Performance evaluation of a UOWC system based on the FRS/OCDMA code for different types of Jerlov waters.

In this work, the fixed right shift (FRS) code is utilized for the optical code division multiple access (OCDMA) technique in an underwater optical wireless communication (UOWC) system. Additionally, in this system, a 532 nm laser diode (LD) source is employed to generate optical signals. The investigation encompasses an analysis of five distinct Jerlov water types, each exhibiting diverse chlorophyll concentrations. The performance of the proposed system is evaluated when each channel that is assigned a unique FRS code sequence carries different data rates (2.5, 5, and 10 Gbps). Underwater (UW) ranges, bit error rate (BER), eye diagrams, and quality factor (Q-factor) are the performance metrics used to evaluate the system performance. The proposed UOWC-FRS/OCDMA system is simulated, and the obtained results show that the eye diagram openings close, the BER increases, and the Q-factor decreases as the data rate per each channel increases from 2.5 to 10 Gbps, and the attenuation of water becomes higher. Moreover, the lower attenuation values caused by the Jerlov type I (JI) waterbody allow each channel to carry 10 Gbps of data to propagate longer UW for a range of 35 m with a log(BER) ≤-6.33 and Q-factor greater than 4.9. On the other hand, at the same values of BER and Q-factor, the shortest ranges of 12 and 5.15 m are obtained for JII and JIII waters, respectively, where their attenuation coefficient values are 0.5297 (JII) and 1.8998 m -1 (JIII). Furthermore, as our model uses three channels, the overall achieved capacity is 3×10G b p s=30G b p s.

6G enabling FSO communication system employing integrated PDM-OAM-OCDMA transmission: impact of weather conditions in India.

Currently, free space optics (FSO) transmission has gained attention due to its capability to deliver high data rates with a high level of security. In addition, using multiplexing techniques with FSO makes it capable of handling the excessive increase in traffic data and supporting the 5G and 6G wireless network requirements. Accordingly, in this paper, a novel, to the best of our knowledge, FSO system integrating three multiplexing techniques-orbital angular momentum (OAM) (four OAM beams are used) polarization-division multiplexing (two polarization states are used), and optical code division multiple access (four channels assigned with permutation vector codes are used)-is proposed. Additionally, the effects of rainy, foggy, dusty weather and the real weather for four different Indian cities that have different geographical locations are studied and investigated. The system performance is evaluated based on the bit error rate (BER), quality factor (Q-factor), maximum FSO range, and eye diagram opening. The simulation results show successful transmission of 320 Gbps overall capacity with a maximum achievable FSO range of 7 km under clear weather. On the other hand, the shortest FSO range of 0.105 km is achieved when there are heavy dust storms. As for the Indian cities, Srinagar (hilly area of India) achieves the shortest FSO link, which is 4.2 km while the largest range of 7 km is observed for Chennai city (coastal area of India). All these ranges are evaluated for a log(BER) value <-7. Consequently, this proposed transmission model is suggested for use in 6G applications of FSO communication systems.

Impact of Fireworks Industry Safety Measures and Prevention Management System on Human Error Mitigation Using a Machine Learning Approach.

