Estimating signal strengths in the design of an indoor wireless network

One issue in the design and implementation of a wireless local area network is the selection of access point (AP) locations. Proper AP placement is necessary to provide adequate signal coverage and also to minimize cochannel coverage overlap. The impact of incorrect placement of APs is significant. Placing APs too far apart can lead to gaps in coverage. On the other hand, placing the units too close together leads to excessive cochannel coverage overlap, degrading system performance. Currently, AP placement involves a "trial and error" technique. When a technician tests the effect of moving an AP from one location to another, it is necessary to spend considerable time manually measuring signal strengths in order to determine how this move affects the AP's coverage area. In this letter, we describe a procedure for estimating the coverage areas of relocated APs. The procedure can be used as part of a manual design process or as part of an automated design tool.     

硬件锁中的无线USB

无线USB的前途似乎无与伦比——它能消除那些把大家桌面弄得像鼠窝一样小小的不怎么灵便的电缆。但事实上,只有需要大量的外设时无线USB设备才有优势,而且它必须非常微型而廉价,否则带来的麻烦远多于缠绕的电缆。因此,插在PC USB端口作为无线基站的硬件锁就必须有尽可能高的集成度。但一片芯片中要包含USB有线接口、控制器、无线基带和RF电路,技术上还无法实现。下面我们将看到一家供应商Wisalr的一种可量产参考设计,它是如何接近于解决这个问题的。     

Stochastic integrators indexed by a multi-dimensional parameter

Summary Multi-parameter stochastic integrators are described and classified according to directions of integrability. Sets of directions are distinguished precisely by the combinatorial dimension of corresponding fractional Cartesian products. The main theorem establishes existence of stochastic processes which are integrators in prescribed directions but not others.     

Space-dependent color gamut mapping: a variational approach.

Gamut mapping deals with the need to adjust a color image to fit into the constrained color gamut of a given rendering medium. A typical use for this tool is the reproduction of a color image prior to its printing, such that it exploits best the given printer/medium color gamut, namely the colors the printer can produce on the given medium. Most of the classical gamut mapping methods involve a pixel-by-pixel mapping and ignore the spatial color configuration. Recently proposed spatial-dependent approaches for gamut mapping are either based on heuristic assumptions or involve a high computational cost. In this paper, we present a new variational approach for space-dependent gamut mapping. Our treatment starts with the presentation of a new measure for the problem, closely related to a recent measure proposed for Retinex. We also link our method to recent measures that attempt to couple spectral and spatial perceptual measures. It is shown that the gamut mapping problem leads to a quadratic programming formulation, guaranteed to have a unique solution if the gamut of the target device is convex. An efficient numerical solution is proposed with promising results.     

对电压参考进行滤波以获得低噪声性能

输出电压相对于电压参考的短期变化即为噪声。参考电压噪声一般发生在以下两个频段：短期噪声在0．1Hz～10Hz，宽带噪声在10Hz～1kHz。由于噪声电压一般与参考电压成正比，故常用每百万分之一（ppm）来表示噪声，并借此使每百万分之一值恒定。能隙（或带隙）电压参考具有介于3ppm～16ppm之间的噪声电压，但埋入式齐纳电压参考的噪声更低，介于0．1ppm～0．5ppm之间。噪声随参考电流的增加而减小，但增加参考电流并不是大多数电压参考的选项。     

Permeability of N2, Ar,He, O2, and CO2 through as‐extruded amorphous and biaxially oriented polyester films: Dependence on chain mobility

For as‐extruded amorphous and biaxially orientated polyester films based on poly(ethylene terephthalate), poly(ethylene naphthalate), and copolymers containing poly(ethylene terephthalate) and poly(ethylene naphthalate) moieties, permeability, diffusion, and solubility coefficients are interpreted in terms of chain mobility. The influence of polymer morphology is determined by comparison of the data for as‐extruded amorphous sheets and materials produced with different biaxial draw ratios. The crystallinities of the samples were assessed using differential scanning calorimetry and density measurements. Changes in mobility at a molecular level were investigated using dielectric spectroscopy and dynamic mechanical thermal analysis. The study, in conjunction with our earlier work, leads to the conclusion that the key to understanding differences in gas transport is the difference in local chain motions rather than in free volume. This was illustrated by the permeability results for He, Ar, N₂, and O₂ in the range of polyesters. However, the permeability of CO₂ was found to require alternative explanations because of polymer–penetrant interactions. For biaxially oriented samples, the differences in diffusivity are not only due to differences in local chain motions, but also additional constraints resulting from the increased crystallinity and chain rigidity—which also act to hinder segmental mobility. The effectiveness of the reduction in permeability in the biaxially oriented films is consequently determined by the ability of the polymer chains to effectively align and form crystalline structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2916–2929, 2004     

Measurement of PLL phase error caused by power supply noise

The measurement of the accumulated phase error of phase-locked loops (PLLs) in microprocessor systems is discussed. A system which creates controlled power supply noise and measures the PLL response is described. Examples of the use of this technique are shown for a PLL used in a 400 MHz microprocessor     

混合信号SoC设计的现状与未来

从消费电子市场最容易得到的经验是集成为王。移动型战胜便携型,掌上型战胜移动型,而衬衫口袋型又超过掌上型。即使像游戏机这类桌面设备,时髦的外形和低制造成本目标也要靠更高集成度才能实现。这一趋势并不限于低成本的消费电子产品。军用、汽     

Identification of gate electrode discontinuities in submicron CMOStechnologies, and effect on circuit performance

An experiment to determine the effect of gate electrode resistivity on circuit speed gave unexpected results: circuits with the lowest sheet resistance had the poorest circuit speed. Explanation of this behaviour required development of a new high-frequency method of measuring the impedance of the gate electrode. This method revealed that the circuits with a composite gate electrode had been formed with a partial discontinuity. The measurement technique is described, and the evidence of the discontinuity is shown. The effect of the discontinuity on device and circuit speed is demonstrated     

A new method for approximation of physiological signals

A new robust method for the approximation of physiological signals is proposed. The noise must satisfy only one condition: that the probabilities for positive and negative values are equal. The authors' results illustrate that the proposed method provides a more accurate approximation of signals than either the least square error or the least absolute deviation method in cases that include unknown noise density