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Design of a power-spectrum-based ATM connection admission controller for multimedia communications
(1998-02-01)
Chang, CJ
;
Lin, CH
;
Guan, DS
;
Cheng, RG
;
電信工程研究所
This paper proposes a power-spectrum-based connection admission controller design in asynchronous transfer mode (ATM) switches for multimedia communications, The controller contains a power-spectrum-indexed table for managing multimedia call requests, where traffic characteristics of call requests are described by the power spectrum, The power spectrum can be obtained from the claimed traffic parameters of peak rate, mean rate, and peak rate duration; the pow er spectrum has been shown to have a dominant effect on system performance, The results show that the proposed power-spectrum-based connection admission control method achieves higher system utilization and lower call-blocking probability than the equivalent-capacity allocation method.
A combined channel assignment mechanism for hierarchical cellular systems
(1998-09-01)
Lo, KR
;
Chang, CJ
;
Chang, C
;
Shung, CB
;
電子工程學系及電子研究所
This paper proposes a combined channel assignment (CCA) mechanism for hierarchical cellular systems with overlaying macrocells and overlaid microcells. The proposed CCA mechanism combines overflow, underflow, and reversible schemes, where new or handoff calls having no available channel to use in the overlaid microcell can overflow to use free channels in the overlaying macrocell, handoff calls from a neighboring macrocell can underflow to use free channels in the overlaid microcell, and handoff attempts from a macrocell-only region to an overlaid microcell can be reversed to use free channels in the microcell. We apply the CCA mechanism in two different hierarchical cellular systems of Strip type and Manhattan type and compare the CCA with the overflow channel assignment (OCA) scheme. Simulation results show that the CCA mechanism outperforms the OCA scheme by once in forced termination probability, by several times in new call blocking probability, and by 4.7% in system utilization for a hierarchical cellular system, and the CCA mechanism is more suitable for the Manhattan type than for the Strip type. (C) 1998 Elsevier Science B.V.
A QoS-provisioning neural fuzzy connection admission controller for multimedia high-speed networks
(1999-02-01)
Cheng, RG
;
Chang, CJ
;
Lin, LF
;
電信工程研究所
;
電信研究中心
This paper proposes a neural fuzzy approach for connection admission control (CAC) with QoS guarantee in multimedia high-speed networks. Fuzzy logic systems have been successfully applied to deal with traffic-control-related problems and have provided a robust mathematical framework for dealing with real-world imprecision. However, there is no clear and general technique to map domain knowledge on traffic control onto the parameters of a fuzzy logic system. Neural networks have learning and adaptive capabilities that can be used to construct intelligent computational algorithms for traffic control. However, the knowledge embodied in conventional methods is difficult to incorporate into the design of neural networks. The proposed neural fuzzy connection admission control (NFCAC) scheme is an integrated method that combines the linguistic control capabilities of a fuzzy logic controller and the learning abilities of a neural network. It is an intelligent implementation so that it can provide a robust framework to mimic experts' knowledge embodied in existing traffic control techniques and can construct efficient computational algorithms for traffic control. We properly choose input variables and design the rule structure for the NFCAC controller so that it can have robust operation even under dynamic environments. Simulation results show that compared with a conventional effective-bandwidth-based CAC, a fuzzy-logic-based CAC, and a neural-net-based CAC, the proposed NFCAC can achieve superior system utilization, high learning speed, and simple design procedure, while keeping the QoS contract.
Effect of the sensitizer on the properties of fully functionalized photorefractive epoxy polymers and their performance in the hologram image storage
(1999-06-01)
Chang, CJ
;
Whang, WT
;
Hsu, KY
;
Hsieh, ML
;
材料科學與工程學系
The 3-amino-9-ethyl carbazole (AEC)/Dispersed Orange 3 (DO3)/diglycidyl 1,2 cyclohexanedicarboxylate (DCD) main chain copolymers are synthesized and studied on their photorefractive (PR), photoconductive, and holographic characteristics. They are good hologram recording media because not only the stored hologram exhibits excellent fringe contrast with the resolution at about 20 mu m, but also the image can be stored, erased, and overwritten. The UV/Vis spectra shows that AEC segments may form charge transfer complexes with either DO3 segments or TNF sensitizers. By incorporating the sensitizer or increasing the charge transfer component concentration, the grating growth rate can be speeded up. Applying an electric field on the polymer film containing no sensitizer helps to elevate the grating growth speed, but it shows little influence on the grating growth speed of the films with sensitizers. More nonlinear optical (NLO) segments in the copolymer result in higher diffraction efficiency. The dark decay of the film depends on the dark conductivity. Incorporating sensitizers or more charge transport segments leads to more dark decay because of increasing dark conductivity. The dark decay of the PR properties at elevated temperature can also be evaluated by the thermal stimulated discharge current (TSDC) spectroscopy technique. (C) 1999 John Wiley & Sons, Inc.
Analysis of a hierarchical cellular system with reneging and dropping for waiting new and handoff calls
(1999-07-01)
Chang, C
;
Chang, CJ
;
Lo, KR
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we analyze a hierarchical cellular system with finite queues for new and handoff calls. Both the effect of the reneging of waiting new calls because of the callers' impatience and the effect of the dropping of queued handoff calls as the callers move out of the handoff area are considered, besides the effect of guard channel scheme. We successfully solve the system by adopting the multidimensional Markovian chain and using the transition-probability matrix and the signal-flow graph to obtain the average new-call blocking probability, the forced termination probability, and the average waiting time of queued new and handoff caps. We further investigate how the design parameters of buffer sizes and guard channel numbers in macrocell and microcells affect the performance of the hierarchical cellular system. The results show that provision of buffering scheme and guard channel scheme can effectively reduce the new-call blocking probability and the forced termination probability in the hierarchical cellular system, and the effectiveness is more significant in the macrocell than in the microcells.
