Properties Of Fading Research Articles

Tripolarizated MIMO: Experimental Analysis and Modeling of Channel Properties in Both Indoor and Outdoor Scenarios

The tripolarized MIMO system can provide one more degree of freedom and have a more compacted size over a dual-polarized MIMO system, which is attractive for high-capacity wireless communication systems. In this paper, we analyze and model channel properties for tripolarized MIMO systems based on experimental channel measurements in typical indoor and outdoor scenarios. Firstly, channel measurement campaigns in the laboratory and the Urban Micro (UMi) scenarios on sub-6 GHz bands are presented. Then, based on measured data, path loss, delay spread (DS), and cross-polarization discrimination (XPD) for 9 polarization combinations are analyzed and modeled in a statistical way. Statistical results of these channel properties are also given. It is observed that channel properties of both large-scale fading and small-scale fading depend strongly on the polarization direction. Furthermore, we evaluate the performance of tripolarized MIMO systems by analyzing the Demmel condition number and channel capacity gain (CG). For both the indoor and the outdoor scenarios, it is found that colocated tripolarized antenna can bring a nearly threefold CG with respect to the unipolarized one. These results can give good insights into the design and evaluation of tripolarized MIMO systems.

Analysis the physical properties of laser fading on denim fabric

The laser fading process is acknowledged as a very strong alternative compared to the conventional physical and chemical processes used for aged worn look on denim fabrics In this study the beams from a CO micro m laser was used for the fading of denim fabrics In terms of both color and mechanical properties it is found that and micro s pulse times are suitable for laser fading process of denim fabrics This study aims that the effects of laser beam on denim fabrics were investigated and optimum process conditions were determined by tensile strength tear strength rubbing fastness of fabric According to the observation from this project both tensile and tearing strength decreased respectively on both warp and weft direction and color fastness to rubbing was decreased in significant level comparison with both before and after fading effect of denim fabrics

Statistical Properties of Double Hoyt Fading With Applications to the Performance Analysis of Wireless Communication Systems

In this paper, we investigate the statistical properties of double Hoyt fading channels, where the overall received signal is determined by the product of two statistically independent but not necessarily identically distributed single Hoyt processes. Finite-range integral expressions are first derived for the probability density function (PDF), cumulative distribution function (CDF), level-crossing rate (LCR), and average duration of fades of the envelope fading process. A closed-form approximate solution is also deduced for the LCR by making use of the Laplace approximation theorem. Applying the derived PDF of the double Hoyt channel, we then provide analytical expressions for the average symbol error probability of both coherent M-ary phase-shift keying and square M-ary quadrature amplitude modulation schemes. It is shown that all the obtained theoretical results include those that are already known for double Rayleigh channels as a special case. In addition, simplified expressions for the Hoyt $\times $ Rayleigh, Rayleigh $\times $ one-sided Gaussian, and double one-sided Gaussian channels are presented. Moreover, the applicableness of the proposed model to measured real-world propagation channels is examined and discussed by comparing the derived CDF and LCR with published measurement data collected in inter-vehicular propagation environments. Numerical and simulation results are also provided to confirm the validity of the derivations.

Statistical modeling of the high altitude platform dual-polarized MIMO propagation channel

In order to investigate the benefit of multiple-input multiple-output (MIMO) technique applying to the high altitude platform (HAP), a 2×2 MIMO statistical model, which can accurately describe the channel between HAP and high-speed train, is presented. And dual polarization diversity is particularly considered. Based on first-order three-state Markov chain, the single-input single-output (SISO) channel, a subset of the MIMO channel is first established. The ray tracing approach applied to the digital relief model (DRM) which covers the railway between Xi'an and Zhengzhou is used to obtain the state probability vector and matrix of the state transition probability. The proposed model considers both Doppler shift and temporal correlation, and the polarization correlation and spatial correlation statistical properties of large-scale fading and small-scale fading are analyzed. Moreover, useful numerical results on the MIMO HAP channel outage capacity are provided based on which, significant capacity gains with respect to the conventional SISO case are illustrated. Such statistical channel model can be applied to the future wireless communication system between HAP and high-speed train.

Contour Erasure and Filling-in: Old Simulations Account for Most New Observations.

Three recent studies used similar stimulus sequences to investigate mechanisms for brightness perception. Anstis and Greenlee (2014) demonstrated that adaptation to a flickering black and white outline erased the visibility of a subsequent target shape defined by a luminance increment or decrement. Robinson and de Sa (2012, 2013) used a flickering disk or annulus to show a similar effect. Here, a neural network model of visual perception (Francis & Kim, 2012), that previously explained properties of scene fading, is shown to also explain most of the erasure effects reported by Anstis and Greenlee and by Robinson and de Sa. The model proposes that in normal viewing conditions a brightness filling-in process is constrained by oriented boundaries, which thereby define separate regions of a visual scene. Contour adaptation can weaken the boundaries and thereby allow brightness signals to merge together, which renders target stimuli indistinguishable from the background. New simulations with the stimuli used by Anstis and Greenlee and Robinson and de Sa produce model output very similar to the perceptual experience of human observers. Finally, the model predicts that adaptation to illusory contours will not produce contour erasure.

