Browsing by Author "Chang, Hung-Cheng"

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A Study on Factors Affecting Airborne LiDAR Penetration
(2015-04-01)
Hsu, Wei-Chen
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Shih, Peter Tian-Yuan
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Chang, Hung-Cheng
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Liu, Jin-King
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土木工程學系
This study uses data from different periods, areas and parameters of airborne LiDAR (light detection and ranging) surveys to understand the factors that influence airborne LiDAR penetration rate. A discussion is presented on the relationships between these factors and LiDAR penetration rate. The results show that the flight height above ground level (AGL) does not have any relationship with the penetration rate. There are some factors that should have larger influence. For example, the laser is affected by a wet ground surface by reducing the number of return echoes. The field of view (FOV) has a slightly negative correlation with the penetration rate, which indicates that the laser incidence angle close to zero should achieve the best penetration. The vegetation cover rate also shows a negative correlation with the penetration rate, thus bare ground and reduced vegetation in the aftermath of a typhoon also cause high penetration rate. More return echoes could be extracted from the full-waveform system, thereby effectively improving the penetration rate. This study shows that full-waveform LiDAR is an effective method for increasing the number of surface reflected echoes. This study suggests avoiding LiDAR survey employment directly following precipitation to prevent laser echo reduction.
Application Performance Profiling in Android Dalvik Virtual Machines
(2016-05-01)
Chang, Hung-Cheng
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Chang, Kuei-Chung
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Lin, Ying-Dar
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Lai, Yuan-Cheng
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資訊工程學系
Most Android applications are written in JAVA and run on a Dalvik virtual machine. For smartphone vendors and users who wish to know the performance of an application on a particular smartphone but cannot obtain the source code, we propose a new technique, Dalvik Profiler for Applications (DPA), to profile an Android application on a Dalvik virtual machine without the support of source code. Within a Dalvik virtual machine, we determine the entry and exit locations of a method, log its execution time, and analyze the log to determine the performance of the application. Our experimental results show an error ratio of less than 5% from the baseline tool Traceview which instruments source code. The results also show some interesting behaviors of applications and smartphones: the performance of some smartphones with higher hardware specifications is 1.5 times less than the phones with lower specifications. DPA is now publicly available as an open source tool.
Empirical Experience and Experimental Evaluation of Open5GCore over Hypervisor and Container
(2018-01-01)
Chang, Hung-Cheng
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Qiu, Bo-Jun
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Chen, Jyh-Cheng
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Tan, Tze-Jie
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Ho, Ping-Fan
One of the most important technologies for future 5G networks is to utilize Network Function Virtualization (NFV) to virtualize the network components. NFV provides flexibility, short time to market, and low cost solution to build network services, which are important features of 5G networks. Although the idea of virtualization is just being applied to cellular networks, it has been used in the community of cloud computing. There are two main virtualization techniques, hypervisor and container. In this paper, we present our practical experience of virtualizing Open5GCore, a commercial product of SDN-enabled Evolved Packet Core (EPC), over hypervisor and container. In addition to describing how to virtualize Open5GCore, we also present the experimental performance evaluation of the systems. Finally, some important lessons learned are provided.
Observing Land Subsidence and Revealing the Factors That Influence It Using a Multi-Sensor Approach in Yunlin County, Taiwan
(2015-06-01)
Hsu, Wei-Chen
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Chang, Hung-Cheng
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Chang, Kuan-Tsung
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Lin, En-Kai
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Liu, Jin-King
Land subsidence is a worldwide problem that is typically caused by human activities, primarily the removal of groundwater. In Western Taiwan, groundwater has been pumped for industrial, residential, agricultural, and aquacultural uses for over 40 years. In this study, a multisensor monitoring system comprising GPS stations, leveling surveys, monitoring wells, and Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) was employed to monitor land subsidence in Western Taiwan. The results indicate that land subsidence in Yunlin County was mainly affected by the compaction of subsurface soils and over-pumping of groundwater from deep soils. The study area comprised western foothills, characterized by sediments containing predominantly gravel, and coastal areas, where clay was predominant. The subsidence in coastal areas was more severe than that in the western foothills, as a result of groundwater removal. An additional factor affecting subsidence was the compaction of deep layers caused by deep groundwater removal and the deep-layer compaction was difficult to recover. Based on multisensor monitoring results, severe subsidence is mainly affected by compaction of subsurface soils, over-pumping of groundwater from deep soils, and deep soil compaction.
Performance Evaluation of Open5GCore over KVM and Docker by Using Open5GMTC
(2018-01-01)
Chang, Hung-Cheng
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Qiu, Bo-Jun
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Chiu, Chen-Hao
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Chen, Jyh-Cheng
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Lin, Fuchun Joseph
Virtualizing the EPC (Evolved Packet Core) in modern carrier-grade networks provides more flexible and reliable network services by decoupling dependence on the hardware. Hypervisor and container are two popular virtualization techniques nowadays to enable virtualization of EPC. In this paper, we compared the Open5GCore, a 5G EPC prototype, over KVM and Docker, which are representatives of the hypervisor and container techniques. Moreover, to verify how each supports new services for Internet of Things (IoT) and Machine-to-Machine (M2M) communications, we also analyze the performance of two systems with the IoT and M2M traffic generated by Open5GMTC, a prototype tool for IoT/M2M platforms.