Basic HTML-Version
EIRP
(dBW)
Modulation / Error
Correction
Data Rate Zone
Amount of
Bandwidth
Resulting
Bandwidth
53
16-ASP 2/3
~ 35 MB/s
1
20%
~ 7 Mbps
52
8-PSK 3/4
~ 30 MB/s
2
20%
~ 6 Mbps
51
8-PSK 2/3
~ 26 MB/s
3
20%
~ 5 Mbps
50
QPSK 8/9
~ 23 MB/s
4
20%
~ 4.5 Mbps
49
QPSK 4/5
~ 21 MB/s 5 + further
20%
~ 4.2 Mbps
Total:
~ 27 Mbps
■
242
TELE-satellite International — The World‘s Largest Digital TV Trade Magazine
— 12-01/2012
— www.TELE-satellite.com
DVB-S2 MIS Reception
with VCM/ACM
Thomas Haring
Thanks to VCM technology, multiple transponder streams with different
parameters can be made available on a single transponder
With the change from DVB-S to DVB-
S2, a more efficient method was cre-
ated that permits more channels to be
carried over one and the same tran-
sponder. This increase in efficiency is
due in large part to the significant im-
provement in error correction so that
fewer error correction bits need to
be transmitted. From a mathematical
point of view the increase in efficiency
compared to DVB-S is roughly 30%, a
value that in reality isn‘t quite reached,
but it is definitely showing potential.
There are a variety of ways that pro-
gramming can be transmitted. With
DVB-S and for the moment also with
DVB-S2, it‘s mostly CCM (Constant
Coding and Modulation) that is used.
In this process the programming or-
ganizer selects a fixed error correction
and modulation process with which
every receiver within a satellite‘s foot-
print can receive a usable signal with
a reasonable amount of effort. If the
programming organizer wants to also
be able to reach as many viewers as
possible at the edge of a satellite‘s
footprint, he chooses an all around
correction process so that these users
can also obtain an acceptable signal.
If the provider is looking to reach only
those viewers in the heart of the foot-
print, he‘d choose a less costly error
correction.
The operator has to make some deci-
sions. But how? It would be much more
efficient and the operator could avoid
having to make these technical deci-
sions if the signal was transmitted in
exactly the same way that it would be
needed by the receiver.
This is precisely the strategy behind
VCM (Variable Coding and Modulation)
as well as ACM (Adaptive Coding and
Modulation): the entire bandwidth of a
transponder is split into multiple seg-
ments and through the use of vari-
ous modulations and error correction
processes, these bandwidth segments
would be filled with different program-
ming content corresponding to the
available bandwidth. For receivers in
the heart of the satellite‘s footprint, a
very small error correction and high-
ly efficient modulation process could
be used so that a relatively high data
rate could be achieved. At the same
time, the lower the signal level along
the edge of the footprint, the better
the error correction and more reliable
modulation that could be used.
This all takes place within one tran-
sponder, that is, one and the same
transponder transmits through VCM
different modulation and error correc-
tion processes! We‘re referring in this
case here to MIS (Multi Input Streams).
With MIS a satellite receiver can re-
ceive multiple transponder streams
from one transponder that are trans-
mitted completely independent from
each other with differing modulations
and error correction. The idea behind
all of this is that depending on the re-
ception location, not every transpon-
der stream from a transponder can be
received. The end user can only re-
ceive signals that are strong enough
at his location. This means that the
receiver would automatically measure
the signal and use these values to de-
termine which transponder streams it
could process and use.
A VCM target area could look some-
thing like this: in the heart of the sat-
ellite‘s footprint the available TV chan-
nels would be receivable in HD or 3D
while on the outer edge of the footprint
these channels would only be available
in SD; all of this would occur over one
single transponder. The TV viewers in
the center of the footprint would prof-
it from the higher data transmission
rates while the viewers on the foot-
print‘s edge could still receive the sig-
nal with smaller antennas thanks to the
more complex error correction and the
more reliable modulation that would
be used, it just wouldn‘t be HD or 3D.
It’s important to note that no return
channel from the receiver is necessary
with VCM while ACM is geared more
towards studio transmissions (feeds)
since here the reception quality of the
return channel has to be taken into
consideration and the modulation and
error correction are matched from the
transmitting end.
This transmission technology is so
new that VCM or ACM transponders
cannot be received by most DVB-S2
receivers. Once more PayTV providers
have switched over to this new VCM
method or have begun some intensive
testing, we can assume that more and
more receivers will support this clev-
er system that optimizes a satellite‘s
bandwidth use. There‘s already an ex-
citing opportunity to receive this new
transmission technology: the PC card
manufacturer Tenow has already in-
tegrated this technology in its profes-
sional PC card TBS6925. An initial test
report on the TBS6925 was presented
in the 10-11/2011 edition of TELE-
satellite. Now we can actually take a
closer look at the MIS capabilities of
this PC card.
If you try to look for ACM/VCM tran-
sponders in your favorite Internet sat-
ellite list, you won‘t have much luck.
Most providers of this kind of informa-
tion have not included this data in their
lists simply because there‘s hardly any
reception hardware available that can
receive these transponders. So the
first you would do is to search for ACM/
VCM transponder using blindscan tools
such as CrazyScan and TBS Blind-
scan - you may check this forum for
FEATURE
Satellite Reception