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Transport aspects 2

In order to force the final state of the convolutional encoder to the zero state (0, 0, 0, 0), the two LSBs u1
and u2 of the final two 4-dimensional elements in the symbol are constrained to u1  S1  S3, and u2  S2.

For data symbols, the convolutional encoder state shall be terminated to (0, 0, 0, 0) only once at the end of
the data frame (i.e., symbol). For RMC symbols, the convolutional encoder state shall be terminated to (0,
0, 0, 0) twice: first at the end of the RMC frame, and second at the end of the user data part, i.e., at the end
of the symbol.

Figure 10-6 – Conversion of u to v and w

Figure 10-7 – Convolutional encoder: Finite state machine representation

10.2.1.3.3 Coset partitioning and trellis diagram (informative)
In a trellis coded modulation system, the expanded constellation may be labelled and partitioned into
subsets ("cosets") using a technique called mapping by set-partitioning. The 4-dimensional cosets in Wei's
code can each be written as the union of two Cartesian products of two 2-dimensional cosets.
For example, C 0   C 0  C 0    C 3  C 3 . The four constituent 2-dimensional cosets, denoted by 0,
4 2 2 2 2
3
1, 2 and 3 for C 0 , C 1 , C 2 , C , respectively, are shown in Figure 10-8.
2 2 2 2

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