• 정보통신설비학회논문지
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• 제7권1호
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• pp.41-58
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• 2007

A compact and broadband $4{\times}1$ array antenna was developed for 3G smart antenna system testbed. The $4{\times}1$ uniform linear array antenna was designed to operate at 1.885 to 2.2GHz with a total bandwidth of 315MHz. The array elements were based on the novel broadband L-probe fed inverted hybrid E-H (LIEH) shaped microstrip patch, which offers 22% size reduction to the conventional rectangular microstrip patch antenna. For steering the antenna beam, a commercial variable attenuator (KAT1D04SA002), a variable phase shifter (KPH350SC00) with four units each, and the corporate 4-ways Wilkinson power divider which was fabricated in-house were integrated to form the beamforming feed network. The developed antenna has an impedance bandwidth of 17.32% ($VSWR{\leq}1.5$), 21.78% ($VSWR{\leq}2$) with respect to center frequency 2.02GHz and with an achievable gain of 11.9dBi. The design antenna offer a broadband, compact and mobile solution for a 3G smart antenna testbed to fully characterized the IMT-2000 radio specifications and system performances.

• 한국전자파학회논문지
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• 제23권6호
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• pp.756-759
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• 2012

본 논문은 한반도 지역에 보편적 위성 통신 서비스를 제공하기 위한 정지궤도 위성의 다중 빔 서비스 커버리지 요구에 따라, 서비스 영역 내의 이득을 높일 수 있는 구현 가능한 안테나 구성 시나리오를 제안하였다. 제안된 시나리오는 위성 탑재가 가능하도록 안테나 및 급전 네트워크 구성을 간소화하고, 제한된 주파수 및 편파자원을 효율적으로 사용하기 위한 급전 네트워크 설계를 포함하고 있다. 또한, 전기적 성능 만족을 위하여 배열소자의 배치 및 여기 계수 최적화가 수행되었다.

• IEIE Transactions on Smart Processing and Computing
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• 제3권2호
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• pp.83-87
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• 2014

This paper introduces a refined opportunistic interference alignment (OIA) technique that uses minimum mean square error (MMSE) detection at the receivers in multiple-input multiple-output multi-cell uplink networks. In the OIA scheme under consideration, each user performs the optimal transmit beamforming and power control to minimize the level of interference generated to the other-cell base stations, as in the conventional energy-efficient OIA. The result showed that owing to the enhanced receiver structure, the OIA scheme shows much higher sum-rates than those of the conventional OIA with zero-forcing detection for all signal-to-noise ratio regions.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2012년도 하계학술대회
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• pp.185-187
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• 2012

단일주파수방송망을 이용하여 지상파 3D-HDTV 전송 시 단일주파수방송망에서 발생하는 다중경로채널은 지상파 3D-HDTV 수신성능을 열화시킨다. 최대 다중경로채널의 길이는 단일주파수방송망 내 송신기간 거리에 의해 결정되며, 최소 다중경로 개수는 수신기에 근접한 송신기 개수에 의해 결정된다. 이에 본 논문에서는 다중경로채널의 각 경로 입사각을 추정하기 위한 스마트안테나기반 수신기를 설계하고, beamforming과 nulling 기법 적용 시 지상파 3D-HDTV 수신성능을 분석하였다.

• Journal of Communications and Networks
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• 제15권4호
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• pp.398-406
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• 2013

In this paper, we investigate two types of in-phase and quadrature-phase (IQ) data transfer methods for cloud multiple-input multiple-output (MIMO) network operation. They are termed "after-precoding" and "before-precoding". We formulate a cloud massive MIMO operation problem that aims at selecting the best IQ data transfer method and transmission strategy (beamforming technique, the number of concurrently receiving users, the number of used antennas for transmission) to maximize the ergodic sum-rate under a limited capacity of the digital unit-radio unit link. Based on our proposed solution, the optimal numbers of users and antennas are simultaneously chosen. Numerical results confirm that the sum-rate gain is greater when adaptive "after/before-precoding" method is available than when only conventional "after-precoding" IQ-data transfer is available.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.2386-2388
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• 2005

As anti-crash and pre-crash systems in vehicles become more extensively used, the need for high performance short-range radars is playing an increasing role. This paper presents the design of a micromachined, ultra-wideband beamformer centered at 24 GHz for automotive short-range radar systems. This beamformer is a Butler matrix designed using ultra-wideband transmission-line couplers, which consist of a multilayered structure that exhibits wider bandwidth compared to conventional microstrip branch-line couplers. The circuit has been designed on a quartz substrate, and to achieve the desired coupling, lines suspended on BCB layers located at specific parts of the circuit were used, achieving a three metal layered structure in form of wide microstrips, that give low loss and a wideband response. In this paper the design and fabrication procedure of the proposed beamformer are fully described.

