Physical layer security analysis of a dual-hop hybrid RF-VLC system

In this paper, we investigate the secrecy performance of a dual-hop hybrid radio frequency–visible light communication (RF–VLC) system in which we consider a single source antenna (S) transmitting data signals via RF channel through decode and forward (DF) relay (R) toward an authorized receiving antenna (D) at the destination via VLC channel. In this system, we assume that the eavesdropper (E) attempts to eavesdrop the RF channel (S,R) during transmission of the signal. The relay decodes the incoming RF signal into corresponding optical signal and retransmits toward destination via VLC channel (R,D). The RF and VLC channels of the hybrid system are modelled using generalized-K fading distribution and generalized Lambertian radiant intensity distribution respectively. Also the receiver is assumed to be mobile and its mobility is defined by random waypoint (RWP) model. The channels statistics are used to derive the exact analytical expressions for average secrecy capacity and intercept probability in terms of Meijer’s G-function. The derived closed form analytical expressions are the efficient tool to illustrate the impact of variation in different channel parameters on the secrecy performance, namely, shadowing parameters of RF channel, field of view (FOV), semiangle, and the order of Lambertian emission of the VLC channel. Further, numerical analysis is carried out to support the mathematical analysis of the RF–VLC hybrid system.

Design of a uniform irradiance source based on light emitting diodes

Many applications in various fields require uniform illumination from light sources, for example, in medical imaging in the biophotonics area. In this work, the design and application of an annular light-emitting diode array capable of producing a homogeneous irradiance pattern is presented. As part of the design process, software that allows the simulation of the irradiance pattern as a function of the LED’s radiant intensity distribution, and the position and inclination angle of the LEDs, was developed and validated. Based on the simulation results, a source that produces homogeneous illumination over an area of 20 mm in diameter, where the lowest irradiance is more than 94% of the maximum irradiance, was constructed and tested in real conditions. The simulation method and theoretical calculations on which the array is based can be applied to the design of sources for other applications where a homogeneous irradiance is required.

A Refinement Of The Determination Method Of The Linear low-pressure Uv Lamps Radiant Flux

For the measurement of linear low-pressure UV lamps radiant flux the method proposed by the IUVA, which is based on the Keitz method, has become widely used. For deriving the equation that connects the irradiance generated by a lamp at a close distance and its radiant flux, the authors of the method presume that the lamp is the cylinder of equal radiance. According to our estimates, this assumption leads to the inaccuracy of 3 % to 5 % with respect to goniophotometric measurements. In this research, a general formula is derived that connects the irradiance generated by a linear emitter and its radiant flux. This formula does not impose restrictions on the radiant intensity curve in the longitudinal plane. The Keitz equation is its particularcase. To reduce the inaccuracy of the IUVA method, the angular distribution of the radiant intensity of the UV lamps is proposed to be approximated by a cosine polynomial. In order to find the coefficients of the polynomial,clarify the Keitz formula, as well as to estimate the inaccuracy of the refined and classical versions of this formula, the series of goniophotometric measurements of the DB15, DB18, DB30 lamps at various distances was carried out. It was found that at a scanning step Δθ = 5° the first 9 terms of the trigonometric expansion are sufficient to describe the radiant intensity curve with accuracy satisfactory for practical use. It was also shown that the Keitz method needs to be refined only on the basis of goniophotometric data obtained upon condition r / l ≥ 6 where r is the test distance, l is the lamp length. It was identified that in the case of a differentiated approach, the approximation of the low-pressure UV lamps radiant intensity curve by a cosine polynomial makes it possible to provide an inaccuracy of simplified methods that does not exceed 1 % in relation to the goniophotometric method. It is in dicated that in order to find a universal factor applicable for the entire range of linear low-pressure UV lamps, the development and the analysis of statistical data is required.

