• Korean Journal of Optics and Photonics
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• v.33 no.6
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• pp.245-251
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• 2022

We have developed a multi-channel fiber laser for tiled laser beam combining and a laser output array system for multi-beam alignment. The fiber laser is a master oscillator power amplifier configuration that has a common seed, a preamplifier, and a 7-channel amplifier. The output power of each channel is more than 10 W. The laser output array system is a packed cylindrical configuration for a high fill-factor, and it has capabilities for collimation and tilt control with built-in PZT. Multi-beam alignment to a target is successfully implemented using PZT controlled with a stochastic parallel gradient descent (SPGD) algorithm.

• Information and Communications Magazine
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• v.32 no.5
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• pp.49-55
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• 2015

본 논문에서는 실제적인 다중 셀 하향링크 네트워크 중 하나인 간섭 브로드캐스트 채널에서 유망한 간섭 정렬 기술인 반복적 간섭 정렬 기술을 소개한다. 또한, 가정하는 네트워크에서 상향링크/하향링크 채널 사이의 채널 상호성을 활용함으로써 다중안테나(MIMO: multiple-input multiple-output) 다중셀 하향링크 네트워크를 위한 개선된 반복적 간섭 정렬 기술을 제안한다. 구체적으로, 제안한 기술은 다중사용자 MIMO 기반 반복적 간섭 정렬 알고리즘을 설계하기 위해 반복적 빔형성과 하향링크 간섭 정렬 이슈를 지능적으로 결합한다. 각 기지국에서는 전처리기를 설계하기 위해 두 개의 순차적인 빔형성 행렬을 사용하는데, 이는 간섭 누수로 불리는 타 셀 기지국으로부터 생성된 셀 간 간섭을 효율적으로 줄일 뿐만 아니라 같은 셀 안에서의 셀 내 간섭을 완벽히 제거가 가능하다. 송신 및 수신 빔형성 행렬은 수렴할 때까지 반복적으로 업데이트된다. 컴퓨터 모의실험을 통해 제안하는 간섭 정렬 기술이 기존 두 가지 반복적 간섭 정렬 기술과 비교하여 더 높은 합 용량을 나타냄을 보인다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.11-19
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• 2021

In this paper, we propose a non-orthogonal multiple access (NOMA) method based on channel alignment to simultaneously transmit multiple unicast and multicast streams in frequency-efficient manner. In this method, all receivers in a multicast cluster use the receive beamforming vectors that align their channels, and the base station uses the aligned channel information to design the transmit beamforming vectors that eliminate interference between multicast clusters. Using the effective receive channel information combined with the transmit beamforming vectors, unicast receivers design their own receive beamforming vectors that eliminate interference between unicast receivers. Since the proposed method effectively eliminates the interference, it achieves a higher sum rate than the existing orthogonal multiple access (OMA) method in high SNR regions. In addition, we present a hybrid method that exploits the benefits of the proposed NOMA method and the existing OMA method. Depending on the channel state, the hybrid method adaptively employs the existing OMA method, which improves the received signal power, in low SNR regions and the proposed NOMA method, which effectively eliminates the interference, in high SNR regions, thereby achieving a good sum rate over the entire SNR region.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1637-1642
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• 2010

In this paper, we present the fabrication of a high-quality diffractive-lens mold having submicron patterns, which is suitable for an ultra-slim optical system. In order to fabricate high-quality diffractive lens with a variety of submicron patterns, the multi-alignment method was used; high-resolution electron-beam lithography and FAB plasma etching were carried out to obtain the patterns. The most important key technology in the multi-alignment method is to reduce alignment error, lithography error, and etching error. In this paper, these major fabrication errors were minimized, and a high-quality diffractive lens with a diameter of $267\;{\mu}m$ (NA = 0.25), minimum pattern width of 226 nm, and thickness of 819 nm was successfully fabricated.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6A
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• pp.488-496
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• 2012

In this paper, the scheme for designing optimal beamforming matrix for interference control is proposed. The optimal beamforming matrix is found though linear combination of interference alignment conditions and renewal of linear combination coefficient. The proposed scheme has advantages that the complexity is reduced and there is no multiplying operation in matrix calculations even if proposed scheme has the form similar to that of existing least square based scheme. The simulation results show that proposed scheme has about 4bps/Hz higher gain than existing least square scheme. Also there is no additional multiplying calculation and increase of matrix size when the number of transmit and receive antennas is increased.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.217-218
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• 2010

