Filter-less WDM for visible light communications using colored pulse amplitude modulation

This paper demonstrates, for the first time, a new wavelength-division multiplexing (WDM) scheme for visible light communications using multi-level coloured pulse amplitude modulation (M-CPAM). Unlike traditional WDM, no optical bandpass filters are required and only a single optical detector is used. We show that, by transmitting n independent sets of weighted on-off keying non-return-to-zero data on separate wavelengths over a line-of-sight transmission path, the resultant additive symbols can be successfully demodulated. Hence, the data rates can be aggregated for a single user or divided into individual colours for multiple user access schemes. The system is empirically tested for M = 4 and 8 using an off-the-shelf red, green and blue (RGB) chip light emitting diode (LED). We demonstrate that for M = 4, using the R and B chips a bit error rate (BER) of ≤10-6 can be achieved for each wavelength at bit rates up to 10 Mbps, limited by the LEDs under test. For M = 8 using R, G and B a BER of ≤10-6 can be achieved for each wavelength at bit rates up to 5 Mbps

Bandwidth Dependency of (O)LEDs on Bias current

This work investigates the modulation bandwidth (Bmod) dependency of organic and non-organic light emitting diodes (OLED\LED) on the applied bias current (IB). The equivalent lumped element transient circuit models are shown with the critical components empirically extracted for both types of device. Four OLEDs of varying sizes are tested in addition to four high power LEDs (white phosphor, red, green and blue). Through analysis of the current-voltage characteristics, the device and dynamic diode resistances are determined as well as the ideality factors. We show that OLEDs have higher ideality factors to the traditional LEDs (almost double) hence the increased turn-on voltage, however have similar AC drive voltage characteristics across the emitting portion of the device between 8-12%. Furthermore, both devices exhibit an increase in Bmod with an increase in IB. It is shown that the OLEDs Bmod increases linearly in relation to IB, reaching =80% of the maximal Bmod at =60% of their maximum IB rating. Conversely, the LEDs display an exponential rise in Bmod in relation to IB, with =80% of the maximal Bmod at =35% of their maximum IB rating, with the red LED showing the greatest results at just 17%

Implementación de un sistema de comunicaciones por luz visible (VLC) basado en FPGA

El crecimiento gradual del uso de LEDs para iluminación en detrimento de las tecnologías de alumbrado tradicionales ha abierto un nuevo campo de investigación en el que las comunicaciones VLC podrían ser una solución ante la escasez del espectro electromagnético disponible.En este trabajo se abordará el desarrollo de las partes analógica y digital básicas necesarias para la implementación de un sistema de comunicaciones por luz visible. Se diseñará en VHDL tanto la etapa de emisión como la de recepción del sistema correspondientes a la parte digital del mismo mediante la utilización de bloques IP, mientras que la parte analógica se montará en primer lugar en una placa de pruebas para, una vez verificado el funcionamiento, desarrollar el sistema en una PCB.<br /