Characterization of a Computer Board-to-Board Ultra-Wideband Channel

In this paper we present the results of an extensive ultra-wideband (UWB) measurement campaign performed inside the chassis of two desktop computers. The purpose of the campaign is to analyze the possibility of board-to-board communications, replacing cable connections. Measurements of the propagation channel are performed over a frequency range of 3.1 - 10.6 GHz using a vector network analyzer and antennas small enough to enable integration on a circuit board. The results show that the propagation environment is very uniform, with small variations in the path gain between different positions within a computer. We also performed interference measurements, showing that the interference is restricted to certain subbands.     

Channel Uncertainty in Ultra-Wideband Communication Systems

Channel uncertainty limits the achievable data rates of certain ultra-wideband systems due to the need to estimate the channel. The use of bursty duty-cycled transmission reduces the channel uncertainty because the receiver has to estimate the channel only when transmission takes place, but the maximum amount of burstiness and hence the possible reduction of channel uncertainty both depend on the spectral efficiency of the modulation scheme used. This general principle is demonstrated by comparing the channel conditions that allow duty-cycled direct-sequence spread spectrum (DSSS) and pulse position modulation (PPM) to achieve the additive white Gaussian noise (AWGN) channel capacity in the wideband limit. We show that duty-cycled DSSS systems achieve the wideband capacity as long as the number of independently faded resolvable paths increases sublinearly with the bandwidth, while duty-cycled PPM systems can achieve the wideband capacity only if the number of paths increases sublogarithmically. The difference is due to the fact that DSSS is spectrally more efficient than PPM and hence allows more bursty transmission     

MIMO Channel Characterization for Short Range Fixed Wireless Propagation Environments

This paper reports results from wideband MIMO measurements performed in short range fixed wireless environments at 5.2 GHz. The objective is to provide MIMO channel characterization results for the measured environments and contribute to the limited available similar studies. Two kinds of propagation scenarios are investigated, rooftop to rooftop and street to rooftop, at three different sites always under LOS propagation conditions. The analysis of measurement data is performed in the context of non physical modeling, providing insight into the statistics of the measured channels. In particular, the slow time varying nature of the channel is studied and the narrow Doppler spectrum shape is approximated. Furthermore, frequency correlation results are obtained and the typical delay dispersion measures are extracted. Then, the antenna correlation is studied and the error of the Kronecker product approximation is evaluated. Finally, capacity results are provided and the channel measurements are characterized in terms of spatial multiplexing quality and multipath richness through condition number analysis. Nikolaos D. Skentos received his Diploma in Electrical and Computer Engineering from the National Technical University of Athens (NTUA), Greece in October 2000. Since January 2001 he has been a research associate at the Mobile Radio Communications Laboratory at the NTUA, and he is currently working towards the Ph.D. degree. His research interests include channel measurements, MIMO channel characterization, MIMO algorithms and space time processing. He has been active in the IST STINGRAY project, the COST 273 Action and the ACE Network of Excellence. He is also a member of the National Technical Chamber of Greece since 2001. Athanasios G. Kanatas received the Diploma in Electrical Engineering from the National Technical University of Athens, Greece, in 1991, the M.Sc. degree in Satellite Communication Engineering from the University of Surrey, Surrey, UK in 1992, and the Ph.D. degree in Mobile Satellite Communications from the National Technical University of Athens, Greece in February 1997. From 1993 to 1994 he was with National Documentation Center of National Research Institute. In 1995 he joined SPACETEC Ltd. where he was Technical Project Manager for VISA/EMEA VSAT Project in Greece. In 1996 he joined the Mobile Radio Communications Laboratory as a research associate. From 1999 to 2002 he was with the Institute of Communication & Computer Systems. In 2000 he became a member of the Board of Directors of OTESAT S.A. He is an Assistant Professor in the Department of Technology Education and Digital Systems at University of Piraeus. His current research interests include channel characterization and estimation, simulation and modeling for mobile, mobile satellite, and future wireless communication systems. He has been a Senior Member of IEEE since 2002, and is also a member of the Technical Chamber of Greece. In 1999 he was elected Chairman of the Communications Society of the Greek IEEE Section. Panagiotis I. Dallas was born 1967 in Thessaloniki, Greece. He obtained his diploma and Ph.D. degree from the Electrical and Computer Engineering Department of Aristotle University of Thessaloniki, Greece, in 1990 and 1997, respectively. Since 1998 he joined with INTRACOM where he currently is Section Manager of Advanced Communications Technologies branch of Emerging Technologies & Markets department, leading the next generation of broadband wireless access systems for internal and EU projects. He runs the relevant standardization activities (IEEE 802.16 and ETSI/BRAN HIPERMAN) in INTRACOM and he represents the company in WiMAX forum. Finally, he has over 30 publications in international journals and conferences. Philip Constantinou received the Diploma in Physics from the National University of Athens in 1972, the Master of Applied Science in Electrical Engineering from the University of Ottawa, Ontario, Canada in 1976, and the Ph.D. degree in Electrical Engineering in 1983 from Carleton University, Ottawa, Ontario, Canada. From 1976 to 1979 he was with Telesat Canada as a Communications System Engineer. In 1980 he joined the Ministry of Communications in Ottawa, Canada where he was engaged in the area of Mobile Communication. From 1984 to 1989 he was with the National Research Center Demokritos in Athens, Greece where he was involved in several research projects in the area of Mobile Communications. In 1989 he joined the National Technical University of Athens where he is currently a Professor and Director of the Mobile Radio Communications Laboratory. His current research interests include Personal Communications, Mobile Satellite Communications, and Interference Problems on Digital Communications Systems.     

