• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제9권5호
• /
• pp.1768-1789
• /
• 2015

The maximal signal-to-interference-plus-noise ratio (Max-SINR) algorithm for interference alignment (IA) has received considerable attention for its high sum rate achievement in the multiple-input multiple-output (MIMO) interference channel. However, its complexity may increase dramatically when the number of users approaches the IA feasibility bound, and the number of iterations and computational time may become unacceptable. In this paper, we study the properties of the Max-SINR algorithm thoroughly by presenting theoretical insight into the algorithm and by providing the potential of reducing the overall computational cost. Furthermore, a novel IA algorithm based on the principle direction search is proposed, which can converge more rapidly than the conventional Max-SINR method. In the proposed algorithm, it searches along the principle direction, which is found to approximately point to the convergence values, and can approach the convergence solutions rapidly. In addition, the closed-form solution of the optimal step size can be formulated in the sense of minimal interference leakage. Simulation results demonstrate that the proposed algorithm outperforms the conventional minimal interference leakage and Max-SINR algorithms in terms of the convergence rate while guaranteeing the high throughput of IA networks.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제8권6호
• /
• pp.1881-1900
• /
• 2014

Since 802.11 wireless LANs are so widely used, it has become common for numerous access points (APs) to overlap in a region, where most of those APs are managed individually without any coordinated control. This pattern of wireless LAN usage is called the private OBSS (Overlapping Basic Service Set) environment in this paper. Due to frame collisions across BSSs, each BSS in the private OBSS environment suffers severe performance degradation. This study approaches the problem from the perspective of congestion control rather than noise or collision resolution. The retry limit, one of the 802.11 attributes, could be used for traffic control in conjunction with TCP. Reducing the retry limit causes early discard of a frame, and it has a similar effect of random early drops at a router, well known in the research area of congestion control. It makes the shared link less crowded with frames, and then the benefit of fewer collisions surpasses the penalty of less strict error recovery. As a result, the network-wide performance improves and so does the performance of each BSS eventually. Reducing the retry limit also has positive effects of merging TCP ACKs and reducing HOL-like blocking time at the AP. Extensive experiments have validated the idea that in the OBSS environment, reducing the retry limit provides better performance, which is contrary to the common wisdom. Since our strategy is basically to sacrifice error recovery for congestion control, it could yield side-effects in an environment where the cost of error recovery is high. Therefore, to be useful in general network and traffic environments, adaptability is required. To prove the feasibility of the adaptive scheme, a simple method to dynamically adjust the value of the retry limit has been proposed. Experiments have shown that this approach could provide comparable performance in unfriendly environments.

• Korean Journal of Geomatics
• /
• 제1권1호
• /
• pp.1-5
• /
• 2001

This paper presents an investigation into the operational comparison of SPOT triangulation to build GCP library by analytical plotter and DPW (digital photogrammetric workstation). GCP database derived from current SPOT images can be used to other image sensors of satellite, if any reasons, such as lack of topographic maps or GCPs. But, general formulation of a photogrammetric process for GCP measurement has to take care of the scene interpretation problem. There are two classical methods depending on whether an analytical plotter or DPW is being used. Regardless of the method used, the measurement of GCPs is the weakest point in the automation of photogrammetric orientation procedures. To make an operational comparison, five models of SPOT panchromatic images (level 1A) and negative films (level 1AP) were used. Ten images and film products were used for the five GRS areas. Photogrammetric measurements were carried out in a manual mode on P2 analytical plotter and LH Systems DPW770. We presented an approach for exterior orientation of SPOT images, which was based on the use of approximately eighty national geodetic control points as GCPs which located on the summit of the mountain. Using sixteen well-spaced geodetic control points per model, all segments consistently showed RMS error just below the pixel at the check points in analytical instrument. In the case of DPW, half of the ground controls could not found or distinguished exactly when we displayed the image on the computer monitor. Experiment results showed that the RMS errors with DPW test was fluctuated case by case. And the magnitudes of the errors were reached more than three pixels due to the lack of image interpretation capability. It showed that the geodetic control points is not suitable as the ground control points in DPW for modeling the SPOT image.