Experimental Characterization of Radio Channel in Ruins Environment

This letter addresses the fading statistics of a radio propagation channel in a ruins environment, which is of vital importance for a pedestrian localization system based on cellphone signals. The channel of ruins is investigated in eight typical rescue scenarios at two common mobile communication bands (900 MHz and 1.8 GHz). To characterize the channel, an empirical path loss model is parameterized through experiments. Based on extensive measurements, large-scale fading characteristics at different polarizations and various antenna heights are examined and analyzed. Furthermore, the properties of small-scale fading including coherence bandwidth, decorrelation distance, and distance-dependent features are studied in this work. The results reported here can be applied to simulate the ruins channel and design the rescue system.

Measurement and Analytical Study of the Correlation Properties of Subchannel Fading for Noncontiguous Carrier Aggregation

The new multichannel/multicarrier technologies can potentially support much higher data rates in mobile multiple- access environments, such as carrier aggregation (CA) defined in the fourth-generation Long-Term Evolution Advanced enhance- ment. The correlation properties of noncontiguous subchannels are critical for the performance of CA, including cell coverage, frequency diversity, and channel state estimation. This paper has studied the correlation of the large-scale fading (LSF) and small-scale fading (SSF) of arbitrarily separated subchannels by realistic channel measurement and analytical modeling. We first obtain the subchannel correlation from the ultrawideband (UWB) channel measurement. This new approach avoids probing multiple subchannels simultaneously with channel sounders, which would be prohibitively complicated. The cross correlation of two distinct subchannels and the autocorrelation of a single subchannel are evaluated. Second, a new propagation model for the Nakagami-m fading in a multipath environment is proposed. The frequency- domain level crossing rate (FD-LCR) is defined and derived based on the propagation model. Then, a Markov chain for the frequency fading of the wideband channel is established, which can generate the correlated gain/power of subchannels in a wide bandwidth. Therefore, this model can be used as a fast simulator of CA over correlated subchannels. Finally, the cross correlation coefficients (CCCs) between two Nakagami-m fading subchannels obtained from the measurement and the proposed Markov model are compared with the analytical results in the literature. This paper provides important insights into the fading correlation of the multicarrier channels and can be applied to the design and simulation of indoor/outdoor multicarrier communications. Index Terms—Carrier aggregation (CA), channel measurement, channel modeling, CLEAN, fading, ultrawideband (UWB).

Colour Properties of Plasma-Induced Ozone Fading of Cotton Fabric

This study concerned with colour fading of cotton fabric by plasma-induced ozone treatment. Cotton knitted fabrics were dyed with reactive dye of red colour with a depth of 0.5% and were subjected to ozneo generated by a plasma machine for colour fading. In order to investigate the colour properties of the plasma-induced ozone treated cotton fabric. The plasma-induced ozone treatment was conducted with different parameters: (i) air concentration = 10%, 30%, 50% and 70%; (ii) water content in fabric = 35% and 45% and (iii) treatment time = 10 minutes, 20 minutes and 30 minutes. After the plasma-induced ozone treatment, the colour properties of the fabric were measured by spectrophotometer under illuminant D65to obtain the CIE L*, CIE a* and CIE b* values.

Small-Scale Fading Characteristics in Cellular Networks in Ghana

Fading is the most observed and frustrating problem in transmitting and receiving radio signals. A Study in correlation properties of fading helps to design proper communication systems that are robust to it. In this work, received power signal was obtained by drive-test technique. The analysis was determined using distribution fitting tool in Matlab software 7.5.0 (R2007b). The following fading distributions were used, Rayleigh, Rician, Nakagami-m, Lognormal and Weibull. Weibull fading distribution was found to give the best description of fading experienced in Ghana.On the other hand, Rician distribution, Nakagami-m distribution and lognormal distribution have less agreement with the measured data while Rayleigh fading distribution has much less agreement with measured data. The obtained mean scale parameter and the mean shape parameter in the Weibull distribution for the environment considered were 133.76 and 15.93, respectively. Furthermore, the path loss exponents in the near and far fields were also calculated; and the standard deviation of shadowing fell in the range of 4.368dB to 6.180dB.

