Search

This work proposes a new hybrid bidirectional standard single mode fiber (SSMF)/free space optical (FSO) dual polarization quadrature amplitude modulation (DP‐QAM) employing optical orthogonal frequency division multiplexing (OFDM). An optical multicarrier generator (OMG) source is utilized. The suggested model is simulated using VPI photonics software. Thirty‐two optical OFDM channels are used; each carrier's 30 Gbps information data with DP‐QAM are employed to improve the performance of the fifth‐generation passive optical network (5G‐PON) for downstream and upstream transmission. In addition, 16‐QAM signals are used in DP. The impact of continuous wavelength (CW) lasers and high data rates in the proposed 5G‐PON has been investigated for DP‐QAM‐OFDM. The results reveal 0.96 Tb/s and 0.1 Tb/s for the downstream and upstream directions, respectively, under different turbulence effects. Furthermore, the simulation results show that the proposed model can achieve an SSMF length and FSO propagation ranges of 20 km and 2 km, respectively, with the symbol error rate (SER) (<10−9) and error vector magnitude (EVM) (<0.186). [ABSTRACT FROM AUTHOR]

We report the designing of a free-space-optics (FSO) transmission system capable of transmitting high rate information by utilising novel mode division multiplexing (MDM) transmission technique. In the work reported, 2-channels transmitting 10 Gbps data, using either non-return-to-zero (NRZ) encoding scheme or return-to-zero (RZ) encoding scheme are modulated by using different Hermite–Gaussian (HG) modal beams of the single laser beam to realize of 20 Gbps transmission system. The system proposed is simulative analysed under the effect of different weather states. Also, we have compared the bit error rate (BER) and Quality factor (Q Factor) performance for RZ and NRZ encoding schemes in the system for varying weather states. The results reported show that NRZ encoding exhibits a superior performance. Also, we have analysed the system performance by taking into consideration atmospheric scintillation effect and the reported results show notable signal degradation in the presence of scintillation. [ABSTRACT FROM AUTHOR]

Free space optical (FSO) communication has shown promising advantages among other wireless schemes. It provides a very high data rate, freedom from licensing, low cost of deployment and requires low power. FSO is a technology that has undergone rapid development over the last several years. These communication systems are a line-of-sight technology in which information is transmitted through the atmosphere on modulated laser beams or light-emitting diode (LED) beams. When FSO technology was first introduced, it was seen as an attractive option to bridge the "last mile bottleneck" that is present in many of today's optical fiber-based networks. As compared to existing radio frequency (RF) based wireless systems, this technology possesses multiple advantages, such as high bandwidth, license-free band use, long operational range, spatial reusability, security and immunity to electromagnetic interference. The narrow and directional characteristics of a laser beam employed in FSO enable spatial reuse and make it hard to eavesdrop, thus raising the level of security. The use of light as carrier in this technology provides immunity to electromagnetic interference. Despite its many advantages, this technology is susceptible to some weather conditions, such as fog, rain, sleet and snow, and to misalignment of transmitter–receiver terminals. Atmospheric conditions will impair the propagation of an optical signal because the propagation of light may undergo absorption and scattering. Pointing error caused by misalignment of the transceivers is another major challenge in FSO communication system. The pointing error may result in degradation or even total loss of the received signal. This error may arise because of transceiver sway, platform vibration, the motion of mobile stations, errors or uncertainties in the tracking system. Another type of pointing error is beam wandering caused by the in-homogeneity of large-scale eddies in the atmosphere (i.e., atmospheric turbulence), where the transmitted beam may deviate from its intended path. This survey paper focuses on the systems involved in the alignment of the transmitter and the receiver so that the maximum amount of power is collected by the receiver and the analysis of beam profile in various atmospheric conditions and their mitigation methods. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) can be a desirable method since it can utilize resources efficiently to provide larger capacity. Similarly, optical transmission is also becoming popular due to the availability of licence-free large bandwidth and low-cost transceiver implementation. Although optical NOMA system can be promising for long range wireless systems, investigation of its reliability performance is essential for different channel models. In this study, outage probability, channel capacity, symbol error rate expressions, diversity and coding gains for arbitrary number of users are obtained for downlink-NOMA over free space optical links modeled with Málaga distribution. Theoretical results are verified by numerical examples for various scenarios providing useful background for future analyses and designs. [ABSTRACT FROM AUTHOR]

In different atmospheric conditions, Free Space Optical (FSO) transmission is vital because it sends data via light beams through the atmosphere. This technique transmits data quickly and efficiently with low signal attenuation in clear weather. This makes it ideal for short- to medium-range communication, especially in urban areas where cables or radio frequency spectrum are impractical. However, fog, rain, and snow can absorb or disperse the light signal, reducing transmission range and reliability for FSO. This research creates an effective FSO system that supports many channels and transmission distances. The suggested system will be tested in four weather conditions (light air, light rain, medium rain, and heavy rain) with attenuation values of 0.47, 1.988, 5.844, and 9.29 dB/km. Optisystem program version 21 designs and evaluates system performance based on QF, BER, and other criteria. In this research, multiple modulation formats are evaluated for best performance. QF exhibited a reversal relationship with distance, while BER showed a direct one. The suggested system can transmit for 25 km, 12 km, 10 km, and less than 6 km in light air, light rain, medium rain, and severe rain. This research also examines system performance under NRZ and RZ modulation formats. NRZ modulation is better for light air and clear weather transmission than RZ modulation since it requires less equipment and is easier to install. Since NRZ modulation requires no clock recovery overhead, bandwidth efficiency is usually higher. In light rain, RZ modulation minimizes optical fiber dispersion, extending transmission distances and improving signal quality. NRZ excels within 10 kilometers. NRZ works for 6 km and 4 km in medium and severe rain, although RZ's dispersion tolerance and synchronization make it better for longer transmission distances. For short distances, NRZ is suitable, but for longer distances, RZ is more resilient due to its better dispersion management and signal transmission.

