Terrestrial Free Space Optics Research Articles

Estimation of intelligent-based quality of service in terrestrial FSO links: A case of South Africa propagation paths

Free Space Optical (FSO) communication is one of the popular technologies’ dominants in the optical communication domain. Despite all the advantages, FSO links are grossly affected by severe atmospheric conditions such as fog, rain, snow, smoke, and dust or aerosol particles suspended in the air. Fog is one of the major challenges for free-space optics to achieve carrier-class availability and causes extreme attenuation. A 10-year (2010––2019) visibility data were obtained from the South African Weather Services (SAWS) with a special focus on Cape Town (–33.925° S, 18.424° E). This extracted and processed Cape Town data was used to estimate the needed fog-induced attenuation. The intelligent algorithm is rooted in the theory of Artificial Neural Networks (ANN) systems which intelligently control the sub-tropical climate conditions of the chosen region. The adopted network-based technique is capable to interact with ever-changing weather by generating appropriate improvements to the free space optical communication link quality of service for efficient services to the customers. In this study, an Intelligent Algorithm (IA) based on an Artificial Neural Network (ANN) has been utilized to improve the reliability of QoS that can satisfy customer SLAs and improve received signal over FSO communications. The results obtained by implementing the IA system indicates that the power transmitted range from 8 to 100 dB and the adjusted Signal to Noise Ratio (SNR) between 390–––420 dB at 650 nm optical wavelength, whereas the same trend could be observed when the optical wavelength of 1550 nm was applied. Subsequently, the model effectively estimated the automatic transmit power control for enhancement in SNR and resulting in better QoS at the receiving end, regardless of the related weather changes along with the transmission link.

Analysis of hybrid RF/FSO wireless communications links under foggy weather conditions

Abstract Terrestrial free-space optical (FSO) links are based on the fundamental idea of a light beam transporting information, enabling extremely high data rates. Fog still presents a significant obstacle to enhancing the availability and dependability of terrestrial FSO lines because the fog particles scatter the light as it travels and only significantly attenuate the signal. Using a hybrid network with an FSO link and a backup link will solve the problem. GHz offers outstanding performance in this frequency band. In this research, the attenuation caused by fog is predicted using an empirical model based on measurements of visibility and their impacts on FSO/RF links. Multiple functioning FSO and RF links operating at 1 GHz, 10 GHz, and 25 GHz, as well as visibility, were simultaneously monitored for changes in signal intensity. The bit error rate (BER) for the optical modulation formats NRZ-OOK, L-PPM, and RZ-OOK is investigated under various fog scenarios. According to the results of the simulation, RF link performance at 25 GHz is better suited for hybrid system fog weather circumstances. On the other hand, we discuss the appropriateness of fog models within these various modulation formats.

Impact of Scintillation Effect on Clear Weather and Fog Conditions using MDM-WDM Modulation Technique

The 5th generation optical wireless communication technologies have unique features of higher data rate, scalability in bandwidth, license free spectrum, cost effectiveness, easy deplorability and secured transmission. The role of free space optical (FSO) communication becomes important as the applications of next generation technologies are evolving in almost every sector. In this work, the performance of the terrestrial FSO MDM-WDM link has been investigated through a DP-QPSK modulation scheme at a data rate of 1000 Gbps. The link attenuation has been analysed with the help of Gamma- Gamma and Lognormal scintillation models considering clear weather and varying fog conditions. The link performance has been evaluated through SNR and received optical power for a varying distance of up-to 20 Km.

