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Workload and Capacity Optimization for Cloud-Edge Computing Systems with Vertical and Horizontal Offloading
(2020-03-01)
Thai, Minh-Tuan
;
Lin, Ying-Dar
;
Lai, Yuan-Cheng
;
Chien, Hsu-Tung
;
交大名義發表
A collaborative integration between cloud and edge computing is proposed to be able to exploit the advantages of both technologies. However, most of the existing studies have only considered two-tier cloud-edge computing systems which merely support vertical offloading between local edge nodes and remote cloud servers. This paper thus proposes a generic architecture of cloud-edge computing with the aim of providing both vertical and horizontal offloading between service nodes. To investigate the effectiveness of the design for different operational scenarios, we formulate it as a workload and capacity optimization problem with the objective of minimizing the system computation and communication costs. Because such a mixed-integer nonlinear programming (MINLP) problem is NP-hard, we further develop an approximation algorithm which applies a branch-and-bound method to obtain optimal solutions iteratively. Experimental results show that such a cloud-edge computing architecture can significantly reduce total system costs by about 34%, compared to traditional designs which only support vertical offloading. Our results also indicate that, to accommodate the same number of input workloads, a heterogeneous service allocation scenario requires about a 23% higher system costs than a homogeneous scenario.
End-to-End Slicing With Optimized Communication and Computing Resource Allocation in Multi-Tenant 5G Systems
(2020-02-01)
Chien, Hsu-Tung
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Lin, Ying-Dar
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Lai, Chia-Lin
;
Wang, Chien-Ting
;
交大名義發表
Slicing is a key technology in 5G networks to provide scalability and flexibility in allocating computing and communication resources among multiple tenants. Typically, 5G networks have a 2-tier architecture consisting of a central office and transport network in the upper tier and a multi-access edge and radio access network in the lower tier. The tenants which share the 2-tier architecture typically have different service-dependent resource requirements. This study proposes an algorithm, designated as Upper-tier First with Latency-bounded Over-provisioning Prevention (UFLOP), to adjust the capacity and traffic allocation in such a way as to minimize the "over-provisioning ratio" while still satisfying the latency constraints and Service Level Agreements (SLAs) of the tenants. The performance of UFLOP is evaluated experimentally with a real testbed on an end-to-end slicing framework using three typical 5G services, namely Enhanced Mobile Broadband (eMBB), Ultra-Reliable Low Latency (URLLC), and massive Machine Type Connection (mMTC). It is shown that UFLOP successfully determines the critical traffic allocation ratio between the central office and the edge which achieves an over-provisioning ratio close to zero while still meeting the latency requirements. The results suggest optimal resource allocation ratios of 10:0, 1.5:8.5 and 7.8:2.2 for the eMBB, URLLC and mMTC applications, respectively. Furthermore, it is shown that the computing resource behaves as a bottleneck for the eMBB and mMTC services, while the communication resource serves as a bottleneck for the URLLC service.
Flood hazard mitigation in land subsidence prone coastal areas by optimal groundwater pumping
(2019-11-01)
Chang, Yin-Lung
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Tsai, Tung-Lin
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Yang, Jinn-Chuang
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土木工程學系
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防災與水環境研究中心
Continuing land subsidence can aggravate flood hazard and diminish the effectiveness of existing flood mitigation systems. This paper presents a study of groundwater- pumping management for mitigating flood hazard in a subsidence infested area in the southwest coast of Taiwan. An optimal groundwater-pumping model is developed for preventing flood hazard from worsening and for satisfying the groundwater demand. In an area where the land is susceptible to pumping-induced subsidence, the study shows that proper long-term pumping strategy to manage spatial-temporal variation of future land subsidence should be an integral part of flood risk management as it can sustain the effectiveness of the flood mitigation measures.
