PROJECT TITLE :
Differentially Coherent Multichannel Detection of Acoustic OFDM Signals
During this paper, we propose a class of ways for compensating for the Doppler distortions of the underwater acoustic channel for differentially coherent detection of orthogonal frequency-division multiplexing (OFDM) signals. These strategies are based on multiple fast Fourier rework (FFT) demodulation, and are implemented as partial (P), shaped (S), fractional (F), and Taylor (T) series enlargement FFT demodulation. They replace the conventional FFT demodulation with some FFTs and a combiner. The input to each FFT is a specific transformation of the input signal, and therefore the combiner performs weighted summation of the FFT outputs. The four ways differ in the selection of the pre-FFT transformation (P, S, F, T), whereas the remainder of the receiver remains identical across these ways. We have a tendency to style an adaptive algorithm of stochastic gradient kind to learn the combiner weights for differentially coherent detection. The algorithm is cast into the multichannel framework to require advantage of spatial diversity. The receiver is also equipped with an improved synchronization technique for estimating the dominant Doppler shift and resampling the signal before demodulation. An additional technique of carrier sliding is introduced to help within the post-FFT combining method when residual Doppler shift is nonnegligible. Artificial knowledge, and experimental data from a recent mobile acoustic communication experiment (few kilometers in shallow water, 10.5-15.5-kHz band) are used to demonstrate the performance of the proposed methods, showing vital improvement over conventional detection techniques with or while not intercarrier interference equalization (five-7 dB on average over multiple hours), as well as improved bandwidth potency [ability to support up to 2048 quadrature section-shift keying (QPSK) modulated carriers].
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