ETSI EN 300 175-8 V1.7.1 (2003-07)

SLOVENSKI STANDARD
01-julij-2005
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Digital Enhanced Cordless Telecommunications (DECT); Common Interface (CI); Part 8:
Speech coding and transmission
Ta slovenski standard je istoveten z: EN 300 175-8 Version 1.7.1
ICS:
33.070.30 'LJLWDOQHL]EROMãDQH Digital Enhanced Cordless
EUH]YUYLþQHWHOHNRPXQLNDFLMH Telecommunications (DECT)
'(&7
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

European Standard (Telecommunications series)

Digital Enhanced Cordless Telecommunications (DECT);
Common Interface (CI);
Part 8: Speech coding and transmission

2 ETSI EN 300 175-8 V1.7.1 (2003-07)

Reference
REN/DECT-000201-8
Keywords
DECT, radio, speech
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ETSI
3 ETSI EN 300 175-8 V1.7.1 (2003-07)
Contents
Intellectual Property Rights.6
Foreword.6
1 Scope.7
2 References.7
3 Definitions and abbreviations.8
3.1 Definitions.8
3.2 Abbreviations.8
4 Configurations.10
4.1 Reference configuration.10
4.1.1 Basic configuration.10
4.1.2 Portable Part (PP) .11
4.1.2.1 Functional organization.11
4.1.2.2 Volume control.11
4.1.3 Fixed Part (FP).12
4.1.3.1 Digital interface.12
4.1.3.2 Analogue interface.12
4.1.3.3 FP adaptive volume control .13
4.2 Test configurations.13
5 Encoding.13
5.1 32 kbit/s full term (ADPCM) .13
5.1.1 Algorithm.13
5.1.2 Bit sequence.13
5.2 Other codings.13
6 Transmission aspects.14
6.1 Relative level.14
6.2 Acoustic reference level .14
6.3 Volume control.14
7 Speech performance characteristics .14
7.1 PP frequency responses .14
7.1.1 Sending.14
7.1.2 Receiving.15
7.2 PP sending and receiving loudness ratings.15
7.2.1 Nominal values.15
7.2.2 User-controlled volume control in PP.15
7.2.3 PP adaptive volume control .16
7.2.4 FP adaptive volume control .16
7.3 Sidetone.16
7.3.1 Talker sidetone.16
7.3.2 Listener sidetone.17
7.4 Terminal coupling loss .17
7.4.1 Weighted Terminal Coupling Loss (TCLw).17
7.4.1.1 PP for the 3,1 kHz service (PSTN or ISDN).17
7.4.1.2 FP with 4-wire interface.17
7.4.1.3 FP with analogue 2-wire interface .18
7.4.1.4 PP for unrestricted 64 kbit/s service.18
7.4.2 Stability loss.18
7.4.2.1 Requirement.18
7.4.2.2 Test conditions.19
7.4.2.3 Fixed geometry PP .19
7.4.2.4 Variable geometry PP .19
7.5 Distortion.19
7.5.1 Sending.19
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4 ETSI EN 300 175-8 V1.7.1 (2003-07)
7.5.2 Receiving.19
7.5.3 Sidetone.19
7.5.4 Recommended value for network planning .19
7.6 Out of band signals.19
7.6.1 Sending (discrimination against out of band input signals) .19
7.6.2 Receiving (spurious out of band signals).20
7.7 Noise.20
7.7.1 Sending.20
7.7.2 Narrow-band noise.20
7.7.3 Receiving.20
7.7.4 Level of sampling frequency (receiving) .20
7.8 Acoustic shock.20
7.8.1 Continuous signal.20
7.8.2 Peak signal.20
7.9 Delay.21
7.9.1 DECT network.21
7.9.2 PP.21
7.9.3 FP.21
7.10 Network echo control .21
7.11 PP ambient noise rejection .22
7.12 Additional requirements for DECT systems provided with a 2-wire PSTN interface.22
7.12.1 General.22
7.12.1.1 Polarity independence.22
7.12.1.2 Feed Conditions.22
7.12.1.3 Power supply.22
7.12.2 Speech performance characteristics.22
7.12.2.1 Sensitivity/frequency response.23
7.12.2.2 Sending and Receiving Loudness Ratings (SLR and RLR) .23
7.12.2.3 Distortion.23
7.12.2.4 Noise.23
7.12.2.5 Echo Return Loss.23
8 Additional features.23
8.1 Loudspeaking and hand-free facilities.23
8.2 Tandem with mobile radio network.23
8.2.1 Tandem with GSM.24
8.2.1.1 Network echo control.24
8.2.1.2 Terminal coupling loss.24
8.2.1.3 The GSM mobile transmitter operates in continuous mode .24
8.2.1.4 The GSM mobile transmitter operates in discontinuous mode, DTX .24
8.3 DECT connected to the GSM fixed network.24