본 논문은 3-사용자 X 채널 상황에서 다중안테나를 이용하여 간섭을 완벽하게 제어하는 기법에 대해 제안한다. 기존에 제안된 방식이 빔포밍(beamforming) 벡터를 다수의 채널을 사용하여 만드는데 따른 비현실적인 문제와 간섭을 완벽하게 제어하기 위한 무한한 채널 사용의 필요성에 따른 문제점을 본 논문에서는 다중안테나를 이용하여 공간적 특성을 이용한 빔포밍 벡터를 형성하고 채널의 확장 없이 간섭을 완벽히 제어하도록 하는 시스템을 제안한다. 제안한 시스템은 9개의 DOF(Degrees of freedom)을 얻을 수 있음을 모의실험 결과를 통해 확인할 수 있다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.9
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• pp.2014-2021
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• 2015

Opportunistic interference alignment (OIA) has been proposed for multi-cell random access networks (RAN), which minimizes the generating interference to neighboring RANs and yields better performance compared with the conventional techniques. The OIA for RANs considers both physical (PHY) and medium access control (MAC) layers. In this paper, we introduce a protocol of which each user maximizes the transmit signal regardless of the generating interference to neighboring RANs, contrary to the OIA technique. In addition, we compare the performance of the signal-maximization technique with the OIA technique.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.5
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• pp.61-69
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• 2017

The study on interference channel is very important information theoretically and many studies have been done on it. However, even in the simplest case, even in the case of two user interfering channels, the channel capacity is not yet known except in special cases. Recently, research on the multiplexing gain that shows the tendency of the transmission rate in the high signal to noise ratio (SNR) band has been actively carried out, instead of accurately grasping the channel capacity. Obtaining optimal multiplexing gain can reveal trends in channel capacity at high signal-to-noise ratio bands. In an interfering channel with two users, the best multiplexing gain can be obtained by eliminating the interference. However, recent research shows that when the number of users is more than three, the optimal multiplexing gain can not be obtained only by zero forcing and a new technique called interference sorting is needed. There are two types of interference sorting techniques. Beamforming A method of effectively separating signals and interference by properly selecting matrices and constructing structured codes using rational numbers and irrational numbers. The interference alignment technique can achieve optimal multiplexing gain in various environments such as interference channel, X channel, compound broadcast channel, and multi hop network for multi source multi destination. In recent years, it has also been applied to distributed storage. Lee et al., "Lattice Code Interference Alignment in Cooperative Multipoint Transmission (COMP) for Interference Channels of Three Users", Journal of the Institute of Electronics Engineers, vol.49-TC,no.6,2012. In this paper, the DoF of delayed channel information is obtained.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1639-1644
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• 2016

In this paper, we consider the performance improvement that can be obtained with interference alignment (IA) technique applied to 802.11ac based multi-BSS WiFi service. To this end, we developed a system simulator consisting of a link-level PHY simulator, based on 802.11ac specification, and multi-BSS proportional-fair scheduler. Specifically, assuming perfect channel side information and synchronization of signals from multiple APs, we used a SLNR based interference alignment algorithm proposed in [13] and compared its performance with that of multiuser beamforming based time-sharing system. The performance was evaluated in terms of average throughput per BSS and 5% worst user throughput. The results show that 70 to 100% throughput gain can be obtained in this ideal scenario.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.23 no.1
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• pp.1-8
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• 2005

Multi-beam echo sounder is more precise and efficient than single beam echo sounder relatively because it is able to survey a wide area with 3 times or 4 times swath width as much as the depth of water using multi-beam echo sounder. It is sure to be needed to control supplementary equipment accurately, however, because the principle of creation and measurement of the beam is elaborate and influenced a great deal by vessel's motion. We analyzed using visual and statistical methods in both sections of the depth of water where were the places of the center of the beam and ± 45° angles from the central beam to improve the precise of Multi-beam echo sounder in this study. In result, it was required to control supplementary equipment because of errors from the vibration of an inertia governor and misalignment of extra units. Therefore, we reduced the vibration from the vessel's engine by sticking rubbers to the inertia governor and measured the offset values of extra units accurately, converted them to the values of horizontal position and lined up. In result, the precise in sounding the depth at the place of ± 45° from the center of the beam was improved from the level of the 1st order to the special order in a hydrographic survey of the IHO S44 standards and a phenomenon of ripple patterns in the overlapped area by misalignment was decreased remarkably.