Combined effect of turbulence and aerosol on free-space optical links

[EN] Despite the benefits of free-space optical (FSO) communications, their full utilization is limited by the influence of atmospheric weather conditions, such as fog, turbulence, smoke, snow, etc. In urban environments, additional environmental factors such as smog and dust particles due to air pollution caused by industry and motor vehicles may affect FSO link performance, which has not been investigated in detail yet. Both smog and dust particles cause absorption and scattering of the propagating optical signal, thus resulting in high attenuation. This work investigates the joint impact of atmospheric turbulence and dust particle-imposed scattering on FSO link performance as part of the last-mile access network in urban areas. Propagation of an optical wave is at first analyzed based on the microphysic approach, and the extinction caused by small particles is determined. An experimental measurement campaign using a dedicated test chamber is carried out to assess FSO link performance operating wavelengths of 670 nm and 830 nm and under dust and turbulent conditions. The measured attenuation and the 𝑄Q factor in terms of the velocity of particle flow and turbulence strength are analyzed. We show that for an airflow of 2 m/s, the 𝑄Q factor is almost 3.5 higher at the wavelength of 830 nm than at 670 nm. However, for a wavelength of 670 nm, the FSO link is less affected by the increase in airflow compared to 830 nm. The 𝑄 factor reduces with turbulence. Under similar turbulence conditions, for ash particles, the 𝑄Q factor is higher than that of sand particles.European Social Fund (ESF) (CZ.1.07/2.3.00/30.0034); Ministerio de Economia y Competitividad (MINECO) (JCI-2012-14805); European Cooperation in Science and Technology (COST) (IC 1101); Ceske Vysoke Uceni Technicke v Praze (CVUT) (SGS14/190/OHK3/3T/13).Libich, J.; Perez, J.; Zvanovec, S.; Ghassemlooy, Z.; Nebuloni, R.; Capsoni, C. (2017). Combined effect of turbulence and aerosol on free-space optical links. Applied Optics. 56(2):336-341. https://doi.org/10.1364/AO.56.000336S336341562Khalighi, M. A., & Uysal, M. (2014). Survey on Free Space Optical Communication: A Communication Theory Perspective. IEEE Communications Surveys & Tutorials, 16(4), 2231-2258. doi:10.1109/comst.2014.2329501Wang, C.-X., Haider, F., Gao, X., You, X.-H., Yang, Y., Yuan, D., … Hepsaydir, E. (2014). Cellular architecture and key technologies for 5G wireless communication networks. IEEE Communications Magazine, 52(2), 122-130. doi:10.1109/mcom.2014.6736752Parca, G. (2013). Optical wireless transmission at 1.6-Tbit/s (16×100  Gbit/s) for next-generation convergent urban infrastructures. Optical Engineering, 52(11), 116102. doi:10.1117/1.oe.52.11.116102Kedar, D., & Arnon, S. (2004). Urban optical wireless communication networks: the main challenges and possible solutions. IEEE Communications Magazine, 42(5), S2-S7. doi:10.1109/mcom.2004.1299334Awan, M. S., Horwath, L. C., Muhammad, S. S., Leitgeb, E., Nadeem, F., & Khan, M. S. (2009). Characterization of Fog and Snow Attenuations for Free-Space Optical Propagation. Journal of Communications, 4(8). doi:10.4304/jcm.4.8.533-545Nauerth, S., Moll, F., Rau, M., Fuchs, C., Horwath, J., Frick, S., & Weinfurter, H. (2013). Air-to-ground quantum communication. Nature Photonics, 7(5), 382-386. doi:10.1038/nphoton.2013.46Perez, J., Zvanovec, S., Ghassemlooy, Z., & Popoola, W. O. (2014). Experimental characterization and mitigation of turbulence induced signal fades within an ad hoc FSO network. Optics Express, 22(3), 3208. doi:10.1364/oe.22.003208Kim, I. I., McArthur, B., & Korevaar, E. J. (2001). Comparison of laser beam propagation at 785 nm and 1550 nm in fog and haze for optical wireless communications. Optical Wireless Communications III. doi:10.1117/12.417512Rekab-Eslami, M., Esmaeili, M., & Aaron Gulliver, T. (2017). Generic Linear Network Code Construction Using Transversal Matroids. IEEE Communications Letters, 21(3), 448-451. doi:10.1109/lcomm.2016.2619706Corrsin, S. (1951). On the Spectrum of Isotropic Temperature Fluctuations in an Isotropic Turbulence. Journal of Applied Physics, 22(4), 469-473. doi:10.1063/1.1699986Ghassemlooy, Z., Le Minh, H., Rajbhandari, S., Perez, J., & Ijaz, M. (2012). Performance Analysis of Ethernet/Fast-Ethernet Free Space Optical Communications in a Controlled Weak Turbulence Condition. Journal of Lightwave Technology, 30(13), 2188-2194. doi:10.1109/jlt.2012.2194271Clifford, S. F., Ochs, G. R., & Lawrence, R. S. (1974). Saturation of optical scintillation by strong turbulence*. Journal of the Optical Society of America, 64(2), 148. doi:10.1364/josa.64.00014

