IEC 61603-7:2003

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.