English

The spatial diversity techniques are broken down and explained systematically along with its combination which includes Maximum Ratio Combining (MRC), Equal Gain Combining (EGC) and Simple Selection Combining (SC) under the influence of atmospheric-induced turbulence fading in Free Space Optical (FSO) communication. Diversity is a technique used to prevent or reduce multipath. Multipath is a phenomenon describing propagation that results in the signals reaching the antenna by two or more paths. There is an extreme difficulty for a transmitted signal to be detected by a receiver in a case of increased turbulence. This research provides a forum for the receiver with some forms of diversity. The validation of the recommended simulation is through Additive White Gaussian Channel without combiner of the same process. The results display that Maximum Ratio Combining (MRC) has the greatest mitigation level of fading in comparison with others. Consequently, where fading is more dominant like on a terrestrial FSO link, Maximum Ratio Combining (MRC) can be used. Overall, the findings suggest the capability of the model in mitigating atmospheric turbulence especially for the 5G wireless networks in the terrestrial link. Key words: Free Space Optical Communication (FSO), Atmospheric Turbulence, Additive White Gaussian Channel (AWGC), Maximum Ratio Combining (MRC), Equal Gain Combining (EGC), Selection Combining (SC) and Additive White Gaussian Noise (AWGN).

Analysis of RIS-Based Terrestrial-FSO Link Over G-G Turbulence With Distance and Jitter Ratios

One of the main problems faced by communication systems is the presence of skip-zones in the targeted areas. With the deployment of the fifth-generation mobile network, solutions are proposed to solve the signal loss due to obstruction by buildings, mountains, and atmospheric or weather conditions. Among these solutions, reconfigurable intelligent surfaces (RIS), which are newly proposed modules, may be exploited to reflect the incident signal in the direction of dead zones, increase communication coverage, and make the channel smarter and controllable. This paper tackles the skip-zone problem in terrestrial free-space optical (T-FSO) systems using a single-element RIS. Considering link distances and jitter ratios at the RIS position, we carry out a performance analysis of RIS-aided T-FSO links affected by turbulence and pointing errors, for both heterodyne detection and intensity modulation-direct detection techniques. Turbulence is modeled using the Gamma-Gamma distribution. We analyze the model and provide exact closed-form expressions of the probability density function, cumulative distribution function, and moment generating function of the end-to-end signal-to-noise ratio. Capitalizing on these statistics, we evaluate the system performance through the outage probability, ergodic channel capacity, and average bit error rate for selected binary modulation schemes. Numerical results, validated through simulations, obtained for different RIS positions and link distances ratio values, reveal that RIS-based T-FSO performs better when the RIS module is located near the transmitter.

A spectral-efficient 1 Tbps terrestrial free-space optics link based on super-channel transmission

A spectral-efficient 1 Tbps terrestrial free-space optics link based on super-channel transmission

Experimental Model Development for the Attenuation Coefficient Estimation of Terrestrial Optical Wireless Links over the Sea

Free space optical (FSO) systems have become a reliable solution for modern communications networks, due to the high performance, availability, reliability and security they can provide. However, their characteristics depend strongly on the conditions of the atmosphere, which is the propagation path of the optical beam. In this work, this dependence is experimentally investigated through a terrestrial horizontal FSO link, which was installed a few meters above the sea. Thus, the procedure presented hereis an accurate empirical model for the estimation of the attenuation coefficient for an optical wireless link, as a function of the atmospheric temperature, the relative humidity, and the wind speed. Its accuracy is verified by comparing the estimated outcomes—obtained from the empirical model—versus the measured—experimental—ones. Such accurate empirical models can be used for designing high performance and reliability FSO links, as parts of the upcoming 5G/5G+ networks, for areas where the behavior of the atmospheric conditions and parameters are known.

Characterization of terrestrial FSO link performance for 850 and 1310 nm transmission wavelengths

Abstract Over past few years, optical wireless communication has gained increased interest due to high achievable data rates, unlicensed bandwidth, inherited secure links and ease of deployment. In this paper, we analyse the performance of terrestrial free space optical (FSO) communication link considering internal parameters of the system. The performance of the system has been investigated and optimized by examining quality factor of the received signal considering different input powers, type of detectors, link ranges, beam divergence, data rates and modulation schemes employing 850 and 1310 nm transmission wavelength. Better quality of received signal has been achieved in case of different modulation schemes at a wavelength of 1310 as compared to 850 nm.