A Free Space Optic/Optical Wireless Communication: A Survey

The exponential demand for the next generation of services over free space optic and wireless optic communication is a necessity to approve new guidelines in this range. In this review article, we bring together an earlier study associated with these schemes to help us implement a multiple input/multiple output flexible platform for the next generation in an efficient manner. OWC/FSO is a complement clarification to radiofrequency technologies. Notably, they are providing various gains such as unrestricted authorizing, varied volume, essential safekeeping, and immunity to interference.

An Improved Transmission Equation under Environmental Influences

Radio frequency (RF) communication channel severely suffers from tropospheric scintillation fading caused by the dynamic nature of the atmospheric conditions thereby impairing i ts performance and availability : this induced channel fading effect must be accounted for in the link transmission equation. In this paper, we have proposed an improved transmission link equation by taking into account scintillation fading effect a nd magnitude of the refractive - index structure parameter that play very important role in l inks calculations. This transmission model provides the basis for communication engineers a platform to work with in the link budgetary for planning and design of lo w margin systems of free space communication lin

An Assessment on the Requirements for Deep Space Optical Communications

Over the last decade, terms such as big data and IoT have become part of our everyday vocabulary, and as time goes by, more and more systems are collecting larger amounts of data in order to provide new services or improve quality, and aerospace sector is not an exception. Space probes and rovers, which originally communicated with ground stations using S-band, have moved to higher frequencies in order to be able to transmit more information per unit of time. As the frequency of the system increases, the optical band is reached, 40 years ago, the first experiment in aerospace to demonstrate laser communication, the Airbone Flight Test System (AFTS), was conducted. Numerous efforts have been made to demonstrate that optical communications are possible. When sending an exploration mission, the scientific community maximises the performance of the instruments by taking into account multiple criteria, such as whether the particular device has been previously tested in space and the likelihood of failure. Therefore, the use of new technologies requires a process of multiple demonstration missions prior to be accepted. This thesis compiles the state of the art, i.e. the knowledge acquired over the last four decades, and covers three main points: ground infrastructures, the flight terminal and the method of communication between both systems. In the first point, the study focuses on explaining the parameters that must be taken into account when designing an international ground station network, equivalent to its counterpart in the RF band, NASA’s DSN networks or ESA’s ESTRACK, among others. One of the most relevant variables that determines the location of a ground stations are the atmospheric conditions. For this reason, a series of files containing information about the planet’s atmosphere has been downloaded and processed from NASA’s LAADS DAAC database. Secondly, the link equation of a signal emitted in optical band has been studied. Each of the terms that make up the equation are presented in detail in several sections, in particular the obscuration losses in Cassegrain type antennas, the pointing losses and those due to atmospheric absorption and turbulence. Finally, two practical studies have been carried out in which it is possible to see how the mathematics described in the previous chapters have been applied to execute missions whose purpose is to communicate in deep space. To achieve this, the JPL library and toolkit called SPICE has been used in a fictitious but realistic Mars-Earth downlink mission. Thanks to the high reliability of SPICE, all the data related to the orbital mechanics of a space mission has been obtained and compared, in order of magnitude, with a mission called Psyche and DSOC, scheduled for launch in August 2022. Apart from didactically exemplifying the terms of the link equation in a specific mission, key elements such as capacity or bit rate have also been retrieved, which allow immediate conclusions to be drawn in favour of this technology and thus contribute to its consolidation in the field of deep space communications

