Turbo coding for bandwidth efficiency and high reliability

In this dissertation, new code designs and iterative turbo decoding techniques for bandwidth efficient applications are presented. These forward error correcting coding schemes combine the power efficiency of turbo codes with the bandwidth efficiency of coded modulation.; The design of nonsystematic turbo codes with low convergence thresholds using mutual information based EXIT charts is described. Nonsystematic turbo codes have larger effective free distances d_eff, and hence better error floor performance, than systematic turbo codes of the same complexity.; Bit interleaved bandwidth efficient coding schemes using asymmetric turbo codes and low complexity multiple turbo codes that outperform classical turbo code based designs are then presented. The usefulness of feedforward encoders in a multiple turbo code configuration is demonstrated using a new convergence analysis method developed for multiple turbo codes.; High reliability bandwidth efficient Type-I and Type-II hybrid-ARQ protocols using turbo codes are proposed. Several packet combining schemes are described for use in conjunction with iterative turbo decoding over AWGN and time-varying Rayleigh fading channels. These packet combining schemes provide improved throughput and reliability compared to standard Type-I hybrid-ARQ with no combining and require only a small increase in transmitter and receiver complexity.; Also, a new approach to designing bandwidth efficient codes that combines low rate turbo codes and multilevel signaling is demonstrated using bit-interleaved coded modulation. We investigate the gains achievable with this approach compared to conventional binary signaling techniques.; Finally, a computational complexity analysis of turbo decoders is presented. As a particular example, the number of decoding computations required by low complexity multiple turbo codes is compared to the computational requirements of standard turbo codes used in wireless systems.