Robust Precoding and Postcoding for Multicell Multiuser Transmission using Imperfect CSI

Nguyen-Le, Hung,Nguyen-Duy-Nhat, Vien,Tang-Tan, Chien,Bao, Vo Nguyen Quoc The Korea Institute of Information and Commucation 2016 Journal of communications and networks Vol.18 No.5

This paper studies the problem of precoding and post-coding design for multicell multiuser downlink transmissions in the absence of perfect channel state information (CSI). Using statistical information of imperfect CSI, an iterative multiuser multicell transceiver design is formulated by minimizing the mean squared error (MSE) cost function of signal and leakage interference under per-base station power constraint (PBPC). The convergence of the iterative precoding and postcoding algorithm is verified by analytical and empirical results. The proposed precoding and postcoding algorithm offers a low computational complexity and robustness against CSI imperfection.

An Improved LEACH Routing Protocol for Energy-Efficiency of Wireless Sensor Networks

Nguyen Duy Tan,Longzhe Han,Nguyen Dinh Viet,Minho Jo 한국산학기술학회 2012 SmartCR Vol.2 No.5

A wireless sensor network (WSN) is a wireless network consisting of a base station (BS) and multiple micro-sensor nodes. The micro-sensor nodes run on batteries that are not recharged during the network’s lifetime. Therefore, prolonging WSN lifetime is a significant problem. There are some energy-efficient hierarchical routing protocols designed especially for WSNs, such as sensor protocols for information negotiation (SPIN), low-energy adaptive clustering hierarchy (LEACH) and LEACH-centralized (LEACH-C). In this article, we propose an improvement on the LEACH routing protocol to decrease energy consumption and prolong network lifetime. LEACHDistance Energy (LEACH-DE) selects a cluster head node not only by considering residual energy of the node greater than the average residual energy level of nodes in network, but also by examining the geometric distance between the candidate node to the BS as a key parameter. The results of simulation show our proposed algorithm outperforms LEACH and LEACH-C in terms of conserving energy and prolonging WSN lifetime.

Robust Precoding and Postcoding for Multicell Multiuser Transmission using Imperfect CSI

Hung Nguyen-Le,Vien Nguyen-Duy-Nhat,Chien Tang-Tan,Vo Nguyen Quoc Bao 한국통신학회 2016 Journal of communications and networks Vol.18 No.5

This paper studies the problem of precoding and post-coding design for multicellmultiuser downlink transmissions in theabsence of perfect channel state information (CSI). Using statisti-cal information of imperfect CSI, an iterative multiuser multicelltransceiver design is formulated by minimizing the mean squarederror (MSE) cost function of signal and leakage interference underper-base station power constraint (PBPC). The convergence of theiterative precoding and postcoding algorithm is verified by analyt-ical and empirical results. The proposed precoding and postcodingalgorithm offers a low computational complexity and robustnessagainst CSI imperfection.

콩과 옥수수 재배적지 평가에서 GIS 와 AHP 방법의 적용 -베트남의 Tien Giang도-

윙위단 ( Nguyen Duy Tan ),김한중 ( Han Joong Kim ) 한국농공학회 2019 한국농공학회 학술대회초록집 Vol.2019 No.-

The purpose of this research is to build a model using Geographic Information System (GIS) and Analytical Hierarchy Process (AHP), to illustrate which areas are suitable for Maize and soybean production in Tien Giang Province, Vietnam. Based on the suitable conditions for growing of soybean and maize, experts’ opinions, previous researches and the available data resources, the criteria to be used for land suitability analysis are soil type, soil depth, mean temperature, relative humidity, precipitation, slope and distance to water source. On the basis of these criteria and using GIS technique single-criterion maps were generated and then the standardization will be conducted to these single-criterion maps through fuzzy membership function. Land suitability analyses were performed by using analytical hierarchical process (AHP) to give a specific weight for each criterion, which represents its relative importance in the suitability evaluation. The weighted linear combination (WLC) will be used to combine the standardized factors and their corresponding weights to obtain an overall suitability map for the cropland. The result of this study is expected to show the suitability ratios of highly, moderately, marginally and not suitable area for maize and soybean. The model is expected to improve the planning, and also assist in accurately recognizing the additional sites for soybean and maize planting in the future.

