Ad hoc FSO communication

In this paper, the distant source communicates with the underwater destination using High Altitude Platform Station (HAPS) and a triple-hop relay setup. In this setup, the source transmits information using hybrid Radio Frequency (RF)/Free Space Optical Communication (FSO) link to the decode-and-forward (DF) based relay at HAPS, which forwards the signal to the relay at the water surface using FSO link, which further transmits the signal to the underwater destination using Under Water Optical Communication (UWOC) link. Both the relays use DF relaying protocols. HAPS are used to increase the reliability of the system and range of transmission. FSO links offers a high bandwidth and better data rates than the RF links. But they often get affected by the atmospheric conditions, turbulence, and pointing errors. RF link on the other hand acts as a good complement to FSO links, thereby increasing the reliability of the system when both are used in parallel to transmit the information. UWOC link has several benefits like higher data rates, less attenuation and low power consumption in comparison to acoustic links. New statistical characteristics for the signal-to-noise-ration (SNR) of the proposed system are developed using which the outage probability of the system is derived. The numerical results shows that the outage probability of the system proposed gets affected by the RF shadowing, FSO turbulence parameters and turbulence parameters of UWOC links such as salinity, temperature gradient and bubble level concentration. Also the asymptotic analysis matched with the analytical results.

The foundation of any smart city requires an innovative and robust communication infrastructure. Many research communities envision free-space optical communication (FSO) as a promising backbone technology for the services and applications provided by such cities. However, the channel through which the FSO signal travels is the atmosphere. Therefore, the FSO performance is limited by the local weather conditions. The variation in meteorological variables leads to variations of the refractive index along the transmission path. These index inhomogeneities (i.e., atmospheric turbulence) can significantly degrade the performance of FSO systems. Thus, a practical implementation of the FSO link must carefully consider the atmospheric turbulence effect. This paper aims to investigate the feasibility of FSO communication for NEOM, a promising smart city in Saudi Arabia. We study the effect of weather conditions on FSO links using the micrometeorology model, taking into account actual weather data. The FSO performance in winter and summer was compared in terms of the bit error rate, signal-to-noise ratio (SNR), link availability, and transmission distance. The study shows that the atmospheric turbulence strength is moderate and strong in winter and summer, respectively. The temperature has the biggest impact on the FSO system when compared to the other meteorological elements included in this study. Furthermore, at transmission distances less than 300 m, atmospheric turbulence does not significantly affect the FSO for the operating wavelength of 1550 nm. Furthermore, it has been shown that at transmission distances greater than 300 m, the SNR in summer is more than 18% higher than in winter. The findings of this research enable understanding of the effect of turbulence caused by NEOM weather on the FSO link, thus assisting engineers in establishing a reliable FSO backbone link by adjusting the relevant parameters.

Free-space optical communications (FSOC) is becoming an important option for both atmospheric and space-based high data rate networks. Long-range, mobile FSOC links in the former environments must mitigate the effects of turbulence if they are to provide reliable, high link availability under cloud-free atmospheric conditions. Adaptive optics (AO) has been proposed as one means of reducing link degradation in turbulence, but field validated AO performance models are few and not definitive. These models are important if credible FSOC high performance links are expected to be deployed using AO systems. This paper reviews the Strehl ratio for the Andrews AO model and provides comparisons between predicted AO-based FSOC link budgets and measured link performance derived from several field trials. These results suggest that AO systems perform well under weak turbulence or short range under 10 km, but only offer limited tip/tilt gain in moderate turbulence and no gain under high/saturation regime turbulence at longer ranges. Long range links close to the ground in high moderate turbulence may degrade AO performance further.

Free Space Optical (FSO) communication is an emerging transmission technique to transmit high data rates without using cables. This technology is expected to revolutionize the present communication system architectures both in the terrestrial and the in -space architecture. Atmospheric effects can significantly degrade the performance of FSO systems. This reduces the SNR and leads to impaired performance. FSO channels can be modeled using Gamma-Gamma, Weibull, Log-Normal, K distribution functions. Error control codes can help to mitigate atmospheric turbulence induced signal fading in free space optical communication links. Luby Transform codes belong to a class of error control codes called Fountain codes and are meant for erasure channels. In this paper, we propose encoding FSO links with Luby Transform (LT) codes for error channels. Decoding is done using belief propagation with Log Likelihood Ratio and results are obtained for different modulation schemes under different channel distributions.

