| Summary: | 碩士 === 國立臺灣海洋大學 === 電機工程學系 === 92 === An important problem of the underwater acoustic communication system is to overcome multi-path and Doppler effects in the severe fading channel. Therefore an optimum equalizer needs to be continuously developed to avoid inter-symbol interference and to improve the quality of communications.
In this thesis, the implementation algorithms based on the blind adaptive decision feedback equalizer (BADFE), which function can be automatically adjusted according to variations of channel, are investi- gated. The BADFE has starting and tracking modes. The starting mode is for opening eye diagram, and the tracking mode is for decreasing mean square errors. The decision-directed structure and constant-modulus algorithm (CMA) are combined with the BADFE to get a modified equalization scheme. The bit error rates as well as the transmission efficiency are improved. In addition to numerical simulations, the off-line analysis of transmission experiments in a water tank with the all-digital modem is conducted for testing the performance of the modified equalizer. The modified BADFE of an all-digital underwater modem, imple- mented with the digital signal processor TMS320C6711 and C coding language, is investigated. In the water tank experiments, the modified BADFE always has better convergence speed and lower bit error rate than that of BADFE.
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