Real signals demodulation on a highly selective channel

Summary form only given. The underwater acoustic channel is probably one of the most complicated environments for data communication. The characteristics of this channel, which include fading, multipath and therefore frequency selectivity, Doppler shift preclude direct application of standard communications techniques. But there are many situations in which it would be desirable to have the means to communicate underwater. The use of well known estimation methods for digital communication is the new approach of this paper. Indeed, the adaptation of the propagation parameters in the demodulation algorithm allows to improve the system performance. Moreover, the knowledge, a priori, of the emitted signals allows to calculate the error rate after the adaptive demodulation. This paper shows the main results obtained with real signals emitted in shallow water (testing pool and ocean) and recorded on a DAT tape. The correlation figure of the received signals permits the estimation of time delay and attenuation of the different paths. The figure of phase estimation and tracking allows the extraction of the Doppler shift for each path. The comparison between the error rate performance with and without adaptive demodulation shows the improvement brought by this demodulation.<
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