Free Space Optical (FSO) communication is a low cost and license free high bandwidth access technique, is a primary research area from last few years. Atmospheric turbulence plays a vital role in degrading the link performance. This paper presents the model study on the effects of atmospheric turbulence in FSO links. The study is based on the most popular gamma-gamma model distribution. The theoretical model is simulated by varying the height of link and the results are plotted in Mathworks® MATLAB®. The research demonstrates that the effects of turbulence depend primarily on wind speed and height of established FSO link. After varying the height of link, the effects of atmospheric turbulence on link performance can be clearly seen. The result also plotted for the attenuation of signal with varying visibility range conditions.

Availability analysis of free-space-optical links based on rain rate and visibility statistics from tropical a climate

In free-space optical communication links using intensity modulation/direct detection (IM/DD), atmospheric turbulence can cause signal fading. Error-control codes can help to mitigate this fading and improve system performance. To study the performance of various coding schemes, we derive an upper bound on the pairwise codeword error probability for transmission through channels with correlated turbulence-induced fading. Computing this probability involves complicated multidimensional integration. To simplify the computations, we derive an approximate upper bound under the assumption of weak turbulence. The accuracy of this approximation under weak turbulence is verified by numerical simulation. Its invalidity when applied to strong turbulence is also shown. This simple approximate upper bound to the pairwise codeword error will be useful in the study of coding for free-space optical communication through weak atmospheric turbulence channels.

Free-space optical communication (FSOC) systems require precise pointing, acquisition, and tracking to send and receive optical beams for effective operation. In a lens-assisted beam steering (LABS) system, light is steered by controlling the emission location in a focal plane. The emitted light is directed into the scene by a lens, like a camera but operating in reverse. In this paper, we demonstrate a novel free-space optical communication link using a micro-opto-electro-mechanical-system (MOEMS) based photonic integrated circuit (PIC) for LABS between multiple receive locations. The MOEMS PIC operates via selective electrical actuation of an array of small grating switches (30 μm × 30 μm footprint, 100 μm pitch). Data rates up to 10 Gbps and a 3 dB optical bandwidth covering the infrared C and L bands (1530 nm to 1625 nm) are measured over a 1 m free-space link distance. Eye diagrams indicate a quality communication link for data rates up to 10 Gbps and bit-error-rates <10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−10</sup> are measured for on-off keying (OOK) modulation. A measured beam profile is propagated into the far-field via simulation, and used to calculate link budgets for example CubeSat crosslink and downlink scenarios. Link budget calculations indicate potential >1 Gbps CubeSat FSOC crosslinks for link lengths >1000 km and 1 W of input optical power, using identical 90 mm transmit and receive apertures and a commercially-available fiber-coupled InGaAs avalanche photodiode (APD) receive detector.

In free-space optical communication (FSOC) systems, atmospheric turbulence can bring about power fluctuations in receiver ends, restricting channel capacity. Relay techniques can divide a long FSOC link into several short links to mitigate the fading events caused by atmospheric turbulence. This paper proposes a Reinforcement Learning-based Relay Selection (RLRS) method based on Deep Q-Network (DQN) in a FSOC system with multiple transceivers, whose aim is to enhance the average channel capacity of the system. Malaga turbulence is studied in this paper. The presence of handover loss is also considered. The relay nodes serve in decode-and-forward (DF). Simulation results demonstrate that the RLRS algorithm outperforms the conventional greedy algorithm, which implies that the RLRS algorithm may be utilized in practical FSOC systems.

