48
TELE-audiovision International — The World‘s Leading Digital TV Industry Publication
— 1 -12/2014
—
more complex error correc-
tion would be needed as well
as a less efficient modulation
mode in order to be able to
receive a good-enough sig-
nal.
That‘s why VCM/ACM was
developed. The strategy be-
hind VCM/ACM (Variable Cod-
ing and Modulation/Adaptive
Coding and Modulation) is
that the entire bandwidth of a
transponder is split into mul-
tiple parts and by employing
various modulation and er-
ror correction methods the
resulting bandwidth sections
can now be occupied with
different programming con-
tent that corresponds to the
available bandwidth.
An example of this would
be the transmission of an HD
channel in a satellite‘s prima-
ry footprint and an SD chan-
nel at the outer edges.
The receivers used in the
satellite‘s primary footprint
can have very small error
correction along with an ef-
ficient modulation such that
high data rates can be trans-
mitted. But at the same time,
the lower the received signal
level as you move towards
the outer edges of the foot-
print, a better error correc-
tion and more reliable modu-
lation would be needed.
This all takes place with-
in a transponder, in other
words, with VCM the same
transponder transmits using
different modulations and
error correction methods.
In this case we are talking
about MIS (Multiple Input
Streams). This means that
the receiver can receive mul-
tiple transponder streams
from one transponder that
were transmitted completely
independent of each other
and therefore could have dif-
ferent modulation and error
correction methods in use.
From the large number
of transponder streams, an
MIS-compatible
receiver
looks for those streams that
can be received with suffi-
cient quality. In the satellite‘s
primary footprint this would
be those streams carrying
HD channels while at the out-
er edges of the footprint, it
would be those streams with
SD channels. But we‘re not
quite there yet; the desired
streams must still be select-
ed manually - as long as an
MIS-compatible receiver is
used. These streams can not
(yet) be received with today‘s
normal DVB-S2 receivers.
VCM was developed with
the normal TV viewer in
mind since in this case the
individual streams are trans-
mitted with constant values.
ACM, on the other hand, was
developed with professional
applications in mind, such as
for feeds. Here the reception
quality can be sent back to
the broadcaster through a
return channel so that the
modulation and error cor-
rection can be adapted as
needed.
One of the few boxes avail-
able that can receive this kind
of technology is the QBOX.
The included TBSViewer
from Tenow and most of the
other available DVB recep-
tion tools are currently not
able to correctly process MIS
frequencies.
That‘s why Tenow has
made available for download
a small tool that goes by the
name of TS Recorder; with
the help of the tuner box, it
will let you dial in the desired
MIS stream so that a match-
ing signal can be made avail-
able to the DVB reception
software. But there‘s a cer-
tain procedure to follow if you
want to change MIS streams:
first you have to exit out of
the DVB reception software
and then start TS Recorder.
From there you would select
the desired new stream and
then switch back to the DVB
reception software.
The TS Recorder can be
individually adapted to the
available reception system
whereby the local oscilla-
tor frequencies (LOFs), the
switching point between low
and high band as well as
the DiSEqC 1.0 parameters
can be entered individually.
The user then simply needs
to select the desired recep-
tion frequency, polarization
and symbolrate of the MIS
transponder. Once this is all
taken care of, all that‘s need-
ed is a click of the „Lock TP“
button after which the soft-
ware will read in the desired
transponder.
More information on the
selected transponder can be
found near the bottom of the
