Digital cellular-its roots and its future

Cellular radio started in the early 1980s by using analog technologies. Research in voice coding, modulation, and channel coding resulted in second-generation cellular radio based on digital technologies, which were introduced in the early 1990s. These were all based on advanced time division multiple access technology, resulting in better capacity and lower cost. Today, these digital technologies-based on the Global System for Mobility, digital Advanced Mobile Phone System, and personal digital cellular-have more than 100 million subscribers worldwide. The next step is to introduce wide-band packet services for wireless Internet up to 2 Mb/s. These so-called third-generation systems (Universal Mobile Telecommunications Services, IMT2000) are planned to be introduced in the early 2000s     

具有阻力特性材料的σ_f－σ关系及一种新的阻力曲线测定方法

通过对相变增韧陶瓷及一种可切削玻璃－陶瓷动态疲劳（恒应力速率）试验中高应力速率区断裂应力下降现象的理论分析，发现这种现象与材料的阻力特性（Ｒ－ｃｕｒｖｅ）密切相关。确立的σ_ｆ－σ理论关系能够很好地描述整个应力速率区间内的动态疲劳试验结果。高应力速率区σ_ｆ－σ在双对数坐标下为负斜率直线，直线斜率为（ｍ为阻力曲线ＫＲ＝ｋ（△ａ）~ｍ的指数），断裂主要由材料阻力行为控制；低应力速率区，σ_ｆ－σ在双对数坐标下为正斜率直线，直线斜率为　（ｎ为应力腐蚀指数），断裂主要由材料应力腐蚀行为控制。建立了测定材料阻力特性的一种新方法，分别用这种方法及压痕／弯曲方法对一种可切削玻璃－陶瓷的阻力特性进行了实验测定，两种方法所得结果有很好的一致性。     

A hybrid spreading/despreading function with good SNR performancefor band-limited DS-CDMA

Code-division multiple-access (CDMA) implemented with direct-sequence spread spectrum (DS/SS) signaling is a promising multiplexing technique for cellular telecommunications services. The efficiency of a direct-sequence spread-spectrum code-division multiple-access (DS-CDMA) system depends heavily on the shape of the spectrum of the spread signal. Maximum efficiency is obtained with an ideal brick-wall bandpass spectrum. There are two approaches toward achieving such a spectrum. One is to use a simple spreader that produces a broad spectrum and then follow it with a precise, high order filter to band limit the spectrum. A second approach, which is the approach taken in this paper, is to use a spreader that produces a spectrum close to the ideal spectrum and then employ a simple filter to control the out-of-band power. The proposed spreader/despreader is based on a simple hybrid function and can be easily implemented. An analysis provides a compact expression for the signal-to-noise ratio (SNR) of a RAKE receiver. The expression includes the effects of baseband, intermediate frequency (IF) and RF filtering as well as the effects of the spectral densities of the spreading/despreading functions. The analysis shows that the proposed spreader/despreader yields superior performance over a conventional pseudo noise (PN) spreading/despreading mechanism     

Shear horizontal wave propagation in periodically layeredcomposites

The transverse resonance approach to guided wave analysis is applied to shear horizontal (SH) wave propagation in periodically layered composites. It is found for SH waves that at high values of the guided wavevector β, the wave energy is trapped in the slower of the two media and propagates accordingly at the slower wavespeed. At low values of β, however, the modes demonstrate a clustering behavior, indicative of the underlying Floquet wave structure. The number of modes in a cluster is observed to correlate with the number of unit cells in the layered plate. New physical insights into the behavior of these systems are obtained by analyzing the partial waves of the guided SH modes in terms of Floquet waves. We show that the fast and slow shear waves in the periodically layered composite play an analogous role to the longitudinal and shear partial waves comprising Lamb waves in a homogeneous plate     

Densification involved in the UV-based photosensitivity of silicaglasses and optical fibers

A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models     

A wafer level monitoring method for plasma-charging damage usingantenna PMOSFET test structure

A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices     

Electrical linewidth test structures fabricated in monocrystallinefilms for reference-material applications

The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features     

A unified diode model for circuit simulation

A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications     

Soft commutation in capacitive idling converters

The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency