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151.
C. Labaune K. Lewis H. Bandulet S. Depierreux S. Hüller P. E. Masson-Laborde D. Pesme P. Loiseau 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(2):283-288
Many nonlinear processes may affect the laser beam propagation and the laser
energy deposition in the underdense plasma surrounding the pellet. These
processes, associated with anomalous and nonlinear absorption mechanisms,
are fundamental issues in the context of Inertial Confinement Fusion. The
work presented in this article refers to laser-plasma interaction
experiments which were conducted under well-controlled conditions, and to
their theoretical and numerical modeling. Thanks to important diagnostics
improvements, the plasma and laser parameters were sufficiently
characterized in these experiments to make it possible to carry out
numerical simulations modeling the laser plasma interaction in which the
hydrodynamics conditions were very close to the experimental ones. Two sets
of experiments were carried out with the LULI 2000 and the six beam LULI
laser facilities. In the first series of experiments, the interaction
between two single hot spots was studied as a function of their distance,
intensity and light polarization. In the second series, the intensity
distribution of stimulated Brillouin scattering (SBS) inside the plasma was
studied by means of a new temporally resolved imaging system.
Two-dimensional (2D) simulations were carried out with our code Harmony2D in
order to model these experiments. For both series of experiments, the
numerical results show a very good agreement with the experimental ones for
what concerns the main SBS features, namely the spatial and temporal
behavior of the SBS-driven acoustic waves, as well as the average SBS
reflectivities. Thus, these well diagnosed experiments, carried out with
well defined conditions, make it possible to benchmark our theoretical and
numerical modelings and, hence, to improve our predictive capabilities for
future experiments. 相似文献
152.
无线信道是整个现代数字无线移动通信研究的基础,从电磁波传播方式、无线信道对传输信号的影响以及等效低通信道的时变冲激响应等几个方面对无线信道的特性进行了研究。结果表明,信号通过无线信道传播时,会产生各种形式的衰落,衰落对无线移动通信系统传输性能的影响是很大的,在实际中应设法消除。 相似文献
153.
HUO Yong-qing PENG Qi-cong SHAO Huai-zong 《中国电子科技》2007,5(1):13-17
We present two adaptive power and bit allocation algorithms for multicarrier systems in a frequency selective fading environment. One algorithm allocstes bit based on maximizing the channel capacity, another allocates bit based on minimizing the bit-error-rate (BER). Two algorithms allocate power based on minimizing the BER. Results show that the proposed algorithms are more effective than Fischer's algorithm at low average signal-to-noise ration (SNR). This indicates that our algorithms can achieve high spectral efficiency and high communication reliability during bad channel state. Results also denote the bit and power allocation of each algorithm and effects of the number of subcarriers on the BER performance. 相似文献
154.
The commonly used models for shadowed fading channels arise by compounding the Nakagami distribution with others such as the
log-normal and gamma distributions. A distribution that is more flexible than the Nakagami distribution is the well known
Weibull distribution. In this paper, we derive a collection of generalized models for shadowed fading channels by compounding
the Weibull distribution with other distributions belong to some fifteen flexible families. We also illustrate the superior
performance of these models over the standard Nakagami models. 相似文献
155.
The orthogonal frequency division multiplexing (OFDM) transmission scheme is currently experiencing increased popularity due
to advances in very large scale integration technology. It is used for a variety of broadband systems such as asymmetric digital
subscriber lines, very-high-speed digital subscriber lines, digital video, and audio broadcasting, and wide local area network
standards such as IEEE 802.11a, IEEE 802.11 g, and ETSI Hiperlan/2. However, propagation impairments can cause severe degradation
in bit error rates (BER) for coherent detection. We derive a semi-analytical method to evaluate BER of a quadrature phase
shift keying (QPSK)-OFDM system in Nakagami, m < 1 fading and additive noise where pilot-assisted linear channel estimation and channel equalization are used. This allows
modeling of more severe fading environments than can be depicted by a Rayleigh distribution. Numerical simulations are used
to validate the proposed methods. The techniques developed can be applied to other channel estimation techniques, modulation
schemes and the performance evaluation of equalized single carrier narrowband systems. 相似文献
156.
Performance Analysis of Multiuser Detectors for Uplink Quasi-synchronous MC-CDMA Systems 总被引:1,自引:1,他引:1
Felip Riera-Palou Guillem Femenias Jaume Ramis 《Wireless Personal Communications》2007,43(4):1511-1521
This paper analyses and compares the average bit error rate (BER) of different multiuser detectors (MUD) in the uplink of
a multicarrier code- division multiple access (MC-CDMA) system. In particular, maximum likelihood, zero-forcing, minimum mean-square
error and interference cancellation-based multiuser detectors have been analysed for the special case of uncorrelated subcarriers.
