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TECHNICAL REPORT
Digital Enhanced Cordless Telecommunications (DECT);
Study of Super Wideband Codec in DECT for narrowband,
wideband and super-wideband audio communication
including options of low delay
audio connections (≤ 10 ms framing)
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2 ETSI TR 103 590 V1.1.1 (2018-09)
Reference
DTR/DECT-00316
Keywords
codec, DECT, superwideband
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3 ETSI TR 103 590 V1.1.1 (2018-09)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
Introduction . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definitions and abbreviations . 7
3.1 Definitions . 7
3.2 Abbreviations . 7
4 Investigations on an enhanced DECT codec . 8
4.1 Overview . 8
4.2 Design constraints/features to be supported . 9
4.2.1 Improved exploitation on DECT slots . 9
4.2.2 Transmission latency . 9
4.2.3 Supported sampling rates, audio bandwidths and sample depths . 9
4.2.4 Support for music streaming . 9
4.2.5 Packet loss concealment . 9
4.2.6 Low codec complexity . 9
4.3 Investigations on impact of block-based codec . 10
4.3.1 Probability and distribution of bit errors . 10
4.3.1.1 Normal slots - transmission error profile I . 10
4.3.1.2 Long slots - transmission error profile II . 13
4.3.2 Study of CRC/FEC protection schemes . 16
4.3.2.1 Static rates . 16
4.3.2.2 Dynamic rate switching of source and channel coder . 19
4.3.2.2.1 General . 19
4.3.2.2.2 Graceful degradation at DECT range limit . 19
4.3.2.2.3 Audio bandwidth switching . 19
4.3.2.2.4 Potential channel coder configuration . 20
4.3.3 Comparison to current DECT codecs . 20
4.3.4 Usability of I _minimum_delay service . 20
N
4.4 Evaluation results of LC3 . 21
4.4.1 Audio quality evaluation for clean channels . 21
4.4.1.1 NB/WB experiment tandeming I . 21
4.4.1.1.1 Setup . 21
4.4.1.1.2 Observations . 23
4.4.1.2 SSWB/SWB experiment tandeming I . 23
4.4.1.2.1 Setup . 23
4.4.1.2.2 Observations . 25
4.4.1.3 WB/SWB experiment on short frame size . 25
4.4.1.3.1 Setup . 25
4.4.1.3.2 Observations . 26
4.4.2 Audio quality evaluation for error prone channels . 26
4.4.2.1 Reference conditions . 26
4.4.2.2 Codec characterization depending on PLR . 27
4.4.2.2.1 Setup . 27
4.4.2.2.2 Observations . 28
4.4.2.3 Codec characterization depending on PLR and BER . 28
4.4.2.3.1 Setup . 28
4.4.2.3.2 Observations . 31
4.5 Integration of LC3 in existing DECT infrastr ucture . 31
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4 ETSI TR 103 590 V1.1.1 (2018-09)
4.5.1 General . 31
4.5.2 High-level codec description . 31
4.5.2.1 Codec overvie w . 31
4.5.2.2 Audio channels . 31
4.5.2.3 Complexity . 31
4.5.2.4 Audio bandwidth detection . 31
4.5.3 High-level options for LC3 integration into the DECT specifications. 32
4.5.3.1 Fixed bitrate, multi-mode or adaptive multi-mode operation . 32
4.5.3.2 Codec negotiation at session setup . 33
4.5.3.3 Codec mode set negotiation . 33
4.5.3.4 Adaptation signalling . 34
4.5.3.5 Audio bandwidth selection/adaptation . 35
4.5.3.6 DTX . 35
4.5.3.7 Acoustic front-end . 36
4.5.3.8 VoIP, RTP payload format . 36
4.5.3.9 Backwards compatibility . 36
4.5.3.10 Interworking with external networks and devices . 36
4.5.3.11 Repeater operation, relays . 37
5 Conclusions . 37
Annex A: Change History . 39
History . 40
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5 ETSI TR 103 590 V1.1.1 (2018-09)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is 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 IPR Policy, no investigation, 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.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Digital Enhanced Cordless
Telecommunications (DECT).
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.
