Free Space Optical (FSO) systems offer tremendous channel capacity, which can significantly contribute to the bandwidthhungry next generation networks. FSO technology is certainly highly vulnerable to atmospheric Mie scattering, which leads to severe degradation of the established optical communication link. To address this key-issue, the current paper is focused on detailed investigation of the fog effect using artificially built fog environment. Low-visibility conditions are adjusted within a 50 m long corridor covered with PVC and including two artificial fog machines and a signal flare. The Particle Size Distributions (PSDs) of the simulated fog are measured with a sophisticated and so-called “Spraytec” device provided by Malvern Instruments Company. Once the main characteristics of the artificial fog are assessed, the measurements are compared with an empirical estimated fog model using modified gamma function. The comparison is accomplished in terms of theoretically defined PSDs where both radiation as well as advection fog modelling are taken into account. In order to calculate the relevant FSO channel attenuation only based on our measured fog PSDs, Mie theory is applied. For this purpose, Mie scattering efficiencies of a fog water sphere with arbitrary radius and refractive index are shown and examined. Respectively, apart from the presented figures with comparison of various PSDs, also the specific attenuation in dependence on fog particles size is introduced and discussed. Taking into account that particle density of the artificial fog can be manually setup in accordance with the applied theoretical models, our simulations offer attenuation up to 210 dB/km in the presence of continental moderate and dense fog effects. Consequently, we have the possibility to simulate significantly well various fog conditions in artificially simulated environment.
Optical Wireless Communication (OWC) systems rapidly increase their importance in very long-distance deep space communication scenarios. However, the high performance requirements of deep space OWC systems demand preliminary experiments which are unmanageable in real conditions. Regarding this issue, an innovative approach for testing deep space optical communication links in controlled laboratory environment is developed. The proposed testbed is based on fibre optics technology and combines various modules which represent a real deep space OWC link. Similar to already demonstrated deep space missions, the implemented optical receiver is Superconducting Nanowire Single- Photon Detector (SNSPD) characterized with single photon sensitivity and high detection efficiency. Consequently, in this paper an authentic deep space Poisson channel is emulated and examined. The given theoretical description of the Poisson process is supported by real SNSPD measurements in terms of high efficient single photon detection. The provided measured graphs clearly show the operation of SNSPD. In addition, a variable optical attenuator (VOA) is applied as a main device emulating the tropospheric part of a deep space optical Poisson channel characterized predominantly by Mie scattering (fog and clouds) and turbulence effects. This OWC channel emulator also contains self-developed software and attenuator control unit based on external Digital Analog Converter (DAC). Moreover, the response time parameter of channel emulator is examined in detail. Two different times in terms of reaching the lowest and the highest allowed attenuation are measured and shown. Finally, the developed channel emulator is tested and evaluated under real attenuation data. The experimental results show that the proposed method can evaluate various deep space optical scenarios.
Visible light communication (VLC) has been extensively studied for car-to-car (C2C) communication due to its inherent benefits. It is the idea of using light-emitting diodes for both illumination and data communications. The main motivations are longer lifetime of high-brightness light emitting diodes (LED) and growing popularity of the solid state of lighting sources compared to other sources of artificial light. These two features have made a whole range of developing applications such as C2C communication since the level of reliability and power efficiency offered by LED are excellent compared to the traditional incandescent light sources used for lightning. Car industry and automobile lighting market are more and more motivated also to use Laser diodes instead of LED because of higher intensity (Power). Fiber Laser and Glass Photonics could be the next generation components for carto-car VLC. This paper presents the main features of physical layer for VLC based on the IEEE 802.15.7 standard including useful Modulations, Forward Error Correction Coding for single light source also a comparison to wireless RF-Technology and different weather influences are considered. These aspects would also be of main interest for safety, availability and security for autonomous driving in the future applications