Visible Light Communication Technology Research Articles

Tuning carrier lifetime in InGaN/GaN LEDs via strain compensation for high-speed visible light communication.

In recent years, visible light communication (VLC) technology has attracted intensive attention due to its huge potential in superior processing ability and fast data transmission. The transmission rate relies on the modulation bandwidth, which is predominantly determined by the minority-carrier lifetime in III-group nitride semiconductors. In this paper, the carrier dynamic process under a stress field was studied for the first time, and the carrier recombination lifetime was calculated within the framework of quantum perturbation theory. Owing to the intrinsic strain due to the lattice mismatch between InGaN and GaN, the wave functions for the holes and electrons are misaligned in an InGaN/GaN device. By applying an external strain that “cancels” the internal strain, the overlap between the wave functions can be maximized so that the lifetime of the carrier is greatly reduced. As a result, the maximum speed of a single chip was increased from 54 MHz up to 117 MHz in a blue LED chip under 0.14% compressive strain. Finally, a bandwidth contour plot depending on the stress and operating wavelength was calculated to guide VLC chip design and stress optimization.

Improvement of indoor VLC network downlink scheduling and resource allocation.

Indoor visible light communications (VLC) combines illumination and communication by utilizing the high-modulation-speed of LEDs. VLC is anticipated to be complementary to radio frequency communications and an important part of next generation heterogeneous networks. In order to make the maximum use of VLC technology in a networking environment, we need to expand existing research from studies of traditional point-to-point links to encompass scheduling and resource allocation related to multi-user scenarios. This work aims to maximize the downlink throughput of an indoor VLC network, while taking both user fairness and time latency into consideration. Inter-user interference is eliminated by appropriately allocating LEDs to users with the aid of graph theory. A three-term priority factor model is derived and is shown to improve the throughput performance of the network scheduling scheme over those previously reported. Simulations of VLC downlink scheduling have been performed under proportional fairness scheduling principles where our newly formulated priority factor model has been applied. The downlink throughput is improved by 19.6% compared to previous two-term priority models, while achieving similar fairness and latency performance. When the number of users grows larger, the three-term priority model indicates an improvement in Fairness performance compared to two-term priority model scheduling.

Transmission of Signals Using White LEDs for VLC Application

ABSTRCTIn this paper a photodetector working as an active optical filter device is used to detect modulated visible optical signals for applications based on Visible Light Communication (VLC). The proposed application demonstrates the viability of indoor positioning using VLC technology established by the modulation of indoor ultra-bright RGB white LEDs. The signals of the internal red and blue chips of the white LEDs were modulated at specific frequencies and the generated photocurrent was measured by a pin-pin photodetector based on a-SiC:H/a-Si:H. This device operates as a visible optical filter with controlled wavelength sensitivity through the use of adequate optical biasing light. Thus it is able to detect different wavelengths which allow the detection of the individual components of the tri-chromatic white LED. This possibility is the basis for the indoor location algorithm. We demonstrate the possibility of decoding four transmission optical channels supplied by two different wavelengths of white LEDs modulated under different bit sequences. The identification of the signals received by the photodetector allows the location identification of the photodetector position and supplies indoor navigation.

PSK to CSK mapping for hybrid systems involving the radio frequency and the visible spectrum

This paper presents an efficient technique to map phase shift keying (PSK) signalling to colour shift keying (CSK) constellation, to establish a full link in hybrid systems involving the radio frequency (RF) and the visible spectrum. It fits in systems combining (first link) wireless communication technologies such as the wireless fidelity (WiFi) or wired communication technologies such as power line communications (PLC) to visible light communications (VLC) technology (second link). On the first link, PSK technique is used to convey the information, while, on the second link, a technique based on colour variation is deployed. WiFi standards targeted are those that employ PSK as sub-carrier modulation techniques (IEEE 802.11a/11g/11n). The PSK complex constellation observed at the output of the first link is converted into colours using the hue-saturation-value/intensity (HSV/I) colour models. The constant lighting required in VLC corresponds with the coordinate I of the HSI and the colour constraint is met by assigning adequate current intensities to the red-green-blue LEDs (RGB-LEDs) used. The design meets the requirements of CSK constellation design outlined in IEEE 802.15.7. The performance of the system is analysed through bit error rate curves obtained by simulations, for binary PSK (BPSK) and quadrature PSK (QPSK), 8PSK and 16PSK constellations. The results show that as the constellation size increases, the performance of the system decreases.

