Iterative Algorithm Of Carrier Recovery In Multilevel Turbo Coded Modulation System

In this dissertation, we propose a new binary turbo-coded system with carrier recovery where 16-QAM modulation is employed. Comparing with the conventional Turbo TCM scheme, the soft symbol to bit mapping technique and iterative carrier recovery algorithm are implemented into this system.The soft symbol to bit mapping technique is an effective way to combine the multilevel modulation and binary decoding. It divides the signal constellations into the subsets specified by each binary digit, and then maps the soft symbol information to soft bit information by Maximum-A-posteriori Probability (MAP) algorithm to realize the binary decoding.Our proposed iterative carrier recovery algorithm is based on the Maximum Likelihood (ML) approach. It makes iteratively soft decisions provided by the soft-in soft-out decoders within the overall iterative turbo decoding scheme to estimate the phase error. In doing so, iterative decoding and carrier phase recovery go together step by step in the iterative "soft decision-directed" mode. In the proposed system, based on the soft symbol to bit mapping technique, we first get the soft bit information from the received signals and then send them to the binary turbo decoders. The soft outputs of the turbo decoders are recombined and feedback to phase recovery part to perform iterative maximum likelihood estimation of the carrier phase error. Then the phase errors of the received signals are partially corrected by using the phase estimation. Later on, we mapped the partially corrected received signals to bit information for the next decoding iteration. The iteration process will keep on up to its maximum required times. In addition, the parallel decoding implementation of the turbo coded 16QAM system is given based on the soft symbol to bit conversion.We also discussed the carrier recovery algorithm performance under different conditions, e.g. mean-squared estimation error, and its effect on the bit error rate (BER) of the whole system. The computation complexity of the proposed system and its comparison with the Turbo TCM system are also presented in this dissertation. In summary, this system can be considered as an effective alternative to the conventional carrier recovery in Turbo TCM schemes.