Comtech EF Data SDM-9000, Installation And Operation Manual

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Theory of Operation SDM-9000 Satellite Modem
5–16 Rev. 4
5.4 Viterbi Decoder
5.4.1 Description
The modem Viterbi decoder circuitry is located on the demodulator PCB (bottom slot of
the modem chassis) and operates in conjunction with the convolutional encoder at the
transmit modem. The decoder uses a decoding algorithm to provide FEC on the received
data stream for errors occurring in the transmission channel.
A block diagram of the Viterbi decoder is shown in Figure 5-5.
5.4.2 Specifications
BER See Figure 1-4 and Table 1-2
Maximum Data Rate 25 Mbit/s (on each of 3 channels)
Synchronization Time 8000 bits (maximum)
Output Fault Indicators Activity detection of I and Q data sign bits
Raw BER Detection From 0 to 255 bits out of 1024 samples
Constraint Length 7
Figure 5-5. Viterbi Decoder Block Diagram