Some thermoluminescence parameters of blue–green emission band of pegmatite rock

The thermoluminescence glow curve of natural pegmatite has a broad band with two peaks at 255 and 270 °C in the blue- green emission region. The initial rise measurements indicate that these peaks have thermal activation energies of 1.056 and 1.086 eV respectively. The laboratory-induced peaks at 110, 140, 185, 240, 255 and 270 °C have thermal activation energies of 0.77, 0.83, 0.92, 1.026, 1.056 and 1.086 eV, respectively. The pre-heat treatment at 1,000 °C for 2 h and air-cooling enhances the TL sensitivity of pegmatite by up to ~6 times of that treated at 400 °C. Thermoluminescence fading of the storage pegmatite has been monitored after storage in the dark at room temperature for 8 days. The properties of fading are well explained with the tunneling model. The results show that pegmatite is a promising material for dosimetry and luminescence dating.

Communication techniques and coding for atmospheric turbulence channels

In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received light signal, impairing link performance. In this paper, we describe several communication techniques to mitigate turbulence-induced intensity fluctuations, i.e., signal fading. These techniques are applicable in the regime in which the receiver aperture is smaller than the correlation length of the fading, and the observation interval is shorter than the correlation time of the fading. We assume that the receiver has no knowledge of the instantaneous fading state. The techniques we consider are based on the statistical properties of fading, as functions of both temporal and spatial coordinates. Our approaches can be divided into two categories: temporal domain techniques and spatial domain techniques. In the spatial domain techniques, one must employ at least two receivers to collect the signal light at different positions or from different spatial angles. Spatial diversity reception with multiple receivers can be used to overcome turbulence-induced fading. When it is not possible to place the receivers sufficiently far apart, the fading at different receivers is correlated, reducing the diversity gain. We describe a ML detection technique to reduce the diversity gain penalty caused by such fading correlation. In the temporal domain techniques, one employs a single receiver. When the receiver knows only the marginal statistics of the fading, a symbol-by-symbol ML detector can be used to optimize performance. When the receiver also knows the temporal correlation of the fading, maximum-likelihood sequence detection (MLSD) can be employed, yielding a further performance improvement, but at the cost of very high complexity. We describe two reduced-complexity implementations of the MLSD, which make use of a single-step Markov chain model for the fading correlation in conjunction with per-survivor processing. Next, we also investigate the performance of using error-control coding and pilot symbol-assisted detection schemes through atmospheric turbulence channels.

Inter- and Intrasite Correlations of Large-Scale Parameters from Macrocellular Measurements at 1800 MHz

The inter- and intrasite correlation properties of shadow fading and power-weighted angle spread at both the mobile station and the base station are studied utilizing narrowband multisite MIMO measurements in the 1800MHz band. The influence of the distance between two base stations on the correlation is studied in an urban environment. Measurements have been conducted for two different situations: widely separated as well as closely located base stations. Novel results regarding the correlation of the power-weighted angle spread between base station sites with different separations are presented. Furthermore, the measurements and analysis presented herein confirm the autocorrelation and cross-correlation properties of the shadow fading and the angle spread that have been observed in previous studies.

Performance Analysis of Wireless Systems With Doubly Selective Rayleigh Fading

Theoretical error performances of wireless communication systems suffering from both doubly selective (time varying and frequency selective) Rayleigh fading and sampler timing offset are analyzed in this paper. Single-input-single-output systems with doubly selective fading channels are equivalently represented as discrete-time single-input-multiple-output (SIMO) systems with correlated frequency-flat fading channels, with the correlation information being determined by the combined effects of sampler timing phase, maximum Doppler spread, and power delay profile of the physical fading. Based on the equivalent SIMO system representation, closed-form error-probability expressions are derived as tight lower bounds for linearly modulated systems with fractionally spaced equalizers. The information on the sampler timing offset and the statistical properties of the physical channel fading, along with the effects of the fractionally spaced equalizer, are incorporated in the error-probability expressions. Simulation results show that the new analytical results can accurately predict the error performances of maximum-likelihood sequence estimation and maximum a posteriori equalizers for practical wireless communication systems in a wide range of signal-to-noise ratio. Moreover, some interesting observations about receiver oversampling and system timing phase sensitivity are obtained based on the new analytical results

Spectral properties of signal fading and Doppler spectra distribution in urban mobile communication links

AbstractIn this work, we continue the analysis of a probabilistic approach and the corresponding stochastic multi‐parametric model of wave propagation, in built‐up areas with randomly distributed buildings. We have concentrated on the spectral properties of signal strength spatial variations and on Doppler spread spectrum distribution of signal power. The analysis is based on a unified stochastic approach of radio wave propagation above the built‐up terrain with applications to mobile communications. We analyze the signal power spectrum of spatial frequencies and the signal power distribution in the Doppler domain for moving vehicles, taking into account a Doppler shift proportional to the vehicle antenna speed relative to the base station. The comparison between the theoretical prediction and experimental data was motivated by the proposed stochastic model and other existing statistical models to verify the signal power distribution in the Doppler domain for various urban environments and terminal heights with respect to building rooftops. New effects of terrain features on signal spectrum are obtained, examined and compared with existing models. Copyright © 2006 John Wiley & Sons, Ltd.

