Visible light communication networks for the Internet-of-Things

For the last century, Radio Frequency (RF) technology has completely taken over wireless communication. Nevertheless, the ever-increasing demand and popularity of wireless embedded devices are rapidly consuming the available radio spectrum. The research communities are exploring the other parts of the electromagnetic spectrum to complement the RF frequency bandwidth with the intention to solve the RF spectrum crunch issue. Among the potentially available options, the visible spectrum is a vast and unregulated band that could be effectively used for wireless Visible Light-based Communication (VLC). VLC offers a critical alternative to the spectrum-challenged RF-based forms of data transmission by tapping an unutilized and unregulated frequency band. VLC also possess added advantage of being more safe and secure compare to RF technology. With the evolution of Light Emitting Diode (LED) technology, now LEDs are more cost and energy effective, higher switching rates, and modulated at comparable rates to radio-frequency technologies. The advancement in LED technology is a significant step towards VLC. VLC applications include wireless sensor networks, indoor localization, smart homes, vehicular networks etc. VLC systems could be used in conjunction with tradi- tional RF-based devices to build networks with higher robustness, throughput, and spectrum efficiency. Furthermore, the seamless integration of VLC transceivers with traditional illumination devices can result in pervasive deployment. Hence, hybrid RF/VLC systems can provide an effective solution for the ubiquitous networking required by IoT deployments. Carefully designed low-cost VLC devices have the potential to enable the Internet of Things (IoT) at scale by reducing the current RF spectrum congestion, which is one of the major obstacles to the pervasiveness of the IoT. To bring the vision of illumination and communication in visible lights closer to reality, we need to identify the key challenges for reliable communication in a noisy indoor environment. However, the wide adoption of VLC devices is hindered by their current shortcomings, including low data rate, very short-range, and inability to communicate in a noisy environment. In this regard, we propose a new software-defined VLC prototype named VuLCAN for Visible Light Communication And Networking that overcomes these limitations. VuLCAN is based on an ARM Cortex M7 core microcontroller with a fast sampling analog-to-digital converter and power-optimized Digital Signal Processing (DSP) libraries. Using BFSK modulation, the prototype achieves a data rate of 65 Kbps over a communication range of 4.5 m comparable to the state-of-the-art prototypes. VuLCAN also provides robust and reliable communications in highly illuminated environments (up to 800 lux) using only a low power Light Emitting Diode (LED), largely exceeding the capabilities of current state-of-the-art prototypes. So far, the main focus of the research in VLC has been on the PHY layer, and less attention has been paid on the higher network layers. Studies and work on MAC/routing layers for VLC demands a new set of performance analysis tools. Simulations are useful for performance analysis in testing different setups and scenarios repetitively and optimally in terms of time and cost. We have extended the GreenCastalia simulator to implement the wireless VLC channel and VLC RADIO layer. It is based on the Lambertian model for intensity-modulated point-to-point LED signals in indoor scenarios and the specifications of the VuLCAN prototype. There is a need to explore more sophisticated networking approaches to unleash the potential of VLC for IoT applications and networking. There has been limited work on MAC protocols for VLC with restricted topologies like a star, broadcast, and peer-to-peer and cannot be extended easily to distributed ad-hoc networks. The MAC schemes proposed are mostly inherited directly from RF communication without much modification. Being complementary to RF, the issues in the MAC layer for VLC like directionality, hidden nodes, and blockage need to be adequately addressed. In this work, we study the limitations of RF MAC protocols when applied to VLC systems. We design and implement a novel MAC layer protocol, named Li-MAC, along with the neighbor discovery scheme considering the directional nature of VLC and its challenges. As a summary, in this thesis, we push the envelope of existing low-end embedded VLC design towards pervasive networking and expands the range of applications of VLC for IoT.