Free-space Optical Networks Research Articles

Integrated Free-Space Optics and Fiber Optic Network Performance Enhancement for Sustaining 5G High Capacity Communications

In this paper, the integrated free-space optics (FSO) and fiber optic model is evaluated using new radio (NR) sub-THz link to sustain next generation 5G capacity. The proposed integrated model effectively applies over 25 km single mode fiber, 0.5 m RF wireless, and 500 m optical wireless. In addition, four different sub-THz frequencies (125, 150, 175, and 200 GHz) are estimated on NR-based 5G FSO network, including 22 Gbps 64quadrature amplitude modulation-orthogonal frequency division multiplexing (64QAM-OFDM) signal speed. The proposed FSO enabled fiber optic system is also measured mathematically to satisfy the data transmission accuracy. For confirmation, the theoretical approach of the presented FSO and fiber optic network is realized with an aggregate 342 Gbps speed 16 × 22 . The performance metrics comprising forward error limit (FEL), bit error rate (BER), and error vector magnitude (EVM) are used for weighing simulation results. The outlets of an integrated fiber-FSO network show that by applying NR 5G sub-THz, a high data rate with multiple inputs and multiple outputs (MIMO) transmission capacity can be adjusted victoriously.

PERFORMANCE ENHANCEMENT OF DWDMFSO SYSTEM UNDER DIVERSE WEATHER CONDITIONS WITH OPTIMIZED MODULATION FORMAT

This paper is successfully demonstrating simulating comparison and investigation of 48 channels of dense wavelength division multiplexing free space optical (DWDM−FSO) network with a 10 GB/s data rate on each channel separated by 100 GHz frequency spacing under a clear sky, haze and light rain climate conditions. Apart from this, comparison of a series of modulation formats such as non−return to zero (NRZ), return to zero (RZ), carrier suppressed return to zero (CSRZ), Soliton pulse, and offset quadrature phase shift keying (OQPSK) have been performed and optimized the performance of the designed system with best suited modulated system. The performance of the proposed work has been evaluated in terms of bit error rate (BER), quality factor (Q), signal−to−noise ratio (SNR), received signal power and eye diagrams. It has been observed that OQPSK modulated system has shown more robust performance as compared to other line encoding techniques. The minimum simulation work reports for OQPSK modulated system have been recorded with the acceptable performance BER ≤ 10−10, Q ≥ 6 dB at the 2000 meters FSO link range.

An optoelectronic system for controlling a direct current motor

The software for an optoelectronic system for controlling a direct current (DC) motor is presented in Part 2 of the article. The structure of the designed control system was described in Part 1. The developed system processes data received from an infrared transmitter. The project was upgraded in successive stages of development, and it ultimately evolved into a small computer with a motor controller. The designed system automatically adjusts the motor’s rotation and speed. The user is tasked only with conveying operational commands. The entire system is based on a single microcontroller. The designed optoelectronic system receives user commands (the program can be modified to support free-space optical communication networks conforming to all communication standards). The system activates the motor, counts the number of rotations and adjusts the motor’s position. The designed system operates on the following principle: the user sends commands to the motor via a remote control with an infrared diode. The keys on the remote control have been programmed with different commands. The transmitted data are processed by the system which activates the motor and sets the desired motor speed. The task is completed, and the system is ready to process the next command. If the number of rotations differs from the preset value, the motor’s position is adjusted. If the physical position of the rotor axis is altered, the system corrects the offset to the last programmed position. The designed system can be easily adapted to various types of motors and IR controllers.

An optoelectronic system for controlling a direct current motor

An optoelectronic system for controlling a direct current (DC) motor is presented in Part 1 of the article. The software for the designed motor is described in Part 2. A system for processing data from an infrared transmitter was built. The project was upgraded in successive stages of development, and it ultimately evolved into a small computer with a motor controller. The designed system automatically adjusts the motor’s rotation and speed. The user is tasked only with conveying operational commands. The entire system is based on a single microcontroller. The designed optoelectronic system receives user commands (the program can be modified to support free-space optical communication networks conforming to all communication standards). The system activates the motor, counts the number of rotations and adjusts the motor’s position. The designed system operates on the following principle: the user sends commands to the motor via a remote control with an infrared diode. The keys on the remote control have been programmed with different commands. The transmitted data are processed by the system which activates the motor and sets the desired motor speed. The task is completed, and the system is ready to process the next command. If the number of rotations differs from the preset value, the motor’s position is adjusted. If the physical position of the rotor axis is altered, the system corrects the offset to the last programmed position. The designed system can be easily adapted to various types of motors and IR controllers.

