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Glossary

Codeword Decoding
Forward Direction Message Word
Reverse Direction Trace Back
Trellis Block Trellis Branch
Trellis State Trellis Section

Codeword:
A codeword is a group of bits whose length you define in the
Encoder Rate field. It is the code bits associated with one period of the encoder or one trellis section.

Decoding:
The act of deciphering the estimate message word from a known codeword. In the "Block" and "Continuous"
Decoding Styles the Viterbi algorithm does not do decoding until it has traced back the number of trellis sections specified in the Trace Length field.

Forward Direction:
The forward direction in time. The direction of increasing time index. This is the direction in which the Viterbi algorithm computes the branch and path measures for the branches and states.

Message Word:
A message word is a group of bits whose length you define in the
Encoder Rate field. It is the message bits associated with one period of the encoder or one trellis section.

Reverse Direction:
The reverse direction in time. The direction of decreasing time index. This is the direction in which the Viterbi algorithm follows the surviving branches back through the trellis to determine the estimate codewords and message words.

Trace Back:
The trace back is the act of following the surviving branches from the end of a group of trellis sections back to the beginning of the group. Here, a group is the number of trellis sections per one trace back operation as defined for the different
Decoding Styles.

Trellis Block:
The definition of the trellis block depends on the
Decoding Style, but basically it is the group of blocks involved in the forward calculation in one cycle of the Viterbi algorithm. A cycle here is the calculation in the "forward direction" followed by the "trace back" in the "reverse direction".

Trellis Branch:
The link in the trellis diagrams that connects one state to another representing the state change for one period of the encoder.

Trellis Section:
The collection of possible Trellis States for one point in
time.

Trellis State:
One possible value of the encoder delay elements at one point in time.



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