共查询到20条相似文献,搜索用时 0 毫秒
1.
《Vehicular Technology, IEEE Transactions on》2009,58(1):14-20
Ricean fading is common in dense urban cellular networks and, as a mobile moves through that environment, the K-factor of the Ricean fading will change. This paper presents a statistical model for dense urban vehicular nonstationary Ricean fading, where the K-factor gradually changes due to movement through changing surroundings. This model is empirical and is based on K-factor fluctuations that are observed in dense urban cellular radio channel measurements. The K -factor is modeled using a random process with a distribution that is fit to the measured K-factor values. An autoregressive (AR) model is also used to ensure that the autocorrelation of the simulated K-factor process matches the empirical data. The nonstationary Ricean fading envelope that is generated using this model is verified by comparing it with the fading envelope that is observed in the measurements. 相似文献
2.
This article analyzes the connectivity of multihop radio networks in a log-normal shadow fading environment. Assuming the nodes have equal transmission capabilities and are randomly distributed according to a homogeneous Poisson process, we give a tight lower bound for the minimum node density that is necessary to obtain an almost surely connected subnetwork on a bounded area of given size. We derive an explicit expression for this bound, compute it in a variety of scenarios, and verify its tightness by simulation. The numerical results can be used for the practical design and simulation of wireless sensor and ad hoc networks. In addition, they give insight into how fading affects the topology of multihop networks. It is explained why a high fading variance helps the network to become connected.Christian Bettstetter is a senior researcher in the Future Networking Lab at DoCoMo Euro-Labs. His current research interests are in the area of self-organized networking, especially, in wireless ad hoc and sensor networks. He published several technical articles in this area and co-authored the Wiley book ‘GSM: Switching, services and protocols.’ From 1998 to 2003, he was with the Institute of Communication Networks at the Technische Universität München (TUM), where he did research and teaching on mobile communication networks, and managed a new international graduate program. Christian received the Dr.-Ing. degree (summa cum laude) and the Dipl.-Ing. degree in electrical engineering and information technology from TUM in 2004 and 1998, respectively. During his graduate studies, he worked for Wacker Siltronic, Portland, OR, USA, and wrote his master thesis on turbo decoding at the University of Notre Dame, IN, USA. He is a member of the IEEE and ACM SIGMOBILE.Christian Hartmann studied electrical engineering at the University of Karlsruhe (TH), where he received the Dipl.-Ing. degree in 1996. In 1997 he joined the Institute of Communication Networks at the Technische Universität München (TUM), where he earned the Dr.-Ing. degree (summa cum laude) in 2003. He is currently a senior researcher and member of the teaching staff at the same institution. During a research leave in the winter of 2000/2001 Christian was with the Wireless Research Lab of Lucent Bell Labs, Crawford Hill, NJ. His main research interests are in the area of mobile and wireless networks, including capacity and performance evaluation, radio resource management, modeling and simulation. He is a member of the IEEE. 相似文献
3.
The focus of this paper is on the higher order statistics of spatial simulation models for shadowing processes. Such processes are generally assumed to follow the lognormal distribution. The proposed spatial simulation model is derived from a non-realizable lognormal reference model with given correlation properties by using Rice’s sum-of-sinusoids. Both exact and approximate expressions are presented for the level-crossing rate (LCR) and the average duration of fades (ADF) of the simulation model. It is pointed out that Gudmundson’s correlation model results in an infinite LCR. To avoid this problem, two alternative spatial correlation models are proposed. Illustrative examples of the dynamic behavior of shadow fading processes are presented for all three types of correlation models. Emphasis will be placed on two realistic propagation scenarios capturing the shadowing effects in suburban and urban areas. 相似文献
4.
Jiandong Tian Jing Sun Yandong Tang 《IEEE transactions on image processing》2009,18(10):2355-2363
Shadows, the common phenomena in most outdoor scenes, bring many problems in image processing and computer vision. In this paper, we present a novel method focusing on extracting shadows from a single outdoor image. The proposed tricolor attenuation model (TAM) that describe the attenuation relationship between shadow and its nonshadow background is derived based on image formation theory. The parameters of the TAM are fixed by using the spectral power distribution (SPD) of daylight and skylight, which are estimated according to Planck's blackbody irradiance law. Based on the TAM, a multistep shadow detection algorithm is proposed to extract shadows. Compared with previous methods, the algorithm can be applied to process single images gotten in real complex scenes without prior knowledge. The experimental results validate the performance of the model. 相似文献
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6.
