Browsing by Issue Date, starting with "2003-09-01"

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Two-stage dynamic uplink channel and slot assignment for GPRS
(2003-09-01)
Hsu, YC
;
Lin, YD
;
Chiang, MY
;
資訊工程學系
;
Department of Computer Science
General packet radio service (GPRS) uses a two-stage mechanism to allocate uplink radio resource to mobile stations (MSs). In stage-1, the base station (BS) assigns several packet data channels (PDCHs) to an MS. Furthermore, a PDCH may be assigned to multiple MSs. In stage-2, therefore, the BS selects one of the multiplexed MSs in a PDCH to use the radio resource. In this paper, maintaining a load balance between PDCHs in stage-1 is examined and several selection schemes to lower the mis-selection rate in stage-2 are proposed. From our simulation results, the cost deduced from the poor load balancing and selection schemes render a lower system throughput and a non-negligible increase in packet queuing delay. Among the various stage-2 selection policies, round robin with linearly-accumulated adjustment (RRLAA) has the lowest mis-selection rate and outperforms the one without any heuristic by up to 50%.
TCP with sender-based delay control
(2003-09-01)
Kung, HT
;
Tan, KS
;
Hsiao, PH
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
This paper describes a congestion control method for TCP that adjusts the transmission rate of a TCP connection by changing not only the congestion window size as in normal TCP, but also by delaying the transmission of packets at the sender. We refer to this method as TCP with sender-based delay control, or simply SDC. SDC can keep the window size of a TCP connection above a certain threshold even when its fair share of bandwidth is arbitrarily small. Since TCP fast retransmit and recovery is likely to work when the window size of the connection is sufficiently large, the new method can result in reduced frequency of TCP timeouts for the connection. In particular, SDC allows many TCP flows to share a link without experiencing many timeouts. In addition, SDC can reduce a well-known TCP bias against connections with large RTTs. This paper presents the principle behind SDC, and simulation results demonstrating its properties and advantages. (C) 2003 Elsevier Science B.V. All rights reserved.
The effects of dielectric type and thickness on the characteristics of dynamic threshold metal oxide semiconductor transistors
(2003-09-01)
Lee, YJ
;
Chao, TS
;
Huang, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper, we discuss dynamic threshold MOS (DTMOS) operations for nMOSFETs of different dielectric types and thicknesses. We found that, under the DT mode of operation, all devices exhibit a threshold voltage close to 0.7 V, independent of the thickness and gate dielectric type of the device. This is due to the diminished influence of the body effect factor. Formulations of threshold voltage and subthreshold swing of DTMOS are developed to gain insights into this unique phenomenon, and simulation of the subthreshold swing is also provided.
A low-complexity multi-user CDMA receiver with blind channel estimation and partially adaptive MAI suppression
(2003-09-01)
Lin, GJ
;
Lee, TS
;
資訊工程學系
;
電信工程研究所
;
Department of Computer Science
A low complexity multi-user receiver with blind channel estimation and multiple access interference (MAI) suppression is proposed for a CDMA system under multipath fading and frequency offset. The design of the receiver involves the following procedure. First, a method of joint MAI suppression and channel estimation is developed based on the generalized side-lobe canceller (GSC) technique. In particular, channel estimates are obtained blindly in the form of the effective composite signature vectors (CSV) of the users. Second, a low-complexity partially adaptive (PA) realization of the receiver is proposed which incorporates reduced-rank processing based on the information of multi-user CSV's. By a judiciously designed decorrelating procedure, a new PA receiver is obtained with a much lower complexity. Finally, pilot symbols assisted frequency offset estimation and channel gain compensation give the estimate of users' symbols. Further performance enhancement is achieved by a decision aided scheme in which the signal is reconstructed and subtracted from the receiver input data, leading to significantly faster convergence. The proposed receiver is shown to be robust to multipath fading and frequency offset, and achieves nearly the same performance of the optimal maximum SINR and MMSE receivers with a much lower overhead for pilot symbols.
