 decoded bit error for a specified Eb/No is found when further increases in wrap depth do not decrease the error probability, as shown in Figure 9-51. It can be seen that the link-level BER performance improves when increasing the depth and the performance does not significantly change after a certain limit. The effect of different data frame sizes (6, 9, 18, 27, and 36 bytes) on the BER performance has been investigated and is shown in the figure. 9.12 Channel coding and modulation QPSK 1/2, 6 Bytes, Depth 0 QPSK 1/2, 6 Bytes, Depth 1 QPSK 1/2, 6 Bytes, Depth 2 QPSK 1/2, 6 Bytes, Depth 3 QPSK 1/2, 6 Bytes, Depth 4 QPSK 1/2, 6 Bytes, Depth 5 QPSK 1/2, 6 Bytes, Depth 6 QPSK 3/4, 9 Bytes, Depth 6 QPSK 3/4, 18 Bytes, Depth 6 QPSK 3/4, 27 Bytes, Depth 6 QPSK 3/4, 36 Bytes, Depth 6 16QAM 3/4, 18 Bytes, Depth 6 16QAM 3/4, 36 Bytes, Depth 6 64QAM 3/4, 27 Bytes, Depth 6 Eb/No(dB) FIGURE 9-51 Performance of an example tail-biting convolutional coder 9.12.4 HARQ-IR Physical Layer Procedures The incremental redundancy HARQ is performed by changing the starting position Pik of the bit selection for HARQ re-transmissions. For downlink HARQ, the starting point for the bit selection algorithm is determined as a function of the HARQ sub-packet ID as shown in Table 9-9. For the uplink HARQ, the starting position for the bit selection algorithm is determined as a function of HARQ sub-packet ID Pik = (iNCTC)mod NFB_Bufferk For the uplink HARQ, the sub- packets are transmitted in sequential order. Table 9-9 Starting Position Determination for Downlink HARQ [2] HARQ Sub-packet ID Starting Position Pik (-NCTCK) mod NFB_Bufferk (NFB_Buffer / 2 - NCTC/2) mod NFB_Bufferk (NFB_Bufferk - NCTC/2) mod NFB_Buffer CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) 9.12.5 Constellation Rearrangement It was mentioned earlier that the performance of adaptive modulation generally suffers from the power inefficiencies of multi-level modulation formats. This is due to the variations in bit reliabilities caused by the bitmapping onto the signal cons