Introduction
Since the introduction of additional codecs in New Generation DECT [i.5] in 2007, wideband services have been widely
established for fixed line, mobile and OTT communications networks. This trend is gaining even more momentum by
services using cutting edge codecs like 3GPP EVS and the upcoming new Bluetooth™ codec by offering super-
wideband audio bandwidth.
NOTE: Bluetooth™ is the trade name of a wireless technology standard for exchanging data over short distances
(using short-wavelength UHF radio waves in the ISM band from 2,4 - 2,485 GHz) from fixed and mobile
devices, and building personal area networks (PANs), owned by the Bluetooth Special Interest Group.
This information is given for the convenience of users of the present document and does not constitute an
endorsement by ETSI of the technology named. Equivalent technologies may be used if they can be
shown to lead to the same results.
Recent market research from several relevant DECT infrastructure providers indicates a demand for upgrading DECT
services and standard with additional features enabled by evolved speech and audio codecs.
The present document collects performance requirements to add a real benefit to current and upcoming DECT
applications and evaluates the Low Complexity Communication Codec (LC3) on suitability for this as well as discusses
possible adaptations for DECT environments in terms of error protection and signalling.
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6 ETSI TR 103 590 V1.1.1 (2018-09)
1 Scope
The present document provides a study of technical updates to the DECT standard to enable super wideband (SWB)
audio calls in existing DECT slot formats as well as technical improvements to narrowband (NB) and wideband (WB)
calls. All required change requests are listed and defined for the different DECT layers to enable high quality audio
communication between DECT FP and PP including DECT repeaters (relays). The study includes an investigation on
FEC for block-based codecs. Information is provided on the audio quality in some DECT use cases for NB, WB and
SWB and potential improvements by a new audio codec are studied.
2 References
2.1 Normative references
Normative references are not applicable in the present document.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long-term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI EN 300 175-1: "Digital Enhanced Cordless Telecommunications (DECT); Common
Interface (CI); Part 1: Overview".
[i.2] ETSI EN 300 175-8: "Digital Enhanced Cordless Telecommunications (DECT); Common
Interface (CI); Part 8: Speech and audio coding and transmission".
[i.3] EP2901594B1: "Error Detection for sub-band ADPCM encoded sound signal".
[i.4] ETSI EN 300 175-3: "Digital Enhanced Cordless Telecommunications (DECT); Common
Interface (CI); Part 3: Medium Access Control (MAC) layer".
[i.5] ETSI TS 102 527-3: "Digital Enhanced Cordless Telecommunications (DECT); New Generation
DECT; Part 3: Extended wideband speech services".
[i.6] ETSI EN 300 700: "Digital Enhanced Cordless Telecommunications (DECT); Wireless Relay
Station (WRS)".
[i.7] ETSI EN 300 175-5: "Digital Enhanced Cordless Telecommunications (DECT); Common
Interface (CI); Part 5: Network (NWK) layer".
[i.8] ETSI EN 300 176-2: "Digital Enhanced Cordless Telecommunications (DECT); Test
specification; Part 2: Audio and speech".
[i.9] Recommendation ITU-T P.863 (09-2014): "Perceptual objective listening quality assessment".
[i.10] Recommendation ITU-T P.800 (08-1996): "Methods for subjective determination of transmission
quality".
[i.11] Recommendation ITU-T G.191 (03-1996): "Software tools for speech and audio coding
standardization" .
[i.12] Recommendation ITU-T G.722 (09-2012): "7 kHz audio-coding within 64 kbit/s".
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7 ETSI TR 103 590 V1.1.1 (2018-09)
[i.13] Recommendation ITU-T G.726 (12-1990): "40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code
Modulation (ADPCM)".
[i.14] ETSI TS 126 071: "Digital cellular telecommunications system (Phase 2+) (GSM); Universal
Mobile Telecommunications System (UMTS); LTE; Mandatory speech CODEC speech
processing functions; AMR speech Codec; General description (3GPP TS 26.071)".
[i.15] ETSI TS 126 171: "Digital cellular telecommunications system (Phase 2+) (GSM); Universal
Mobile Telecommunications System (UMTS); LTE; Speech codec speech processing functions;
Adaptive Multi-Rate - Wideband (AMR-WB) speech codec; General description (3GPP
TS 26.171)".