In the fireworks industry (FI), many accidents and explosions frequently happen due to human error (HE). Human factors (HFs) always play a dynamic role in the incidence of accidents in workplace environments. Preventing HE is a main challenge for safety and precautions in the FI. Clarifying the relationship between HFs can help in identifying the correlation between unsafe behaviors and influential factors in hazardous chemical warehouse accidents. This paper aims to investigate the impact of HFs that contribute to HE, which has caused FI disasters, explosions, and incidents in the past. This paper investigates why and how HEs contribute to the most severe accidents that occur while storing and using hazardous chemicals. The impact of fireworks and match industry disasters has motivated the planning of mitigation in this proposal. This analysis used machine learning (ML) and recommends an expert system (ES). There were many significant correlations between individual behaviors and the chance of HE to occur. This paper proposes an ML-based prediction model for fireworks and match work industries in Sivakasi, Tamil Nadu. For this study analysis, the questionnaire responses are reviewed for accuracy and coded from 500 participants from the fireworks and match industries in Tamil Nadu who were chosen to fill out a questionnaire. The Chief Inspectorate of Factories in Chennai and the Training Centre for Industrial Safety and Health in Sivakasi, Tamil Nadu, India, significantly contributed to the collection of accident datasets for the FI in Tamil Nadu, India. The data are analyzed and presented in the following categories based on this study's objectives: the effect of physical, psychological, and organizational factors. The output implemented by comparing ML models, support vector machine (SVM), random forest (RF), and Naïve Bayes (NB) accuracy is 86.45%, 91.6%, and 92.1%, respectively. Extreme Gradient Boosting (XGBoost) has the optimal classification accuracy of 94.41% of ML models. This research aims to create a new ES to mitigate HE risks in the fireworks and match work industries. The proposed ES reduces HE risk and improves workplace safety in unsafe, uncertain workplaces. Proper safety management systems (SMS) can prevent deaths and injuries such as fires and explosions.

Enhanced ADO-OFDM-based adaptive digital dimming VLC system.

Visible light communication (VLC) has shown significant growth in recent years. VLC simultaneously offers illumination and communication. In VLC systems, dimming control is used to handle the lighting and energy consumption constraints. In this paper, a new, to the best of our knowledge, adaptive digital dimming optical-orthogonal frequency division multiplexing (ADDO-OFDM) based on pulse width modulation is proposed to combine enhanced asymmetrically clipped DC biased optical OFDM (EADO-OFDM) and negative EADO-OFDM (ENADO-OFDM). It exploits the performance benefits of EADO-OFDM and ENADO-OFDM. The proposed ADDO-OFDM controls the dimming level in a vast range with an acceptable bit error rate with a favorable data length.

Performance analysis of serial relay orbital satellite optical communication over turbulent channels.

Optical space communication has been proven to be a reliable relay satellite transmission system. The difficulty that occurs in RF satellite communication (SatCom) can be alleviated by using free-space optical (FSO) or laser SatCom. In this work, we analyze a proposed laser downlink relay SatCom model with existing channel turbulence employing intensity modulation and direct detection (IM/DD), and amplify-and-forward (AF) technology and compare it with the optical direct link SatCom. Accounting for atmospheric attenuation and turbulence, the effect of model parameters such as zenith angle, receiver aperture radius, best number of optical ground stations (OGSs), and end-to-end operating wavelength on system performance is investigated for different OGS height scenarios. We provide exact closed-form expressions for the proposed model and optimize system performance by selecting the best number of OGSs using a selective diversity technique that can boost the system signal-to-noise (SNR) by up to 37 dB (99.9%).

LED nonlinearity mitigation in LACO-OFDM optical communications based on adaptive predistortion and postdistortion techniques.

The preinstalled white light emitting diodes (WLEDs) inside buildings can be exploited as an optical source in visible light communications (VLC) motivated by high optical efficiency and low cost. One of the main challenges for VLC is LED nonlinear distortion, which has a detrimental effect on system performance. Estimation and compensation of the LED nonlinear behavior can be accomplished using predistortion or postdistortion techniques. Three compensation techniques are adopted to mitigate the effect of LED nonlinearity on layered asymmetrically clipped optical, orthogonal frequency division multiplexing. Their performance and efficiency are discussed and compared with the aid of error vector magnitude and bit error rate (BER) in an additive white Gaussian noise channel. The obtained results reveal that polynomial-based predistorters and postdistorters can overcome the LED nonlinear behavior with extra SNR of only 0.25 dB at BER of 10-3. Furthermore, the look-up-table-based predistorter can provide the same BER with lower SNR penalty than the previous two systems.

Exploring the effect of LED nonlinearity on the performance of layered ACO-OFDM.

