• 한국통신학회논문지
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• 제37권3A호
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• pp.135-140
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• 2012

이 논문은 순환 지연 다이버시티 OFDM 시스템의 성능을 향상시키기 위하여 주파수 다이버시티를 적용하는 알고리즘을 제안한다. OFDM 시스템에서 주파수 다이버시티 적용은 동일한 심볼을 상관관계가 없는 부반송파로 반복 전송하는 것으로 수행되며, 반복 전송 회수에 비례하여 변조 레벨을 증가시켜서 종래의 전송 시스템의 성능과 비교한다. 이 방법은 순환 지연 다이버시티 알고리즘과 같이 송신기 개수가 많아짐에 따라 수신기에서 부가적인 특별한 하드웨어가 필요하지 않다는 동일한 장점이 있게 되며, 성능 시험을 위해서 다중 송수신 안테나 환경하에서 모의 실험을 수행하였다. 제안하는 알고리즘은 종래의 순환 지연 다이버시티를 활용한 OFDM 시스템과 비교하여 저밀도 변조 레벨에서 성능 향상이 현저함을 보여준다.

• 대한전기학회논문지
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• 제39권9호
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• pp.997-1005
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• 1990

Integral Error and State Feedback (IESF) controller which incorporates state feedback as a modern control scheme and integral action as a classical control scheme has better performance than that of conventional PID controller in linear time invariant system. But the structure of the IESF controller requires all the state variables of the system and is applicable only to pole assignable linear time invariant systems without time delay. Many industrial processes have large time delay and it is impossible to directly apply IESF control scheme to those processes. In this paper, a new controller structure, Modified Integral Error and State Feedback (MIESF) has been suggested in order to effectively control processes having time delay and its performance has been analyzed and its effectiveness has also been confirmed. As the proposed controller uses output feedback scheme based on integral error and state feedback (IESF) method, it can be simply designed by pole assignment algorithm irrespective of the order of the process. The MIESF controller can follow setpoint changes without overshoot. It is robuster than conventional Smith-Predictor plus PI(D) controller in case of occurring time delay mismatch and extra parameter mismatches between the process and the model. It can enhance control performance by intentional time delay mismatch.

• 한국통신학회논문지
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• 제38A권4호
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• pp.310-317
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• 2013

본 논문에서는 실시간 위치 추적 시스템 (RTLS: real-time locating system)을 위한 ESPRIT 기반의 초 분해능 지연 시간 추정 (super-resolution time delay estimation) 알고리즘을 개발하고 여러 가지 다중 경로 환경에서 성능을 분석한다. 지연 시간 추정을 위한 기존의 코릴레이션 방식은 다중 경로들의 지연 시간의 차이가 한 칩 이내일 경우 성능이 급격히 저하되는 문제점이 있다. 이러한 문제를 해결하기 위해 대표적인 초 분해능 도래각 추정 알고리즘인 ESPRIT을 지연 시간 추정에 적용하여 주파수 영역 초 분해능 지연 시간 추정 알고리즘을 개발하고 여러 가지 다중 경로 환경에서 알고리즘의 성능을 분석한다.

• 한국컴퓨터정보학회논문지
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• 제5권3호
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• pp.126-131
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• 2000

TCP는 인터넷에서 이미 많은 사용자들이 사용하고 있고 그 성능도 입증되어 왔지만, 망 구조의 급격한 변화에 따라서 TCP의 성능을 이에 맞게 개선하려는 노력들도 많이 제안되고 있다. 특히, 망이 고속화되고 위성링크 등에서 지연이 증가하면서 Bandwidth-Delay Product도 상당히 커지게 되었다. 이에 대응시키기 위한 방법으로 TCP 옵션에 Window Scale Option과 TimeStamp option, 및 PAWS(Protection Against Wrap Sequence Numbers) 등을 추가하는 방법이 제안되었다. Bandwidth-Delay Product가 큰 망에서는 TCP의 윈도우 크기도 증가하게 됨으로, 현재 사용중인 TCP의 곱 감소 선형적인 증가 방식으로는 망 내의 버퍼 언더플로우 및 망의 불안정을 야기하여, 결국은 TCP처리율의 감소를 초래하게 된다. 그러므로, 본 논문에서는 위와 같이 윈도우 크기가 큰 망에서의 TCP 흔잡제어 알고리즘을 개선하기 위한 방법으로 TCP의 TimeStamp 옵션을 이용하여 윈도우 크기를 조절하는 혼잡제어 방안을 제시하였다.

