G.4.6 modcod selection – Comtech EF Data CDM-760 User Manual
Page 346
Appendix G
Revision 2
CDM-760 Advanced High-Speed Trunking Modem
MN-CDM760
G–12
G.4.6 ModCod Selection
Table G-5 and Table C-6 show the guaranteed Es/No at QEF for each ModCod in the DVB-S2 and
DVB-S2-EB1 Network Specifications, along with spectral efficiency and ModCod “pruning”.
The
ModCod elements that are shaded in these tables are pruned from ACM operation because they
are not monotonic. Figure G-5 and Figure G-6 show considerable overlap of ModCod
combinations for both
the DVB-S2 and DVB-S2-EB1 Network Specifications.
The pruning and overlap depicted in these tables and figures infer omission of some ModCods;
therefore, without dropping some of these ModCods, there is a non-monotonic change of
Bits/Hz with changing Es/No. As this would result in an unstable system, re-sorting the DVB-S2
or DVB-S2-EB1 tables resolves this.
For example: When moving from QPSK 5/6 to the next best ModCod choice, when the Es/No is
increasing, the modem would be better suited to switch to 8PSK 3/5, which requires only 5.8dB
Es/No and provides 1.74 bits/Hz. You have intentionally pruned QPSK 8/9 and QPSK 9/10, which
have Es/No requirements of 6.4 and 6.8 dB – higher than 8PSK 3/5, yet providing less spectral
efficiency than 8PSK 3/5.
Table G-5. DVB-S2 Symbol Rate and Data Rate by ModCod in ACM Mode
(Normal Block, Pilot ON, QEF (~PER 10
-7
)
MOD
ModCod
#
FEC
Min SR
(Msps)
Max SR
(Msps)
Min DR
(Mbps)
Max DR
(Mbsp)
Spectral Efficiency
(Bits / Hz)
QEF
Eb/No
QEF
Es/No
QPSK
04
1/2
0.1
150
0.10
144.80
0.97
1.4
1.2
05
3/5
0.1
150
0.12
174.00
1.16
1.9
2.5
06
2/3
0.1
150
0.13
193.70
1.29
2.2
3.3
07
¾
0.1
150
0.15
217.80
1.45
2.7
4.3
08
4/5
0.1
150
0.15
232.40
1.55
3.0
4.9
09
5/6
0.1
150
0.16
242.30
1.62
3.3
5.4
10
8/9
0.1
150
0.17
258.60
1.72
4.0
6.4
11
9/10
0.1
150
0.17
261.40
1.75
4.2
6.6
8PSK
12
3/5
0.1
120
0.17
208./80
1.74
3.4
5.8
13
2/3
0.1
120
0.19
232.30
1.94
4.0
6.9
14
¾
0.1
120
0.22
261.40
2.18
4.7
8.1
15
5/6
0.1
120
0.24
290.60
2.42
5.7
9.6
16
8/9
0.1
120
0.26
310.30
2.59
6.9
11.0
17
9/10
0.1
120
0.26
314.20
2.62
7.0
11.2
16APSK
18
2/3
0.1
90
0.26
231.80
2.58
5.3
9.4
19
3/4
0.1
90
0.29
260.60
2.90
6.0
10.6
20
4/5
0.1
90
0.31
278.10
3.09
6.5
11.4
21
5/6
0.1
90
0.32
290.00
3.22
6.9
12.0
22
8/9
0.1
90
0.34
309.60
3.44
7.8
13.2
23
9/10
0.1
90
0.35
313.50
3.48
8.1
13.5
3APSK
24
3/4
0.1
72
0.36
260.90
3.62
7.5
13.1
25
4/5
0.1
72
0.39
278.40
3.87
8.2
14.1
26
5/6
0.1
72
0.40
290.20
4.03
8.6
14.7
27
8/9
0.1
72
0.43
309.80
4.30
9.9
16.2
28
9/10
0.1
72
0.44
313.70
4.36
10.1
16.5