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이동 트랜잭션의 완료율 향상을 위한 다중버전 타임스탬프 순서화 스케줄링 기법
김치연(Kim Chi Yeon),황부현(Hwang Bu Hyun) 한국정보처리학회 1999 정보처리학회논문지 Vol.6 No.5
A Mobile computing environment is a new paradigm which provides users with the access to information irrespective of users' location. A transaction scheduling method for the mobile computing environment must be designed so that database consistency is maintained with considering the limited performance of mobile hosts and the narrow bandwidth of a wireless network. The scheduling method using a lock has some problems : the high message overhead between a server and a mobile host for maintaining a lock and the high abort ratio of the mobile transactions owing to violating the serializability when a mobile host uses a cache. So, in this paper, we propose an efficient transaction management method using timestamp to resolve these problems. The proposed method is used in the environment under which a mobile host uses a cache having two versions for each cached data item and a server maintains several versions for each data item. So, even though a mobile transaction is executed during several broadcasting interval, can be committed. As a result, the proposed method can improve the commit ratio of the mobile transaction by maintaining multiversion for each data item and does not require the additional message exchange to schedule transactions by using timestamp.
이동 컴퓨팅 시스템에서 캐쉬 록을 이용한 동시성 제어 기법
김치연(Kim Chi Yeon),황부현(Hwang Bu Hyun) 한국정보처리학회 1998 정보처리학회논문지 Vol.5 No.2
A cache used by a mobile host in mobile computing environments is the important device that can reduce the power consumption and improve the system performance. A mobile host uses the cache to store the data that can be frequently accessed. When read-only transactions and update transactions under the caching environment are executed, the serializability of the transactions can be destroyed. Many studies focus on the consistency between the data in the cache and the data in the server rather than maintenance of transaction serializability. In this paper, we propose two caching strategies in which transaction serializability is maintained between read-only transactions and update transactions. And we propose a concurrency control method that uses one of two caching strategies. The proposed concurrency method, which is based on the locking, guarantees the serializability of transactions by introducing the new lock mode that is called a cache lock.
몬테카를로 시뮬레이션 기반 공동주택 전기자동차 충전수요 예측을 고려한 최대부하 시간 변화 분석
김치연(Chi-Yeon Kim),김채린(Chae-Rin Kim),조수환(Soo-Hwan Cho) 대한전기학회 2021 전기학회논문지 Vol.70 No.1
The penetration of Electric Vehicles(EV) has been increasing worldwide recently to reduce greenhouse gases(GHG), and the government plans to supply about 3 million EV until 2030. The EV charging pattern is determined by the ToU(Time-of-Use) tariff, and is mainly charged from 18:00 to 23:00, which is the middle load period. The EV charging demand will further increase the power demand for apartments, which surges after 18:00 after returning home, so it is necessary to accurately forecast the EV charging demand pattern. In this paper, we determine the probability variables of input data such as SoC(State-of-Charge), charging start time, and charging method of EV users to forecast the EV charging demand pattern based on Monte Carlo simulation. In addition, the changes in the power demand patterns of the apartment according to the EV charging demand patterns are estimated using the actual data of the apartment power demand pattern. Furthermore, we estimate changes in the pattern of power demand and changes in the peak load time according to the ratio of EVs per household of apartments nationwide.
커뮤니티급 전력수요 예측 정확도 향상을 위한 Scaled RMSE와 Shewhart Control Chart 기반의 비정상 참고일 감지 방안
김치연(Chi-Yeon Kim),김채린(Chae-Rin Kim),김동근(Dong-Keun Kim),최형진(Hyeong-Jin Choi),박시삼(Si-Sam Park),조수환(Soo-Hwan Cho) 대한전기학회 2020 전기학회논문지 Vol.69 No.2
Accurate short-term power demand forecasting is a key-technique for the optimal generator operation planning and the power market pricing. Especially, the accurate demand forecasting ability in city or community level micro-grids is more essential for local power utilities to obtain the optimal solutions for the economic energy mix and the daily energy supply planning. The forecasting error can increase the cost of purchasing additional power, cause economic losses by wasting energy, and exacerbate the system reliability. In order to minimize the forecasting error in city or community microgrid, the following two factors should be considered. One is how to determine the similar days whose time patterns of daily power demand are similar to each other and the other is how to detect and remove abnormal reference days of the similar days. Since the first issue applying the scaled RMSE method has been dealt in the previous related paper, we will summarize it in chapter 2 and focus at the second issue applying the control chart technique. In this paper, an abnormal reference days detection method based on the quality control charts such as Ⅹ,Ⅹ-R, and Ⅹ-s will be proposed and the detection performances will be compared and analyzed by simulations with actual annual demand data.
