M.A. Chavez Tapia
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6 records found
1
Sunlight-based Passive VLC
Utilizing the sun to establish wireless connections
To tackle this challenge, researchers have proposed using a different carrier: visible light. With Visible Light Communications (VLC), devices communicate with each other by modulating the intensity of their light-emitting diodes (LEDs) and demodulating it using light sensors. The key advantage of VLC is the utilization of the visible light spectrum, with free bands that do not interfere with traditional RF systems. Nonetheless, despite the efficiency of LED technology, luminaries still require several Watts to generate light. The need for this considerable amount of energy has triggered interest in a new research area: Passive VLC. The fundamental principle of Passive VLC is to exploit ambient light to create wireless links, thus reducing the energy required by transmitters to generate their own light.
Passive VLC is a promising area, but poses a daring challenge: modulate light without any control over the source. The research community has proposed using optical surfaces that block or reflect light dynamically as modulators, but these platforms provide limited data rates, ranging froma few tens of bps to a few kbps. Moreover, using the sun as the source of ambient light introduces another challenge: variations in position and intensity.
This dissertation aims to improve the performance of Passive VLC systems operating with sunlight, with a particular focus on increasing the data rate and resilience to the changing sun’s position.
Our first contribution is a short-range wireless link using a tiny screen as a transmitter and a camera as a receiver. The screen is a reflective surface, adapted to work with ambient light. The sunlight reaching the screen is modulated to transmit information to a smartphone’s camera, creating a stream of optical data. This screen-to-camera link using sunlight attains up to 10 kbps, ten times faster than previous similar systems, working from sunrise to sunset - independent of the sun’s position.
Inspired by the concept of Li-Fi, which combines illumination and VLC, our second contribution envisions the creation of a natural light bulb with wireless communication capabilities. Our design combines optical modulators, optical filters and sunlight collectors to track the sun’s position during the day and radiate modulated beams of sunlight in indoor scenarios. These beams of natural light provide illumination and communication and are the first to divide sunlight into two color channels to double the data rate.
Our third contribution proposes a novel link for robots to communicate using sunlight. We leverage a material used in solar technology, the Luminescent Solar Concentrator (LSC). An LSC surface absorbs light fromits top and emits it on its edges. We place LSCs on top of robots, together with liquid crystal cells (LCs), so sunlight arriving from the top can be modulated into data packets transmitted toward the edges. This novel communication systemallows task coordination between robots using sunlight.
Overall, this dissertation presents new Passive VLC systems focusing on applications that exploit the sun as the light source. Within this scenario, our focus has been to increase the data rate, with the first two contributions, and on making the systems resilient to the sun’s position, with all three contributions. ...
To tackle this challenge, researchers have proposed using a different carrier: visible light. With Visible Light Communications (VLC), devices communicate with each other by modulating the intensity of their light-emitting diodes (LEDs) and demodulating it using light sensors. The key advantage of VLC is the utilization of the visible light spectrum, with free bands that do not interfere with traditional RF systems. Nonetheless, despite the efficiency of LED technology, luminaries still require several Watts to generate light. The need for this considerable amount of energy has triggered interest in a new research area: Passive VLC. The fundamental principle of Passive VLC is to exploit ambient light to create wireless links, thus reducing the energy required by transmitters to generate their own light.
Passive VLC is a promising area, but poses a daring challenge: modulate light without any control over the source. The research community has proposed using optical surfaces that block or reflect light dynamically as modulators, but these platforms provide limited data rates, ranging froma few tens of bps to a few kbps. Moreover, using the sun as the source of ambient light introduces another challenge: variations in position and intensity.
This dissertation aims to improve the performance of Passive VLC systems operating with sunlight, with a particular focus on increasing the data rate and resilience to the changing sun’s position.
Our first contribution is a short-range wireless link using a tiny screen as a transmitter and a camera as a receiver. The screen is a reflective surface, adapted to work with ambient light. The sunlight reaching the screen is modulated to transmit information to a smartphone’s camera, creating a stream of optical data. This screen-to-camera link using sunlight attains up to 10 kbps, ten times faster than previous similar systems, working from sunrise to sunset - independent of the sun’s position.
Inspired by the concept of Li-Fi, which combines illumination and VLC, our second contribution envisions the creation of a natural light bulb with wireless communication capabilities. Our design combines optical modulators, optical filters and sunlight collectors to track the sun’s position during the day and radiate modulated beams of sunlight in indoor scenarios. These beams of natural light provide illumination and communication and are the first to divide sunlight into two color channels to double the data rate.
