Joint signaling techniques and spectral optimization for symmetric bit-rate communication over self-NEXT-dominated channels

We present a framework for maximizing the capacity of symmetric bit-rate communication services dominated by Gaussian crosstalk, in particular, digital subscriber line (DSL) services. We solve for optimal transmit power spectral densities (PSDs) that maximize the joint capacity of same-service users and yield significant gains in bit rates (or performance margins) over current schemes. Our results differ from previous work in that we develop transmit spectra in the presence of self-far-end crosstalk in addition to self-near-end crosstalk, present optimal contiguous spectra for practical modulation schemes, and derive optimal spectra under an additional frequency-domain peak-power constraint. Furthermore, by design, the optimal transmit PSDs are spectrally compatible with existing services on neighboring lines.     

Flexible a-Si:H Position-Sensitive Detectors

Flexible and large area (5 mm /spl times/80 mm with an active length of 70 mm) position-sensitive detectors (PSDs) deposited onto polymeric substrates (polyimide-Kapton VN) have been fabricated. The optimized structure presented is based on a heterojunction of amorphous silicon (a-Si:H)/ZnO:Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity, and position detection measurements. The set of data obtained on one-dimensional PSDs based on the heterojunction show excellent performances with a maximum spectral response of 0.12 A/W at 500 nm and a nonlinearity of /spl plusmn/10% over 70-mm length. The produced sensors present a nonlinearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the a-Si:H film. In order to prove this behavior, it was measured the defect density obtained by the constant photocurrent method on a-Si:H thin films deposited on polymeric substrates and bent with different radii of curvature.     

Impact of defect on I(V) instabilities observed on Ti/4H–SiC high voltage Schottky diodes

Anomaly in current at low forward bias is observed for large-area Ti Schottky diodes on n type 4H–SiC. Random telegraph signal (RTS) measurements, carried out on these defective devices, show discrete time switching of the current. Thermal activation of RTS signal gives two related trap signature (activation energy and cross section). Frequency analysis, using power spectral densities (PSDs) numerically calculated, confirms the presence of an extended defect which presents different charge states (i.e. an extended defect decorated by punctual traps). PSDs show two cut-off frequencies proving the individual response of two traps. Simulations of the I–V characteristics using two barrier heights modulated by a Gaussian function which represents the defect distribution show a good agreement with the experimental results. Finally we note that there's a strong correlation between traps observed by telegraph noise techniques and excess current.     

负载电阻对四边形PSD的影响实验研究

通过实验研究了负载电阻对四边形PSD的影响规律。实验结果表明,负载电阻对四边形PSD的总光电流没有影响,但对光斑定位有影响。其对PSD四个角位置附近定位误差的影响最大。随着负载电阻值的增大,计算光斑位置不断向PSD几何中心收缩,位置测量均方根误差及非线性度呈现先减小后增大的变化规律。研究还发现适当的负载电阻还可以改善PSD中央大部区域的枕形失真并减小定位误差。     

位敏器件及在微小位移测量中的应用

介绍了半导体位敏器件的原理及特点，光切法测量微小位移原理以及利用ＰＳＤ的光切法测量的有关光路和信号处理电路。该装置可实现对金属及非金属表面位移的非接触测量。     

Design of Costas/PSK continuous wave LPI radar signal

Low probability of intercept (LPI) radar signal design is a very important issue on modern battlefield. Different phase coding technologies are used to modulate Costas frequency hop sequence, and five kinds of continuous wave radar signals including Costas, Costas_qbarker, Costas_frank16, Costas_px16 and Costas_zadoff-chu13 are proposed and designed in this paper. The target resolution and LPI performance of the Costas and Costas/PSK continuous wave radar signals are analysed and compared. The ambiguity function and power spectral densities (PSDs) of five different kinds of signals are also simulated and studied. The results show that the target resolution and LPI performance of proposed Costas/PSK signal are better than Costas signal.     

Microstructure coarsening during static annealing of 60Sn40Pb solder joints: I stereology

The phase size distributions (PSDs) of the Sn, Pb, and the combined Pb and Sn phases, and the shape factor δ were determined for as-reflowed 60Sn40Pb solder joints and following their annealing at 50°C to 150°C. The PSDs in all cases had a positive skew which was approximated by a log-normal function. The PSDs were time invariant and were in accord with the Bitti and Nunzio model for phase coarsening. The shape factor, δ, decreased with the mean of the combined Pb and Sn phase size, and with temperature. Whether or not δ affects the PSDs is not clear.     