Jamming Threats in Free-Space Optics

Free space optical (FSO) technology has recently found a strong foothold in the telecommunication market due to its technical superiority and high-end applicability. Its technological advancement has caused rising implementation of FSO systems in defence, aerospace, and telecommunication industries. Although it is cutting edge, the fundamental benefits of this technology may be adversely affected by several foreign elements such as atmospheric turbulence, physical obstructions, and weather conditions. Along with these natural disrupting phenomena, for the deployment of FSO systems in security-constrained sectors like military and defence units, where extra data protection mechanism is needed, fabricated adversaries like jamming become feasible which is concerning for FSO applicability. It therefore becomes a challenging task to decipher legitimate FSO data in the presence of jammers and to secure an FSO system from jamming activities. On this account, a detailed discussion on jamming effects in FSO communication systems is showcased in this article. Also, the potential efforts to mitigate jamming in FSO networks are highlighted.

Space-Air-Ground FSO Networks for High-Throughput Satellite Communications

The next generation of satellite communication systems aims to achieve terabit-per-second throughput. Because of the limited spectrum available, traditional radio frequency (RF) communication links cannot provide such high throughput. Free-space optical (FSO) transmission is a possible alternative that has recently gained increased attention in the satellite community. However, FSO communications are vulnerable to the severe effects of atmospheric turbulence, such as beam-wandering-induced pointing errors and beam scintillation. To successfully remedy such effects, we propose a space-air-ground (SAG) FSO network with a strategically deployed high-altitude platform acting as a relay. We show that such a design can substantially mitigate the effects of atmospheric turbulence, especially when the satellite zenith angle is relatively high. Then we present a novel SAG satellite communication network that integrates the suggested SAG-FSO transmission and conventional hybrid single-hop FSO/RF transmission to improve overall system reliability and performance even further. The numerical results clearly show the potential of the proposed, highly innovative SAG-FSO network architecture.

160 Gbps capacity and sub-us latency of polarization-independent optical packet switch architecture for free-space optical network using PLZT optical switch

In this paper, we discuss the challenges and limitations of current free-space optical (FSO) networks toward scaling beyond the 100 Gbps switch capacity era while achieving low-latency and high-reliability. Owing to the slowdown of Moore’s law, to avoid electronically-induced bottlenecks, we construct an FSO switch network and experimentally evaluate the feasibility of ultrafast optical packet switch architecture based on polarization-independent plomb lanthanum zirconate titanate (PLZT) switch without buffering. The bit error ratio of 160 Gbps ([Formula: see text]) data was validated based on measurements while still preserving the sub-us latency metrics ([Formula: see text] ns). The experimental results may offer a significant reference for FSO communication and network.

Improved Buffer-Aided Selective Relaying for Free Space Optical Cooperative Communications

This paper tackles the performance analysis and relaying strategies for two-relays buffer-aided (BA) parallel relaying cooperative free space optical (FSO) networks. We first provide an asymptotic analysis of the existing selective relaying scheme that simultaneously activates the strongest source-relay (S-R) and relay-destination (R-D) optical links. We then propose an improvement of this scheme and highlight on its advantages by deriving closed-form accurate expressions for the asymptotic values of the outage probability (OP) and average packet delay (APD). The theoretical evaluation and numerical analysis demonstrate the capability of the improved scheme in enhancing the diversity order with finite buffer sizes unlike the selective relaying scheme that achieves diversity gains only with infinite-size buffers entailing infinite delays. The OP performance is significantly enhanced for all network topologies whether the relays are closer to S, closer to D or placed at the same distance from S and D. On the other hand, the reaped APD gains depend on the positions of the relays.

Free Space Optics Transmission Performance Enhancement for Sustaining 5G High Capacity Data Services.

Enhanced bandwidth issues for 5G system are fruitfully resolved by organizing free space optics (FSO) communication frameworks. The high bandwidth, the maximum number of channel transmission requirements, and high data rate have been boosted during the last years because of the COVID-19 pandemic. The online services and digital applications have increased pressure on installed optical network models. In addition, the optical networks with high capacity transmission produce nonlinear distortions, which degrade system efficiency. This paper presents a mixed FSO and fiber network to tackle the factors of nonlinearities and enrich the system capacity and range. Furthermore, the issues related to radio frequency, FSO pointing, and co-channel interference are considered in this work. The theoretical and simulation structures are validated using advanced measuring parameters, such as bit error rate (BER), peak to average power ratio (PAPR), cumulative distribution function (CDF), and outage probability. The nonlinear factors are addressed successfully, and the capacity is developed from current models. Finally, the proposed model’s limitations and future direction are discussed in this paper.