Growth and field emission of carbon nanofibers on electroless Ni-P alloy catalyst
(2003-09-01)
Tsai, TK
;
Chuang, CC
;
Chao, CG
;
Liu, WL
;
材料科學與工程學系
Carbon nanofibers (CNFs) were grown on a Ni-P alloy catalyst deposited on a silicon substrate in a microwave heating chemical vapor deposition system with methane gas at 650 degreesC. The Ni-P alloy catalyst films with various thicknesses were produced using an electroless plating nickel technique. The nanosized clusters on the clustered surface of the Ni-P alloy catalyst film directly provided the nucleation sites for CNFs without any pretreatment before the growth of the CNFs. The CNFs grown on the Ni-P alloy catalyst showed random orientation and it composed of parallel graphite planes with defects tilted from their axis. Field emission measurement indicated that the Ni-P catalyzed-CNFs exhibited excellent field emission properties. The diameter, growth rate and field emission properties show a strong correlation with the thickness of the Ni-P alloy catalyst film. (C) 2003 Elsevier Science B.V. All rights reserved.
Comparative behavior of laterally loaded groups of bored and driven piles in cohesionless soil
(2003-09-01)
O'Neill, MW
;
Huang, AB
;
土木工程學系
;
Department of Civil Engineering
The lateral load performance of 2 pile groups, one consisting of driven displacement piles, the other of bored piles, is described. The effect of installing the piles is to reduce the soil stiffness within the bored pile group, making the soil less efficient in resisting lateral pile movements than in the driven pile group. Structurally, however, the bored piles were more resistant to flexural loading. The net effect was that the system of bored piles was stiffer than the system of driven displacement piles.
Electronic and magnetic instability in Pr0.65Ca0.25Sr0.1MnO3
(2003-09-01)
Mollah, S
;
Huang, HL
;
Liu, SJ
;
Ho, PL
;
Huang, WL
Electronic and magnetic instability in polycrystalline Pr0.65Ca0.25Sr0.1MnO3 manganite has been established from a systematic study of resistivity (p), magnetization (M) and specific heat (C). The sample shows a charge ordering transition at T-CO similar to 200 K, an antiferromagnetic (AFM) ordering transition at T-N similar to 175 K, a metal-insulator (MI) transition at T-MI similar to 80 K and an unusual magnetic ordering transition at T-M(*) similar to 45 K in the absence of magnetic fields. Though the C data do not show any anomaly at T-MI for MI transition, these illustrate a much smaller anomaly than expected one at T-M* and is suppressed by magnetic fields. This indicates that the unusual magnetic ordering in this sample is of canted, fluctuated or phase separation of AFM and ferromagnetic in nature which is established from the T-H phase diagram, as well as the thermal and magnetic hysteresis in p, M and C. (C) 2003 Elsevier Science B.V. All rights reserved.
N-sided hole filling and vertex blending using subdivision surfaces
(2003-09-01)
Hwang, WC
;
Chuang, JH
;
資訊工程學系
;
Department of Computer Science
To fill an N-sided hole on a NURBS surface and to blend a corner formed by NURBS surfaces, we propose a regular N-sided open uniform quadratic subdivision surface derived by applying the open uniform quadratic subdivision scheme to a regular N-sided control mesh which is confined to the hole or to the region of the vertex blend. Boundary conditions such as C(0) and G(1)-continuity required for the hole filling and vertex blending, are ensured by certain refinement steps performed in the course of the subdivision. The shape of the filling or blending surface is controlled by using fullness parameters. Methods are also proposed to represent the resulting regular N-sided open uniform quadratic subdivision surface using non-uniform rational B-spline surfaces.
