Performance Improvement of Optical Multiple Access CDMA Network Using a New Three-Dimensional (Spectral/Time/Spatial) Code

2021 ◽  
Author(s):  
Mohanad Alayedi ◽  
Abdelhamid Cherifi ◽  
Abdelhak Ferhat Hamida ◽  
Boubakar Seddik Bouazza ◽  
Syed Alwee Aljunid
Keyword(s):  
Performance Improvement ◽  
Multiple Access ◽  
Three Dimensional ◽  
Spatial Code

Advances in coupled axial turbine and nonaxisymmetric exhaust volute aerodynamics for turbomachinery

2020 ◽  
pp. 095441002096645
Author(s):  
Jie Gao ◽  
Chunde Tao ◽  
Dongchen Huo ◽  
Guojie Wang
Keyword(s):  
Performance Improvement ◽  
High Efficiency ◽  
Three Dimensional ◽  
Great Influence ◽  
Aerodynamic Characteristics ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Axial Turbine ◽  
Flow Interactions ◽  
And Performance

Marine, industrial, turboprop and turboshaft gas turbine engines use nonaxisymmetric exhaust volutes for flow diffusion and pressure recovery. These processes result in a three-dimensional complex turbulent flow in the exhaust volute. The flows in the axial turbine and nonaxisymmetric exhaust volute are closely coupled and inherently unsteady, and they have a great influence on the turbine and exhaust aerodynamic characteristics. Therefore, it is very necessary to carry out research on coupled axial turbine and nonaxisymmetric exhaust volute aerodynamics, so as to provide reference for the high-efficiency turbine-volute designs. This paper summarizes and analyzes the recent advances in the field of coupled axial turbine and nonaxisymmetric exhaust volute aerodynamics for turbomachinery. This review covers the following topics that are important for turbine and volute coupled designs: (1) flow and loss characteristics of nonaxisymmetric exhaust volutes, (2) flow interactions between axial turbine and nonaxisymmetric exhaust volute, (3) improvement of turbine and volute performance within spatial limitations and (4) research methods of coupled turbine and exhaust volute aerodynamics. The emphasis is placed on the turbine-volute interactions and performance improvement. We also present our own insights regarding the current research trends and the prospects for future developments.

scholarly journals Author Correction: Subpixel three-dimensional laser imaging with a downscaled avalanche photodiode array using code division multiple access

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Fan Xu ◽  
Yuan-Qing Wang ◽  
Xiao-Fei Zhang ◽  
Cai-Yun Wang
Keyword(s):  
Code Division Multiple Access ◽  
Multiple Access ◽  
Three Dimensional ◽  
Avalanche Photodiode ◽  
Laser Imaging ◽  
Photodiode Array ◽  
Code Division Multiple

A Correction to this paper has been published: https://doi.org/10.1038/s42005-021-00520-8.

scholarly journals Performance Improvement of Ultra Wideband Multiple Access Modulation System using a new Optimal Pulse Shape

2017 ◽  
Vol 6 (1) ◽  
pp. 20
Author(s):  
V. Goyal ◽  
B. S. Dhaliwal
Keyword(s):  
Performance Improvement ◽  
Pulse Shape ◽  
Multiple Access ◽  
Energy Levels ◽  
Rake Receiver ◽  
Correct Choice ◽  
Low Energy ◽  
Ultra Wideband ◽  
High Data ◽  
Very High

Ultra-wideband (UWB) uses very low energy levels to transfer data at very high data rate and bandwidth. An optimal and correct choice of transmission pulse shape is an important criterion in this technology. In this paper, we will present an approach for the generation of an optimal pulse shape with the optimal generation of pulse shape values that can provide effective results when transmitted using multiple access modulation technique over a multipath channel and received by a RAKE type receiver. The bit error analysis of constructed model is also given using Ideal Rake, selective RAKE, and partial RAKE receiver configurations.

scholarly journals Performance Improvement on Nonorthogonal Multiple Access without CSIT

2020 ◽  
Vol 2020 ◽  
pp. 1-6 ◽  
Author(s):  
Wenlong Xia ◽  
Yuanping Zhou ◽  
Qingdang Meng
Keyword(s):  
Performance Improvement ◽  
Multiple Access ◽  
Euclidean Distance ◽  
Computational Cost ◽  
Optimal Solution ◽  
The Novel ◽  
Channel State ◽  
State Information ◽  
Virtual Channels ◽  
Constrained Capacity

In this paper, a downlink virtual-channel-optimization nonorthogonal multiple access (VNOMA) without channel state information at the transmitter (CSIT) is proposed. The novel idea is to construct multiple complex virtual channels by jointly adjusting the amplitudes and phases to maximize the minimum Euclidean distance (MED) among the superposed constellation points. The optimal solution is derived in the absence of CSIT. Considering practical communications with finite input constellations in which symbols are uniformly distributed, we resort to the sum constellation constrained capacity (CCC) to evaluate the performance. For MED criterion, the maximum likelihood (ML) decoder is expected at the receiver. To decrease the computational cost, we propose a reduced-complexity bitwise ML (RBML) decoder. Experimental results are presented to validate the superior of our proposed scheme.

