Michael Cheffena

On the Space-Time Variations of Rain Attenuation

Rain attenuation shows a considerable temporal and spatial variability. To simulate fade mitigation techniques such as route diversity, a space-time channel model which accounts for the spatial and temporal variation of rain attenuation is needed. In this paper we investigate the space-time correlation of rain attenuation utilizing 42 GHz star-like network measurements. By combining the spatial and temporal correlation properties of rain attenuation, a simulation model for generating multiple correlated rain attenuation time series based on the Maseng-Bakken model is developed. The model is validated by comparing the statistical and angular diversity properties of the model with those of measurements and theoretical diversity gain models. Furthermore, parameters for the Maseng-Bakken dynamic rain attenuation model were extracted from the star-like network measurements. In addition, using a systematic multivariable technique a model for the parameter betas which controls the dynamics of rain attenuation in the Maseng-Bakken model was developed. Moreover, using available rain attenuation measurements the advantage of route diversity with selection combining is investigated.

Industrial Wireless Sensor Networks: Channel Modeling and Performance Evaluation

A complete dynamic wideband channel model for industrial wireless sensor network is presented. The model takes into account the noise, interferences, and heavy multipath propagation effects present in harsh industrial environments. A first-order two-state Markov process is adopted to describe the typical bursty nature of the impulsive noise usually present in industrial environments. The interference effects are modeled as multiple narrowband signals operating on the same frequency band as the desired signal. The multipath propagation is described by assuming the scatterers to be uniformly distributed in space within an elliptical region where the transmitting and receiving nodes are located at the foci of the ellipse. Furthermore, performance evaluations of IEEE 802.15.4 in terms of bit error rate using the developed channel model are presented. The results show that in addition to spread spectrum techniques, link diversity can further improve the link quality in harsh industrial environments.

Prediction Model of Fade Duration Statistics for Satellite Links Between 10-50 GHz

A new model for predicting fade duration statistics has been developed using a large database compiled for this purpose. Two lognormal functions have been used to model the short and long fade durations due to scintillation and rain events, respectively. The performance of the new model has been compared with existing prediction models such as the ITU-R, COST 205 and Dissanayake-Haidara (D-H). The test results show that the new model has the best performance at Ku, Ka, and Q/V frequency bands. In addition, when results for all the data available are considered, the new model gives the best prediction on average, followed by the D-H, COST 205 and the ITU-R models, respectively.

Dynamic model of signal fading due to swaying vegetation

In this contribution, we use fading measurements at 2.45, 5.25, 29, and 60 GHz, and wind speed data, to study the dynamic effects of vegetation on propagating radiowaves. A new simulation model for generating signal fading due to a swaying tree has been developed by utilizing a multiple mass-spring system to represent a tree and a turbulent wind model. The model is validated in terms of the cumulative distribution function (CDF), autocorrelation function (ACF), level crossing rate (LCR), and average fade duration (AFD) using measurements. The agreements found between the measured and simulated first- and second-order statistics of the received signals through vegetation are satisfactory. In addition, Ricean K-factors for different wind speeds are estimated from measurements. Generally, the new model has similar dynamical and statistical characteristics as those observed in measurements and can thus be used for synthesizing signal fading due to a swaying tree. The synthesized fading can be used for simulating different capacity enhancing techniques such as adaptive coding and modulation and other fade mitigation techniques.

Channel Simulator for Land Mobile Satellite Channel Along Roadside Trees

We study the signal fading for the land mobile satellite channel caused by roadside trees. A channel simulator is developed which takes into account the signal fading caused by position-dependent tree scattered fields and by swaying tree components. In the model, the tree canopy is modeled as a vertically oriented cylindrical volume containing randomly distributed and oriented leaves and branches. The tree trunk is modeled as a finite lossy dielectric cylinder. Leaves are modeled as thin lossy dielectric disks and branches as finite lossy dielectric cylinders. The scattering pattern of the new model has a narrow forward lobe with an isotropic background which is comparable to the one found using the radiative energy transfer theory. In addition, the variation of the specific attenuation with frequency of the model is fairly similar to the one given in the ITU Recommendation. The model is validated using measurements at 2 GHz in terms of the cumulative distribution functions of the received signal and the Ricean K-factor, average fade duration and level crossing rate. Good agreement is found between the measured and simulated statistics.

