In Broadcast - June 2013 - 57

ISSUE 20 - JUNE 2013 | WWW.INBROADCAST.COM

I N T E R N A T I O N A L

N E W S

InFILE
Wireless Video Links: An Overview Cont.
ﬂexible you are in the production.
Note that the range is measured
in clear line-of-site and the actual
range will be determined by the
number and material of obstacles
in the way between the transmitter
and receiver;
Compression: Most wireless
video links in the market utilise
a compression CODEC to
reduce content size, as wireless
transmission has limited capacity.
Wireless systems use compression
CODECs like MPEG-2, H.264,
JPEG2000 and in the future the
upcoming H.265. Most systems
compress the video before wireless
transmission and un-compress it at
the receiver side. Some solutions, in
an effort to save cost, transfer the
video directly without compression.
This can be done only for a very
short range (of few meters) and it
compromises image quality;
Unlicensed / Licensed
Frequencies: Until a few years
ago, only large networks could
use wireless equipment because
it required purchasing expensive
frequency licenses from the
regulator. In recent years, however,
governments and regulators around

ABonAir demonstrate Wireless HD

the world provide unlicensed
frequencies for public use for
any purpose – including video
transmission – allowing even smaller
productions to use wireless links
easily and free of charge. To answer
this demand, manufacturers started
to develop unlicensed solutions.
Unlicensed systems’ volume grew
and drove cost down, motivating
big networks to also use them even

though they own frequencies;
Uni-directional / Bi-directional
Technologies: In uni-directional links,
the transmitter sends video content
to the receiver without receiving
any feedback. In bi-directional
links, both transmitter and receiver
can send and receive data and
control information: a packet
acknowledgment mechanism
identiﬁes errors and quickly ﬁxes

them (by re-transmitting the
corrupted data), before the frame
is presented. This enables bidirectional solutions to assure that
all the data is well received without
errors hence increase picture quality;
Delay between transmission and
reception can vary from 1ms in
short range solutions to up to 10
seconds for cellular based solution.
In most applications like ENG and
Sports, delay of 100ms does not
pose a problem; in live concerts
minimal delay is preferred. Most
OFDM based solutions offer delay
between 40ms to 200ms.
The WiFi and Cellular solution
typically have 1-2 second delay
and uncompressed solutions have
about 1ms of latency.
Wireless video link solutions also
differ in their feature set. Some
support CCU (Camera Control
Unit) to control the camera from the
central point, other support Intercom
for communication between the
Cameraman and the director and
some have Tally light. Some high
end solutions support all these
features that are mainly needed for
more complex productions, where
more than one camera is used.
57

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In Broadcast - June 2013

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