Analysis of the Channel Energy Capture in Ultra-Wideband Transmitted Reference Systems

In this letter, we analyze the expected value of the channel energy capture as a function of the integration interval of the correlator in a transmitted reference system. A modified Saleh-Valenzuela channel model is employed. We observe that for the system specifications (such as channel model, data rate, and signal-to-noise ratio) considered here, an integration interval that captures approximately 84%-89% of the expected value of the channel energy provides a bit-error probability close to the minimum one     

S波段超宽带抗干扰发射信道的设计与实现

S 波段超宽带抗干扰发射信道作为卫星通信系统机载终端的核心设备,其信道的抗干扰能力直接影响着整个系统的性能。通过跳频技术来提升通信系统的抗干扰能力的关键是提高跳频速度和拓展跳频带宽,因此该超宽带信道杂散、增益平坦度以及载波的低相噪、捷变频速度等性能指标的优劣就显得极为重要。本文基于传统通用芯片设计了采用二次变频的宽带收发信道, 通过切换混频本振、分段开关滤波、多通道一体化集成设计,实现了超宽带信道低杂散、低相位噪声以及高速换频等关键技术指标,并在实际工程应用上得到了验证。     

Channel Characterization and Link Quality Assessment of IEEE 802.15.4-Compliant Radio for Factory Environments

Wireless sensors have started being utilized for process monitoring in factory environments, which are typically harsh for low-power wireless communication due to their complicated layout and plentiful stationary/moving obstacles. Sensor radios available so far have been engineered for consumer-grade applications, featuring low cost, low power, and minimal radio complexity. In order to utilize such radios for factory applications, their channel characteristics and link quality must be investigated for optimal design and reliability assessment. In this paper, a series of measurements were made with IEEE 802.15.4-compliant sensor radios to study both their spatial and temporal characteristics with respect to the factory surroundings found in a university machine shop. Critical communication properties were investigated in terms of received signal strength, link quality indication, and packet error rate. It is found that received signal strength shows dependency on surrounding structures, radio link qualities with respect to received signal strength and link quality indication are stable before a grey zone is reached, and average link quality indicator serves as a better packet success rate indication than average received signal strength indication. The findings in this paper provide a useful guidance to the ongoing explorations for a methodology to predict radio performance at any location within a given factory floor plan and to online assess the time-variant link qualities.     