Real-world environment models for mobile network evaluation

Simulation environments are an important tool for the evaluation of new concepts in networking. The study of mobile ad hoc networks depends on understanding protocols from simulations, before these protocols are implemented in a real-world setting. To produce a real-world environment within which an ad hoc network can be formed among a set of nodes, there is a need for the development of realistic, generic and comprehensive mobility, and signal propagation models. In this paper, we propose the design of a mobility and signal propagation model that can be used in simulations to produce realistic network scenarios. Our model allows the placement of obstacles that restrict movement and signal propagation. Movement paths are constructed as Voronoi tessellations with the corner points of these obstacles as Voronoi sites. Our mobility model also introduces a signal propagation model that emulates properties of fading in the presence of obstacles. As a result, we have developed a complete environment in which network protocols can be studied on the basis of numerous performance metrics. Through simulation, we show that the proposed mobility model has a significant impact on network performance, especially when compared with other mobility models. In addition, we also observe that the performance of ad hoc network protocols is effected when different mobility scenarios are utilized.

Thermoluminescence of the blue emission band of perthite

The thermoluminescence (TL) glow curve of natural monoclinic perthite has a broad band with peaks at 210, 250, 290 and 340 °C in the blue region. The initial rise measurements indicate that these peaks have thermal activation energies of 0.96, 1.12, 1.18 and 1.21 eV, respectively. The laboratory-induced peaks at 120, 150 and 200 °C have thermal activation energies of 0.12, 0.23 and 0.59 eV, respectively. The pre-heat at 900 °C for 2 h and air-cooling enhanced the TL sensitivity of perthite by up to ∼4 times of that annealed at 400 °C. Thermoluminescence fading of the disordered perthite was monitored six months after storage in the dark at room temperature. The properties of fading are well explained with the localized transition model. The results show that perthite is a promising material for dosimetry of luminescence dating.

Experimental analysis of the joint statistical properties of azimuth spread, delay spread, and shadow fading

Empirical results characterizing the joint statistical properties of the local azimuth spread (AS), the local delay spread (DS), and the shadow (slow) fading component are presented. Measurement data from typical urban, bad urban, and suburban (SU) environments have been analyzed. It is found that a log-normal distribution accurately fits the distribution function of all the investigated parameters. The spatial autocorrelation function of both AS, DS, and shadow fading can be modeled with an exponential decay function. However, for SU environments the spatial autocorrelation function is better characterized by a composite of two exponential decaying functions. A positive cross correlation is found between the AS and the DS, while both parameters are negatively correlated with shadow fading. All essential parameters required for the implementation of a simulation model considering the joint statistical properties of the AS, DS, and shadow fading are provided.

Measurement of angular and distance correlation properties of log-normal shadowing at 1900 MHz and its application to design of PCS systems

This paper investigates the correlation properties of shadow fading as a function of the angle between two PCS base stations over urban, light urban, and suburban terrain. Results from this study are relevant to the analysis of interference, handoff gain, and to various frequency planning applications in modern cellular and PCS systems. Using a significantly larger data set than previous experiments, we observed that on the average, the shadow fading components of the signals are not correlated, even at small angles. Our results contradict the conventional wisdom, as expressed in several papers, which says that there is relatively high correlation at small angles. Our results indicate that a mathematically simpler uncorrelated model for the relationship between signals from multiple base stations at small angles can be used in analysis tools. Distance correlation measurements computed by forming the autocorrelation function on a large number of data sets showed that the correlation distance of the shadowing process ranges from about 25 to 100 m.

Site diversity measurements of low-angle fading and comparison with a theoretical model

Since 1974, several experiments have been conducted at Eureka, Canada (80° N, 86° W), to investigate the properties of lowangle fading. For a variety of site diversity configurations, it was found that neither a horizontal spacing of 500 m nor a vertical spacing of 20 m provided good diversity performance. For a vertical spacing of 180 m, however, fading at the two sites was essentially uncorrelated. Lowangle fading was more prevalent and severe in the summer and absent when the atmosphere was wellmixed or during radiative temperature inversions. A model of the refractive index structure of the atmosphere has been developed which predicts these characteristics and shows that deep fades need not result from interference fading.

Finding the statistical properties of the median values of a fading signal directly from its decibel values

A method is introduced by which the statistical properties of the long-term fading of a signal can be found from a section of decibel-scale data. First the median of a subsection of signal fading in decibels is found directly from the average of its decibel values over each given time interval; then the long-term fading can be plotted. From such fading data, the statistical properties can be found directly and quickly from the measured level-crossing-rate (LCR) curve.