Visible light communication (VLC) depends on light emitting diodes (LEDs) for data transmission. This is one of the strengths of VLC motivated by high optical efficiency and low cost. However, LEDs impose nonlinear effects on the transmitted signal and limit overall system performance, especially in the case of multicarrier modulation systems. This paper extends to the layered asymmetrically clipped optical, orthogonal frequency division multiplexing (LACO-OFDM) and investigates the impact of LED nonlinearity on system performance. The effect of the second-order nonlinear distortion in addition to the clipping noise is presented and analyzed at different power values assuming different strengths of nonlinearity. With a variable number of layers, the system performance is explored considering a nonlinear LED model. Finally, the impact of nonlinearity is investigated in the case of ACO-OFDM for the sake of comparison, bearing in mind that ACO-OFDM represents the first layer of LACO-OFDM.

On the performance of adaptive hybrid MQAM-MPPM scheme over Nakagami and log-normal dynamic visible light communication channels.

In this paper, we introduce the idea of using adaptive hybrid modulation techniques to overcome channel fading effects on visible light communication (VLC) systems. A hybrid $ M $M-ary quadrature-amplitude modulation ($ M{\rm QAM} $MQAM) and multipulse pulse-position modulation (MPPM) technique is considered due to its ability to make gradual changes in spectral efficiency to cope with channel effects. First, the Zemax optics studio simulator is used to simulate dynamic VLC channels. The results of Zemax show that Nakagami and log-normal distributions give the best fitting for simulation results. The performance of $ M{\rm QAM} $MQAM-MPPM is analytically investigated for both Nakagami and log-normal channels, where we obtain closed-form expressions for the average bit-error rate (BER). The optimization problem of evaluating the hybrid modulation technique settings that lead to the highest spectral efficiency under a specific channel status and constraint of outage probability is formulated and solved using an exhaustive search. Our results reveal that the adaptive hybrid scheme improves system spectral efficiency compared to ordinary QAM and MPPM schemes. Our results reveal that the adaptive hybrid scheme improves system spectral efficiency compared to ordinary QAM and MPPM schemes. Specifically, at low average transmitted power, $ - 32\;{\rm dBm} $-32dBm, the adaptive hybrid scheme shows 280% improvement in spectral efficiency compared to adaptive versions of ordinary schemes. At higher power, $ - 20\;{\rm dBm} $-20dBm, 6.5% and 725% improvement are obtained compared to ordinary QAM and ordinary MPPM, respectively. Also, the adaptive hybrid scheme shows great improvement in average BER and outage probability compared to ordinary schemes. The hybrid scheme shows 28%, 34%, and 38% improvement, respectively, for $ m = 1,2,3 $m=1,2,3 for Nakagami channels at $ {\rm BER}{ = 10^{ - 3}} $BER=10-3. Also, the outage probability of hybrid schemes of $ {\rm BER}{ = 10^{ - 3}} $BER=10-3 shows 30% and 14% better performance than ordinary $ M{\rm QAM} $MQAM and MPPM schemes, respectively.

A Generalized Spatial Modulation System Using Massive MIMO Space Time Coding Antenna Grouping.

Massive multiple input multiple output (MIMO), also known as a very large-scale MIMO, is an emerging technology in wireless communications that increases capacity compared to MIMO systems. The massive MIMO communication technique is currently forming a major part of ongoing research. The main issue for massive MIMO improvements depends on the number of transmitting antennas to increase the data rate and minimize bit error rate (BER). To enhance the data rate and BER, new coding and modulation techniques are required. In this paper, a generalized spatial modulation (GSM) with antenna grouping space time coding technique (STC) is proposed. The proposed GSM-STC technique is based on space time coding of two successive GSM-modulated data symbols on two subgroups of antennas to improve data rate and to minimize BER. Moreover, the proposed GSM-STC system can offer spatial diversity gains and can also increase the reliability of the wireless channel by providing replicas of the received signal. The simulation results show that GSM-STC achieves better performance compared to conventional GSM techniques in terms of data rate and BER, leading to good potential for massive MIMO by using subgroups of antennas.

