Atmospheric Communication Links Research Articles

Effects of Tropospheric Turbulence on Radio Signal Data Passing Atmospheric Communication Links

AbstractThis paper analyzes the effects of turbulent structures of different sizes on the structural parameter of the refractive index and, consequently, on the scintillation index of radio waves passing through atmospheric channels with fading. The relationships between these parameters are analyzed and discussed not only for weak turbulence, but also for moderate and strong turbulences occurring in the mid‐latitude troposphere. By using the relationship between the scintillation index of signal intensity and the well‐known Rician parameter of fast fading, and by obtaining the relationships between the signal data stream parameters, capacity, spectral efficiency, and bit error rate, and factor of fast fading, we have numerically analyzed various cases of data transmission over tropospheric communication links with fading. This analysis considers the effects of weak, moderate, and strong turbulence on the quality of data transmission over such communication links. The results of this study can be used to improve the design and performance of tropospheric communication links in the presence of turbulence.

Analysis of total signal decay and capacity of information data in wireless atmospheric communication links. Part 2

Introduction: Analysis of total signal decay is based on prognosis of the total path loss occurring in the atmospheric communication links, accounting for effects of gaseous structures attenuation and scattering, hydrometeors (rain, snow and clouds) absorption and attenuation, and turbulent structures fast fading on radio and optical signals passing atmospheric channels with fading. Purpose: To perform a novel methodology of definition and estimation of effects of decay, absorption, scattering, and fading of radio and optical signals propagating in atmospheric channels in various meteorological conditions. Results: Wasanalyzed the impact of gaseous structures, hydrometeors and turbulent structures in total path loss for link budget design and in degradation of data stream parameters, such as capacity, spectral efficiency and bit-error-rate, which lead in loss of information data signals passing such kinds of channels with fast fading and decrease of quality of service. An optimal algorithm was found of the total path loss prediction for various meteorological situations occurring in the real atmosphere at different heights and for various frequencies of radiated signals. A method was proposed of how to evaluate the data stream parameters, capacity, spectralefficiency and bit-error-rate, accounting for the effects of atmospheric turbulence impact on fast fading, which corrupts information passing such kinds of channels. All practical tests were illustrated by the use of the MATLAB utility. A new methodology was proposed on how to evaluate and estimate the capacity, the spectral efficiency, and the loss in energy and in the information data stream for different scenarios of radio and optical signals propagation via atmospheric channels with fading caused by different meteorological conditions. Practical relevance: The results obtained allow to achieve better accuracy of prognosis and increase quality of service in atmospheric communication channels.

Laser Transmitter for Undersea Communications Using Third-Harmonic Generation of Fiber-Laser System at 1.5 $\mu$m

We report a viable laser transmitter for free-space undersea communications. An all-fiber, picosecond, Watt-level master-oscillator-power-amplifier (MOPA) system at 1.5 mum based on rapid amplification of mode-locked pulses in heavily Er:Yb codoped phosphate fiber is combined with fiber pigtailed lithium niobate intensity modulator (pulse picker), to construct a fully integrated eye-safe transmitter operating at 65-Mb/s data rate, that can be used in intermediate-range (few kilometers) atmospheric communication links. For undersea use, the output of the MOPA system is frequency-tripled into the blue-green transparency window of ocean water. The wavelength conversion occurs in a simple single-pass setup utilizing a sequence of two periodically poled lithium niobate crystals, both of which are operated at room temperature. The conversion efficiency from fundamental to third harmonic reached 14% and resulted in generation of 140 mW of average power at 518 nm. The conversion efficiency can be straightforwardly increased threefold using properly antireflection-coated optics in the free-space part of the setup, and the data rate can be scaled up into the gigabit-per-second range by using a faster mode-locked oscillator in the MOPA system.

Effects of attenuation of 1.064-μm optical waves by humid aerosols and fog over horizontal atmospheric communication links

Ben-Gurion University of the NegevDepartment of CommunicationSystems EngineeringP.O. Box 653Beer-Sheva, 84105IsraelAbstract. Effects of humid aerosols and fog on optical wave propaga-tion at 1.064 mm over various horizontal atmospheric communicationlinks are investigated both experimentally and theoretically by use oftheoretical and empirical models as best fits of experimental data. Miescattering is used to describe the attenuation of optical waves by aero-sols for lower elevation horizontal atmospheric links. The geometricaloptics approximation is used to obtain the extinction coefficient for opticalwaves at 1.064 mm passing through clouds, fog, water droplets, andatmospheric particles with dimensions larger than the wavelength. Goodagreement between a new model of propagation effects through suchparticles, and measurements carried out at two different sites in southernand northen Israel, is obtained.

Aperture-averaged level-crossing probability in an atmospheric communication link

The intensity statistics of light pulses in an atmospheric communication link are studied here for the case of a finite (nonpoint) detector aperture. The calculation of the statistics of the pulse intensities averaged over the aperture is performed by using a discrete aperture model and applying the multidimensional ognormal distribution. The results of the numerical calculations demonstrate the dependence of the level-crossing probability on aperture radius, number of pulses, and the length of a pulse sequence. The level-crossing probabilities were measured experimentally and found to be in close agreement with the theoretical values.

Level crossing and fading probabilities in an atmospheric communication link for a non-Markov process: errata

Level crossing and fading probabilities in an atmospheric communication link for a non-Markov process: errata

Level crossing and fading probabilities in an atmospheric communication link for a non-Markov process

The statistics of light pulses in an atmospheric communication link are studied here. The correlation between light pulses propagating through a turbulent atmosphere is described by a nonexponential function. As this leads to a non-Markov process, the statistics of the pulse sequence are investigated using a multidimensional distribution. The multidimensional calculations were performed for level crossing and fading probability. The results demonstrate in some cases essential differences from the results obtained in Markov approximation. The level crossing probabilities for the non-Markov process have been fitted by analytical expressions which permit the approximate calculation of these probabilities in a simple way.

On Laser-beam Size for Atmospheric Communication Links

Maximum illumination of the receiver aperture of an atmospheric optical communication link can be achieved in the presence of random laser-beam deviations, with a proper choice of the laser-beam size. The variation in the received intensity level would be limited to 4·3 dB for 99·9 per cent of the time.