Development and Performance Investigation of a Single-Channel 160 Gbps Free Space Optics Transmission Link Using Higher Order Modulation Scheme

This article reports the development of a high bit rate terrestrial free space optics (FSO) transmission link. Spectral-efficient polarisation division multiplexed-quadrature phase-shift keyed signals are used to transmit high bit rate data. Coherent receiver is proposed to ameliorate the demodulator performance under environmental conditions. Also, digital signal processing techniques at the receiver are used to mitigate the adverse channel effects on the information signal. The bit error rate analysis for different environmental conditions is carried out using numerical simulations and the results demonstrate reliable 160 Gbps transmission. The impact of atmospheric scintillation due to turbulent channel conditions on the link performance is also investigated. Further, the transmission performance is compared with previous reported studies which shows that the system demonstrates better achievable range and information bit rate performance. The reported work provides a suitable reference to realize bandwidth-efficient high-capacity FSO links under dynamic weather conditions.

Investigation of 340-Gbps terrestrial FSO link incorporating spectral-efficient DP-QPSK-PolSK hybrid modulation scheme

A high-capacity spectral-efficient dual-polarization quadrature phase-shift keying (DP-QPSK)-polarization shift-keying (PolSK) hybrid modulation scheme for terrestrial free-space optics (FSO) transmission link is proposed and investigated. A DP-QPSK signal modulated at 300 Gbps and a PolSK signal modulated at 40 Gbps are simultaneously transmitted using a single optical carrier over the FSO link. The proposed link performance is investigated under different weather conditions, where the bit error rate metric is used to evaluate the performance of the PolSK modulated signal and the error vector magnitude parameter is used for the DP-QPSK signal. The FSO link range and the required received power are carefully explored. The conducted numerical simulations of the proposed system showed reliable 340-Gbps data transmission over link ranges varying from 1.6125 to 50 km depending on the weather conditions. The impact of the channel scintillation due to atmospheric turbulence is also investigated. The proposed high-speed FSO transmission system offers a promising solution for high-bandwidth hungry systems used for the internet of things, 5G, and smart cities. It can also be used in developing fronthaul/backhaul links for future wireless networks and optical access networks. The performance of the proposed transmission system is compared with recently published work in the literature.

Secrecy Analysis of FSO Systems Considering Misalignments and Eavesdropper’s Location

The use of free-space optical (FSO) systems as secure transmission media has recently attracted research efforts worldwide. However, their secrecy performance may be compromised by the presence of an adversarial eavesdropper. In addition, misalignments between transceivers could severely affect the legitimate FSO channel and increase eavesdropping risks. This paper, for the first time, offers a complete framework to analyze the impact of an eavesdropper’s location on the secrecy performance of terrestrial FSO systems under generalized misalignments and atmospheric turbulence conditions. Particularly, the probability density functions (PDFs) of the eavesdropping channel are newly developed and presented in closed-form expressions. Capitalizing on the derived PDFs, secrecy performance metrics in the physical-layer security (PLS) and intensity modulation/direct detection (IM/DD) continuous-variable quantum key distribution (CV-QKD) systems can be analytically analyzed, incorporating all combined effects of the atmospheric turbulence, transceiver misalignments, receiver noises, and the eavesdropper’s location. Monte-Carlo (MC) simulations are also implemented to corroborate the analytical results.

