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Atmospheric turbulence and different environmental conditions severely reduce the performance and reliability of free-space optical (FSO) links. This paper describes a simulation-based analysis of signal quality of the proposed FSO link under various climatic conditions. It specifically examines the performance of a 25 Gbps 4-quadrature amplitude modulation (QAM)-based coherent optical OFDM (CO-OFDM) FSO system that is with and without the deployment of low-density parity-check (LDPC) channel coding. Several key performance indicators, such as bit error rate (BER), signal-to-noise ratio (SNR), received power, distance of the link and general reliability are considered. Simulation outcomes confirm that the use of LDPC channel coding makes the system resist atmosphere attenuation and turbulence by a much higher margin; that is, lower BER, higher SNR, good amount of received power, and more extended reliable communication distance. These enhancements reflect the practical advantages of LDPC coding in FSO link performance in adverse environmental conditions.

Optical camera communications (OCC) research field has grown recently, aided by ubiquitous digital cameras; however, atmospheric conditions can restrict their feasibility in outdoor scenarios. In this work, we studied an experimental OCC system under environmental phenomena emulated in a laboratory chamber. We found that the heat-induced turbulence does not affect our system significantly, while the attenuation caused by fog does decrease the signal quality. For this reason, a novel strategy is proposed, using the camera’s built-in amplifier to overcome the optical power loss and to decrease the quantization noise induced by the analog-digital converter of the camera. The signal quality has been evaluated using the Pearson’s correlation coefficient with respect to a reference template signal, along with the signal-to-noise ratio that has been empirically evaluated. The amplification mechanism introduced allows our system to receive the OCC signal under heavy fog by gradually increasing the camera gain up to 16 dB, for meteorological visibility values down to 10 m, with a correlation coefficient of 0.9 with respect to clear conditions.

Free Space Optical (FSO) communication systems are gaining popularity due to its tremendous speed, advanced capacity, cost effectiveness, secure and easy to deploy wireless networks. This technology has proven an effective choice for last mile applications and hard to reach areas where deployment of optical fibre links is not feasible. But FSO link is highly weather dependent and as signal passes through the atmospheric channel, the main impairments are the atmospheric turbulence, which induce fading and deteriorate the system performance. Delhi has a great potential for FSO communication because of its clear skies. Since there is no analysis for weather condition found in Delhi, this work provides analysis of typical Delhi weather condition ranging from heavy to light rain, fog and clear sky. The performance of FSO link is analysed in terms of attenuation and link length margin under different weather condition. The results are concluded to identify which atmospheric condition influences more on FSO link performance.

In this study, the generalized Lorenz–Mie theory (GLMT) is used to calculate the scattered electromagnetic field components of vortex Bessel beams (VBB) by a foggy atmosphere. The interaction of VBB with scattering particulates is very distinct due to its complex optical fields and orbital angular momentum (OAM). By employing the integral localized approximation (ILA), the beams shape coefficients (BSCs) for VBB are evaluated. To describe the VBB, the BSCs are considered as a crucial part in the GLMT. Numerical results on extinction efficiency, scattering efficiency, absorption efficiency, radiation pressure efficiency, albedo factor, and scattering asymmetry parameter are presented in relation to the OAM mode index. Also, results on generalized Gamma distribution as a function of particle diameter for diverse visibility factors are presented and discussed. Moreover, attenuation associated with advection fog and radiation fog for different OAM mode index versus visibility is explored using GLMT. The computations show that fog attenuation is highly influenced by the OAM mode number. The numerical results dictate distinct signatures regarding VBB that there exists higher transmission of optical VBB propagation in the specific foggy environments. Moreover, this research work has potential applications to study the scattering dynamics of the OAM in marine atmosphere, rainy atmosphere, and environmental optics.

In case of future telecommunication technologies, extremely high data rates above 100 Gbps is the expectations, which can be fulfilled by utilizing higher spectrum bands. Higher frequency bands like terahertz wave bands are expected to have far broader bandwidths then 5G, therefore 6G will need to encourage R&D activities to utilize so called terahertz waves with frequencies ranging from 100 to 200 GHz. The challenge in utilizing these higher frequency bands is their sensitive nature toward outdoor environmental conditions like cloud, Fog, dust and Rain. To address these issues, this paper proposes a Machine Learning Model based on Artificial Neural Network to predict the attenuation caused due to Clouds and Fog at D and G bands. The model was trained using AMSER–2 Satellite data. The trained model is further optimized using different optimizing techniques. Obtained results was compared with the different existing models.

