• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.8A
• /
• pp.827-835
• /
• 2007

In this paper, the extension method of data transmission range as adapting AAS(Adaptive Antenna Systems) in ECMA(European Computer Manufacturers Association) standard MB-OFDM(MultiBand-Orthogonal Frequency Division Multiplexing) UWB systems is proposed, and the complementary beamforming method which can solve hidden beam problem when we adapt AAS in CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) systems is proposed. To design the complementary beamforming, Gram-Schmidt orthogonalization is utilized, whose beam pattern exhibits perfect nulling at the main beam angles and provides uniform power for detection of channel utilization out of main beam. The proposed method can be utilized with any arbitrary beamforming when we make main beamforming. Through computer simulation, it can be shown that proposed AAS and complementary beamforming increase data transmission range from 2m to 3.95m in 480Mbps data transmission system and increase throughput about 20% as compared with general UWB AAS systems.

• Journal of Satellite, Information and Communications
• /
• v.9 no.2
• /
• pp.85-90
• /
• 2014

In this paper, we propose a novel UE(User Equipment) position tracking algorithm of visible light signals, and analyze BER performance when optical beamforming scheme is applied in VLC(Visible Light Communications) system. The optical beamforming scheme as an interference mitigation method provides good optical channel conditions between UE(Rx) and LED light(Tx), and lead to better BER performance because UE is able to get a better RSSI(Received Signal strength indication) value. For the system BER, the proposed UE position tracking method for optical beamforming transmission demonstrates the performance enhancement compared to a system not applied the optical beamforming transmission scheme, and up to about 5~6dB SNR performance gain is achieved. The results of the paper can be applied to design of various VLC and LBS applications for ubiquitous home network systems.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.05d
• /
• pp.449-454
• /
• 1996

원자력발전소 증기발생기 전열관의 레이저 슬리브 용접시, 레이저 전송 및 용접상태의 광학적 감시방법을 개발하였다. 전열관 레이저용접은 용접 중의 레이저 출력, 레이저 전송 광학계의 파손여부, 광학 정렬상태 등을 정확히 감시하며 수행하여야 하지만, 작업공간의 협소함과 방사능 공간이라는 어려움 때문에 적절한 감시방법이 없었다. 본 연구에서는 레이저 빔 전송을 위한 광섬유 광학계를 그대로 이용하여, 용접시 발생되는 radiation과 용접 표면에서 반사되는 Nd:YAG 레이저 빔을 측정하여 레이저 및 광학계 상태를 실시간 감시할 수 있는 기술을 실험적으로 확인하였다. 실험은 Inconel plate를 시편으로 이루어졌으며, 레이저 펄스길이, 레이저 반복률에 따른 감시 조건과 초점확인 기능에 대해서도 논의하였다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.4A
• /
• pp.318-324
• /
• 2011

In this paper, three coordinated random beamforming (CRBF) schemes are analyzed in a two-cell symmetric interference channel. A simple partial coordination of RBF with base station selection (BSS) is shown to achieve the same average sum rate performance of CRBF with joint encoding (JE). To improve the sum rate performance further, we also propose a transmission mode selection (TMS) between the BSS and JE which is shown to have additional sum rate gain for the large number of users. Simulation results verify the eectiveness of the proposed CRBF schemes and accuracy of the proposed analysis.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.174.2-174.2
• /
• 2013

사이클로트론에서 가속된 70 MeV 양성자 빔은 stripper에서 인출된 후 ISOL 표적에 조사하게 된다. 이 때 희귀동위원소를 생산하기 위한 ISOL 표적의 온도는 평균 $2,000^{\circ}C$ 5%로 유지하여야 한다. 사용하고자 하는 원판형태의 우라늄 표적은 직경이 45 mm 이므로 50 mm 이상의 균일한 양성자 빔이 필요하다. 본 연구에서는 stripper에서부터 ISOL 표적 까지 빔전송에 필요한 최적 조건을 연구하였다. 총 길이는 15 m 이며 두 개의 dipole을 사용하여 빔을 90도 전환시키며 3개의 4중극전자석을 사용하였다. ISOL 표적에 균일한 빔을 조사하기 위해 wobbling 방법을 활용하여 직경 50 mm 의 균일빔을 발생하고자 한다. 빔 전송 프로그램 TRANSPORT을 이용하여 stripper에서 wobbler 전까지의 빔 광학을 계산한 결과를 보고자 하고 TRANSPORT의 결과를 TURTLE 프로그램에 적용시켜 ISOL 표적에서의 균일도를 5% 미만으로 유지하는 최적조건을 발표한다.

• Journal of Advanced Marine Engineering and Technology
• /
• v.40 no.9
• /
• pp.818-823
• /
• 2016

Millimeter wave (mm-wave) communication systems provide high data rates owing to the large bandwidths available at mm-wave frequencies. Recently, analogue and digital combined beamforming, namely "hybrid beamforming" has drawn attentions owing to its ability to realize the required link margins in mm-wave systems. Taking into account the radio frequency (RF) hardware limitations, such as the analogue phase shifter gain constraint and the low resolution of the phase controller, we introduce an uplink hybrid beamforming system that includes discrete Fourier transform (DFT) based "fixed" analogue beamforming. We adopt a zero-forcing (ZF) multiple-input multiple-output (MIMO) equalizer to eliminate the uplink inter-user interferences. Moreover, to improve the sum-rate performances, we propose a transmit beam selection algorithm which makes the uplink effective channels, i.e., the beamformed channels, become near orthogonal. The effectiveness of the proposed beam selection algorithm was verified through numerical simulations.

