New Code Design and Analysis Tools for Serially Concatenated Systems

Licentiate thesis, 2005

In-line bit interleaving has over the last decade been used in a number of papers, and has proven to be very effective. Although it has several advantages over conventional bit interleaving, the use of conventional bit interleaving is still far more common. One reason for this is that the advantages of in-line bit interleaving are not widely recognized yet. Another reason is that the most commonly used code design principles cannot be used with in-line bit interleaving. Hence, in this thesis we will propose new code design principles that can be used for systems with in-line bit interleaving. Design rules will be proposed for both the inner and the outer code of a serially concatenated system. The system considered throughout this thesis is serially concatenated trellis coded modulation (SCTCM) with throughput 2 bits/symbol and 8PSK signaling over the additive white Gaussian noise (AWGN) channel. Several of the new ideas are, however, applicable to any bit interleaved system that use iterative decoding. The new design rules for the inner code are based upon the characteristics of bit interleaved coded modulation with iterative decoding (BICM-ID). BICM-ID can be seen as an SCTCM system with a one-state inner code. We use this fact and extend the design principles of BICM-ID to be valid for inner codes with more than one state. Furthermore, we will analyze the in-line bit interleaver and explain its advantages. In the analysis, the mutual information (MI) constellation is proposed. The MI constellation becomes a very useful tool in the design of the the outer code. We propose new design rules for the outer code that explains how to design the outer code in respect to the MI constellation.