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SDM-300A Satellite Modem
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.
A.1.4.9
Reed-Solomon Decoder
Refer to Section A.2, Conventional Options, for Reed-Solomon information.
Rev. 4
Options
A–45
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