scholarly journals Mixed Topology of DF Relayed Terrestrial Optical Wireless Links with Generalized Pointing Errors over Turbulence Channels

Technologies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 121 ◽  
Author(s):  
GeorgeK. Varotsos ◽  
Hector E. Nistazakis ◽  
Argyris N. Stassinakis ◽  
Christos K. Volos ◽  
Vasileios Christofilakis ◽  
...  
Keyword(s):  
Performance Metrics ◽  
Cooperative Diversity ◽  
Optical Signal ◽  
Decode And Forward ◽  
Pointing Error ◽  
Pointing Errors ◽  
Mathematical Expressions ◽  
Negative Exponential Distribution ◽  
Negative Exponential ◽  
Signal Fading

This study investigated the outage performance of a terrestrial FSO communication system that uses mixed series and parallel decode-and-forward (DF) relay-assisted (i.e., cooperative diversity) configurations, taking into account the influence of both atmospheric turbulence and pointing error effects. Turbulence-induced optical signal fading is modeled by gamma-gamma or the negative exponential distribution for weak to strong and saturated turbulence conditions, respectively. Additionally, weak to strong non-zero boresight misalignment-induced optical signal fading is modeled by the generalized Beckmann distribution. Under these conditions, an outage analysis of the examined FSO system is performed, in terms of both outage probability and mean outage duration metrics. Thus, fairly accurate closed-form mathematical expressions for both performance metrics are derived, while their corresponding analytical results demonstrate concrete performance and availability improvements for the total FSO system, especially when the number of the connected in parallel DF relays increases. Moreover, the obtained results are verified through the corresponding simulation results.

scholarly journals Transdermal Optical Wireless Links with Multiple Receivers in the Presence of Skin-Induced Attenuation and Pointing Errors

Computation ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 33 ◽  
Author(s):  
Varotsos ◽  
Nistazakis ◽  
Aidinis ◽  
Jaber ◽  
Rahman
Keyword(s):  
High Speed ◽  
Optical Signal ◽  
Optical Wireless ◽  
Implantable Medical Devices ◽  
Optical Wireless Communications ◽  
Pointing Error ◽  
High Data ◽  
Modulation Format ◽  
Pointing Errors ◽  
Mathematical Expressions

The last few years, the scientific field of optical wireless communications (OWC) has witnessed tremendous progress, as reflected in the continuous emergence of new successful high data rate services and variable sophisticated applications. One such development of vital research importance and interest is the employment of high speed, robust, and energy-effective transdermal optical wireless (TOW) links for telemetry with implantable medical devices (IMDs) that also have made considerable progress lately for a variety of medical applications, mainly including neural recording and prostheses. However, the outage performance of such TOW links is significantly degraded due to the strong attenuation that affects the propagating information-bearing optical signal through the skin, along with random misalignments between transmitter and receiver terminals, commonly known as pointing error effect. In order to anticipate this, in this work we introduce a SIMO TOW reception diversity system that employs either OOK or more power-effective L-PPM schemes. Taking into account the joint impact of skin-induced attenuation and non-zero boresight pointing errors, modeled through the suitable Beckmann distribution, novel closed-form mathematical expressions for the average BER of the total TOW system are derived. Thus, the possibility of enhancing the TOW availability by using reception diversity configurations along with the appropriate modulation format is investigated. Finally, the corresponding numerical results are presented using the new derived theoretical outcomes.

Performance Analysis of Reconfigurable Intelligent Surface in a Dual-Hop DF Relay Empowered Asymmetric RF/FSO Networks

2021 ◽  
Author(s):  
Kehinde O Odeyemi ◽  
Pius A. Owolawi ◽  
Oladayo O. Olakanmi
Keyword(s):  
Performance Analysis ◽  
Closed Form ◽  
Atmospheric Turbulence ◽  
Performance Metrics ◽  
Beam Width ◽  
High Signal ◽  
Free Space Optical ◽  
Decode And Forward ◽  
Pointing Errors ◽  
The Impact

Abstract 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.

scholarly journals Serial DF Relayed FSO Links over Mixture Gamma Turbulence Channels and Nonzero Boresight Spatial Jitter

