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DMD50 Universal Satellite Modem
Type of
Data Rate
Service
(Kbps)
Small IDR
64
(With 16/15
128
O/H)
256
384
512
768
1024
1536
IDR
1544
(With 96
2048
Kbps O/H)
6312
8448
8PSK
1544
2048
6312
8448
DVB
All
1. n = code length, k = information symbols and t = symbol error correcting capability.
2. Design objective.
3.9 Asynchronous Overhead Operation (Framing/Multiplexer Capability)
The Asynchronous Framing/Multiplexer is capable of multiplexing a relatively low-speed overhead
channel onto the terrestrial data stream resulting in a slightly higher combined or aggregate data
rate through the modem. The overhead channel is recovered at the far end. This added channel
is termed variously "An Overhead Channel", "Service Channel", "Async Channel" or in IESS
terminology an "ES to ES Data Channel." The basic frame structure used by the multiplexer is
that specified in the IESS-309 Standard, resulting in a 16/15 Aggregate ratio of overhead & data
to data rates.
For Regular Async:
For Enhanced Async:
The maximum Baud Rate is 19,200 bps for IBS Async. Two software-controlled modes are
designed into the card to best utilize the available bits; "Standard IBS" and "IBS (Async)". The
characteristics of the Channel Interface is also determined by the standard or Async mode.
The Async Channel can be set under software-control to either RS-232 or RS-485 mode. The pin
assignments for both modes are shown in Table 5-3.
TM118 – Rev. 1.1
Table 3-1. Reed-Solomon Codes
R-S Code
Bandwidth
1
(n, k, t)
Expansion
[ (n/k) -1 ]
(126, 112, 7)
0.125
(126, 112, 7)
0.125
(126, 112, 7)
0.125
(126, 112, 7)
0.125
(126, 112, 7)
0.125
(126, 112, 7)
0.125
(126, 112, 7)
0.125
(126, 112, 7)
0.125
(225, 205,10)
0.0976
(219, 201, 9)
0.0896
(194, 178, 8)
0.0899
(194, 178, 8)
0.0899
(219, 201, 9)
0.0896
(219, 201, 9)
0.0896
(219, 201, 9)
0.0896
(219, 201, 9)
0.0896
(204, 188, 8)
0.0851
(Standard IBS), the Baud Rate is approximately 1/2000
of the Data Rate listed in Table 3-3.
(IBS Async.), the Baud Rate is selectable, but Data Rate
is limited.
Theory of Operation
Interleaving
Maximum
Depth
R-S Codec
Delay (ms)
4
115
4
58
4
29
4
19
4
15
4
10
4
8
4
5
4
9
4
7
4
2
4
<2
8
18
8
13
8
4
8
3
12
-
2
3-17
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