HKUST Institutional Repository
(5.016 recursos)
Repository of Hong Kong University of Science and Technology. Managed by the HKUST Library.
Mostrando recursos 1 - 20 de 126
1.
Fuzzy based rate control for real-time MPEG video - Tsang, Danny H. K.; Bensaou, Brahim; Lam, Shirley Tung Ching
In this paper, we propose a fuzzy logic based control scheme for real time MPEG video to avoid long delay or excessive loss at the user-network interface (UNI) in an ATM network. The system consists of a shaper whose role is to smooth the MPEG output traffic to reduce the burstiness of the video stream. The input and output rates of the shaper buffer are controlled by two fuzzy logic based controllers. To avoid a long delay at the shaper, the first controller aims to tune the output rate of the shaper based on the number of available transmission credits...
2.
Pole assignment for stochastic systems with unknown coefficients - Chen, Hanfu; Cao, Xiren
This paper solves the exact pole assignment problem for the single-input stochastic systems with unknown coefficients under the controllability assumption which is necessary and sufficient for the arbitrary pole assignment for systems with known coefficients. The system noise is required to be mutually independent with zero mean and bounded second moment. Two approaches to solving the problem are proposed: One is the iterative learning approach which can be applied when the state at a fixed time can be repeatedly observed with different feeback gains; the other is the adaptive control approach which works when the trajectories satisfy a nondegeneracy condition....
3.
Distribution of the liquid crystal director under applied voltage and its viewing characteristics - Wang, Qian; Yi, Feihong; Kwok, Hoi-Sing
New difference iterative method for calculating the liquid crystal director distribution is presented. This new method is very simple and intuitive and can give accurate results in a much shorter time, and is applicable for various types of liquid crystal displays, such as twist nematic cell, nematic cell with asymmetric pretilt or chiral super twist nematic cell. The viewing characteristic of the liquid crystal display is also calculated with a faster 4*4 matrix method with the FP elimination method.
4.
Non-singular 2*2 matrix method for liquid crystal display - Wang, Qian; Yu, Fei-Hong; Cen, Zhaofeng; Kwok, Hoi-Sing
Based on the theory of electromagnetic propagation in anisotropic media and optical reflection and refraction theory, a simple and non-singular 2*2 matrix representation is presented. This 2*2 matrix representation is very simple, accurate and has no singular point.
5.
Universal lattice decoding : principle and recent advances - Mow, Wai Ho
The idea of formulating the detection of a lattice-type modulation, such as M-PAM and M-QAM, transmitted over a linear channel as the so-called universal lattice decoding problem dates back to at least the early 1990s. The applications of such lattice decoders have proliferated in the last few years because of the growing importance of some linear channel models, such as multiple-antenna fading channels and multi-user CDMA channels. The principle of universal lattice decoding can trace its roots back to the theory and algorithms developed for solving the shortest/closest lattice vector problem for integer programming and cryptoanalysis applications. In this semi-tutorial...
6.
Comb-on-Plane switching electrodes for liquid crystal displays - Meng, Zhiguo; Kwok, Hoi-Sing; Wong, Man
Though the common twisted-nematic (TN) liquid crystal displays have excellent contrast and low color dispersion, they suffer from small viewing angle when driven into the homeotropic state. Among the many techniques proposed, "in-plane-switching" (IPS) has been quite effective in improving the viewing angles. However, there may be difficulty in adopting the conventional IPS to higher definition displays because it suffers from limited storage capacitance and reduced transmittance. A new comb-on-plane switching (COPS) electrode design is presently proposed. Compared to the conventional IPS, COPS allows for lower switching voltage and offers advantages including naturally scalabe storage capacitance, wide viewing angle with...
7.
Characterization of buried nitride silicon-on-insulator substrate - Poon, Vincent M. C.; Lam, Y. W.; Wong, S. P.
Buried nitride silicon-on-insulator (SOI) substrates prepared using stationary beam synthesis have been characterized. It is found that surface Si layers and alpha and beta-phase silicon nitride layers of good quality can be formed in the SOI structure if the implant and annealing conditions are suitably controlled. However, the high nitrogen content inside the surface Si layer has been found to create new problems to the direct fabrication of devices on the SOI substrate.
