IEC 61603-7:2003

Transmission systems of audio and/or video and related signals using infra-red radiation - Part 7: Digital audio signals for conference and similar applications

describes the characteristics of a digital multiple channel, multiple carrier audio transmission system as an extension to conference interpretation or similar systems using the frequency ranges 45 kHz to 1 MHz and 2 MHz to 6 MHz.

General Information

• Status: Published
• Publication Date: 21-May-2003
• ICS: 33.040.20 - Transmission systems
• ICS: 33.160.99 - Other audio, video and audiovisual equipment
• Technical Committee: TA 4 - Digital system interfaces and protocols
• Current Stage: PPUB - Publication issued
• Start Date: 22-May-2003
• Completion Date: 15-Jul-2003

Overview

IEC 61603-7:2003 specifies a digital, multi-channel, multi-carrier audio transmission protocol using infrared (IR) radiation as an extension to conference interpretation and similar systems. The standard defines the physical and data-link layers for infrared audio links operating primarily in the 2 MHz–6 MHz band (primary) and optionally in 45 kHz–1 MHz (secondary). It covers optical characteristics (peak wavelength ~875 nm ± 25 nm), sub-carrier allocation, modulation, filtering and the framing/protocol structure required for reliable digital audio and associated data in conference environments.

Key topics and technical requirements

• Frequency bands and sub-carriers: Primary band 2–6 MHz with six sub-carrier centre frequencies (e.g., ~2333.333 kHz, 3000 kHz, 3666.667 kHz, 4333.333 kHz, 5000 kHz, 5666.667 kHz). Secondary band 45 kHz–1 MHz is noted for consideration.
• Physical layer (Layer 1): IR medium compliant with IEC 61920 and IEC 61603-1; optical peak intensity at ~875 nm.
• Modulation: Differential Quadrature Phase Shift Keying ((D)QPSK) for sub-carrier modulation, with defined constellation and differential decoding rules.
• Filtering: Square-root raised cosine (SRRC) transmit/receive filters yielding a raised-cosine overall response; roll-off factor β = 0.4 used for occupied bandwidth calculations.
• Bandwidth calculation: Occupied bandwidth is a function of symbol/bit rate and roll-off factor (standard provides the bandwidth relationship).
• Data-link and protocol: Layer 2 defines framing (superframes, RS frames), audio block structures, CRC checks, data messages, packet segmentation and protocol messages (configuration, display, etc.).
• Audio encoding elements: Sub-band Adaptive Pulse Code Modulation (APCM) encoder concepts, audio quality modes (MQ/HQ/MONO variants), and bit-pool/sample structures are defined to map audio channels to carriers.
• Robustness features: Frame structures and CRC/forward-error measures specified to support reliable conference audio and ancillary data.

Applications and who uses this standard

• Primary applications
  • Conference interpretation systems (multilingual audio distribution)
  • Wireless IR assistive listening in meetings, courtrooms, auditoria
  • Multi-channel audio distribution in secure/closed venues where RF is unsuitable
• Who should consult IEC 61603-7
  • AV system designers and integrators specifying IR audio links
  • Hardware manufacturers of IR transmitters/receivers and codec modules
  • Test laboratories and compliance engineers validating IR audio equipment
  • Facility managers and specification authors for conference facilities

Related standards

• IEC 61603-1: Transmission of audio/video signals using infrared radiation - General
• IEC 61603-3: Transmission systems for audio signals for conference and similar systems
• IEC 61920: Infrared transmission systems - Free air applications
• ISO/IEC 7498-1: OSI Basic Reference Model (context for layer mapping)

By defining modulation (DQPSK), filtering (SRRC β=0.4), sub-carrier allocation and the Layer‑2 protocol for audio/data framing, IEC 61603-7 enables interoperable, reliable digital infrared audio systems for conference and similar applications. Keywords: IEC 61603-7, infrared audio transmission, conference interpretation, DQPSK, SRRC, multi-channel IR.

