Publicité
USER'S MANUAL. TV EXPLORER HD +
In a digital reception system for satellite signals (DVB-S), after the QPSK decoder
two different correction methods are applied (see following Figure). Obviously, each time
we apply an error corrector to a digital signal, the error rate changes, therefore if we
measure in a digital satellite television system, for example, the error rate at the output of
the QPSK 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. This is the
reason because the BER measurement is provided before FEC, after Viterbi (VBER).
Figure 39.- Digital reception system via satellite. (DVB-S)
Figure 40.- DVB-S (QPSK) signals VBER measurement screen.
In a digital reception system for satellite signals (DVB-S2), after the QPSK
decoder other two different correction methods are applied (see following Figure). In this
case, as the previous one, each time we apply an error corrector to a digital signal, the
error rate changes, therefore if we measure in a digital satellite television system, for
example, the error rate at the output of the QPSK/8PSK demodulator, at the output of
the Low Density Parity Check (LDPC) decoder, and at the output of the BCH decoder,
we obtain nothing more than different error rates. This is the reason because the BER
measurement is provided after LDPC (LBER). It also shows the amount of packet errors
(PER), that is, the amount of packets receiving during the measurement time, which are
not correctable by the demodulator (WP).
Figure 41.- Digital reception system via satellite. (DVB-S2).
12/2011
Page 61
Publicité