NLoS underwater VLC system performance: static and dynamic channel modeling.

In this paper, the impact of water channels under different communication link parameters is studied for underwater visible light communication (UVLC). The objective is to highlight the best results for non-line of sight (NLoS) communication links. In addition, NLoS links are studied under different parameters: LED colors, viewing angle, receiving angle, and data rates. The results are obtained and plotted using MATLAB simulation. The performance of the received power is first measured at different wavelengths and data rates. Then, the best results are further investigated at different viewing angles and receiving angles. The obtained results show that using cyan color provides more depth for the NLoS case, as well as a low bit error rate compared to the other colors. Most of the literature is concerned with unpractical configurations in underwater scenarios, such as an empty sea or assuming no human-object or blockage environment. We use the practical setup in Zemax Optics Studio to allow a precise description of ray tracing and high order of reflections inside a sea water environment. The channel impulse response (CIR) is obtained for static channel modeling, including a blockage environment to evaluate the best transmitters in sea water. Also, we are able to compare the average delay and the average delay spread of the source colors. The reflection characteristics of the sea water are considered as wavelength dependent. The CIR obtained by Zemax Solver and MATLAB indicates that cyan is the best source in sea water for different LED chips. Moreover, other previous studies assume perfect alignment scenarios between divers, which is not practical and not suitable for real channel gain results. Accordingly, we present a comprehensive dynamic channel modeling and characterization study for UVLC. Our study is based on Zemax programming language (ZPL) combined with Zemax Optics Studio. Using ZPL enables us to apply a mobility algorithm for divers and measure the channel gain variations due to random motion. We introduce a dynamic motion in a single-input single-output scenario and a single-input multiple-output scenario in the presence of blockage divers. Statistical analyses are studied for the appropriate distributions that can fit the data with various transmitter and receiver specifications. All dynamic scenarios are performed using cyan color in sea water, as it is proven to have satisfactory performance. The statistical results are beneficial for further analysis. As case studies, we consider various underwater scenarios, and the resulting parameters of statistical distributions can be used for future analysis in UVLC dynamic environments.

Cerebral Artery Vasospasm Detection Using Transcranial Doppler Signal Analysis.

OBJECTIVES: Silent cerebral artery vasospasm in aneurysmal subarachnoid hemorrhage causes serious complications such as cerebral ischemia and death. A transcranial Doppler (TCD) ultrasound system is a noninvasive device that can effectively detect cerebral artery vasospasm as soon as it sets in, even before and in the absence of clinical deterioration. Continuous or even daily TCD monitoring is challenging because of the operator expertise and certification required in the form of a trained sonographer and interpretive experience required in the form of an additionally trained and certified physician to perform these studies. This barrier exists because of a lack of automation for detection (without human intervention) of cerebral artery vasospasm using TCD ultrasound. To overcome this barrier, we present an algorithm that automates detection of cerebral artery vasospasm. METHODS: We extracted features such as the energy, energy entropy, zero-crossing rate, spectral centroid, spectral speed, spectral entropy, spectral flux, spectral roll-off, harmonic ratio, chroma, and Mel frequency cepstral coefficients for signal classification. Then we applied principal component analysis to reduce the data dimensionality. RESULTS: All of the chosen features were used for training a decision-tree classifier. The algorithm had high accuracy for cerebral artery vasospasm detection, with overall sensitivity of 87.5% and specificity of 89.74%. CONCLUSIONS: The algorithm has the potential for development into a continuous cerebral artery vasospasm monitor.

Performance analysis of multiple NLOS UV communication cooperative relays over turbulent channels.

