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(o)d(i) and d(o)(2)d(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(o)d(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(o)d(i) up to d(o)(2)d(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.