The derived BER expressions are based upon previous results on diversity combining and also on recent findings on multiple
input multiple output (MIMO) architectures. The subcarrier correlation is considered in the context of physical parameters
currently under discussion for future wireless systems to give an indication up to what extent the assumption of uncorrelated
subcarrier fading is plausible. 相似文献
157.
In this paper, blind adaptive multiuser detection (MUD) technique is developed for uplink transmission in multiuser space
diversity DS-CDMA system to overcome multipath fading effect and multiple access interference. The system consists of a space
diversity, a precombining blind adaptive detector (PBAD), and a weight adaptation technique based on the minimization of the
mean output energy (MOE). The bit error rate (BER) performance of this receiver for asynchronous DS-CDMA signals with independent
and correlated antenna branches under Nakagami fading channel for BPSK system is evaluated. It has been seen that the use
of antenna diversity can yield substantial improvement in performance even if the correlation between the antenna elements
is relatively large (up to 0.795). However, the large correlation values pose a significant reduction in the diversity gain
in comparison with the zero correlation situation. It has also been confirmed by simulations that the PBAD provides a significant
receiver performance in comparison with the RAKE receiver employing antenna diversity.
Khodr A. Saaifan Born in lebanon 1978, received B.S.c. degree in electrical and electronics engineering (with honors) from Benha higher institute
of technology, Benha, Egypt, in 2001, and the M.S.c. degree in communications from Cairo University, Giza, Egypt, in 2005.
He is currently pursuing for the Ph.D. degree at the Cairo University. His current research interest includes space–time-coded
transmission, multiple-input multiple-output (MIMO) systems, fading channels, equalization, turbo (iterative) processing,
and wideband code division multiple access (WCDMA).
Emad K. Al-Hussaini received his B.Sc degree in Electrical Communication Engineering from Ain-Shams University, Cairo, Egypt, in 1964 and his
M.Sc and Ph.D. degrees from Cairo University, Giza, Egypt, in 1974 and 1977, respectively. From 1964 to 1970, he was with
the General Egyptian Aeroorganization. Since 1970, he has been with the Department of Electronics and Communications, Faculty
of Engineering, Cairo University, and is currently professor there. He was a research fellow at Imperial College, London,
UK, and at the Moore School of Electrical Engineering, University of Pennsylvania, Philadelphia, PA, USA, in the academic
years 1976/1977 and 1981/1982, respectively. In 1990, he received the Egyptian national encouragement award for outstanding
engineering research. He has written several papers for technical international journals and conferences. His research interests
include signal processing, fading channel communication, modulation, and cellular mobile radio systems. Dr Al-Hussaini is
a senior member of IEEE. He is listed in Marquis Who's Who in the World and in the IBC (International Biographical Center,
Cambridge) for outstanding people of the 20th century. 相似文献
158.
Matthias Pätzold Bjørn Olav Hogstad Dongwoo Kim 《Wireless Personal Communications》2007,40(3):267-279
In this paper, we introduce a new technique for the design of high-performance Rayleigh fading channel simulators. The proposed
design method uses set partitioning – a technique, which plays a key role in the design of trellis-coded modulation schemes.
We show how set partitioning can be used to design multiple uncorrelated fading waveforms enabling the simulation of Rayleigh
fading channels. For the important case of isotropic scattering, we show that the sample average of the generated waveforms
results in a deterministic process, the autocorrelation function (ACF) of which tends to the zeroth-order Bessel function
of the first kind as the number of sample functions increases. The proposed procedure is completely deterministic. The comparison
with a stochastic procedure using Monte Carlo techniques will be made. A study of the performance shows clearly that the new
technique using set partitioning outperforms by far existing Monte Carlo methods. 相似文献
159.
介绍了平板显示器件。如场发射显示器、等离子体显示器、液晶显示器、有机电致发光显示器驱动电路.分析了不同驱动电路的优点、缺点。 相似文献
160.
平板显示产业的发展现状和前景分析(液晶专题) 总被引:2,自引:0,他引:2
近年来,平板显示技术,尤其是液晶显示与等离子显示技术,在我国得到突飞猛进的发展,对我国显示产业从传统显示器向平板显示器的转型具有重要意义。本文从平板显示技术的基本概念、分类和产业链结构出发,结合近年来全球平板显示产业发展的背景,分析了我国平板显示产业的发展现状和趋势,并就深圳市平板显示产业的发展策略提出了建议。 相似文献