This paper proposes a novel approach to enhance the multichannel fiber optic sensing systems by integrating an Inverse Fast Fourier Transform-based Deep Neural Network (IFFT-DNN) to accurately predict sensor responses despite signals overlapping and crosstalk between sensors. The IFFT-DNN leverages both frequency and time domain information, enabling a comprehensive feature extraction which enhances the prediction accuracy and reliability performance. To investigate the IFFT-DNN's performance, we propose a multichannel water level sensing system based on Free Space Optics (FSO) to measure the water level at multiple points in remote areas. The experimental results demonstrate the system's high precision, with a Mean Absolute Error (MAE) of 0.07 cm, even in complex conditions. Hence, this system provides a cost-effective and reliable remote water level sensing solution, highlighting its practical applicability in various industrial settings. [ABSTRACT FROM AUTHOR]

Summary: The technique to overcome the challenge while implementing the fiber optical link is investigated using an alternative optical link called a free‐space optical (FSO) link with advanced modulation and signal processing techniques. A dual‐polarized 16‐quadrature amplitude‐modulated signal is transmitted over single and multi‐FSO channels under various atmospheric attenuation conditions. High bandwidth and data rates (up to 10 Gbps), unlicensed spectrum (above 300 GHz), and simplicity of deployment are significant benefits of the FSO system. However, the weather conditions of haze, rain, and fog cause signal attenuation when the optical carrier wave is transmitted over free space, and atmospheric turbulence is a challenge to FSO implementation, which degrades the transmission performance of optical signals for long‐distance communication. For 120 Gbps data transmission, the performance of a multi‐input and multi‐output (MIMO) FSO system is evaluated by observing the bit error rate (BER) and received signal constellation diagram. Optical signal‐to‐noise ratio (OSNR) parameters were iterated to determine the optimal value for back‐to‐back, single‐input, single‐output (SISO), and MIMO systems. Moreover, we examined the proposed system's output with recent articles, including MIMO, multiplexing, and various modulation techniques. The comparison of results shows that the suggested MIMO‐FSO model has enhanced the performance with the lower BER as less than 3.8 × 10−3 (log of BER is −2.42) forward error correction (FEC) limit for 18.7 km link range in clear air with 0.54 dB/km attenuation, 4.8, 4.5, 1.35, and 0.57 km under haze, light fog, medium, and heavy fog with 4.6, 6.9, 28.9, and 75 dB/km attenuations. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to optical communication systems by introducing a hybrid MGDM–FSO (Mode Group Diversity Multiplexing—Free Space Optical) system. The primary objective of this innovative system is to address the limitations of traditional communication systems, particularly in challenging environmental conditions. By combining the advantages of MGDM, which enhances transmission capacity in optical fibers, with the flexibility and high data rates offered by FSO technology, the hybrid MGDM–FSO system aims to overcome obstacles encountered during data transmission. In this study, we provide a detailed analysis of the proposed system's architecture and performance characteristics under various operating conditions. Specifically, we investigate both single-input single-output (SISO) and multiple-input multiple-output (MIMO) configurations of the MGDM–FSO system. Performance metrics such as received power levels, bit error rate (BER), and quality factor (Q-factor) are evaluated to assess the system's efficiency across different weather conditions. Numerical simulations are conducted to analyze the system's performance under a range of scenarios. Our findings indicate that under clear weather conditions, both SISO and MIMO configurations exhibit optimal performance, characterized by high Q-factor and low BER. However, as weather conditions deteriorate to heavy rain and heavy fog, the Q-factor of the received signal decreases, highlighting the impact of environmental factors on system performance. This study contributes valuable insights into the behavior of hybrid MGDM–FSO systems and emphasizes the importance of robust communication techniques to mitigate environmental challenges. The findings presented here have implications for the design and implementation of optical communication systems in real-world scenarios. [ABSTRACT FROM AUTHOR]