• 한국건설관리학회:학술대회논문집
• /
• 한국건설관리학회 2001년도 학술대회지
• /
• pp.513-518
• /
• 2001

국내 건설프로젝트는 점차 대형화·복잡화 되어가고 있으며, 과거에 비해 더욱 방대한 양의 건설정보가 생성되어 공사관리에 이용되고 있는 추세이다. 그러나, 기존의 건설프로젝트 관리체계 하에서는 현장에서 발생되는 정보를 수집·관리함에 있어 대부분 이를 기술자들의 경험과 수작업에 의존하고 있으며, 결국 이로 인한 현장 정보의 신뢰도 결여는 건설정보의 재 입력을 통한 공사관리 업무의 비효율성을 초래하고 있는 실정이다. 최근 건설을 포함한 다양한 산업분야에 걸쳐 컴퓨터를 기반으로 IT기술을 응용하는 제반 연구가 활발히 진행되고 있으며, 다양한 가시적인 성과를 이루어 내고 있다. 따라서, 본 연구에서는 건설현장에서 발생하는 정보의 수집 및 활용에 대한 문제점을 규명하고 건설정보 관리와 관련한 연구동향과 적용사례를 살펴본 후, 건설정보 수집 도구로써의 IT 기술 및 적용 분야를 분석하여 국내 현장 관리체계에 적합한 IT 기술 도입 방안을 제시하고자 한다. 또한 본 연구의 결과는 향후 국내 건설산업에 있어 효율적 공사관리 및 실적자료의 구축을 위한 기반 환경을 제공할 수 있을 것으로 사료된다.

• 한국통신학회논문지
• /
• 제35권2A호
• /
• pp.202-208
• /
• 2010

WDM/SCM-PON에서 상향 전송을 할 때 다수의 ONU가 단일 광 채널을 공유하여 다수의 신호를 전송할 경우에 수신부에서 잡음으로 작용하는 OBI가 발생하게 되어 전체 시스템의 성능을 악화시키기 때문에 OBI에 대한 문제 해결이 필수적인 과제이다. 본 논문은 SCM-PON에서 상향 전송을 할 때 발생하는 OBI를 헤테로다인 검출 방식으로 극복하는 새로운 방안을 제시하였다. 제안된 방식은 수신 광검출기 앞부분에 별도의 LD를 사용하여 heterodyne detection을 가능케 함으로써, OBI 성분을 검출신호와 구분되도록 하여 OBI로 인한 문제를 해결하는데 근거를 두고 있다. 또한, 가입자단에서 R-SOA를 사용함으로써 경제적인 저가형 ONU 구현을 가능케 하는 장점을 갖는다.

• Structural Engineering and Mechanics
• /
• 제66권2호
• /
• pp.217-227
• /
• 2018

In the last decades, valuable results have been reported regarding conventional passive, active, semi-active, and hybrid structural control systems on two-dimensional and a few three-dimensional shear buildings. In this research, using a three-dimensional finite element model of high-rise concrete structures, designed by performance based plastic design method, it was attempted to construct a relatively close to reality model of concrete structures equipped with Tuned Mass Damper (TMD) by considering the effect of soil-structure interaction (SSI), torsion effect, hysteresis behavior and cracking effect of concrete. In contrast to previous studies which have focused mainly on linearly designed structures, in this study, using performance-based plastic design (PBPD) design approach, nonlinear behavior of the structures was considered from the beginning of the design stage. Inelastic time history analysis on a detailed model of twenty-story concrete structure was performed under a far-field ground motion record set. The seismic responses of the structure by considering SSI effect are studied by eight main objective functions that are related to the performance of the structure, containing: lateral displacement, acceleration, inter-story drift, plastic energy dissipation, shear force, number of plastic hinges, local plastic energy and rotation of plastic hinges. The tuning problem of TMD based on tuned mass spectra is set by considering five of the eight previously described functions. Results reveal that the structural damage distribution range is retracted and inter-story drift distribution in height of the structure is more uniform. It is strongly suggested to consider the effect of SSI in structural design and analysis.

• Structural Engineering and Mechanics
• /
• 제59권3호
• /
• pp.455-473
• /
• 2016

Methods for the seismic demands evaluation of structures require iterative procedures. Many studies dealt with the development of different inelastic spectra with the aim to simplify the evaluation of inelastic deformations and performance of structures. Recently, the concept of inelastic spectra has been adopted in the global scheme of the Performance-Based Seismic Design (PBSD) through Capacity-Spectrum Method (CSM). For instance, the Modal Pushover Analysis (MPA) has been proved to provide accurate results for inelastic buildings to a similar degree of accuracy than the Response Spectrum Analysis (RSA) in estimating peak response for elastic buildings. In this paper, a simplified nonlinear procedure for evaluation of the seismic demand of structures is proposed with its applicability to multi-degree-of-freedom (MDOF) systems. The basic concept is to write the equation of motion of (MDOF) system into series of normal modes based on an inelastic modal decomposition in terms of ductility factor. The accuracy of the proposed procedure is verified against the Nonlinear Time History Analysis (NL-THA) results and Uncoupled Modal Response History Analysis (UMRHA) of a 9-story steel building subjected to El-Centro 1940 (N/S) as a first application. The comparison shows that the new theoretical approach is capable to provide accurate peak response with those obtained when using the NL-THA analysis. After that, a simplified nonlinear spectral analysis is proposed and illustrated by examples in order to describe inelastic response spectra and to relate it to the capacity curve (Pushover curve) by a new parameter of control, called normalized yield strength coefficient (${\eta}$). In the second application, the proposed procedure is verified against the NL-THA analysis results of two buildings for 80 selected real ground motions.

