Search results for "fading"

The performance of the INLSA in comparison with the ESPRIT and SAGE algorithms

2014

In this paper we investigate the application potential of three known algorithms, namely the ESPRIT, SAGE and INLSA, to properly emulate the statistical properties of the mobile fading channel. The performance comparisons of those methods will be carried out with respect to their fitting accuracy to the autocorrelation function (ACF) of the reference model. The methods' accuracy will be assessed in the synthetic reference channel model, which is based on the sum-of-cisoids (SOC) principle. In our reference model, we consider the scenarios with equal gains and Rayleigh distributed gains. The obtained results indicate that in both scenarios the INLSA method is more preferable than the ESPRIT …

Recovery Capabilities of Rateless Codes on Simulated Turbulent Terrestrial Free Space Optics Channel Model

2013

Free Space Optics (FSO) links are affected by several impairments: optical turbulence, scattering, absorption, and pointing. In particular, atmospheric optical turbulence generates optical power fluctuations at the receiver that can degrade communications with fading events, especially in high data rate links. Innovative solutions require an improvement of FSO link performances, together with testing models and appropriate channel codes. In this paper, we describe a high-resolution time-correlated channel model able to predict random temporal fluctuations of optical signal irradiance caused by optical turbulence. Concerning the same channel, we also report simulation results on the error mi…

Selected Topics in Mobile Radio Channel Modelling

2011

Performance analysis of Alamouti coded OFDM systems over wideband MIMO car-to-car channels correlated in time and space

2014

In this paper, the performance of Alamouti coded orthogonal frequency division multiplexing (OFDM) systems over car-to-car (C2C) fading channels correlated in time and space is analyzed. Taking different geometrical scattering models into account, a generalized expression of the time-variant transfer function (TVTF) is derived for wideband multiple-input multiple-output (MIMO) C2C channels. We present a generalized expression for the bit error probability (BEP), which will be used to describe the performance of Alamouti coded OFDM systems over different types of C2C channel models, such as the rectangle model, the tunnel model, the street model, and the curve model. The effect of the maximu…

On-body to on-body channel characterization

2011

Interest in on-body communication channels is growing as the use of wireless devices increases in medical, consumer and military sensor applications. This paper presents an experimental investigation and analysis of the narrowband on-body propagation channel. This analysis considers each of the factors affecting the channel during a range of stationary and motion activities in different environments with actual wireless mote devices on the body. Use of such motes allows greater freedom in the subject's movements and the inclusion of real-world indoor and outdoor environments in a test sequence. This paper identifies and analyses the effect of the different components of the signal propagati…

A Novel Method of Distance Measurement Based on Pulse Position Modulation and Synchronization of Chaotic Signals Using Ultrasonic Radar Systems

2009

This paper deals with a novel method of transmission and receipt of a signal based on both the property of two chaotic systems generating the same chaotic signal when they are synchronized and the property of pulse position modulation (PPM) to be insensitive to the distortions of the transmission channel. The method is discussed in the context of ultrasonic radar systems, in which the transmitter and receiver, which consist of ultrasonic sensors, are near each other, and the received signal consists of the transmitted signal reflected by an obstacle. A reference sinusoidal signal is superimposed to a chaotic signal generated by a master chaotic system, and the whole signal is modulated acco…

Revealing transmit diversity mechanisms and their side-effects in commercial IEEE 802.11 cards

2008

Service differentiation in WLAN has been traditionally faced at the MAC layer. However, some PHY layer parameters, such as the transmission power, the antenna, and the modulation/coding scheme, have a deep impact on network performance. Since the criterion for selecting these parameters is left to the vendor specific implementations, the performance spread of most experimental results about 802.11 WLAN could be affected by vendor proprietary schemes. The focus of this paper is an experimental analysis of the undisclosed antenna diversity mechanisms employed by some widely used cards (namely, the Atheros and Intel based cards), and a thorough understanding of the optimization goals which gui…

Orthogonal Multicarrier Transmission with Modal Channel Estimation

2009

A novel multi-carrier orthogonal transmission scheme is presented. While being simpler to implement, it has a spectral efficiency and design parameters similar to those of Orthogonal Frequency Division Multiplexing based on Offset Quadrature Amplitude Modulation (OFDM/OQAM). A parametric channel estimation technique is subsequently reported. The proposed technique is based on an algorithm obtained from classic Multiple Signal Classification (MUSIC) by relaxation of the hypothesis on the number of measurements with respect to the number of sensors. Numerical simulations show that our proposal outperforms previous works in this field.

Studying the stability of Solvent Red 19 and 23 as excise duty components under the influence of controlled factors

2020

Abstract In this study, we examine the chemical stability of two disazo dyes, namely Solvent Red 19 and 23 (SR 19 and SR 23), under simulated conditions. Both dyes are considered to be chemically stable under normal exploitation conditions and therefore, are used extensively as excise duty components that enable a rapid visual verification of the tax levels that were imposed on fuel products as well as identifying fuel usage. However, the results from this study confirmed that the colour of the samples that had been fortified with either SR 19 or SR 23 fades under the influence of external conditions such as UV-A irradiation and temperature over time. The UV-A irradiation was the dominant f…

Fast Estimation of Diffusion Tensors under Rician noise by the EM algorithm

2016

Diffusion tensor imaging (DTI) is widely used to characterize, in vivo, the white matter of the central nerve system (CNS). This biological tissue contains much anatomic, structural and orientational information of fibers in human brain. Spectral data from the displacement distribution of water molecules located in the brain tissue are collected by a magnetic resonance scanner and acquired in the Fourier domain. After the Fourier inversion, the noise distribution is Gaussian in both real and imaginary parts and, as a consequence, the recorded magnitude data are corrupted by Rician noise. Statistical estimation of diffusion leads a non-linear regression problem. In this paper, we present a f…