A Multi-Level Optimization Method for Elastic Constants Identification of Composite Laminates
(2019-10-01)
Huang, Chien Yang
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Kam, Tai Yan
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機械工程學系
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Department of Mechanical Engineering
Featured Application Material testing for elastic constants determination. Abstract A new and effective elastic constants identification technique is presented to extract the elastic constants of a composite laminate subjected to uniaxial tensile testing. The proposed technique consists of a new multi-level optimization method that can solve different types of minimization problems, including the extraction of material constants of composite laminates from given strains. In the identification process, the optimization problem is solved by using a stochastic multi-start dynamic search minimization algorithm at the first level in order to obtain the statistics of the quasi-optimal design variables for a set of randomly generated starting points. The statistics of the quasi-optimal elastic constants obtained at this level are used to determine the reduced feasible region in order to formulate the second-level optimization problem. The second-level optimization problem is then solved using the particle swarm algorithm in order to obtain the statistics of the new quasi-optimal elastic constants. The iteration process between the first and second levels of optimization continues until the standard deviations of the quasi-optimal design variables at any level of optimization are less than the prescribed values. The proposed multi-level optimization method, as well as several existing global optimization algorithms, is used to solve a number of well-known mathematical minimization problems to verify the accuracy of the method. For the adopted numerical examples, it has been shown that the proposed method is more efficient and effective than the adopted global minimization algorithms to produce the exact solutions. The proposed method is then applied to identify four elastic constants of a [0 degrees/+/- 45 degrees](s) composite laminate using three strains in 0 degrees, 45 degrees, and 90 degrees directions, respectively, of the composite laminate subjected to uniaxial testing. For comparison purposes, several existing global minimization techniques are also used to solve the elastic constants identification problem. Again, it has been shown that the proposed method is capable of producing more accurate results than the adopted available methods. Finally, experimental data are used to demonstrate the applications of the proposed method.
Investigation of the Impact of Drive Current and Phosphor Thickness on the Reliability of High Power White LED Lamp
(2019-06-01)
Singh, Preetpal
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Tan, Cher Ming
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Zhao, Wenyu
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Kuo, Hao Chung
;
交大名義發表
Lumen flux of white light-emitting diodes (LEDs) can be increased by increasing phosphor layer thickness and blue LED's drive current. Higher LED currents will lead to an increase in blue light in the output lumen along with higher temperatures which is not acceptable, and a corresponding decrease in the yellow light emission. The physical reason for this decrease is attributed to the finite phosphor particles in the layer and re-emission occurring due to scattered or back reflected blue light rays. A parameter called blue to yellow ratio (BYR) is used which can lead to a current with maximum phosphor utilization while preventing the LED output color to shift from white toward blue. As the degree of impact on reliability from drive current and thickness is different, a careful adjustment of the drive current and phosphor layer thickness shall be made for a given lumen. Response surface method is employed to obtain an optimal combination of the current and thickness where the temperature is the minimum for a given lumen level. The temperature difference for different combinations of current and thickness for a given lumen can be as high as 15 degrees C as found in this paper.
Coding optimization for the absolute optical rotary encoder
(2018-01-01)
Wang, Ting-Feng
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Yan, Yung-Jhe
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Chiang, Hou-Chi
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Chen, Tsan Lin
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Ou-Yang, Mang
Precise positioning system is assuming increasing importance. One of Implementation is an optical rotary encoder system which is composed of a fixed light source, a group of photodetectors, and a coding disc. In fact, position resolution is affected with a permutation of coding on the disc. Unstable dc voltage was found from an analog signal transmitted by photoelectric detectors. Setting up a threshold voltage for digital binariz ation become difficult in this case. In this paper, the limitations, characteristics and operation mode of coding on the disc operation mode arrangement rules of coding on the disc was observed. After collecting the relevant literature, the mathematical sequence named De Bruijn sequence which matches to the arrangement of the above rules and restrictions was found. The desired requirements are summarized and used to filter out the best solution in all solution sets with the designed algorithm. Finally, the characteristics of new and old solutions are compared and discussed.
A two-level optimization procedure for material characterization of composites using two symmetric angle-ply beams
(2007-10-01)
Chen, C. M.
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Kam, T. Y.