Analysis of a general limited scheduling mechanism for a distributed communication system
(1999-08-17)
Hwang, LC
;
Chang, CJ
;
電信工程研究所
;
電信研究中心
;
Institute of Communications Engineering
This paper studies an alternative scheduling mechanism of general limited service discipline for a distributed communication system, where the distributed system has a modular architecture and the module has tasks in the queue. We successfully analyze the system by way of imbedded Markov chains acid use a recursive method to derive the mean waiting time of task. The arrival processes for modules are assumed to be Poisson processes; the service time of a task in queues and the walking time between queues are assumed to be generally distributed. We also presents an optimal-pattern design of the general limited scheduling mechanism for the distributed communication system via a genetic algorithm. A distributed communication system, if designed with the general limited scheduling mechanism and its optimal pattern, can be flexible to meet the system requirements as much as possible. (C) 1999 Elsevier Science B.V. All rights reserved.
Synthesis and relationships between the nonlinear optical and holographic properties of dual functional azocarbazole chromophores based on photorefractive polymers
(1999-08-24)
Chang, CJ
;
Whang, WT
;
Hsu, CC
;
Ding, ZY
;
Hsu, KY
Two kinds of dual functional carbazole-based chromophores are synthesized to enhance the photorefractive (PR) performance of the polymers by attaching the electron-donating and electron-accepting groups with a diazo bridge on the 3- and 6-positions of the N-ethylcarbazole. The electron-donating group is N,N-diethanol aminophenyl. The electron-accepting group is either p-nitrophenyl or 5-nitrothiazole. The peak maximum of the UV/vis absorption spectra of the 5-nitrothiazole-containing chromophore PANTAC at 535 nm is longer than that of the p-nitrophenyl-containing PANPAC at 477 nm. Both chromophores exhibit a large first hyperpolarizability in the hyper-Rayleigh scattering experiment due to the extended chain length. The first hyperpolarizability of PANTAC is 1100 x 10(-30) esu, almost the double of that of PANPAC (590 x 10(-30) esu). The diffraction efficiencies of both polymers are the function of the film thickness and the laser beam wavelength with a maximum eta(max) at a thickness d(max) between 15 and 23 mu m Surprisingly, the PANPAC-based PR polymer reveals a higher maximum diffraction efficiency (eta(max)) and better fringe of the stored holograms than the PANTAC-based PR polymer does. Both the PR polymers written/read by the green/red laser have greater eta(max) values than those written/read by the green/green laser. These phenomena are related to the balance between absorption and transmission of the laser beam through the PR polymer.
Fuzzy/neural congestion control for integrated voice and data DS-CDMA/FRMA cellular networks
(2000-02-01)
Chang, CJ
;
Chen, BW
;
Liu, TY
;
Ren, FC
;
電信工程研究所
The paper proposes congestion control using fuzzy/neural techniques for integrated voice and data direct-sequence code division multiple access/frame reservation multiple access (DS-CDMA/FRMA) cellular networks. The fuzzy/neural congestion controller is constituted by a pipeline recurrent neural network (PRNN) interference predictor, a fuzzy performance indicator, and a fuzzy/neural access probability controller It regulates traffic input to the integrated voice and data DS-CDMA/FRMA cellular system by determining proper access probabilities for users so that congestion can be avoided and throughput can be maximized. Simulation results show that the DS-CDMA/FRMA fuzzy/neural congestion controllers perform better than conventional DS-CDMA/PRMA with channel access function in voice packet dropping ratio, corruption ratio, and utilization. In addition, the neural congestion controller outperforms the fuzzy congestion controller.
A light-induced tunneling state in a submicron double barrier tunneling diode with a center-doped well
(2000-02-01)
Suen, YW
;
Young, CC
;
Chang, CJ
;
Wu, JC
;
Wang, SY
We will present the observation of a light-induced meta-stable impurity state in a submicron center-doped double barrier tunneling diode (DBRTD) manufactured by a novel single-step e-beam lithography process in which no further alignment for the interconnect between the bonding pad and the small active device region is required. We attribute the mete-stable tunneling state, which can be switched by light and high voltage bias, to the light- or field-induced charge redistribution in the active tunneling region. (C) 2000 Elsevier Science B.V. All rights reserved.
A QoS-guaranteed fuzzy channel allocation controller for hierarchical cellular systems
(2000-09-01)
Lo, KR
;
Chang, CJ
;
Chang, C
;
Shung, CB
;
電信工程研究所
This paper proposes a fuzzy channel allocation controller (FCAC) for hierarchical cellular systems. The FCAC mainly contains a fuzzy channel allocation processor (FCAP) which is designed to be in a two-layer architecture that consists of a fuzzy admission threshold estimator in the first layer and a fuzzy channel allocator in the second layer. The FCAP chooses the handoff failure probability, defined as quality-of-service (QoS) index, and the resource availability as input linguistic variables for the fuzzy admission threshold estimator, where the Sugeno's position gradient-type reasoning method is applied to adaptively adjust the admission threshold for the fuzzy channel allocator. And the FCAP takes the mobility of user, the channel utilization, and the resource availability as input variables for the fuzzy channel allocator so that the channel allocation is finally determined, further based upon the admission threshold. Simulation results show that FCAC can always guarantee the QoS requirement of handoff failure probability for all traffic loads, Also it improves the system utilization by 31.2% while it increases the handoff rate by 12.9% over the overflow channel allocation (OCA) scheme [7]; it enhances the system utilization by 6% and still reduces the handoff rate by 6.7% as compared to the combined channel allocation (CCA) scheme [10], under a defined QoS constraint.

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