8.3.1 Network echo control.25
8.3.2 Terminal coupling loss.25
8.4 Wireless Relay Stations (WRS).25
8.4.1 Modified FP network echo control requirements for implementation of 2 and 3 CRFP links in
cascade.26
Annex A (informative): Description of "reference" echo control devices.27
A.1 Handset echo.27
A.1.1 Overview.27
A.1.1.1 Connection to the PSTN/ISDN.27
A.1.1.1.1 Local and national calls.27
A.1.1.1.2 Long distance connections with echo control devices in the PSTN/ISDN, e.g. calls via satellites.27
A.1.1.2 Connection to the GSM network .28
A.1.2 Implementation of the FP echo control function .28
A.1.2.1 Suppression threshold.29
A.1.2.2 Static characteristics of activation control .29
A.1.2.3 Dynamic characteristics of activation control.29
A.2 Network echo.29
A.2.1 Soft suppressor implementation of requirement 2.30
A.2.1.1 Static characteristics.31
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5 ETSI EN 300 175-8 V1.7.1 (2003-07)
A.2.1.2 Dynamic characteristics.31
A.2.2 Additional echo control for a 2-wire interface of requirement 1.31
A.2.3 Echo canceller used for both requirements 1 and 2.32
Annex B (informative): Local loop application .33
B.1 DECT tethered local loop replacement with 2-wire PP end system.33
B.1.1 TCLw requirements.33
B.1.2 Network echo.34
B.2 Quantization distortion considerations.34
Annex C (informative): GSM Discontinuous Transmission (DTX), and Voice Activity
Detection (VAD).35
Annex D (informative): Speech levels in relation to ambient room noise and examples of
adaptive volume control settings .36
Annex E (informative): Bibliography.37
Annex F (informative): Change history .38
History .39

ETSI
6 ETSI EN 300 175-8 V1.7.1 (2003-07)
Intellectual Property Rights
IPRs essential or potentially essential to the present document 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 (http://webapp.etsi.org/IPR/home.asp).
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.
Foreword
This European Standard (Telecommunications series) has been produced by ETSI Project Digital Enhanced Cordless
Telecommunications (DECT).
The present document is part 8 of a multi-part deliverable. Full details of the entire series can be found in part 1 [1].
Further details of the DECT system may be found in TR 101 178 and ETR 043 (see Bibliography).

National transposition dates
Date of adoption of this EN: 27 June 2003
Date of latest announcement of this EN (doa): 30 September 2003
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 31 March 2004
Date of withdrawal of any conflicting National Standard (dow): 31 March 2004

ETSI
7 ETSI EN 300 175-8 V1.7.1 (2003-07)
1 Scope
The present document gives an introduction and overview of the complete Digital Enhanced Cordless
Telecommunications (DECT) Common Interface (CI).
This part of the DECT CI specifies the speech coding and transmission requirements.
In order to ensure satisfactory interworking of different portable and fixed units, it is necessary to specify the
transmission performance of the analogue information over the digital link. This requires not only use of a common
speech algorithm, but also standardization of frequency responses, reference speech levels (or loudness) at the air
interface and various other parameters.
The present document applies to DECT equipment which includes all the necessary functions to provide real-time
two-way speech conversation. A 3,1 kHz telephony teleservice conveyed over a DECT link (including Fixed Part (FP)
and Portable Part (PP)) which is capable of being connected (directly or indirectly) to the public network access point
should comply with the requirements in the present document.
Tethered fixed point local loop applications are not required to comply with the requirements of the present document.
