SEFRAM 7803B Manuel D'utilisation page 21

2 - BER/MER (Bit Error Rate COFDM/QAM in digital networks)
Please do first:
−
Recall a setup previously saved in a table.
Refer to « Parameters »
−
Or choose directly the parameters (manually):
For a COFDM measure: Frequency or channel, COFDM
standard, band width (6-7-8 MHz), number of carriers (2-8
K), modulation type of each carrier (QPSK-16QAM-64QAM),
guard space (1/32-1/16-1/8-1/4), Viterbi rate (1/2-2/3-3/4-
5/6-7/8).
- When using the 7803B, it is just necessary to set the frequency or the channel, the COFDM
standard and the bandwidth for the integrated decoder to determine the other parameters.
- When using the 7804B, the Bit Error Rate is simulated depending on the C/N value (carrier/noise)
calculated. All the parameters must be chosen manually.
For a QAM measure (7804B): Frequency or channel, QAM
standard, constellation
128QAM-256QAM-4QAM for DVB-C 64QAM-256QAM for
MCNS), norm J83A (DVB-C) or J83B (MCNS), symbol rate
(from 5 to 7 Ms/s).
In order to have a correct measure; it is imperative that all the modulation parameters
be entered.
For all the instruments, the standard taken in account is the standard selected in the level
measure.
In COFDM coding, there are 2 successive correction algorithms: Viterbi and Reed Solomon.
In QAM coding, there is only one correction algorithm: Reed Solomon.
The instrument shows the following measures:
−
Bit Error Rate before Viterbi (in COFDM coding) or Bit Error Rate before Reed
Solomon (in QAM) on the main display. The typical value is 1.0
error is corrected when 10,000 bits are received.
−
VBER (Viterbi Bit Error Rate): Error Rate after Viterbi.
−
UNC (UNCorrected packets): Error Rate after a complete correction. This rate corresponds
to the packets uncorrected by the 2 successive correction algorithms. For correct signal, the
value must be 0.
−
MER (Modulation Error Ratio): it is similar to the C/N measure and is a good indicator of
the quality of the signal. A value up to 30.0 dB is ideal.
If the words « Sync ? » appear on the display, that means that there is no signal or that the signal
is not locked.
The sign « < » written in front of an Error Rate value means that there has been no error detected
yet.
– 7802/3/4 –
type (16QAM-32QAM-64QAM-
p. 21
E
-4, which means that the