Performance Of Optical Communication Systems Research Articles

On Secrecy Analysis of DF Based Dual Hop Mixed RF-FSO Systems

In this paper, the secrecy performance of a mixed radio frequency-free space optical (RF-FSO) communication system that consists of a source (S), a relay (R), a destination (D), and an eavesdropper (E), is studied. In this system, it is assumed that the E can overhear the free space optical (FSO) link between R and D as it is close to D. It is further assumed that the radio frequency (RF) and FSO links experience Rayleigh and Gamma-Gamma fading, respectively. Considering atmospheric turbulence, pointing errors, two types of detection techniques, and decode-and-forward scheme, the closed-form expressions for the lower bound of secrecy outage probability and the probability of strictly positive secrecy capacity are derived. Monte Carlo simulation results are also presented to validate the accuracy of the derivations.

Experimental Study of Atmospheric Turbulence Detection Using an Orbital Angular Momentum Beam Via a Convolutional Neural Network

Atmospheric turbulence (AT) tends to impair the performance of free space optical (FSO) communication systems. Detecting AT strength is significant for turbulence effect mitigation, which can appropriately guide the selection of turbulence mitigation techniques and modulation formats. Orbital angular momentum (OAM) beam aberrations received through the turbulence channel are closely related to the turbulence strength. In this paper, we experimentally detect the AT strength using an OAM beam based on a convolutional neural network (CNN). We collect 8 kinds of superposed OAM beam intensity images after 5 levels of turbulence in the laboratory as datasets and test the AT detector performance with respect to the number of pixels, mode number of OAM beams, different AT sets and training set size. The results show that the AT detection accuracy is near 100% for 3 kinds of ATs, and the accuracy remains at approximately 85% for 5 kinds of ATs. In addition, using data augmentation methods or a hybrid dataset can improve the AT detection accuracy. The CNN-based method in this paper can help detect the AT strength in atmospheric channels and provide references for choosing appropriate techniques to mitigate turbulence effects and then enhance the OAM-FSO system performance.

Effects of air bubbles on underwater optical wireless communication [Invited

The received signal intensity fluctuation and communication performance of an underwater optical wireless communication (UOWC) system under the air bubble effects are experimentally investigated. For different bubble density and size, lognormal, gamma, Weibull, and generalized extreme value distributions are tested to fit the fluctuation of the signal intensity at the receiving end. The best fitting distribution is found to vary with bubble parameters. The communication system performance with on–off keying and pulse position modulation is further studied.

Performance of multiple-input multiple-output free space optics using hybrid subcarrier intensity modulation with avalanche photodiode receiver

In order to improve the performance of a free space optical (FSO) communication system, hybrid pulse position modulation-binary phase shift keying-subcarrier intensity modulation (PPM-BPSK-SIM) technique is proposed. The system performance is further improved by using multiple-input multiple-output (MIMO) configuration and avalanche photodiode (APD) receiver. The use of multiple lasers and photo detectors in MIMO FSO system reduces the scintillation effect in the atmosphere. In this study, the impact of different parameters like irradiance, link distance, and turbulence level have been considered for the bit error rate (BER) analysis. The relevant mathematical model is also presented. The simulation results show that the hybrid PPM-BPSK-SIM scheme performs better compared to PPM and BPSK-SIM schemes. Also, APD receiver shows a noticeable BER improvement than p-type intrinsic n-type (PIN) receiver in our proposed scheme.

Underwater optical communication performance under the influence of the eddy diffusivity ratio.

Generally, the eddy diffusivity ratio of salinity to temperature is not equal to one, especially in the upper and mid-to-high latitude ocean. In this paper, the performance of practical underwater optical communication (UOC) systems is investigated by considering the influence of the eddy diffusivity ratio other than one. Specifically, using the Rytov theory in weak turbulence, the aperture-averaged scintillation indices for the plane and spherical waves are derived. The typical performance criteria including the mean signal-to-noise ratio and bit error rate are further studied. It is found that the scintillation index and the associated UOC performance differ between the cases of the unity and variable eddy diffusivity ratio. Such a difference becomes smaller as the receiving aperture increases.

Error performance of optical wireless communication systems exercising BPSK subcarrier intensity modulation in non-Kolmogorov turbulent atmosphere

Abstract Subcarrier intensity modulation (SIM) scheme is preferred due to efficient bandwidth usage superiority over other modulation techniques such as on–off keying (OOK), pulse position modulation (PPM). In this paper, we investigate the bit error rate (BER) performance of optical wireless communication (OWC) system using binary phase shift keying (BPSK) SIM in non-Kolmogorov turbulent atmosphere. We pay attention to the weak turbulence conditions by using Rytov approximation and considering that the receiver is a PIN photodetector. Propagating beam type is Gaussian. It is seen that BER performance of the BPSK SIM OWC is significantly affected from non-Kolmogorov power law exponent, load resistor, responsivity of the PIN photodetector, bandwidth, beam source size, turbulence strength and noise factor.

