• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권7호
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• pp.3095-3111
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• 2018

Spectrum sensing (SS) is one of the fundamental tasks for cognitive radio. In SS, decisions can be made via comparing the test statistics with a threshold. Conventional adaptive algorithms for SS usually adjust their thresholds according to the radio environment. This paper concentrates on the issue of adaptive SS whose threshold is adjusted based on the Markovian behavior of primary user (PU). Moreover, Bayesian cost is adopted as the performance metric to achieve a trade-off between false alarm and missed detection probabilities. Two novel adaptive algorithms, including Markov Bayesian energy detection (MBED) algorithm and IMBED (improved MBED) algorithm, are proposed. Both algorithms model the behavior of PU as a two-state Markov process, with which their thresholds are adaptively adjusted according to the detection results at previous slots. Compared with the existing Bayesian energy detection (BED) algorithm, MBED algorithm can achieve lower Bayesian cost, especially in high signal-to-noise ratio (SNR) regime. Furthermore, it has the advantage of low computational complexity. IMBED algorithm is proposed to alleviate the side effects of detection errors at previous slots. It can reduce Bayesian cost more significantly and in a wider SNR region. Simulation results are provided to illustrate the effectiveness and efficiencies of both algorithms.

• 산업공학
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• 제12권1호
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• pp.19-25
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• 1999

The time slot scheduling problem for a satellite cluster with an arbitrary number of satellite is considered, which is one of the most interesting problems in the satellite communication scheduling area. This problem is known to be NP-complete, and several heuristic algorithms have been proposed. In this paper, a new efficient algorithm is suggested, which has lower computational complexity and provides much better solution than other existing algorithms.

• 대한원격탐사학회지
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• 제26권2호
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• pp.189-207
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• 2010

GOCI(정지궤도 해색센서) 해수환경분석 알고리즘들은 해양 광 특성 현장관측 자료들을 이용하여 개발되었다. 사용된 자료는 1998년부터 2009년까지 한반도 주변 해역에서 총 1348개 정점에서 얻어진 엽록소 농도(Chl-a), 부유물 농도(SS), 용존유기물의 흡광계수($a_{dom}$), 원격반사도($R_{rs}$) 현장자료들이다. GOCI 엽록소 농도 산출 알고리즘(GOCI Chl-a)은 부유물과 용존유기물의 영향을 모두 고려하고 네 개의 원격반사도 밴드비를 이용하여 개발하였다. GOCI Chl-a 알고리즘은 다른 알고리즘들보다 현장관측자료에 근사한 엽록소 농도 값을 산출하였다. SeaWiFS 영상자료에서 GOCI Chl-a 알고리즘은 SeaWiFS 표준 엽록소 산출 알고리즘들보다 평균 46 % 정도 보정된 엽록소 농도 값을 산출하였다. GOCI 부유물 농도 산출 알고리즘(GOCI SS)은 보편적인 두 개의 원격반사도 밴드비를 사용하지 않고, Ahn et al.(2001)의 원격반사도 단일밴드 방법을 사용하여 개발하였다. GOCI 용존유기물 산출 알고리즘(GOCI $a_{dom}$)은 원격반사도 밴드비 $R_{rs}(412)/R_{rs}(555)$와 $a_{dom}(\lambda)$)의 상관관계를 이용하여 개발하였다. GOCI 엽록소 형광 알고리즘과 GOCI 적조분석 알고리즘은 Ahn and Shanmugam(2007)와 Ahn and Shanmugam(2006)의 연구들에 의해 각각 개발되었다. 2010년 6월경에 GOCI의 성공적인 발사가 이루어지면 추후 GOCI 자료의 검보정 연구를 통해 개발된 알고리즘들의 문제점을 분석하고, 한반도 주변 해역의 해양 광 특성 현장자료의 지속적인 업데이트를 통한 알고리즘들의 개선작업이 이루어질 것이다.

• 대한원격탐사학회지
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• 제17권4호
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• pp.285-295
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• 2001

We developed a CASE-II water model that will enable the simulation of remote sensing reflectance($R_{rs}$) at the coastal waters for the retrieval of suspended sediments (SS) concentrations from satellite imagery. The model has six components which are: water, chlorophyll, dissolved organic matter (DOM), non-chlorophyllous particles (NC), heterotrophic microorganisms and an unknown component, possibly represented by bubbles or other particulates unrelated to the five first components. We measured $R_{rs}$, concentration of SS and chlorophyll, and absorption of DOM during our field campaigns in Korea. In addition, we generated $R_{rs}$ from different concentrations of SS and chlorophyll, and various absorptions of DOM by random number functions to create a large database to test the model. We assimilated both the computer generated parameters as well as the in-situ measurements in order to reconstruct the reflectance spectra. We validated the model by comparing model-reconstructed spectra with observed spectra. The estimated $R_{rs}$ spectra were used to (1) evaluate the performance of four wavelengths and wavelengths ratios for accurate retrieval of SS. 2) identify the optimum band for SS retrieval, and 3) assess the influence of the SS on the chlorophyll algorithm. The results indicate that single bands at longer wavelengths in visible better results than commonly used channel ratios. The wavelength of 625nm is suggested as a new and optimal wavelength for SS retrieval. Because this wavelength is not available from SeaWiFS, 555nm is offered as an alternative. The presence of SS in coastal areas can lead to overestimation chlorophyll concentrations greater than 20-500%.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권12호
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• pp.3166-3181
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• 2012

