Televes T.0X Series User Manual page 20

DVBS2 - COFDM / COFDM CI
NOTE: We suggest choosing one of the DVBT modes
from the chart. Those modes which have
not been included have a lower information
service output.
One the right hand side of the chart are the
different unit step functions (64 QAM 2/3, 64QAM
3/4, 64QAM5/6, 64QAM 7/8), each one corresponds
to a degree of protection against errors which the
DVB-T signal can carry.
The higher the step selected, the greater the
information service output (Mbits/s) of the relevant
DVB-T mode, although it´s level of protection
against errors will be inferior and it will require a
higher C/N to receive the signal.
We will now look at the level of protection against
echoes.
To do so, one must select one of the four possible
vertical axes that appear on the left side of the
previous chart (GI=1/4, GI=1/8, GI=1/16, GI=1/32).
The further left the selected axis is, the greater
the DVB-T mode´s information service output
(Mbits/s) will be, but its level of protection against
echoes will be lower, in other words, the maximum
supported echo delay will be inferior.
In short, the higher and further to the left the DVB-
T mode selected is, the more powerful this mode
will be in terms of information service output
(Mbits/sg).
On the other hand, the lower and further to the
right the DVB- T mode selected is, the more robust
this mode will be in terms of interferences which
could affect the signal.
The terrestrial transmission channel (transmission
aerial - terrestrial atmosphere – receiving aerial) is
very complex, with numerous interferences that
can potentially affect the DVB-T signal.
Due to this, in Spain, the DVB- T signal is generally
disseminated with the following features:
(1) Type of modulation: 64QAM
(2) Level of protection against Errors: 2/3
(3) Level of protection against echoes: 1/4
If one looks at the previous chart, one can see that
the information service output of the DVB-T mode
is 19.91 Mbits/s.
In our case, the DVB-T signal generated by the
DVBS2-COFDM (CI) transmodulator, is not going to
be transmitted through the terrestrial transmission
channel, but through a channel that is generally
much more benign: the distribution network of
the building.
NOTE: The better the quality of the building´s
distribution network, the
transmission channel will
transmitting signals.
Given that our transmission channel is better, we
can use the DVBS2-COFDM (CI) transmodulator,
by selecting a higher DVB-T output mode than
that used by terrestrial channels to disseminate.
This will have a greater information service output
(Mbits/s) and will therefore enable us to include a
greater number of TV and Radio
services.
Therefore, when setting up the DVBS2- COFDM (CI)
transmodulators, one should follow a procedure
such as the one below:
1 - Select one of the stronger DVB-T output
modes.
E.g. 64QAM-5/6 with GI=1/32, information
service output of 30.16 Mbits/s.
2 - Check the quality of the signal received at
various points within the building.
If the signal quality is good, the technician can
consider using an even stronger DVB-T mode,
in other words, one with a greater information
service output. On the other hand, in cases where
the signal quality is insufficient, they must consider
using a more robust DVB-T mode.
In most cases, the distribution network within
the building should support those DVB-T modes
that have a lower protection level against echoes.
better the Therefore, if a more robust mode is necessary,
be when one should first try using, one at a time, greater
protection levels against errors.
20