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Related Concept Videos

Beams with Unsymmetric Loadings01:17

Beams with Unsymmetric Loadings

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Analyzing a supported beam under unsymmetrical loadings is essential in structural engineering to understand how beams respond to varied force distributions. This analysis involves calculating the deflection and identifying points where the slope of the beam is zero, which are crucial for ensuring structural stability and functionality.
The first moment-area theorem determines the slope at any point on the beam. This theorem indicates that the change in slope between two points on a beam...
218
Beams with Symmetric Loadings01:15

Beams with Symmetric Loadings

280
The moment-area method is an analytical tool used in structural engineering to determine the slope and deflection of beams under various loads. Consider a cantilever with a concentrated load and moment at the free end. The first step is constructing a free-body diagram to calculate the reactions at the fixed end. Next, the bending moment diagram is plotted to visualize how the bending moment varies along the beam's length, focusing on points where the bending moment equals zero.
The M/EI...
280
Shearing Stresses in a Beam: Problem Solving01:14

Shearing Stresses in a Beam: Problem Solving

366
A cantilever beam with a rectangular cross-section under distributed and point loads experiences shearing stresses. The analysis begins by identifying the loads acting on the beam. Then, the reactions at the beam's fixed end are calculated using equilibrium equations. The vertical reaction is a combination of the distributed and point loads, while the moment reaction is the sum of their moments. The shear force distribution along the beam, resulting from these loads, is established by...
366
Distributed Loads: Problem Solving01:21

Distributed Loads: Problem Solving

849
Beams are structural elements commonly employed in engineering applications requiring different load-carrying capacities. The first step in analyzing a beam under a distributed load is to simplify the problem by dividing the load into smaller regions, which allows one to consider each region separately and calculate the magnitude of the equivalent resultant load acting on each portion of the beam. The magnitude of the equivalent resultant load for each region can be determined by calculating...
849
Maximum Power Transfer01:16

Maximum Power Transfer

539
Numerous practical applications within engineering disciplines, such as telecommunications, necessitate optimizing power delivery to a connected load. This pursuit, however, entails inherent internal losses, which can either equal or exceed the power supplied to the load. The Thevenin equivalent circuit is helpful in finding the maximum power a linear circuit can deliver to a load. It is assumed in this context that the load resistance can be adjusted.
By substituting the entire circuit with...
539
Distribution of Stresses in a Narrow Rectangular Beam01:11

Distribution of Stresses in a Narrow Rectangular Beam

303
In studying beam stress distribution, examining an elemental section is essential. To determine the average shearing stress on this face, the calculated shear is divided by the surface area. Importantly, shearing stresses on the beam's transverse and horizontal planes mirror each other, indicating a consistent stress distribution along the upper region of the beam. Notably, shearing stresses are absent at the beam's upper and lower surfaces due to the absence of applied forces in these...
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Related Experiment Video

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Joint Resource Allocation for Multiuser Opportunistic Beamforming Systems with OFDM-NOMA.

Wen-Bin Sun1, Ming-Liang Tao1, Ling Wang1

  • 1School of Electronics and Information, Northwestern Polytechnical University, Xi'an 710072, China.

Entropy (Basel, Switzerland)
|July 2, 2021
PubMed
Summary

This study introduces a new downlink multiuser opportunistic beamforming (OBF) system combining orthogonal frequency division multiplexing (OFDM) and non-orthogonal multiple-access (NOMA). The proposed method significantly enhances spectrum efficiency (SE) and reduces bit error ratio (BER) with low complexity.

Keywords:
NOMAOFDMmultiuseropportunistic beamformingspectrum efficiency

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Area of Science:

  • Wireless communication systems
  • Signal processing for communications

Background:

  • Opportunistic beamforming (OBF) enhances spectrum efficiency (SE) in multiple-input-multiple-output (MIMO) systems.
  • Existing OBF multiple-access schemes often yield unsatisfactory SE.
  • Low complexity and feedback are key OBF advantages.

Purpose of the Study:

  • To propose a novel downlink multiuser OBF system integrating OFDM and NOMA.
  • To maximize SE and minimize BER in frequency selective fading channels.
  • To address the non-convex optimization problem for resource allocation.

Main Methods:

  • Developed a downlink multiuser OBF system combining OFDM and NOMA.
  • Derived closed-form expressions for equivalent channels and SE.
  • Formulated and solved a non-convex optimization problem using a joint iterative algorithm for subcarrier mapping, user pairing, and power allocation.

Main Results:

  • The proposed method achieved approximately 5 dB gain in SE and BER compared to existing OBF techniques.
  • Achieved ~2 (bps/Hz) higher SE than sparse code multiple-access (SCMA) under specific conditions.
  • Demonstrated high SE and low BER with limited feedback and computation complexity.

Conclusions:

  • The proposed OFDM-NOMA OBF scheme effectively improves SE and BER in wireless systems.
  • The joint iterative optimization algorithm provides an efficient solution for resource allocation.
  • The system offers robust performance with limited feedback and computational load.