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An underwater multiuser cooperative communication system based on minimum mean-square error decision feedback detection (MMSE-DFD) algorithm is proposed, where communication between two source nodes and one destination node is assumed. In this paper, underwater acoustic (UWA) channel is modeled as a sparse multipath channel experiencing Rayleigh fading. Compared with the traditional multiuser cooperative...
It is very important to estimate the signal to noise ratio (SNR) of receive signal accurately because this parameter will play an important role in the equalization and detection modules. LFM signal is often used as a synchronization signal due to its good autocorrelation property and Doppler tolerance in underwater acoustic (UWA) channels. A new SNR estimation algorithm making use of the LFM signal...
A parallel combinatory (PC) multicarrier frequency-hopped spread spectrum (FHSS) underwater acoustic (UWA) communication system is proposed in this paper. Parallel combinatory is first applied in FHSS system to accomplish the subcarrier mapping, which makes the communication system not only to preserve the ability of resisting fading and narrow band interference randomly during the transmission over...
Wavelet packet transform is an efficient method in speech denoising processing. In this paper, we research on various wavelet packet basis, decomposition layers, values of the threshold and threshold functions which are key parameters in wavelet packet denoising. Furthermore, we adopt three methods to evaluate the effects of denoised speech, including signal-noise-ratio(SNR), wavelet spectrum distortion...
Sea noise is a non-stationary random series. The acoustic channel noise of shallow sea has the features of remarkable nonlinear and non-Gaussian characteristics of pulse. We use wavelet packets to analyse this kind of noisy signal, and study on different wavelet basis, threshold functions and values of the threshold which will influence the extraction of a LFM signal under the background of strong...
This paper proposes a basic MC-CMDA. via carrier interferometry Codes (CI codes) in an Underwater Acoustic(UWA) Channel. Compared with OFDM in UWAC, it can allow a number of users simultaneously and asynchronously accessing the UWA channel. A trade off relation exists between diversity gain and user capacity as well as between spread spectrum gain and system efficiency. Then diversity combining scheme...
Depending on the tolerable delay latency, we can benefit from some degree of time diversity in free-space optical links, by employing channel coding and interleaving. We present a comparative study of the performance of different channel coding techniques at the presence of time diversity. We show that turbo-codes are particularly efficient under strong turbulence conditions. For relatively weak turbulence,...
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