Mobile number portability
(2003-09-01)
Lin, YB
;
Chlamtac, I
;
Yu, HC
;
科技管理研究所
;
Institute of Management of Technology
Mobile number portability allows a mobile subscriber to switch operators without chaning his/her phone number. This article describes and analyzes mobile number portability routing mechanisms and their implementation costs. We first describe the Signaling Relay Function (SRF)-based solution for call related and non-call related routing. Then we describe the Intelligent Network (IN)-based solution for call related routing. Cost recovery issues for number portability are discussed in this article from a technical perspective. We note that rules for cost recovery also depend on business and regulatory factors that vary from country to country.
DSP implementation of successive interference cancellation (SIC) receiver for 3GPP WCDMA uplink transmission
(2003-09-01)
Chang, YJ
;
Lin, YN
;
Lin, DW
;
電子工程學系及電子研究所
;
電信研究中心
The 3GPP WCDMA is a widely accepted third-generation cellular system standard. By using nonorthogonal codes for different users. the Multiple access interference (MAI) can be a limiting factor for system performance, as for other CDMA systems. Multiuser detection (MUD) is known to reduce MAI and improve CDMA system performance. but many Such techniques have high complexity. Successive interference cancellation (SIC) is an effective MUD technique with relatively low complexity. We consider the software implementation of an SIC receiver for WCDMA uplink transmission on a commercially available general-purpose multi digital signal processor (DSP) platform. This also goes in line with the recent interest in software-defined radio. Issues addressed in this work include job partitioning and signal routing for multiprocessor implementation, design of SIC components (especially the channel estimator and the si mal regenerator), determination of the precision of fixed-point computations. consideration of the receiver's error performance and analysis of the implementation's complexity and efficiency. These issues are tightly coupled with the 3GPP WCDMA specifications. Because the employed platform only contains four DSPs, the implementation only considers up to three users. But this is sufficient for Lis to appreciate various DSP implementation issues of an SIC receiver. Moreover, by the nature of SIC, it is easy to extend the implementation to handle more users with an enlarged platform. Our present implementation achieves real-time speed in the RAKE receiver part of the complete receiver. Due to the complexity in signal regeneration, the overall SIC receiver still falls short of the real-time requirement when interference cancellation is activated. In fact, the platform employed presently cannot support real-time processing when the number of multipaths is four or more, unless either the system architecture or the SIC algorithm is redesigned. Such and other ways of improvement are relegated to potential future work. Copyright (C) 2003 John Wiley Sons, Ltd.
Anisotropic electronic structure of in-plane aligned a-axis YBa2Cu3O7-delta thin films
(2003-09-01)
Luo, CW
;
Chen, MH
;
Liu, SJ
;
Wu, KH
;
Juang, JY
Polarization-dependent x-ray absorption near-edge spectra (XANES) of the O 1s has been measured on a highly in-plane aligned a-axis YBa2Cu3O7-delta (YBCO) thin film. The in-plane XANES, with the electric field E of the linearly polarized synchrotron light being parallel to the b or c axis of YBCO films (E//b or E//c) were obtained in a normal-incidence alignment. The XANES for E//a was then calculated from the data obtained by varying the angle. The results lend strong support to those obtained by using detwinned YBCO single crystals in all crystalline orientations, including the extrapolated c-axis spectra. (C) 2003 American Institute of Physics.
Radionuclide transport in a multiple and parallel fractured system
(2003-09-01)
Liu, CT
;
Yeh, HD
;
環境工程研究所
;
Institute of Environmental Engineering
This paper is to study the effects of fracture width on the transport of a radionuclide in a multiple and parallel fractured rock formation. The equation describing the transport of the radionuclide released from the geological repository includes the following mechanisms: advection, dispersion, radioactive decay, and adsorption on the fracture surfaces. The concentration at the inlet of each fracture is assumed constant. An analytical solution was derived based on such a mathematical model by the Laplace transform technique. The solution indicates that identical concentration distributions can be observed in each fracture of the equal-width parallel fractured system. In an unequal-width fractured system, the penetration distances along wide fractures are generally larger than that in a single uniform fractured system. The radionuclide concentration in the wide fracture quickly reaches source concentration in the near-field environment, confirming that the fracture width plays an important role in radionuclide transport through a system of multiple and parallel fractured media.
