Passive Visible Light Communication using low-cost colour filters

Abstract

Due to trends such as the Internet of Things, there has been a growing number of devices that use wireless technologies for communication. This increase leads to bandwidth limitations that forced researchers to explore other types of wireless communication. One of these alternatives is Visible Light Communication (VLC). VLC encodes data by rapidly changing the intensity of a source emitting light in the visible spectrum. One branch of VLC is Passive VLC. Passive VLC uses ambient light, such as sunlight or ceiling lamps, as a source. An advantage of this approach is the drastically reduced power consumption. Since the light is already present, no energy has to be used to power a source. However, a flaw of Passive VLC is the lower throughput due to limitations in the available modulation devices. This thesis aims to mitigate the limited throughput by creating separate independent bands that can simultaneously transmit data. Taking advantage of the relatively wide visible light spectrum, the use of colour filters will be explored to divide the spectrum into distinct bands where independent data can be transmitted. To keep it as accessible as possible, there is a focus on low-cost filters, reducing computational complexity and real-time communication. A characterisation of low-cost colour filters is presented as well as a channel estimation algorithm to mitigate the shortcomings of inexpensive filters. To reduce the computational overhead, an encoding algorithm is presented that drastically reduces the computation needed to decode data. Ultimately, we provide a physical platform that achieves multi-channel passive VLC by exploiting cost-effective colour filters. The platform allows for simple expansion to greater numbers of channels as well as real-time communication due to the ability to adjust to the surrounding conditions.