김치연,배석찬,Kim, Chi-Yeon,Bae, Seok-Chan 한국정보처리학회 2003 정보처리학회논문지D Vol.10 No.3
A crucial limitation in environments where data is broadcast to very large client populations is the low bandwidth available for clients to communicate with servers. Many advanced applications are developed in mobile computing environments, but conventional concurrency controls are not suitable because of the low bandwidth of wireless network. In this paper, we propose a new optimistic concurrency control protocol for mobile transactions. In this protocol, mobile read-only transactions can be completed locally at the clients without additional communication, only mobile update transactions are sent to the server for global validation. Our protocol reduces unnecessary aborts occurred in the previous study using only conflict information. In addition to, our algorithm can detect and resolve non-serializable execution using by data table maintained in a server. 많은 수의 클라이언트들에게 데이터를 방송하는 환경에서 가장 큰 제약은 서버와 통신하는데 이용가능한 대역폭이 낮다는 점이다. 이동 컴퓨팅 환경에서 많은 응용들이 개발되고 있으나, 무선망의 낮은 대역폭으로 인하여 전통적인 동시성 제어 방법을 그대로 적용하기 어렵다. 이 논문에서는 이동 트랜잭션을 위한 새로운 낙관적 동시성 제어 방법을 제안한다. 제안하는 방법에서 판독 전용 트랜잭션은 서버와 부가적인 메시지 교환없이 지역적으로 완료가 가능하며, 이동 갱신 트랜잭션은 서버로 보내져 전역적 검증을 수행한다. 또한 충돌 정보를 이용한 낙관적 방법에서 발생하는 트랜잭션의 불필요한 철회를 줄이고, 데이터 테이블에 유지된 정보를 이용하여 직렬가능하지 않은 수행을 찾아 직렬성 위배를 해결할 수 있다.
김치연,김건웅,최조천,Kim Chi-Yeon,Kim Geon-Ung,Choi Jo-Cheon 한국정보통신학회 2005 한국정보통신학회논문지 Vol.9 No.4
교통관제시스템을 구축하려면 이동체들의 실시간 위치데이터를 제공할 수 있는 GPS-MDT(Mobile Data Terminal 이동데이터단말기)와 이동체들의 위치데이터를 수신하여 GIS 상에 위치를 표시할 수 있는 교통 관제용 SW가 필요하다. 이동체의 위치데이터를 VHF 송수신기를 이용하여 전송하기 위해서는 GPS 정보를 취득하고 데이터를 전송하기 위한 모뎀이 필요하며, 관제실에는 GIS기반 이동체들의 교통상황을 모니터링하는 프로그램을 개발하여야 한다. 이동체들과 관제실 간에서 자동으로 이동체의 ID를 포함하여 GPS의 시각 및 위치정보를 지속적으로 전송하여 취득할 수 있는 통신프로토콜도 연구되어야 한다. 본 논문에서는 음성과 문자정보를 동시에 전송할 수 있는 VHF 송수신기용 모뎀과 GIS-tool을 이용한 관제용 S/W에 대하여 연구하였다. For the structure of AVLS is required to the GPS-MDT for realtime acquisition the position reporting of vehicle and traffic management S/W. It is necessary that the MODEM using VHF transceiver base on GPS and monitoring program for display base on GIS the traffic status by vehicles position report in management system. The other wise, vehicles among management system that is required the automatic communications protocol for GPS information and mobile's ID. In his paper have studied the VHF modem for transmission the voice and data at same time and S/W for management system using GIS-tool.