Glossary
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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 State:
One possible value of the encoder delay elements at one point in
time.
- Trellis
Section:
The collection of possible Trellis States for one point in time.
- 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".