scholarly journals Performance Analysis Of VSF-OFCDM Femtocells

2021 ◽  
Author(s):  
Fatima Hussain
Keyword(s):  
Frequency Domain ◽  
Maximal Ratio Combining ◽  
Simulation Studies ◽  
Operating Environment ◽  
Spreading Factor ◽  
Penetration Factor ◽  
Efficient Performance ◽  
Heterogenous Network ◽  
The Relationship ◽  
Penetration Loss

In this thesis, we analyze the performance of a variable spreading factor (VSF) OFCDM employed in femtocells, with OFDM used in macrocells in a hybrid heterogenous network. Orthogonal subcarriers are assigned to macro users and for femtocell users, non-contiguous subcarrier grouping is employed. We derive the analytic expression of the BER for uplink VSF-OFCDM femto and OFDM macro users for the case of maximal ratio combining receiver. We evaluate the performance of femto/macro users in VSF-OFCDM system through numerical and Monte Carlo simulation studies. Improvement in BER of the femtocell users is also noted. The relationship between the femto spreading factor and femto/macro BER is analyzed. We present, the relationship between the channel load and optimum spreading factor employed by femtocell users for the energy efficient performance of macro users. Femto wall penetration loss, that is the important parameter to evaluate the femto performance, is also taken into account. Also, effect of femto wall penetration on macro BER is evaluated for various spreading factors. Following our study, we find that interference-limited system favors increased time spreading especially when number of subcarriers is limited and noise-limited system favors increased frequency domain spreading. When large number of subcarriers are available, optimum spreading (from macro perspective) favors increased frequency domain spreading regardless of the femto-macro loads, or whether operating environment is noise or interference limited. Once the optimum spreading factor is determined, increase or decrease in the femto Eb/No does not matter. Also, femto wall penetration factor not only effects the femto BER directly, but also reduce the potential interference faced by macro user equipment (UEs). As a result macro BER is improved, but the choice of optimal spreading factor for macro UEs remain unaffected with the variation in femto wall penetration loss.

scholarly journals Performance Analysis Of VSF-OFCDM Femtocells

2021 ◽  
Author(s):  
Fatima Hussain
Keyword(s):  
Frequency Domain ◽  
Maximal Ratio Combining ◽  
Simulation Studies ◽  
Operating Environment ◽  
Spreading Factor ◽  
Penetration Factor ◽  
Efficient Performance ◽  
Heterogenous Network ◽  
The Relationship ◽  
Penetration Loss

In this thesis, we analyze the performance of a variable spreading factor (VSF) OFCDM employed in femtocells, with OFDM used in macrocells in a hybrid heterogenous network. Orthogonal subcarriers are assigned to macro users and for femtocell users, non-contiguous subcarrier grouping is employed. We derive the analytic expression of the BER for uplink VSF-OFCDM femto and OFDM macro users for the case of maximal ratio combining receiver. We evaluate the performance of femto/macro users in VSF-OFCDM system through numerical and Monte Carlo simulation studies. Improvement in BER of the femtocell users is also noted. The relationship between the femto spreading factor and femto/macro BER is analyzed. We present, the relationship between the channel load and optimum spreading factor employed by femtocell users for the energy efficient performance of macro users. Femto wall penetration loss, that is the important parameter to evaluate the femto performance, is also taken into account. Also, effect of femto wall penetration on macro BER is evaluated for various spreading factors. Following our study, we find that interference-limited system favors increased time spreading especially when number of subcarriers is limited and noise-limited system favors increased frequency domain spreading. When large number of subcarriers are available, optimum spreading (from macro perspective) favors increased frequency domain spreading regardless of the femto-macro loads, or whether operating environment is noise or interference limited. Once the optimum spreading factor is determined, increase or decrease in the femto Eb/No does not matter. Also, femto wall penetration factor not only effects the femto BER directly, but also reduce the potential interference faced by macro user equipment (UEs). As a result macro BER is improved, but the choice of optimal spreading factor for macro UEs remain unaffected with the variation in femto wall penetration loss.

scholarly journals Performance enhancement techniques for variable spreading factor OFCDM systems