Standards Content (Sample)

INTERNATIONAL IEC
STANDARD
61603-7
First edition
2003-05
Transmission systems of audio and/or video and
related signals using infra-red radiation –
Part 7:
Digital audio signals for conference and
similar applications
Reference number
Publication numbering
As from 1 January 1997 all IEC publications are issued with a designation in the
60000 series. For example, IEC 34-1 is now referred to as IEC 60034-1.
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edition numbers 1.0, 1.1 and 1.2 refer, respectively, to the base publication, the
base publication incorporating amendment 1 and the base publication incorporating
amendments 1 and 2.
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INTERNATIONAL IEC
STANDARD
61603-7
First edition
2003-05
Transmission systems of audio and/or video and
related signals using infra-red radiation –
Part 7:
Digital audio signals for conference and
similar applications
 IEC 2003  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: [phone] Telefax: [phone] E-mail: [e-mail]  Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale
U
International Electrotechnical Commission
Международная Электротехническая Комиссия
For price, see current catalogue

– 2 – 61603-7  IEC:2003(E)
CONTENTS
FOREWORD . 4
1 Scope . 5
2 Normative references. 5
3 Terms and definitions . 5
4 Abbreviations. 5
5 Explanation of terms and general information . 6
6 System considerations. 6
7 Basic system concept . 6
8 Protocol . 7
8.1 System context . 7
8.2 Physical layer . 8
8.3 Data link layer .13
8.4 Detailed overview of audio frame structures.15
9 Data protocol .17
9.1 General .17
9.2 Data messages.18
9.3 Data packet structure.21
Annex A (normative) Definition of prototype filter .23
Annex B (informative) Example of λ/f diagram in the user area conference.24
Annex C (informative) Provision for future developments .25
Bibliography.26
Figure 1 – System . 7
Figure 2 – Conceptual model. 7
Figure 3 – Band allocation for 6 modulated sub-carriers. 8
Figure 4 – (D)QPSK constellation and differential decoding algorithm . 9
Figure 5 – Pulse response of a raised cosine channel filter .10
Figure 6 – Scrambler.11
Figure 7 – Block diagram of sub-band APCM encoder.12
Figure 8 – Quantization of sub-band samples.13
Figure 9 – Superframe structure.14
Figure 10 – RS frame structure .14
Figure 11 – Audio block structure.15
Figure 12 – CRC calculation.15
Figure 13 – Audio block structure for medium quality .16
Figure 14 – Bit-pool sample structure for medium quality .16
Figure 15 – Audio block structure for high quality.16
Figure 16 – Bit-pool sample structure for high quality.17
Figure 17 – Positioning of the data protocol .18

61603-7  IEC:2003(E) – 3 –
Figure 18 – Data message build-up.18
Figure 19 – Configuration message structure .19
Figure 20 – Display message structure for ASCII display data.20
Figure 21 – Display message structure for bitmap display data .21
Figure 22 – Segmentation of data messages.21
Figure 23 – Data packets fitted on to the superframe structure.22
Table 1 – Sub-carrier centre frequencies. 8
Table 2 – Phase transitions of the differential encoding algorithm . 9
Table 3 – Characteristics of sub-band APCM encoder.12
Table 4 – Definition of audio mode bits .15
Table 5 – Audio blocks and audio quality .17
Table 6 – Data message identifier definition.18
Table 7 – SCI definition.19
Table 8 – Channel allocation table .19
Table 9 – Audio quality mode (AQM) to number of audio blocks used.20
Table C.1 – Sub-carrier allocation .25

