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In this study, the authors propose a simple yet tighter approximations for the special two-dimensional Gaussian Q functions using the Trapezoidal rule of numerical integration. This enables a simplified and accurate symbol error probability (SEP) approximation of the hexagonal-quadrature amplitude modulation (HQAM) in additive white Gaussian noise channel. The proposed approximation further simplifies the SEP calculation of HQAM in parametric α - μ, η - μ, and λ - μ fading distributions. Also, the SEP of HQAM over log-normal shadowing is calculated in this study. The accuracy of the analytical framework is verified using computer simulations. [ABSTRACT FROM AUTHOR]

Miniature GPS devices now allow for measurement of the movement of animals in real time and provide high- quality and high-resolution data. While these new data sets are a great improvement, one still encounters some measurement errors as well as device failures. Moreover, these devices only measure position and require further reconstruction techniques to extract the full dynamical state space with the velocity and acceleration. Direct differentiation of position is generally not adequate. We report on the successful implementation of a shadowing filter algorithm that (1) minimizes measurement errors and (2) reconstructs at the same time the full phase-space from a position recording of a flying pigeon. This filter is based on a very simple assumption that the pigeon's dynamics are Newtonian. We explore not only how to choose the filter's parameters but also demonstrate its improvements over other techniques and give minimum data requirements. In contrast to competing filters, the shadowing filter's approach has not been widely implemented for practical problems. This article addresses these practicalities and provides a prototype for such application. [ABSTRACT FROM AUTHOR]

Path loss models are the most fundamental part of wireless propagation channel models. Path loss is typically modelled as a (single-slope or multi-slope) power-law dependency on distance plus a log-normally distributed shadowing attenuation. Determination of the parameters of this model is usually done by fitting the model to results from measurements or ray tracing. The authors show that the typical least-square fitting to those data points is inherently biased to give the best fitting to the link distances that happen to have more evaluation points. A weighted fitting method is developed that emphasises the accuracy at the distance range that is consciously chosen by the user as most important for a system simulation. As a further important point that is typically not taken into account for path loss parameter extraction, the authors show that typically measurement data (but also ray tracing) is censored, i.e. path loss values above a certain threshold cannot be measured. The authors present examples of weighted fitting models, and models with and without the censored data, for 28 GHz channels in urban macrocells, and show that these effects have a significant impact on the extracted parameters and that the fitting accuracy can be improved with the presented methods. [ABSTRACT FROM AUTHOR]

In this study, a new composite channel model for land mobile satellite (LMS) systems under tree shadowing is proposed utilising the inverse Gaussian (IG) distribution to model the shadowing component. Using the experimental data of received power under tree shadowing at L-band, which were carried out at Stromovka Park in Prague, the Czech Republic, the assumption of the IG distribution for the description of the first-order statistics of large-scale effects is investigated and validated. A new LMS channel model is developed as a sum of a signal experiencing IG shadowing and a signal under Rayleigh multipath effects. Moreover, a methodology to generate accurate time series of the received signal envelope using the IG distribution is presented. Such methodology and generally time series generators can be used for the evaluation of system's performance and for end-to-end simulations. Finally, it is shown that the proposed time series generator reproduces the first-order and second-order statistics of the LMS channel model with a very good accuracy. [ABSTRACT FROM AUTHOR]

A computational scheme is presented that takes into account the topography, i.e. the shadowing and hence the local emission angle of the electrons when evaluating AR-XPS data of macroscopic rough surfaces. The topography of the sample surface is supposed to be recorded by atomic force microscopy and/or opticalmicroscopy. The emitted photoelectrons are simulated based on an extension of the Beer-Lambert law that includes the shadowing, the current local emission angle, and the geometrical instrument setup. The obtained angle-resolved XPS spectra are optimized in accordance with experimental ones via a self-consistentminimization algorithmthat also allows one to determine the layer thicknesses of the corrugated sample. In order to validate the proposed numerical scheme, the simulationprogram simulationof electron spectra for surface analysis is used. An additional analysis is then performed considering only experimental data. The numerical scheme gives good agreement in simulation-simulation as well as simulation-experiment comparisons and permits a comprehensible interpretation of themeasured data. [ABSTRACT FROM AUTHOR]

