• Current Optics and Photonics
• /
• v.3 no.4
• /
• pp.311-319
• /
• 2019

A hybrid free-space-optical/radio-frequency (FSO/RF) communication system is considered, with the help of amplify-and-forward (AF) relaying. We consider various weather conditions to investigate their effects on the system's performance. We begin by obtaining the cumulative distribution function and probability density function of the end-to-end signal-to-noise ratio for the AF dual-hop FSO communication system with RF backup link. Then, these results are used to derive closed-form expressions for the outage probability, average bit-error rate, and average ergodic capacity. The results show that the considered system efficiently employs the complementary nature of FSO and RF links, resulting in impressive performance improvements compared to non-hybrid systems.

• International Journal of Advanced Culture Technology
• /
• v.10 no.3
• /
• pp.307-312
• /
• 2022

The commercialization of the fifth generation (5G) mobile systems has quested enabling technologies, such as intelligent reflecting surface (IRS) transmissions, towards the sixth generation (6G) networks. In this paper, we present a bit-error rate (BER) performance analysis on IRS transmissions in 5G non-orthogonal multiple access (NOMA) networks. First, we derive a closed-form expression for the BER of IRS-NOMA transmissions under Rician fading channels. Then, by Monte Carlo simulations, we validate the proposed approximate BER expression, and show numerically that the derived BER expression is in good agreement with Monte Carlo simulations. Furthermore, we also analyze the BER performance of IRS-NOMA networks under Rician fading channels with different numbers of reflecting elements, and demonstrate that the performances improve monotonically as the number of reflecting devices increases.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.15 no.3
• /
• pp.1174-1192
• /
• 2021

With the assistance of non-orthogonal multiple access (NOMA), the spectrum efficiency and the number of users in cloud radio access network (CRAN) can be greatly improved. In this paper, the system performance of NOMA-assisted CRAN is investigated. Specially, the outage probability (OP) and ergodic sum rate (ESR), are derived for performance evaluation of the system, respectively. Based on this, by minimizing the OP of the system, a suboptimal power allocation (PA) scheme with closed-form PA coefficients is proposed. Numerical simulations validate the accuracy of the theoretical results, where the derived OP has more accuracy than the existing one. Moreover, the developed PA scheme has superior performance over the conventional fixed PA scheme but has smaller performance loss than the optimal PA scheme using the exhaustive search method.

• International Journal of Advanced Culture Technology
• /
• v.9 no.4
• /
• pp.307-314
• /
• 2021

Recently, positively asymmetric binary pulse amplitude modulation (2PAM) has been proposed to improve the bit error rate (BER) performance of the weak channel gain user, with a tolerable BER loss of the strong channel gain user, for non-orthogonal multiple access (NOMA). However, the BER loss of the stronger channel gain user is inevitable in such positively asymmetric 2PAM NOMA scheme. Thus, we propose the negatively asymmetric 2PAM NOMA scheme. First, we derive closed-form expressions for the BERs of the negatively asymmetric 2PAM NOMA. Then, simulations demonstrate that for the stronger channel gain user, the BER of the proposed negatively asymmetric 2PAM NOMA improves, compared to that of the conventional positively asymmetric 2PAM NOMA. Moreover, we also show that for the weaker channel gain user, the BER of the proposed negatively asymmetric 2PAM NOMA is comparable to that of the conventional positively asymmetric 2PAM NOMA, over the power allocation range less than about 10 %.

• Advances in Computational Design
• /
• v.8 no.1
• /
• pp.77-96
• /
• 2023

Calculating size-dependent mechanical properties of the nano-scale materials usually involves cumbersome numerical and theoretical works. In this paper, we aim to present a closed-form relation to calculate the length-dependent Young's modulus of carbon nanotubes (CNTs) based on nonlocal elasticity theory. In this regard, a single wall carbon nanotube (SWCNT) is considered as a rod structure and the governing nonlocal equations are developed under uniaxial tensile load. The equations are solved using analytical methods and strain distribution, total displacement and the size-dependent equivalent Young's modulus are obtained. Further, the results are compared with the molecular dynamics results from the literature. The outcome indicates that the calculated relations are coincident with the molecular dynamics results.

• ETRI Journal
• /
• v.44 no.6
• /
• pp.966-976
• /
• 2022

Optical wireless communication, or free space optics, is a promising solution for backhauls in sixth-generation mobile systems. However, the susceptibility of optical links to weather conditions has led to FSO links being furnished with radio frequency (RF) backups. These Hybrid FSO/RF systems provide enhanced link availability but lead to RF resource wastage. Cognitive radio technology, in contrast, is well known for its optimal use of RF resources and may be combined with an FSO link to create a Cognitive Hybrid FSO/RF system. This work uses such a system to analyze a configuration for a mobile backhaul in sixth-generation mobile systems. This configuration can seamlessly coexist with established large scale RF cellular networks. The performance of this configuration is analyzed with respect to outage probability and average bit error by considering the impact of optical channel turbulence, misalignment loss, RF interference, and noise. Mathematical closed-form expressions are verified by simulations.

