the quality of experience across the listed KPIs (speech quality, speech
intelligibility, error resiliency, and call capacity) of AMR-WB in today's commercial VoLTE networks.
For instance AMR-WB at 12.65 kbps operating over a unicast LTE PS channel with 1% FER per mobile link (as
specified for QCI=1) resulting in 2% total FER in mobile-to-mobile calls.
To characterize the reference coverage in a VoLTE system using unicast power-controlled channels with HARQ Re-TX
and QCI = 1 this document uses the VoLTE field test results illustrated in figures 5.1.1.6.1-1 and 5.1.1.6.1-2 below.
Figure 5.1.1.6.1-2 excludes the zero RTP loss rate data to allow the reader to see the non-zero cases more clearly.

Figure 5.1.1.6.1-1 CDF of end-to-end RTP packet loss rate for VoLTE mobile-to-mobile calls. Zero RTP
loss values INCLUDED.
These measurements are based on logs taken over 6000 calls over various commercial LTE networks spanning multiple
continents, with each call averaging 34 seconds in duration (actually a mix of many short 30s calls and several hours of
long calls). The RTP loss rate is calculated over 1 second windows and includes stationary and mobile UE's in good and
bad coverage conditions.
It can that seen that about only about 90% of the cell area has an end-to-end FER <=2%. This is interpreted to mean that
the reference "HD Voice" coverage is equivalent to 90% of the cell area. In the remaining 10% the AMR-WB codec
speech quality starts to degrade at FERs above 2%.
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 21 ETSI TR 126 989 V17.0.0 (2022-05)

Figure 5.1.1.6.1-2 CDF of end-to-end RTP packet loss rate for VoLTE mobile-to-mobile calls. Zero RTP
loss values EXCLUDED.
5.1.1.6.2 MCPTT Bearers
The MCPTT service can be operated over three types of bearers depending on the network topology that is most
appropriate among those available. The following clauses describe these bearers and also the channel models used to
provide the simulation results in the next clause.
5.1.1.6.2.1 Unicast bearer
MCPTT can be operated over unicast channels in the same way the teleconferencing is performed in today's mobile
networks using a central conferencing server for duplicating and distributing media (Figure 5.1.1.6.2.1-1).
Each of the LTE unicast channels is a power-controlled channel that also use retransmission schemes such as HARQ to
provide a target BLER or packet loss rate to the VoIP frames transmitted over the channel.

