Multiple interleavers for modified Turbo codes

Turbo Convolutional Codes (TCC) are excellent error correcting codes. However, TCC decoders require large number of computations. Recently, a class of low complexity modified Turbo codes termed as Low Complexity Hybrid Turbo Codes (LCHTC) and Improved Low Complexity Hybrid Turbo Codes (ILCHTC) have been proposed. Simulation results show that the proposed codes achieve performance close to that of TCC. Both LCHTC and ILCHTC encode information bits arranged in 2-dimensional array. However, design of TCC interleavers is based on interleaving 1-dimensional array of information bits. Therefore, interleavers designed for TCC are not suitable for LCHTC and ILCHTC codes. This paper proposes the design of 2-stage interleavers for all the modified Turbo codes in which constituent encoders encode information bits arranged in 2-dimensional array. Proposed design is focused on improving minimum distance while maintaining minimum dispersion of the code. Simulation of LCHTC and ILCHTC show that codes with 2-stage interleavers have more minimum free distance than that with Random interleaver. Therefore, LCHTC and ILCHTC with proposed interleaver achieve superior performance in error floor region as compared to that of the code with Random interleaver. Moreover, analysis shows that the code with 2-stage interleaver requires less memory storage than Random interleaver.