 has been used for both new and the legacy transmission chains. In addition, the performance of the channel coding and HARQ transmission chains in the downlink and uplink for the new (as shown in Figure 9-45) and the legacy systems have been evaluated under a different channel model and is shown in Figure 9-54. In these link-level simulations, ITU PedB 3 km/h channel model (Rayleigh fading), SISO antenna configuration, data frame size of 1864 bits inclusive of the 16-bit CRC, 64 QAM modulation, 6 LRUs and 96 sub-carriers per LRU, a maximum of four HARQ re-transmissions, and max-log MAP detection have been assumed. Furthermore, a CTC encoder rate of 1/ 3 has been used for both the new and the legacy transmission chains. The figure shows that the use of new schemes and parameters as described earlier significantly improves the overall performance compared to that of the legacy transmission chain. It is further shown that the use of HARQ re-transmissions significantly and progressively decreases the block error rate and consequently improves performance. In Figure 9-55, the performance of the channel coding and HARQ transmission chain of the IEEE 802.16n in the downlink direction has been compared with that of the legacy system, assuming ITU PedB 3 km/h channel model (Rayleigh fading), SISO antenna configuration, data frame size of 2328 bits inclusive of the 16-bit CRC, adaptation of modulation order (16 QAM and 64 QAM), and different number of LRUs per MCS. 9.12 Channel coding and modulation Table 9-10 Constellation Rearrangement Version [2] Constel- lation Rank > 1 Mapping Rule Modu- Modu- Rearran- Rank = 1 lation lation gement Mapping Scheme Order Version Symbol Odd Symbol 16 QAM 16 QAM 64 QAM 64 QAM 1st Transmission (IEEE 802.16-2009) 1st Transmission (IEEE 802.16m) 2nd Transmission (IEEE 802.16-2009) 2nd Transmission (IEEE 802.16m) 3rd Transmission (IEEE 802.16-2009) 3rd Transmission (IEEE 802.16m) 4th Transmission (IEEE 802.16-2009) 4th Transmission (IEEE 802.16m) SNR (dB) FIGURE 9-52 A comparison of the uplin