National Cheng Kung University

About: National Cheng Kung University is a education organization based out in Tainan City, Taiwan. It is known for research contribution in the topics: Population & Thin film. The organization has 49723 authors who have published 69799 publications receiving 1437420 citations. The organization is also known as: NCKU.

M2M Communications in 3GPP LTE/LTE-A Networks: Architectures, Service Requirements, Challenges, and Applications

Abstract: Machine-to-machine (M2M) communication is an emerging technology to provide ubiquitous connectivity among devices without human intervention. The cellular networks are considered a ready-to-use infrastructure to implement M2M communications. However, M2M communications over cellular pose significant challenges to cellular networks due to different data transactions, diverse applications, and a large number of connections. To support such a large number of devices, M2M system architecture should be extremely power and spectrum efficient. In this paper, we provide a comprehensive survey on M2M communications in the context of the Third-Generation Partnership Project (3GPP) Long-Term Evolution (LTE) and Long-Term Evolution-Advanced (LTE-A). More specifically, this paper presents architectural enhancements for providing M2M services in 3GPP LTE/LTE-A networks and reviews the features and requirements of M2M applications. In addition, the signal overheads and various quality-of-service (QoS) requirements in M2M communications also deserve our attention. We address M2M challenges over 3GPP LTE/LTE-A and also identify the issues on diverse random access overload control to avoid congestion caused by random channel access of M2M devices. Different application scenarios are considered to illustrate futuristic M2M applications. Finally, we present possible enabling technologies and point out the directions for M2M communications research.

Novel High Step-Up DC–DC Converter for Fuel Cell Energy Conversion System

Abstract: A novel high step-up dc-dc converter for fuel cell energy conversion is presented in this paper. The proposed converter utilizes a multiwinding coupled inductor and a voltage doubler to achieve high step-up voltage gain. The voltage on the active switch is clamped, and the energy stored in the leakage inductor is recycled. Therefore, the voltage stress on the active switch is reduced, and the conversion efficiency is improved. Finally, a 750-W laboratory prototype converter supplied by a proton exchange membrane fuel cell power source and an output voltage of 400 V is implemented. The experimental results verify the performances, including high voltage gain, high conversion efficiency, and the effective suppression of the voltage stress on power devices. The proposed high step-up converter can feasibly be used for low-input-voltage fuel cell power conversion applications.

Combination voltage-controlled and current-controlled PWM inverters for UPS parallel operation

Abstract: In this paper, a scheme of combination of voltage-controlled and current-controlled PWM inverters for parallel operation of a single-phase uninterruptible power supply (UPS) is proposed. The voltage-controlled PWM inverter (VCPI) unit as a master is developed to keep a constant sinusoidal wave output voltage. The current-controlled PWM inverter (CCPI) units are operated as slave controlled to track the distributive current. The power distribution center (PDC) performs the function of distributing the output current of each active unit. In this proposed scheme of parallel operation, each of the units can be designed as nearly independent, and the CCPI units do not need a PLL circuit for synchronization. As a result, the parallel operation of UPS is easy to implement and to expand system capacity. For the purpose of illustration, the system, including three single-phase units which operate in parallel, is analyzed and experimental results are given. >

International r&d spillovers: an application of estimation and inference in panel cointegration

Abstract: In this paper, we consider the application of recent results on the estimation and inference in panel cointegration to the study of empirical economic growth. The emergence of endogenous growth theory in the 1980s has led to a resurgence of interest in the sources of economic growth. Coe and Helpman (1995), among other researchers, state that commercially oriented innovation efforts which respond to economic incentives are the major engine of technological progress and productivity growth. Coe and Helpman argue that, in a global economy, a country’s productivity depends on its own R&D efforts as well as the R&D efforts of its trading partners. Using data from 21 OECD countries plus Israel during 1971-1990, they find that both domestic and foreign R&D capital stocks have important effects on total factor productivity (TFP). We intend to re-examine the econometric foundation of Coe and Helpman’s paper. Coe and Helpman (1995) discovered that all of their data exhibit a clear trend, and unit root tests on these data indicate that the TFP and both the domestic and foreign R&D capital stocks are non-stationary. They then confirm the presence of cointegration for TFP and the domestic and foreign R&D capital stocks by testing for a unit root in the residuals. In other words, although all the variables are individually non-stationary, there exists a linear combination of these variables so that the regression containing these variables has a stationary error term. Coe and Helpman’s use of a cointegrating regression enables us to exploit the relationship among the variables in levels, without transforming the data, such as differencing, to avoid the spurious regression problem. Unfortunately, at the time of their article the econometrics of panel cointegra