Constrained Interleaving of Serially Concatenated Codes with Inner Recursive Codes

A novel constrained interleaving technique is proposed to improve serially concatenated codes (SCCs) with inner recursive convolutional codes (IRCCs). In this study, constrained interleavers are designed to achieve a minimum Hamming distance (MHD) for the SCC, d_SCC, between d_od_i and d_o²d_i while simultaneously maximizing the interleaver gain, where d_o and d_i are the MHD of the outer and inner codes respectively. Constrained interleavers can be constructed to achieve d_SCC=d_od_i while almost maintaining the interleaver gain of uniform interleaving. By imposing additional inter-row constraints, d_SCC of constrained interleaving is increased beyond d_od_i up to d_o²d_i, however, at the expense of some interleaver gain. Numerical results demonstrate that constrained interleaving is an efficient way to construct SCCs with low error floors while achieving interleaver gain at relatively short interleaver sizes.