Assessment of fog and rain induced-attenuation on terrestrial FSO links

Launching into the next generation of wireless communication network (5G network) requires secure highdata rate, high speed and huge bandwidth links. With the tremendous increase in broadband users, the existingcommunication systems such as radio frequency (RF) and microwave links cannot meet up with the challenges due totheir link interference and low bandwidth. A current technology that promises such requirements and more is FreeSpace Optical (FSO) communication. The FSO basically involves the transmission of signal-modulated opticalradiation from a transmitter to a receiver through the atmosphere or outer space. It is designed to complement thetraditional fibre optical communication links. However, location-variant atmospheric channel degrades the qualityand performance of an FSO system under severe atmospheric conditions. This paper attempts to assess both fog- andrain-induced attenuation on the performance of FSO link in a terrestrial terrain using measured visibility and rainrate data at Akure, Nigeria. 5-year (2012-2016) archived visibility data and measured rain rate data of 1-minuteintegration time obtained from Nigerian Meteorological Agency (NIMET) and the Department of Physics, FederalUniversity of Technology, Akure respectively, were used to compute the fog- and rain-induced specific attenuationsusing Kruse and Carboneur models. The performance of the FSO system was analyzed through link margin by usingthe parameters of a commercial optical transceiver, Terescope 5000. Findings from this work will be useful for FSOsystem design in the area.

Generalized channel estimation and data detection for MIMO multiplexing FSO parallel channels over limited space

In this paper, to increase the data rate of free-space optical (FSO) links, we consider multiple parallel FSO links arranged over a specified space (transceivers arranged over two rings with specified radius). Due to its ease of implementation, stability, and low cost, intensity modulation with direct detection (IM/DD) based on On–Off-Keying (OOK) is widely employed in practical terrestrial FSO links. For long-haul FSO links, avalanche photo diodes (APDs) are commonly used, which provide an internal gain in photo-detection, allowing larger transmission ranges, as compared with PIN photo-detector counterparts. Over the considered general case, firstly, we propose maximum likelihood (ML)-based detection methods when the receivers are aware of the instantaneous channel fading coefficients (CSI). Secondly, we propose an efficient OOK data detection method for a more practical case when the instantaneous CSI is not available at the receiver. For this state, initially, the channel coefficients are estimated by employing some pilot symbols and then, we use the channel estimated coefficients to detect OOK signals. For a specified space, due to crosstalk between parallel channels and pointing errors, performance of proposed data detection methods depends on the optimum value for beam waist. By providing Monte-Carlo simulation results, the optimum value of beam waist is obtained for various channel conditions. To evaluate the BER performance, we also provide analytical results and derive an analytical expression for the considered MIMO multiplexing scheme. The validity of our analytical results are confirmed by Monte-Carlo simulations.

Modeling and topology design for free-space optical networks

To date, free-space optical (FSO) networks play an important role in current network construction to support large-capacity transmission, where randomly distributed FSO terminals desire to exchange a tremendous amount of information over atmospheric turbulence channels. However, in the presence of atmospheric turbulence and misalignment fading channels, FSO network topology can be dynamic and disconnected. To mitigate the impact of dynamic network environments, appropriate higher-layer protocols should be designed. We explore a practical terrestrial mobile ad-hoc FSO network based on the bundle protocol of disruption-tolerant network, and the theoretical cross-layer system model between physical layer and network layer is derived. To design the topology, at the bundle layer, the distributed routing scheme centrality and probability (CAP) is proposed, where contact probability, sociocentric measure, and message replication strategy are considered simultaneously, and the joint forwarding decision rule is given. Simulation results on the opportunistic networking environment simulator are presented, which show that CAP can be better compared with the conventional end-to-end protocol-based routing scheme.