• International journal of advanced smart convergence
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• 제9권4호
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• pp.156-166
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• 2020

In this paper, to improve spectral efficiency and mitigate interference in coordinated millimeter-wave systems, we proposes an optimal user group and beam selection scheme. The proposed scheme improves spectral efficiency by mitigating intra- and inter-cell interferences (ICI). By examining the effective channel capacity for all possible user combinations, user combinations and beams with minimized ICI can be selected. However, implementing this in a dense environment of cells and users requires highly complex computational abilities, which we have investigated applying multiclass classifiers based on machine learning. Compared with the conventional scheme, the numerical results show that our proposed scheme can achieve near-optimal performance, making it an attractive option for these systems.

• Smart Structures and Systems
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• 제6권3호
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• pp.197-209
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• 2010

The structural state of a bridge is currently examined by visual inspection or by wired sensor techniques, which are relatively expensive, vulnerable to inclement conditions, and time consuming to undertake. In contrast, wireless sensor networks are easy to deploy and flexible in application so that the network can adjust to the individual structure. Different sensing techniques have been used with such networks, but the acoustic emission technique has rarely been utilized. With the use of acoustic emission (AE) techniques it is possible to detect internal structural damage, from cracks propagating during the routine use of a structure, e.g. breakage of prestressing wires. To date, AE data analysis techniques are not appropriate for the requirements of a wireless network due to the very exact time synchronization needed between multiple sensors, and power consumption issues. To unleash the power of the acoustic emission technique on large, extended structures, recording and local analysis techniques need better algorithms to handle and reduce the immense amount of data generated. Preliminary results from utilizing a new concept called Acoustic Emission Array Processing to locally reduce data to information are presented. Results show that the azimuthal location of a seismic source can be successfully identified, using an array of six to eight poor-quality AE sensors arranged in a circular array approximately 200 mm in diameter. AE beamforming only requires very fine time synchronization of the sensors within a single array, relative timing between sensors of $1{\mu}s$ can easily be performed by a single Mote servicing the array. The method concentrates the essence of six to eight extended waveforms into a single value to be sent through the wireless network, resulting in power savings by avoiding extended radio transmission.

• 한국정보통신학회논문지
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• 제23권8호
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• pp.975-980
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• 2019

본 논문에서는 차세대 이동통신 시스템의 핵심 요소 기술 중의 하나로 각광 받고 있는 다중 사용자 다중 안테나 네트워크에서 사용자 선택을 위한 심화 학습 기반 스케쥴링 기법을 제안한다. 제안된 신경망을 학습시키기 위하여 기존의 최적 방식을 통해서 90,000 데이터 샘플을 확보하였으며, 추가적인 10,000 데이터 샘플을 이용하여 최종 학습된 신경망의 과최적화 여부를 확인하였다. 제안된 신경망 기반의 스케쥴링 알고리즘은 초기 학습 시에는 상당한 복잡도와 학습 시간이 필요하지만, 일단 학습이 완료된 이후에는 추가적인 복잡도가 유발되지 않는 장점이 있다. 반면에, 기존의 최적 방식은 매 스케쥴링마다 동일한 복잡도의 계산이 지속적으로 요구된다. 다양한 컴퓨터 시뮬레이션 결과에 따르면, 제안된 심화 학습 기반의 스케쥴링 기법은 10dB 보다 낮은 SNR에서는 기존 최적 알고리즘의 약 88~96%에 이르는 평균 전송 속도의 합을 얻을 수 있으며, 10dB 이상의 SNR에서는 최적의 평균 전송 속도의 합을 얻을 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권9호
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• pp.4145-4164
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• 2016

Energy harvesting is an increasingly attractive source of power for cellular networks, and can be a promising solution for green networks. In this paper, we consider a cellular network with power beacons powering multiple mobile terminals with microwave power transfer in energy beamforming. In this network, the power beacons are powered by grid and renewable energy jointly. We adopt a dual-level control architecture, in which controllers collect information for a core controller, and the core controller has a real-time global view of the network. By implementing the water filling optimized power allocation strategy, the core controller optimizes the energy allocation among mobile terminals within the same cluster. In the proposed green energy cooperation paradigm, power beacons dynamically share their renewable energy by locally injecting/drawing renewable energy into/from other power beacons via the core controller. Then, we propose a new water filling optimized green energy cooperation management strategy, which jointly exploits water filling optimized power allocation strategy and green energy cooperation in cellular networks. Finally, we validate our works by simulations and show that the proposed water filling optimized green energy cooperation management strategy can achieve about 10% gains of MT's average rate and about 20% reduction of on-grid energy consumption.