• Korean Journal of Optics and Photonics
• /
• v.31 no.6
• /
• pp.274-280
• /
• 2020

In this paper, the effect of atmospheric turbulence is numerically modeled and analyzed via a phase-screen model, in regard to long-range optical energy transfer using coherent beam combination. The coherent-beam-combination system consists of three channel beams pointing at a target at a distance of 1-2 km. The phase and propagation direction of each channel beam are assumed to be corrected in an appropriate manner, and the atmospheric turbulence that occurs while the beam propagates through free space is quantified with a phase-screen model. The phase screen is statistically generated and constructed within the range of fluctuations of the structure constant Cn2 from 10-15 to 10-13 [m-2/3]. Particularly, in this discussion the shape, distortion, and combining efficiency of the 3-channel combined beam are calculated at the target plane by varying the structure constant used in the phase-screen model, and the effect of atmospheric turbulence on beam-combination efficiency is analyzed. Analysis with this numerical model verifies that when coherent beam combination is used for long-range optical energy transfer, the received power at the target can be at least three times the power obtainable by incoherent beam combination, even for maximal atmospheric fluctuation within the given range. This numerical model is expected to be effective for analyzing the effects of various types of atmospheric-turbulence conditions and beam-combination methods when simulating long-range optical energy transfer.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37A no.12
• /
• pp.1133-1139
• /
• 2012

In this paper, hybrid mode beamforming (HMB) which allows simultaneous transmission of joint beamforming and disjoint beamforming is proposed. HMB is proven to be asymptotically optimal beamforming for sum rate growth. Extensive simulations show that HMB achieves nearly the same performance as joint encoding (JE) in symmetric interference channel. It is also shown that it outperforms JE in a more realistic asymmetric interference channel environment, though it still experiences some performance degradation due to power inefficiency of joint beamforming in asymmetric channel.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.10
• /
• pp.851-868
• /
• 2015

A radio telescope which has been dominantly used for millimeter and submillimeter wave radio astronomy is a cassegrain antenna. A various receivers with specified observing bandwidths are installed on cassegrain antenna so as to carry out to investigate a diverse radio astronomy. A beam guiding system should be required so that a various receiver can be conducted their own observational frequency bands. The beam guiding system based on Gaussian beam transmission theory consists of quasi-optical circuit used such ellipsoidal mirror, dielectric lens and feed horn. In this paper, not only Gaussian beam transformations based on Gaussian beam theory are presented, but also design techniques for quasi-optical circuit are given. By using proposed design techniques, both Gaussian beam quasi-optical circuits to be used for cassegrain antenna and design results are also described. Properties of key focusing elements such ellipsoidal mirror and dielectric lens and feed horn are also discussed. It is expected that beam guiding system to be applied cassegrain antenna could be easily designed by using proposed design techniques.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.288-288
• /
• 2010

현대사회의 급속한 고령화로 암 환자의 수는 2002년 기준 약 10만 명에서 매년 7~10 %씩 증가되어 2012년에는 20만 명이 될 것으로 추정되어지고 있다. 수술, 방사선 치료, 약물요법 등이 주요 치료방법이며, 암 환자의 30-50 %가 전리 방사선치료를 받고 있다. 방사선치료는 19세기 말에 발견된 미지의 X-선이 희망의 방사선으로 변화하여 암의 진단 및 치료에 활용되고 있으며, 인간 삶의 질 향상에 핵심적인 역할을 담당하고 있다. 기존의 X-선이나 감마선의 단점을 극복 할 수 있는 입자 빔을 1970년대 미국의 캘리포니아 대학 Berkely National Laboratory에서 처음으로 암 치료에 적용하였다. 현재는 일본과 독일에서 활발하게 활용되고 있으며 국내에서도 입자 치료시설을 구축 또는 개발계획 중에 있다. 방사선치료의 완치율을 높이기 위해서는 정확한 선량을 암세포에 전달해야 한다. 환자에 전달되는 입자빔을 실시간으로 측정하는 기술이 연구되어지고 있다. 지금까지는 빔의 특성을 측정하기 위해 간섭적인 방법을 사용하였으나, 투과형 검출기를 개발하여 실시간으로 치료와 빔 특성을 동시에 수행하는 기술개발연구가 보고되고 있다. 본 연구에서는 Multileaf Faraday Cup (MLPC) 검출기 설계구조와 데이터 측정방법에 관한 연구를 수행하고자 한다. 빔의 전송 방향으로 3개층의 $4{\times}4$ 배열의 구조로 48 channel의 전류값을 측정하여 입자빔의 분포를 실시간으로 관측하고, 측정된 전류는 ADC를 거쳐 치료계획에 의해 선택된 영역의 SOBP를 유지하도록 range modulation propeller를 조절하는 feed-back system을 갖춘 방사선치료빔 실시간 측정장치 개발에 관한 결과를 보고하고자 한다.