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機械工程學系
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Department of Mechanical Engineering
A two-level optimization procedure for determining elastic constants E-1, E-2, G(12), and v(12) of laminated composite materials using measured axial and lateral strains of two symmetric angle-ply beams with different fiber angles subjected to three-point-bending testing is presented. In the first-level optimization process, the theoretically and experimentally predicted axial and lateral strains of a [(45 degrees/-45 degrees)(6)](s) beam are used to construct the strain discrepancy function which is a measure of the sum of the squared differences between the experimental and theoretical predictions of the axial and lateral strains. The identification of the material constants is then formulated as a constrained minimization problem in which the best estimates of shear modulus and Poisson's ratio of the beam are determined to make the strain discrepancy function a global minimum. In the second-level optimization process, shear modulus and Poisson's ratio determined in the first level of optimization are kept constant and Young's moduli of the second angle-ply beam with fiber angles different from 45 degrees are identified by minimizing the strain discrepancy function established t this level of optimization. The suitability of the proposed procedure for material characterization of composite materials has been demonstrated by means of a number of examples. (c) 2007 Elsevier Ltd. All rights reserved.
A raster-based C program for siting a landfill with optimal compactness
(1996-10-01)
Kao, JJ
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環境工程研究所
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Institute of Environmental Engineering
Landfill siting requires performing spatial analyses for various factors to evaluate site suitability. A geographical information system, although capable of effectively manipulating spatial data, lacks the capability to locate an optimal site when compactness and other factors are considered simultaneously. In our previous work, a mixed-integer compactness model was proposed to overcome this difficulty. However, computational time with a conventional mixed-integer programming package for solving the model is time consuming and impractical. Therefore, in this work, a C program is developed, based on a proposed raster-based branch-and-bound algorithm. The program can implement multi-factor analyses for compactness and other siting factors with weights prespecified by the user. An example is provided to demonstrate the effectiveness of the program. Copyright (C) 1996 Elsevier Science Ltd
Toward Optimal Resource Allocation of Virtualized Network Functions for Hierarchical Datacenters
(2018-12-01)
Wang, Chih-Chiang
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Lin, Ying-Dar
;
Wu, Jang-Jiin
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Lin, Po-Ching
;
Hwang, Ren-Hung
Telecommunications service providers (TSPs) previously provided network functions to end users with dedicated hardware, but they are resorting to virtualized infrastructure for reducing costs and increasing flexibility in resource allocation. A representative case is the Central Office Re-architected as Datacenter (CORD) project from AT&T, which aims to deploy virtualized network functions (VNFs) to over 4000 central offices (COs) across the U.S. However, there is a wide spectrum of options for deploying VNFs over the COs, varying from highly distributed to highly centralized manners. The former benefits end users with short response time but has its inherent limitation on utilizing geographically dispersed resources, while the latter allows resources to be better utilized at a cost of longer response time. In this work, we model the TSP's virtualized infrastructure as hierarchical datacenters, namely hierarchical CORD, and provide a resource allocation solution to strike the optimal balance between the two extreme options. Our evaluations reveal that in general, the 3-tier architecture incurs the least cost in case of deploying VNFs under moderate or loose delay constraints. Furthermore, the margin of improvement on the resource allocation cost increases inversely with the overall system utilization rate. Our results also suggest that as heavy request load overwhelms the network infrastructure, the relevant VNFs shall be migrated to lower-tier edge datacenters or to some nearby datacenters with superior network capacity. The evaluations also demonstrate that the proposed model allows highly adaptive VNF deployment in the hierarchical architecture under various conditions.
Optimal Power Control and Beamforming for Full-Duplex Small Cell Wireless Networks
(2017-01-01)
Gau, Rung-Hung
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Xiao, Zh-Hong
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Yuan, Tseng-Lung
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電信工程研究所
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Institute of Communications Engineering
In this paper, we propose an optimization framework for selecting an optimal downlink beamforming vector and an optimal uplink transmission power level in full-duplex small cell wireless networks. We study the case in which the full-duplex base station is equipped with multiple antennas and each half-duplex UE is equipped with a single antenna. To benefit from recent progresses in all-digital self-interference cancellation, we formulate an optimization problem to achieve optimal beamforming and power control. Since the studied optimization problem is not convex, we first choose the optimal direction for the beamforming vector. Next, we adopt difference of concave programming to obtain the optimal magnitude of the beamforming vector and the optimal uplink transmission power level. Simulation results show that the proposed approach could significantly improve the performance of small cell wireless networks, especially when the residual self-interference is small.

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