Research of the synthesis of radiant intensity indicatrix of multicomponent beam diode module

Widespread use of semiconductor radiation sources in optoelectronic devices for various purposes requires further study of the mechanisms of formation of photometric characteristics of the integrated device in the near illumination zone, where the law of inverted squares is violated. A mathematical model of the multicomponent beam-diode module is proposed. On its basis the analysis of influence of the parameters of separate beam sources on the deformation of the indicatrix of radiant intensity at transition from the far zone to the near one is carried out. It is shown that the determining parameter of the indicatrix change in longitude and polar distance is the distribution in the plane of the modulus of the product of the radiant intensity of a single diode on its polar radius vector. The displacement of the polar angle of the maximum of the vector of the diode radiant intensity is more significant for wide radiation patterns than for concentrated ones. For specific parameters of diodes and geometry of their location the suitability of the proposed model for a priori modeling of beam-diode modules is illustrated.

Generating and Mapping Amazonian Urban Regions Using a Geospatial Approach

(1) background: Urban representations of the Amazon are urgently needed in order to better understand the complexity of urban processes in this area of the World. So far, limited work that represents Amazonian urban regions has been carried out. (2) methods: Our study area is the Ecuadorian Amazon. We performed a K-means algorithm using six urban indicators: Urban fractal dimension, number of paved streets, urban radiant intensity (luminosity), and distances to the closest new deforested areas, to oil pollution sources, and to mining pollution sources. We also carried out fieldwork to qualitatively validate our geospatial and statistical analyses. (3) results: We generated six Amazonian urban regions representing different urban configurations and processes of major cities, small cities, and emerging urban zones. The Amazonian urban regions generated represent the urban systems of the Ecuadorian Amazon at a general scale, and correspond to the urban realities at a local scale. (4) conclusions: An Amazonian urban region is understood as a set of urban zones that are dispersed and share common urban characteristics such a similar distance to oil pollution sources or similar urban radiant intensity. Our regionalization model represents the complexity of the Amazonian urban systems, and the applied methodology could be transferred to other Amazonian countries.

Experimental investigation on efficient heat collection of aboveground pipes

Prospects for low-cost utilization and storage of solar energy are promising. In this study, the change of shallow geo-temperature was monitored, and the influence of solar radiation on shallow geo-temperature was discussed. Three series of field experiments on heat transfer of aboveground pipes were designed, and the variations of water temperature in the aboveground pipes were also monitored. According to the experimental data, the relevant factors affecting the water temperature inside the pipe (such as solar radiant intensity, pipe?s material, pipe?s spatial location, heat-accumulating wall and so on) were analyzed. Based on the field test, a 3-D model of aboveground pipe heat transfer was established to verify and temperature prediction was carried out. The results show that the water temperature in the pipe is most significantly affected by solar radiation, and is also related to the color of the pipe and its spatial position. The water temperature of galvanized steel pipe wrapped with black plastic film is the highest under solar radiation, and the op?timum distance between the pipe and the heat-accumulating wall and the Earth?s surface is, respectively, 0.90~1.25 times of the outer diameter of the pipe. The way the pipe is covered has a great influence on the water temperature inside the pipe. When the black and polyethylene pipe covered with the white plastic film is in the best spatial position, the highest heat of the three series of tests is obtained, and the difference between the water temperature inside the pipe and the atmospheric temperature reaches 36.3?C.

AS-CRI: A New Metric of FTIR-Based Apparent Spectral-Contrast Radiant Intensity for Remote Thermal Signature Analysis

Infrared signature analysis that considers both the target and background is fundamentally important to the development of target detection systems as well as in the design of ships for thermal stealth. This paper presents the analysis results of long-term infrared signature variations in terms of the apparent spectral-contrast radiant intensity measured using Fourier transform infrared (FTIR)-based hyperspectral images. A novel apparent spectral-contrast radiant intensity (AS-CRI) measure is proposed to evaluate the spectral infrared signature accurately at the sensor point of view. The spectral information by AS-CRI can provide the optimal band for either target detection or thermal stealth purposes, considering the background and atmospheric transmittance. In addition, the effects of seasonal and weather variations were analyzed from the long-term hyperspectral image database constructed during 2018.01–2018.08 (three times a day). A TELOPS HYPER-CAM MWE camera was adopted to acquire 374 bands in 1.5–5.5 μm. The automatic weather system (AWS) can provide 24 h weather recordings for the signature evaluation. The experimental results validate the utility of the novel AS-CRI method to find spectral bands for a range of infrared signature applications including small infrared target detection.