Publication: Implementación de DCO-OFDM mediante SDR
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2017-10
Defense date
2017-10-17
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Abstract
El presente trabajo realiza el estudio y el diseño de un sistema VLC completo,
transmisiones de datos a través del espectro de luz visible, utilizando la técnica de
multiplexación en el dominio de la frecuencia OFDM, con adición de una señal DC
óptica, la cual permite optimizar el uso del espectro a través de ondas subportadoras
ortogonales.
El proyecto está dividido en diferentes secciones que explican los procesos realizados
hasta la definitiva construcción del trabajo.
DCO-OFDM toma como entrada el flujo de bits que se desea transmitir, los agrupa en
símbolos utilizando bien QPSK o 16-QAM. Sobre estos símbolos genera su matriz
Hermítica y posteriormente pasa a trabajar del dominio de la frecuencia al dominio del
tiempo gracias a la transformada inversa rápida de Fourier. Para lograr adaptarse al
sistema óptico transmitiendo valores positivos se adiciona una señal DC óptica al
convencional OFDM.
La implementación del software DCO-OFDM se ha generado utilizando el lenguaje
gráfico de programación LabVIEW y se han realizado las conexiones pertinentes entre
el ordenador maestro y los dispositivos USRP.
En el apartado posterior se realiza el diseño teórico tanto del hardware emisor como del
receptor. El transmisor está formado por un drive conversor voltaje – intensidad, dónde
la señal generada por el USRP, cuya amplitud viene dada en voltaje y corresponde con
la señal DCO-OFDM programada, es transformada a corriente y alimentado al diodo
LED. El receptor por el contario está compuesto por un fotodiodo y un
circuito amplificador de transimpedancia, logrando pasar de las variaciones de luz
capturadas a una señal de corriente, dicha señal es enviada de vuelta al USRP para su
posterior demodulación.
Se concluye el trabajo fin de grado mostrando y analizando diferentes alternativas a la
propuesta seleccionada para esta implementación.
The present work performs the study and design of a complete VLC system, transmissions of data through the visible light spectrum, using the technique of multiplexing in the OFDM frequency domain, with the addition of an optical DC signal, which allows optimizing the use of the spectrum through orthogonal subcarrier waves. The project is divided into different sections which explain the processes carried out until the final construction of the work. DCO-OFDM takes as input the bit stream to be transmitted, groups them into symbols using either QPSK or 16-QAM. On these symbols generates its Hermitical matrix and later it goes away to work from the domain of the frequency to the time domain thanks to the fast inverse Fourier transform. In order to adapt to the optical system by transmitting positive values an optical DC signal is added to the conventional OFDM. The implementation of the DCO-OFDM software has been generated using the Lab VIEW graphical programming language and relevant connections have been made between the master computer and the USRP devices. In the following section, the theoretical design of both the sending and the receiving hardware is carried out. The transmitter is formed by drive converter, voltage - current, where the signal generated by the USRP, whose amplitude is given in voltage and corresponds to the programmed DCO - OFDM signal, is transformed to current and fed to the LED. The receiver on the other hand is composed of a photodiode and a transimpedance amplifier circuit, able to pass from the captured light variations to a current signal, that signal is sent back to the USRP for later demodulation. The End of Grade Work is concluded showing and analyzing different alternatives to the proposal selected for this implementation.
The present work performs the study and design of a complete VLC system, transmissions of data through the visible light spectrum, using the technique of multiplexing in the OFDM frequency domain, with the addition of an optical DC signal, which allows optimizing the use of the spectrum through orthogonal subcarrier waves. The project is divided into different sections which explain the processes carried out until the final construction of the work. DCO-OFDM takes as input the bit stream to be transmitted, groups them into symbols using either QPSK or 16-QAM. On these symbols generates its Hermitical matrix and later it goes away to work from the domain of the frequency to the time domain thanks to the fast inverse Fourier transform. In order to adapt to the optical system by transmitting positive values an optical DC signal is added to the conventional OFDM. The implementation of the DCO-OFDM software has been generated using the Lab VIEW graphical programming language and relevant connections have been made between the master computer and the USRP devices. In the following section, the theoretical design of both the sending and the receiving hardware is carried out. The transmitter is formed by drive converter, voltage - current, where the signal generated by the USRP, whose amplitude is given in voltage and corresponds to the programmed DCO - OFDM signal, is transformed to current and fed to the LED. The receiver on the other hand is composed of a photodiode and a transimpedance amplifier circuit, able to pass from the captured light variations to a current signal, that signal is sent back to the USRP for later demodulation. The End of Grade Work is concluded showing and analyzing different alternatives to the proposal selected for this implementation.
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Keywords
OFDM (Orthogonal Frequency-Division Multiplexing), OFDM-DCO, LabVIEW, Fotodiodo, Comunicaciones ópticas inalámbricas