The speech performance characteristics defined in the present document typically conform to TBR 008, which specifies
the overall performance between the handset acoustic interface and a 64 kbit/s A-law Pulse Code Modulated (PCM)
digital network interface. The deviations from TBR 008 are mainly due to the consequences of non-PCM coding and
transmission delay.
The additional features described in clause 8 are those which are not included in TBR 008, but which are likely to occur
in a DECT system: analogue interface, loudspeaking and hand-free facilities, tandeming with a mobile radio network.
Headsets are not covered by the present specifications.
For the DECT systems which connect to the Public Switched Telephone Network (PSTN) via an analogue interface, the
additional requirements, which are implemented in the FP, have as much as possible been aligned with TBR 038.
ETSI/STC TM5 has prepared a technical report, ETR 041, to be used as a guide for network planning.
A summary of the control and the use of the DECT echo control functions, to guide on need for options to
manufacturers and installers, is found in annex A.
Information concerning test methods can be found in EN 300 176 [3]. The test methods take into account that DECT is
a digital system.
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 and/or edition number or version number) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
[1] ETSI EN 300 175-1: "Digital Enhanced Cordless Telecommunications (DECT); Common
Interface (CI); Part 1: Overview".
[2] ETSI EN 300 175-5: "Digital Enhanced Cordless Telecommunications (DECT); Common
Interface (CI); Part 5: Network (NWK) layer".
ETSI
8 ETSI EN 300 175-8 V1.7.1 (2003-07)
[3] ETSI EN 300 176: "Digital Enhanced Cordless Telecommunications (DECT); Approval test
specification; (Part 1: Radio; Part 2: Speech)".
[4] ITU-T Recommendation G.101 (1996): "The transmission plan".
[5] ITU-T Recommendation G.131 (1996): "Control of talker echo".
[6] ITU-T Recommendation G.164 (1988): "Echo suppressors".
[7] ITU-T Recommendation G.165 (1993): "Echo cancellers".
[8] ITU-T Recommendation G.701 (1993): "Vocabulary of digital transmission and multiplexing, and
pulse code modulation (PCM) terms".
[9] ITU-T Recommendation G.726 (1990): "40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code
Modulation (ADPCM)".
[10] Void.
[11] ITU-T Recommendation P.10: "Vocabulary of terms on telephone transmission quality and
telephone sets".
[12] ITU-T Recommendation P.340: "Transmission characteristics of hands-free telephones".
[13] ITU-T Recommendation G.113 (1996): "Transmission impairments".
[14] ITU-T Recommendation G.111 (1993): "Loudness Ratings (LRs) in an international connection".
[15] ETSI ETS 300 540: "Digital cellular telecommunications system (Phase 2) (GSM); Transmission
planning aspects of the speech service in the GSM Public Land Mobile Network (PLMN) system
(GSM 03.50)".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions defined in ITU-T Recommendations P.10 [11],
G.701 [8], in EN 300 175-1 [1] and the following apply:
dBm: absolute power level relative to 1 milliwatt, expressed in dB
dBm0: absolute power level in dBm referred to a point of zero relative level (0 dBr point)
dBPa: sound pressure level relative to 1 Pa, expressed in dB
dBPa(A): a-weighted sound pressure level relative to 1 Pa, expressed in dB
dBr: relative power level of a signal in a transmission path referred to the level at a reference point on the path (0 dBr
point)
3.2 Abbreviations
For the purposes of the present document, the abbreviations defined in ITU-T Recommendations P.10 [11], G.701 [8]
and the following apply:
ADPCM Adaptive Differential Pulse Code Modulation
BSS Base Station Sub-system
CRFP Cordless Radio Fixed Part
CI Common Interface
CLRR Circuit Loudness Rating, Receiving
CLRS Circuit Loudness Rating, Sending
DTX Discontinuous Transmission
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9 ETSI EN 300 175-8 V1.7.1 (2003-07)
ERP Ear Reference Point
ES End System
EUT Equipment Under Test
FP Fixed Part
FT Fixed radio Termination
GAP Generic Access Profile
GSM Global System for Mobile communications
ISDN Integrated Services Digital Network
LL Local echo Loss
e
LSTR Listener SideTone Rating
MRP Mouth Reference Point
MSC Mobile Switching Centre
NLP Non-Linear Processor
NWK NetWorK
OLR Overall Loudness Rating
PABX Private (Automatic) Branch eXchange
PCM Pulse Code Modulated
PP Portable Part
PSTN Public Switched Telephone Network
PT Portable radio Termination
QDU Quantization Distortion Unit
ReFP Reference Fixed Part
REP REpeater Part
RePP Reference Portable Part
RFP Radio Fixed Part
RLR Receiving Loudness Rating of the Handset
H
SLR Sending Loudness Rating of the Handset
H
STMR SideTone Masking Rating
TA Terminal Adaptors
TCLw weighted Terminal Coupling Loss
TDMA Time Division Multiple Access
TELR Talker's Echo Loudness Rating
VAD Voice Activity Detection
WBS Wireless Base Station
WRS Wireless Relay Station
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10 ETSI EN 300 175-8 V1.7.1 (2003-07)
4 Configurations
4.1 Reference configuration
4.1.1 Basic configuration
The basic reference configuration for voice transmission over DECT is shown in figure 1.