Inter-satellite optical wireless communication (IsOWC) is frequently utilized for fast data transmission between various far away satellites in free space. Thousands of users are connected via broad-area applications that use network topologies with many frequencies per optical fiber and a range of transmission rates and capacities. Multiple frequencies being transmitted simultaneously on a fiber having a nanometer range (1300–1600) that is a powerful feature of an optical communications link. When coupled with optical amplifiers, the WDM idea creates communication lines that provide rapid user-to-user communication throughout national borders. A well-known drawback of free space optics (FSO) or Inter-Satellite Link (ISL) is degradation in optical signal power, in addition to its appealing advantages. The traditional system is improved in order to solve this issue. Using the optisystem-15 simulator, we analyzed the IsOWC link's capability for fast data transfer based on subjective factors including received power, Q-factor and BER. 16-channels multiplexed with modulation technique transmitters to the system are explained by the projected model. The link has been used at various data rates, distances, and external Match-Zehnder modulation. Applied a series hybrid optical amplifier of erbium-doped fiber amplifier (EDFA) and a laser amplifier that exists prior to and after the OWC line with the given parameters. Different OWC ranges with a loop control of 3 loops that made total link length 1600 km, and searching different data rates to show their impact on system efficiency, which showed a great enhancement in results that are crucial to the current inter-satellite OWC link. [ABSTRACT FROM AUTHOR]

Due to the massive rise in the adoption of user applications having ultra speed along with the evolution of 5G/6G networks and the Internet of Things (IoT) framework, the requirement of ultra transmission rates has raised concerns for service providers and researchers across the globe. Consequently, a high-speed framework has become the necessity of today’s communication network and the research community is carrying out intensive research in this field globally. In this work, we have proposed a hybrid wavelength division multiplexing (WDM) based single-mode fiber (SMF)-free space optical (FSO) link employing multiple input multiple output (MIMO) transmission. The proposed hybrid design supports a channel length of 20 km (SMF) + 1.51 km (FSO) + 20 km (SMF) and we have examined the system performance for supporting a diverse range of optical network units (ONUs). The proposed model has demonstrated promising results for supporting a large number of ONUs at the receiver section while ensuing bit error rate of 10 - 9 . [ABSTRACT FROM AUTHOR]

The forecast of rain rate and the accompanying attenuation is a crucial factor for analyzing the efficacy of a terrestrial-based 'Free Space Optical' communication technology. The optical beam in a terrestrial-based FSO communication system commonly propagates through open air, where it is susceptible to atmospheric hazards like rain, dust, fog, snow, etc., as a result, the optical beam is diminished by these hazards. In this paper, experimentation has been carried out in the developed artificial rain simulation chamber with a 980 nm Laser source. The considered modulated Laser beam propagates in the different rain rates that are generated by the artificial rain simulation chamber. The obtained optical power attenuation for wavelength (980 nm) is compared with other existing conventional models and developed a new rain attenuation model. With the research of optical power attenuation, the impact of various rain rates on communication channels has been investigated as well, and eventually, an optical power attenuation mitigation strategy known as the "Aperture Averaging" technique has been Introduced in the system. As a consequence, the optical link performance has been improved significantly in terms of received optical power, signal-to-noise ratio, bit error rate, etc., at different rain rate scenarios. [ABSTRACT FROM AUTHOR]

The analysis of average spectral efficiency (ASE) of multi-pulse position modulation (MPPM) scheme with optimal rate adaptation (ORA) and channel inversion with fixed rate (CIFR) adaptation schemes over the gamma–gamma free space optical (FSO) channel has been carried out in this paper. The performance of the adaptation schemes has been analyzed in terms of the average channel capacity and has been further scrutinized under the aperture averaging effects in moderate and strong atmospheric turbulence. For the first time, closed form expressions for MPPM with ORA and CIFR transmitter adaptation schemes have been derived in terms of Meijer's G functions. Using the derived expressions, the performance of the two adaptation policies have been compared for different transmitter power and varying FSO length, MPPM modulation order and aperture averaging. The analysis results revealed that generally, ORA performs better than CIFR under the considered turbulence strength, modulation order and aperture averaging. However, aperture averaging offers more gain in ASE in strong turbulence than moderate turbulence for both ORA and CIFR. Furthermore, the results revealed that aperture averaging effects offers much more gain in ASE when used with CIFR than ORA. [ABSTRACT FROM AUTHOR]

In this paper, we have proposed and demonstrated a 100 Gbps data transmission system over hybrid single mode fiber (SMF)-free space optics (FSO) link using optical comb lines in wavelength-division-multiplexing technique. A continuous wave laser, two dual drive Mach-Zehnder modulators and four electrical attenuators are employed to generate optical frequency comb lines (OFCL). The OFCL generator generates 52 comb lines by optimizing biasing voltages. The OFCL lines with a side mode suppression ratio of ∼ 50dB and flatness ∼∼ 0.01dB are generated and used as an optical carrier in the proposed system. The performance of the system is investigated in different weather conditions, such as clear weather, hazy weather, heavy rain, light fog, moderate fog, and heavy fog. [ABSTRACT FROM AUTHOR]

Since free-space optical links (especially fully photonic ones) are very challenging to accurately align; scanning algorithms are used for the initial search and alignment of the transceivers. The initial alignment aims to intercept the optical beam so that it hits a position-sensitive detector. However, this operation can be very time-consuming (depending on the system parameters, such as transceiver parameters, distance between transceivers, divergence of the transmitter, angle of view of the receiver, etc.). A spiral scan is used as the most widespread pattern for scanning. This article examines the effects of system parameters (e.g., global navigation satellite systems and compass accuracy) on the angular area of uncertainty that must be scanned to find the optical beam. Furthermore, several types of spiral pattern are compared depending on the time of the scan execution and the required number of points for scanning the given uncertainty area. The cut hexagonal spiral scan achieved the best results as it required 18.1% less time than the common spiral scan for the presented transceiver. [ABSTRACT FROM AUTHOR]

