This paper presents the results of a practical experiment of underwater acoustic transmission, which was performed in Arraial do Cabo, RJ. The primary focus of this experiment is analyzing the performance of different types of equalizers, namely: zero-forcing (ZF), minimum mean square error (MMSE) and decision feedback equalizer (DFE). The mean square error (MSE) and bit-error rate (BER) are the figures of merit used to compare their performances. Results show that in terms of MSE, the DFE has better performance than the other equalizers, achieving an MSE of −25.6 dB for signal-to-noise ratio (SNR) equal to 10 dB. Furthermore, the DFE outperformed the ZF and MMSE equalizers, improving BER by 5.3 dB with respect to the ZF equalizer, and 3.4 dB with respect to the MMSE equalizer.
Resumo-Este trabalho utiliza o método do Gradiente Conjugado para a solução de sistemas de grande porte de equações afins simultâneas. O algoritmo é aplicado ao problema de localização em ambientes fechados utilizando WLAN fingerprinting. Palavras-Chave-Gradiente Conjugado, WLAN fingerprinting, localização em ambientes fechados.
Underwater Acoustic (UWA) communication systems still rely heavily on at-sea trials. This work presents an operational framework that significantly reduces the need for practical experiments. The key idea is to generate channel impulse responses (CIRs) drawn from probability density functions constructed based on trusted information and to employ Monte Carlo simulations to develop new UWA communication systems. Hence, the proposed operational framework depends only on cheaper-to-acquire physical measurements to produce CIRs. It comprises a model-based CIR replay tool and a stochastic-based UWA channel simulator. The former can be any model-based CIR replay tool, and the latter is proposed in this work and validated using data from four different practical experiments. We also carried out experiments for a transmit beamforming with signals digitally modulated in binary phase-shift keying, which were transmitted by an array and by a single source with equivalent power. For the array, the ideal transmit direction comes from the lowest bit error rate (BER) obtained with computer simulations. This paper compares the performance of the transmit array to the single source transmission and the results of a practical experimental transmission with a Monte Carlo simulation employing the proposed technique. We show that both achieved close results regarding BER and mean squared error. The conclusion is that the proposed operational framework, once adjusted to the specific transmission site, can be used to design new UWA communication systems, eliminating the burden of at-sea trials for tests of new transceivers. Finally, we conducted real-life transmit beamforming experiments to verify the BER gain obtained in practice using the steering angle obtained from simulations.
This paper presents the application and the comparison of the least absolute shrinkage and selection operator (LASSO) and the Conjugate Gradient (CG) algorithm for solving the fingerprinting indoor localization problem. LASSO's ability to generate sparsity via selection of variables results in a judicious and automatic removal of spurious measurements that often corrupt large fingerprint data sets. These spurious measurements usually have to be individually discarded before the CG algorithm, or other solver for the normal equation, is used. The paper also compares LASSO with a sparse version of the ordinary least squares solution obtained by simply discarding the variables with the smallest absolute value. The results are presented for two data sets recorded independently at the
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