ETSI
3GPP TR 26.989 version 17.0.0 Release 17 22 ETSI TR 126 989 V17.0.0 (2022-05)
h
c
e
e
A
p
S
m
T
o
T
r
P f
S P
p
T
e
T
e
c
h
Figure 5.1.1.6.2.1-1 MCPTT topology using unicast bearers
When using AMR-WB in this topology, the coverage, error-resiliency, speech quality, speech intelligibility, and call
capacity is equivalent to that of "HD Voice."
When evaluating the performance of EVS and AMR-WB over the unicast bearers, the EVS characterization report [3]
used the delay-loss profiles defined in [4] and introduced additional delay-loss profiles.
5.1.1.6.2.2 MBMS bearer
When multiple participants in a group are in a single cell the system can reduce the resources needed to support the
users by having them share a common downlink MBMS bearer. This shared channel has the following characteristics:
1) It is not power-controlled. There is no dynamic feedback by which the eNB can decide to dynamically adjust its
transmission resources to improve error performance or meet a target error rate.
2) Use of retransmissions is "blind" in that the retransmissions are not sent based on dynamic feedback such as
ACK/NACKs. These retransmissions cannot be used to guarantee a certain level of performance or target error
rate throughout the cell.
Therefore, error rates on the MBMS bearer can vary considerably throughout the cell, e.g., indoors, basements,
elevators, stairwells, or the edge of cell in an SC-PTM topology (see below).
The topology for using an MBMS bearer can be configured in two ways:
1) As a Single-Cell Point-to-Multipoint (SC-PTM) bearer where adjacent cells do not necessarily transmit the same
group's content on the same MBMS bearer. In this topology the adjacent cells typically interfere with the MBMS
bearer in the serving cell resulting in poorer coverage than the MBSFN topology.
2) As part of a MBSFN, where all the cells are broadcasting the same content on the same MBMS bearers,
preventing inter-cell interference and allowing the users to combine these transmissions to improve coverage and
reception.
The simulation model used to evaluate the performance of 3GPP speech codecs over MBMS bearers is described in
clause A.1
5.1.1.6.2.3 LTE-D bearer
LTE-Direct communication is a broadcast mechanism (no physical layer feedback) that defines two physical channels,
control and data, for communication between two (or more) UEs. The resources used for direct communication
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 23 ETSI TR 126 989 V17.0.0 (2022-05)
comprise of control and data resources. For in-network operation, a control resource pool is provided via RRC
signalling while for off-network operation, the control resource pool is pre-configured. Further, two modes of resource
allocation are supported: Mode 1 (in-network) and Mode 2 (in-network and off-network) as illustrated in Figure
5.1.1.6.2.3-1.
Figure 5.1.1.6.2.3-1 LTE-D operation
Here, the focus is on Mode 2 (off-network) scenario. In Mode 2, the transmitting UEs determine the resources to be
used for control and data transmission. UE transmits control to announce resources to be used for subsequent data
transmission. Receiving UEs monitor the control resources to determine when to wake-up and listen for data
transmission.
The performance of LTE-D based on system and link level simulations for off-network scenario is evaluated. In
particular, the mandatory Option 5 hotspot drop has been used for system level simulations.
5.1.1.6.3 AMR-WB and EVS Performance over the MCPTT Bearers
5.1.1.6.3.0 General
Enhanced Voice Services (EVS) is a new speech codec standard (part of 3GPP Release 12) which offers a wide range
of new features and improvements for low delay real-time communication. The key advancements fall into three
categories namely significantly improved quality for clean/noisy speech and music content, higher compression
efficiency and unprecedented error resiliency to packet loss and delay jitter experienced in PS systems. In addition to
voice quality and intelligibility aspects, we present methods on how to utilize some of the EVS codec advancements to
realize MCPTT system level benefits such as improved coverage and call capacity gains.
5.1.1.6.3.1 EVS Speech Quality
EVS Selection and Characterization Phase Test Results are summarized in the main body and detailed in Annex D of
TR 26.952 [3]. In this clause a few test results are highlighted to quantify the improvements of the EVS codec along the
three dimensions listed above, i.e., speech quality, compression efficiency, and error resiliency. To further simplify the
performance comparison a reference point for benchmarking is established, namely AMR-WB at a bit-rate of 12.65
kbps based on commercial grade HD Voice services available today.
NOTE. The correlation between voice quality and intelligibility is dependent on the test parameters. In general,
improved voice quality may result in improved intelligibility. However, it is also possible e.g., in noisy
conditions of [-30 dB to 5 dB SNR], that the improvements observed using subjective voice quality
testing and the improvements observed using subjective intelligibility testing may not correlate well. In
the other end of spectrum, e.g., in clean speech, while the voice quality may have improved significantly,
the intelligibility may already have approached a level of saturation.
Three mixed bandwidth DCR (Degradation Category Rating) tests were performed as a part of EVS Characterization
testing whose results are shown in Figure 13.
ETSI
3GPP TR 26.989 version 17.0.0 Release 17 24 ETSI TR 126 989 V17.0.0 (2022-05)
In general, EVS-WB codec offers quality significantly better than AMR-WB at a similar bit-rate and quality equivalent
to AMR-WB at a lower bit rate. The EVS-SWB codec performance is significantly better than both AMR-WB and
corresponding bit rates of EVS-WB.
For clean speech content (Figure 13a), the lowest bit-rate of EVS-WB namely 5.9 kbps can offer quality significantly
better than AMR-WB at 8.85 kbps and equivalent to AMR-WB at 12.65 kbps. The subjective quality of EVS-WB
coding starting at 9.6 kbps is significantly better than the AMR-WB coding at its highest bit rate of 23.85 kbps. The
super-wideband mode of EVS at 13.2 kbps achieves transparency to the direct source and offers quality significantly
better than both 23.85 kbps of AMR-WB and 24.4 kbps of EVS-WB.
For noisy speech (Figure 13b), EVS-WB at 9.6 kbps offers quality on par with AMR-WB at 12.65 kbps. This has also
been shown across different languages/noise types and summarized in TR 26.952. How
...