Fall Detection Using Smartphone Audio Features

An automated fall detection system based on smartphone audio features is developed. The spectrogram, mel frequency cepstral coefficents (MFCCs), linear predictive coding (LPC), and matching pursuit (MP) features of different fall and no-fall sound events are extracted from experimental data. Based on the extracted audio features, four different machine learning classifiers: k-nearest neighbor classifier (k-NN), support vector machine (SVM), least squares method (LSM), and artificial neural network (ANN) are investigated for distinguishing between fall and no-fall events. For each audio feature, the performance of each classifier in terms of sensitivity, specificity, accuracy, and computational complexity is evaluated. The best performance is achieved using spectrogram features with ANN classifier with sensitivity, specificity, and accuracy all above 98%. The classifier also has acceptable computational requirement for training and testing. The system is applicable in home environments where the phone is placed in the vicinity of the user.

Physical-statistical channel model for signal effect by moving human bodies

A novel physical-statistical channel model for simulating the signal effect by moving human bodies is presented. The human body is modeled as vertically oriented dielectric cylindrical volume. The received signal is assumed to be composed of a direct component which might be subject to shadowing and a multipath component due to reflection and diffuse scattering, i.e., a Ricean channel. The shadowing effect of the direct signal component is calculated using Kirchhoff diffraction equation. The multipath component is parameterized by calculating the reflected fields from the floor, ceiling and walls of the indoor environment as well as scattered fields from moving human bodies. Poisson and Exponential distributions are used to describe the shadowing and inter-shadowing events caused by multiple bodies, respectively. Furthermore, simulation results of the first and second order statistics of the received signal affected by moving human bodies for 3.35 GHz and 60 GHz signals are presented. In addition, initial validation of the developed model are performed using an empirical model for human body shadowing and reported measurement results.

Performance Evaluation of Wireless Body Sensors in the Presence of Slow and Fast Fading Effects

A theoretical method for analyzing the performance of wireless body sensors in terms of channel capacity and bit-error-rate (BER) in the presence of slow and fast fading effects is presented. Analytical closed-form expressions for the channel capacity and BER for implant-to-implant, implant-to-body-surface, and body-surface-to-body-surface propagation scenarios are developed. Numerical results of the channel capacities and the BERs are presented utilizing realistic channel models for wireless body area networks (WBANs). The results indicated high system outage probability and degraded channel capacity caused by the complex propagation mechanisms of radio frequency signals on the surface and inside the human body. The communication links of WBANs should thus be optimized using fade mitigation techniques suitable for miniature wireless electronic devices to achieve the targeted high quality-of-service requirements of biomedical systems. In general, the results give an insight into the effect of the propagation channel on system performance, and may allow service providers to evaluate the technical feasibility of biomedical systems for various propagation scenarios.

Modeling the Dynamic Effects of Vegetation on Radiowave Propagation

In this contribution we use available measurements at 2.45, 5.25, 29 and 60 GHz to study the dynamic effects of vegetation on propagating radiowaves. The complex responses of a tree to induced wind force has been studied, and used to explain different phenomena observed in measurement results. Generally, the power spectrum of the received signal through vegetation has lowpass characteristics, and the effects of swaying tree components are manifested as spectral peaks in the power spectrum of the received signal. Radiowaves scattered from these swaying tree components have a time varying phase changes which results in fading of the received signal. Furthermore, due to further dissipation of the wind energy by the interaction of tree crowns, less signal variation is to be expected from a grove of several trees than from a single/few tree(s). The Ricean K- factor for different wind conditions has been estimated from measurements. In addition, by utilizing a lowpass filter and a mass-spring system, a new simulation model for generating signal fading due to a swaying tree has been developed. Depending on the wind speed and physical characteristics of the tree, the new model can be used for simulating signal fading due to a swaying tree with similar dynamical and statistical characteristics as those observed from measurement results.

Land mobile satellite dual polarized MIMO channel along roadside trees: Modeling and performance evaluation

We present a novel physical-statistical, generative model for the land mobile satellite (LMS), dual polarized, multiple-input-multiple-output (MIMO) channel along tree-sided roads. Said model is parameterized by means of a physical model based on the multiple scattering theory (MST) which accounts for the signal attenuation and scattering by trees. Moreover, finite-difference time-domain (FDTD) electromagnetic computations were performed to characterize the scattering pattern of an isolated tree, and to calculate the MIMO shadowing correlation matrix required by the model, and not provided by MST. This modeling framework also encompasses the single-input-multiple-output (SIMO)/space diversity case. To illustrate the capabilities of the developed model, time series were generated and used in system performance calculations. The obtained results give an insight into the advantages of dual polarized MIMO and SIMO/space diversity techniques in these very frequent scenarios and may help service providers in evaluating the technical feasibility of such systems.