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D2D Power Control in the Cellular System
Changyoon Oh(오창윤) 한국컴퓨터정보학회 2017 韓國컴퓨터情報學會論文誌 Vol.22 No.9
In this paper, we consider the case where D2D users and the cellular user share the uplink of the cellular system. We propose an iterative power control algorithm that converges to the optimum power value. Each user iteratively updates its transmit power level according to the interference function. Finally, all D2D users and cellular user that participate in the transmission get the optimum transmit power level. We first investigate the interference structure and define the interference function. Then, we show that the considered interference function belongs to the standard interference function that converges the unique transmit power level. Through numerical examples, the convergence of the proposed power control algorithm is examined in the various transmission scenarios.
Study on the Transmit Power, MMSE Receiver Filter, and Access Point Selection Optimization Algorithm
Changyoon Oh(오창윤) 한국컴퓨터정보학회 2021 韓國컴퓨터情報學會論文誌 Vol.26 No.9
다중 엑세스포인트에 적용하는 전송전력, 최소평균제곱오차(MMSE) 수신필터와 최적의 엑세스포인트 선택 최적화문제를 살펴본다. 지난 연구에서는 전송전력과 MMSE 수신필터 최적화문제[1]와 전송전력과 최적의 엑세스포인트 선택문제[2]를 다루었다. 각각의 문제에 대한 알고리즘을 제안하고 알고리즘의 전송전력의 최소값에 수렴함을 증명하였다. 본 논문에서는 세 가지 변수를 함께 최적화하여 알고리즘의 성능을 개선한다. 구체적으로, 1) 전송전력, MMSE 수신필터, 엑세스포인트 선정을 동시에 고려하여 알고리즘을 제안한다. 2) 또한, 제안하는 알고리즘이 최적화 전송전력값에 수렴하는 것이 보장하는 것을 증명한다. 제안하는 알고리즘이 기존에 제안되었던 두 개의 알고리즘인 1)전송전력과 MMSE 수신필터 최적화 알고리즘, 2) 전송전력 최적화 알고리즘보다 전송전력 소모량에서 성능이 우수함을 실험을 통해서 확인하였다. We consider the joint optimization problem of transmit power level, MMSE receiver filter and access point(AP) selection for multi access points environment. In the previous work, transmit power and MMSE receiver filter were jointly optimized[1] and transmit power and best access point were optimized jointly[2]. For each case, the algorithm was proposed and its convergence which guarantees the minimum total transmit power was proved. In this paper, we further improve the algorithm by jointly optimizing three parameters. More specifically, 1) we propose the algorithm by considering transmit power, MMSE receiver filter and access point selection jointly. 2) we prove that the proposed algorithm guarantees convergence with minimum transmit power consumption. In the simulation results, it is shown that proposed algorithm outperforms two other algorithms, i.e., 1) algorithm with transmit power and MMSE receiver filter, and 2) algorithm with transmit power and best access point selection.
Energy Optimized Transmission Strategy in CDMA Reverse Link
Changyoon Oh(오창윤) 대한전자공학회 2015 전자공학회논문지 Vol.52 No.6
본 논문에서는 짧은 지연시간을 요구하는 CDMA 시스템 환경에서 전송률 스케줄링과 전력량 할당 문제를 연구한다. 구체적으로, 본 논문은 각각의 단말이 짧은 구간 동안의 평균 전송률을 유지하는 동시에 에너지 효율적인 스케줄링 방안을 제안한다. 다중 코드를 적용한 CDMA 시스템을 고려하며, 각각의 코드는 가상의 사용자로 해석할 수 있다. 논문의 최종 목적은 전송률 과정에서 소모하는 에너지가 최소화되도록 각각의 시간슬럿에 가상의 사용자를 스케줄링하는 방안을 제안하는 것이다. 주목할만한 점은, 본 논문에서 고려하는 전송률 최적화 문제가 최단 경로 알고리즘으로 해결 가능하다는 점이다. 마지막으로, 본 논문이 제안하는 에너지 최적화 스케줄링 방안을 TDMA 형식의 스케줄링 방안과 성능 비교 분석한다. We investigate rate scheduling and power allocation problem for a delay constrained CDMA systems. Specifically, we determine an energy efficient scheduling policy, while each user maintains the short term (n time slots) average throughput. We consider a multirate CDMA system where multirate is achieved by multiple codes. Each code can be interpreted as a virtual user. The aim is to schedule the virtual users into each time slot, such that the sum of transmit energy in n time slots is minimized. We then show that the total energy minimization problem can be solved by a shortest path algorithm. We compare the performance of the optimum scheduling with that of TDMA-type scheduling.
VocaBot: Language Learning App Powered by a Conversational Agent
Changyoon Lee(이창윤),Kyung Je Jo(조경제),Juho Kim(김주호) 한국HCI학회 2019 한국HCI학회 학술대회 Vol.2019 No.2
Both linguistic and communicative skills are important when learning a foreign language. Language learners need to acquire vocabulary and use the words in practice for comprehensive learning experience. Since many learners do not have the opportunity to practice conversation, conversational agents can provide the opportunities for language learners to learn and practice the target language at one go. To investigate the effects of combining vocabulary learning and conversation practice, we designed VocaBot, a two-stage language learning app that teaches important vocabulary and interacts with learners using a conversational agent. We evaluated the system through a user study with 7 participants learning Korean. VocaBot led the participants to use over 50% of the learned words in the conversation correctly. The NASA-TLX scores show that VocaBot’s two-stage design did not introduce severe workload to the language learners. Learners perceived the conversational agent to be fun, instructive and natural. These results suggest that the use of conversational agent as a language practice partner may be beneficial, especially in practicing the newly acquired words.
Energy Optimal Transmission Strategy in CDMA System
Changyoon Oh 한국컴퓨터정보학회 2015 韓國컴퓨터情報學會論文誌 Vol.20 No.9
We investigate rate scheduling and power allocation problem for a delay constrained CDMA systems. Specifically, we determine an energy efficient scheduling policy, while each user maintains the short term (n time slots) average throughput. More importantly, it is shown that the optimal transmission strategy for the uplink is same as that of the downlink, called uplink and downlink duality. We then examine the performance of the optimum transmission strategy for the uplink and the downlink for various system environments.
Implementation of Dialogue System for Intelligent Service Robots
Changyoon Lee,You-Sung Cha,Tae-Yong Kuc 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10
This paper presents a dialogue system for intelligent service robot application. The dialogue system consists of an audio speech recognition module, a text-to-speech conversion module, and a dialogue manager for supervision of timely conversion of input command to output robotic service. The dialogue manager is implemented in the framework of task supervisor for HRI(Human-Robot-Interface) module and makes use of finite state machine module for each robotic service. Since the number of services generated grows larger as the complexity of robotic task increases, the set of finite state machine modules is designed in compact modular form in the dialogue manager enhancing the capability of intelligent service robot handling various missions. The effectiveness of proposed dialogue system is demonstrated by applying it to information delivery service of weather and news, scheduling service, and entertainment game service for robotic user.