Pré-ênfase utilizando modulação por largura de pulso aplicada a sistemas de comunicação por luz visível

Abstract

In this work we adress the bandwidth limitation presented in phospor-layered LEDs, which use this layer to generate the white color and are preferred by the industry due to the low cost of production. It is noteworthy that the frequency response of this semiconductor device is between 2 and 3 MHz, limiting the transmission data rate when used in visible light communication systems. From an On-Off signal, a pre-emphasis technique is proposed using pulse-width modulation (PWM), considering a fixed signal-to-noise ratio, to reduce the inter-symbolic interference when transmitting at frequencies above the cut-off frequency of the LED. A measure of the Q factor of the signal using eye diagram was employed, which allows the assessment of the system error rate. Finally, a bit error rate below 10−6 was achieved at a data rate of 36 Mbps, which is considerably higher than the data rate achieved by original system under identical signal quality conditions.