PP (handset) FP (fixed part)
Acoustic Air
interface interface Line
Line
MRP
Acoustic interface
Transcoder Transcoder
interface +
+ echo
Uniform Uniform
Volume control
PCM PCM
control +
to/from to/from
+ Volume control
air code air code
] coder +
coder
ERP
Uniform Uniform
PCM PCM
reference reference
point point
Figure 1: Basic reference configuration
The PP and the FP are delimited by physical interfaces:
Acoustic: from the PP towards the speaker-listener, with the Ear and Mouth Reference Points (ERP and
MRP).
Air(RF): the interface between PP and FP.
Line: the interface from the FP towards the network.
Uniform PCM reference points shall be introduced in both the PP and the FP to materialize the limits of the
transmission segment which is affected by the air interface coding scheme. This allows the transmission requirements to
be specified independently from the coding at the air interface. The various transcoding algorithms are
level-transparent, i.e. with an encoder and decoder connected in tandem, the "levels" of the digital signals at the uniform
PCM input of the encoder and output from the decoder are identical. In a particular implementation, the reference points
may be embedded within an IC, and thus will not be physically accessible.
Each of the three sections thus delimited deals with distinct functions:
a) the PP electro-acoustic section (between acoustic interface and PP uniform PCM reference point) which
includes the acoustic interface, the volume control and the analogue to digital conversion;
b) the air-code section (between PP and FP uniform PCM reference points) considers the transcoding between
uniform PCM and the air-code, as well as the transmission over the air interface;
c) the FP line interface section (between FP uniform PCM reference point and line interface) comprises the
interface to the line, digital or analogue, and the FP voice processing, e.g. echo control.
Typically, the transmission features conform to TBR 008 for the PP electro-acoustic section, and the line interface
section in the case of digital interface. In the case of analogue interface, the line interface section realizes in the FP the
adaptation to clause 7.12 and to the relevant attachment requirements.
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11 ETSI EN 300 175-8 V1.7.1 (2003-07)
4.1.2 Portable Part (PP)
4.1.2.1 Functional organization
Figure 2 represents the basic functional organization of a PP from the voice transmission point of view:
Uniform PCM Air
Acoustic
reference point interface
interface
SLR
H
MRP
0 A/D
Transcoder
Electro-
Uniform PCM
acoustic
to/from
interface
air code
D/A
+
ERP filter
RLR
H
Figure 2: PP functional organization
The various functions represented in figure 2 are:
a) the electro-acoustic function, which performs the interface to the transducers and the volume control. The
Handset Loudness Ratings (SLR ) and (RLR ) are defined between the acoustic interface and the uniform
H H
PCM reference point;
b) the analogue to digital and digital to analogue coding to the uniform PCM reference point;
c) the transcoder between uniform PCM and air-code.
4.1.2.2 Volume control
The volume control facility is optional, and can be implemented in a number of different ways:
1) in the simplest implementation, it affects only the receiving level and is under the manual control of the PP
user;
2) the volume adjustment may also be adaptive, e.g. taking into account the average level of ambient noise at the
MRP;
3) the volume control may affect both receiving and sending levels in opposite directions. This has the advantage
of reducing the influence on the terminal coupling loss when the receive volume is increased. Such an
implementation would fit a noisy environment, as the need for an increased receiving volume is likely to come
from a loud ambient noise, and it is then combined with a loud speech level.