A Robust Mixing Plane and Its Application in Three-Dimensional Inverse Design of Transonic Turbine Stages

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Saurya Ranjan Ray ◽  
Mehrdad Zangeneh
Keyword(s):  
Performance Improvement ◽  
Load Distribution ◽  
Flow Direction ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Inverse Design ◽  
Transonic Turbine ◽  
Machine Configuration ◽  
Lp Turbine ◽  
Flow Variables

A robust mixing plane method satisfying interface flux conservation, nonreflectivity and retaining interface flow variation; valid at all Mach numbers and applicable for any machine configuration is formulated and implemented in a vertex based finite volume solver for flow analysis and inverse design. The formulation is based on superposing perturbed flow variables derived from the three-dimensional (3D) characteristics obtained along the flow direction on the exchanged mixed out averaged quantities. The method is extended for low speed applications using low Mach number preconditioning. Subsequently, inverse design runs over a single stage transonic low pressure (LP) turbine configuration conducted at a fixed mass flow boundary condition and spanwise loading condition similar to the baseline generates optimized configurations providing performance improvement while achieving prespecified target meridional load distribution.

Design Tools for the Performance Improvement of a 76 MW Francis Turbine Runner

2009 ◽  
Author(s):  
Jose´ Manuel Franco-Nava ◽  
Oscar Dorantes-Go´mez ◽  
Erik Rosado-Tamariz ◽  
Jose´ Manuel Ferna´ndez-Da´vila ◽  
Reynaldo Rangel-Espinosa
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Finite Element ◽  
Performance Improvement ◽  
Three Dimensional ◽  
Francis Turbine ◽  
Design Tools ◽  
Turbine Runner ◽  
Induced Stresses ◽  
Fluid Behaviour

Application of two mayor design tools, Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD), for the performance improvement of a 76 MW Francis turbine runner is presented. In order to improve the performance of the runner, not only a CFD based optimization for the runner but also its structural integrity evaluation was carried out. In this paper, a number of analyses included within the design tools-based runner optimization process are presented. Initially, a reference condition for the fluid behaviour through turbine components was carried out by means of the computation of fluid conditions through the spiral case and stays vanes, followed by CFD-based fluid behaviour for the wicket so as to include the flow effects induced by these components in the final CFD analysis for the runner. All CFD computations were generated within the three dimensional Navier-Stoke commercial turbomachinery oriented CFD code FINE™/Turbo from NUMECA. The whole hydraulic turbine performance was then compared against actual data from a medium-head Francis type hydro turbine (76 MW). Then, CFD-based flow induced stresses in the turbine runner were computed by using a three dimensional finite element model built within the FEA commercial code ANSYS. Appropriate boundary conditions were set in order to obtain the results due to the different type loads (pressure and centrifugal force). The FEM model was able to capture the pressure gradients on the blade surfaces obtained from the CFD results. Improvement of efficiency and power for the runner was computed by using a parametric model built within 3D CFD code integrated environment FINETM/Design3D from NUMECA which combines genetic algorithms and a trained artificial neural network. During the optimization process the artificial neural network is trained with a database of geometries and their respective CFD computations in order to determine the optimum geometry for a given objective function. The optimisation process and the trend curve of the optimization or design cycle that included 29 parameters (corresponding to the control points of runner blade primary sections) which could vary during the process is presented. Finally, the flow induced stresses of the optimized Francis turbine runner was computed so as to evaluate the final blade geometry modifications related to the efficiency and power improvement.

MMSE Equalization Based Performance of Chaotic Interleaving Scheme for Iterative IDMA System

2019 ◽  
Vol 9 (2) ◽  
pp. 237-246
Author(s):  
Aasheesh Shukla ◽  
Atul Bansal ◽  
Vinay Kumar Deolia ◽  
Karan Veer
Keyword(s):  
Computational Complexity ◽  
Performance Improvement ◽  
Multiple Access ◽  
Pulse Shaping ◽  
Minimum Mean Square Error ◽  
Logistic Map ◽  
Mean Square ◽  
Chaotic Interleaving ◽  
Mmse Equalizer ◽  
Bpsk Modulation

Background: In this paper, a chaotic interleaving scheme is proposed for further performance improvement of Interleave Division Multiple Access (IDMA). Interleavers are used to generate permuted sequence of signals to be transmitted with optimum correlation. Methods: Random interleaving (RI) was the fundamental taxonomy and used to distinguish the different users in IDMA scheme. The logistic map based chaotic interleaving scheme is suggested for IDMA. The system is also combined with Minimum Mean Square Error (MMSE) equalizer to combat the effect of Inter Symbol Interference (ISI). Results: For the sake of simplicity, no pulse shaping is assumed at the transmitter and ISI channel is considered to be a fixed 3 tap channel. Simulations are performed in MATLAB. BPSK modulation is used. Furthermore, the results show that the IDMA with proposed logistic map based chaotic interleaver outperforms the traditional random interleaving scheme in terms of BER without the need of extra memory and computational complexity. Conclusion: The obtained results show the noticeable performance improvement of CI-IDMA with MMSE equalization in deep fading situations. Chaos based interleaver also offers other advantages such as less requirement of memory and small implementation complexity.

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