In this paper, a new 5G Passive Optical Network (5G-PON) employing all-optical orthogonal frequency division multiplexing (AO-OFDM) is proposed in hybrid bidirectional standard single mode fiber (SSMF)/free space optical (FSO). Additionally, an optical frequency generator (OFG) source is utilized. The proposed model is simulated using VPI photonics software. Analytical modeling and simulations have been conducted for a new approach to generate OFG by cascaded two-frequency modulators and one electro-absorption modulator. A sinusoidal RF signal source is utilized to drive all these modulators. The results reveal that 64 optical multiplexed carriers with a frequency spacing of 30 GHz are generated. These optical carriers have power variations of < 1 dB. Moreover, the center wavelength of the generated OFG can be tuned from 1300 nm for upstream transmission to 1577 nm for downstream transmission in the proposed 5G-PON. The proposed network achieves 960 Gbps and 10 Gbps for the downstream and upstream directions, respectively, under different turbulence effects. Furthermore, when 32 AO-OFDM channels are used, the simulation results show that the proposed model can achieve a SSMF length and FSO propagation ranges of 20 km and 2 km, respectively, with bit error rate (BER) ( < 10 - 3 ). [ABSTRACT FROM AUTHOR]

In this paper, we present a study investigating the impact of jamming in a Dual-Hop free-space optical (FSO) communication system assisted by reconfigurable intelligent surfaces (RIS) in the presence of a malicious jammer. We analyze the combined effects of atmospheric turbulence (AT), pointing error (PE), and angle of arrival (AoA) fluctuation of unmanned aerial vehicles (UAVs). Closed-form expressions for the overall average bit error rate (ABER) are derived while considering these impairments. To mitigate the jamming effect, we explore a Single-Input Multiple-Output (SIMO) FSO system and derive the end-to-end Average Bit Error Rate (ABER) under various jamming scenarios. Additionally, we conduct a comprehensive study by examining different placements of the malicious UAV jammer and RIS, drawing insightful conclusions on system performance. The analytically derived expressions are validated through Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Free-space optical (FSO) communication can be subject to various types of distortion and loss as the signal propagates through non-uniform media. In experiment and simulation, we demonstrate that the state of polarization and degree of polarization of light passed though underwater bubbles, causing turbulence, is preserved. Our experimental setup serves as an efficient, low cost alternative approach to long distance atmospheric or underwater testing. We compare our experimental results with those of simulations, in which we model underwater bubbles, and separately, atmospheric turbulence. Our findings suggest potential improvements in polarization based FSO communication schemes. [ABSTRACT FROM AUTHOR]

In this paper, the design of an atmospheric turbulence simulation system for free-space optical (FSO) communication is proposed. The system can accurately simulate repeatable atmospheric turbulent fading channels. It has a dynamic execution range of 30 dB with an execution rate of 1 MHz. The execution accuracy of the system is higher than 0.1 dB. In addition, the reliable TCP/IP protocol is used for communication, which ensures the convenience and versatility of the system. Experiments are carried out to investigate the performance of the system, and the results prove its superiority. Hence, the atmospheric turbulence simulation system can effectively simulate the influence of atmospheric turbulence channels on FSO communication systems. [ABSTRACT FROM AUTHOR]

Circular polarization division multiplexing (CPDM) is a pioneering technology that has superiority over linear polarization division multiplexing (LPDM) due to the absence of polarization axis alignment synchronization at the receiver and because it distributes the scattered light evenly. In this work, a wavelength division multiplexed (WDM) 2 × 320 Gbps free space optical (FSO) system has been presented by incorporating CPDM, 256-quadrature amplitude modulation (256-QAM), and digital signal processing (DSP). Moreover, matched filters are employed due to their anti-jamming and noise-cancelation properties. For the investigation of the proposed system at varied FSO ranges in terms of bit error rate (BER) under different weather disturbances, we have considered clear weather, heavy rain, heavy fog, and heavy dust. Results revealed that the proposed system can withstand very high power levels as high as 100 dBm and can cover 38 km under clear weather, 5 km under heavy rain, 3 km under heavy fog, and 400 m under heavy dust at 10–3 BER. [ABSTRACT FROM AUTHOR]

Hybrid wavelength-division-multiplexing (WDM) and free space optical (FSO) access networks are getting great attention due to numerous advantages. In this work, hybrid WDM-FSO system is demonstrated for 55 km at capacity of 5 × 10 Gbit/s using compressed spectrum return to zero (CSRZ) WDM-FSO in downstream and nonreturn to zero (NRZ) in upstream for demonstrating transmitter diversity which inturn decrease the interchannel interference. For the suppression of Rayleigh backscattering (RB) interferometric beat noise, bidirectional cyclic multiplexer is employed. Cyclic multiplexer provide λ1 to λ5 wavelengths for optical line terminal (OLT) to ONU transmission and λ2 to λ6 for ONU to OLT transmission. Insertion losses of each component are considered and in the end, power budget is also calculated. Results revealed that FSO length of 780–1050 m are obtained using various WDM-FSO downstream signals and their power budget, redundant budget, maximum distance, and insertion losses also calculated. [ABSTRACT FROM AUTHOR]

