Both Visible Light Communication (VLC) and Optical Camera Communication (OCC), as technologies and applications of the Optical Wireless Communication (OWC), have been intensely investigated in recent years. Because of their advanced implementations prove to be reliable candidates as partners of the various wireless transmissions based on radio frequency waves, and in some special situations, principal actors for different wireless communication scenarios in particular situations such as the medical field, petrochemical industry or indoor spaces overcrowded where the radio frequency spectrum crunch becomes obvious. We analyze several indoor setups and unique situations that incur alleged security breaches and future challenges in secure VLC and OCC data communication. We also present here an investigation of topologies and transmission scenarios with influences on a secure, reliable wireless transmission system as well as vulnerabilities and threads in VLC and OCC networks. The optical properties of the visible light as a reliable communication medium are explored here, as well. Both VLC and OCC have their own benefits, as well as drawbacks, from the point of view of the overall security and performance, as well as the ability to keep the communication as a continuous operational, intact, and trusty service. An experiment conducted using low frame rate cameras in OCC shown the minimum distance between the centers of the LEDs that still allow an appropriate separation of the frames captured.
As time passes, the optical wireless communication systems (OWC) are seeing more and more technological advancement. The complete replacement of conventional lighting with LED based solutions seems to be in sight. Technology and its development always match the world's current needs, and as the whole economy is shifting towards ecology and sustainability, moving towards low consumption LEDs would seem to be a good approach. The LED's ability to switch on and off at a fast rate enables the possibility of developing new optical communication systems. In Visible Light Communication (VLC) systems, the LEDs represent the transmitter and the photodetectors represent the receiver. A similar technology to VLC, known as Optical Camera Communications (OCC) uses image sensors as the receiver. The paper investigates the performances of different OWC technologies and provides a detailed overview of the areas and applications in which they can be found.
With the emergence of LEDs, the conventional incandescent or fluorescent lighting solutions tends to be replaced by LED lighting systems. Historically, the lighting system was invented before radio communications, therefore its infrastructure is more widespread and simpler. One property of the conventional lighting sources is that the optical radiation emitted by them cannot be switched on and off fast. In the latest trends in high-speed communication, LED lighting solutions are used to transfer data. This field is known as Visible Light Communications (VLC). In previous work, the authors investigated the available bandwidth of four power LEDs1 that could be used for VLC systems. A typical low pass filter cutoff frequency identification procedure was used. For a complete characterization, the authors propose to determine the available bandwidth by investigating the switch-on time. The paper investigates the response time of power LEDs by studying four different LEDs: green, red, infrared and white. The LED driver circuit was especially designed for this application because it required very fast switch-on time.
In the context of a hybrid continuous-discrete time chaos-based secret communication scheme, the present work replaces the non-linear element of a known jerk-type chaotic system, with a LED. The circuit is simulated in Matlab-Simulink and its behavior analyzed when switching the control parameter - the value of one of the resistors in the scheme. The cases illustrated are relevant for emphasizing the route towards randomness. This is achieved through period-doubling starting from the initial period of the signal corresponding to the LED’s output power, which depends on the value of the control parameter. This paper also presents an experimental implementation of the proposed modified Sprott’s jerk-type circuit, as well as a comparison between simulation and empirical results. Qualitative and quantitative interpretations of bifurcation diagrams and Lyapunov exponents for the two situations are to be compared in a future research.
The electroluminescent panel is a light emitting device that requires for normal operations alternative voltages with peak to peak amplitudes in 100V… 300V range and frequencies in 100Hz … 2 kHz range. Its advantages, when compared with standard light sources like incandescent lamps, gas-discharge lamps or light emitting diodes (LEDs), are lower power consumption, flexible substrate and uniform light without observable luminous points. One disadvantage of electroluminescent panels is the complex power supply required to drive them, but the continuous improvement in passive and active integrated devices for switched mode power supplies will eventually solve this issue. The present paper studies different topologies for these power supplies and the effect of the electric parameters like the amplitude, frequency, waveform of the supplying voltage on the light emission and on power consumption for electroluminescent panels with different size and colors.
This paper continues our investigations in relatively new developed printed electrochromic displays (ECDs). There are some advantages of ECDs that recommend them for specific low end and short time disposable display applications, for instance the ECD devices present low power consumption (they are non-emissive, reflective, i.e. passive) and have a good viewing angle, looking like ink on paper. It is to note that these displays are still in research, and partly present on the market. There are a lot of papers regarding the chemistry and electro-chemistry of the device, but very few about concrete schematics for driving these displays. Due to their low penetration in applications, and due to lack of standardization, there are not yet realized custom drivers in form of integrated circuits. The driving of these circuits is not at all so simple. These are very sensitive devices in what it concerns exceeding the drive pulse duration and voltage level. In order to take full advantage of the low power consumption of this device, a good driver circuitry needs to be realized also in the “low power” class. We propose in this paper an original driving circuit, that has very low consumption and that can be even supplied by a supercapacitor or by a printed battery. The whole structure can be further integrated as a system on foil.