– 4 – 61603-7  IEC:2003(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
TRANSMISSION SYSTEMS OF AUDIO AND/OR VIDEO
AND RELATED SIGNALS USING INFRA-RED RADIATION –
Part 7: Digital audio signals for conference and
similar applications
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the
two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61603-7 has been prepared by Technical Area 3, Infrared systems
and applications, of IEC technical committee 100: Audio, video and multimedia systems and
equipment.
This first edition cancels and replaces 2.6.2 of IEC 61603-3 (1997).
The text of this standard is based on the following documents:
FDIS Report on voting
100/649/FDIS 100/676/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until 2005.
At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
61603-7  IEC:2003(E) – 5 –
TRANSMISSION SYSTEMS OF AUDIO AND/OR VIDEO
AND RELATED SIGNALS USING INFRA-RED RADIATION –
Part 7: Digital audio signals for conference and
similar applications
1 Scope
This part of IEC 61603 describes the characteristics of a digital multiple channel, multiple
carrier audio transmission system as an extension to conference interpretation or similar
systems using the frequency ranges 45 kHz to 1 MHz and 2 MHz to 6 MHz.
NOTE These frequency ranges are also covered by analogue pulse systems used for the same applications.
Interference is not expected because both transmission systems are normally not applied at the same time in the
same room.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 61603-1:1997, Transmission of audio and/or video and related signals using infrared
radiation – Part 1: General
IEC 61603-3:1997, Transmission of audio and/or video and related signals using infrared
radiation – Part 3: Transmission systems for audio signals for conference and similar systems
IEC 61920, Infrared transmission systems – Free air applications
ISO/IEC 7498-1:1994, Information technology – Open Systems Interconnection – Basic
Reference Model: The Basic Model
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61603-1 apply.
4 Abbreviations
APCM Adaptive pulse code modulation
AQM Audio quality mode
CAT Channel allocation table
CM Configuration message
CRC Cyclic redundancy check
DCI Display changed identifier
DM Display message
DM-CRC Data message CRC
___________
To be published. For the purposes of the reference in C.1, IEC 61920:1998 is equally valid.

– 6 – 61603-7  IEC:2003(E)
DMI Data message identifier
DML Data message length
DQPSK Differential quadrature phase shift keying
HQ High quality
MAXCN Maximum channel number
MHQ Mono high quality
MMQ Mono medium quality
MQ Medium quality
OSI Open systems interconnection
PCM Pulse code modulation
PRBS Pseudo-random binary sequence
SCI Source coding identifier
SEI Setting changed identifier
SF Scale factor
SHQ Stereo high quality
SMQ Stereo medium quality
SRRC Square root raised cosine
Exclusive OR
XOR
5 Explanation of terms and general information
For the purposes of this part of IEC 61603, the explanation and information given in
IEC 61603-3, Clause 2, apply.
6 System considerations
For the purposes of this part of IEC 61603, the considerations given in IEC 61603-3, Clause
3, apply.
NOTE With regard to the primary band, the special caution advised in IEC 61603-3, 3.3 should be observed,
especially for inductive lighting and future developments.
7 Basic system concept
The basic system concept is shown in Figure 1.
The system consists of a number (N) of audio sources, either analogue or digital, which are
connected to a transmitter. The transmitter processes the audio signals (in accordance with
the protocol described in Clause 8) into an electrical output to feed the infrared radiator. The
infrared signal is received by the infrared receiver that processes the signal and outputs an
audio signal and/or associated data.

61603-7  IEC:2003(E) – 7 –
N sources
Audio Audio
Audio Audio
source
source source source
Transmitter
Infrared
Infrared
radiator
receiver
IEC  1548/03
Figure 1 – System
8 Protocol
8.1 System context
In terms of the conceptual OSI reference model, the transmission protocol shall implement the
following layers:
User data
Audio streams
(low rate, limited)
Higher OSI protocol Higher OSI protocol
layers layers
Data link layer (layer 2)
IEC 61603-7
IEC 61603-7
Physical layer (layer 1) IEC 61603-1
IEC 61920
Medium
IEC  1549/03
Figure 2 – Conceptual model
Figure 2 shows the system context using the OSI reference model. Layers 1 and 2 will be part
of the transmission protocol defined in this standard.