Ultraviolet (UV) communication overcomes pointing and tracking errors and is superior to other modern optical wireless communication technologies at short range. Using effective wavelengths from 200 to 280 nm, enables the non-line-of-sight (NLOS) outdoor UV communication in the presence of strong molecular and aerosol scattering. Because of these characteristics, solar blind NLOS UV communications offers broad coverage and high security. In this paper, NLOS UV communication is considered with decode and forward (DF) relays in the presence of log-normal (LN) channels using the best relay selection technique according to the channel state information (CSI). Then the outage probability of the multi-relay UV system is discussed for the proposed model. Simulation results verify the effectiveness of our employed analytical model. The outage probability for both serial and cooperative relays is compared with a different number of relays. Numerical simulations are further presented for many factors influencing the functioning of the system such as elevation angle, atmospheric scattering parameters and receiver field of view (FOV) angles. The obtained results demonstrate that increasing the number of UV NLOS cooperative relays does not necessarily improve the system performance, but there are other factors that must be considered such as the value of the elevation angle and the number of relays.

Solution of dispersion relations of multilayer optical fibers: a comprehensive study.

The exact solution of the modal dispersion relation of multilayer optical fibers is very critical and complicated, especially in the case of complex refractive indices of some layers added to the fiber. In this paper, a different methodology is proposed to solve the complex dispersion relations for cladding modes, based on the well-defined proper expressions of electromagnetic fields in the different layers of optical fibers. An optical fiber, coated by a dielectric nonlinear layer, is analyzed using the exact four-layer model, and the results obtained are compared with those analyzed in the literature based on the approximate three-layer model, where the effect of the coating layer is neglected when solving the dispersion relation. The results obtained show a remarkable difference between the exact and the approximate values of the effective refractive indices of the cladding modes. Inappropriate values of the effective refractive indices strongly affect phase matching and coupling between modes, which are required in different applications such as second-harmonic generation. The proposed approach for solving general dispersion relations is also employed to obtain complex values of the effective refractive indices of the cladding modes for a five-layer optical fiber with a metallic thin film inserted between the nonlinear layer and the fiber cladding. Using the appropriate expressions that describe the electric field in the different dielectric and metallic layers of optical fibers, field distributions are displayed for some cladding modes.

Amendment performance of an apodized tilted fiber Bragg grating for a quasi-distributed-based sensor.

In this work, the characteristics of reflectivity spectra produced inside a reflective-tilted fiber Bragg grating (R-TFBG) are investigated, seeking a remarkable performance that could be able to upgrade the sensitivity range for temperature-strain sensors of quasi-distribution type. We introduce an optimized performance through a comparative investigation among different evaluation parameters, such as core radius, tilt angle, and the elite selection of apodization profiles, in addition to the traditional parameters, such as grating length, L, and index modulation amplitude, Δn. Regarding the tilt angle, its increase affects the full width at half-maximum (FWHM) affirmatively, while having a negative impact on the maximum reflectivity. By controlling L and Δn, a compromised solution is achieved to retrieve the maximum reflectivity to be around 1.0. Regarding the sidelobes, the Kaiser profile is the best candidate that minimized the main sidelobe level (MSL) and raised the sidelobe suppression ratio (SLSR) at any tilt angle, while tanh apodization is the best choice from the perspective of raising the ramp down sidelobes asymptotic decay. The contrasts in the optimization process are examined through investigating the R-TFBG quasi-distributed sensors to be applied to a temperature-strain sensing system. The objective is to evaluate an assessment for the performance of a sensor system that extends the range and efficiency of temperature-strain ranges. Based on our analysis, the sensitivity range is upgraded for a temperature change to reach 179°C and for strain to be 3000 µÏµ at a tilt angle of 10° with a FWHM of 0.063 nm, attenuation of -154 dB for an MSL of 75.5%, and an SLSR of -60 dB/nm.

DBPSK and DQPSK crosstalk in single-span WDM systems using DRA.