In this work, a free-space optical (FSO) communication system with the integration of mode division multiplexing and circular polarization shift keying (CpolSK) is proposed at 2 × 40 Gbps using LG00 and LG01 modes. Effects of diverse weather conditions such as clear weather, light rain, moderate rain, heavy rain, thin fog, thick fog, and heavy fog are studied on system performance. Further, a detailed comparison of CpolSK and polarization shift keying (PolSK) is performed at different FSO lengths in terms of log bit error rate. For implementation, analysis, and comparison, Optiwave Optisystem software is used and results show that CpolSK covers 100 km link distance and PolSK limits to 90 km only. Also, LG00 mode performs better than LG01 mode under all weather instabilities in the proposed system. [ABSTRACT FROM AUTHOR]

Optical wireless communication systems employing free-space optical (FSO) links utilize modulated lasers to transmit information. FSO–fiber optic (FO) link provides an alternative possible way in scenarios where infrastructures employing optical fibers are widely destroyed due to disasters or when difficulties are faced during the installation of FO links. Furthermore, the link is integrated with decision-making ability. To encounter the distortions in the received signal carrier-suppressed return-to-zero modulation format has been used. FSO–FO hybrid link has been compared with simple FSO channel. The terrestrial links depend strongly on weather conditions as optical beams propagate through the atmosphere. Atmospheric attenuation could affect the FSO channel and has been considered to analyze the performance of the designed system. [ABSTRACT FROM AUTHOR]

This article has indicated optical coherent differential polarization (DP) 16 quadrature amplitude modulation (QAM) transceiver systems with free-space optical (FSO) channel in the presence of differential coding scheme. The optical coherent DP 16-QAM receiver executes the reverse process conversion of the optical signal into an electrical one that is detected to the users. The proposed optical coherent DP-16 QAM transceiver systems based FSO channel model with differential coding has been presented and compared with the previous model. However, the simulation results have confidence realization about the superiority of the proposed simulation model. Hence the proposed optical coherent DP-16 QAM transceiver systems simulation model with differential coding is verified and validated the enhancement performance based on simulation performance parameters. [ABSTRACT FROM AUTHOR]

The performance of free space optical communication system using multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) with a modified receiver structure is evaluated in this paper referred to as MIMO-OFDM-FSO with the modified receiver (MIMO-OFDM-FSO-MR). Utilizing equal gain combining the analysis is done by taking closed-form expression of average bit error rate and throughput. The simulation is performed to estimate various performance parameters such as throughput and bit error rate (BER) for the proposed MIMO-OFDM-FSO-MR model under different turbulence and weather conditions. Simulation reveals that the proposed model exhibits significant BER performance and provides better throughput and spectral efficiency as compared with conventional FSO systems, OFDM-FSO systems, MIMO-FSO systems and Low-density Parity Check (LDPC) coded MIMO-OFDM-FSO systems. [ABSTRACT FROM AUTHOR]

The performance and reliability of a free-space optical (FSO) communication system can be greatly increased using various methods. The primary goal of each technique is to reduce the effect of disturbances that lead to intensity or phase fluctuations in the system's receiver. Recent issues include increased data consumption and a crowded radio frequency spectrum, where free-space optical communication (FSOC) has changed the way people share information in a big way. In place of wired communication systems, it is possible to transport voice, video, and data effectively through air. High speed, cost savings, small buildings, low power consumption, energy economy, maximum transfer capacity, and adaptability are some of the main advantages of FSOC. Repair downtime can be reduced because of the quick advancement of high-speed connection technology. It is also now possible to quickly establish a backup network in an emergency or crisis. The design of FSO systems for two types of digital modulation techniques is the primary focus of this work. An examination of the FSO link's performance in various channel conditions using various modulation techniques is conducted. This analytical mechanism can aid a modulation strategy for various channel conditions. The results indicated that PSK modification is stronger against atmospheric turbulence than ASK modification in terms of quality factor and signal-to-noise ratio (SNR). In addition, the values of received power, quality factor, and signal-to-noise ratio were higher in the case of atmospheric turbulence during rain than in the case of fog, followed by dust conditions. The systems can operate using adaptive optics and evaluate the system's performance in the presence of atmospheric turbulence in terms of signal quality, received power, and signal-to-noise ratio.

Efforts are being made to commercialize optical inter-satellite links (O-ISL) in low earth orbit (LEO) satellite networks as it is a crucial technology for next-generation communication networks. However, installing the pointing, acquisition, and tracking (PAT) modules is vital due to the long link distances among the fast-orbiting satellites. This research investigates the configurations of multiple PAT modules (multi-PAT) and the tradeoff between data-rate and latency, considering practical constraints such as link distance back-off and the atmospheric bypass. An ego-centric coordinate conversion method facilitates the field-of-view analysis from an ego-satellite perspective optimization of the multi-PAT. Simulation results suggest that around 70% of angular coverage around the ego-satellite through the multi-PAT allows reliable O-ISLs. The link distance back-off constraining the maximum distance of an individual link sensitively governs the number of hops, but the total O-ISL path distance is less affected. Regarding the atmospheric bypass restricting the lowest altitude for each link, the side-effect is insignificant even when the atmosphere up to 100 km from the ground is bypassed. The communication and latency performances are in a tradeoff relationship since the per-link distance and the number of hops are inversely related in O-ISLs. The individual link distance significantly affects the channel loss, and the number of hops directly influences latency. Depending on the multi-PAT configurations, an O-ISL system with ~10 Gb/s within ~200 ms can be established from New York to Seoul.