BER minimized OFDM systems with channel independent precoders
(2003-09-01)
Lin, YP
;
Phoong, SM
;
電控工程研究所
;
Institute of Electrical and Control Engineering
We consider the minimization of uncoded bit error rate (BER) for the orthogonal frequency division multiplexing (OFDM) system with an orthogonal precoder. We analyze the BER performance of precoded OFDM systems with zero forcing and minimum mean squared error (MMSE) receivers. In the case of MMSE receivers, we show that for quadrature phase shift keying (QPSK), there exists a class of optimal precoders that are channel independent. Examples of this class include the discrete Fourier transform (DFT) matrix and the Hadamard matrix. When the precoder is the DFT matrix, the resulting optimal transceiver becomes the single carrier system with cyclic prefix (SC-CP) system. We also show that the worst solution corresponds to the conventional OFDM system; the conventional OFDM system has the largest BER. In the case of zero forcing receivers, the design of optimal transceiver depends on signal-to-noise ratio (SNR). For higher SNR, solutions of optimal precoders are the same as those of MMSE receivers.
Burst synchronization of slotted random access with preamble power ramping in the reverse link of CDMA systems
(2003-09-01)
Sheen, WH
;
Tseng, CC
;
Ho, JS
;
電信工程研究所
;
Institute of Communications Engineering
Efficient random access is one of the key designs in code-division multiple-access (CDMA) cellular systems. Random access is used by user equipment for initial access, requesting dedicated channels and transmitting short packet data to a base station. In random access, a preamble part is usually devised for fast and reliable burst synchronization, which is essential in order to avoid excessive access delay and/or repeated transmissions that may reduce the overall system capacity. This paper investigates the issue of burst synchronization for the slotted random access with preamble power ramping in the reverse link of CDMA systems. A flexible burst synchronizer based on a parallel-serial code-phase detector is proposed, which can be easily configured to achieve different complexity/performance tradeoffs. A general analysis is also presented with important design parameters being taken into account, including the number of correlators, power control error, power ramping step, diversity order, frequency offset, multipath combining, and others. The analysis is verified by computer simulations.
Fast dynamic code assignment in next generation wireless access networks
(2003-09-01)
Wan, CS
;
Shih, WK
;
Chang, RC
;
資訊工程學系
;
Department of Computer Science
In this paper, a fast dynamic code assignment (FDCA) algorithm is proposed to assign a single Orthogonal Variable Spreading Factor (OVSF)-code for a data rate requirement in next generation wireless access networks. Our algorithm uses the code assignment operation to evaluate the cost for an OVSF-code allocation. The cost is determined by maintaining the data structure that keeps track the number of available and occupied descendant codes of the code. Based on the cost assignment operation, FDCA algorithm can assign an OVSF-code by reassigning occupied descendant codes for a requested data rate. The OVSF-codes assigned by our algorithm is unrestricted with decreasing spreading factor. Moreover, two types of simulations and experimental measurements are presented. First, the proposed algorithm is applied on the OVSF-code assignment of restricted spreading vector. Our experimental results show that the number of reassigned OVSF-codes within FDCA algorithm is reduced comparing to other scheme proposed in the literature. Then, for serving higher data rate requirements, our scheme also shows significant improvement on the spectral efficiency over fixed code assignment scheme. (C) 2003 Elsevier Science B.V. All rights reserved.
A multivariate parallelogram and its application to multivariate trimmed means
(2003-09-01)
Shiau, JJH
;
Chen, LA
;
統計學研究所
;
Institute of Statistics
This paper introduces a multivariate parallelogram that can play the role of the univariate quantile in the location model, and uses it to define a multivariate trimmed mean. It assesses the asymptotic efficiency of the proposed multivariate trimmed mean by its asymptotic variance and by Monte Carlo simulation.
