Browsing by Author "Yang, WH"

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Designing authentication protocols for third generation mobile communication systems
(2005-03-01)
Cheng, SM
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Shieh, SP
;
Yang, WH
;
Lee, FY
;
Luo, JN
Security is considered an important issue for mobile communication systems. In particular, the design of authentication mechanisms has received considerable research interest recently. However, most of the current authentication schemes for mobile systems only have simple security functions and usually have some weaknesses, such as leakage of user identities and high update overhead of temporary identities. Moreover, these schemes cannot fulfill the security requirements specified in third generation mobile systems (IMT-2000, UMTS). In this paper, we propose a secure and flexible authentication framework for mobile communication systems. In the proposed framework, service providers can dynamically choose authentication mechanisms without the cooperation of network operators in visited domains. Based on the new framework, a secure authentication protocol is proposed. The proposed protocol can satisfy the security requirements of third generation mobile systems and is secure against network attacks, such as the replay attack and substitution attack. In short, our approach is secure and practical such that it can satisfy the security requirements of third generation mobile communication systems.
Environment-adaptation mobile radio propagation prediction using radial basis function neural networks
(1997-02-01)
Chang, PR
;
Yang, WH
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交大名義發表
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電信工程研究所
;
National Chiao Tung University
This paper investigates the application of a radial basis function (RBF) neural network to the prediction of Field strength based on topographical and morphographical data, The RBF neural network Is a two-layer localized receptive field network whose output nodes from a combination of radial activation functions computed by the hidden layer nodes. Appropriate centers and connection weights in the RBF network lead to a network that is capable of forming the best approximation to any continuous nonlinear mapping up to an arbitrary resolution. Such an approximation introduces best nonlinear approximation capability into the prediction model in order to accurately predict propagation loss over an arbitrary environment based on adaptive learning from measurement data, The adaptive learning employs hybrid competitive and recursive least squares algorithms, The unsupervised competitive algorithm adjusts the centers while the recursive least squares (RLS) algorithm estimates the connection weights. Because these two learning rules are both linear, rapid convergence is guaranteed. This hybrid algorithm significantly enhances the real-time or adaptive capability of the RBF-based prediction model, The applications to Okumura's data are included to demonstrate the effectiveness of the RBF neural network approach.
Low threshold and high power output of a diode-pumped nonlinear mirror mode-locked Nd : GdVO4 laser
(2005-08-22)
Lin, JH
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Yang, WH
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Hsieh, WF
;
Lin, KH
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光電工程學系
We demonstrated nonlinear mirror mode-locking of a diode-pumped Nd:GdVO4 laser by using a 10 mm long KTP crystal. The stable CW mode locking can be reached with the relative low threshold pump power as low as 2.3W. The highest output power of 2.65W at the 10W pump powers are generated with the 121-MHz repetition rate of pulses. It confirms the excellent laser performance of the Nd: GdVO4 for high-peak power of the pulse operation. (c) 2005 Optical Society of America.
Nonlinear mirror mode-locked Nd : GdVO4 laser with splitting double pulses
(2005)
Lin, JH
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Yang, WH
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Hsieh, WF
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光電工程學系
;
Department of Photonics
We report on passive mode-locking of a cw diode-pumped Nd:GdVO4 laser using the nonlinear mirror technique. The nonlinear mirror is made by a KTP frequency doubling crystal and a dichroic mirror that partially transmits the fundamental frequency and totally reflects the second harmonic. In addition, the nanosecond splitting double-pulses are first time observed in the NLM locked picosecond laser.
Password authentication schemes with smart cards
(1999)
Yang, WH
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Shieh, SP
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資訊工程學系
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Department of Computer Science
In this paper, two password authentication schemes with smart cards are proposed. In the schemes, users can change their pass-words freely, and the remote system does nor need the directory of passwords or verification tables to authenticate users. Once the secure network environment is see up, authentication can be handled solely by the two parries involved. For a network without synchronized clocks, the proposed nonce-based authentication scheme is able to prevent malicious reply attacks.
Programmable switched-capacitor neural network for MVDR beamforming
(1996-01-01)
Yang, WH
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Chang, PR
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
In this paper, a real-time adaptive antenna array based on a neural network approach is presented, Since an array operating in a nonstationary environment requires a programmable synaptic weight matrix for the neural network, the switched-capacitor (SC) circuits with the capability of programmability and reconfigurability is conducted to implement the neural-based adaptive array. Moreover, the SC techniques can directly implement the neural network with less chip area and provide the ratio of SC-equivalent resistors with accuracy of 0.1 percent. Programming of the switched-capacitor values could be made by allocating each synaptic weight to a set of parallel capacitors with values in a digitally programmable capacitor array (PCA), A relatively wide range of values (5 to 10 binary bits resolution) can be realized for each synaptic weight. A simulation tool called SWITCAP is used to verify the validity and performance of the proposed implementation, Experimental results show that the computation time of solving a linear array of 5 elements is about 0.1 ns for 1 ns time constant and is independent of signal power levels.
Protecting network users in mobile code systems
(2004-02-01)
Shieh, SP
;
Yang, WH
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資訊工程學系
;
Department of Computer Science
Conventional access control mechanisms are rather insensitive to occurrences of context-dependent illegal accesses. Insensitivity to context-dependent accesses may lead to failure to protect network users and resources. Context-dependent illegal accesses resulting from data and privilege flows in open networks cannot be prevented by either authentication or access control mechanisms since unauthorized access need not be attempted. In this paper we present a protection model which tracks data and privilege flows in mobile code systems. It can uniformly define various types of illegal access patterns and has the advantage of preventing context-dependent illegal accesses such as those caused by inadvertent execution of remote mobile code containing viruses or Trojan Horses. The proposed flow control model is expected to complement the conventional model for access control. (C) 2003 Elsevier Inc. All rights reserved.