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- Title
- FADE STATISTICS FOR A LASERCOM SYSTEM AND THE JOINT PDF OF A GAMMA-GAMMA DISTRIBUTED IRRADIANCE AND ITS TIME DERIVATIVE.
- Creator
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Stromqvist Vetelino, Frida, Young, Cynthia, University of Central Florida
- Abstract / Description
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The performance of lasercom systems operating in the atmosphere is reduced by optical turbulence, which causes irradiance fluctuations in the received signal. The result is a randomly fading signal. Fade statistics for lasercom systems are determined from the probability density function (PDF) of the irradiance fluctuations. The expected number of fades per second and their mean fade time require the joint PDF of the fluctuating irradiance and its time derivative. Theoretical integral...
Show moreThe performance of lasercom systems operating in the atmosphere is reduced by optical turbulence, which causes irradiance fluctuations in the received signal. The result is a randomly fading signal. Fade statistics for lasercom systems are determined from the probability density function (PDF) of the irradiance fluctuations. The expected number of fades per second and their mean fade time require the joint PDF of the fluctuating irradiance and its time derivative. Theoretical integral expressions, as well as closed form, analytical approximations, were developed for the joint PDF of a gamma-gamma distributed irradiance and its time derivative, and the corresponding expression for the expected number of fades per second. The new approximation for the conditional PDF of the time derivative of a gamma-gamma irradiance is a zero mean Gaussian distribution, with a complicated irradiance depending variance. Fade statistics obtained from experimental data were compared to theoretical predictions based on the lognormal and gamma-gamma distributions. A Gaussian beam wave was propagated through the atmosphere along a horizontal path, near ground, in the moderate-to-strong optical turbulence. To characterize the propagation path, a new method that infers atmospheric propagation parameters was developed. Scintillation theory combined with a numerical scheme was used to infer the structure constant, Cn2, the inner scale and the outer scale from the optical measurements. The inferred parameters were used in calculations for the theoretical PDFs. It was found that fade predictions made by the gamma-gamma and lognormal distributions provide an upper and lower bound, respectively, for the probability of fade and the number of fades per second for irradiance data collected in the moderate-to-strong fluctuation regime. Aperture averaging effects on the PDF of the irradiance fluctuations were investigated by comparing the irradiance distributions for the three receiver apertures at two different values of the structure parameter and, hence, different values of the coherence radius. For the moderate-to-strong fluctuation regime, the gamma-gamma distribution provides a good fit to the irradiance fluctuations collected by finite-sized apertures that are significantly smaller than the coherence radius. For apertures larger than or equal to the coherence radius, the irradiance fluctuations appear to be lognormally distributed.
Show less - Date Issued
- 2006
- Identifier
- CFE0001440, ucf:47069
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001440
- Title
- FREQUENCY DOMAIN INDEPENDENT COMPONENT ANALYSIS APPLIED TO WIRELESS COMMUNICATIONS OVER FREQUENCY-SELECTIVE CHANNELS.
- Creator
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Liu, Yuan, Mikhael, Wasfy, University of Central Florida
- Abstract / Description
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In wireless communications, frequency-selective fading is a major source of impairment for wireless communications. In this research, a novel Frequency-Domain Independent Component Analysis (ICA-F) approach is proposed to blindly separate and deconvolve signals traveling through frequency-selective, slow fading channels. Compared with existing time-domain approaches, the ICA-F is computationally efficient and possesses fast convergence properties. Simulation results confirm the effectiveness...
Show moreIn wireless communications, frequency-selective fading is a major source of impairment for wireless communications. In this research, a novel Frequency-Domain Independent Component Analysis (ICA-F) approach is proposed to blindly separate and deconvolve signals traveling through frequency-selective, slow fading channels. Compared with existing time-domain approaches, the ICA-F is computationally efficient and possesses fast convergence properties. Simulation results confirm the effectiveness of the proposed ICA-F. Orthogonal Frequency Division Multiplexing (OFDM) systems are widely used in wireless communications nowadays. However, OFDM systems are very sensitive to Carrier Frequency Offset (CFO). Thus, an accurate CFO compensation technique is required in order to achieve acceptable performance. In this dissertation, two novel blind approaches are proposed to estimate and compensate for CFO within the range of half subcarrier spacing: a Maximum Likelihood CFO Correction approach (ML-CFOC), and a high-performance, low-computation Blind CFO Estimator (BCFOE). The Bit Error Rate (BER) improvement of the ML-CFOC is achieved at the expense of a modest increase in the computational requirements without sacrificing the system bandwidth or increasing the hardware complexity. The BCFOE outperforms the existing blind CFO estimator [25, 128], referred to as the YG-CFO estimator, in terms of BER and Mean Square Error (MSE), without increasing the computational complexity, sacrificing the system bandwidth, or increasing the hardware complexity. While both proposed techniques outperform the YG-CFO estimator, the BCFOE is better than the ML-CFOC technique. Extensive simulation results illustrate the performance of the ML-CFOC and BCFOE approaches.