Computation ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 34 ◽  
Author(s):  
Androutsos ◽  
Nistazakis ◽  
Khalid ◽  
Muhammad ◽  
Tombras
Keyword(s):  
Communication Systems ◽  
Optical Signal ◽  
Propagation Path ◽  
Atmospheric Conditions ◽  
Free Space Optical ◽  
Decode And Forward ◽  
Pointing Error ◽  
Composite Channels ◽  
Turbulence Effects ◽  
Significant Phenomenon

Over the past few years, terrestrial free space optical (FSO) communication systems have demonstrated increasing research and commercial interest. However, due the signal’s propagation path, the operation of FSO links depends strongly on atmospheric conditions and related phenomena. One such significant phenomenon is the scintillation caused by atmospheric turbulence effects; in order to address the significant performance degradation that this causes, several statistical models have been proposed. Here, turbulence-induced fading of the received optical signal is investigated through the recently presented mixture Gamma distribution, which accurately describes the irradiance fluctuations at the receiver’s input of the FSO link. Additionally, at the same time, it significantly reduces the mathematical complexity of the expressions used for the description of composite channels with turbulence along with nonzero boresight pointing error-induced fading. In order to counterbalance the performance mitigation due to these effects, serial decode-and-forward relays are employed, and the performance of the system is estimated through derived mathematical expressions.

scholarly journals Reliability and Sensitivity Analysis of a Repairable System with Warranty and Administrative Delay in Repair

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Mohamed S. El-Sherbeny ◽  
Zienab M. Hussien
Keyword(s):  
Performance Metrics ◽  
Failure Time ◽  
Relative Sensitivity ◽  
Sensitivity Analyses ◽  
Inspection Time ◽  
Industrial Systems ◽  
Negative Exponential Distribution ◽  
Product Warranty ◽  
Negative Exponential ◽  
The Cost

The purpose of this study is to analyze the behavior of some industrial systems in light of the cost-free warranty policy. According to this policy, we assume that the repairman is not always present in the system. When the active unit fails, the repairman will be called to visit the system; however, administrative procedures may delay the visit for some time. Once on the system, the repairman first inspects whether the fault is caused by the user or not and whether it is repairable or not. According to product warranty laws, the repairman carries out the repair or replacement of the faulty unit. The failure time, administrative delay time, inspection time, and repair time are assumed taken as a negative exponential distribution. The system model is analyzed by the supplementary variable technique and Laplace transform, as various performance metrics of system efficiency have been obtained. The sensitivity and relative sensitivity analyses for the system parameters have also been performed. Finally, an illustrative example is taken to illustrate the efficiency of the system.

The Comparison Between the Bayes Estimator and the Maximum Likelihood Estimator of the Reliability Function for Negative Exponential Distribution

2018 ◽  
pp. 439
Author(s):  
Hazim Mansour Gorgees ◽  
Bushra Abdualrasool Ali ◽  
Raghad Ibrahim Kathum
Keyword(s):  
Maximum Likelihood ◽  
Maximum Likelihood Estimator ◽  
Exponential Distribution ◽  
Reliability Function ◽  
Bayes Estimator ◽  
Likelihood Estimator ◽  
Monte Carlo Simulation Technique ◽  
Negative Exponential Distribution ◽  
Negative Exponential ◽  
Better Than

     In this paper, the maximum likelihood estimator and the Bayes estimator of the reliability function for negative exponential distribution has been derived, then a Monte –Carlo simulation technique was employed to compare the performance of such estimators. The integral mean square error (IMSE) was used as a criterion for this comparison. The simulation results displayed that the Bayes estimator performed better than the maximum likelihood estimator for different samples sizes.

Ehrenfest urn models

1965 ◽  
Vol 2 (02) ◽  
pp. 352-376 ◽  
Author(s):  
Samuel Karlin ◽  
James McGregor
Keyword(s):  
Exponential Distribution ◽  
Continuous Time ◽  
Random Variables ◽  
Independent Random Variables ◽  
Urn Models ◽  
Time Intervals ◽  
Negative Exponential Distribution ◽  
Negative Exponential ◽  
Random Times

In the Ehrenfest model with continuous time one considers two urns and N balls distributed in the urns. The system is said to be in stateiif there areiballs in urn I, N −iballs in urn II. Events occur at random times and the time intervals T between successive events are independent random variables all with the same negative exponential distributionWhen an event occurs a ball is chosen at random (each of theNballs has probability 1/Nto be chosen), removed from its urn, and then placed in urn I with probabilityp, in urn II with probabilityq= 1 −p, (0 <p< 1).

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