Our third contribution proposes a novel link for robots to communicate using sunlight. We leverage a material used in solar technology, the Luminescent Solar Concentrator (LSC). An LSC surface absorbs light fromits top and emits it on its edges. We place LSCs on top of robots, together with liquid crystal cells (LCs), so sunlight arriving from the top can be modulated into data packets transmitted toward the edges. This novel communication systemallows task coordination between robots using sunlight.
Overall, this dissertation presents new Passive VLC systems focusing on applications that exploit the sun as the light source. Within this scenario, our focus has been to increase the data rate, with the first two contributions, and on making the systems resilient to the sun’s position, with all three contributions.
Edge-Light
Exploiting Luminescent Solar Concentrators for Ambient Light Communication
A recent advance in embedded Internet of Things (IoT) exploits ambient light for wireless communication. This new paradigm enables highly efficient links via simple light modulation, but the design space has a fundamental constraint: in most State of the Art (SoA) studies, the link can only follow the propagation direction of ambient light. Consider, for example, a swarm of drones and ground robots that want to communicate with sunlight. Drone-to-robot communication could be possible because sunlight travels downwards from the air (drone) to the ground (robot), allowing drones to modulate light to send information to robots beneath them. Robot-to-robot communication, however, is not possible because sunlight does not travel sideways (parallel to the ground). To allow ‘lateral communication’ with ambient light, we propose using Luminescent Solar Concentrators (LSC). These optical components receive ambient light on their surface and re-direct part of the spectra towards their edges. Considering this optical property of LSC, our work has three main contributions. First, we benchmark various optical properties of LSC to assess their performance for ambient light communication. Second, we combine LSC with liquid crystal (LC) shutters to form lateral links with ambient light. Third, we test our links indoors and outdoors with artificial and natural ambient light, by enhancing two robots with our LSC transceivers and showing that they can exchange basic commands and coordinate tasks by communicating only with sunlight.
There is a growing interest in exploiting ambient light for wireless communication. This new research area has two key advantages: it utilizes a free portion of the spectrum and does not require modifications of the lighting infrastructure. Most existing designs, however, rely on a single type of optical surface at the transmitter: liquid crystal shutters (LCs). LCs have two inherent limitations, they cut the optical power in half, which affects the range; and they have slow time responses, which affects the data rate. We take a step back to provide a new perspective for ambient light communication with two novel contributions. First, we propose an optical model to understand the fundamental limits and opportunities of ambient light communication. Second, based on the insights of our analystical model, we build a novel platform, dubbed PhotoLink, that exploits a different type of optical surface: digital micro-mirror devices (DMDs). Considering the same scenario in terms of surface area and ambient light conditions, we benchmark the performance of PhotoLink using two types of receivers, one optimized for LCs and the other for DMDs. In both cases, PhotoLink outperforms the data rate of equivalent LC-transmitters by factors of 30 and 80: 30 kbps & 80 kbps vs. 1 kbps, while consuming less than 50 mW. Even when compared to a more sophisticated multi-cell LC platform, which has a surface area that is 500 times bigger than ours, PhotoLink's data rate is 10-fold: 80 kbps vs. 8 kbps. To the best of our knowledge this is the first work providing an optical model for ambient light communication and breaking the 10 kbps barrier for these types of links.
SunBox
Screen-To-camera communication with ambient light
A recent development in wireless communication is the use of optical shutters and smartphone cameras to create optical links solely from ambient light. At the transmitter, a liquid crystal display (LCD) modulates ambient light by changing its level of transparency. At the receiver, a smartphone camera decodes the optical pattern. This LCD-To-camera link requires low-power levels at the transmitter, and it is easy to deploy because it does not require modifying the existing lighting infrastructure. The system, however, provides a low data rate, of just a few tens of bps. This occurs because the LCDs used in the state-of-The-Art are slow single-pixel transmitters. To overcome this limitation, we introduce a novel multi-pixel display. Our display is similar to a simple screen, but instead of using embedded LEDs to radiate information, it uses only the surrounding ambient light. We build a prototype, called SunBox, and evaluate it indoors and outdoors with both, artificial and natural ambient light. Our results show that SunBox can achieve a throughput between 2 kbps and 10 kbps using a low-end smartphone camera with just 30 FPS. To the best of our knowledge, this is the first screen-To-camera system that works solely with ambient light.