Time filter

Source Type

Bucharest, Romania

Pistea A.-M.,Military Technical Academy
Progress In Electromagnetics Research C | Year: 2014

Most wireless channel models assume fixed scatterers with specific geometrical distributions in the propagation environment. In reality most scatterers move with random movements on the azimuth plane. In this paper, the effects of such scatterers' random movements on the cross correlation function (CCF) of wideband (WB) and ultra-wideband (UWB) non-isotropic multiple-input multiple-output (MIMO) channels are characterized. The CCF of WB/UWB MIMO channels is calculated not by assuming a specific geometry for scatterers in space but based on specific mathematical relationships between physical parameters of the wireless channel along with appropriate assumptions on their probability density functions (pdfs). The CCF is used to determine the influence of moving scatterers, in a stationary scenario, on the power spectral density (PSD) and the coherence time of WB and UWB multiple-input single-output (MISO) channels, as a particular case of MIMO channels. Unlike the fixed scatterers case, the PSD is not a band-limited process, it decays with frequency. Source

Vizitiu I.-C.,Military Technical Academy
Progress In Electromagnetics Research C | Year: 2014

It is well known that in the pulse compression radar theory, the sidelobe reduction using nonlinear frequency modulation (NLFM) signal processing represents a major and present research direction. Accordingly, the main objective of this paper is to propose an interesting approach related to the design of effcient NLFM waveforms namely, a temporal predistortioning method of LFM signals by suitable nonlinear frequency laws. Some aspects concerning the optimization of the specific parameters involved into analyzed NLFM processing procedure are also included. The achieved experimental results confirm the significant sidelobe suppression related to other NLFM processing techniques. Source

Uy N.Q.,Military Technical Academy | Hoai N.X.,Hanoi University | O'Neill M.,University College Dublin | McKay R.I.,Seoul National University
Information Sciences | Year: 2013

Locality has long been seen as a crucial property for the efficiency of Evolutionary Algorithms in general, and Genetic Programming (GP) in particular. A number of studies investigating the effects of locality in GP can be found in the literature. The majority of the previous research on locality focuses on syntactic aspects, and operator semantic locality has not been thoroughly tested. In this paper, we investigate the role of semantic locality of crossover in GP. We follow McPhee in measuring the semantics of a subtree using the fitness cases. We use this to define a semantic distance metric. This semantic distance supports the design of some new crossover operators, concentrating on improving semantic locality. We study the impact of these semantically based crossovers on the behaviour of GP. The results show substantial advantages accruing from the use of semantic locality. © 2012 Elsevier Inc. All rights reserved. Source

Curelaru F.,Military Technical Academy
2015 International Conference on Speech Technology and Human-Computer Dialogue, SpeD 2015 | Year: 2015

This paper takes advantage of the MIT Mobile Device Speaker Verification Corpus (MIT-MDSVC) availability in order to evaluate the performance of three well known text-independent speaker verification approaches on handheld devices, considering the MIT-MDSVC as a representative corpus designed for robust speaker verification tasks on limited vocabulary and limited amount of training data collected on handheld devices. Several experiments with either mismatched testing conditions, or with samples collected from multiple test conditions were conducted for evaluating both text-independent approaches: generative (based on Gaussian Mixture Models) and discriminative (based on Support Vector Machines with Fisher kernel and GMM Supervector Linear kernel), without using the transcription of the utterances or knowledge about the acoustic conditions of the recordings (environment and microphone). An equal error rate less than 3% was achieved using Gaussian Mixture Models, and a slightly greater equal error rate (less than 3.5%) was achieved using Support Vector Machines with Fisher kernel and with GMM Supervector Linear kernel, against any possible acoustic conditions. © 2015 IEEE. Source

Roatesi S.,Military Technical Academy
International Journal of Rock Mechanics and Mining Sciences | Year: 2014

This paper presents both a numerical and an analytical approach for tunnel excavation and support mounting. The three-dimensional aspect of the tunnel face advance and the lining installation is simulated by a two-dimensional study assuming the hypothesis of gradual decompression of the primary stress on the outline of the tunnel. The numerical approach consists of a tunnel axis in an elasto-viscoplastic rock mass and a concrete elastic lining. This study emphasizes some important factors that influence the tunnel calculation, such as tunnel face, history of excavation phases, timing of the lining mounting, lining stiffness, and depth of the tunnel. The analytical approach is based on the determination and integration of the rock-lining interface differential equation. The author presents the analytical solution for (a) constant and non-constant lining pressure, and (b) taking into account the tunnel face influence. The comparison of the numerical results with the analytical solution is performed, and a good agreement is obtained. © 2014 Elsevier Ltd. Source

Discover hidden collaborations