Performance evaluation of an efficient RZ-MQAM modulation scheme in all-optical OFDM transmission systems

All optical orthogonal frequency division multiplexing (AO-OFDM) technique is a promising technique and employed in many military applications for data transmission over long distance. But AO-OFDM signals are very sensitive to nonlinear distortion and these systems suffer from nonlinear impairments. This paper describes a novel nonlinear phase noise reduction technique by decreasing interaction time between subcarriers in AO-OFDM transmission systems. This technique mitigates the effects of nonlinearity on all-optical OFDM transmission systems and improves performance of transmission systems. The proposed AO-OFDM transmission system has been successfully simulated and analyzed for estimating phase noise due to cross-phase modulation, self-phase modulation and four-wave mixing. The proposed RZ-8QAM AO-OFDM system with 29 subcarriers is examined and the transmission distance is fixed at 550km

Analytical simulation of non-linearity effects compensation in all-optical orthogonal frequency division multiplexing systems

All-Optical Orthogonal Frequency Division Multiplexing (AO-OFDM) modulation technique has attracted significant attention of the optical communication community for the high speed transmission systems. This research investigates the effects of the fiber nonlinear impairments on the performance of the AO-OFDM transmission systems and proposes three AO-OFDM systems which have high tolerance against the nonlinear impairments. The first AO-OFDM system employs Differential Quadrature Phase Shift Keying (DQPSK), while the second and third systems employ m-array Quadrature Amplitude Modulation (m-QAM), and Non Return to Zero (NRZ) DQPSK, respectively. Each proposed system employs 29 subcarriers which are generated by an Optical Frequency Comb Generator (OFCG). The generated signals are transmitted over the transmission link and received by the coherent receiver. The analytical model of each system is developed to investigate the effects of various parameters such as the transmission distance, number of fiber spans, fiber dispersion, number of subcarriers, and power of subcarrier on the Nonlinear Phase Noise (NLPN) which induced by the fiber nonlinearity effects. The impacts of the NLPN due to Four-Wave Mixing (FWM), Self-Phase Modulation (SPM), and Cross-Phase Modulation (XPM) on the performance of the proposed systems are also investigated. The proposed systems are numerically simulated at the symbol rate of 25 Gsymbol/s. The optical multi-carrier signals were generated, modulated, de-correlated, and detected by the VPI transmission maker software 9.0. The received signals were linked to Matlab software and processed by using the Digital Signal Processing (DSP) algorithm in order to compensate the effects of the nonlinear impairments and improve the performance of the transmission system. The digital processing of the detected signals and Bit Error Rate (BER) calculation are performed by using DSP algorithm in Matlab software. In order to quantify the effectiveness of the proposed techniques, three AO-OFDM systems are demonstrated numerically before and after employing the nonlinearity mitigation techniques. The total phase noise variances, BER, and Error Vector Magnitude (EVM) are investigated to explore the effectiveness of the proposed technique. The results show that after using the phase noise mitigation technique, the EVM and BER are decreased by 20% and 7%, respectively. In addition, by employing the proposed technique the total phase noise variance is reduced by 50%. The simulation results clearly indicate that the constellation diagrams of the proposed system become more squeezed around the ideal constellation and the received signals are closer to the ideal point compared with the original system. That means, after employing the proposed techniques, the received signals have higher tolerance towards the fiber nonlinear impairments as compared to the original system. The obtained results show the significant improvements on the transmission performance of the proposed system after employing the post-compensation DSP or Optical Phase Conjugation (OPC) module

Incremental and diffusion compressive sensing strategies over distributed networks

Abstract Compressive sensing (CS) has been widely used in wireless sensor networks (WSNs). In WSNs, the sensors are battery-powered and hence their communication and processing powers are limited. One of the dominant features of the CS is its complex recovery phase. Thus, great care should be taken into account when designing the CS recovery algorithm for WSNs. In this paper, we propose a distributed and cooperative recovery algorithm for two different cooperation modes of sensor networks including incremental and diffusion. The theoretical performance analysis of the proposed algorithms in both exact and noisy measurements is investigated. The obtained results show the superiority of the proposed method in terms of convergence rate and steady-state error compared with the non-cooperative scenario and the well-known distributed least absolute shrinkage and selection operator (D-LASSO) approach. Furthermore, the proposed structure requires much fewer measurements for exact recovery