分形粗糙面的电磁散射－扩展边界条件

用扩展边界条件方法对分形粗糙良导体面及介质面的电磁散射问题进行了分析。用推广的Floquet模式，在分界面处将场分量用Fourier级数展开，根据边界条件及扩展边界条件得到了水平极化和垂直极化散射场的幅度分量的表达式。用其它近似方法（Kirchhoff和Rayleigh方法）及能量守恒准则验证了此方法的有效性。     

Frequency-Dependent UWB Channel Characteristics in Office Environments

This paper reports frequency-dependent ultrawideband (UWB) channel characteristics. Measurements were performed in 103 receiver locations of six different office environments. From the measured data, the effect of frequency on the pathloss properties of a UWB signal is analyzed. After analyzing the pathloss behavior to propagation environments, the pathloss exponent variation models are developed in various environments as a function of frequency. Based on these models, pathloss prediction is performed, and the accuracy of the prediction is compared with those of existing pathloss models. In addition, the frequency-dependent UWB channel correlation characteristics are investigated. For the frequency correlation statistics of the UWB channel, double-slope models representing correlation coefficients are established with and without line-of-sight (LOS) paths. Using these correlation models, a channel gain estimation algorithm is proposed. The performance of the proposed estimation algorithm is evaluated with estimation parameters, and it is confirmed that the proposed estimation algorithm has better performance than the conventional algorithm using a linear interpolation algorithm.      

Concurrent Blind Channel Equalization in Impulsive Noise Environments

In some communication systems the trans- mitted signal is contaminated by impulsive noise with a non-Gaussian distribution. Non-Gaussian noise caused significant performance degradation to communication re- ceivers. The new constant modulus blind equalizer based on Fractional lower-order statistics of the equalizer input, which is defined as FLOS_CMA, is able to mitigate impul- sive channel noise while restoring the constant modulus character of the transmitted communication signal. How- ever, like the Constant modulus algorithm （CMA）, the steady-state Mean square error （]VISE） of the FLOS_CMA algorithm may not be sufficient low for the system to ob- tain adequate performance. This paper proposes a con- current equalizer, in which a Decision-directed least mean p norm （DD_LMP） equalizer operates cooperatively with a FLOS_CMA equalizer, controlled through a non-linear link. Simulation results using M-QAM and 8-PSK signal- ing have shown that besides the capability of compensating the phase offset, the proposed concurrent FLOS_CMA and DD_LMP blind equalizer has faster convergence rate and lower steady-state MSE than the FLOS_CMA approach.     

High Performance Anion Exchange Membranes with Confined Sub-2-nm Ion Channel

As a key component of low-cost anion exchange membrane fuel cells (AEMFCs), anion exchange membranes (AEMs) are far from commercial application, because of dissatisfactory alkaline stability and conductivity. Herein, a new insight is proposed to prepare high performance AEMs by constructing of confined ion channel. With an intermediate oligomer produced before the main copolymerization, novel poly(vinyl-carbazolyl aryl piperidinium) AEMs with confined sub-2-nm ion channel are successfully prepared. The unique sub-2-nm ion channel enable membranes ultrahigh hydroxide conductivity of 261.6 mS cm⁻¹, and the state-of-the-art chemical stability over 5000 h. Moreover, the AEMs also exhibit good mechanical stability with lower water uptake and dimensional swelling. Based on the as-prepared AEMs and ionomer, fuel cells exhibit outstanding peak power density of 1.8 and 0.2 W cm⁻² with Pt-based catalysts and completely non-precious metal catalysts, respectively.     

