Abstract

The outstanding performance of turbo codes at low signal-to-noise ratio is deteriorated in the error-floor region, due to the low values of the free distance of turbo codes. Interleaver design for turbo codes can improve the minimum distance of the code, by eliminating low-weight input sequences that result in low-weight codewords. Interleaver can also be designed to improve the performance of the sub-optimal iterative decoding methods. While the relating criteria to satisfy these conditions are known, we are not able to find an interleaver that fulfills all these conditions in reasonable time. In this thesis, we have proposed a Joint interleaver design methods , for multiple turbo codes, where we have at least three constituent codes and two interleavers to design. In our proposed methods each interleaver is designed to satisfy some of the conditions and the other conditions are satisfied by the other interleaver. This will decrease the load on one interleaver to satisfy all the conditions at the same time and enable us to satisfy tougher conditions. It is shown that the proposed Sequential joint interleaver design converges very fast and can satisfy very tough conditions, which means better performance at error-floor region of the turbo code.