3
1.2 System technology
1.2.1 Basic system concept
The basic system concept is shown in figure 1.2.
The system consists of a number (N) of audio sources,
either analog or digital, which are connected to a
transmitter. The transmitter processes the audio signals
into an electrical output to feed the infrared radiator (see
section 1.2.3). The infrared signal is received by the
infrared receiver that processes the signal and outputs
an audio signal and/or associated data.
Figure 1.2 The basic system concept
1.2.2 IR radiation
HCS-5100 series audio signal is based on transmission
by modulated infrared radiation (IR). Infrared radiation
is part of the electro-magnetic spectrum, which is
composed of visible light, radio waves and other types
of radiation. The IR wavelength is larger than the
wavelength of visible light.
Conference hall privacy: the congress venue itself acts
as a barrier to infrared signals escaping. As Infrared is
unable to pass through opaque objects such as walls,
the signal cannot be overheard. Moreover, HCS-5100
series does not emit radio radiation. Operating the
system does not require a radio frequency license,
worldwide.
1.2.3 Signal processing
HCS-5100 uses high frequency carrier signals
(typically 2-8 MHz) to prevent interference by modern
light sources. Fully digital audio processing guarantees
a constant high audio quality.
The signal processing in the transmitter consists of the
following main steps (see figure 1.3):
1. Code – each analog audio channel is converted to a
digital signal; the digital signals are compressed to
increase the amount of information that can be
distributed on each carrier (compression ratio is
related to required audio quality); groups of up to 4
digital signals are combined into a digital information
stream. Extra fault algorithm information is added.
This information is used by the receivers for fault
detection and correction.
2.
Modulation – a high frequency carrier signal is
phase-modulated with the digital information stream
by DQPSK digital modulation technique.
3. Filter.
4. Magnify.
5. Radiation – up to 8 modulated carrier signals are
combined and sent to the IR radiators, which convert
the carrier signals to modulated infrared light.
In the IR receivers, a reverse processing is used to
convert the modulated infrared light to separate digital
audio channels.
(a) Digital infrared transmitter schematic
(b) Digital infrared radiator schematic
(c) Digital infrared receiver schematic
Figure 1.3 Overview of the signal processing
Audio
source
Audio
source
Audio
source
Audio
source
Transmitter
Infrared
radiator
Infrared
receiver
N
