Comtech EF Data SNM-1001L Installation And Operation Manual page 231

SNM-1001L Satellite Modem
Decoder
The branch metrics are then processed by the ASC computer. The ASC computer makes
decisions about the most probable transmitted symbol stream with the state metrics computed
for the previous 64 decoder inputs.
The results of the ASC computer are stored in the path memory (80 states in depth). The path
with the maximum metric is designated as the survivor path, and its data is used for output. The
difference between the minimum and the maximum path metrics is used as the means of
determining synchronization of the decoder.
The output data is then descrambled and differentially decoded. Both of these processes are
optional, and may be selected by the user locally or remotely. The data from the differential
decoder is sent to the interface PCB for formatting and output. The synchronization signal is
used for lock-detect and sent to the M&C.
The raw BER count is generated from the minimum and maximum metrics and sent to the
M&C for further processing. Refer to Chapter 1 for Viterbi decoder BER specifications.
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