A closed-loop formula is derived for the nonlinear crosstalk degradation due to self-phase modulation and cross-phase modulation in a wavelength-division multiplexing system. The crosstalk is investigated in differential binary phase-shift keying (DBPSK) and differential quadrature phase-shift keying (DQPSK) schemes. The system under consideration is standard single-mode fiber with a single-span distributed Raman amplifier. The backward DBPSK shows a better performance with minimum crosstalk performance of 71%, as compared to backward DQPSK.

Second harmonic generation in thin optical fibers via cladding modes.

Since silica goes under the category of amorphous materials, it is difficult to investigate important processes such as second harmonic generation (SHG) in silica-based fibers. In this paper, we proposed a method for SHG relaying on cladding modes as pump modes. Cladding modes are introduced in optical fibers through tilted long period grating (T-LPG), where power of core mode is transferred into cladding modes. By functionalizing T-LPG with nonlinear coating, the interaction occurs between cladding modes and the coating material, consequently second harmonic signal (SHS) is generated with efficiency up to 0.14%.

Performance characteristics of dual-pumped hybrid EDFA/Raman optical amplifier.

This paper suggests a hybrid amplifier using an erbium-doped fiber amplifier (EDFA) and Raman amplifier (RA) with dual-pump configuration. This hybrid EDFA/RA optical amplifier (HOA) is dual pumped. The EDFA is forward biased with 980 nm while the RA is reverse biased with 1450 nm in the dual-pump configuration. Both the gain and noise figure are experimentally studied and compared with experimental values of the EDFA/Raman HOA with different pump configurations. The optimum values of the affecting parameters are investigated to get the best characteristics of the HOA, including high gain and a low noise figure. A high gain of 31 dB and low noise of 3.8 dB are achieved. In addition, the flat gain in the wavelength range 1545-1565 nm and the optical signal-to-noise ratio is reduced to 24 dB.

Free space optical communications system performance under atmospheric scattering and turbulence for 850 and 1550 nm operation.

In this work, a free space optical communication (FSO) link is proposed and utilized to explore and evaluate the FSO link performance under the joint occurrence of the atmospheric scattering and turbulence phenomena for 850 and 1550 nm operation. Diffraction and nondiffraction-limited systems are presented and evaluated for both wavelengths' operation, considering far-field conditions under different link distances. Bit error rate, pointing error angles, beam divergence angles, and link distance are the main performance indicators that are used to evaluate and compare the link performance under different system configurations and atmospheric phenomena combinations. A detailed study is performed to provide the merits of this work. For both far-field diffraction-limited and nondiffraction-limited systems, it is concluded that 1550 nm system operation is better than 850 nm for the whole presented joint occurrences of atmospheric scattering and turbulence.

Sensitivity improvement of reflective tilted FBGs.

Tilted fiber Bragg gratings are used as energy couplers in which the core mode and cladding modes can be coupled together. Cladding modes have extensive importance in sensing applications due to their sensitive characteristics to the surrounding refractive index. The cladding modes are investigated theoretically by studying a three-layer model of optical fibers, whereas the core mode is investigated by studying a two-layer model of optical fibers. The analysis reveals that to increase the coupling of the energy transferred from the core mode to cladding modes, the cladding radius needs to be decreased. Such behavior is illustrated through studying the change in the electric field distribution and is used to improve the sensitivity of the sensing refractive index of the surrounding medium.

Numerical characterization of InP-based quantum dot semiconductor optical amplifier.

This paper is devoted to the development of a steady-state behavior of a quantum dot-semiconductor optical amplifier (QD-SOA). The investigated performance characteristics cover a wide range that includes material gain coefficient, spatial distribution of the occupation probabilities, fiber to fiber gain, gain spectrum as a function of the bias current, relaxation time, and capture time. A set of traveling-wave equations is used to model the signal and spontaneous photons along the device active region. The obtained results indicate a high gain that reaches 34 dB for an InAs/InGaAsP/InP-based QD-SOA, with a corresponding device length of 4 mm. The obtained signal-to-noise ratio is larger than 75 dB for all input powers without using an output filter.