Photovoltaics as high-speed optical wireless communication receiver
With an ever-growing network of billions of interconnected smart devices in the era of the Internet of Things, high-speed communication has inspired research into the use of low energy and high-speed free-space optical (FSO) communication systems. In FSO communication, light-emitting diodes (LEDs) and lasers are used for wireless data transmission in indoor and outdoor environments and photodiodes are used as data receivers. But these receivers have two main disadvantages – they require an external power source to operate, and their small active area makes alignment challenging. A promising solution to these problems is the use of solar panels as data receivers. As photovoltaic (PV) panels have a larger active area compared to that of conventional photodiodes, they relax the strict alignment requirements and can also simultaneously harvest energy from sunlight. The current work investigates the use of Si-based off-the-shelf PV panels as FSO receivers to build an energy-neutral and high-speed FSO system. As solar panels were never built as optical data communication receivers, they have a very small communication bandwidth compared to photodiodes. In this work, a theoretical model of the solar panel is provided and, using analogue equalization, the usable communication bandwidth of a solar panel is extended. PV panels were primarily designed to harvest energy from sunlight. Using the analytical model, simultaneous energy harvesting, and data communication performances are evaluated. Moreover, the trade-off between the energy harvesting and data communication capability of the solar panel is shown. Furthermore, the use of different spectrally efficient modulation techniques such as direct current optical orthogonal frequency division multiplexing (DCO-OFDM) and discrete multitone pulse-amplitude modulation (DMT-PAM) are compared when used with a solar panel as an optical receiver. It has been found that each modulation scheme is usable under different applications. Using the simulated results from the analytical model an FSO prototype was designed and developed, demonstrating the use of solar panels as the receivers. A receiver circuit to interface the solar panel with the FSO system was designed and developed to demonstrate the data communication and energy harvesting performance. Data rates as high as 75 Mb/s is demonstrated using DCO-OFDM and offline processing using an off-the-shelf Si-based solar panel. The PV panel-based FSO system was used to provide internet access to two residential properties on a remote island in the northern part of Scotland. The performance of the prototype was carefully studied under various weather conditions. Furthermore, the maximum user throughput achieved by the prototype is 28.3 Mb/s with the simultaneous energy harvesting capability of up to 4.5 W. Lastly, the design of a custom-built solar panel is proposed which doubles the data rates shown in this work and can be implemented alongside a small-scale to large-scale solar energy harvesting infrastructure.