In recent years, wireless communication systems have exploded in popularity. Optical wireless technology is an excellent alternative to RF wireless, but it has high capacity, data speed, frequency, and license-free spectrum, and it is simple to implement. Optical wireless communication sends data through air using optical beams. Atmospheric turbulence degrades the functioning of free-breathing space photosensitive interaction methods by causing interruptions due to weather conditions like fog, smoke, and different pollutants. In this paper, free-space optical communications using snow and fog attenuations and Numerical Weather Prediction (NWP) method is used to determine the turbulence due to the atmosphere. This method improves the data transmission during unfavorable weather conditions by changing the various parameters like receiver aperture size, the wavelength of the transmitter, etc. Furthermore it shows that decrease in air quality and instability are the double significant causes, that can degrade general usage routine, especially when it’s foggy or raining heavily. The result shows that the aperture size and wavelength should be changed as per the weather condition.

The latest trends in mobile technology have increased the need for higher spectrum bands from every sector of using wireless applications. As the internet is growing rapidly it has increased the need for wireless services, which require radio spectrum and thus becoming more congested. Engineers show that due to high demand for spectrum, government authorities are regularly introducing schemes to regulate the use of spectrum. New researches are enhancing to resolve the crisis. In order to fix the spectrum for future technologies, propagation studies are required. In this paper an empirical model is proposed for prediction of attenuation due to clouds and fog based on the Rayleigh approximation model. In this model a new concept of calculating dielectric constants of water are also introduced. The implementation results of the proposed model are compared with the other cloud attenuation models. The proposed model proved to be better than the ITU-R model.

Free Space Optical (FSO) communication systems, offering high-speed and high-bandwidth transmission, have emerged as a possible substitute for conventional wired and wireless communication systems. However, FSO links are susceptible to atmospheric deficiencies including attenuation, scintillation, and turbulence, which may severely impact the performance of the communication link. In this research paper, we propose and analyze the performance of a 25 Gbps dual-polarization quadrature phase shift keying (DP-QPSK) coherent optical orthogonal frequency division multiplexing (CO-OFDM)-based FSO communication link with spatial diversity technique under various climatic conditions in four different geographical locations of India, i.e., Delhi, Ahmedabad, Kolkata, and Chennai in the year 2021. The proposed FSO communication system is evaluated through performance analysis and parametric evaluation under various weather conditions such as clear sky, fog, haze, rain, cloud, and thermal gradient. Key performance metrics such as bit error rate (BER), Q-factor, signal-to-noise ratio (SNR), received power, communication range, and reliability are analyzed based on the simulation results. The proposed FSO communication system provides high data rates, improved power efficiency, better resilience to atmospheric impairments, reliable communication links under different weather conditions, and a practical solution for high-speed and high-bandwidth communication in various applications.

The Rayleigh approximation model is used for analyzing fog attenuation of the HAP-based communication system, the influence of transmitter elevation to fog attenuation under different temperature and liquid water density are studied, Numerical results show the optimum transmitter elevation angle in a ka-band HAP-based communication system under fog attenuation.

Investigating the absorption and scattering effects of atmospheric particles, i.e., raindrops and fog droplets, is required to establish a comprehensive and accurate channel model. However, for long-distance communication in outdoor scenarios, research on the propagation characterization of fog and rain attenuation in the terahertz (THz) band is insufficient. In this study, fog and rain attenuation characterization with different conditions are characterized. First, fog attenuation at different temperatures and diverse visibility is explored using Rayleigh approximation theory and Mie theory. The results demonstrate that visibility and frequency have a stronger effect than temperature on fog attenuation. Then, rain attenuation as a function of rainfall rate is theoretically determined using Mie theory and the Joss, M-P, and Weibull distribution. The results show that rainfall rate and frequency have greater impact than raindrop distribution on rain attenuation. There are large differences in rainfall attenuation under diverse distributions. Accurate fog and rainfall attenuation information can be used to better estimate path loss and the link budget for terahertz communication in outdoor scenarios.