Optical Pre-Amplification for Pointing Errors Mitigation in Free-Space Optical Networks: Datasets

Optical Pre-Amplification for Pointing Errors Mitigation in Free-Space Optical Networks: Datasets

PERFORMANCE ANALYSIS OF FSO LINK UNDER EXTREME WEATHER CONDITIONS

free space optics is currently a well-known technology for its use in the systematic transport of enormous volumes of data. It has proven to be a feasible technique for assisting existing networks with high data transfer safely across a moderate distance without the usage of fiber. Free space optics has emerged as the most viable option to the broadband market's current bottlenecks. However, certain external characteristics have a significant impact on the performance of free space optics. We calculate signal loss owing to environmental elements such as fog, snow, rain, blurring,and scintillation, as well as a detailed approach for reducing their impact on free space optical network performance. Signal quality has improved significantly using the provided methods.

Performance analysis of cognitive hybrid radio frequency and free space optical cooperative networks

This paper studies the exact performance of hybrid radio frequency and free space optical cooperative amplify and forward communication networks in a cognitive radio environment, where secondary users cannot transmit signals at any power level since the existence of the primary users restrict the behavior of the secondary users within an acceptable and reasonable range. In particular, a secondary relay station connects a destination through a free space optical link, whose random characteristics follows a widely used gamma–gamma fading distribution with non zero pointing error to characterize the assignable effects of atmospheric turbulence. Different from the traditional analysis methods in probability theory based on cumulative distribution function or outage probability, the complicated integral domain division is avoided by virtue of the moment generating function of reciprocal signal to noise ratio. Under the maximum interference level constraint of the primary user, exact closed form expressions of moments of signal to noise ratio, ergodic capacity, higher order statistics of the capacity, and average bit error probability are derived naturally. Finally, simulation results are provided to flawlessly demonstrate the theoretical analysis.

Performance Analysis of Multi User Optical Wireless Network (IR, or UV light for signal carrying) under Different Environmental Conditions

<p>The field of optics is flourishing day by day on account of the wide usage of the internet and its associated technologies. Free Space Optics (FSO) is a data transmission technique that employs light propagation to send data. This technology is effective in those circumstances where fiber optic cables cannot be deployed. This paper provides a model and simulation of the Fiber Bragg Grating (FBG) based FSO network under different environmental conditions, such as modulation types and data rates. Also, investigation of the impact of Multiple Access Interference (MAI) on FSO under design parameters has been done. The designed system performance is analyzed under the multiuser optical wireless network by changing data rates and modulation types. The proposed model's security is achieved through the use of the FBG encoder/decoder and the FSO channel for transmission. It has been inferred that the CRZ modulation type provides the best BER and Q factor compared to other formats, and a data rate as high as 1Gbps can be achieved using the CRZ modulation format. It has been noticed that as the number of users grows, the BER value begins to deteriorate.</p>

Fault tolerance and noise immunity in freespace diffractive optical neural networks

Free-space diffractive optical networks are a class of trainable optical media that are currently being explored as a novel hardware platform for neural engines. The training phase of such systems is usually performed in a computer and the learned weights are then transferred onto optical hardware (‘ex-situ training’). Although this process of weight transfer has many practical advantages, it is often accompanied by performance degrading faults in the fabricated hardware. Being analog systems, these engines are also subject to performance degradation due to noises in the inputs and during optoelectronic conversion. Considering diffractive optical networks trained for image classification tasks on standard datasets, we numerically study the performance degradation arising out of weight faults and injected noises and methods to ameliorate these effects. Training regimens based on intentional fault and noise injection during the training phase are only found marginally successful at imparting fault tolerance or noise immunity. We propose an alternative training regimen using gradient based regularization terms in the training objective that are found to impart some degree of fault tolerance and noise immunity in comparison to injection based training regimen.

Agile neighbor discovery in MEMS-based free space optical networks: a computer vision approach

Highly directional laser-based wireless optical radios are able to spatially reuse several THz of spectrum but suffer from link setup delays. In delay averse and high-throughput self-configuring networks, agile neighbor discovery is of critical importance. Given an optical wireless network with microelectromechanical systems based receivers, we explore the use of adaptive combinatorial group testing and contour tracing to achieve very low neighbor discovery latency. We propose a pattern-based algorithm that leverages group testing and contour tracing techniques to significantly reduce latency. Evaluating our algorithms, we compare hierarchical group testing algorithms to state-of-the-art raster and Lissajous pattern-based scanning and report 99.92% and 87% reduction in latency, respectively, for an array of one million micromirrors. The proposed pattern-based algorithm, when compared to hierarchical group testing and the Moore-neighbor contour tracing algorithms, achieves 63.4% and 4.91% reduction in latency, respectively.