ETSI
12 ETSI EN 300 175-8 V1.7.1 (2003-07)
4.1.3 Fixed Part (FP)
4.1.3.1 Digital interface
Figure 3 shows the functional organization of a FP with a digital interface.
Air Uniform PCM Line
interface reference point interface
Echo
Transcoder Transcoder
control
Uniform PCM Uniform PCM
handset
to/from to/from
+
air code A-law
network
Figure 3: FP functional organization
The various functions represented in figure 3 are:
a) a transcoder between air-code and uniform PCM;
b) an echo control function which processes echoes coming back from both the handset and the network. It
provides additional losses that compensate for the increased length of the echo path due to the DECT
transmission delay over the air interface;
c) a transcoder from uniform PCM to A-law PCM towards the line interface.
4.1.3.2 Analogue interface
The implementation of a FP with an analogue interface is shown in figure 4.
Air Uniform PCM Line
interface reference point interface
CLRS
D/A
+
filter
Echo
Transcoder
control
Uniform PCM
to/from
including
air code
hybrid
A/D
CLRR
Figure 4: FP with an analogue interface
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13 ETSI EN 300 175-8 V1.7.1 (2003-07)
The various functions represented in figure 4 are:
a) the line interface comprises the digital to analogue coder-decoder and the adaptation to the line, that can be
either 2- or 4-wire. The Circuit Loudness Ratings (CLRR and CLRS) are defined between uniform PCM
reference point and the line interface;
b) in the case of a 2-wire line, the network echo controller deals both with the local hybrid echo and the far end
network echo.
4.1.3.3 FP adaptive volume control
An adaptive dual volume adjustment, as described in clause 4.1.2.2, may optionally be implemented into the FP, for
base stations where the associated PPs may be used in a noisy environment (e.g. public access).
4.2 Test configurations
A DECT system comprises a FP and a PP. As these parts are not always purchased together, it is a requirement that
either the complete system or each of the two separate parts shall be capable of being tested (see EN 300 176 [3]).
5 Encoding
5.1 32 kbit/s full term (ADPCM)
5.1.1 Algorithm
The speech coding algorithm shall conform to ITU-T Recommendation G.726 [9] for 32 kbit/s Adaptive Differential
Pulse Code Modulation (ADPCM).
The A-law companding and synchronous tandem adjustment maybe omitted in FPs with an analogue line interface and
in PPs.
NOTE: ITU-T Recommendation G.726 [9] 32 kbit/s ADPCM codecs support the use of the voice channel for
telefax of group 2 and group 3. For group 3 the data speed, which is automatically negotiated, is in
practice normally limited to 9,6 kbit/s.
5.1.2 Bit sequence
The ADPCM words comprised in each burst shall be transmitted in chronological order, and with the most significant
bit transmitted first within each word.
5.2 Other codings
No other coding scheme is specified at this time. When introducing a new coding the following speech performance
characteristics shall be reviewed:
- frequency response;
- distortion;
- delay; and
- if the latter is widely affected, terminal coupling loss and network echo control.
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14 ETSI EN 300 175-8 V1.7.1 (2003-07)
6 Transmission aspects
6.1 Relative level
The digital line interface is a 0 dBr point according to ITU-T Recommendation G.101 [4]. As the various digital
transcoding algorithms are essentially loss-less, the relative level is constant over the whole digital path in the PP and
the FP.
6.2 Acoustic reference level
The acoustic reference level is defined as the acoustic level which corresponds to a level of -10 dBm0 at the digital
interface.
6.3 Volume control
Unless stated otherwise, if a user-controlled volume control is provided at the PP, the requirements apply for all
positions of the volume control, and the compliance tests shall be carried out at the maximum setting of this volume
control.
NOTE: The testing of a PP with a dual or an adaptive volume control requires further study.
7 Speech performance characteristics
7.1 PP frequency responses
7.1.1 Sending
The sending sensitivity-frequency response (from MRP to the digital interface) shall be within a mask as defined in
table 1.
Table 1: Sending sensitivity-frequency mask
Frequency (Hz) Upper limit (dB) Lower limit (dB)
100 -9
200 0
300 0 -14
800 0 -10
2 000 4 -8
3 400 4 -11
4 000 4
8 000 -13
NOTE 1: The limits at intermediate frequencies lie on a straight line drawn
between the given values on a log (frequency) - linear (dB) scale.