• Journal of Positioning, Navigation, and Timing
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• 제11권1호
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• pp.23-28
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• 2022

The eLoran system is a high-power terrestrial navigation system that is recognized as the most appropriate alternative to complement the GNSS's vulnerability to radio frequency interference. Accordingly, Korea has conducted eLoran technology development projects since 2016. The eLoran system developed in Korea provides 20 m positioning accuracy to maritime user in Incheon and Pyeongtaek harbor. To accurately calculate the position with the eLoran signal, it is necessary to apply a compensation method that mitigates the propagation delay. In this paper, we develop the compensation method to mitigate the eLoran signal propagation delay and evaluate the positioning performance in Incheon harbor. The propagation delay due to the terrain characteristics is pre-surveyed and stored in the user receiver. Real-time fluctuations in propagation delay compared to the pre-stored data are mitigated by the temporal correction generated at a nearby differential Loran station. Finally, two performance evaluation tests were performed to verify the positioning accuracy of the Korean eLoran system. The first test took place in December 2020 and the second in April 2021. As a result, the Korean eLoran service has been confirmed to provide 20 m location accuracy without GPS.

• 국제학술발표논문집
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• The 6th International Conference on Construction Engineering and Project Management
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• pp.527-531
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• 2015

With the mounting concerns over environmental issues, green construction is gaining a place in the global construction industry. However, rare research has been conducted to analyze green construction projects, especially in the aspect of project schedule performance. As a result, this study aims to investigate the degree of project delay in green building construction, analyze the factors affecting schedule delay of green building projects, and finally provide recommendations to improve schedule performance of green building project. To achieve the objectives, a comprehensive literature review was carried out, followed by a survey conducted with 30 companies that provided data from 220 traditional and 96 green building projects. The analysis of the responses identified that 15.9% of the traditional building projects were delayed while 32.3% of the green building projects were completed behind schedule. Furthermore, the amount of the delays in green building projects was an average of 4.8% of their planned schedule. The top 5 critical factors that can cause delay in green building projects were identified as: (1) speed of decision-making by clients; (2) speed of decision-making involving all project teams; (3) communication/coordination between key parties; (4) level of experience of consultants; and (5) difficulties in contractors' project financing. Lastly, a list of recommendations was introduced, aiming to reduce schedule delay in green building construction projects based on the observations. This study will serve as s a base for further research on the enhancement of green building project schedule performance.

• 한국통신학회논문지
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• 제25권5A호
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• pp.593-601
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• 2000

다중 대역 확산 CDMA 시스템에서 확산 대역폭과 레일리 페이딩 채널의 지연 확산에 대한 다중 선택 결합 RAKE 수신기의 성능을 분석하여, 지연 확산이 다른 여러 채널 환경에서 RAKE 수신기 차수에 따른 전체 수신 에너지와 다중 경로 다이버시티 이득간의 상호 관계를 규명하였다. 분석 결과, 지역 확산이 작은 환경에서의 광대역 확산을 이용하여 확산 대역폭을 증가시키는 것이 더 좋은 성능을 나타냈다. 높은 차수와 낮은 차수의 선택 결합기간의 성능 비교 결과, 확산 대역폭이 증가할수록 그 성능 차가 더 크게 나타났다. 또한, 확산 대역폭을 일정수준 이상으로 증가시킬 경우 수신 성능이 저하되었으며, 각 채널 환경에서의 최적 확산 대역폭은 채널의 지연 확산이 증가할수록 감소하였다.

• 대한교통학회지
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• 제9권2호
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• pp.27-40
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• 1991

Delay is an widely-used tool for evaluating the operation of signalized intersections. This paper presents two mathematical models: a model converting stop delay into approach delay : and a model estimating delay at isolated signalized intersection. To develop the delay-conversion model, actual stop delay and approach delay experienced by individual vehicles were measured and then their relationship was formulated using ma-thematical procedure. the formula expressing the approach-delay to stop-delay ratio was a monotonously decreasing function of effective red time. New delay model was developed based on the following criteria; the fitness to measured delay for undersaturated traffic condition and the convergence to the deterministic overflow delay for oversaturated traffic condition. Performance of this model was better than those of other existing models based on the comparison study.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2020년도 제62차 하계학술대회논문집 28권2호
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• pp.77-80
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• 2020

In this paper, we analyze and compare the performance of different publish and subscribe protocols in the real application environment. This paper provides a horizontal comparison of current publish/subscribe protocols in terms of security, throughput, and delay performance. Thanks to the use of lightweight frameworks, the MQTT protocol has demonstrated excellent performance in terms of delay performance. However, the AMQP protocol has more advantages in security and throughput. Although the REST/HTTP protocol has the worst delay performance, it is excellent in terms of compatibility because it is based on the HTTP protocol.

• ETRI Journal
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• 제35권5호
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• pp.935-938
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• 2013

This letter presents an algorithm for selecting a low delay for the modified discrete cosine transform (MDCT) and inverse MDCT (IMDCT). The implementation of conventional MDCT and IMDCT requires a 50% overlap-add (OLA) for a perfect reconstruction. In the OLA process, an algorithmic delay in the frame length is employed. A reduced overlap window and MDCT/IMDCT phase shifting is used to reduce the algorithmic delay. The performance of the proposed algorithm is evaluated by applying the low-delay MDCT to the G.729.1 speech codec.