o classical turbo codes, including better convergence of the iterative decoding, large minimum distances (i.e., large asymptotic gains), less sensitivity to puncturing patterns, reduced latency, and robustness towards the flaws of the component decoding algorithm, in particular when the MAP algorithm is simplified to the Max-Log-MAP scheme. The input bits are alternatively fed to the constituent encoders, starting with the MSB of the first byte that is fed to constituent encoder 1 fol- lowed by the next bit being fed to constituent encoder 2. The encoder is fed by blocks of NFB bits. The order in which the encoded bits are fed to the bit separation block is as follows: A, B, Y1, Y2, W1, W2 = A0, A1, A2, ..,AN-1, Bo, B1, B2, BN-1, Y1,0, Y1,1, Y1,2, ,...Y1,N-1, (9-36) Y2,0, Y2,1, Y2,2,...Y2,N-1,W1,o,W1,1,W1,2,...W1,N-1,W2,0 W2,1, W2,2,...W2,N-1 CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) Systematic Bits Interleaver (Permutation) Circular Trellis -k bits Interleaver (Permutation) Circular Trellis Interleaver (Permutation) Circular Interleaver Trellis (Permutation) Parity Bits FIGURE 9-47 Parallel concatenation of N CRSC codes [85,86,91] where A, B are the systematic bits, Y1, W1 are the parity bits from constituent encoder 1 and Y2, W2 are the parity bits from constituent encoder2. It was mentioned earlier that the IEEE 802.16m CTC encoder relies on a parallel concatenation of N CRSC encoders. They are called circular recursive systematic because they use circular or tail-biting termination. Figure 9-47 illustrates the principle of the encoding for blocks of k bits with 1/2 global rate. Due to the circular termination mechanism, which involves making the initial and the final state of the encoder equal, no additional bit is needed to transform each RSC code into a block code. Moreover, if the permuted sequence at the input of a particular component encoder is not a return to zero sequence, the entire redundancy set of the corresponding circle is affected by this sequence, not only the part after it as would 