Optimized LEDs Footprinting for Indoor Visible Light Communication Networks

Indoor access to the Internet via visible light communication (VLC) technology is becoming an issue and in this sense system planning requires to look at the number of light-emitting diodes (LEDs) to be used. This task can be accomplished by looking at different performance metrics. We consider the problem of optimal footprint mapping by taking into account the achievable user rate when handover procedures take place due to user mobility. This problem is equivalent to the optimal LEDs placement. In this regard, it is shown that several parameters influence system performance starting from the data rate of download, the speed of the user in the room as well the handover time. In this context, we derive a mathematical tool for VLC network planning and show the performance that can be achieved as a function of different parameters.

Evaluation of the Effects of Hidden Node Problems in IEEE 802.15.7 Uplink Performance.

In the last few years, the increasing use of LEDs in illumination systems has been conducted due to the emergence of Visible Light Communication (VLC) technologies, in which data communication is performed by transmitting through the visible band of the electromagnetic spectrum. In 2011, the Institute of Electrical and Electronics Engineers (IEEE) published the IEEE 802.15.7 standard for Wireless Personal Area Networks based on VLC. Due to limitations in the coverage of the transmitted signal, wireless networks can suffer from the hidden node problems, when there are nodes in the network whose transmissions are not detected by other nodes. This problem can cause an important degradation in communications when they are made by means of the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) access control method, which is used in IEEE 802.15.7 This research work evaluates the effects of the hidden node problem in the performance of the IEEE 802.15.7 standard We implement a simulator and analyze VLC performance in terms of parameters like end-to-end goodput and message loss rate. As part of this research work, a solution to the hidden node problem is proposed, based on the use of idle patterns defined in the standard. Idle patterns are sent by the network coordinator node to communicate to the other nodes that there is an ongoing transmission. The validity of the proposed solution is demonstrated with simulation results.

Visible Light Communication: Importance and Thai Preparations

Since the Internet of Thing allows devices to be interconnected across communication networks, the demand for bandwidth in personal communication are growing rapidly as the number of devices increases. Moreover, the location estimation in an indoor environment requires a proper technology because the global positioning system cannot provide satisfactory accuracy. Thus, a visible light communication (VLC) technology is introduced so as to add extra capacity to an existing radio frequency infrastructure. In practice, the VLC can utilize the lighting system infrastructure to transmit data via light intensity together with illumination. Several VLC standards have been published by the visible light communication consortium (VLCC) and the institute of electrical and electronics engineers (IEEE) in 2003 and 2011 respectively. In the past five years, many researchers in Thailand have focused on both VLC basic research and technology implementation. Additionally, the inter-University co-operation known as LED-SmartCon has also been established by ECTI Association to promote the VLC technology in Thailand.

Indoor multi-robot intelligent coordination based on omni-directional visible light communication

Multi-robot coordination (MRC) is a key challenge for complex artificial intelligence systems, and conventional wireless-communication-based MRC mechanisms that cannot be deployed in radio-frequency-limited environments. In this Letter, we present a promising solution that utilizes indoor omni-directional visible light communication (VLC) technology to realize efficient multi-robot intelligent coordination (MRIC). The specific design is presented along with the implemental details of a practical MRIC experimental platform. The experimental results show that a 50 Mb/s on-off-keying-based omni-directional VLC can be realized with an effective distance of 2.3 m and a bit error rate of <10?6 in the proposed MRIC platform.

가시광통신을 이용한 선박 내 위치 기반 응급호출 시스템

Due to metallicity of materials, a vessel has a limitation to adopt RF-based wireless communication technologies for the inner communication means. Visible Light Communication(VLC) can be a sound alternative to dissolve such a limitation. Using a visual light as a transmission medium, VLC is free from radio interferences and restriction of radio usages which are typically related to RF-based wireless communications. In addition, VLC can not only require the facility cost relatively low because of being possibly converged with existing LED illumination, but also be harmless to the human body. This paper proposes an indoor location-based emergency call service system solution for ships using the VLC technology that supports 256Kbps data rate and 5m transmission distance. This paper presents real implementation and testing results of the solution which verifies the propriety of the proposal.

Indoor Positioning System using LED Lights and a Dual Image Sensor

In recent years, along with the rapid development of LED technology, indoor positioning systems based on visible light communication (VLC) have been researched. In this paper, we propose an accurate indoor positioning method using white-light LEDs and a dual image sensor. Indoor LED lights are located at the ceiling in a room and broadcast information on their positions using VLC technology. A mobile device with a dual image sensor receives LED position information by VLC and estimates its position and azimuth angle. Simulation and experimental results are given to show the performance of the proposed indoor positioning system.

