Visible Light Communication is a method of wireless communication that avoids the oversaturated frequencies used by radio communication. Prior research typically uses the camera on smartphone for communication, but using a camera is energy-intensive and inefficient. Some alternatives are photodiodes and ambient light sensors, however the former is often not available on phones and the latter is too slow to be useful. This thesis introduces a system, JAB, which combines two sensors to achieve high throughput while keeping energy usage low. The impact of distance, modulation frequency and light are measured on the system implemented on an Android smartphone. Overall, the system is usable and does greatly improve the energy effiency of using VLC. An important next step is creating a custom hardware setup with a kernel driver implementation for a full system test. ... Read more

Visible Light Positioning (VLP) is an emerging field of research with several possible application. While most state-of-the-art VLP systems work with active modulation of light (switching lights on/off rapidly), this poses issues such as the flickering problem and excessive power consumption. In contrast, passive modulation of light (twisting/bending of light), with the properties of polarizers and birefringent materials, allows cost-effective modulation. This paper analyzes two birefringent materials - plastic (cling-wrap) and transparent adhesive tape - to test them for their usability in a visible light positioning system, in particular, the visibility range, hue-orientation mapping, and ambient light interference. These materials allow to create color patterns visible only to a camera. The patterns can encode data about identifiers of light anchors, while the color detected can be used to find the orientation of the receiver. It was observed that transparent adhesive tape gave much more reliable results, with a step-pattern-like hue-orientation mapping, and low errors ($\pm$ 5) on the hue value detected in the range of 30-250 cm from the light anchor, making it ideal for VLP. ... Read more

Visible Light Communication (VLC) is becoming an important research area where Visible Light Sources such as LED, Halogen Lamps and even the sun can be used for Wireless Communication. LED-to-Camera Communication is a form of VLC, where the camera can notice intermittent stimuli changes above a certain threshold frequency (flicker fusion frequency) which human eyes cannot no- tice. There exist numerous methods to encode data (= Modulation Schemes) for LED-to-Camera Communication, however, with some modulation schemes, VLC cannot support any practical appli- cations because the achievable data rate either is too low or the system is difficult to be implemented on off-the-shelf devices.
In this paper, we will propose a system design for LED-to-Camera Communication with Color Shift Keying (CSK) as a modulation scheme to encode the transmitted data. In Color Shift Keying, the sys- tem makes use of colors to encode bits, the receiver will then decode the received color into the corre- sponding bits. The proposed design provides a sys- tem outline which may obtain a more practical data rate by using CSK as a modulation method and a CMOS image sensor as receiver. A CMOS image sensor consists of a matrix of photodiodes which combined make up the captured image. The rolling shutter effect makes use of this matrix-like struc- ture by scanning each line separately, by using the rolling shutter effect the camera captures lines with different colors which can be decoded into bits. ... Read more

Augmented Reality has the potential to expand our interaction with our surrounding environment. A potential solution to improve this interactability is Visible Light Communication through blinking Light Emitting Diodes (LEDs). Data is encoded and then transmitted by blinking the LED, a smart-phone camera is then pointed at the LED to decode the message from the blinking light. The light must blink at a high enough frequency, otherwise the blinking LED causes flicker which has negative health risks. In this research, an experiment is conducted to check the viability of this technology, by transmitting a message to multiple phones with different recording frame rates and checking whether the technology functions adequately for each frame rate. The viability is checked through multiple factors, with the most important one being flicker, due to the negative health risks. If there is no flicker, the throughput of the LED at that frame rate and blinking frequency is checked at multiple distances. The results show that only the highest recording frame rate used in the experiment is viable and that the ones below all cause flicker. This makes it hard to consider the technology viable, due to it only functioning on a limited amount of smartphones. ... Read more

In the recent years, several papers have implemented methods which seamlessly integrate data streams into high frame rate monitors without affecting casual viewer experience. This paper proposes an improvement to existing systems which can in theory increase the data throughput of the data stream several times. Exploiting the same characteristics of human vision as related papers, grid containing different colours is encoded into a video. Testing was conducted to determine the possible uses of this approach. It was determined that 2x or even higher increase is possible however there seems to always be a visual artifact present. The testing also revealed a need for further testing to determine the best possible configuration (amount of colours) to use as well. This testing would also increase the reliability of the data gathered as the experiment was limited by time. ... Read more

In the field of Visible Light Sensing, light sensors are used to extract information from objects which do not actively communicate any information. Previous research within this field proposed the system called SolAR, and proved the possibility of using a solar cell as both a power source and an activity sensor. A wrist mounted solar cell generates more energy than it uses during operation, while achieving a high classification accuracy for different activities. While the wearer performs different activities, the power output of the solar cell fluctuates. In turn, these fluctuations are used to recognise activities. To extend on the concept of SolAR, this paper introduces a prototype to obtain data from different activities while performing day-to-day tasks. During these activities, ordinary actions are performed to emulate natural circumstances. Analysis of this data initially shows no significant drop in accuracy when compared to SolAR. Further examination shows significant differences in mislabelling rates when comparing to the results of SolAR. ... Read more

Visible Light Communication (VLC) has seen drastic improvements in recent years, one approach uses active light sources like LEDs, switching them at hight speeds to send data. Another approach uses the fundamental characteristics of liquid crystals (birefringence and thickness) to transmit data to a single pixel receiver. These characteristics allow for alterations in the color of the light. Little power is being used to transmit this data in comparison with using LEDs, and is significant faster than switching the LCs fully on or off like other research has done. This paper proposes an algorithm to decode the data transmitted by LCs with a high-end smartphone instead of the single pixel receiver. This algorithm called ChromaCam has real time transmitter detection and decoding of data. A demonstration is shown using a prototype, achieving data rates of 31 bits per second. ... Read more

The popularity of various wireless communication applications is crowding the radio spectrum. As an alternative medium, the visible light spectrum is be- ing exploited. Camera-based visible light communication systems are gaining much attention due to the widespread use of smartphones equipped with small embedded cameras. Screens (e.g., liquid-crystal displays) are ideal choices as multi-pixel transmitters that can send high-capacity packets continuously. Al- though there are many works on screen-to-camera links, only very few are ex- ploiting micro-screens as transmitters. State-of-arts are mainly optimizing the performance of the optical link, less attention is paid to the system’s com- pleteness and practical applications. Thus, the goal of this work is to deliver a self-contained visible light communication system that can send information over a micro-screen-to-camera link at a high data rate.
To achieve our goal, an Android application with real-time image reading and processing is developed. Furthermore, a multi-transmitter system is designed to increase the bandwidth of the communication channel and the system is tweaked to transmit information at a high frame rate. The evaluation results show that this work improves the data rate by over 7-fold, from a baseline of 1.5 kbps to 11.4 kbps. Additionally, a standalone prototype is built based on a Raspberry Pi Zero W. Finally, to showcase the potential of the platform, a smart-city application is developed, where users can download information from Google Maps with the newly developed optical link.
Although the result of this project is encouraging, there is much room for improvement. We envision this work will motivate more research near-field, especially on micro-screen-to-camera links. ... Read more