It is used together with channel observationsL in the next APP decoding of the mth component code.A discussion on this global decoder can also be found in6] 5.9.4 PC-TCM In this scheme,two parallel concatenated ratek/(+1)convolutional codes use all their information bits to produce the parity bit which is sent to their respective symbol mappers,but the information bits are punctured in such a fashion that one half of them are used in the first trellis code and the other half in the second trellis code [Benede o-Divsalar].This is done transmitted by the two trellis encoders are interleaved by different bit interleavers(see Figure 5.9.11).In [Fragouli-Wesel01].a variation of this scheme is presented where a symbol interleaver is used instead of bit interleavers,resulting in improved BER performance in the waterfall region Figure5.9.11 5.10 Multilevel Codes and Multistage Decoding MLC was first proposed by Imai and Hirakawa in 1977,with the idea of protecting each 11 11 It is used together with channel observations (m) Lc in the next APP decoding of the mth component code. A discussion on this global decoder can also be found in [16]. 5.9.4 PC-TCM In this scheme, two parallel concatenated rate k/(k+1) convolutional codes use all their information bits to produce the parity bit which is sent to their respective symbol mappers, but the information bits are punctured in such a fashion that one half of them are used in the first trellis code and the other half in the second trellis code [Benedetto-Divsalar96]. This is done to limit the number of points in the signal constellation to 2(k/2)+1. Also, the information bits transmitted by the two trellis encoders are interleaved by different bit interleavers (see Figure 5.9.11). In [Fragouli-Wesel01], a variation of this scheme is presented where a symbol interleaver is used instead of bit interleavers, resulting in improved BER performance in the waterfall region. Figure 5.9.11 5.10 Multilevel Codes and Multistage Decoding MLC was first proposed by Imai and Hirakawa in 1977, with the idea of protecting each