8.
Nearly-noncritical phase matching in MgO:LiNbO3 optical parametric oscillators - Yao, Jian-Quan; Yu, Yi-Zhong; Wang, Peng; Wang, Tao; Zhang, Bai-Gang; Ding, Xin; Chen, Jin; Peng, H. J.; Kwok, Hoi-Sing
We have proposed and demonstrated a nearly-noncritical phase-matched (NCPM) optical parametric oscillation (OPO) in an MgO:LiNbO3 crystal with 5 mol% MgO by temperature tuning. By giving up perfect NCPM, the practical tuning range for the OPO is increased by two times. For the crystal, the operated temperature decreases with the phase-matching angle at degeneracy. With a cutting angle of 82° instead of the noncritical case of 90°, the tuning range was increased. In order to obtain a sufficiently high output pulse energy for both signal and idler throughout the entire tuning range, five sets of mirrors were used for the...
9.
The optical functions of metal phthalocyanines - Liu, Z. T.; Kwok, Hoi-Sing; Djuris?ic?, A. B.
The optical properties of five metal phthalocyanines (MPcs) thin films (cobalt phthalocyanine (Pc), copper Pc, iron Pc (FePc), nickel Pc, and zinc Pc), were studied by spectroscopic ellipsometry. Thin films of these MPcs were evaporated in high vacuum onto glass substrates, quartz substrates, and silicon substrates. Spectroscopic ellipsometry measurements were performed in the wavelength range 250800 nm. The absorption spectra were measured, and the film thickness and surface roughness were studied by atomic force microscopy. Determination of optical functions was performed by simultaneous fitting of the experimental data for samples on glass and silicon substrates. Fitting results using point-to-point fitting,...
10.
Preliminary study of detecting neoplastic growths in vivo with real time calibrated autofluorescence imaging - Wu, Tao; Qu, Jianan; Cheung, Tak-Hong; Lo, Keith Wing-Kit; Yu, Mei-Yung
The goal of this study was to evaluate the capabilities of a calibrated autofluorescence imaging method for detecting neoplastic lesions. An imaging system that records autofluorescence images calibrated by the cross-polarized reflection images from excitation was instrumented for the evaluation. Cervical tissue was selected as the living tissue model. Sixteen human subjects were examined in vivo with the imaging system before routine examination procedures. It was found that calibrated autofluorescence signals from neoplastic lesions were generally lower than signals from normal cervical tissue. Neoplastic lesions can be differentiated from surrounding normal tissue based on the contrast in the calibrated autofluorescence....
11.
OCT elastography : imaging microscopic deformation and strain of tissue - Schmitt, Joseph M.
Optical coherence tomography (OCT) has been applied to the study of the microscopic deformation of biological tissue under compressive stress. We describe the hardware and theory of operation of an OCT elastography system that measures internal displacements as small as a few micrometers by using 2D cross-correlation speckle tracking. Results obtained from gelatin scattering models, pork meat, and intact skin suggest possible medical applications of the technique.
12.
Multirate periodic systems and constrained analytic function interpolation problems - Chai, Li; Qiu, Li
Multirate periodic systems and some related constrained analytic function interpolation problems are studied in this paper. After showing how to convert a general multirate periodic system to an equivalent LTI system with a structural constraint, we formulate some analytic function interpolation problems with such constraint which can find various applications in the study of multirate and periodic systems. Both the
solvability conditions and characterization of all solutions are presented to these constrained interpolation problems.
13.
Unitarily invariant metrics on the Grassmann space - Qiu, Li; Zhang, Yanxia; Li, Chi-Kwong
It is shown that ?(?1(?, Y),...,?m(?, Y)) defines a unitarily invariant metric on the Grassmann space Gm,n of m-dimensional subspaces of Fn for every symmetric gauge function ?, where ?1(?, Y),...,?m(?, Y) are the canonical angles between subspaces X, Y ? Gm,n. This provides a wide class of new metrics on Gm,n. Some related results on perturbation and approximation of subspaces in Gm,n, as well as the canonical angles between them, are also discussed. Furthermore, the equality case of the triangular inequality for several unitarily invariant metrics are analyzed.
14.