Exploring buckling and post-buckling behaviour of incompressible hyperelastic beams through innovative experimental and computational approaches

The objective of this paper is to conduct a comprehensive investigation into the buckling and post-buckling behavior of hyperelastic beams through both computational and experimental means. Natural rubber is used in the construction of a beam with a square cross-section. To determine the mechanical properties of natural rubber, a uniaxial tensile test is performed in accordance with ASTM D412. In finite element modeling (FEM), the nonlinear behavior of rubber is modeled using hyperelastic theory and the Yeoh strain energy function. The Static-Riks method is also implemented using Abaqus for the analysis of nonlinear buckling. To validate the present investigation results with FEM, an experimental test of digital image correlation (DIC) is conducted. The critical buckling force obtained via numerical methods exhibits an error of nearly 5% when compared to the corresponding results obtained from experimental testing. In order to ascertain the impact of various design parameters on the buckling behavior of the system, a comprehensive parametric analysis has been conducted. The parameters studied include the cross-sectional thickness, length of the structure, eccentric loads, as well as the mechanical properties of the materials used in the system. Consistent with the FEM outcomes, the critical buckling force exhibited by the hyperelastic beam demonstrates a positive correlation with increasing levels of hardness, cross-sectional thickness, and eccentric loads. The buckling behavior of the system is adversely affected by increasing its length. To ultimately validate the precision and reliability of the model, a supervised neural network (NN) learning method is employed

Distributed sparse diffusion estimation with reduced communication cost

Abstract The issue considered in the current study is the problem of adaptive distributed estimation based on diffusion strategy which can exploit sparsity in improving estimation error and reducing communications. It has been shown that distributed estimation leads to a good performance in terms of the error value, convergence rate, and robustness against node and link failures in wireless sensor networks. However, the main focus of many works in the field of distributed estimation research is on convergence speed and estimation error, neglecting the fact that communications among the nodes require a lot of transmissions. In this work, the focus is on a solution based on sparse diffusion least mean squares (LMS) algorithm, and a new version of sparse diffusion LMS algorithm is proposed which takes both communications and error cost into account. Also, the computation complexity and communication cost for every node of the network, as well as performance analysis of the proposed strategy, is provided. The performance of the proposed method in comparison with the existing methods is illustrated by means of simulations in terms of computational and communicational cost, and flexibility to signal changes

Stauprimide Priming of Human Embryonic Stem Cells toward Definitive Endoderm

Objective: In vitro production of a definitive endoderm (DE) is an important issue in stem cell-related differentiation studies and it can assist with the production of more efficient endoderm derivatives for therapeutic applications. Despite tremendous progress in DE differentiation of human embryonic stem cells (hESCs), researchers have yet to discover universal, efficient and cost-effective protocols. Materials and Methods: In this experimental study, we have treated hESCs with 200 nM of Stauprimide (Spd) for one day followed by activin A (50 ng/ml; A50) for the next three days (Spd-A50). In the positive control group, hESCs were treated with Wnt3a (25 ng/ml) and activin A (100 ng/ml) for the first day followed by activin A for the next three days (100 ng/ml; W/A100-A100). Results: Gene expression analysis showed up regulation of DE-specific marker genes (SOX17, FOXA2 and CXCR4) comparable to that observed in the positive control group. Expression of the other lineage specific markers did not significantly change (p<0.05). We also obtained the same gene expression results using another hESC line. The use of higher concentrations of Spd (400 and 800 nM) in the Spd-A50 protocol caused an increase in the expression SOX17 as well as a dramatic increase in mortality rate of the hESCs. A lower concentration of activin A (25 ng/ml) was not able to up regulate the DE-specific marker genes. Then, A50 was replaced by inducers of definitive endoderm; IDE1/2 (IDE1 and IDE2), two previously reported small molecule (SM) inducers of DE, in our protocol (Spd-IDE1/2). This replacement resulted in the up regulation of visceral endoderm (VE) marker (SOX7) but not DE-specific markers. Therefore, while the Spd-A50 protocol led to DE production, we have shown that IDE1/2 could not fully replace activin A in DE induction of hESCs. Conclusion: These findings can assist with the design of more efficient chemically-defined protocols for DE induction of hESCs and lead to a better understanding of the different signaling networks that are involved in DE differentiation of hESCs