SUMMARY An existing elevation dependent shadowing model for high-altitude platform (HAP) mobile communication in built-up areas is employed to perform the area coverage probability analysis and fading margin computation for HAP mobile communication systems. A generalized expression for the PDF of the received signal power in the HAP coverage is derived. The shadowing fade margin model that can characterize different types of built-up area is developed. Theoretical relations between shadowing fade margin and outage probability and cell coverage probability are given. Numerical simulation for isoflux coverage HAP-based system shows that there is great difference in the value of shadowing fade margin under line-of-sight and non-line-of-sight conditions for the same outage probability. It is also found that the cell coverage probability is insensitive to the variance of the shadowing fade margin in suburban environment whatever the size of the cell and for small cells in urban high-rise environments.Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY The problem concerning short-term fading and long-term fading (shadowing) and their deleterious effects on wireless systems performance has been in focus for a long time. In this paper, motivated by the results of propagation measurements in land-mobile and indoor-mobile systems, and by the fact that gamma distribution can describe shadowing reliably, Nakagami- m distribution is used to model the signal envelope and gamma distribution is used to model the average signal power. Receive diversity with maximal-ratio combining and selection combining is implemented at the microlevel and macrolevel, respectively. The general case is explored, which assumes that microdiversity and macrodiversity are provided through arbitrary number of channels. Because shadowing has larger correlation distance than short-term fading, correlated macrodiversity channels are studied. This paper investigates the dynamics of the received signal. A novel rapidly converging infinite-series expression for average level crossing rate and average fade duration are obtained. Numerical results are graphically presented to examine the impact of fading severity, shadowing severity, number of diversity branches at the microlevel, number of base stations and correlation between base stations to the system's performance. Computer simulations are also performed to verify the validity and the accuracy of proposed theoretical analysis. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We have simulated asteroid lightcurves for simple shape models using a realistic surface scattering law. The scattering law includes a shadowing function computed with numerical ray-tracing. We computed lightcurves in a variety of illumination geometries for both the traditional Lommel-Seeliger law and our seminumerical law. We observe a shift in the rotational phase of the lightcurves, which depends on the parameters of the scattering law as well as the illumination geometry and the direction of the spin axis of the asteroid. This phase shift is always zero at opposition, and can be as large as 10° for illumination geometries typical for Main Belt asteroids. The phase shift has implications on the accuracy of other results which are based on asteroid lightcurve analysis, such as spin-state or shape determination. [ABSTRACT FROM AUTHOR]

Language has been shown to play a key role in the development of a child's theory of mind, but its role in adult belief reasoning remains unclear. One recent study used verbal and nonverbal interference during a false-belief task to show that accurate belief reasoning in adults necessarily requires language (Newton & de Villiers, 2007). The strength of this inference depends on the cognitive processes that are matched between the verbal and nonverbal inference tasks. Here, we matched the two interference tasks in terms of their effects on spatial working memory. We found equal success on false-belief reasoning during both verbal and nonverbal interference, suggesting that language is not specifically necessary for adult theory of mind. [ABSTRACT FROM AUTHOR]

A time domain (TD) solution based on uniform theory of diffraction-physical optics (UTD-PO) is presented to analyze the multiple-building diffraction in urban areas where a wedge-shaped hill causes shadowing of the transmitter from the receiver.We derive the channel impulse response of the renowned Bertoni's model, which utilizes a recursion relation and does not need to incorporate the slope diffraction in the transition zone. The received signals can be predicted through a simple operation of convolution, which provides a faster and easier final solution for UWB radio propagation and significantly reduces the computational time. The TD result can be applied to analyze the UWB pulse distortion by multiple-building diffraction in urban areas where the city is surrounded by hilly areas. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:426-429, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25730 [ABSTRACT FROM AUTHOR]

If there is a frequency offset in the local oscillator circuit in QPSK demodulation, the BER is degraded. Previously, methods for estimating this frequency offset have been proposed. However, few techniques that have been studied can estimate this offset in an environment with a large frequency offset or noise. A digital adaptive IIR notch filter is effective for estimation of a large frequency offset in an environment with noise. However, the noise is colored in the receiver due to the IF band BPF inserted in order to suppress out-of-band noise. Therefore, the converged value has a bias error with respect to the target value. The method proposed in this paper is based on the fact that the phase of the digital IIR-BPF is zero at the center frequency of the amplitude characteristic. This characteristic is used for control by applying a negative feedback to the digital IIR-BPF coefficients. Then, no bias error is generated because the noise in the in-phase channel and that of the quadrature channel in QPSK are uncorrelated. Further, the proposed method does not drift but maintains the present status due to the uncorrelated character described above, even in the case of channel disconnection such as shadowing. Therefore, this is a frequency offset estimation method suitable for mobile communications. As a result of evaluation of the proposed method in terms of the BER in a white Gaussian noise channel, it is confirmed that the proposed method provides a BER lower than that of the conventional digital adaptive IIR notch filter. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 86(9): 1–12, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.10089 [ABSTRACT FROM AUTHOR]

This Letter presents capacity analysis of Fisher-Snedecor F fading channels under different transmission strategies. To this end, novel analytical expressions are proposed for optimal rate adaptation with constant transmit power, channel inversion with a fixed rate and truncated channel inversion with fixed rate schemes in this Letter. Then, analytical results are illustrated for different fading and shadowing parameter values. [ABSTRACT FROM AUTHOR]

The effect of spectral shadowing and multiple reflections in a serial fiber Bragg grating (FBG)-array are investigated. The wavelength detection errors for the distal FBG (reflectivity = 1%) in a 50-FBG array are 18 pm and 12 pm for spectral shadowing and multiple reflections, respectively. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 2–4, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10653 [ABSTRACT FROM AUTHOR]

Shadowing determination is a crucial step in methods based on the physical optics approximation, which are widely used for electromagnetic scattering analysis of electrically large, conducting bodies. When the surface current is represented by basis functions on a mesh of triangle elements, this involves determining for each mesh edge and/or elemental face whether it is visible to the source or obscured by another mesh element. A field-of-view buffer-based shadowing determination algorithm for plane wave illumination of triangle-element meshes is presented, with special provision to maintain efficiency in case of grazing incidence. For homogeneous meshes, the computational costs in runtime and memory are both directly proportional to the number of mesh elements. [ABSTRACT FROM AUTHOR]