Key Determinants of Repurchase Intention toward Organic Cosmetics

Phuong Ngoc Duy NGUYEN,Vinh Tan NGUYEN,Nguyen Ngoc Thao VO 한국유통과학회 2019 The Journal of Asian Finance, Economics and Busine Vol.6 No.3

This paper aims to discover factors and their influences degree to repurchase organic cosmetic in Vietnam. In addition, this research also discloses the main segments that have high demand re-buying intention based on demographic groups of gender, age, income, educational level, job, type of products, and place of production. Twenty-eight scale was designed based on previous studies and adjusted to match the 5-point Likert scale to conduct measurement. By using survey method to test hypotheses and set up conceptual models to collect 295 Vietnamese consumers who have experience in consuming organic cosmetic by explain the results through Smart PLS software. The findings show that there is positive attitude of customers to the intention of acquiring organic cosmetics, green perceived and customer satisfaction. In addition, customer satisfaction, knowledge of products, safety values, and environmental protection consciousness also play important roles to form a positive attitude of customers for products. Moreover, the consciousness of green living of consumers accounts for a high proportion in creating customer satisfaction for organic products. The results show useful information for current premises to determine the factors that influence the decision to repurchase organic cosmetic product, that provide business strategies.

What Influences Decision on Seasoned Equity Offerings of Listed Vietnamese Companies?

LE, Long Hau,NGUYEN, Thi Binh Nhi,PHAM, Xuan Quynh,VUONG, Quoc Duy,LE, Tan Nghiem Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.5

This paper investigates the determinants on decision to conduct seasoned equity offerings (SEOs) of listed companies on the Ho Chi Minh Stock Exchange in Vietnam. Seasoned equity offerings (SEOs) are defined as the issue of more stocks by a firm to raise more capital after a primary issue. Using panel data collected from audited financial statements of 99 listed companies on the Ho Chi Minh Stock Exchange during 2014-2018, the study employs a logit regression model by fixed effects method to examine factors that affect the decision to implement seasoned equity offerings of those companies. The findings of this study show that profit, revenue growth and company's size have a positively significant impact on the decision, while dividend pay-out ratio negatively significantly influences the equity issuing decision. Furthermore, these results are robust after controlling for the forms of equity offerings, i.e. bonus stocks, stock dividends and rights to buy shares. These findings are consistent with economic theories such as agency theory, pecking order theory, and growth opportunity theory, and also could be explained by the real situations of the Vietnamese stock exchange. This study has important implications for corporate managers, policy makers and investors.

LED Driver with TRIAC Dimming Control by Variable Switched Capacitance for Power Regulation

Lee, Eun-Soo,Sohn, Yeung-Hoon,Nguyen, Duy Tan,Cheon, Jun-Pil,Rim, Chun-Taek The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.2

A TRIAC dimming LED driver that can control the brightness of LED arrays for a wide range of source voltage variations is proposed in this paper. Unlike conventional PWM LED drivers, the proposed LED driver adopts a TRIAC switch, which inherently guarantees zero current switching and has been proven to be quite reliable over its long lifetime. Unlike previous TRIAC type LED drivers, the proposed LED driver is composed of an LC input filter and a variable switched capacitance, which is modulated by the TRIAC turn-on timing. Thus, the LED power regulation and dimming control, which are done by a volume resistor in the same way as the conventional TRIAC dimmers, can be simultaneously performed by the TRIAC control circuit. Because the proposed LED driver has high efficiency and a long lifetime with a high power factor (PF) and low total harmonic distortion (THD) characteristics, it is quite adequate for industrial lighting applications such as streets, factories, parking garages, and emergency stairs. A simple step-down capacitive power supply circuit composed of passive components only is also proposed, which is quite useful for providing DC power from an AC source without a bulky and heavy transformer. A prototype 60 W LED driver was implemented by the proposed design procedure and verified by simulation and experimental results, where the efficiency, PF, and THD are 92%, 0.94, and 6.3%, respectively. The LED power variation is well mitigated to below ${\pm}2%$ for 190 V < $V_s$ < 250 V by using the proposed simple control circuit.

