Promax PROLINK-3 Premium Manual De Instrucciones página 161

USER'S MANUAL. PROLINK-3/3C
The CSI measure (Channel Status Information) is a qualitative measure about
channel state, between 0 and 100%. The optimum value corresponds to 0%. This
measure permits to look for the best situation even in those measuring conditions where
the measured BER is best than the minimum readout (in this way, in the example of the
previous figure, the measured BER is lower that the minimum readout, 1.0x10
CSI measurement, 27%, still can be improved).
Next it is shown the BER after Viterbi measurement both in numeric and graphic
bar format.
In a reception system of terrestrial digital signal, after the COFDM decoder two
error correction methods are applied. Obviously, each time we apply an error corrector
to the digital signal, the error rate changes, therefore if we measure the error rate at the
output of the COFDM demodulator, at the output of the Viterbi decoder, and at the
output of the Reed-Solomon decoder, we obtain nothing more than different error rates.
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Wrong packets received after Reed- Solomon.
The BER measurement is provided in scientific notation (i.e. 3.1 E-7 means
-7
3.1x10 , that is to say 3.1 wrong bits of each 10000000) and through a graphic bar (as
its length is smaller the signal quality will be better). The analogue representation is
done on a logarithmic scale (not linear), that is to say, the bar divisions correspond to
the exponent of the measurement.
With the aim to have a reference about the signal quality, it is considered that a
system has a good quality when it decodes less than one non-correctable error for
every transmission hour. This border is known as QEF (Quasi-Error-Free) and it
corresponds approximately to a BER after Viterbi of 2.0E-4 BER (2.0x10
2 wrong bits of each 10000). This value is marked on the measurement bar of the BER
and therefore, BER for acceptable signals must be at the left side of this mark.
In the lower line of the screen it appears the W. P. counter (Wrong Packets
counter). This counter shows the number of non-correctable packets received after
Reed-Solomon during the measuring time. This counter is automatically activated when
the unit detects an MPEG-2 signal.
If at any time, the received signal stops to satisfy the requirements of the MPEG-2
standard, this counter will deactivate, that is to say it will keep the number of non-
correctable packets received and the measuring time, later, if an MPEG-2 signal is
received again, it will activate with no reset.
When during any measuring time interval the counter has been deactivated, in other
words the signal has not satisfied the MPEG-2 synchronism, the presentation of this
counter will alternate with another counter titled FAIL. This second counter shows the time
that the detected signal has not fulfilled the MPEG-2 standard requirements (12 seconds
06/2005
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provides the BER after Viterbi and the number of
Figure 14.- COFDM reception system.
-7
, but the
-4
, that is to say
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