[i.16] ETSI TS 126 441: "Universal Mobile Telecommunications System (UMTS); LTE; Codec for
Enhanced Voice Services (EVS); General overview (3GPP TS 26.441)".
[i.17] SIG Bluetooth™ Hands-Free Profile 1.7.1.
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in ETSI EN 300 175-1 [i.1] and the following
apply:
Fullband (FB): speech or audio sampled at 48 kHz
Fullband, compact disc (FBCD): speech or audio sampled at 44,1 kHz
Narrowband (NB): speech or audio sampled at 8 kHz
Semi-Super Wideband (SSWB): speech or audio sampled at 24 kHz
Super Wideband (SWB): speech or audio sampled at 32 kHz
Wideband (WB): speech or audio sampled at 16 kHz
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
rd
3GPP 3 Generation Partnership Project
ACR Absolute Category Rating
NOTE: See Recommendation ITU-T P.800 [i.10].
AMR Adaptive Multi-Rate,
NOTE: See ETSI TS 126 071 [i.14].
AMR-WB Adaptive Multi-Rate Wideband
NOTE: See ETSI TS 126 171 [i.15].
BCH Bose-Chaudhuri-Hocquenghem
BER Bit Error Rate
CELT Constrained Energy Lapped Transform
CMR Codec Mode Request
CNG Comfort Noise Generation
CRC Cyclic Redundancy Check
CS Circuit Switched
DECT Digital Enhanced Cordless Telecommunications
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8 ETSI TR 103 590 V1.1.1 (2018-09)
DSP Digital Signal Processor
DTX Discontinuous Transmission
EP Error Protection
ETSI European Telecommunications Standards Institute
EVS Enhanced Voice Service
NOTE: See ETSI TS 126 441 [i.16].
FB Fullband
FBCD Fullband Compact Disc
FEC Forward Error Correction
FER Frame Erasure Rate
FP Fixed Part (DECT bas station)
FT Frame Type
GFSK Gaussian Frequency-Shift Keying
GSM Global System for Mobile Communications
IETF Internet Engineering Task Force
I higher layer Information channel (unprotected), minimum delay operation
NA
NOTE: See ETSI TS 102 527-3 [i.5].
I higher layer Information channel (unprotected), normal delay operation
NB
NOTE: See ETSI TS 102 527-3 [i.5].
IP Internet Protocol
LAN Local Area Network
LC3 Low Complexity Communication Codec
MIPS Million Instructions Per Second
MNRU Modulated Noise Reference Unit
MOS-LQO Mean Opinion Score - Listening Quality Objective
mSBC modified Subband Coding
NOTE: See [i.17].
NB Narrowband
OTT Over-The-Top content
PLC Packet Loss Concealment
PLR Packet Loss Rate
PP Portable Part (DECT handset)
RAM Random-Access Memory
RSSI Received Signal Strength Indicator
RTP Real-Time Protocol
SSWB Semi-Super Wideband
STL Software Tool Library
SWB Super Wideband
VoIP Voice over Internet Protocol
WB Wideband
WMOPS Weighted Millions of Operations Per Second
WRS Wireless Relay Station
4 Investigations on an enhanced DECT codec
4.1 Overview
The investigations are organized as follows:
1) Definition of general required codec features (clause 4.2).
2) Study on error profiles and protection schemes for DECT systems (clause 4.3).
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9 ETSI TR 103 590 V1.1.1 (2018-09)
3) Characterization of the LC3 as potential candidate (clause 4.4).
4) Definition of required update to DECT specifications (clause 4.5).
4.2 Design constraints/features to be supported
4.2.1 Improved exploitation on DECT slots
Table 1 compares the slot related requirements of the legacy DECT codecs with the proposed new DECT codec.
Table 1: Overview of DECT slot related requirements for new codec
Slot usage Legacy DECT codecs Enhanced DECT codec
Normal slots NB calls (G.726) NB and WB calls
Long slots WB calls (G.722) WB and SWB calls
NB and WB audio quality should be comparable to or better relative to the legacy DECT codecs.
The user experience for error prone channels is expected to be comparable to or better relative to the legacy DECT
codecs.
4.2.2 Transmission latency
The codec should operate on 10 ms frame sizes as provided by the DECT transmission slots [i.1]. On top of the framing
delay of 10 ms, the additional algorithmic delay should be less than or equal to 2,5 ms.
