• Journal of Communications and Networks
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• 제5권2호
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• pp.96-103
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• 2003

Asymptotic theorems are very commonly used in probability. For systems whose performance depends on a set of n random parameters, asymptotic analyses for n${\to}{\infty}$ are often used to simplify calculations and obtain results yielding useful hints at the behavior of the system for finite n. These asymptotic analyses are especially useful whenever the convergence to the asymptotic results is so fast that even for moderate n they yield results close to the true values. This tutorial paper illustrates this principle by applying it to capacity calculations of multiple-antenna systems.

• Steel and Composite Structures
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• 제35권5호
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• pp.611-625
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• 2020

Experimental investigation and finite element analysis of corroded cold-formed steel (CFS) columns are presented. 11 tensile coupon specimens and 6 stub columns of corroded CFS that had a channel section of C160x60x20 were subjected to monotonic tensile tests and axial compression tests, respectively. The degradation laws of the mechanical properties of the tensile coupon specimens and stub columns were analysed. An appropriate finite element model for the corroded CFS columns was proposed and the influence of local corrosion on the stability performance of the columns was studied by finite element analysis. Finally, the axial capacity of the experimental results was compared with the predictions obtained from the existing design specifications. The results indicated that with an increasing average thickness loss ratio, the ultimate strength, elastic modulus and yield strength decreased for the tensile coupon specimens. Local buckling deformation was not noticeable until the load reached about 90% of the ultimate load for the non-corroded columns, while local buckling deformation was observed when the load was only 40% of the ultimate load for the corroded columns. The maximum reduction of the ultimate load and critical buckling load was 57% and 81.7%, respectively, compared to those values for the non-corroded columns. The ultimate load of the columns with web thickness reduced by 2 mm was 53% lower than that of the non-corroded columns, which indicates that web corrosion most significantly affects the bearing capacity of the columns with localized corrosion. The results predicted using the design specifications of MOHURD were more accurate than those predicted using the design specifications of AISI.

• Steel and Composite Structures
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• 제29권1호
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• pp.23-37
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• 2018

In this paper, seismic provisions related to built-up special concentrically braced frames (BSCBFs) are investigated under cyclic loading using non-linear finite element analysis of a single-bay single-story frame. These braces, which contain double angle and double channel brace sections, are considered in two types of single diagonal and X-braced frames. The results of this study show that current seismic provisions such as observing the 0.4 ratio for slenderness ratio of individual elements between stitch connectors are conservative in BSCBFs, and can be increased according to the type of braces. Furthermore, such increments will lead to decreasing or remaining the current middle protected zone requirements of each BSCBFs. Failure results of BSCBFs, which are related to the plastic equivalent strain growth of members and ductility capacity of the models, show that the behaviors of double channel back-to-back diagonal braces are more desirable than those of similar face-to-face ones. Also, for double angle diagonal braces, results show that the failure of back-to-back BSCBFs occurs faster in comparison with face-to-face similar braces. In X-braced frames, cyclic and failure behaviors of built-up face-to-face models are more desirable than similar back-to-back braces in general.

• 한국통신학회논문지
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• 제36권6C호
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• pp.337-342
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• 2011

2009년 Arikan에 의해 처음 제안된 극 부호(polar codes)는 실용적인 부 복호화 복잡도로 채널 용량을 달성하는 것이 종영된 채널 부호이다. 채널 양극화(channel polarization) 현상을 이용하는 극 부호는 현재 보안 및 데이터 압축 등에 응용되어 활발히 연구되고 있다. 본 논문에서는 극 부호의 실제 통신 시스템 적용을 고려하여, 유한한 길이와 고정 부호율을 갖는 극 부호의 설계 방법을 제안한다. 그리고 모의실험을 통하여 경험적으로 찾아낸 가장 우수한 성능을 보이는 극 부호의 성능과 설계 방법을 제시한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권4호
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• pp.1026-1040
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• 2012

For a single relay channel, we compare the capacity of two different amplify-and-forward (AF) protocols, which are orthogonal AF (OAF) and non-orthogonal AF (NAF). The NAF protocol has been proposed to overcome a significant loss of performance of OAF in the high spectral efficiency region, and it was also theoretically proved that NAF performs better than OAF in terms of the diversity-multiplexing tradeoff. However, existing results have been evaluated at the asymptotically high signal to noise ratio (SNR), thus the power allocation problem between the source and the relay was neglected. We examine which protocol has better performance in a practical system operating at a finite SNR. We also study where a relay should be located if we consider the power allocation problem. A notable conclusion is that the capacity performance depends on both SNR and power allocation ratio, which indicates OAF may perform better than NAF in a certain environment.