Měření vlivu kapek pro optický bezvlaknový spoj a matematické modelování vícefázového proudění

Free space optics will emerge alongside major communications technologies as an important player in the field of wireless communications. This technology, like other technologies, has to face the challenges caused by unstable and unfavorable atmospheric conditions that determine the resulting quality of the transmitted signal. The paper is intended to determine the extent of a deterioration of the transmitted signal during rainfall. The precipitation is simulated in laboratory conditions, and the resulting knowledge of the droplet formation is transferred to a mathematical model that helps simulate multiphase flow under given conditions.Optické bezvláknové spoje se v budoucnosti vyskytnou po boku majoritních komunikačních technologií jako důležitý hráč na poli bezdrátových komunikací. Tato technologie, stejně jako jiné technologie, musí čelit výzvám pramenícím z nestálých a nepříznivých atmosférických podmínek, které rozhodují o výsledné kvalitě přenášeného signálu. Tato práce má za úkol zjistit míru zhoršení přenášeného signálu během dešťových srážek. Srážkový úhrn je simulován v laboratorních podmínkách a výsledné poznatky o tvorbě dešťových kapek jsou přeneseny do matematického modelu, který napomáhá simulování vícefázového proudění v daných podmínkách.440 - Katedra telekomunikační technikyvýborn

LHA(R): Amphibious Assault Ships For The 21st Century

Amphibious assault ships such as the current LHA and LHD classes are an essential element of the country's ability to exert influence anywhere in the world. The current amphibious assault ships represent the most capable amphibious ships in the world. The LHA 1 class ships are aging, however, with most reaching the end of their expected service lives between 2011 and 2015. It is not feasible to extend the service life of the LHA 1 class due to the rapid technological advances that have taken place during their lifetime. Most have already used their entire growth margin in areas such as combat systems and topside weights. The evolving combat systems and aircraft requirements will only exacerbate these matters. The best solution is to replace the LHA. As the US faces a future with uncertain threats, it is necessary to field a flexible force. In order to make the amphibious forces flexible, selective offload capability must be considered. This allows Marines to access the equipment and vehicles they need for any given operation at any time. A second change that adds a great deal of flexibility is the addition of more ships. Currently, an Amphibious Ready Group (ARG) consists of three ships, an LHA or LHD, an LSD, and an LPD. Replacing the LHA with two ships has several advantages, ranging from increasing the selective offload capability of the ARG to optimally distributing assets among the ships. Most importantly, though, is the ability of the ARG to exert influence over a greater geographic area. In this study, four different options were considered for the future ARG: a. LPD 17, LSD 41, modified LHD 8 plus complement ship variants b. LPD 17, LSD 41, two small LHD variants (2 ships with same hull) c. LPD 17, LSD 41, two new design variants d. LPD 17, LSD 41, single ship LHA(R) variants After modeling a number of variants representing each option, an Overall Measure of Effectiveness (OMOE) and a total lifecycle cost was calculated. Analysis of these variants showed that the variants in Option (a) have a higher OMOE and a relatively lower cost than other options. This study now focuses on the complement ship to a modified LHD 8. A comparison of hull forms, including catamarans, surface effect ships, hydrofoils, trimarans, monohulls, semi-planing monohulls, led to the selection of a trimaran, primarily for its ability to transport equipment at a high speed over a long range. In order to keep the size (and cost) of the ship down, the ship will not carry any landing craft. The nominal amphibious lift capacity of the trimaran complement ship i