• 산업경영시스템학회지
• /
• 제40권2호
• /
• pp.145-149
• /
• 2017

One of the challenges facing precision manufacturers is the increasing feature complexity of tight tolerance parts. All engineering drawings must account for the size, form, orientation, and location of all features to ensure manufacturability, measurability, and design intent. Geometric controls per ASME Y14.5 are typically applied to specify dimensional tolerances on engineering drawings and define size, form, orientation, and location of features. Many engineering drawings lack the necessary geometric dimensioning and tolerancing to allow for timely and accurate inspection and verification. Plus-minus tolerancing is typically ambiguous and requires extra time by engineering, programming, machining, and inspection functions to debate and agree on a single conclusion. Complex geometry can result in long inspection and verification times and put even the most sophisticated measurement equipment and processes to the test. In addition, design, manufacturing and quality engineers are often frustrated by communication errors over these features. However, an approach called profile tolerancing offers optimal definition of design intent by explicitly defining uniform boundaries around the physical geometry. It is an efficient and effective method for measurement and quality control. There are several advantages for product designers who use position and profile tolerancing instead of linear dimensioning. When design intent is conveyed unambiguously, manufacturers don't have to field multiple question from suppliers as they design and build a process for manufacturing and inspection. Profile tolerancing, when it is applied correctly, provides manufacturing and inspection functions with unambiguously defined tolerancing. Those data are manufacturable and measurable. Customers can see cost and lead time reductions with parts that consistently meet the design intent. Components can function properly-eliminating costly rework, redesign, and missed market opportunities. However a supplier that is poised to embrace profile tolerancing will no doubt run into resistance from those who would prefer the way things have always been done. It is not just internal naysayers, but also suppliers that might fight the change. In addition, the investment for suppliers can be steep in terms of training, equipment, and software.

• 한국컴퓨터정보학회논문지
• /
• 제13권1호
• /
• pp.273-281
• /
• 2008

지식 정보화 시대가 도래하게 되면서 IT산업의 효율적인 관리 방안 및 이에 따른 정보 가치의 중요성과 상호 운영의 중요성이 과거 어느 때보다 높아지고 있다. 따라서 정보 기술을 체계적으로 계획하고 관리하는 ITA/EA가 2005년 법률로 제정 공포 시행되어 새로운 IT관리 방법론으로 인지되고 있으나 ITA와 EA의 새로운 표준화에 대한 논의는 미비한 게 현실이다. 이에 본 연구에서는 EA/ITA가 정보기술에 성공적으로 적용 활용될 수 있는 요인을 찾는 것이 가장 시급한 문제라고 판단하여 그에 대한 연구를 진행하였다. 그 결과 '용어 및 업무의 표준화', '인력양성의 표준화'를 통해 전문 인력 양성 시스템의 체계화 및 자격 제도신설의 필요성을 강조하고, ITA와 EA의 개념이 혼용되어 발생하는 이중적 구조를 제거해야 하는 당위성을 역설하였다. 그럼으로써 ITA/EA는 IT공학으로 인정하고 전문공학 인들로 하여금 학술적 분야로 수용할 수 있도록 국내 표준화를 위한 새로운 모델을 제시하였다. 종합적으로, ITH/EA를 통해 정보 관리의 효율성을 높일 수 있는 요인들에 대해 제언하고자 했다.

• 한국정보과학회논문지:데이타베이스
• /
• 제33권4호
• /
• pp.423-436
• /
• 2006

최근 XML 문서 필터링에 기반한 출판 -구독 (publish-subscribe) 시스템이 많은 관심을 받고 있다. 전형적인 출판 구독 시스템에서, 구독자들은 XPath 언어로 명세된 프로파일로 자신들의 관심을 표현하고, 새로운 내용들은 사용자 프로파일에 대하여 매칭 여부를 판단하여 관심을 가지고 있는 사용자들에게만 배달된다. 구독자의 수와 그들의 프로파일이 증가할수록, 시스템의 확장성이 출판 구독 시스템의 중요한 성공 요소가 된다. 이 논문에서는 XPath 로 명세된 가지형 패턴과 입력 XML 문서들을 Prufer의 방법을 사용하여 시퀀스로 변환하는 FiST라 불라는 새로운 필터링 시스템을 제안한다. FiST 시스템은 가지형 패턴을 구성하는 선형 경로들에 대하여 각각 매칭을 수행하고 후처리 과정에서 그 결과들을 병합하는 방법을 이용하는 대신에 가지형 패턴 전체를 사용하여 입력 문서에 대하여 매칭을 수행한다. 또한 효율적인 필터링을 위하여 시퀀스들을 해시 기반의 동적 인덱스로 구성한다. 실험 결과를 통해 전체 매칭 접근 방법이 다양한 환경에서 낮은 필터링 비용과 좋은 확장성을 가짐을 알 수 있다.