A new empirical model for indoor propagation prediction - Cheung, K. W.; Sau, J. H. M.; Murch, Ross David
In this paper a new empirical model for indoor propagation prediction is presented. The inspiration for our model is to enhance existing empirical models for indoor propagation prediction by incorporating additional phenomena suggested by electromagnetic techniques such as the Uniform Theory of Diffraction but still retain the straightforwardness of the empirical approach. The advantage is that computation time for indoor propagation prediction is low without greatly compromising prediction accuracy. Comparisons of our predicted results to measurements indicate that improvements in accuracy over conventional empirical models are achieved.
15.
A compact PIFA suitable for dual frequency 900/1800MHz operation - Rowell, Corbett Ray; Murch, Ross David
Planar Inverted F Antennas (PIFA) have been proposed as possible candidates for mobile telephone handsets. In this letter we describe the design of a compact PIFA suitable for operation at 900MHz. In addition we provide modications to this design that allow it to operate in dual frequency bands at 900MHz and 1800MHz. FDTD and experimental results are provided.
16.
A capacitively loaded PIFA for compact mobile telephone handsets - Rowell, Corbett Ray; Murch, Ross David
A capacitively loaded planar inverted-F antenna (PIFA) is proposed and studied. It is found that the capacitive load reduces the resonance length of the PIFA from ?/4 to less than ?/8. A design with a bandwidth of 178MHz centered at 1.8GHz is provided to demonstrate that compact antennas for mobile telephone handsets can be constructed using this approach. The finite difference time domain method is used in the study and experimental verification is also provided.
17.
Antenna diversity combining and finite-tap decision feedback equalization for high-speed data transmission - Ng, John C. L.; Letaief, K. B.; Murch, Ross David
The next-generation wireless communication systems are expected to support high speed data transmission. However, associated with high transmission rates is the problem of multipath inter-symbol interference (ISI) due to frequency-selective fading. Decision feedback equalization (DFE) and antenna diversity combining are two practical techniques for combating multipath ISI. In this paper, we investigate the performance of diversity combining together with DFE under various numbers of antenna branches and equalization taps in a quasi-stationary frequency-selective fading environment with AWGN and co-channel interference (CCI) by means of simulations. We consider joint optimization combining and power selection diversity combining. We simulate the combiner using...
18.
Complex optimal sequences with constant magnitude for fast channel estimation initialization - Ng, John C. L.; Letaief, K. B.; Murch, Ross David
Optimal sounding sequences which satisfy a certain autocorrelation property are useful for fast channel estimation techniques which are based on non-iterative channel sounding methods. In this paper, we study optimal sequences consisting of complex symbols with constant magnitude. An indirect sequence construction method is derived by considering the phase difference between sequence symbols. Our construction method includes periodic and non-periodic optimal sequences, and provides insight into the nature and properties of optimal sequences that are based on consecutive roots-of-unity phase difference sequences.
19.
Modified least loaded routing in virtual path based ATM networks - Chu, Hon-Wai; Tsang, Danny H. K.
We consider a Virtual Path (VP) based ATM network supporting multiple traffic classes with heterogeneous traffic characteristics. Using simple FIFO scheduling policy at the ATM multiplexer, we assume that all traffic require identical end-to-end quality of service (QoS) requirement. The concept of effective bandwidth is used to determine the required bandwidth to guarantee the specified QoS requirement. We study the problem of using dynamic routing to VP-based ATM networks by transforming it into an equivalent multi-rate circuit-switched network problem. To further simplify the analysis, we restrict the choice of path to single-link and two-link routes. We propose a dynamic routing...
20.
Tight upper bounds for cell loss probabilities and required bandwidth estimation in ATM multipl[e]xers - Liu, Xiaoming; Bensaou, Brahim; Tsang, Danny H. K.; Liu, Liming
Estimating the cell loss probability in an ATM multiplexer is a key issue in network management and traffic control tasks such as call admission control and bandwidth allocation. In this paper, we derive a new approximation to estimate the total and individual cell loss probabilities in an ATM multiplexer fed by a superposition of heterogeneous on-off-sources. Based on this approximation, a simple algorithm is proposed to estimate accurately the aggregate required bandwidth to guarantee a given cell loss probability. Numerical results and comparisons to alternative approaches are also shown.
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