Additionally, the codec should support frame sizes of 5 ms as well to enable new low delay application besides
telephony. For instance, in-room conferencing/amplification or parliament systems require a microphone to loudspeaker
delay of less than 20 ms. This guarantees lip-synchronism of the speaker to the amplified signal.
4.2.3 Supported sampling rates, audio bandwidths and sample depths
The codec should support NB, WB, SWB and FB audio bandwidths at the native sample rates of 8 kHz, 16 kHz, 32 kHz
and 48 kHz. Additionally, 24 kHz (SSWB) should be supported.
The codec should support the coding of lower audio bandwidths for a given sample rate, e.g. coding of NB signals at
32 kHz. The codec should support the coding of audio samples with 16 bits per samples and may support coding of
audio samples with 24 bits per sample.
4.2.4 Support for music streaming
The codec should provide decent audio quality for music streaming services and may provide additional coding features
to support stereo music channels.
4.2.5 Packet loss concealment
The codec should support packet loss concealment without adding further algorithmic delay. As the main application is
voice, the packet loss concealment should perform well for speech signals.
4.2.6 Low codec complexity
The codec should run with a low computational complexity and low memory footprint to be implementable on typical
DECT handheld devices. The complexity should be measured and reported using the latest ITU-T STL complexity
measurement toolbox [i.11].
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10 ETSI TR 103 590 V1.1.1 (2018-09)
4.3 Investigations on impact of block-based codec
4.3.1 Probability and distribution of bit errors
4.3.1.1 Normal slots - transmission error profile I
An error profile was measured using a real DECT system simulating that a DECT caller is moving through an office
building. The caller starts close to the base station and walks away through the office. The measurement recorded the
number of bit errors, the position of the bit error, the signal strength (RSSI, in steps of eight) and complete frame losses.
Figure 1 outlines the error profile where complete frame losses are indicated by 384 bit errors (A+B field) in
combination with signal strength zero.
Figure 1: Characterization of Error Profile I
Regarding the position of the bit errors inside the frame, no specific dependency can be found. In order to structure the
analysis of the pattern, the bit error profile is further grouped into certain signal strength classes as outlined in Figure 2.
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11 ETSI TR 103 590 V1.1.1 (2018-09)
Figure 2: Plot of absolute number (blue) and average number (red) of bit errors for each signal
strength (top); Histogram of number of bit errors inside frame for
signal strength levels 32 dB, 40 dB, 48 dB and 56 dB
The plots show that:
• For this profile, bit errors only occur for a signal strength level ≤ 56 dB.
• For the signal strength level 48 dB and 56 dB, most packets show less than three bit errors in one packet.
• For signal strength level 40 dB, the bit error rate per packet is significantly higher compared to level 48 dB.
• For signal strength level 32 dB, almost all bits are affected; this level is thus not considered for any recovery
activity.
• Four different error protection classes may be appropriate to address the different error characteristics
depending on the signal strength, i.e. clean channel, 56 dB, 48 dB, 40 dB.
The packet loss rate (PLR) per signal strength can be estimated by averaging the signal strength over one second.
Figure 3 shows packet losses in relation to the averaged signal strength.
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12 ETSI TR 103 590 V1.1.1 (2018-09)
Figure 3: Packet loss rate estimation
According to the given data, a specific PLR can be assigned to a certain signal level as outlined in Table 2.
Table 2: Packet loss and bit error rates
Normalized Averaged signal # Frames # Packet PLR PLR rounded BER rounded
strength (RSSI) losses [%] [%] [%]
1 (136 dB) 430 0 0 0
0,94 (128 dB) 728 0 0 0
0,88 (120 dB) 41 0 0 0
0,82 (112 dB) 78 0 0 0
0,76 (104 dB) 20 0 0 0
0,71 (96 dB) 28 0 0 0
0,65 (88 dB) 75 0 0 0
0,59 (80 dB) 2 380 0 0 0
0,53 (72 dB) 320 0 0 0
0,47 (64 dB) 436 5 1,15 1
0,41 (56 dB) 203 2 0,99 1 0,01
0,35 (48 dB) 3 195 28 0,88 1 0,31
0,
...