P. M. Shankar 《Wireless Personal Communications》2012,64(4):665-680
Wireless channels are subject to short term fading and shadowing. Such shadowed fading channels are described using a Nakagami-lognormal
process, with the Nakagami-m (short term fading) and lognormal distributions (shadowing). This approach does not result in
a closed form solution for the density function of the signal-to-noise ratio (SNR) making wireless systems analysis difficult.
It was suggested that a gamma or an inverse Gaussian distribution can be used in place of the lognormal distribution providing
an analytical framework. The match of these two distributions to the lognormal was less than ideal. Invoking shadowing as
multiplicative process, the distribution of the product of N gamma variables is proposed in place of the lognormal pdf resulting in the Nakagami-N-gamma model. It is shown that this
model leads to simple solutions to the density and distribution functions as well as error rates for coherent phase shift
keying modems. The outage probabilities and error rates based on the Nakagami-lognormal (NL) and Nakagami-N-gamma (NNG) models
were compared. Results showed excellent match at levels of shadowing generally observed in wireless systems. While values
of N as low as 3 was sufficient for low values of m and weak to moderate shadowing, values of N in the range of 7–9 provided better match for higher levels of shadowing and higher values of m. By varying N, it is also possible to get the NNG pdf to move closer to the NL pdf making the new model an ideal one for the shadowed fading
channels with its flexibility and availability of analytical expressions. 相似文献
7.
L.‐Z. Fan Y.‐S. Hu A. J. Bhattacharyya J. Maier 《Advanced functional materials》2007,17(15):2800-2807
Solid polymer electrolytes with high ionic conductivities are prepared by using poly(ethylene oxide) (PEO) and poly(vinylidene fluoride‐co‐hexafluoropropylene) (P(VDF‐HFP)) as polymer matrixes, succinonitrile (SN) as an additive, and lithium bis‐trifluoromethanesulfonimide (LiTFSI) and lithium bisperfluoroethylsulfonylimide (LiBETI) as salts. In these systems, the introduction of succinonitrile into the polymer electrolytes increases the material's ionic conductivity and conveys excellent mechanical properties. The described composites, with their beneficial combination of mechanical and electric properties, are expected to have significant potential for lithium batteries. 相似文献
8.
This paper introduces a fading model, which explores the nonlinearity of the propagation medium. It derives the corresponding fading distribution-the alpha-mu distribution-which is in fact a rewritten form of the Stacy (generalized Gamma) distribution. This distribution includes several others such as Gamma (and its discrete versions Erlang and central Chi-squared), Nakagami-m (and its discrete version Chi), exponential, Weibull, one-sided Gaussian, and Rayleigh. Based on the fading model proposed here, higher order statistics are obtained in closed-form formulas. More specifically, level-crossing rate, average fade duration, and joint statistics (joint probability density function, general joint moments, and general correlation coefficient) of correlated alpha-mu variates are obtained, and they are directly related to the physical fading parameters 相似文献
9.
10.
BCCD器件解析物理模型与仿真研究 总被引:1,自引:0,他引:1
基于半导体图像传感器CCD的物理图像和相应的基本特性微分方程组,经过离散和线性化处理,并引用解三对角矩阵方程的递归算法,实现了其解析模型求解.据此及其相关的编程软件,对电注入埋沟CCD器件进行了仿真测试.结果表明,随着栅长减小、栅间隙长度增加和沟道深度减小,传输栅电荷容量约从6.5×106下降到6.1×106电子电荷,转移效率从96%增高到99%.同时,暗电流只与少子寿命密切相关,转移效率对栅间隙长度在1 μm以内的变化不敏感.该理论模拟结果有助于BCCD模型参数提取和设计研究. 相似文献
11.
本文讨论了陆地移动卫星业务(LMSS)中的多径衰落分布,综合国外有关实验数据导出了适用于地面多径接收环境中的经验衰落预测模式。比较结果表明,该模式有较好的精度,而Nakagami—Rice分布偏离实验结果较大。 相似文献
12.
