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Accounting for source depth variations in time-reversal communications
Jesus, S.M.; Ijaz, S.; Silva, A.Passive Time Reversal (pTR) is a low complexity receiver scheme that uses multichannel probing for time signal refocusing, thus reducing time spreading and improving inter-symbol interference. Recognizing that signals travelling through different paths are subject to arrival-angle-related Doppler displacements, this letter proposes a further improvement to pTR that applies correcting frequency shifts optimized ...
Arrival-based equalizer for underwater communication systems
Ijaz, S.; Silva, A.; Jesus, S. M.One of the challenges in the present underwater acoustic communication systems is to combat the underwater channel effects which results in time and frequency spreading of the transmitted signal. The time spreading is caused by the multipath effect while the frequency spreading is due to the time variability of the underwater channel. The passive Time Reversal (pTR) equalizer has been used in underwater communi...
Potential of vertical line array beamforming in underwater acoustic communications
Ijaz, S.; Silva, A.; Jesus, S. M.Um dos principais tópicos atuais de pesquisa é ́ a concepçãoo de técnicas de processamento de sinal eficazes para comunicações submarinas. Este interesse é reforç ̧ado pelos desafios inerentes às condições incontroláveis, como a batimetria, a temperatura, e as variações temporais (geométricas) das profundidades da fonte e da antena de receptores. A obtenção de taxas de transmissão modestas é ainda um desafio, d...
An environmental equalizer for underwater acoustic communications Tested at Hyd...
Silva, A.; Zabel, F.; Mertins, C.; Ijaz, S.; Jesus, S. M.It is known that small changes in source and receiver locations can cause significant changes in underwater acoustic channel impulse responses. At HYDRALAB III an underwater acoustic experiment was conducted to show that a source depth-shift causes a frequency-shift in the channel impulse response and that such behavior can be used to implement an environmental-based equalizer for underwater communications that...
Compensating for source depth change and observing surface waves using underwat...
Ijaz, S.; Silva, A.; Jesus, S. M.Underwater communications impose great challenges due to the unpredictable changes in the environment. In order to accommodate for these changes, equalizers are used to track the Impulse Responses (IRs) and compensate the intersymbol interference (ISI). Source and array depth shifts are one of the major contributing factors to continuous amplitude and phase changes in IR. These changes magnify the problem of da...
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