ANALISIS REDAMAN SERAT OPTIK TERHADAP PERFORMANSI SKSO MENGGUNAKAN METODE LINK POWER BUDGET (STUDI KASUS PADA LINK PADANG-BUKITTINGGI DI PT. TELKOM PADANG)

Based on the survey data of optical fiber service, the communication network uses optical fiber transmission medium is not maximal yet, because there are some errors in the network, such as the percentage of Network Post Dialing Delay in system is 97.5%, that means there is 2.5% of error a delay occurs in the network when making a call. This research was conducted by analyzing the fiber attenuation of fiber-optic communication systems performance on the link Padang-Bukittinggi in PT. Telkom Padang, SKSO division which uses single mode fiber optic cable types G655. Instrument in this study is the Power Meter and OTDR JDSU MTS-6000 type. Link Power Budget method is used to determine the performance of optical fiber communication systems caused by attenuation based on the value of the received power output. Obtained results on the link Padang-Bukittinggi highest attenuation occurs in core 5 with 26.7226 dB attenuation value and cable length 115 016 km, and in core 7 with 26.1812 dB and cable length 94 462 km. This value is still below of PT. Telkom standard with 28.10352 dB for core 5. While the attenuation value at 7 cores exceeds standard attenuation values​​, with 24.18186 dB, so the performance of the core is declared bad and needs to be evaluated. From optical fiber attenuation value, result of the link power budget analysis is obtained from the calculation of the value of Rx is smaller when compared with -27 dBm the value of Rx sensitivity, it can be said the performance of optical fiber communication systems on the link in the normal state and can be used to operate because the power output can be accepted by the receiver in the device. Keywords: fiber optic cable, optical fiber attenuation, SKSO, link power budget.

All-Optical FSO Relaying Under Mixture-Gamma Fading Channels and Pointing Errors

The performance of all-optical dual-hop relayed free-space optical communication systems is analytically studied and evaluated. We consider the case when the total received signal undergoes turbulence-induced channel fading, modeled by the versatile mixture-Gamma distribution. Also, the misalignment-induced fading due to the presence of pointing errors is jointly considered in the enclosed analysis. The performance of both amplify-and-forward and decode-and-forward relaying transmission is studied, when heterodyne detection is applied. New closed-form expressions are derived regarding some key performance metrics of the considered system; namely, the system outage probability and average bit-error rate.

Asymptotic analysis of V-BLAST MIMO for coherent optical wireless communications in Gamma-Gamma turbulence

This paper investigates the asymptotic BER performance of coherent optical wireless communication systems in Gamma-Gamma turbulence when applying the V-BLAST MIMO scheme. A new method is proposed to quantify the performance of the system and mathematical solutions for asymptotic BER performance are derived. Counterintuitive results are shown since the diversity gain of the V-BLAST MIMO system is equal to the number of the receivers. As a consequence, it is shown that when applying the V-BLAST MIMO scheme, the symbol rate per transmission can be equal to the number of transmitters with some cost to diversity gain. This means that we can simultaneously exploit the spatial multiplexing and diversity properties of the MIMO system to achieve a higher data rate than existing schemes in a channel that displays severe turbulence and moderate attenuation.

Fundamental quantum limits in optical metrology from rate-distortion theory

We derive fundamental lower bounds on the performance of optical metrology and communication systems in a Bayesian framework. The derivation uses classical rate-distortion theory in conjunction with bounds on the capacity to transmit classical information of various optical channels specified by the system design. The bounds are expressed in terms of the system parameters, the prior probability distribution of the parameter, and the average energy, i.e. number of photons E in the probe state. For phase estimation, the bounds pertain to a cyclic mean squared error criterion incorporating the cyclic nature of the phase. In the absence of optical loss, our bounds are applicable to multimode linear phase modulation schemes (including ancilla-assisted ones), and to nonlinear modulations on a single mode. The bounds display inverse-quadratic Heisenberg-limit scaling of the cyclic mean square error with respect to E. In the presence of any finite amount of loss, a lower bound on ancilla-assisted phase estimation with standard quantum limit scaling is derived, which is shown to be little different from a similar bound for coherent-state probes. For systems involving a single optical mode, we also obtain lower bounds on the mean squared error of estimating any classical parameter, and on the average error probability of any M-ary communication system under an average energy constraint. The bounds are valid for arbitrary quantum measurements, for any prior probability distribution, and do not rely on unbiasedness assumptions.

