A First-Order Model for Depolarization of Propagating Signals by Narrowband Ricean Fading Channels

We show by simulation that when the fading signals observed on orthogonally polarized diversity branches follow Ricean statistics, the distribution of polarization states on the Poincar′e sphere is well-approximated by a Fisher distribution. Further, we show that the Fisher concentration parameter is: (1) completely determined by the corresponding Ricean Kfactors and the cross-correlation coefficient between the diversity branches, both of which can be estimated from simple measurements of received power vs. time, and (2) a good indicator of the level of cross-polar discrimination (XPD) on the channel. The insights gained are potentially useful to those engaged in the development and validation of schemes that use either polarization re-use or polarized MIMO.     

Commutation Signaling to Combat ISI over Nakagami and Ricean Fading

Bandwidth expanding signaling with quasi-orthogonal short codes is considered. The evaluation of the average probability of error analytically and by simulation is presented, for channels with multipath induced intersymbol interference (ISI) and for two different fading distributions. Namely Nakagami and Ricean fading distributions. The effect of intercell interference due to frequency reuse is also taken into account. Bit error rates (BER) for rake receiver with equal gain combining and postdetection integrator are presented. Both DBPSK and /41 DQPSK modulations with noncoherent demodulation are analysed. The effect of TCM coding, in the expected BER is also evaluated.     

A Novel Method for Performance Analysis of OFDM Polarization Diversity System in Ricean Fading Environment

OFDM (Orthogonal Frequency Division Multiplexing) is proven to be a very effective modulation and multiple access technique that enables high data rate transmission. Due to its good performance it is already implemented in several standardized technologies, and it is very promising technique for the next generation wireless communication systems. Still, further system performance improvements under severe frequency selective fading conditions are necessary, and they can be obtained implementing diversity, at either transmit or/and receive end of a wireless link. Since polarization diversity can be realized using only one compact, dual polarized antenna, it can be considered as an attractive, space and cost effective solution. Analysis presented in this paper shows that implementation of dual polarized antenna at the receiver can lead to significant performance improvement, under certain propagation conditions. In order to calculate BER (Bit Error Rate) for the considered OFDM polarization diversity system with a certain level of the received signals correlation, we propose a novel analytical method. The obtained results are compared with the ones attained by simulation.     

An Additive Model as a Physical Basis for Shadow Fading

Received signal power in mobile wireless communications is typically modeled as a product of three factors: distance-dependent average path loss law, variation in the local mean power (shadow fading), and small-scale fading. Of these three factors, the least investigated is the shadow fading, which is usually explained as a result of multiplication of large number of random attenuating factors in the radio channel. In this paper, the authors propose an additive model as an alternative physical basis for shadow fading within an "extended local area" where path loss is constant. Starting from a sum-of-sinusoids signal model, they show that under mild statistical assumptions on the powers of the sinusoids, the resulting signal power will have approximately Gaussian distribution in logarithmic scale. A cluster-based model for shadow fading emerges as a special instance of the general result. They present simulation and measurement results that support their theoretical findings. The new physical basis for shadow fading also provides insights into simulation and modeling of radio channels     

A Nonstationary Model for the Electromyogram

A theoretical model of the electromyographic (EMG) signal has been developed. In the model, the neural pulse train inputs were considered to be point processes which passed through linear, time-invariant systems that represented the respective motor unit action potential. The outputs were then summed to produce the EMG. It was assumed, that in the production of muscle force, the controlled parameter was the number of active motor units, n(t). The model then showed that the EMG can be represented as an amplitude modulation process of the form EMG = [Kn(t)1/2 w(t) with the stochastic process, w(t), having the spectral and probability characteristics of the EMG during a constant contraction. Various assumptions made in the model development have been verified by experiments.     

A Nonstationary Offered-Load Model for Packet Networks

Motivated by the desire to appropriately account for complex features of network traffic revealed in traffic measurements, such as heavy-tail probability distributions, long-range dependence, self similarity and nonstationarity, we propose a nonstationary offered-load model. Connections of multiple types arrive according to independent nonhomogeneous Poisson processes, and general bandwidth stochastic processes (not necessarily Markovian) describe the individual user bandwidth requirements at multiple links of a communication network during their connections. We obtain expressions for the moment generating function, mean and variance of the total required bandwidth of all customers on each link at any designated time. We justify Gaussian approximations by establishing a central limit theorem for the offered-load process. We also obtain a Gaussian approximation for the time-dependent buffer-content distribution in an infinite-capacity buffer with constant processing rate. The offered-load model can be used for predicting future bandwidth requirements; we then advocate exploiting information about the history of connections in progress.     

