des. In contrast to a serial code Suppose that the systematic part of the codeword, CO = concatenation where the output of one encoder forms (u1, Uk), is received as yo, while the two parity parts, the input for the next one, in a parallel concatenation, C1 = (C1,1, C1,k) and C2 = (c2,1, C2,k), are received as both encoders operate on the same input block. In y1 and y2, respectively. In the first iteration, the first Figure 3.4-11, an input information block of length k bits, decoder generates a reliability information L (i) for each u = (u1, ..., uk), is encoded by the first RSC encoder; at information bit Ui, i=1,..., k, based on its input, (yo, y1). the same time, it is passed through a k-bit interleaver and This soft-decision output, called extrinsic information, is fed into the second RSC encoder. For each input bit Ui, interleaved and fed to the second decoder. Using its the output consists of that bit Ui and the two parity-check input (y2 and the interleaved version of yo), the second bits C1,i and 2,i from the two RSC encoders. The output decoder computes a reliability information L2 (i) for each corresponding to the input block u is the codeword information bit. Next, the extrinsic information from C = (u1, Uk, C1,1, Clik, C2,1, c2,k). The code rate the first decoder, the extrinsic information from the of the turbo code is 1/3. Higher code rates can be second decoder, and a channel log-likelihood ratio obtained by puncturing the output bits of the two encoders [1]. For example, rate 1/2 can be obtained by Pr{Yi = yo,|U;=1} = alternately puncturing the parity bits of the two RSC encoders. A turbo code is essentially a block code, thus encoding can be seen as a multiplication of the information block by a generator matrix. are summed to provide a first approximation of the One of the many novelties in the turbo code realization a posteriori LLRs. In the second iteration, the extrinsic is the existence of a block interleaver between the two information L2(i) is deinterleaved and sent to the first RSC coders