Broad is the way [ultra-wideband technology]

Ultrawideband (UWB) systems, which combine bandwidths in excess of 1 GHz with very low power spectral densities (PSDs), are currently attracting growing interest as a means of wresting additional capacity from the already heavily utilised store of wireless bandwidth. If the emissions from UWB devices are regulated to avoid causing significant interference to licensed services, then it becomes possible to allow UWB systems to operate on an unlicensed basis, enabling UWB technology to support a diverse range of applications. As yet, there are no regulations for UWB devices. However, the US is in the process of setting up a regulatory framework, while within Europe, where matters are not quite so far advanced, possible approaches to UWB regulation are under consideration. The author describes the basic principles and the role of regulation in determining the UWB devices destined for commercial deployment     

Polarimetric calibration of the SIR-C C-band channel using activeradar calibrators and polarization selective dihedrals

A polarimetric calibration experiment of Shuttle Imaging Radar C (SIR-C) is carried out using several different calibration targets. These are C-band polarimetric active radar calibrators (PARCs), polarization selective dihedrals (PSDs), 22.5° rotated dihedrals, and a trihedral. A novel polarimetric calibration algorithm is proposed that combines existing algorithms and uses one PARC and two PSDs. An error evaluation example is shown to estimate the typical hardware error value of the calibration targets allowable for a given calibration error. The novel algorithm gives polarimetric calibration results comparable to those obtained using the existing algorithm for three PARCs. Since PSDs work at frequencies lower than design frequency, and hence can be commonly used at multiple frequency bands, the simple addition of just one more frequency band PARC allows polarimetric calibration of a dual-frequency polarimetric synthetic aperture radar (SAR) by means of the proposed algorithm     

高能激光辐照诱导声波频率特性的实验研究

为了研究高能激光辐照诱导声波的频率特性以及实验条件对其的影响,采用宽频声传感器接收实验过程中产生的声波,并导入MATLAB中处理,得到其功率谱密度图。激光冲击实验采用铝箔吸收层、水以及不同约束状态下的K9玻璃约束层,对实验中产生声波的功率谱密度图做了详细分析,取得了图中最大峰值频率的分布数据。结果表明,不同约束层以及约束层的不同约束状态都会对声波功率谱密度最大峰值频率的分布有较大影响,而激光能量密度对其影响很小,同时该实验结果对激光冲击强化实现在线检测有重要指导意义。     

短波信道多普勒功率谱密度研究

为研究短波信道多普勒功率谱密度,将电离层的运动假设为正规层与不均匀团块两种不同的运动,推导出了多普勒频移的表达式;在忽略电子密度随时间变化和地磁场影响的情况下,推导出了多普勒频移的一种概率密度函数表达式;在假设接收天线是圆对称的条件下,推导出了信号散射分量的多普勒功率谱密度函数,结果表明,功率谱密度的形状为混合高斯形;采用寻找误差序列标准差最小值的方法对实验所得数据多普勒功率谱密度的形状进行了混合高斯形状拟合,拟合结果表明理论推导的正确性.     

Double Beams to Measure Three-dimensional Rigid Body Displacements

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Optical wavelength response of Ta/p-Si position-sensitive detectors

Position-sensitive detectors, PSDs, are precision optical sensors that operate using the lateral photovoltaic effect. Most commercial and, to a large extent, research devices are based on p–i–n structures involving high-temperature diffused junctions. Our programme is aimed at producing devices that perform as well as commercial devices with desirable response characteristics and extended longevity but based on a more straightforward fabrication technique. In this work we investigate the response of one-dimensional Schottky barrier PSDs fabricated using tantalum films deposited on silicon by electron-beam evaporation, a technique which produces very pure and uniform films and permits repeatable devices to be fabricated. Tantalum was selected for its appropriate electronic properties and the potential for forming long-lived, robust and stable detectors. Here we compare the response of these devices at various thicknesses under different light sources. An optimal thickness of tantalum, trading off transmissivity against good Schottky barrier formation, has been determined as approximately 200?Å. These devices were tested under various light sources: white light, filtered light and a red diode laser. The best properties were found under a 5?mW red broadband filtered light, producing better than 7?mV/mm and excellent linearity.     