We study the problem of approximating the family of hard-decision frequency-shift keying demodulated correlated flat Rician fading channels via a recently introduced queue-based channel (QBC) model for binary communication channels with memory. For a given ldquodiscretizedrdquo fading channel, we construct a QBC whose noise process is statistically ldquocloserdquo in the Kullback-Leibler sense to the error or noise process that is generated by the fading channel, and the modeling accuracy is evaluated in terms of noise autocorrelation function (ACF) and channel capacity. Numerical results indicate that the QBC provides a good approximation of the fading channels for a wide range of channel conditions. Furthermore, it estimates the noise ACF more accurately than the finite-state Markov models that have been recently studied by Pimentel , while, at the same time, remaining mathematically tractable. 相似文献
13.
Li-Chun Wang Wei-Cheng Liu Yun-Huai Cheng 《Vehicular Technology, IEEE Transactions on》2009,58(1):32-38
Mobile-to-mobile communication is an important application for intelligent transport systems and mobile ad hoc networks. In these systems, both the transmitter and receiver are in motion, subjecting the signals to Rician fading and different scattering effects. In this paper, we present a double-ring with a line-of-sight (LOS) component scattering model and a sum-of-sinusoids simulation method to characterize the mobile-to-mobile Rician fading channel. The developed model can facilitate the physical-layer simulation for mobile ad hoc communication systems. We also derive the autocorrelation function, level crossing rate (LCR), and average fade duration (AFD) of the mobile-to-mobile Rician fading channel and verify the accuracy by simulations. 相似文献
14.
移动通信过程中由于移动设备所处的环境不同,存在不同的信道衰落,从各种衰落模型的相互关系出发,提出了一种移动无线衰落信道混合应用模型。通过实现瑞利衰落分布和对数正态分布,经线性和非线性变换可以得到Nakagami和Suzuki等分布。对提出的复合衰落模型进行仿真,仿真结果符合理论值。该混合衰落模型设计和仿真方法可以用于指导信道模拟器设计和通信系统仿真。 相似文献
15.
根据GTD—MOM技术给出一种物理模式基的概念 ,并用之分析细理想导电圆柱的电磁散射 ,求解其雷达散射截面积 (RCS)。圆柱表面上的电流假设由三部分组成 :入射波的感应电流和圆柱两端的反射电流。该方法较传统的全域基矩量法减小了计算机内存 ,加快了计算速度 ,而且数值计算结果与全域基的结果吻合较好。 相似文献
16.
The effects of slow and nonselective signal fading on the performance of multilevel noucoherent FSK (NCFSK) systems in an additive mixture of Gaussian and highly impulsive noise are analyzed. For binary systems the bit error rate is derived; forM -ary NCFSK systems upper and lower bounds of the character error probability are obtained. The analysis is performed considering the maximum likelihood receiver for additive white Gaussian noise. 相似文献
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Pooi Kam Cho Teh 《Communications, IEEE Transactions on》1984,32(6):654-659
We consider the problem of designing an adaptive receiver with anM -bit memory for binary orthogonal signaling over a slowly fading Rayleigh channel. Both the cases of decision-feedback and no decision-feedback are considered. We present a problem formulation by defining the contents of the receiver's memory. The structure of the Bayes receiver that makes optimum use of the memory information is then established. The LRT that defines the receiver is obtained explicitly, and it dictates a detector-estimator receiver structure. The detector can be interpreted as being partially coherent, with coherence being achieved asymptotically in the limit of perfect estimation of the fading process. Simulation results are given to show the improved error rate performance of the adaptive receiver. Our results also indicate that decision-feedback should be employed in a manner dependent on the SNR. 相似文献
20.
The frequency transfer function of a multipath fading channel is examined in terms of its effects on digital radio signals. The transfer function is expanded into a power series about the channel center frequency and the coefficients are related to the multipath structure. It is then shown that, in the channelized common carrier bands below 15 GHz, the first two (complex) terms of the power series are usually sufficient for characterizing multipath effects. This demonstration is based on a mean-square error-of-fit measure which is applied to the multipath fading response and evaluated under some worst-case assumptions. 相似文献