Assessment of fog and rain induced-attenuation on terrestrial FSO links

Launching into the next generation of wireless communication network (5G network) requires secure high data rate, high speed and huge bandwidth links. With the tremendous increase in broadband users, the existing communication systems such as radio frequency (RF) and microwave links cannot meet up with the challenges due to their link interference and low bandwidth. A current technology that promises such requirements and more is Free Space Optical (FSO) communication. The FSO basically involves the transmission of signal-modulated optical radiation from a transmitter to a receiver through the atmosphere or outer space. It is designed to complement the traditional fibre optical communication links. However, location-variant atmospheric channel degrades the quality and performance of an FSO system under severe atmospheric conditions. This paper attempts to assess both fog- and rain-induced attenuation on the performance of FSO link in a terrestrial terrain using measured visibility and rain rate data at Akure, Nigeria. 5-year (2012-2016) archived visibility data and measured rain rate data of 1-minute integration time obtained from Nigerian Meteorological Agency (NIMET) and the Department of Physics, Federal University of Technology, Akure respectively, were used to compute the fog- and rain-induced specific attenuations using Kruse and Carboneur models. The performance of the FSO system was analyzed through link margin by using the parameters of a commercial optical transceiver, Terescope 5000. Findings from this work will be useful for FSO system design in the area.

Assessment of FOG and Rain Induced-Attenuation on Terrestrial FSO Links

Notice of Retraction-----------------------------------------------------------------------After careful and considered review of the content of this paper by a duly constituted expert committee, this paper has been found to be in violation of APTIKOM's Publication Principles.We hereby retract the content of this paper. Reasonable effort should be made to remove all past references to this paper.The presenting author of this paper has the option to appeal this decision by contacting ij.aptikom@gmail.com.----------------------------------------------------------------------- Launching into the next generation of wireless communication network (5G network) requires secure high data rate, high speed and huge bandwidth links. With the tremendous increase in broadband users, the existing communication systems such as radio frequency (RF) and microwave links cannot meet up with the challenges due to their link interference and low bandwidth. A current technology that promises such requirements and more is Free Space Optical (FSO) communication. The FSO basically involves the transmission of signal-modulated optical radiation from a transmitter to a receiver through the atmosphere or outer space. It is designed to complement the traditional fibre optical communication links. However, location-variant atmospheric channel degrades the quality and performance of an FSO system under severe atmospheric conditions. This paper attempts to assess both fog- and rain-induced attenuation on the performance of FSO link in a terrestrial terrain using measured visibility and rain rate data at Akure, Nigeria. 5-year (2012-2016) archived visibility data and measured rain rate data of 1-minute integration time obtained from Nigerian Meteorological Agency (NIMET) and the Department of Physics, Federal University of Technology, Akure respectively, were used to compute the fog- and rain-induced specific attenuations using Kruse and Carboneur models. The performance of the FSO system was analyzed through link margin by using the parameters of a commercial optical transceiver, Terescope 5000. Findings from this work will be useful for FSO system design in the area.

Classification Framework for Free Space Optical Communication Links and Systems

Free space optical (FSO) communication technology, also known as optical wireless communications, has regained a great interest over the last few years. In some cases, FSO is seen as an alternative to existing technologies, such as radio frequency. In other cases, FSO is considered as a strong candidate to complement and integrate with next-generation technologies, such as 5G wireless networks. Accordingly, FSO technology is being widely deployed in various indoor (e.g., data centers), terrestrial (e.g., mobile networks), space (e.g., inter-satellite and deep space communication), and underwater systems (e.g., underwater sensing). As the application portfolio of FSO technology grows, so does the need for a clear classification for FSO link configurations. Most existing surveys and classifications are single-level classifications, and thus not inclusive enough to accommodate recent and emerging changes and developments of different FSO link configurations and systems. In this paper, we propose a multi-level classification framework to classify existing and future indoor, terrestrial, space, underwater, and heterogenous FSO links and systems using common and simple unified notation. We use the proposed classification to review and summarize major experimental work and systems in the area until 2017. Using the proposed classification and survey, we aim to give researchers a jump-start to tap into the growing and expanding realm of the FSO technology in different environments. The proposed classification can also help organize and systematically present the progress in the research on FSO technology. This makes the identification of the market needs for standards an easier task. Moreover, different entities involved in the standardization process including academic, industry, and regulatory organizations can use the proposed classification as a unified language to communicate during the early stages of standard development which require ambiguity-free discussions and exchange of ideas between different standardization entities. We use the proposed classification to review existing standards and recommendations in the field of FSO. It is also envisioned that the proposed classification can be used as a unified framework to define different FSO channel models for simulation tools.