Free Space Optics (FSO) has emerged as a viable solution to meet the growing demand for high bandwidth, secure data transmission, and high speed. However, the FSO system is highly susceptible to environmental factors, with precipitation in particular having a significant impact on FSO links. Optical loss, phase fluctuation, and multipath fading of the received optical power are all caused by these external factors. From this perspective, to improve the system’s performance in such conditions, a novel image encryption technique based on the Choquet Fuzzy Integral (CFI) in conjunction with the integer wavelet transform is proposed. The security of the proposed method is demonstrated via analysis security on the one, and its efficacy in terms of transmission performance of an encrypted image over an FSO channel exposed to rainy weather conditions is analyzed on the other. Authentic meteorological data from two distinct cities are considered to demonstrate the model’s real-world applicability: Alexandria, Egypt, in Africa, and Jeddah, Kingdom of Saudi Arabia (KSA), in Asia. To evaluate the system’s performance, a variety of metrics such as FSO range, Signal-to-Noise Ratio (SNR), Peak Signal-to-Noise Ratio (PSNR), and the Structural Similarity Index Method (SSIM) are used. Furthermore, the findings from studying the impact of weather conditions reveal that, as the intensity of rainfall increases, the encrypted image experiences a reduction in its propagation range within the FSO channel. For example, under heavy rain (HR) conditions, the maximum FSO range for high-quality received encrypted images is 1055 m, which extends to 2290 m as rain intensity decreases (for light rain). In terms of the two cities, Jeddah, with its lower average rainfall intensity compared to Alexandria, allows the encrypted image to travel an additional 2400 m.

In this paper, an improved adaptive coding and modulation scheme with hybrid switching standard is proposed for UAV-to-Ground free space optical (FSO) communication to mitigate the degradation of turbulence intensity variation. In order to improve bits efficiency in different turbulence, a channel estimator based on Gated Recurrent Unit (GRU) and a hybrid switching standard based on frame error rate (FER) of LDPC decoding are applied. Simulation results show that the GRU estimator achieves approximately 34.9% improvement in training time compared to the LSTM estimator, without degradation in system performance. Moreover, the hybrid switching standard significantly improves the signal-to-noise ratio (SNR) switching threshold deviation of the ACM scheme from 1.8 dB and 4 dB, which were observed in moderate turbulence conditions, to an average of 0.35 dB. This improvement allows for the effective implementation of the ACM scheme in different turbulence intensities at a relatively small cost, thereby enhancing the communication quality of FSO systems in atmospheric channels characterized by turbulent variations.

En el presente artículo, se realiza un estudio orientado a las comunicaciones ópticas en el espacio libre (Free Space Optics - FSO), al identificar sus principales beneficios y limitaciones. Se considera también un caso de estudio práctico en la ciudad de Loja (Ecuador) para el diseño de la tecnología FSO donde se toma en cuenta sitios idóneos para el despliegue, condiciones climáticas y línea de vista entre los nodos seleccionados y características técnicas de los equipos considerados. Se realiza además un análisis de pérdidas de trayecto y geométricas de canal, en donde los resultados obtenidos permiten comprender bajo qué condiciones atmosféricas se dispone de un enlace óptimo. El estudio se valida por medio de la ejecución de simulaciones a través del software Optisystem al considerar varios escenarios de estudio. Uno de los resultados más importantes que se logra identificar, es la tasa de transmisión que soporta la tecnología FSO en diferentes condiciones atmosféricas, que supera los 3 km, además del gran ancho de banda que ofrece en comparación a otras tecnologías como RF que se ven limitadas por factores similares.

We show two experiment setups to verify the applicability of WDM (wavelength division multiplexing)-RoFSO (Radio-over-Free-Space Optics) system: (i) transmission of images files following the data format of IEEE 802.11 wireless local area network; (ii) robust performance analysis of bit error rate for on–off keying signal at a speed of 10 Gbps. Specifically, it is shown that, for 100 m indoor transmission, our testbed satisfies an error-free condition of BER ≤10−12, achieving a total data rate of 20 Gbps. In this paper, we contribute to the evaluation of the practical FSO measurement data by providing experimental measurements.

In this research, the performance of a WDM-FSO communications system is simulated under rain weather conditions utilizing NRZ modulation technology. Weather-related attenuation limits the distance of free-space optical (FSO) communication systems and the availability of line-of-sight terrestrial links. The suitability of distance links under this technology is investigated, and WDM has a greater advantage when employed in optical communication systems. Simulation is made as far as obtained optical power is concerned, so the loss of the receiving power can be investigated by utilizing the range analyzer at the receiving part based on OptiSystem 7. The increasing of transmitter power improves the performance of the signal quality under rain conditions. Our findings show that there is a critical parameters for transmitter/receiver link in FSO channels. The results of the reenactment reveal that the execution of WDM-FSO is better suited for strong attenuation. At a high transmitter power, the system has a low BER. Meanwhile, it has a high Q-factor. [ABSTRACT FROM AUTHOR]