A three-dimensional scattering model for fading channels in landmobile environment

Clarke's (1968) scattering model, one of the most widely accepted channel models for the land mobile environment, is a two-dimensional (2-D) model because of the assumption of horizontal traveling plane waves. By introducing a nonzero elevation angle of the arriving wave, a three-dimensional (3-D) model is more general and accurate, especially for the urban environment. Though the concept of the 3-D model has been proposed already, there is still a lack of satisfying results regarding the distribution of the elevation angle, from both theoretical analysis and field measurement, and the power spectral density (PSD) of the received signal. In this paper, a family of functions with two parameters, {m,n}, where m and n are positive integers, for both the symmetrical and asymmetrical probability density function (PDF) of the elevation angle (EA), is proposed. Among these functions, those with odd m and n lead to analytical solutions of the PSD of the received signal in addition to satisfying other requirements for a PDF of the EA previously proposed in literature. The PSDs in closed form associated with m and n equal to one and three are derived in particular, and the autocorrelation functions are obtained numerically. Since a family of functions rather than a single function is proposed for the PDF of the EA, it provides certain flexibility in application and covers a wide range of environments. Another contribution of this paper is a new expression which directly relates the PDF of the EA in the 3-D model to the PSD of the received signal     

非正弦时域正交编码调制及其功率谱分析

针对传统非正弦时域正交调制(Nonsinusoidal Orthogonal Modulation in Time Domain,NOTDM)系统多址复用容量有限的问题,提出一种基于正交或准正交序列的非正弦时域正交编码调制方法。给出了系统的调制模型和数学表达式,理论推导了调制信号的功率谱表达式并仿真分析了采用不同编码的调制信号的功率谱。理论和结果表明,与非正弦时域正交调制信号相比,编码调制后的信号功率谱能保持原有包络,但是会产生离散谱,提高功率谱旁瓣值.采用自相关性能好的序列进行编码可以降低离散谱的谱线。     

Remote-Touch: A Laser Input User–Display Interaction Technology

In this paper, we present a new user-display interaction technology in which a laser-pointer is used to select objects on a display screen. In this interaction technology, the user points to the object on the display, using a laser-pointer to make a selection. This allows interaction from a distance, which is an advantage over state-of-the-art touchscreen technologies. This interaction technology will be referred to as ldquoremote-touchrdquo. It consists of a laser-pointer, a transparent micro-structured light-guiding substrate, and position-sensitive detectors (PSDs). The substrate, which is patterned with a micro-structure of pyramid-shaped indentations, is put in front of the display. When the laser-light hits the display the micro-structure in the polymethyl methacrylate (PMMA) substrate reflects part of the laser-light to the sides of the display screen. The PSDs at the edge of the PMMA substrate read-out the position of the laser-spot. This paper focuses on the optical performance of the micro-structured PMMA substrate.     

非高斯杂波谱模型下的MTI性能分析

该文主要讨论了在非高斯型的立方及平方型杂波功率谱环境下雷达系统的MTI性能,给出了MTI滤波器平均改善因子的上限。表明在谱宽相同时,立方及平方型杂波谱下的MTI性能远劣于高斯型。对各种杂波谱下的谱宽等效性引入了L2(R)上杂波谱均方根带宽的度量,它较客观地反映了分布型杂波谱的总体平均宽度。最后,给出了MTI滤波器对杂波谱宽失配情况下改善因子的损失曲线,显示在立方和平方杂波谱下,性能损失对失配极不敏感。     

基于FlexPDE的二维PSD数值分析

描述位置敏感探测器(PSD)的Lucovsky方程在一定简化条件下可求得解析解.提出了利用有限元分析软件FlexPDE对非简化Lucovsky方程进行二维区域数值求解的方法,并对四边型PSD进行了分析,结果表明该方法能够准确地分析二维PSD的光电特性,比解析法有更强的适应性.     

一维PSD的光电性能解析研究

位置敏感探测器（ＰＳＤ）是一种基于横向光电效应的光敏器件,本文从描述横向光电效应的Ｌｕｃｏｖｓｋｙ方程出发,分析了几种不同情况下一维ＰＳＤ输出信号的解析解,讨论了一维ＰＳＤ的响应特性、线性条件及位置公式。