Deeoder for C Decoder for C y Demapper i一Decoder for 2-1) a (a) y(0) c y Mapper/ H Demapper noise (b) Figure5.I0.I0将各级的demapper综合在一起的Decoder(a)译码器结构框图(b)Normal graph 5.11 Bit-Interleaved Coded Modulation(BICM)with Iterative Decoding BICM was first developed by Zehavi primarily for fading channels with the aim of increasing the diversity order of Ungerboeck's TCM schemes,but has turned out to be capabl of approching the capacity ofhigSNR AWGN channels as ell5.p dula emes for fading channels.In Fig.5.11.1 (a),the chann el interleave is of symbol-based,which can also be placed between the convolutional encoder and signal mapper.The symbols are interleaved with a depth exceeding the coherent time of the fading process.Fig.(b)is the original BICM scheme proposed by Zehavi.Compared with the TCM encoder in(a),the BICM in(b)uses independent bit interleavers for all the bits of a symbol ath thanasingle symbol-based inere er.The purpo Todisperse the induced by the fading and the diversity order of the system; To render the bits associated with a given transmitted symbol uncorrelated or independent of each other.20 y Demapper Decoder for C0 • • • λ0 λ1 λl−1 Wl−1 W1 W0 1 π1 − 1 π l 1 − − π l−1 π1 (0) cˆ (1) cˆ ( 1) ˆ l c − Decoder for C1 Decoder for Cl−1 (a) • • • • • • C0 Cl−1 π1 π l−1 (0) v (1) v ( 1) l− v (0) u (1) u ( 1) l− u y C1 (b) Figure 5.10.10 将各级的 demapper 综合在一起的 Decoder (a)译码器结构框图 （b）Normal graph 5.11 Bit-Interleaved Coded Modulation (BICM) with Iterative Decoding BICM was first developed by Zehavi primarily for fading channels with the aim of increasing the diversity order of Ungerboeck’s TCM schemes, but has turned out to be capable of approaching the capacity of high-SNR AWGN channels as well. Fig. 5.11.1 depicts the coded modulation schemes for fading channels. In Fig. 5.11.1 (a), the channel interleaver is of symbol-based, which can also be placed between the convolutional encoder and signal mapper. The symbols are interleaved with a depth exceeding the coherent time of the fading process. Fig. (b) is the original BICM scheme proposed by Zehavi. Compared with the TCM encoder in (a), the BICM in (b) uses independent bit interleavers for all the bits of a symbol rather than a single symbol-based interleaver. The purpose of bit interleaving is: „ To disperse the bursty errors induced by the correlated fading and to maximize the diversity order of the system; „ To render the bits associated with a given transmitted symbol uncorrelated or independent of each other