Mode division multiplexing (MDM) has fascinated great attention more recently to strengthen the network capacity. To implement MDM in data centers services, a low power and low cost system is desired. Also, effectively designing a hybrid system comprising of both fiber and free space optics (FSO) links can access the cost efficiency of FSO and resilience of fiber. Therefore, in this paper, a bidirectional hybrid 10 gigabit passive optical network (XG-PON) and FSO using MDM technique is proposed. Four distinct Laguerre–Gaussian (LG) modes, LG[0,0], LG[0,20], LG[0,40] and LG[0,60] are considered in the proposed system using hybrid multimode fiber and fronthaul Gamma Gamma fading FSO links. System performance is investigated for varied hybrid fiber-FSO links with links losses and noise under different weather conditions as well as turbulence effects. The results depicts that 200–320 m fiber length with fixed 100 m FSO range and faithful 300–580 m FSO range with 100 m fiber distance can be obtained for all modes. At bit error rate of 10–9, tolerable additional loss of 1.7–4.3 dB derived under haze, rain, weak and strong turbulent conditions for various operating modes. With the geometric loss of − 15 to 5 dB upto 700 m FSO range can be attained successfully. Also, the proposed system provides high gain (~ 22 dB), low noise figure (~ 22 dB) and high optical signal to noise ratio (~ 58 dB). Besides this, compared to existing systems, the proposed MDM incorporated hybrid XG-PON/FSO system using four LG modes under severe weather conditions represents best performance for future optical networks. [ABSTRACT FROM AUTHOR]

Summary: With the development of free space optical links (FSO) for space‐ground communications comes the need to mitigate the effects of the atmospheric turbulence to guarantee a lossless connection. By having a network of addressable ground stations, we want to guarantee to always target a point where the link is available. Assuming atmospheric transmission is managed thanks to site diversity, we focus only on the influence of atmospheric turbulence on the signal injected into a single mode fiber on the downlink. The use of adaptive optics (AO) is assumed to avoid turbulence‐induced signal disruptions and enable a sufficiently high level of received signal for data transmission. Up to now, AO performance adequate assessment required the knowledge of high‐resolution Cn2 and wind profiles. With the advent of integrated atmospheric parameters measurement instruments, we investigate here the possibility to estimate AO‐corrected performance from a limited number of integrated parameters. In this paper, we propose to use a Gaussian process metamodel to assess the statistics of the received optical power after an AO correction. Taking as input only four integrated parameters of the turbulence profile and associated wind profile, which can be measured with simple instruments, the estimation error on the value of the 1% quantile of the received optical power is inferior to 0.7dB. We also demonstrate the possibility to estimate the half correlation time of the received optical power using the same integrated parameters. [ABSTRACT FROM AUTHOR]

Free space optics (FSO) can be used as an alternative to the currently used wireless radio communication systems to meet the increasing demands for the uninterrupted internet connection in High-Speed Trains (HSTs). FSO is less prone to interference, license-free and more secure as compared to Radio Frequency (RF) technology. In this paper, we have compared three different wavelengths (850, 1330, and 1550 nm) for the dual-wavelength model at a bit rate of 10 Gb/s to see which two wavelengths provide better results. The system is studied for return to zero (RZ) and non-return to zero (NRZ) modulation formats this electronic document is a "live" template and already defines the components of your paper [title, text, heads, etc.] in its style sheet. [ABSTRACT FROM AUTHOR]

Free space optical communication (FSO) is thriving with greater pace nowadays due to its ability to support high speed, greater capacity, improved security, ease of installation, not having of Electromagnetic interference (EMI) and unlicensed spectrum. Atmospheric turbulence like Rain, Fog, and Haze is a prominent issue in FSO system that adversely affects the performance. This paper presents the demonstration of a multibeam FSO system operating at 1.25 Gbps in several haze types, including hazardous, very unhealthy, sensitive, good, moderate, and unhealthy. Additionally, BER and Q factor comparisons are made across three distinct pulse formats: carrier suppressed RZ (CSRZ), return to zero (RZ), and non-return to zero (NRZ). Utmost goal for the deployment of multibeam FSO is to get high received power and to compensate attenuation arising from haze effects. Results revealed that CSRZ performed exceptionally well as compared to NRZ and RZ. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) has recently drawn more attention due to the existing light sources having a bandwidth that can deliver data transmission at higher bit rates. To maintain desired brightness levels along with reliable data transmission, VLC requires to control dimming levels. In this paper, a dimming control scheme based on pulse position modulation (PPM) is proposed, which constructs a dimming encoded frame per symbol of input data. The scheme utilizes multiple headers, which is selected depending on the dimming levels and the number of bits in a symbol of input data. The proposed scheme for the VLC system supports various dimming levels. The multi header PPM frame generation for input data K = 4 and dimming values α = 0.25, 0.375, and 0.5 is simulated using NI Labview. The proposed dimming scheme has an excellent short-run length property which is well under the maximum flickering time period and is thus capable of flicker mitigation. The slot error performance of the proposed dimming control scheme in a VLC system for varying dimming levels is simulated in Matlab. Simulation results show that the proposed scheme has excellent error performance for a low dimming value of α = 0.25. The experimental results are also carried out in the optisystem considering the practical measured parameters of the indoor environment for free space channel and simulating the VLC system for the proposed scheme. The simulation is carried for different data rates over varying link ranges and the experimental results show that the proposed scheme performs best when dimming value α = 0.25 and data rate 2 Gbps. [ABSTRACT FROM AUTHOR]