Localization of mobile station (MS) has now gained considerable attention. Since the hybrid measurements can help to improve the positioning accuracy, several hybrid localization methods have been proposed in the literature. However, the high performance estimator with the closed-form solution and complete performance analysis for time-of-arrival/signal strength (TOA/SS) localization technique is still an opening issue. Two TOA/SS localization algorithms with the closed-form solutions are proposed for the cases with or without uncertainty in the positions of base stations. Furthermore, performance analysis for the TOA/SS localization technique is presented. Both the theoretical variances and Cramer-Rao lower bounds (CRLBs) are derived and the relationship between the cases with or without uncertainty is given. The paper also proves that the TOA/SS scheme has a lower CRLB than the TOA (or SS) scheme. Theoretical analysis and simulations show that the proposed method can reach its CRLB.

• 전자공학회논문지A
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• 제32A권1호
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• pp.1-13
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• 1995

In this paper, a specification for wireless LAN MODEM using direct sequence spread spectrum (DS/SS) technique is presented. Some algorithms and hardware architectures for an efficient implementation of the DS/SS MODEM are suggested. In the method, all baseband signal processing are done digitally for single chip implementation. Schemes of DQPSK baseband modulation/demodulation, despreading with digital matched filter, digital timing recovery, and efficient carrier sensing are among the discussed algorithms. We also performed various kinds of simulations to evaluate the system performance and to extract parameters for hardware implementation. In addition, the pictorial view of ASIC of the SS MODEM is also shown.

• 한국경영과학회지
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• 제28권4호
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• pp.21-29
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• 2003

The traffic scheduling problem for a satellite cluster with an arbitrary number of satellites is considered. which is one of the most interesting problems in the satellite communication scheduling area. This problem is to find a time slot assignment maximizing the transponder utilization for a satellite cluster This problem is known to be NP-complete, and several heuristic algorithms have been proposed. In this paper, we suggest new efficient algorithms for this problem, which have less time complexity than the best existing one and provide much better solution quality. Extensive simulation results are reported.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 1994년도 춘계공동학술대회논문집; 창원대학교; 08월 09일 Apr. 1994
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• pp.13-20
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• 1994

We consider the satellite cluster scheduling problem which is one of the most interesting problems in satellite communication scheduling area. This problem is known to be NP-complete and a couple of heuristic algorithms had been developed. In this paper, we suggest another algorithm for this problem which has the same computational complexity as the best existing one and provides much better solution quality. Extensive computational simulation results are reported.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.82-85
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• 2006

The Geostationary Ocean Color Imager (GOCI) will be loaded in Communication, Ocean and Meteorological Satellite (COMS). To efficiently apply the GOCI data in the variety of fields, it is essential to develop the standard algorithm for estimating the concentration of ocean environmental components (, , and ). For developing the empirical algorithm, about 300 water samples and in situ measurements were collected from sea water around the Korean peninsula from 1998 to 2006. Two kinds of chlorophyll algorithms are developed by using statistical regression and fluorescence technique considering the bio-optical properties in Case-II waters. The single band algorithm for is derived by relationship between Rrs (555) and in situ concentration. The CDOM is estimated by absorption coefficient and ratio of Rrs(412)/Rrs(555). These standard algorithms will be programmed as a module of GOCI Data Processing System (GDPS) until 2008.

• Journal of Computing Science and Engineering
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• 제8권1호
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• pp.43-56
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• 2014

Semi-partitioned scheduling is a new approach for allocating tasks on multiprocessor platforms. By splitting some tasks between processors, semi-partitioned scheduling is used to improve processor utilization. In this paper, a new semi-partitioned scheduling algorithm called SS-DRM is proposed for multiprocessor platforms. The scheduling policy used in SS-DRM is based on the delayed rate monotonic algorithm, which is a modified version of the rate monotonic algorithm that can achieve higher processor utilization. This algorithm can safely schedule any system composed of two tasks with total utilization less than or equal to that on a single processor. First, it is formally proven that any task which is feasible under the rate monotonic algorithm will be feasible under the delayed rate monotonic algorithm as well. Then, the existing allocation method is extended to the delayed rate monotonic algorithm. After that, two improvements are proposed to achieve more processor utilization with the SS-DRM algorithm than with the rate monotonic algorithm. According to the simulation results, SS-DRM improves the scheduling performance compared with previous work in terms of processor utilization, the number of required processors, and the number of created subtasks.