2021 ◽  
Author(s):  
Lamiaa Khalid
Keyword(s):  
Frequency Domain ◽  
Spectral Efficiency ◽  
Carrier Frequency Offset ◽  
Performance Enhancement ◽  
Likelihood Function ◽  
Adaptive Modulation ◽  
Gradient Algorithm ◽  
Maximal Ratio Combining ◽  
Likelihood Principle ◽  
Spreading Factor

n this thesis we investigate the effect of Carrier Frequency Offset (CFO) on the performance of downlink Variable Spreading Factor (VSF) OFCDM systems when subcarrier grouping is used. An analytic expression of the SINR is derived for downlink VSF-OFCDM with CFO for the case of maximal ratio combining receiver. Numerical results show that, when the total spreading factor is fixed, the VSF-OFCDM system with higher frequency domain spreading factor is more sensitive to CFO than that with lower frequency domain spreading factor. Due to the adverse impact of the CFO on VSF-OFCDM systems, we propose a correction scheme based on the maximum likelihood principle. We derive the likelihood function for VSF-OFCDM system with CFO and use a gradient algorithm to estimate and minimize the effect of CFO in a tracking mode. Our results show that the BER performance in the low SNR environment can be improved significantly with few number of iterations for different spreading factors. We also propose a threshold-based group-adaptive modulation algorithm used with an adaptive subcarrier allocation technique for downlink VSF-OFCDM to increase the spectral efficiency for a given target BER. The proposed algorithm provides an increase in spectral efficiency without increasing the total transmit power for different spreading factors with and without coding.

scholarly journals Performance enhancement techniques for variable spreading factor OFCDM systems

2021 ◽  
Author(s):  
Lamiaa Khalid
Keyword(s):  
Frequency Domain ◽  
Spectral Efficiency ◽  
Carrier Frequency Offset ◽  
Performance Enhancement ◽  
Likelihood Function ◽  
Adaptive Modulation ◽  
Gradient Algorithm ◽  
Maximal Ratio Combining ◽  
Likelihood Principle ◽  
Spreading Factor

n this thesis we investigate the effect of Carrier Frequency Offset (CFO) on the performance of downlink Variable Spreading Factor (VSF) OFCDM systems when subcarrier grouping is used. An analytic expression of the SINR is derived for downlink VSF-OFCDM with CFO for the case of maximal ratio combining receiver. Numerical results show that, when the total spreading factor is fixed, the VSF-OFCDM system with higher frequency domain spreading factor is more sensitive to CFO than that with lower frequency domain spreading factor. Due to the adverse impact of the CFO on VSF-OFCDM systems, we propose a correction scheme based on the maximum likelihood principle. We derive the likelihood function for VSF-OFCDM system with CFO and use a gradient algorithm to estimate and minimize the effect of CFO in a tracking mode. Our results show that the BER performance in the low SNR environment can be improved significantly with few number of iterations for different spreading factors. We also propose a threshold-based group-adaptive modulation algorithm used with an adaptive subcarrier allocation technique for downlink VSF-OFCDM to increase the spectral efficiency for a given target BER. The proposed algorithm provides an increase in spectral efficiency without increasing the total transmit power for different spreading factors with and without coding.

scholarly journals A Bootstrap Method to Test Granger-Causality in the Frequency Domain

2021 ◽  
Author(s):  
Matteo Farnè ◽  
Angela Montanari
Keyword(s):  
Stochastic Process ◽  
Frequency Domain ◽  
Granger Causality ◽  
Bootstrap Method ◽  
Money Stock ◽  
Bootstrap Test ◽  
Low Frequencies ◽  
Economic Output ◽  
Stationary Bootstrap ◽  
The Relationship

AbstractWe propose a bootstrap test for unconditional and conditional Granger-causality spectra in the frequency domain. Our test aims to detect if the causality at a particular frequency is systematically different from zero. In particular, we consider a stochastic process derived applying independently the stationary bootstrap to the original series. At each frequency, we test the sample causality against the distribution of the median causality across frequencies estimated for that process. Via our procedure, we infer about the relationship between money stock and GDP in the Euro Area during the period 1999–2017. We point out that the money stock aggregate M1 had a significant impact on economic output at all frequencies, while the opposite relationship is significant only at low frequencies.