Experimental Demonstration of VLC-Based Vehicle-to-Vehicle Communications Under Fog Conditions

Vehicle-to-vehicle (V2V) communication using visible light communication (VLC) technology under fog conditions is presented. Fog is known as one of the most detrimental atmospheric conditions that causes outdoor optical wireless communications to be unreliable. The effect of the fog conditions is experimentally analyzed in the VLC-based V2V system. Recognizing the least attenuation coefficient and a taillight color of a vehicle, a red light-emitting diode (LED) was employed in the experiment. In addition, a Fresnel lens and multiple photodiodes are utilized to efficiently counteract the impairment caused by fog. The experimental results demonstrate that the proposed VLC-based V2V system offers a reliable V2V data transmission over the fog-impaired optical channel with a relatively high signal-to-noise ratio (SNR), even under a heavy-fog condition.

Characterization of the MgO/GaSe0.5S0.5 heterojunction designed for visible light communications

In this study an optoelectronic design is reported and characterized. The device is made of p-type MgO solved in sodium silicate binder and n-type GaSe0.5S0.5 heterojunction. It is described by means of X-ray diffraction, optical absorption and reflection in the incident light wavelength range of 190–1100nm and by means of dark and 406nm laser excited current (I)–voltage (V) characteristics. The optical reflectance was also measured as a function of angle of incidence of light in the range of 35–80°. The structural analysis revealed no change in the existing phases of the device composers. In addition, it was observed that for pure sodium silicate and for a 67% content of MgO solved in sodium silicate binder (33%), the heterojunction exhibits a valence band shift of 0.40 and 0.70eV, respectively. The painting of MgO improved the light absorbability significantly. On the other hand, the angle-dependent reflectance measurements on the crystal displayed a Brewster condition at 70o. The MgO/ GaSe0.5S0.5 heterojunction exhibited no Brewster condition when irradiated from the MgO side. Moreover, for the crystal and the MgO/GaSe0.5S0.5 heterojunction, the dielectric spectral analysis revealed a pronounced increase in the quality factor of the device. The I–V characteristics of the device revealed typical optoelectronic properties with high photo-response that could amplify the dark current 24 times when irradiated with 5mW power laser light. The structural, optical, dielectric and electrical features of the MgO/GaSe0.5S0.5 heterojunction nominate it for use in visible light communication technology.

Scheduling for indoor visible light communication based on graph theory.

Visible light communication (VLC) has drawn much attention in the field of high-rate indoor wireless communication. While most existing works focused on point-to-point VLC technologies, few studies have concerned multiuser VLC, where multiple optical access points (APs) transmit data to multiple user receivers. In such scenarios, inter-user interference constitutes the major factor limiting the system performance. Therefore, a proper scheduling scheme has to be proposed to coordinate the interference and optimize the whole system performance. In this work, we aim to maximize the sum rate of the system while taking into account user fairness by appropriately assigning LED lamps to multiple users. The formulated scheduling problem turns out to be a maximum weighted independent set problem. We then propose a novel and efficient resource allocation method based on graph theory to achieve high sum rates. Moreover, we also introduce proportional fairness into our scheduling scheme to ensure the user fairness. Our proposed scheduling scheme can, with low complexity, achieve more multiplexing gains, higher sum rate, and better fairness than the existing works.

A VLC Based Vehicle Collision Avoidance Scheme for Intelligent Transport Systems

Visible Light Communication (VLC) technology is one of the main candidate solutions for Intelligent Transportation Systems (ITS). This paper presents a comprehensive study on VLC based anti-rear-end collision scheme on the highway. A detailed VLC based rear-end collision avoidance model is proposed with theoretical analysis and numerical simulations.

Three-dimensional light positioning algorithm with filtering techniques for indoor environments

This paper introduces an indoor positioning system based on visible light communication technology with three-dimensional positioning capability. Light-emitting diodes are employed as transmitters, with photodiodes as receivers to obtain the received signal strength (RSS) information. Based on the trilateration technique, the proposed algorithm is able to calculate horizontal coordinates of the receiver with RSS information, after which the height of the receiver is estimated. The system does not require other measurements such as time-of-arrival or angle-of-arrival, thus system design and costs are simplified and minimized. Basic framed slotted ALOHA is applied as the channel access method to enable asynchronous transmissions. In addition, Kalman and particle filters are used in order to realize target tracking. Results show that both filters help to increase the positioning accuracy and the particle filter exhibits a better performance than the Kalman filter, with a higher computational complexity.

