b/No required to achieve a BER of 10-3 and 10 5 for various frame sizes using UMTS turbo encoder with minimum code rate of R = 1/3. In general, turbo codes are more suited for large packet size applications and their performance degrades for small packet sizes. Furthermore, the delay due to turbo interleaver might become prohibitive for delay-sensitive applications. Figure 9-43 shows the BER performance of a BTC coder as a function of Eb/No for various code rates, frame sizes, and detector types. In Figure 9-43, notation (n, k) denotes the number of input (k) and output (n) bytes. The BER performance of the IEEE 802.16 CTC coder with a minimum rate of 1/3 in the AWGN channel at different code rates and various modulation schemes is shown in Figure 9-44. Once again, the effect of code rate and frame size (in number of bytes) on performance can be seen in the figure. CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) (12,6) log-MAP (12,9) log-MAP (24,12) log-MAP (24,20) log-MAP (36,18) log-MAP (72,40) log-MAP (12,6) max-log-MAP (12,9) max-log-MAP (24,12) max-log-MAP (24,20) max-log-MAP (36,18) max-log-MAP (72,40) max-log-MAP Eb/No (dB) FIGURE 9-43 A comparison of the BER performance of a BTC coder in AWGN channel with different code rates, frame sizes, and detector types [124] 9.12.2 Coding and Modulation of Traffic Channels In the IEEE 802.16-2009 standard, the BS selects the most suitable modulation and coding scheme from a finite set of supported modulation and coding schemes based on the channel quality reports from the MS, user traffic QoS requirements, and several other factors. This means that there are a limited number of combinations of code rate R and modulation order M that can be selected. If the allocation size, in terms of number of QAM symbols N, is known, the burst size can calculated as NRM for a given code rate and modulation order. In the latter approach, the burst size is derived based on the knowledge of the allocation size. A limited link adaptation is possible, if one assumes that the perfor