No abstract

Visible light communication (VLC) based localization is a potential candidate for wide range indoor localization applications. In this paper, we propose a VLC architecture based on orthogonal frequency division multiplexing (OFDM) with multiple functionalities integrated in the same system, i.e., the 3-D receiver location, the control of the room illumination intensity, as well as the data transmission capability. Herein we propose an original methodology for LED power discrimination applying spatial optical OFDM (SO-OFDM) structure for position estimation. The hybrid locator initially makes a first estimate using a weighted angle-of-arrival (WAoA)-based locator which is then used as the starting point of the recursive estimator based on the strength of the received signal (RSS). Hence, the first stage is deployed to increase convergence probability, reducing the root-mean-square error (RMSE) and the number of iterations of the second stage. Also, a performance vs computational complexity comparative analysis is carried out with parameter variations of these estimators. The numerical results indicate a decade improvement in the RMSE for each two decades of decrement of power noise on the receiver photodiode. The best clipping factor is obtained through the analysis of locator accuracy and transmission capacity for each simulated system. Finally, the numerical results also demonstrate effectiveness, robustness, and efficiency of the proposed architecture.

The orthogonal frequency division multiplexing (OFDM) transmission has shown promise in applications of visible light communication (VLC). However, the variation of the nonlinearity of the optical power emitted by the high power light emitting diode (HPLED) as a function of current and temperature implies in drastic OFDM-VLC performance degradation. The first part of this work, experimentally confirms and models this degradation due to temperature in a high power white HPLED. The higher attenuation at high frequencies, which is inherent to the HPLED and which is accentuated by the effect of the intrinsic capacitance of the photodiode, is another factor of degradation due to the reduction of the signal-to-noise ratio (SNR) at the receiver for such frequencies. For the mitigation of these effects, we propose a pre-distortion and digital preequalization scheme using a luminous feedback signal in the transmitter module. The system is modeled so that the operating points are mathematically deduced and evaluated by simulations and by an experimental setup. By allowing the linearization of the transmitted light signal and the maintenance of an average SNR in all OFDM subcarriers, the performance improvement is confirmed in comparison with other schemes, such as with non-predistortion, pre-distortion with fixed parameters, and simple post-equalization.

http://dx.doi.org/10.5007/2175-7941.2017v34n1p310Recentes tecnologias tendem a invadir as escolas desencadeando modos diferenciados de se instruir conceitos científicos. Neste sentido, o presente trabalho emprega o dispositivo Arduino em uma inovadora montagem de um analisador de pilhas recarregáveis, que possibilita também uma proveitosa instrução dos conceitos físico-químicos envolvidos. Este analisador realiza a carga e descarga de pilhas, viabilizando o cálculo da sua capacidade de carga e do seu estado de saúde, cujas reflexões então fornecidas subsidiam o educador interessado. Os resultados obtidos em uma avaliação exemplar de três pilhas com diferentes capacidades de carga foram corroborados por um equipamento de laboratório de pesquisa em pilhas e baterias.

Wavelength division multiplexing (WDM) permits the light spectrum to be divided into several parallel channels, allowing the capacity of visible light communication (VLC) systems to be increased. However, the spectral overlap due to the emission spread of differently colored LEDs generates crosstalk interference that can degrade the WDM-VLC. In this context, the adequate design of optical filters (OFs) can mitigate this problem by limiting the spectral capture of the signals from the adjacent WDM channels. Thus, a specific WDM-VLC model is developed to analyze the effects of the width of OFs on the signal-interference-plus-noise ratio (SINR). After confirming the quasi-concavity of the SINR, the optimal widths of the OFs are determined by SINR maximization using iterative search algorithms considering fixed and mobile WDM-VLC systems. Considering mobile receiver operation, it was confirmed that the maximum SINR points shift, implying the variation in optimal OF width according to the optical powers captured, which vary according to the distance and orientation of the LEDs and/or receivers. Finally, a statistical approach is presented that allows the design of non-adaptive OFs.