Long-Lasting and Highly Efficient TRIAC Dimming LED Driver with a Variable Switched Capacitor

Lee, Eun-Soo,Choi, Bo-Hwan,Nguyen, Duy Tan,Choi, Byeung-Guk,Rim, Chun-Taek The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.4

A triode for alternating current (TRIAC) dimming light emitting diode (LED) driver, which adopts a variable switched capacitor for LED dimming and LED power regulation, is proposed in this paper. The proposed LED driver is power efficient, reliable, and long lasting because of the TRIAC switch that serves as its main switch. Similar to previous TRIAC dimmers for lamps, turn-on timing of a TRIAC switch can be controlled by a volume resistor, which modulates the equivalent capacitance of the proposed variable switched capacitor. Thus, LED power regulation against source voltage variation and LED dimming control can be achieved by the proposed LED driver while meeting the global standards for power factor (PF) and total harmonic distortion (THD). The long life and high power efficiency of the proposed LED driver make it appropriate for industrial lighting applications, such as those for streets, factories, parking garages, and emergency stairs. The detailed analysis of the proposed LED driver and its design procedure are presented in this paper. A prototype of 80 W was fabricated and verified by experiments, which showed that the efficiency, PF, and THD at V_s = 220 V are 93.8%, 0.95, and 22.5%, respectively; 65 W of LED dimming control was achieved with the volume resistor, and the LED power variation was well mitigated below 3.75% for 190 V < V_s < 250 V.

Long-Lasting and Highly Efficient TRIAC Dimming LED Driver with a Variable Switched Capacitor

Eun-Soo Lee,Bo-Hwan Choi,Duy Tan Nguyen,Byeung-Guk Choi,Chun-Taek Rim 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.4

A triode for alternating current (TRIAC) dimming light emitting diode (LED) driver, which adopts a variable switched capacitor for LED dimming and LED power regulation, is proposed in this paper. The proposed LED driver is power efficient, reliable, and long lasting because of the TRIAC switch that serves as its main switch. Similar to previous TRIAC dimmers for lamps, turn-on timing of a TRIAC switch can be controlled by a volume resistor, which modulates the equivalent capacitance of the proposed variable switched capacitor. Thus, LED power regulation against source voltage variation and LED dimming control can be achieved by the proposed LED driver while meeting the global standards for power factor (PF) and total harmonic distortion (THD). The long life and high power efficiency of the proposed LED driver make it appropriate for industrial lighting applications, such as those for streets, factories, parking garages, and emergency stairs. The detailed analysis of the proposed LED driver and its design procedure are presented in this paper. A prototype of 80 W was fabricated and verified by experiments, which showed that the efficiency, PF, and THD at Vs = 220 V are 93.8%, 0.95, and 22.5%, respectively; 65 W of LED dimming control was achieved with the volume resistor, and the LED power variation was well mitigated below 3.75% for 190 V < Vs < 250 V.

LED Driver with TRIAC Dimming Control by Variable Switched Capacitance for Power Regulation

Eun-Soo Lee,Yeung-Hoon Sohn,Duy Tan Nguyen,Jun-Pil Cheon,Chun-Taek Rim 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.2

A TRIAC dimming LED driver that can control the brightness of LED arrays for a wide range of source voltage variations is proposed in this paper. Unlike conventional PWM LED drivers, the proposed LED driver adopts a TRIAC switch, which inherently guarantees zero current switching and has been proven to be quite reliable over its long lifetime. Unlike previous TRIAC type LED drivers, the proposed LED driver is composed of an LC input filter and a variable switched capacitance, which is modulated by the TRIAC turn-on timing. Thus, the LED power regulation and dimming control, which are done by a volume resistor in the same way as the conventional TRIAC dimmers, can be simultaneously performed by the TRIAC control circuit. Because the proposed LED driver has high efficiency and a long lifetime with a high power factor (PF) and low total harmonic distortion (THD) characteristics, it is quite adequate for industrial lighting applications such as streets, factories, parking garages, and emergency stairs. A simple step-down capacitive power supply circuit composed of passive components only is also proposed, which is quite useful for providing DC power from an AC source without a bulky and heavy transformer. A prototype 60 W LED driver was implemented by the proposed design procedure and verified by simulation and experimental results, where the efficiency, PF, and THD are 92%, 0.94, and 6.3%, respectively. The LED power variation is well mitigated to below ± 2% for 190 V < Vs < 250 V by using the proposed simple control circuit.