Closed form approximation of the actual spectral power emission of commercial color LEDs for VLC

Publisher Copyright: IEEEMulti-color Light-Emitting Diode (LED) technology enables a simple approach to increase the throughput of a Visible Light Communications (VLC) system, by using Wavelength-Division Multiplexing (WDM) to transmit independent data streams on different colors. However, to compute the data rate that is achievable in such WDM VLC link, the optical power that leaks between the different colors in the form of crosstalk interference needs to be estimated accurately, especially when low-cost optical filters are used to separate the parallel data streams in reception. So far, the approximations that have been reported in the literature to model the spectral power emission of different color LEDs are not good enough to perform these calculations. Starting from the theoretical spectral emission of a color LED, a closed form expression is derived based on an asymmetric Pearson type VII function, which is shown to approximate accurately the measured spectral emission of different color LEDs at different working regimes. In addition, the effect that the DC-bias current has on the key parameters of the approximated spectral power emission of the color LEDs, namely the peak and half-maximum wavelengths, as well as the peak spectral emission, are studied. Finally, a new approach is proposed to assess the level of fitness of the derived closed form approximations, using for this purpose the step-size of the MacAdam ellipses that corresponds to the different color LED spectral emissions in the CIE 1931 chromaticity diagram.Peer reviewe

Reflection-based Relaying Techniques in Visible Light Communications: Will It Work?

Visible Light Communication (Vlc) Is Capable Of Satisfying The Escalating Data Rate Demand In Indoor Scenarios. The Lighting Infrastructure May Also Be Exploited In The Downlink Of A Wireless Local Area Network (Wlan), Where Light-Emitting Diodes Are Used For Transmitting Information. The Backhaul Of Vlc Access Points (Aps) Constitutes A Potential Bottleneck In Wlans, Especially In Large Rooms Where The Number Of Aps Is High. Thus, An Alternative Reflection-Based Cooperative Wireless System Concept Is Proposed, Where No Wired Connections Are Required For Connecting The Aps. Then, Its Data Rate Analysis Is Developed Based On The Signal-To-Noise Ratio Attained. The Results Show That The Performance Of The Cooperative Wireless System Advocated Closely Approximates The Performance Of The Traditional Wired Backhaul. Finally, We Demonstrate By Using Jain&#39 S Index Of Fairness That The Proposed Scheme Provides Fair Coverage Quality For All Users

Downlink performance of optical OFDM in outdoor visible light communication

Visible light communication (VLC) is a promising ubiquitous design alternative for supporting high data rates. Its application has been primarily oriented to indoor scenarios, but the proliferation of light-emitting diodes in the streets warrants its investigation in outdoor scenarios as well. This paper studiesthe feasibility of VLC in a conventional outdoor scenario, when optical orthogonal frequency division multiplexing techniques are employed. The presence of sunlight reduces the system�s performance, hence sophisticated adaptive techniques must be applied. Closed-form expressions of the signal-to-noise ratio and of the mean cell data rate are derived and our simulations demonstrate their accuracy. Besides, the outage probability when adaptive modulation and coding schemes are employed is analytically expressed. It isshown that, when modulation bandwidth adaptation is carried out depending on the time of day and the illuminance from ambient light, the mean cell data rate is increased and the outage probability is reduced.<br/

Telerescuer - reconnaissance mobile robot for underground coal mines

The paper describes conception of a reconnaissance mobile robot TELERESCUER for inspecting underground coal mine areas affected by catastrophic events. The introduction describes the whole project background and the following sections deal with the design of the control system and communication between individual subsystems. The subsystems described include the motion subsystem, the sensory subsystem (temperatures, gas concentration, air flow, navigation and cameras), the subsystem for 3D map data acquisition and the communication subsystem. Mentioned also is the ATEX implementation (where the robot can safely operate in an environment with dangerous concentrations of methane)

Filtering Visible Light Reflections with a Single-Pixel Photodetector

Light-based positioning systems (LPS) are gaining significant attention as a means to provide localization with cm accuracy. Many of these systems estimate the object position based on the received light intensity, and work properly in 'ideal' environments such as large open spaces without obstructions around the light-emitting diode (LED) and the receiver, where reflections are negligible. In more dynamic environments, such as indoor spaces with moving people and city roads with moving vehicles, materials cause a wide variety of reflections. This causes variations in the received light intensity and, as a consequence, gross localization errors in LPS. We propose a new multipath detection technique for improving LPS that does not require the knowledge of the channel impulse response and then, it is suited to be implemented in low-cost positioning receivers that use a single-pixel photodetector. To develop our technique, we (i) analyze the statistical properties of non-line-of-sight (NLOS) components, (ii) develop an automated testbed to study the reflections of different types of surfaces and materials, and (iii) design an algorithm to remove the NLOS components affecting the positioning estimate. Our experimental evaluation shows that, in complex environments, our methodology can reduce the localization error using LEDs up to 93%. Embedded and Networked System