• Journal of applied mathematics & informatics
• /
• v.40 no.1_2
• /
• pp.99-115
• /
• 2022

The problem of Benard double diffusive Marangoni convection is investigated in a horizontally infinite composite layer system consisting of a two component fluid layer above a porous layer saturated with the same fluid, using Darcy-Brinkman model with constant heat sources/sink in both the layers. The lower boundary of the porous region is rigid and upper boundary of the fluid region is free with Marangoni effects. The system of ordinary differential equations obtained after normal mode analysis is solved in closed form for the eigenvalue, thermal Marangoni number for two types of thermal boundary combinations, Type (I) Adiabatic-Adiabatic and Type (II) Adiabatic -Isothermal. The corresponding two thermal Marangoni numbers are obtained and the essence of the different parameters on non-Darcy-Benard double diffusive Marangoni convection are investigated in detail.

• International Journal of Internet, Broadcasting and Communication
• /
• v.15 no.4
• /
• pp.84-89
• /
• 2023

Recently, the sixth generation (6G) networks have become tremendous research topics. Intelligent reflecting surface (IRS) technologies have been envisioned, to increase spectrum and energy efficiency for the fifth generation (5G) mobile networks, towards the sixth generation (6G) communications. In this paper, especially for the strongest channel gain user, we investigate the bit-error rate (BER) of non-orthogonal multiple access (NOMA) systems with intelligent reflecting surface (IRS). First, we derive a BER expression in a closed-form of Q functions. Second, we investigate the BER performance improvement of IRS NOMA systems over NOMA systems versus the power allocation. Moreover, we analyze the BER performance improvement of IRS NOMA systems over NOMA systems versus the number of IRS devices. In results, NOMA equipped with IRS technologies could play an important role in the paradigm shift from 5G mobile networks to 6G mobile networks.

• Structural Engineering and Mechanics
• /
• v.27 no.6
• /
• pp.713-739
• /
• 2007

Nowadays computers can perform symbolic computations in addition to mere number crunching operations for which they were originally designed. Symbolic computation opens up exciting possibilities in Structural Mechanics and engineering. Classical areas have been increasingly neglected due to the advent of computers as well as general purpose finite element software. But now, classical analysis has reemerged as an attractive computer option due to the capabilities of symbolic computation. The repetitive cycles of simultaneous - equation sets required by the finite element technique can be eliminated by solving a single set in symbolic form, thus generating a truly closed-form solution. This consequently saves in data preparation, storage and execution time. The power of Symbolic computation is demonstrated by six examples by applying symbolic computation 1) to solve coupled shear wall 2) to generate beam element matrices 3) to find the natural frequency of a shear frame using transfer matrix method 4) to find the stresses of a plate subjected to in-plane loading using Levy's approach 5) to draw the influence surface for deflection of an isotropic plate simply supported on all sides 6) to get dynamic equilibrium equations from Lagrange equation. This paper also presents yet another computationally efficient and accurate numerical method which is based on the concept of derivative of a function expressed as a weighted linear sum of the function values at all the mesh points. Again this method is applied to solve the problems of 1) coupled shear wall 2) lateral buckling of thin-walled beams due to moment gradient 3) buckling of a column and 4) static and buckling analysis of circular plates of uniform or non-uniform thickness. The numerical results obtained are compared with those available in existing literature in order to verify their accuracy.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2008.04a
• /
• pp.590-595
• /
• 2008

In the present paper, the impact damage behavior of steel plate reinforced concrete panels exposed to shock impulsive loading and fragment impact loading is investigated. To evaluate the retrofit performance of a steel-strengthened concrete panels, a numerical experiment using a numerical simulation with AUTODYN, an explicit analysis program is introduced because a real explosion experiment requires the vast investment and expense for facilities as well as the deformation mechanisms are too complicated to be reproduced with a conventional closed-form analyses. The model for the analysis is simplified and idealized as a two-dimensional and axisymmetric case controled with geometry, boundary condition and material properties in order to obtain a resonable computation time. As a result of the analysis, panels subject to either shock loading or fragment loading without the steel plate reinforcement experience the perforation with spalled fragments. In addition, the panels reinforced with steel plate can prevent the perforation and provide the good mechanical effect such as the increase of global stiffness and strength through the composite action between the concrete slab and the steel plate.