A traffic control system for IEEE 802.11 networks based on available bandwidth estimation

To support Quality of service (QoS)‐sensitive applications like real‐time video streaming in IEEE 802.11 networks, a MAC layer extension for QoS, IEEE 802.11e, has been recently ratified as a standard. This MAC layer solution, however, addresses only the issue of prioritized access to the wireless medium and leaves such issues as QoS guarantee and admission control to the traffic control systems at the higher layers. This paper presents an IP‐layer traffic control system for IEEE 802.11 networks based on available bandwidth estimation. We build an analytical model for estimating the available bandwidth by extending an existing throughput computation model, and implement a traffic control system that provides QoS guarantees and admission control by utilizing the estimated available bandwidth information. We have conducted extensive performance evaluation of the proposed scheme via both simulations and measurements in the real test‐bed. The experiment results show that our estimation model and traffic control system work accurately and effectively in various network load conditions without IEEE 802.11e. The presence of IEEE 802.11e will allow even more efficient QoS provision, as the proposed scheme and the MAC layer QoS support will complement each other. Copyright © 2006 John Wiley & Sons, Ltd.     

ZnO-Based Low-Voltage Inverter With Quantum-Well-Structured Nanohybrid Dielectric

We report on the fabrication of 2-V-operating ZnO-based inverter with two n-channel thin-film transistors (TFTs) on 22-nm-thin organic/inorganic nanohybrid dielectric, which contains AlO_x/TiO_x/AlO_x in triple-layer structure. The inverter shows a high voltage gain of ~20 under the supply voltage (V_DD) of 2 V but with a marginal transition voltage of 0.1 V (operation range of 0-2 V). To control the transition voltage to a more adequate value, an 8-V gate pulse was applied on driving ZnO-TFT so that some of the channel electrons would be tunneled through the AlO_x-based barrier and trapped in the TiO_x-based layer. Our inverter then displayed an optimum transition voltage of 0.75 V.     

Complementary Absorbing Star‐Shaped Small Molecules for the Preparation of Ternary Cascade Energy Structures in Organic Photovoltaic Cells

Two anthracene‐based star‐shaped conjugated small molecules, 5′,5″‐(9,10‐bis((4‐hexylphenyl)ethynyl)anthracene‐2,6‐diyl)bis(5‐hexyl‐2,2′‐bithiophene), HBantHBT, and 5′,5″‐(9,10‐bis(phenylethynyl)anthracene‐2,6‐diyl)bis(5‐hexyl‐2,2′‐bithiophene), BantHBT, are used as electron‐cascade donor materials by incorporating them into organic photovoltaic cells prepared using a poly((5,5‐E‐alpha‐((2‐thienyl)methylene)‐2‐thiopheneacetonitrile)‐alt‐2,6‐[(1,5‐didecyloxy)naphthalene])) (PBTADN):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) blend. The small molecules penetrate the PBTADN:PC₇₁BM blend layer to yield complementary absorption spectra through appropriate energy level alignment and optimal domain sizes for charge carrier transfer. A high short‐circuit current (J_SC) and fill factor (FF) are obtained using solar cells prepared with the ternary blend. The highest photovoltaic performance of the PBTADN: BantHBT :PC₇₁BM blend solar cells is characterized by a J_SC of 11.0 mA cm^?2, an open circuit voltage (V_OC) of 0.91 V, a FF of 56.4%, and a power conversion efficiency (PCE) of 5.6% under AM1.5G illumination (with a high intensity of 100 mW^?2). The effects of the small molecules on the ternary blend are investigated by comparison with the traditional poly(3‐hexylthiophene) (P3HT):[6,6]‐phenyl‐C61‐butyric acid methyl ester (PC₆₁BM) system.     