Technical Research for Photogrammetric System Using Visible Light Communication(&lt;Feature&gt;New Aspects for the Application of LED Light Sources-Merging with Information Technology and Photonics-)

This technology is the three-dimensional survey system using photogrammetry technique and visible light communication technology, The LED light sources are placed at a position to be measured and stereo-photographed by digital cameras installed in two places. In addition, the relation of same lights in different viewpoints can be automatically done by extracting unique blinking patterns of each light. Experimental results show that this system can provide enough accuracy for construction survey. By using this system, many points can be measured at once, in a short time and in better accurate. For this reason, it can be expected surveyor-saving, suppression of aerial work and improvement of surveying accuracy. In addition, it makes possible to measure three-dimensional coordinates of many points automatically and repeatedly. This system has already been used several bridge construction projects and aluminum dome tank. In this paper, the summary of some projects applied this system are presented.

Modulation and Demodulation Techniques in Indoor Visible Light Communication System

Visible light communication technology is a emerging wireless and optical communication technology developed after invention and application of white LED.In this paper, we have a research based on indoor visible light communication system of lighting white LED,discuss of the visible light communication channel characteristics,detailedly analysis of the indoor visible light communication link. This paper focuses on the modulation and demodulation method applied to visible light communication. In the past visible light communication is mainly used off keying modulation,however, the data transfer speed is limited due to the influence of ISI .This paper presents a solution based on OFDM modulation and demodulation, to reduce the impact brought from inter-symbol string under high data transfer speed.Based on data analysis and computer simulation,the program presented in this paper can be used as indoor lighting and high-speed data transmission.Finally, give scheme to achieve visible light communication modulation and demodulation,provide a theoretical basis for further experiments.

Researching the Information of Transmission Technology Based on Traffic Lights

This design is based on Visible Light Communication Technology, to achieve outdoor visible light communications and image recognition etc. through traffic lights. It will play a role on promoting the utilization of traffic lights. The system uses a LED dot matrix to imitate the traffic light, loading QR Code information on the LED dot matrix and then transporting it in a very high-speed flashing. In receiving terminal, first, webcam OV7670 collects information which from the LED dot matrix, then conveys the picture to FPGA, which is the processor. FPGA will handle the picture by gray scale processing, medium filtering and binary processing at last. Thus, the picture from the LED dot matrix will change to ‘0’ and ‘1’ in binary area. Secondly, as there’s a relationship between LED dot matrix and webcam pixels, we can count how many pixels represent one LED. Finally, we can decode the QR Code based on its own style, and display the final result on the TFT screen.

Visible Light Communications (VLC) for Ambient Assisted Living

With the advent of high efficacy light emitting diode directional lamps as a key component in focal lighting, new possibilities emerge for re-designing the smart home scenario. A smart home scenario is characterized by enabled intelligent interworking of various wireless and wired technologies to provide inhabitants with ease of use of appliances, while creating a personalized and safe ambience space. More and more high and low data rate circulates within the indoor ambient space (e.g., home, hospitals, offices). Although, unlicensed technologies, such as wireless local area networks can take upon part of the indoor traffic, the ever increasing demand for such data, and users, calls for either use of licensed or novel unlicensed wireless communication technologies as part of the smart home enablers. This paper focuses on the potentials of visible light communications (VLCs), jointly with radio and fiber communications, to support very dense low and high data rate connectivity, while enabling deployment of secure-sensitive indoor applications, including indoor tracking and localization. The paper proposes a scenario for integrating VLC into the smart home scenario and a conceptual supporting architecture for its deployment. Further, the technical challenges and possible roadmap for the actual deployment are analyzed for the particular case of an eHealth scenario where the utilization of VLC technology is the enabler of the cost-efficient rollout of the required infrastructure and thus the game-changer in a multi-billion eHealth niche that is seeking for cost affordable solutions.

A High Precision Indoor Positioning System Based on VLC and Smart Handheld

This paper proposes an indoor positioning system based on visible light communication technology and intelligent terminals which equipped with image sensors, electronic compasses and gyroscope sensors. Each LED source is modulated with unique codes which represent its absolute location. The receiving terminal gets the LED’s absolute location through the optical link and capture the scene image with image sensor simultaneously. The electronic compass and the gyroscope sensor measure the terminal’s yaw angle, pitch angle and roll angle in real time, together with the scene image, relative position of the terminal and the LED light source can be calculated. Combine the absolute location of the LED light source with the relative position, the system is able to estimate the terminal’s position within the accuracy of about 2 centimeter. Position accuracy can be improved by using high-precision camera and attitude sensors.