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1.
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. 相似文献
2.
本文提出了一种新的多载波码分多址(MC-CDMA)系统.与传统系统相比,其主要区别是采用多个并行MC-CDMA分支,每一个分支用一组正交子载波进行调制.在每个分支上,使用相同扩频序列的不同码片调制子载波.这种系统能更有效地利用传输带宽,实现频率分集.由于该系统降低了每个子载波上的数据速率,扩频序列更容易同步.最后给出了系统在Ricean衰落信道下的性能分析. 相似文献
3.
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. 相似文献
4.
研究了莱斯衰落信道中多用户集中式大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)系统的安全通信问题。基站利用上行训练获取信道状态信息,之后利用最大比传输波束成形算法进行下行数据传输。基于随机矩阵理论,分别分析了合法用户和窃听者的信息速率表达式,从而得到了遍历安全速率的闭合表达式。基于获得的结果,进一步分析了极端莱斯K因子和无限发送数据功率下系统的极限安全性能。最后,通过不同条件下的实验仿真设计,验证了系统的安全性能,同时证实了所得结果的正确性。 相似文献
5.
在空间相关的莱斯衰落信道模型下,针对多用户MIMO(Multiple-Input Multiple-Output)系统潜在的多用户分集增益和空间分集增益,该文提出了一种基于部分信道信息的多用户预编码与调度算法。结合部分瞬时信道信息和统计信息,利用约束最大似然估计对各用户信道矢量进行估计,然后利用估计的各用户信道调度多个用户进行预编码。仿真结果表明,该方案以较少的反馈开销,获得了较大的性能增益。 相似文献
6.
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. 相似文献
7.
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 相似文献
8.
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. 相似文献
9.
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 相似文献
10.
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. 相似文献
11.
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。 相似文献
12.
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
13.
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
15.
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. 相似文献
16.
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. 相似文献
17.
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 相似文献
18.
In this paper, we investigate the Multiple-Input Multiple-Output (MIMO) channel capacity in indoor Ricean channels based on MIMO channel measurements at 2.45 GHz. The measured data is analysed using a super resolution parameter estimation algorithm. Our results demonstrate that the line-of-sight (LOS) component in a Ricean scenario influences indoor MIMO performance through increased spatial correlation between array elements. We found that indoor channels with higher values of Ricean K factor have smaller numbers of effective multipath components and increased spatial correlation. Measurement results also showed that, the effect of varying antenna height on indoor MIMO capacity is also due to the spatial correlation of multipath propagation and has a close relationship with the separation between the transmitter and receiver.
Zhongwei Tang is currently with the Wireless Technologies Laboratory at CSIRO. He was with Microwave and Wireless Technology Research Laboratory (MWTRL), Information and Communication Group, Faculty of Engineering of the University of Technology Sydney, Australia, where he pursued his Ph.D. Degree. His current research interests include RF propagation, MIMO Space-Time channel measurements, characterization and channel modelling, smart antennas, MIMO systems and array signal processing.
Ananda S. Mohan is currently a member of the Faculty of Engineering, University of Technology, Sydney (UTS), Australia where he leads research on antennas, microwaves, wave propagation, and wireless technology. He received a Ph.D. degree in electrical communication engineering from the Indian Institute of Technology, Kharagpur, India and was a Scientist and Senior Scientist at the Research and Training Unit for Navigational Electronics, Hyderabad, India. At UTS, he directed the Sydney microwave design resource centre and was the associate program leader of the co-operative research centre for satellite systems. He currently directs the microwave and wireless technology research laboratory and a core member of the university research centre on health technologies. His current teaching and research interests include wireless mobile communications, microwaves and antennas, smart antennas and applications of microwave and wireless technology in medicine and has obtained many competitive research grants in these areas. Dr. Mohan was a co-recipient of the Priestly memorial award from the Institute of Radio and Electronic Engineers (IREE), Australia. He was a member of the organizing and technical Program Committees of the IEEE Globecom'98, APMC 2000, and International Symposium on Wireless Systems and Networks, 2003 and IASTED International Conference on Antennas, Radar, and Wave Propagation, for 2004 and 2005. 相似文献
19.
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. 相似文献
20.
针对无线快衰落信道,本文提出一种改进的一阶FSMC量化模型,并提出一种通过分析基带差错序列游程分布特性的新方法,来验证Markov模型的性能.文中给出FSMC量化模型参数提取方法,并分别通过对采用选择性合并、等增益合并、最大比合并以及不采取分集合并的Nakagami分布衰落信道的仿真,证实了改进的量化FSMC模型的准确性. 相似文献
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