On indoor visible light communication systems with spatially random receiver

This paper studies the performance of an indoor optical wireless communication system with visible light communication (VLC) technology in a cuboid room with a spatially random receiver. Considering that the receiver is uniformly distributed on the floor of a 4a m x 4b m x H m (where a > 0, b > 0 and H > 0) cuboid room, 4 light emitting diode (LED) lamps are all located at the center of 2a m x 2b m rectangle, which is a quarter of the ceiling area. The receiver chooses the best channel link to receive the information from the LED lamps, which depends on the distance between the receiver and each lamp. By using stochastic geometry theory, we derive the exact/approximated analytical expressions for the outage probability and the ergodic capacity, respectively. Finally, our derived analytical results are verified by Monte Carlo simulations.

M-ary pulse position modulation performance in non-Kolmogorov turbulent atmosphere.

The performance of atmospheric optical wireless communication systems in terms of the bit error rate (BER) is investigated when a Gaussian laser beam propagating in non-Kolmogorov turbulence is M-ary pulse-position-modulated (PPM). BER variations against the changes in different parameters such as the non-Kolmogorov power law exponent, symbol number, data bit rate, avalanche photodetector gain, equivalent load resistor, detector quantum efficiency, wavelength, turbulence structure constant, and the Gaussian beam source size are analyzed. Making the design of the PPM optical wireless communication system able to operate in a non-Kolmogorov atmosphere will give better BER performance if the parameters are taken into account in line with the trends presented in our results.

Analysis of an adaptive orbital angular momentum shift keying decoder based on machine learning under oceanic turbulence channels

Abstract Oceanic turbulence tends to degrade the performance of underwater optical communication (UOC) systems based on orbital angular momentum (OAM) shift keying (SK). A decoder for the UOC-OAM-SK using convolutional neural networks (CNNs) is investigated. We simulate 8 kinds of superposition Laguerre-Gaussian (LG) beams as a trinary OAM-SK encoder; these beams propagate under simulated oceanic channels. The results show that in temperature-dominated situations, the decoders based on the CNN have a high accuracy (nearly 100%) under weak-to-moderate turbulence and have an accuracy greater than 93% under strong turbulence at a distance of 60 m. Under weak-to-moderate turbulence, the accuracies are higher than 95% within 80 m, and under strong turbulence, the accuracies are lower than 90% after 60 m propagation. The decoder with an incorporated CNN is insensitive to the balance parameter in most situations, except for those that are salinity dominated. Furthermore, the CNN trained with a database mixed with several levels of turbulence has a higher accuracy when accommodating an unknown level of turbulence than when trained with a single level of turbulence. This work is expected to aid in the future design of UOC-OAM-SK systems.

OSNR and nonlinear noise power estimation for optical fiber communication systems using LSTM based deep learning technique.

The optical signal-to-noise ratio (OSNR) and fiber nonlinearity are critical factors in evaluating the performance of high-speed optical fiber communication systems. Recently, several deep learning based methods have been put forward to monitor OSNR of a fiber communication system. In this work, we propose a long short-term memory (LSTM) network based method to simultaneously estimate OSNR and nonlinear noise power caused by fiber nonlinearity. In the training step, LSTM network extracts the essential features in frequency domain of the input signal. Then, with the built model in the training step, the LSTM output the OSNR and nonlinear noise power of the signal under test. The simulation by VPI software is carried on a 5-channel long haul optical transmission system with the launched optical power of -3.0~ + 3.0dBm per channel. The results show that the test error of OSNR is less than 1.0dB with the reference OSNR from 15 to 30dB for QPSK, 16QAM and 64QAM signal. The test error of nonlinear noise power is less than 1.0dB for QPSK and 16QAM signal when the Laser linewidth is 6 KHz and 100 KHz respectively. The proposed method is a promising candidate for nonlinearity-insensitive OSNR and accurate nonlinear noise power estimation in multi-channel long haul optical fiber communication systems.

Performance analysis of underwater wireless optical communication systems over a wide range of optical turbulence

The propagation of optical signal under water is affected by three major degrading phenomena, namely absorption, scattering, and turbulence. The statistical distribution of turbulence-induced fading though has not yet been well characterized. In this paper, in order to investigate the effect of different probability density functions (PDFs) proposed for the statistical behavior of fading under water, we evaluate the performance of underwater wireless optical communication (UWOC) systems with respect to the well-known statistical distributions for the optical turbulence such as lognormal, Gamma, K, Weibull, and exponentiated Weibull distributions. For the sake of accuracy, we adopt a general channel model where both absorption and scattering effects are appropriately taken into account based on the Monte Carlo (MC) numerical method, and consider the fading effect as a multiplicative coefficient with the aforementioned PDFs. We derive the closed-form expressions for the average bit error rate (BER) and outage probability, as the system performance metrics, with respect to all of the channel degrading effects and the aforementioned statistical distributions. Our results demonstrate that as the turbulence strength, measured by the scintillation index value, increases, the gap between the system performance predicted by different statistical distributions becomes more, and this gap mainly appears in the form of changing the slope of average BER or outage probability curves versus the average transmitted power per bit. This further emphasizes the importance of accurate channel models for the design of UWOC systems.

