be the case with a "0" initialized encoder. The CTC coder output bits are grouped into six sub-blocks and interleaved to break special patterns in the encoder output. As shown in Figure 9-48, the interleaved sub-blocks are multiplexed into four blocks where those four blocks consist of an interleaved A sub-block, an interleaved B sub-block, a bit- by-bit multiplexed sequence of the interleaved Y1 and Y2 sub-block sequences, which is referred to Y, and a bit-by-bit multiplexed sequence of the interleaved W2 and W1 sub-block sequences, which is referred to W. Information sub-blocks A and B are bypassed while parity sub-blocks are multiplexed bit by bit. The bit-by-bit multiplexed sequence of interleaved Y1 and Y2 sub-block sequences consists of the first output bit from the Y1 sub-block interleaver, the first output bit from the Y2 sub-block 9.12 Channel coding and modulation Sub-block Sub-block Sub-block Sub-block Sub-block Sub-block Sub-block Sub-block Sub-block Sub-block Sub-block Sub-block Interleaver Interleaver Interleaver Interleaver Interleaver Interleaver Circularly Left Shift k Bits Circularly Left Shift 1 Bit Circularly Left Shift k Bits FIGURE 9-48 An illustration of the block interleaving procedure [2] interleaver, the second output bit from the Y1 sub-block interleaver, the second output bit from the Y2 sub-block interleaver, etc. The bit-by-bit multiplexed sequence of interleaved W2 and W1 sub-block sequences comprises the first output bit from the W2 sub-block interleaver, the first output bit from the W1 sub-block interleaver, the second output bit from the W2 sub-block interleaver, the second output bit from the W1 sub-block interleaver, etc. After multiplexing sub-blocks into four blocks, sub-block B and sub-block W are circularly left-shifted by k bits, and sub-block Y is circularly left-shifted by 1 bit. When the FEC block size NFB is equal to a multiple of the modulation order, k is set to one. If KFB > 1, the NRE data sub-carriers allocated for a sub-packet are segmented into KFB blocks, one 