Performance Characterization of Spatial Diversity Based Optical Wireless Communication over Atmospheric Turbulence Channels

Optical wireless communication is regarded as the next-generation high-speed technology. It has demonstrated its capability to deliver data faster than any other state-of-the-art wireless communication technique. This technology has drawn attention as a means of implementing reliable high capacity outdoor systems that cannot be implemented by conventional fiber optics. It has emerged recently as an efficient solution to match the larger bandwidth and high data rates requirement of the upcoming wireless communication systems. However, although FSO (free space optics) system has many appealing features, it has rather disappointing performance for long links due to the degrading effects of atmospheric turbulence-induced fading. In the presence of such type of performance impairments, the received signal exhibits random intensity fluctuations, which increase the BER (bit error-rate), where the severe weather conditions can have a detrimental impact on the performance, which may result in an inadequate availability. The MIMO wireless optical procedure, in which the spatial dimensions are used to improve the reliability and spectral efficiency of point-to-point links, provides a promising approach to mitigate turbulence effects due to its powerful performance enhancing capabilities. In this paper, we investigate a terrestrial atmospheric FSO communication system operating under the influence of strong atmospheric turbulences. Additionally, the MIMO technique with equal gain combining (EGC) is used in this work to enhance the data rate of the proposed system. Atmospheric turbulence impacts are modeled as a lognormal channel with due regard for geometric losses. With the use of NRZ line coding, an FSO highly sensitive receiver using either avalanche photodetector (APD) or PIN is designed and simulated for best system performance. The preference is achieved by using Bessel and Gaussian filters. It has been found that APD receiver using Gaussian filter is suitable for long-range links with APD gain value of 3. Also, the selection of APD gain is critical to the system performance. In addition, the optimal value of APD gain required for best system performance decreases as the size of the MIMO technique increases. The achievable performance improvements including received power levels, BER and Q-factor are also discussed. The results show that the system with optical amplifier at the transmitter gives an optimum performance. In addition the system performance is enhanced in most weather conditions by using an amplified 2×2 MIMO-FSO system with booster amplifier.

Availability Prediction Methods for Terrestrial Free-Space-Optical Link Under Tropical Climate

<p>Free-space optical (FSO) links provide high speed point-to-point wireless communication, but its availability can easily be affected by weather conditions. In heavy rainfall regions, FSO links are relatively sensitive to rain. Availability prediction of FSO is indispensable part, especially in tropical areas. In this paper, methods to predict FSO link availability are presented. The overall performance of FSO link is described in terms of the availability that can be achieved over anticipated link distance. The availability prediction methods demonstrated for an FSO link ranges up to 5 km. The availability prediction methods are based on long-term statistics of atmospheric attenuations and FSO link budget under tropical climate condition. In tropical regions, for a terrestrial FSO link, carrier class availability can be achieved over a few hundred meters only; whereas enterprise class availability can be achieved over a few kilometers link distances. </p>

Availability analysis of terrestrial free space optical (FSO) link using visibility data measured in tropical region

Haze and rain are the most impairments factors to free space optical (FSO) links. These weather conditions limit the visibility, and thereby causes high attenuation of the optical signal. This high attenuation reduces the availability performance of the FSO link. This study evaluates the performance of a terrestrial FSO link under tropical climate conditions. The performance analysis is evaluate over 5 km link distance. The cumulative distribution function (CDF) of the received signal to noise ratio (SNR) is used to study the outage performance of the FSO link under haze conditions. The performance analysis is based on three years measured visibility data in Malaysia. Based on the statistical analysis, link availability of 99.99% can be achieved for 37.44 dB SNR over 1 km link distance. Carrier class availability “five nine” can be achieved for 20 dBm transmission power using 1550 nm wavelength.