Design and implementation of a tuned Analog Front-End for extending VLC transmission range

Visible Light Communications (VLC) is currently considered one of the most promising Optical Wireless Communications (OWC) for commercial applications, due to the widespread deployment of Light Emitting Diodes (LEDs) for energy efficiency, durability and low cost. With the ability to provide several THz of bandwidth, VLC is expected to co-exist with legacy and future Radio Frequency (RF) media as a reliable solution to the rapid demand of high-speed wireless communication. Most current research on VLC is focused on achieving high data rates over short distances through various types of modulation schemes. Limited research work investigates long range VLC employing high power LEDs, while none of them employed analog filter design in the receiver side while using low power LED for transmission. This thesis work explores the design and easy implementation of a low cost visible light communication system for long-range applications. The main idea of the research is increasing the receiver sensitivity by employing an analog filtering stage within the receiver front-end while the transmission is carried out using a low-power commercial white light LED, enabling the system to provide both illumination and digital communication. The proposed VLC front-end employs a high gain, high Quality (Q) factor band pass filter with the Multiple Feed Back (MFB) topology, which operates at a defined centre frequency range. The proposed MFB active filter uses the gain of the operational amplifier at the defined transmission frequency maximizing the gain and therefore extending the transmission range. The band pass filter behaves as a resonant circuit which detects the desired signal at the transmitting centre frequency and rejects unwanted frequencies including ambient light noise frequencies. Two modulations schemes were used through this work On Off Keying (OOK) with Manchester encoding, and Pulse Width Modulation (PWM). To evaluate the viability of the proposed system several prototypes were designed, implemented and tested. Experimental results demonstrated that by employing the proposed front-end the transmission range could be extended up to 2m distance by Manchester coding and up to 5m by using PWM. Moreover, the proposed system showed robustness against ambient light interference under the indoor scenario. Another Arduino prototype was designed and implemented to test the ability of the system to transmit serial data between two PCs. Experimental results demonstrated that the filtering stage is able to improve the receiver sensitivity and extend the transmission distance however, only data rates below 1 kbps were read by the receiver Arduino due to low procession speed of the Arduino boards.