Comtech EF Data CDM-570 - Manual (Page 107)

CDM-570/570L Satellite Modem with Optional IP Module Revision 12
Front Panel Operation MN/CDM570L.IOM
5–21
Selection Sect. Description
Descram 5.2.2.1.4.7 (Descrambler) Used to select whether or not data descrambling is used.
Buf 5.2.2.1.4.8
(Buffer) Used to select whether or not the Plesiochronous/Doppler buffer is
used, and if so, the size of that buffer.
Inv 5.2.2.1.4.9
(Inversion) Used to invert the sense of the received spectrum, or to invert the
sense of the received baseband data.
EbNo 5.2.2.1.4.10 ( E
b
/N
0
Alarm threshold) Used to determine the E
b
/N
0
alarm threshold.
VERY IMPORTANT NOTE: The FEC type takes the highest
configuration priority, and the selection here depends on what, if any,
optional plug-in codecs are installed. The choice of FEC type then
determines what demodulation types, code rates, and data rates are
available.
The order of hierarchy is therefore:
FEC type (Highest) ► Demodulation type ► Code Rate ► Data Rate (Lowest)
If a parameter is changed within this hierarchy, the other parameters may
become invalid. In this case, the software will change those other parameters, in
order that the configuration remains valid at all times.
Example: Suppose you have selected Viterbi + Reed-Solomon, QPSK, Rate 1/2.
Now, the you change the demodulation type from QPSK to 16-QAM. In this case,
Rate 1/2 is no longer a valid code rate, and so it will be automatically changed to
the nearest valid code rate (Rate 3/).
5.2.2.1.4.1 (CONFIG: Rx) FEC (FEC Type)
Rx FEC: Viterbi Vit+RS
TCM+RS TPC Uncoded
IMPORTANT NOTE: All available choices are presented at all times. If an
option is not installed (Hardware or FAST) or valid, the ◄ ► arrow keys will
force the cursor to skip past the unavailable choice.
CASE RULES COMMENT
Viterbi Always valid
Vit+RS
(Viterbi +Concatenated Reed-
Solomon) If the RS codec is installed
TCM+RS
(Trellis Coded Modulation +
Concatenated Reed-Solomon)
If the RS codec is installed
AND 8-PSK FAST is enabled
Fixed at 8-PSK and Rate 2/3
TPC
(Turbo Product Codec)
If the TPC codec is installed
Uncoded
Always valid - BPSK, QPSK and
OQPSK only.
Forces Code Rate to 1:1 (uncoded)