The paper presents a steganographic method which hides a secret message in a video flow. The secret message represents the result of a chaos-based encryption scheme. One of the flaws which make the algorithm unpractical for real-time applications is that, while the elements of the plain-message are represented using 8 bits (ASCII characters) the corresponding encrypted values need to be represented using 16 bits. Since the pixels of a typical image are represented using 24 bits (8 bits for each color component), each encrypted character fits in only one pixel. Moreover, since the resolution of today’s video materials is very large, the pixel previously established to carry in its evolution the hidden content will not be obvious to unaware spectators, but only to the one which knows its coordinates. In addition to the steganographic procedure, the work presents preliminary results on the degree of pseudo-randomness of video flows. The study is based upon the idea behind Lyapunov exponents. The evolution of two pixels which initially differ only by the minimum possible value (the color representation’s resolution) is followed for a large number of video frames. The distance between such points, for pseudo-random behavior, is known to evolve over time in a Gaussian manner. A Kolmogorov-Smirnov statistic is computed and illustrated in order to conclude over the provenience of the data series representing the evolution of the distance between the two initially neighboring pixels from a standard normal law.
The paper presents the experiments performed in order to determine the most suitable measuring mode which could be used to notably increase the accuracy of the photometric parameters determination for a white LED using a light meter with multiple measurement modes for various classic light sources like tungsten (incandescent), fluorescent, mercury and sodium based. Light meters are used for measuring the illuminance, which is a photometric parameter and its determination is based on the properties of human sight sense. Knowing how the sensitivity of the eye varies with the wavelength, the spectral response of the sensor and the spectral composition of the radiation emitted by a certain light source, a correction curve can be applied over the sensed values and obtain an accurate measurement. Nowadays many light meters can contain multiple calibration curves for typical light sources, but not for LEDs, especially for white ones. Since multiple measurements can be done using each correction curve, the authors conducted experiments to determine how to combine the aforementioned results to obtain a good estimate for the illuminance of white LEDs.
In many situations audio recordings can decide the fate of a trial when accepted as evidence. But until they can be taken into account they must be authenticated at first, but also the quality of the targeted content (speech in most cases) must be good enough to remove any doubt. In this scope two main directions of multimedia forensics come into play: content authentication and noise reduction. This paper presents an application that is included in the latter. If someone would like to conceal their conversation, the easiest way to do it would be to turn loud the nearest audio system. In this situation, if a microphone was placed close by, the recorded signal would be apparently useless because the speech signal would be masked by the loud music signal. The paper proposes an adaptive filters based solution to remove the musical content from a previously described signal mixture in order to recover the masked vocal signal. Two adaptive filtering algorithms were tested in the proposed solution: the Normalised Least Mean Squares (NLMS) and Recursive Least Squares (RLS). Their performances in the described situation were evaluated using Simulink, compared and included in the paper.
The idea of having flexible, very thin, light, low power and even low cost display devices implemented using new materials and technologies is very exciting. Nowadays we can talk about more than just concepts, such devices exist, and they are part of an emerging concept: FOLAE (Flexible Organic and Large Area Electronics). Among the advantages of electrochromic devices are the low power consumption (they are non-emissive, i.e. passive) and the aspect like ink on paper with good viewing angle. Some studies are still necessary for further development, before proper performances are met and the functional behavior can be predicted. This paper presents the results of the research activity conducted to develop electric characterization platform for the organic electronics display devices, especially electrochromic displays, to permit a thorough study. The hardware part of platform permits the measuring of different electric and optical parameters. Charging/discharging a display element presents high interest for optimal driving circuitry. In this sense, the corresponding waveforms are presented. The contrast of the display is also measured for different operation conditions as driving voltage levels and duration. The effect of temperature on electrical and optical parameters (contrast) of the display will be also presented.
Organic photovoltaic cells represent a major application of Flexible Organic and Large Area Electronics (FOLAE) field. The advantages of these cells are represented by flexibility and reduced thickness, making them easy to be integrated in electronics designs, removing the necessity of having a large, flat, heavy surface for energy harvesting. Although many studies about the structure1 and chemical reactions that occur exist, not a large amount of information is available about the characteristics that would be useful for an electronics engineer designing an electronic system. This paper presents the investigations of the electrical2 and thermal behavior of OPV cells, offering as results the optimal operating conditions and their evaluation using a comparison with the standard, semiconductor-based cells. Thermal characterization is very important because the targeted light source is the sun. By exposing the panels to sunlight in a summer day will greatly increase the working temperature of the cells, implying the necessity of knowing the impact on their electrical characteristics. The response of the cells at different wavelengths of the incident light, voltage vs. current and output voltage diagrams for different light intensities and different temperatures will be determined. In addition, the behavior of the cell as a light sensor will be investigated and a system that uses organic electronics at both ends: for sensing light intensity and also displaying this information will be built, using an electrochromic display.
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