三维频率复用环境中的信道偏移指配方法

一种新的信道指配法－信道偏移指配方法正受到越来越多的重视，这种方法能在现有的频率资源条件下，较大地提高移动通信系统的容量。本文主要讨论了三维频率复用环境中的信道偏移指配方法，详细地分析了同频复用和相邻信道使用距离，定量地计量了信道偏移系统的频谱节约效率。本文最后还通过几个实例验证了所提算法的实用性。     

Fabrication and Characterization of Superhydrophobic Surfaces with Dynamic Stability

Superhydrophobic surfaces of dynamic stability are crucial for applications in water‐repellent materials. In this work, a hierarchical structure composed of a dendritic microporous surface with nanostructured porosity is demonstrated that shows robust superhydrophobicity with dynamic stability. The hierarchical structures are obtained on both copper foils and wires by a dynamic gas‐bubble template‐assisted electrochemical deposition method. The substrates can then be modified with alkyl thiols to obtain the surface superhydrophobicity. A new kind of testing, mechanical monitor‐assisted continuous water surface strokes, is developed to reveal the dynamic stability of the as‐prepared superhydrophobic copper wires. The as‐prepared superhydrophobic copper wires can exert a high propulsive force, and particularly, show little adhesive force in the process of continuous strokes on the water surface, exhibiting robust superhydrophobicity with dynamic stability. The approach allows a strategy for the fabrication of superhydrophobic surfaces with dynamic stability, and suggests a new method to evaluate the dynamic stability of superhydrophobic surfaces.     

Statistical Properties of Laser Speckles Generated from Far Rough Surfaces

The statistical properties of speckle patterns generated from far rough surfaces, under illumination of a Gaussian beam, are investigated. The surface roughness dependence of the first- and second-order moments of intensity is theoretically investigated, and their analytical expressions have been derived and presented. The analysis indicates that the mean intensity distribution on the receiver plane is closely related to the ratio of the lateral correlation length to the surface root mean square (rms) height. On the other hand, the speckle size and the correlation degree of the speckle intensities are found to be independent of the parameter characterizing the roughness of a surface, and are only determined by the laser beam waist.     

一维随机粗糙表面散射特征的数值分析

本文在Ｋｉｒｃｈｈｏｆｆ近似基础上，利用数值积分方法分析了一维随机粗糙表面的散射特征。结果显示随着粗糙度的增大，单次散射峰值由连续地向后向移动，其强度不断降低。峰值宽度增加。在一个较窄的粗糙度范围内，散射场对称于表面法线呈近似余弦分布而接近于理想朗伯体。当粗糙度超过这一范围时，散射峰值将由线向后向移动，并在粗糙度很大时稳定在后向附近。     

衰落信道下MIMO-OFDM系统信道容量分析

针对以往文献的不足,该文重新推导了衰落信道下MIMO-OFDM系统信道容量公式,分析了子载波数目、时延扩展、角度扩展以及天线间距等因素对信道容量的影响。理论分析和仿真结果符合MIMO-OFDM信道容量特征。     

超宽带室内信道测量及数据处理技术研究

针对研究室内信道传播特性需要获得信道冲激响应函数的问题,提出了室内超宽带(UWB)信道测量方案,搭建了UWB无线信道测量系统,并对实际信道环境实施测量.根据测量数据,研究了数据处理中的相关技术,并分析和解决了数据处理中的若干实际问题.通过实验得到实际信道的冲激响应,实验结果较好地反映了视距和非视距情况下UWB信道的传输特性,为后续UWB室内信道的建模工作奠定了基础.     