Show less - Date Issued
- 2005
- Identifier
- CFE0000756, ucf:46560
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000756
- Title
- Re-Thinking the Intentionality of Fraud: Constructing and Testing the Theory of Unintended Amoral Behavior to Explain Fraudulent Financial Reporting.
- Creator
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Dill, Andrew, Sutton, Steven, Arnold, Vicky, Schmitt, Donna, Schminke, Marshall, University of Central Florida
- Abstract / Description
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My three-paper dissertation is aimed at applying the concepts of bounded ethicality and ethical fading to accounting fraud. Typical of relatively new fields such as behavioral ethics, theoretical models are scarce (Tenbrunsel (&) Smith-Crowe, 2008). As such, the purpose of Study 1 is to unify disparate theories and ideas from psychology and behavioral ethics as a means of constructing a theory, the Theory of Unintended Amoral Behavior (TUAB), which includes the concepts of bounded ethicality...
Show moreMy three-paper dissertation is aimed at applying the concepts of bounded ethicality and ethical fading to accounting fraud. Typical of relatively new fields such as behavioral ethics, theoretical models are scarce (Tenbrunsel (&) Smith-Crowe, 2008). As such, the purpose of Study 1 is to unify disparate theories and ideas from psychology and behavioral ethics as a means of constructing a theory, the Theory of Unintended Amoral Behavior (TUAB), which includes the concepts of bounded ethicality and ethical fading. In addition, the pressure for management to meet earnings expectations is discussed through the lens of the TUAB as an example of how one may unknowingly misreport.Studies 2 and 3 apply the TUAB to investigate how certain contextual factors interact with egocentric biases to increase the likelihood of ethical fading. Specifically, Study 2 consists of an experiment exploring how inferior pay among managers interacts with egocentric perceptions of fairness and envy to affect the likelihood of one engaging in ethical fading and fraudulent behavior. Study 3 also utilizes an experimental methodology to examine how the pressure to meet earnings forecasts interacts with egocentric perceptions of fairness and negative affect to influence the probability of ethical fading and fraudulent acts.The results for Study 2 indicate that one who is paid at a lower rate is more likely to view this disparity as unfair, which leads to a greater feeling of envy. Although envy had no significant direct effect on ethical fading in the primary analyses, a supplemental analysis revealed that a person's risk preference might moderate this relationship. The primary findings of Study 2 suggest that individuals who experience a higher degree of ethical fading are more likely to commit fraud, and that ethical fading, along with perceived unfairness, seem to be significant psychological processes that explain how differences in pay may lead to fraud. The primary finding of Study 3 is that, like Study 2, fraud is more likely to occur as an individual experiences a higher degree of ethical fading. Furthermore, this study suggests that those who are closest to meeting an earnings target are the most likely to engage in fraudulent behavior. Finally, the results failed to find any support that one's egocentric perceptions of fairness and negative affect contribute towards his or her ethical behavior in a goal achievement setting. The primary contributions of this dissertation is that it unifies various theories and ideas from psychology and behavioral ethics to establish a testable theory (TUAB) that includes the concepts of bounded ethicality and ethical fading, serves as an initial test of TUAB, and provides evidence that unethical behavior is not necessarily the result of one consciously forsaking his or her ethics for some other desired goal (i.e., profit).
Show less - Date Issued
- 2016
- Identifier
- CFE0006097, ucf:51211
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006097
- Title
- THE EFFECTIVENESS OF DATA CODES AND HARDWARE SELECTION TO MITIGATE SCINTILLATION EFFECTS ON FREE SPACE OPTICAL DATA TRANSMISSION.
- Creator
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Stein, Keith, Phillips, Ronald, University of Central Florida
- Abstract / Description
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The design of an optical communication link must plan for the random effects of atmospheric turbulence. This study analyses data from an experiment which transmitted from a laser located 8 meters above ground over a 13 Km range to coherent detection devices approximately 162 meters above ground. The effects of a fading and surging beam wave were considered in regards to code techniques for error correction, amplitude modulation and hardware architecture schemes. This study simulated the use...
Show moreThe design of an optical communication link must plan for the random effects of atmospheric turbulence. This study analyses data from an experiment which transmitted from a laser located 8 meters above ground over a 13 Km range to coherent detection devices approximately 162 meters above ground. The effects of a fading and surging beam wave were considered in regards to code techniques for error correction, amplitude modulation and hardware architecture schemes. This study simulated the use of arrays and large apertures for the receiving devices, and compared the resultant scintillation index with the theoretical calculations.
Show less - Date Issued
- 2006
- Identifier
- CFE0001204, ucf:46945
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001204