• Journal of Communications and Networks
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• 제14권2호
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• pp.162-168
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• 2012

This paper considers the scenario in which a set of nodes share a common channel. Some nodes have a rechargeable battery and the others are plugged to a reliable power supply and, thus, have no energy limitations. We consider two source-destination pairs and apply the concept of cognitive radio communication in sharing the common channel. Specifically, we give high-priority to the energy-constrained source-destination pair, i.e., primary pair, and low-priority to the pair which is free from such constraint, i.e., secondary pair. In contrast to the traditional notion of cognitive radio, in which the secondary transmitter is required to relinquish the channel as soon as the primary is detected, the secondary transmitter not only utilizes the idle slots of primary pair but also transmits along with the primary transmitter with probability p. This is possible because we consider the general multi-packet reception model. Given the requirement on the primary pair's throughput, the probability p is chosen to maximize the secondary pair's throughput. To this end, we obtain two-dimensional maximum stable throughput region which describes the theoretical limit on rates that we can push into the network while maintaining the queues in the network to be stable. The result is obtained for both cases in which the capacity of the battery at the primary node is infinite and also finite.

• 한국통신학회논문지
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• 제38C권1호
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• pp.109-117
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• 2013

극 부호(polar codes)는 광범위한 이진 입력 이산 무기억 채널(binary input discrete memoryless channel: BI-DMC)에서 채널 용량에 달성하는 것이 이론적으로 증명된 최초의 채널부호이다. 하지만 유한한 길이를 갖는 극 부호는 연속 제거 리스트(successive-cancellation list: SCL) 복호기에서 오류마루(error floor)가 발생하는 문제점이 있다. 선행 연구에 따르면 이 오류마루 현상은 극 부호에 오류 검출 코드(error detection codes) 중 하나인 CRC(Cyclic Redundancy Check) 부호를 연접했을 때 효과적으로 낮출 수 있는 것으로 알려져 있다. 본 논문에서는 외부 부호(outer codes)를 사용하지 않고 극 부호와 RM(Reed-Muller) 부호의 생성 행렬 연관성을 이용하여 기존 극 부호보다 확장된 최소거리를 갖는 극 부호를 제안한다. 그리고 제안된 극 부호와 CRC 부호를 연접한 극 부호의 성능을 비교한다.

• Steel and Composite Structures
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• 제16권2호
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• pp.157-185
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• 2014

This paper examines the behaviour of two types of practical open beam-to-tubular column connection details subjected to combined moment, axial and/or shear loads. Detailed continuum finite element models are developed and validated against available experimental results, and extended to deal with flexural, axial and shear load interactions. A numerical investigation is then carried out on the behaviour of selected connections with different stiffness and strength characteristics under various load combination scenarios. The influence of applied levels of axial tensile or compressive loads on the bending stiffness and capacity is examined and discussed. Additionally, the interaction effects between shear forces and co-existing bending and axial loads are examined and shown to be comparatively insignificant in terms of stiffness and capacity in most cases. It is also shown that the range of connections considered in this paper can provide rotational ductility levels in excess of those required under typical design scenarios. Based on these findings, a simplified component-based representation is proposed and described, and its ability to represent the connection response under combined loading is verified using results from detailed numerical simulations.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.215-218
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• 2006

A study was made to investigate microstructural evolution and mechanical properties of ultra-fine grained (UFG) pure-Ti produced by equal channel angular (ECA) pressings. The deformed structures were analyzed by finite element method and transmission electron microscopy with the increment of straining. After 4 isothermal ECA pressings, initial coarse grains ($30{\mu}m$) were significantly refined to ${\sim}0.3{\mu}m$ with homogeneous distribution of microstructure which was resulted from $180^{\circ}$ rotation of the sample between pressings. UFG pure-Ti exhibited the considerable improvement in yield strength while losing strain hardening capacity as compared to coarse grained microstructure at ambient temperature, which was mainly attributed to ultra-fine grain microstructure with non-equilibrium grain boundaries.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 합동 추계학술대회 논문집 정보 및 제어부문
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• pp.268-271
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• 2001

This paper presents observer-based on-line overload monitoring scheme for a PMSM(Permanent Magnet Synchronous Motor) drive system. Proposed scheme is to monitor overload status of motor drive system at remote place. The drive system is previously installed on main system and has no communication function. Proposed scheme consists of intelligent sensing head and monitoring part. Intelligent sensing head acquire motor 3-Phase currents and transmit data to monitoring part over serial communication interface. Monitoring part estimates motor speed using state observer. By comparing estimated speed with reference speed, we can detect motor fault. In this scheme observed information must coded and transmitted over a digital communication channel with finite capacity. We consider communication constraint as time delay and we design discrete-time observer. The proposed scheme is tested on the actual drive system.