Comparison of ? Obtained from the Conventional Definition with ? Appearing in the Radar Equation for Randomly Rough Surfaces

A comparison is made of the radar cross section of rough surfaces calculated in one case from the conventional definition and obtained in the second case directly from the radar equation. The objective of the analysis is to determine how well the conventional definition represents the cross section appearing in the radar equation. The analysis is executed in the special case of perfectly conducting, randomly corrugated surfaces in the physical optics limit. The radar equation is obtained by solving for the radiation scattered from an arbitrary source back to a colocated antenna. The signal out of the receiving antenna is computed from this solution and the result put into a form recognizeable as the radar equation. The conventional definition is obtained by solving a similar problem but for backscatter from an incident plane wave. It is shown that these two forms for ?' are the same if the observer is far enough from the surface; However, the usual far-field criteria are not sufficient. For the two cross sections to be the same, the observer must be far from the surface compared to the radii of curvature of the surface at the reflection (specular) points. Numerical comparison of the two cross sections has been made for normally distributed surfaces and the difference can be significant.     

Calculations of the Microwave Brightness Temperature of Rough Soil Surfaces: Bare Field

A model for simulating the remotely sensed microwave brightness temperatures of soils with rough surfaces is developed. The surface emissivity of the soil media is calculated from one minus its reflectivity, which is obtained by the integration of the bistatic scattering coefficients for rough soil surfaces. The soil brightness temperature is obtained from the product of the surface emissivity and the effective soil temperature, which is calculated with measured soil moisture profiles and soil temperature profiles at various soil depths. The roughness of a soil surface is characterized by two parameters, the surface height standard deviation a and its horizontal correlation length l. The model calculations are compared to the measured angular variations of the polarized brightness temperatures at both L-band (1.4 GHz) and C-band (5 GHz) frequencies. A nonlinear least squares fitting method is used to match the model calculations with the data, and the best fit results produce the parameter values of a and l that best characterize the surface roughness. The effect of rough surface shadowing is also incorporated into the model by introducing a shadowing function S(?), which represents the probability that a point on a rough surface is not shadowed by other parts of the surface. The model results for horizontal polarization are in excellent agreement with the data, both qualitatively and quantitatively. For vertical polarization, some discrepancies exist between the calculations and data. Possible causes of the discrepancy are discussed.     

Deep Learning for OFDM Channel Estimation in Impulsive Noise Environments

Impulsive noise suppression is essential in orthogonal frequency division multiplexing (OFDM) systems, since impulsive noise may cause a serious decline in channel estimation performance. To solve this problem, a channel estimator based on denoising autoencoder-deep neural network (DAE-DNN) is proposed in this paper. The proposed method is based on a data-driven deep learning framework. Firstly, DAE preprocesses signals to learn damaged data and recover the complete signal are used in the presence of impulsive noise. Then, the transmitted data processed by DAE are used to train the DNN in the offline training process. Finally, the estimated channel state information (CSI) is offered by the proposed DNN model in the online working process. The simulation results demonstrate that the proposed method improves OFDM channel estimation performance significantly. As expected, the proposed method has a better performance than existing ones, such as least squares, minimum mean square error and orthogonal matching pursuit algorithms. Moreover, the proposed method is robust under impulsive noise environments.

     

Cooperative Communications in Ultra-Wideband Wireless Body Area Networks: Channel Modeling and System Diversity Analysis

In this paper, we explore the application of cooperative communications in ultra-wideband (UWB) wireless body area networks (BANs), where a group of on-body devices may collaborate together to communicate with other groups of on-body equipment. Firstly, time-domain UWB channel measurements are presented to characterize the body-centric multipath channel and to facilitate the diversity analysis in a cooperative BAN (CoBAN). We focus on the system deployment scenario when the human subject is in the sitting posture. Important channel parameters such as the pathloss, power variation, power delay profile (PDP), and effective received power (ERP) crosscorrelation are investigated and statistically analyzed. Provided with the model preliminaries, a detailed analysis on the diversity level in a CoBAN is provided. Specifically, an intuitive measure is proposed to quantify the diversity gains in a single-hop cooperative network, which is defined as the number of independent multipaths that can be averaged over to detect symbols. As this measure provides the largest number of redundant copies of transmitted information through the body-centric channel, it can be used as a benchmark to access the performance bound of various diversity-based cooperative schemes in futuristic body sensor systems.