Flight Simulation for Research

1964 ◽  
Vol 68 (646) ◽  
pp. 645-652 ◽  
Author(s):  
D. H. Perry ◽  
J. M. Naish
Keyword(s):  
Flight Simulation ◽  
Simulation Studies ◽  
Aircraft Control ◽  
Motion Cues ◽  
Stability And Control ◽  
Research Problems ◽  
And Control ◽  
The Relationship ◽  
Aircraft Stability And Control ◽  
Vtol Aircraft

SummarySome of the uses of ground based flight simulation as a research tool to aid the design of new aircraft and their equipment are described. The function of the simulator is to provide a method for investigating humon flying tasks in the laboratory, so that the relationship between the pilot's capabilities and the equipment's characteristics can be systematically studied. The paper is presented in two parts describing recent work on two research simulators at the RAE.Part I deals with the use of simulation for studying aircraft stability and control characteristics. The equipment used at RAE for this work is described, with particular emphasis on methods of presenting to the pilot a simulated view of the outside world, and for reproducing some of the motion cues which he experiences in flight. Experimental evidence of the importance of these simulation cues when making aircraft control assessments is also presented. Several examples of simulation studies into the control of conventional and VTOL aircraft are given, to illustrate the type of research problems in this field which may be tackled and the techniques involved in solving them.

scholarly journals Frequency-Diverse Holographic Metasurface Antenna for Near-Field Microwave Computational Imaging

2021 ◽  
Vol 8 ◽  
Author(s):  
Jiaqi Han ◽  
Long Li ◽  
Shuncheng Tian ◽  
Xiangjin Ma ◽  
Qiang Feng ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Imaging System ◽  
Near Field ◽  
Horn Antenna ◽  
Computational Imaging ◽  
Simulation Studies ◽  
Field Patterns ◽  
Full Wave ◽  
Imaging Reconstruction ◽  
Iterative Shrinkage

This article presents a holographic metasurface antenna with stochastically distributed surface impedance, which produces randomly frequency-diverse radiation patterns. Low mutual coherence electric field patterns generated by the holographic metasurface antenna can cover the K-band from 18 to 26 GHz with 0.1 GHz intervals. By utilizing the frequency-diverse holographic metasurface (FDHM) antenna, we build a near-field microwave computational imaging system based on reflected signals in the frequency domain. A standard horn antenna is adopted to acquire frequency domain signals radiated from the proposed FDHM antenna. A detail imaging restoration process is presented, and the desired targets are correctly reconstructed using the 81 frequency-diverse patterns through full-wave simulation studies. Compressed sensing technique and iterative shrinkage/thresholding algorithms are applied for the imaging reconstruction. The achieved compressive ratio of this computational imaging system on the physical layer is 30:1.

scholarly journals Corporate fraud as a threat to the company’s economic security

2021 ◽  
Vol 110 ◽  
pp. 04011
Author(s):  
Galina Krokhicheva ◽  
Iulia Mezentseva ◽  
Tian Yu
Keyword(s):  
White Collar Crime ◽  
Scientific Work ◽  
White Collar ◽  
Economic Security ◽  
Operating Environment ◽  
Economic Interests ◽  
Corporate Fraud ◽  
Economic State ◽  
Micro Level ◽  
The Relationship

The article is devoted to the study of the organizational and methodological foundations of ensuring economic security through the mechanism of preventing corporate fraud. The influence of “white-collar” crime at the micro level on the overall economic state of the state is considered. The theoretical aspects of corporate fraud are investigated and generalized. The analysis of existing methods and techniques to assess the risk of their occurrence in a particular enterprise is carried out. The emphasis is placed on the assessment of the external operating environment, considered as a source of potential threats to the company’s security, as well as on the study of the risk of corporate fraud in relation to a particular business entity. The authors propose mechanisms to protect the economic interests of the organization from various threats from the staff, which are essential for maintaining the level of its economic security. The findings on the relationship between corporate fraud and micro-level economic security are not conclusive. This indicates the need for further scientific work on the problem, which will logically continue the problems raised in the article.

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