The Impact of Turbulence on MANET FSO Networks Using NS-3

In this paper, the impact of atmospheric turbulence is investigated and analyzed for the Free Space Optical Mobile Ad Hoc Networks (FSO MANET) using the Network Simulator NS-3. The FSO channel random intensity fluctuations have been modeled using the Exponentiated Weibull (EW) distribution. Further, the FSO module has been implemented and integrated with NS3 using the FSO propagation model and the FSO error models. The computation of the key performance indicators (KPI) mainly the throughput and the packet delivery ratio (PDR) shows that the network density affects the network performance. Its effect was illustrated for the different turbulence regimes, strong and weak. It is found that the throughput and PDR values decrease as the number of mobile nodes becomes larger. For instance, at 150 kbps and in the presence of strong turbulence with 25, 50, and 75 nodes, the PDRs are 77%, 76%, and 73% respectively. Moreover, the throughput and PDR values in the strong turbulence regime are lower than those in the weak turbulence regime for the same date rate. The throughput in the strong turbulence regime with 75 mobile nodes at the data rate 150 kbps is 2100 kbps while it is 2300 kbps in the weak turbulence mode at the same rate.

Temporary Laser Inter-Satellite Links in Free-Space Optical Satellite Networks

Laser inter-satellite links (LISLs) between satellites in a free-space optical satellite network (FSOSN) can be divided into two classes: permanent LISLs (PLs) and temporary LISLs (TLs). TLs are not desirable in next-generation FSOSNs (NG-FSOSNs) due to high LISL setup time, but they may become feasible in next-next-generation FSOSNs (NNG-FSOSNs). Using the satellite constellation for Phase I of Starlink, we study the impact of TLs on network latency in an NG-FSOSN (which has only PLs) versus an NNG-FSOSN (which has PLs and TLs) under different long-distance inter-continental data communications scenarios, including Sydney–Sao Paulo, Toronto–Istanbul, Madrid–Tokyo, and New York–Jakarta, and different LISL ranges for satellites, including 659.5 km, 1,319 km, 1,500 km, 1,700 km, 2,500 km, 3,500 km, and 5,016 km. It is observed from the results that TLs provide higher satellite connectivity and thereby higher network connectivity, and they lead to lower average network latency for the NNG-FSOSN compared to the NG-FSOSN in all scenarios at all LISL ranges. In comparison with the NG-FSOSN, the improvement in latency with the NNG-FSOSN is significant at LISL ranges of 1,500 km, 1,700 km, and 2,500 km, where the improvement is 16.83 ms, 23.43 ms, and 18.20 ms, respectively, for the Sydney–Sao Paulo inter-continental connection. For the Toronto–Istanbul, Madrid–Tokyo, and New York–Jakarta inter-continental connections, the improvement is 14.58 ms, 23.35 ms, and 23.52 ms, respectively, at the 1,700 km LISL range.

Performance analysis of reconfigurable intelligent surface in a dual-hop DF relay empowered asymmetric RF/FSO networks

In this paper, the performance analysis of a reconfigurable intelligent surface (RIS) in a dual-hop decode-and-forward (DF) relay empowered asymmetric radio frequency (RF)/free space optical (FSO) systems is presented. The RIS-assisted RF network is subjected to Nakagami-m distribution while the RIS-assisted FSO networks experience Gamma–Gamma distribution in which both atmospheric turbulence and pointing errors are considered. Thus, the closed-form expressions for the system outage probability and average bit error rate (ABER) are derived with limited number of reflecting elements at RIS-assisted RF network and multiple number of reflecting elements at RIS-assisted FSO network. Further, to obtain more insight about the system characteristic, the asymptotic closed-form expressions are derived at high signal-to-noise ratio (SNR) for the system performance metrics. The results illustrate the impact of the system and channel parameters on the proposed system in terms of atmospheric turbulence, pointing errors under beam width condition, \(m\)-fading parameter, and number of reflecting elements. The correctness of the derived analytical expressions is validated via the Monte-Carlo simulations.

HAP-aided two-way relaying for FSO access networks using optical CDMA

A free-space optical access network with multiple ground stations (GSs) connected by a high-altitude platform (HAP) is proposed. The HAP plays a role of a two-way relay node that supports all-optical amplify-and-forward and half-duplex transmission. In the network, optical code-division multiple-access is utilized to enable asynchronous and simultaneous data transmission among GSs. In further steps of the study, the mathematical expressions of two system metrics including bit-error rate (BER) and network throughput are derived. They consider many physical layer impairments, such as power loss, atmospheric turbulence, pointing error, multiple-access interference, and receiver noise. Eventually, numerical results of the system performance under consideration of the number of GSs, the bit rate, and the received power confirm the feasibility of the proposed system as well as provide useful information for network design.

Hybrid WDM free space optical system using CSRZ and Rayleigh backscattering noise mitigation

Abstract 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 λ 1 to λ 5 wavelengths for optical line terminal (OLT) to ONU transmission and λ 2 to λ 6 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.