A General Bivariate Ricean Model and Its Statistics

In this paper, an extensive and detailed investigation of the joint statistics of two narrowband signals with space-frequency separation in a Ricean fading channel is carried out. All the analysis and its results include nonstationary environments, where the parameters of the bivariate Ricean model differ from one signal to the other. A general treatment of the angles of arrival of the multipath propagation waves is also performed. A comprehensive expression for the space-frequency correlation coefficient of arbitrary orders of the envelopes is provided. Some insightful plots of this coefficient are presented and examined. The coherence distance (or time) and the coherence bandwidth are obtained and analyzed     

A Nakagami-N-gamma Model for Shadowed Fading Channels

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.     

一种改进的C.Loo信道模型衰落因子算法

为更好地反映实际无线信道的特性,介绍一种改进的C.Loo信道模型衰落因子算法。原始C.Loo信道模型衰落因子算法中不考虑多普勒频移的影响,本文加载了多普勒频移对衰落因子的影响,并说明其合理性、可行性及优点。     

LMSS中的多径衰落预测模式

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。     

Effect of Channel Estimation Error on Bit Error Probability in OFDM Systems over Rayleigh and Ricean Fading Channels

A characteristic function-based method is used to derive closed-form bit error probability (BEP) expressions for orthogonal frequency-division multiplexing (OFDM) systems in the presence of channel estimation error over frequency-selective Rayleigh fading channels and frequency-selective Ricean fading channels. Both single channel reception and diversity reception with maximal ratio combining (MRC) are examined. The BEP expressions are shown to be sums of several conditional probability functions which can be calculated by using proper complex Gaussian random variable theory and a characteristic function method. The closed-form BEP expressions can be used to accurately investigate the bit error rate performance degradation caused by channel estimation error under different wireless channel environment models. The performances of two interpolation methods, a sine interpolator with Hamming windowing and a Wiener interpolator, are compared.     

General Nakagami approximation for sum of Ricean interferers

The statistical distribution of the sum of interfering signals at the receiving end of a wireless system is important to effect theoretical evaluation of its performances. The authors show that the sum of generic, narrow-band, Ricean interferers can be approximated by a single Nakagami interferer. A theoretical insight about this fact is given and some simulated results are shown to confirm the result     

非平稳信号的一种ARMA模型参数估计法

本文采用一种经过特殊处理的时变自回归滑动平均（ARMA）模型对非平稳随机信号进行分析．将这种模型左边的时变参数假设为一组基时间函数的线性组合，右边时变参数简化为常数，并用反馈线性估计法进行参数估计。该方法的主要特点是简单，计算量小，占用存储空间少．并用仿真的方法对算法予以验证，可用于一些常用的非平稳随机信号的分析．     

An Empirical Model for Prediction of Environmental Attenuation of Millimeter Waves

The latest trends in mobile technology have increased the need for higher spectrum bands from every sector of using wireless applications. As the internet is growing rapidly it has increased the need for wireless services, which require radio spectrum and thus becoming more congested. Engineers show that due to high demand for spectrum, government authorities are regularly introducing schemes to regulate the use of spectrum. New researches are enhancing to resolve the crisis. In order to fix the spectrum for future technologies, propagation studies are required. In this paper an empirical model is proposed for prediction of attenuation due to clouds and fog based on the Rayleigh approximation model. In this model a new concept of calculating dielectric constants of water are also introduced. The implementation results of the proposed model are compared with the other cloud attenuation models. The proposed model proved to be better than the ITU-R model.

     

An Adaptive Receiver with Memory for Slowly Fading Channels

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.     

A Multipath Fading Channel Model for Terrestrial Digital Radio Systems

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.     

Analysis of Non-WSSUS Fading Dispersive Channel Model

1Introduction Basically,whenthepropagationcharacteristicsofra diomobilecommunicationsarestudied[1],italways comestheWSSUSmodel,introducedbyBello[2]first ly,whichregardstheradiomobilechannelasafully stochasticchannelandassumestheuncorrelateddisper sivitybo…     

多径衰落的数学模型及分析

多径效应是影响低仰角测控系统正常工作的重要因素。介绍了多径效应产生的机理,建立了多径衰落的数学模型。无线电信号在收发天线间传播时,存在直射路径和多条反射路径,当直射信号和反射信号相互抵消时就会产生多径效应。依据建立的数学模型,分析了多径衰落产生的条件和对系统影响的程度。多径衰落产生的位置由地面站天线高度、飞行器飞行高度和二者之间的距离决定,多径衰落深度主要由地面对电波的反射系数决定。在上述分析的基础上,提出了避免和减小多径衰落对系统影响的几种措施。