Optimum design of a predistortion RF power amplifier for multicarrier WCDMA applications

This paper provides a design guide for optimum design of an RF power amplifier with a predistortion linearizer. For a two-tone signal, three performance degradation factors, higher order terms, amplitude, and phase mismatches are analyzed quantitatively. The results are implemented to the design of optimized predistortion power amplifier for a WCDMA signal application. For the experiments, a 2.4-GHz class-AB power amplifier is fabricated using an LDMOSFET with a 30-W peak envelope power. A simple third-order predistorter is used to measure the relative phases of the harmonics, as well as to linearize the amplifier. The performance of the optimized predistortion power amplifier is excellent for an IS-95 code-division-multiple-access signal. Finally, a method for reducing the memory effects of the amplifier is devised to get a good cancellation performance for a wide-band signal, and the performance degradation caused by the memory effects is analyzed. For a forward-link four-carrier WCDMA signal, the predistortion power amplifier delivers an adjacent channel leakage ratio of -46 dBc at a 4-W average output power with a cancellation of 13.4 dB.     

Efficient Hybrid Modulation/Demodulation Scheme Using Differential Encoding/Decoding for UWB-IR

An efficient hybrid modulation/demodulation scheme using a short duration pulse in the time-domain for ultra wideband-impulse radio (UWB-IR) systems is proposed. The proposed modulation scheme is pulse position modulation (PPM) of the UWB-IR standard modulation combined with differential encoding, and non-coherent energy detection (ED) adopting differential decoding is proposed for demodulation. Differential encoding makes a pulse that can transfer additive information bit into bits assigned in one symbol without increasing the symbol period. The BER performance is evaluated for 2-PPM, 4-PPM and the proposed HD-2PPM (which has the same symbol duration as BPPM and includes two information bits per symbol). The error performance indicates that the proposed scheme is an outstanding 0.5 dB over existing schemes of UWB-IR, and the data-rate performance shows that the proposed method has higher spectral efficiency than conventional methods that occupy the same duration as the proposed scheme.

     

Gaze Detection by Wearable Eye‐Tracking and NIR LED‐Based Head‐Tracking Device Based on SVR

In this paper, a gaze estimation method is proposed for use with a large‐sized display at a distance. Our research has the following four novelties: this is the first study on gaze‐tracking for large‐sized displays and large Z (viewing) distances; our gaze‐tracking accuracy is not affected by head movements since the proposed method tracks the head by using a near infrared camera and an infrared light‐emitting diode; the threshold for local binarization of the pupil area is adaptively determined by using a p‐tile method based on circular edge detection irrespective of the eyelid or eyelash shadows; and accurate gaze position is calculated by using two support vector regressions without complicated calibrations for the camera, display, and user's eyes, in which the gaze positions and head movements are used as feature values. The root mean square error of gaze detection is calculated as 0.79° for a 30‐inch screen.     

An analytical model of simultaneous switching noise in CMOS systems

An accurate and analytical model for simultaneous switching noise (SSN) on ground lines in CMOS circuits is presented. This model can compute SSN for the case where only some drivers switch and the others remain quiet, that is, the model considers the loading effects on the quiet drivers. It was confirmed that the proposed model is more accurate than the existing ones through HSPICE simulation using the level 28 model for short-channel MOSFETs. The proposed model can provide useful design guides for CMOS driver circuits     

Small-signal substrate resistance effect in RF CMOS cascode amplifier

With common-source RF application amplifier, it is well known that the small substrate resistance helps to improve the output resistance as well as the transconductance. This idea can be easily extended to all CMOS transistors in RF applications. However, with cascode amplifier at high frequencies, the maximum available gain, noise figure minimum, and the tuned output impedance are improved by increasing the substrate resistance of the common-gate transistor, so that the range of operational frequency can be extended. These contradicting phenomenons between the common-source and common-gate topology can be explained theoretically, and the supporting measurement results are presented base on a 0.35 /spl mu/m CMOS technology.     

Analysis and application of nonleaky uniplanar structures with conductor backing

Novel conductor-backed uniplanar structures, including the nonleaky CPW and slotline, are analyzed and applied to the active antenna design. Both the spectral domain analysis and finite-difference time-domain techniques are used to simulate these circuits and to justify the numerical results. The measured gain of the novel active antenna is 1.7 dB higher than the conventional CPW antenna due to the unidirectional radiation of conductor-backed circuits. © 1996 John Wiley & Sons, Inc.