The Influence Factors and Performance Analysis of Optical Communication Systems Based on VPI

How to further improve the performance of optical communication systems will be an important guarantee for the successful construction of next-generation optical networks. This paper builds an optical transmission simulation system on the VPI simulation platform. By changing the system parameters such as fiber length, transmitter bit rate, global bit rate and sampling rate, observed and analyzed the changes of spectrum and eye diagram of the optical transmission simulation system. The experimental results show that the transmitter bit rate and global bit rate have a greater impact on the spectral bandwidth of optical communication systems than the optical fiber length and sampling rate.

Transmitter skew tolerance and spectral efficiency tradeoff in high baud-rate QAM optical communication systems

Residual IQ skew in a coherent transmitter severely degrades the performance of long-haul coherent optical communication systems. The impairment is particularly detrimental for a high baud-rate system using quadrature amplitude modulation (QAM). Furthermore, Nyquist pulse shaping increases the spectral efficiency for WDM systems. However, sharp roll-off of Nyquist pulse shaping further reduces the tolerance to residual IQ skew. Thus, certain trade-offs between spectral efficiency and roll-off factor should be made to improve the tolerance of residual IQ skew. We experimentally studied this trade-off and determined the optimal roll-off factor, channel spacing, receiver bandwidth, and equalizer length. The results serve as a guideline for high baud-rate coherent WDM systems.

Performance enhancement of LEO-to-ground FSO systems using All-optical HAP-based relaying

In this paper, we propose to use all-optical high altitude platform (HAP)-based relaying technique to improve the performance of the free-space optical communication (FSO) system from a low-earth orbit (LEO) satellite to the ground station. Two all-optical relaying techniques are applied to HAP-based relay node including optical amplify-and-forward (OAF) and optical detect-amplify-and-forward (ODAF). A closed-form expression for bit error rate (BER) of the proposed relay-assisted LEO-to-ground FSO system under the effects of free space loss, path loss, and atmospheric turbulence is derived. We also carry out Monte-Carlo (M-C) simulation to verify the theoretical results in terms of BER and the quality of image transmission. The numerical results show that 28 dB power gain at BER of 10−9 can be achieved thanks to the use of HAP-based relaying. Also, lower BER that results in better quality of restored images at the ground station is demonstrated in this paper.

Impact of pointing errors on the SER performance of free space optical communication system with two decision thresholds over exponentiated Weibull fading channels

The impact of pointing errors on the symbol error rate (SER) performance of multiple pulse-position modulation (MPPM) free space optical (FSO) system with optimized decision threshold (ODT) and dynamic decision threshold (DDT) is investigated over exponentiated Weibull atmospheric turbulence channels. The probability density function (PDF) of the aggregated channel model is derived on the basis of Meijer’s G-function and the closed-form SER expression is then obtained by Gauss–Laguerre quadrature function. The variations of SER performance with different jitter variances, beam width, aperture sizes, and turbulence strengths for these two decision threshold schemes are analyzed in detail. The study shows that the impact of jitter variances is more apparent for ODT than that for DDT scheme and the performance difference between ODT and DDT schemes decreases with the increase of beam width. Monte Carlo simulation is also provided to verify the correctness of the proposed SER models. This work is beneficial to the design of FSO system.

DCF with FBG for Dispersion Compensation in Optical Fiber Link at Various Bit Rates using Duobinary Modulation Format

Dispersion is one of the very important parameters that effect on the performance of optical fiber communication systems. It causes pulse broadening, limiting of transmission distance and the number of channels on optical fiber link and low Bit rate. Dispersion compensation fiber (DCF) based on Fiber Bragg Grating (FBG) is widespread used in the dispersion compensation scheme. In this work, the proposed dispersion compensation fiber is included (pre – post–symmetrical) schemes with Fiber Bragg Grating and duo-binary modulation format. These are at various bit rates (10 Gbit/s, 20 Gbit/s, 30 Gbit/s and 40 Gbit/s) and different input laser power from (0 dBm to 10 dBm) for 200 Km distance. Optisystem software version 10 is used to design simulation model. Q- factor and BER are two parameters which used to evaluate the performance analysis of the system, we concluded that, the symmetrical compensation techniques is better than others compensation schemes when the Q factor is 52.977 and bit rate is equal 0, these at 10 Gbit/s and 10 dBm transmitted power.