Operating instructions

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DMD20/DMD20 LBST Universal Satellite Modem Theory of Operation

TM103 – Rev. 2.8 3-17

Table 3-1. Reed-Solomon Codes

Type of

Service

Data Rate

(Kbps)

R-S Code

(n, k, t)

Bandwidth

Expansion

[ (n/k) -1 ]

Interleaving

Depth

Maximum

R-S Codec

Delay (ms)

Small IDR

(With 16/15

O/H)

128

256

384

512

768

1024

1536

(126, 112, 7)

0.125

115

IDR

(With 96

Kbps O/H)

1544

2048

6312

8448

(225, 205,10)

(219, 201, 9)

(194, 178, 8)

0.0976

0.0896

0.0899

8PSK

1544

2048

6312

8448

(219, 201, 9)

0.0896

DVB

All (204, 188, 8) 0.0851 12 -

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: (Standard IBS), the Baud Rate is approximately 1/2000

of the Data Rate listed in Table 3-3.

For Enhanced Async: (IBS Async.), the Baud Rate is selectable, but Data Rate

is limited.

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 are 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 5-2.