The optical wireless communication has been designed by developing a model with the support of MATLAB simulator using Simulink where channel considered to be a free space. In this model, Additive White Gaussian Noise (AWGN) channel has used to analyze bit error rate (BER) and power loss of optical wireless signal at receiver. The consequence due to turbulence in atmosphere of free space on transmitted signal has examined. The BER and signal power have extremely ruined on rigorous atmospheric unstable condition even for a short distance in an optical wireless channel. The BER of less than 10−3 has been achieved for free space optical communication considered to be an excellent BER for FSO. [ABSTRACT FROM AUTHOR]

Fog attenuation causes more loss than other weather conditions in a free space optics (FSO) link thus limiting the visibility distance. This work presents a detailed survey on the attenuation of the transmitted signal as a result of variation in visibility range caused by different fog conditions of the Delhi, Safdarjung region. Kim and Kruse models have been used to calculate attenuation as a result of fog conditions for three specific months (January, February and December) for seven consecutive years starting from 2013 to 2019. Received signal quality has been analyzed as a function of transmitted power, data rate, transmission range and operation wavelength. Descriptive statistical analysis of real time observed visibility data allows for the estimation of specific optical attenuation and enables in determining the link availability of the region for the complete year. [ABSTRACT FROM AUTHOR]

In the present study, the application of free space optics (FSO) transmission system to realize a long-reach high-altitude platform (HAP)-to-satellite communication link has been exploited. High-speed information transmission without interference is accomplished using orthogonal frequency division multiplexing (OFDM). Further, the information capacity of the proposed system is increased by employing mode division multiplexing (MDM). We have investigated the proposed MDM-OFDM-HAP-to-satellite FSO transmission system performance over varying FSO range, diameter of the receiver, pointing errors, and input power. Also, an improved transmission performance of the proposed system using a square root module is reported. [ABSTRACT FROM AUTHOR]

In this work, the integration of free-space optics (FSO) technology for implementing long-haul high-altitude platform (HAP)-to-ground transmission system is proposed. Mode division multiplexing (MDM) and orthogonal frequency division multiplexing (OFDM) are incorporated for carrying high-speed signals without interference. The impact of increasing input power, divergence angle, antenna diameter, and attenuation on the system performance is further investigated. In addition, the performance of the MDM-OFDM-HAP-to-ground FSO transmission system is improved by using a square root module at the receiver for link reach enhancement. The results exhibit a reliable transportation of 40 Gbps information over 20 km FSO distance with good quality of the received signal. [ABSTRACT FROM AUTHOR]

Free Space Optics (FSO) communication provides attractive bandwidth enhancement with unlicensed bands worldwide spectrum. However, the link capacity and availability are the major concern in the different atmospheric conditions. The reliability of the link is highly dependent on weather conditions that attenuate the signal strength. Hence, this study focuses to mitigate the weather and geographic effects using iterative optimization on FSO communication. The optimization maximizes the visibility distance while guaranteeing the reliability by minimizing the Bit Error Rate (BER). The wireless optical communication system is designed for the data rate of 10 Gbps. The performance of the proposed wireless optical communication is compared against the literature in terms of visibility distance, quality factor, BER, and Eye diagram at different atmospheric conditions. The simulation results have shown that the proposed work has achieved better performance. [ABSTRACT FROM AUTHOR]

Satellite-to-Ground Downlink-Free Space Optics (SatGD-FSO) communication systems are emerging as the key driver for telecom investment, with several factors driving this convergence. It is attractive to minimize the size, weight, and power profiles of the space terminals by utilizing high affectability and huge accumulation collection zone ground terminals. Multiaperture coherent receivers using spatial diversity approached is considered on the attractive solution can fulfill this necessity and have numerous focal points over the single enormous opening cognizant recipients. The effects of atmospheric and climatic conditions using various dynamic system parameters have been investigated as a function of bit-error-rate (BER) performance of multiaperture coherent receivers. Types of orbits, aperture averaging, zenith angle, transmit optical power, and modulation schemes are systematically investigated and compared to the SatGD communication system. The proposed solution with a maximum throughput of 2.5 Gbps is useful for a plan and optimization improvement of the SatGD-FSO systems. [ABSTRACT FROM AUTHOR]

This work is focused to carry out the investigation of wavelength division multiplexing (WDM) approach on free space optical (FSO) transmission systems using Erbium Ytterbium Doped Waveguide Amplifier (EYDWA) integrated as post-or pre-amplifier for extending the reach to 30 Km for the cost-effective implementation of FSO system considering weather conditions. Furthermore, the performance of proposed FSO-wavelength division multiplexing (WDM) system is also evaluated on the effect of varying the FSO range and results are reported in terms of Q factor, BER, and eye diagrams. It has been found that, under clear rain the post-amplification was performed and was able to reach transmission distance over 27 Km, whereas, the FSO distance has been limited at 19.5 Km by using pre-amplification. [ABSTRACT FROM AUTHOR]