ComStream CM601, Инструкция по установке и эксплуатации

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Theory of Operation 2-5
Modem Card
The CM601 is typically configured for full-duplex operation, transmitting and
receiving data from the satellite. These two paths are independent for most
applications. The modem card incorporates the modulator, demodulator, data I/O
interface, and Doppler buffer functions.
Modulator
In the transmit process, illustrated in Figure 2-4, the CM601:
1. Accepts user data at the data interface card (modem or I/O option card)
2. Directs the transmit or send data (SD) across the backplane, clocking the data
by either Station Timing (ST) or Transmit Timing (TT), depending upon the
clocking configuration of the unit
3. Directs the data through any optional, transmit-data-processing card (for
example, the Satellite Control Channel card)
Figure 2-4 CM601 Transmit Process
4. Provides the data to the modulator (modem card) for processing; the data
processing consists of:
a. Scrambling (ComStream version V.35 or IDR)
b. Differential encoding
c. Convolutional encoding for error-correction decoding. The modulator can
encode the data with convolutional codes that are Viterbi rate 1/2, 3/4, or
7/8 compatible, as well as IESS-312 compatible Sequential rate 1/2 and
ComStream Sequential rate 3/4.
5. Passes the processed data through a digital matched filter
6. Converts the data from digital to analog (D/A) signal
7. Uses the signal to PSK-modulate an IF carrier. Once the signal reaches the
intermediate frequency, the modulated carrier is available for transmission. In
this illustration, the QPSK modulator is used.
G329-01
Digital
Clock
Synthe-
sizer
Scrambler
Convolutional
Encoder
Differential
Encoder
TT
SD
From
data
interface
module
ST
Digital
Filter
D/A
D/A
QPSK
Modulator
IF
Synthe-
sizer
Power
Control
Backplane
(optional)
TxIF