Comtech EF Data CDM-625A Installation And Operation Manual page 697

CDM-625A Advanced Satellite Modem
Appendix M
Step Task
5 (SELECT) CONFIG: RX  FEC
Set the Rx FEC type as VersaFEC-2 Long, or
VersaFEC-2 Short Block. Note that this does not
have to match the Tx FEC type.
(SELECT) CONFIG: RX  SYMB
6
Enter the desired receive symbol rate. Note that
asymmetric operation is supported – transmit and
receive symbol rates do not have to be equal.
7 (SELECT) CONFIG: ACM 
Configure the desired ACM operating parameters, by
selecting the ACM submenu from the CONFIG:
menu branch.
Proceeding from the CONFIG: ACM submenu:
a)  Min/Max-ModCod: Define the range of
ModCods over which the system will operate.
ModCod 0 is fixed at BPSK Rate 0.489 (0.489
bps/Hz), while ModCod 37 is 32-ARY Rate 0.879
(4.397 bps/Hz).
b)  Unlock-Action: For VersaFEC-2 the unlock
action is fixed. In the event that the distant-end
demod loses lock, the Tx ModCod will automatically
go to ModCod 0.
c)  Target Eb/No margin: This is a VERY important
parameter. The ACM system is designed to switch
based on thresholds that correspond to a BER of 1 x
10 for each ModCod. However, in order to prevent
-8
oscillation around two ModCods at this exact value,
0.3 dB of hysteresis has been added.
8 (SELECT) CONFIG: IP  Switch-set-up  WAN
Enter the desired size of the WAN Buffer. The
minimum size is 20 milliseconds, and is referred to the
data rate corresponding to ModCod 0. Note that this
does not apply if the Packet Processor Card is
installed.
In VersaFEC-2, the Minimum ModCod is fixed at 0, and the user cannot change it.
CAUTION – The value of Max ModCod may be limited by other FAST codes installed.
For example, suppose the 4100 ksps FAST option is installed, and the symbol rate set to
4100 ksps, the theoretical maximum data rate would be ~18 Mbps at ModCod 37.
However, is CnC is being used, with a 10 Mbps FAST limit, the ACM Max ModCod will
be limited to ModCod 21, or 9.8 Mbps.
Front Panel VFD Mnemonic
RxIF Freq FEC Demod Symb Descram Eq EbNo
(Data 02048.000kbps,02184.533ksps)()
Dec=VF2L(VF2L, VF2S)
Reed-Solomon=Off
RxIF Freq FEC Demod Symb Descram Eq EbNo
(Data 02048.000kbps,02184.533ksps)()
RxSymbolRate = 01000.000 ksps (ACM Mode)
Data Invert=Off Clock Invert=Off
CONFIG: All Mode
CnC EDMAC Misc
ACM Config: Min/Max-ModCod
Target-EbNo-Margin
Min Modcod: 00(B
Max Modcod: 37(32-ARY 0.879, 4.397 bps/Hz)
When distant-end demod loses lock:
Go to Tx ModCod 0
Target Eb/No Margin = 0.5 dB (0.0 – 4.5)
Ethernet Switch: Mode
MAC-Learning VLAN Qos Stats
M–17
MN-CDM625A
Revision 4
(Fixed in ACM)
()
()
Tx Rx Clocks ACM
Mask Remote IP ()
Unlock-Action
()
0.489, 0.489 bps/Hz)
(Fixed in VersaFEC-2)
()
WAN PerPortCnfg
()