Influence of different cleaning conditions on cleaning performance of pilot-scale pulse-jet baghouse
(2003-09-01)
Lu, HC
;
Tsai, CJ
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, a pilot-scale pulse-jet baghouse is utilized to control the particulate emission of an oil-fired boiler. The operating and design parameters, such as filtration velocity, initial tank pressure, and nozzle diameter, were varied to evaluate the cleaning effect of the pulse-jet baghouse. Two different cleaning types, (1) high initial tank pressure and one bag cleaning; and (2) low initial tank pressure and two consecutive bag cleanings, are used to compare the bag-cleaning performance in this study. It is found that the cleaning effect increases with the initial tank pressure. However, the cleaning intensity (overpressure) does not increase with the nozzle diameter. There exists an optimum nozzle diameter to achieve higher cleaning intensity and a better cleaning effect. This phenomenon results from the small volume of the baghouse compartment in this study. If an industrial size baghouse was used, it suggests that a nozzle diameter larger than 13 mm and initial tank pressure greater than 2.5 kg/cm(2) should be adopted to achieve a higher cleaning effect. Between the two cleaning types, type 2 is found to be more effective to clean the bag and the energy consumption for compressed air is reduced significantly from type 1. Therefore, type 2 bag cleaning is suggested to be a better method to clean the baghouse.
Study of nickel silicide contact on Si/Si1-xGex
(2003-09-01)
Yang, TH
;
Luo, GL
;
Chang, EY
;
Yang, TY
;
Tseng, HC
The properties of nickel silicide formed by depositing nickel on Si/P+ - Si1-xGex layer are compared with that of nickel germanosilicide on P+ - Si1-xGex layer formed by depositing Ni directly on P+ - Si1-xGex layer without silicon consuming layer. After thermal annealing, nickel silicide on Si/P+ S Si1-xGex layer shows lower sheet resistance and specific contact resistivity than that of nickel germanosilicide on P+ - Si1-xGex layer. In addition, small junction leakage current is also observed for nickel silicide on Si/P+ - Si1-xGex/N - Si diode. In summary, witha Si consuming layer on top of the Si1-xGex, the nickel silicide contact formed demonstrated improved electrical and materials characteristics as compared with the nickel germanosilicide contact which was formed directly on Si1-xGex layer.
A hybrid star-ring architecture for fiber Bragg grating sensor system
(2003-09-01)
Peng, PC
;
Tseng, HY
;
Chi, S
;
光電工程學系
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Department of Photonics
In this letter, we present a hybrid star-ring architecture for a highly reliable fiber Bragg grating (FBG) sensor system and demonstrate its effectiveness. The main trunk of the proposed sensor network is star topology and the sensing branches comprise a series of concatenated ring subnets. The weakness in reliability of the star network is overcome by the ring subnets with a self-healing function based on the reconfigurable optical switches between each subnet. To enhance the signal-to-noise ratio (SNR) of the sensor system, we adopt a linear-cavity FBG laser scheme to construct our proposed hybrid star-ring architecture. Such a fiber-laser scheme results in the SNR over 48 dB for the sensor network. The network survivability of a ten-point FBG sensor is experimentally examined. It is shown that the proposed FBG sensor system can increase the reliability of a sensing network.
Wafer bonding by Ni-induced crystallization of amorphous silicon
(2003-09-01)
Chao, CP
;
Wu, YCS
;
Lee, TL
;
Wang, YH
;
材料科學與工程學系
Wafer bonding by Ni-induced crystallization of amorphous silicon was investigated. It was found that wafers can be bonded through the crystallization of amorphous silicon at temperatures below 550 degreesC. Moreover, when 250 V was applied across the stacked samples, the bonding temperatures could be decreased to as low as 350 degreesC.