Free-space optical (FSO) communication links constitute an alternative option to radio relay links and to optical cables facing growth needs in high-speed telecommunications (abundance of unregulated bandwidth, rapid installation, availability of low-cost optical components offering a high data rate, etc). Their operationalisation requires a good knowledge of the atmospheric effects which can negatively affect role propagation and the availability of the link, and thus to the quality of service (QoS). Better control of these phenomena will allow for the evaluation of system performance and thus assist with improving reliability. The aim of this paper is to compare the behavior of a FSO link located in south of France (Toulouse: with the following parameters: around 270 meters (0.2 mile) long, 34 Mbps data rate, 850 nm wavelength and PDH frame) with airport meteorological data. The second aim of the paper is to assess in-house FSO quality of service prediction software, through comparing simulations with the optical link data and the weather data. The analysis uses in-house software FSO quality of service prediction software (FSO Prediction) developed by France Telecom Research & Development, which integrates news fog fading equations (compare to Kim & al.) and includes multiple effects (geometrical attenuation, atmospheric fading, rain, snow, scintillation and refraction attenuation due to atmospheric turbulence, optical mispointing attenuation). The FSO link field trial, intended to enable the demonstration and evaluation of these different effects, is described; and preliminary results of the field trial, from December 2004 to May 2005, are then presented.

The study was conducted at University of Gujrat during 2015 with an objective to explore the effects of dust on Free Space Optics (FSO) communication. Growing pollution and dust gales motivated studies we presented in this paper. In this paper analysis of the influence of dust on free space optics communication is presented. We focused our studies on Lahore as it is polluted city of Punjab and made a comparison with dust effects in Rahimyar Khan Region. Dense dust consists of large dust particles that raise from Earths sphere and whose atmospheric intensification values are high enough to affect FSO communication links. Dust storm research is based on visibility data. In order to test visibility data, we made calculations of atmospheric conditions for different dust conditions. Visibility of wave is calculated using weather spark. As it is related with the optical attenuation, so we also calculated optical attenuation of dust particles due to influence of dust particles and compared it with that of Rahimyar Khan.

This paper presents performance analysis of decode-and-forward (DF) based asymmetric relaying system, where an outdoor hybrid radio frequency (RF)/free space optical communication (FSO) subsystem is connected with an indoor visible light communication (VLC) subsystem. The RF link is characterized by Nakagami- $m$ fading and the FSO link is characterized by Double Generalized Gamma (DGG) distributed turbulence and Rayleigh distributed pointing errors. Novel mathematical expressions are derived for probability density function and cumulative distribution function of the instantaneous signal-to-noise-ratio (SNR) of hybrid RFIFSO-VLC cooperative system in terms of Meijer-G function. Using these, analytical expressions are obtained for the outage probability (OP) and the average bit error rate (BER) of the proposed system for different modulation techniques in terms of Meijer-G function. The numerical results show that the OP of the system increases as the effects of fading and pointing error increases. The results also show that the BER performance of the system is better in the moderate turbulence environment and using coherent binary detection schemes as compared to strong turbulence scenarios and using direct detection scheme.

This article presents and analyzes fading measurements of optical signal in a terrestrial free space optical communication link using a commercial system. Unlike previous work, the link distance is very short (around 91 meters). Still, it was possible to observe significant scintillation index variations over a day. This behaviour agrees with previous results obtained in the literature for much longer links.

An indoor 100 Gb/s free space optical communication link using an injection locked ∼1621 nm quantum-dash laser has been experimentally demonstrated. The results are achieved using dual-polarization quadrature phase shift keying (DP-QPSK) and coherent detection over a 4 m indoor free space link. The system exhibited a receiver sensitivity of –17.5 dBm to achieve the bit error rate forward error correction (BER FEC) threshold of 3.8 × 10–3. This displays the potential of tunable injection locked far L -band quantum-dash lasers, with less scattering loss compared to C -band counterpart, as promising light sources in both indoor and outdoor future high speed free space optical information and communication technology.

This article reports the development of 200-mW 1.55-μm DFB laser module with RIN below -162 dB/Hz which are well suited for microwave photonics or free space optical communication applications. Specific design has allowed reaching high power (>300 mW), low noise and high spectral purity laser chip. The chip has been packaged in Butterfly module optimized for reducing the module power consumption. DFB laser module system validations have been done on three laboratory test-beds representative of target applications, namely high-frequency optical LO distribution, photonic RF frequency conversion, and free space optical communication links.