NOTE 2: All dB levels are on an arbitrary scale.

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15 ETSI EN 300 175-8 V1.7.1 (2003-07)
7.1.2 Receiving
The receiving sensitivity-frequency response (from the digital interface to the ERP) shall be within a mask as defined in
table 2.
Table 2: Receiving sensitivity-frequency mask
Frequency (Hz) Upper limit (dB) Lower limit (dB)
100 -10
200 2
300 2 -9
1 000 2 -7
3 400 2 -12
4 000 2
8 000 -15
NOTE 1: The limits at intermediate frequencies lie on a straight line drawn
between the given values on a log (frequency) - linear (dB) scale.
NOTE 2: All dB levels are on an arbitrary scale.

7.2 PP sending and receiving loudness ratings
7.2.1 Nominal values
The nominal values are:
Sending Loudness Rating (SLR ) = 7 dB; and
H
Receiving Loudness Rating (RLR ) = 3 dB.
H
There is a manufacturing tolerance of ±3,5 dB on both RLR and SLR .
H H
NOTE: ITU-T test methods on loudness ratings are valid only for codecs that can transmit sinusoids without
excessive distortion.
7.2.2 User-controlled volume control in PP
A user-controlled volume control shall be provided in all PP equipment, except where an adaptive volume control is
incorporated in the PP.
When adjusting the volume control from nominal setting (where RLR is closest to its nominal value) to maximum
H
setting, the decrease in RLR shall be not less than 6 dB.
H
A user-controlled volume control can be implemented either as a receiving volume control (where RLR is changed) or
H
as a "joint-acting" volume control (where SLR and RLR are simultaneously changed in opposite directions). For both
H H
types of volume control RLR and SLR shall simultaneously meet the values given in clause 7.2.1 (including the
H H
tolerances) for at least one setting of the volume control.
The RLR and SLR shall not exceed the limits given in tables 3 and 4.
H H
Table 3: Absolute limits for "joint-acting" volume control
Volume setting Maximum Minimum
RLR -13 dB 19 dB
H
SLR 17 dB 3 dB
H
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16 ETSI EN 300 175-8 V1.7.1 (2003-07)
Table 4: Absolute limits for a receiving volume control
Volume setting Maximum Minimum
RLR -13 dB 19 dB
H
NOTE 1: Minimum setting: The setting where the RLR has its maximum value.
Maximum setting: The setting where the RLR has its minimum value.
NOTE 2: A user-controlled volume control should include an automatic reset function that ensures that the default
setting for each new call is no louder than the nominal setting.
NOTE 3: The basic DECT requirements (echo control, signal levels for A/D converters, etc.) are optimized for
digital (ISDN) transmission characteristics. Analogue networks (see TBR 038) require higher receive
levels (lower RLR) than digital networks (ISDN). This is to compensate for old long lossy analogue lines
that still exist in many PSTNs. Most of the calls do not have lossy lines. Analogue transmissions over a
modern network (from equipment using TBR 038 values of SLR and RLR) will thus often provide higher
receive levels than a digital (ISDN) connection would. This gives an interworking problem between
analogue networks and terminals that use digital codecs as in DECT systems and ISDN terminals, which
could cause distortion in the A/D converters and also lower the margin for the wanted terminal echo loss.
Therefore, noting that DECT PPs have a volume control with at least 6 dB gain to compensate for lossy
connections, it should be allowed to design DECT FP equipment with a receive gain providing typical 4
to 6 dB higher nominal RLR (for FP + PP) than specified in relevant attachment requirements to the
PSTN (see TBR 038). See clause 7.12.2.2. Some administrations have already implemented this principle.
7.2.3 PP adaptive volume control
The PP shall inform the FP if an adaptive volume control is implemented in the PP. Clause 7.7.41 in EN 300 175-5 [2]
describes how this shall be done.
This function is for further study and may follow GSM, or other, specifications when available.
7.2.4 FP adaptive volume control
An adaptive volume control, depending on the level of environmental noise at the PP, may be implemented into the FP.
The gain variation shall be symmetrical, i.e. the increase in the receiving direction shall be equal t
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