– 8 – 61603-7  IEC:2003(E)
8.2 Physical layer
8.2.1 General
OSI layer 1 (physical layer) shall use infrared radiation as the transfer medium between
radiator and receiver as specified in IEC 61920 and IEC 61603-1.
8.2.2 Carrier
λ
Optical wavelength at the optical peak intensity : 875 nm ± 25 nm
P
8.2.3 Sub-carriers
Primary frequency band (band IV): 2 MHz – 6 MHz
Secondary frequency band (band II): 45 kHz – 1 MHz.
NOTE The secondary frequency band, 45 kHz to 1 MHz, is under consideration.
Figure 3 shows the wideband allocation in the primary band, with the frequencies of each sub-
carrier. A guard band between the transmission bands has been included. Table 1 shows the
frequencies of each sub-carrier.
f  MHz
2,333 3 3,667 4,333 5 5,667
Guardband
IEC  1550/03
Figure 3 – Band allocation for 6 modulated sub-carriers
Table 1 – Sub-carrier centre frequencies
Frequency
Sub-carrier
kHz
CC1 2333,333
CC2 3000
CC3 3666,667
CC4 4333,333
CC5 5000
CC6 5666,667
8.2.4 Occupied bandwidth
The occupied bandwidth is defined as follows.
B =r ⋅()1+ β
occ S
where
B is the occupied bandwidth;
occ
61603-7  IEC:2003(E) – 9 –
r
b
r is the symbol rate ( = for (D)QPSK, r is the bit rate (see 8.3));
b
S
β is the roll-off factor (see 8.2.6).
8.2.5 Sub-carrier modulation
The modulation method is (D)QPSK. The constellation is shown in Figure 4a. The differential
decoding algorithm is shown in Figure 4b. The phase transitions for the differential encoding
algorithm are also listed in Table 2.
00 00
Q
01 11
10 11
01 11
I 11
00 10
00 10
00 00
a) b)
IEC  1551/03
Figure 4 – (D)QPSK constellation and differential decoding algorithm
Table 2 – Phase transitions of the differential
encoding algorithm
Phase change Symbol IQ
0° 00
90° 01
180° 11
–90° 10
8.2.6 Filter characteristics
A channel filter is included. A square root raised cosine (SRRC) characteristic, as illustrated
in Figure 5, is implemented in both the transmitter and the receiver resulting in a total transfer
characteristic of a raised cosine.
The roll-off factor of the filter is β = 0,4.

– 10 – 61603-7  IEC:2003(E)
0,8
0,6
0,4
0,2
0Tb 2Tb 3Tb
–0,2
IEC  1552/03
Figure 5 – Pulse response of a raised cosine channel filter
The combined filter characteristic from the transmitting and receiving filter shall be in
accordance with the following equation:
r

b
T f ≤ (1− β )
b


r r r
 π  
b b b
P ( f ) = T • cos f − (β +1) (1− β ) < f ≤ (1+ β )
 

r b
 
4β 2 2 2
 

r

b
0 f > (1+ β )

 2
where
P ( f ) is the power transfer function;
r
f is the frequency (Hz);
is the bit rate (bit/s);
r
b
T =
b
r
b
β is the roll-off factor.
8.2.7 Channel coding
8.2.7.1 Reed-Solomon encoder
A shorted Reed-Solomon encoder (n,k,d) = (28,24,5) on 8-bit symbols is used. The Reed-
Solomon encoder operates in Galois Field GF(2 ).
The field generator polynomial is:
8 4 3 2
p()x = x + x + x + x +1
61603-7  IEC:2003(E) – 11 –
The code generator polynomial is:
i
g()x = ()x +α
∏
i = 0
4 75 3 249 2 78 6
= x +α x +α x +α x +α
α = 02(HEX)
8.2.7.2 Scrambler
The scrambler consists of an XOR gate and a pseudo-random binary sequence (PRBS)
generator. The length of the PRBS is 11 bits and is initialized after every frame sync. The
polynomial that is used for the PRBS is
9 11
1 + x + x
and the initial pattern is
Initial pattern = “10010101000”
A diagram of the scrambler is shown in Figure 6. Scrambling is not applied to the frame sync.
Data in
Initial value
PRBS generator
1 0 0 1 0 1 0 1 0 0 0
Load
0 1 2 3 4 5 6 7 8 9 10
Clock
Data out
IEC  1553/03
Figure 6 – Scrambler
8.2.8 Audio source coding
8.2.8.1 General
The linear PCM audio signal (f = 44,1 kHz) is divided into 4 sub-band signals by an
s
(analysis) filter bank. The 4 sub-band signals are decimated by a factor 4 and quantized
by an adaptive pulse code modulation (APCM) coding scheme. A block diagram of the
encoder is shown in Figure 7.
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