• 한국컴퓨터정보학회논문지
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• 제9권2호
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• pp.97-104
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• 2004

MAI와 ISI를 발생하는 다중로 채널 왜곡은 CDMA시스템의 용량을 제한하는 두 가지 중요한 요소이며 전통적인 CDMA시스템은 원근 문제를 무시하거나 전력제어로 이를 제한하였다. 다중 사용자 검출과 시공간 처리는 MAJ와 ISI를 제거하는 강력한 두 개의 방법이다. 본 논문에서는 DS-CDMA 시스템의 용량을 증대시키고 통화 품질을 향상시키기 위해 기존에 사용하던 빔 형성과 추정 알고리듬을 시공간 영역으로 확장하여 연구하였다. 시뮬레이션 결과, 여러 가지 빔포머의 성능은 다중사용자 빔포머인 역상관 빔포머를 상한으로 하여 부분 공간 기반 빔포머, 최소 분산 빔포머, 전통적인 빔포머 순으로 우수하게 평가되었다. 특히 부분 공간 기반 빔포머는 최소 분산 빔포머에 비해 약 5㏈정도 우수한 성능을 보였으며. 전통적인 빔포머로는 원근 문제를 해결할 수 없음을 확인하였다.

• 대한전자공학회논문지
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• 제25권10호
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• pp.1263-1273
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• 1988

LMS 기법을 이용한 적응 신호 처리상에서 복합적으로 제기 되어온 간섭신호 제거, 수렴속도, 오차조정 및 기준신호 발생 등의 전체적인 문제점들을 합성적으로 고려한 하나의 적응 기법이 제시된다. 제안된 방법은 최소화 적응 처리를 하기전에 먼저 어레이 입력으로 들어오는 복합신호로부터 표적신호를 분리하고, 기준신호를 제거한다. 본 기법은 적응처리기에 있는 잔유잡음의 정도에 제한을 둔다. 분석결과 본 기법은 코히어런트 또는 인코히어런트 간섭신호 제거에 효과적이며 특히, 수렴계수의 동적범위가 넓어 안정도가 좋고 수렴속도가 빠르며 평균자승오차가 매우적다. 또한, 기준신호발생이 필요없다는 장점이 있다. 시뮬레이션 결과는 이론적인 예측과 일치한다.

• 대한전자공학회논문지SP
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• 제49권2호
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• pp.130-136
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• 2012

본 논문에서는 등간격 선형 배열 센서에서 초점빔형성을 이용한 근접장 거리 추정 시에 방위각 오차의 영향을 극복하기 위하여, 거리 방향 탐색 시에 일정 범위 안의 방위각 오차를 보정하여 추정 성능을 향상시키는 기법을 제안하였다. 방위각 오차는 탐색 거리가 주어졌을 때 경사법을 기반으로 빔형성기 출력값이 최대가 되도록 보정하게 된다. 모의실험 결과를 통해, 제안된 기법이 주엽의 폭보다 작은 방위각 오차를 보정하여 거리 추정 오차를 방위각 오차가 없는 경우와 같은 수준으로 감소시킬 수 있음을 확인하였다.

• 대한전자공학회논문지TC
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• 제44권5호
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• pp.63-69
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• 2007

본 논문에서는 이동 차량에 다중 안테나를 설치하여 기존의 이동통신이나 방송시스템의 성능을 향상 시키는 이동 릴레이의 구조를 제안한다. 하드 핸드오버를 사용하는 시스템에서 다중 안테나를 갖는 이동 릴레이가 셀 경계에 있을 때에 스마트 안테나 기법을 적용하기 위해서는 셀 탐색과 입사각을 추정해야 하므로 본 논문에서는 셀 탐색과 입사각을 동시에 추정하는 방법을 제안한다. 본 논문에서 제안한 셀 탐색과 입사각 동시 추정기법의 성능을 모의실험을 통해 검증한다.

• International Journal of Advanced Culture Technology
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• 제7권4호
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• pp.236-241
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• 2019

This paper will read about a multichannel frequency-modulated continuous wave (FMCW) radar sensor with switching transmit (TX) antennas is developed at W-band. To achieve a high angular resolution, a uniform linear array consisting of 5 switching-TX and 12 receive (RX) antennas is employed with the digital beamforming technique. The overall radar front-end module comprises a W-band transceiver and TX/RX antennas. A multichannel transceiver module consists of 5 up-conversion and 12 down-conversion channels, where one of the TX channels is sequentially switched ON. For developing transmitter, we developed an HPA (high power amplified) MMIC chip for W-band radar system and fabricated a transmitter module using this chip. In order to develop the W-band transmitter, we analyzed the important antenna transition structure from HPA MMIC line to W/G (Waveguide)antenna via M/S(microstrip) and fabricated it with 5 transmission channels. As a result, the output power of the transmitter was within 1 dB of the error range after analysis and measurement under normal temperature and environmental conditions.

• 한국군사과학기술학회지
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• 제24권1호
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• pp.41-49
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• 2021

In electronic warfare, beamforming using multiple antennas is applied for effective transmission of electronic attack signals. In order to perform an electronic attack against multiple threats using the same frequency resource, it is necessary to apply a multi-beam transmission algorithm that has been studied in wireless communication systems. For electronic attacks against multiple threats, this paper presents an MMSE(Minimum Mean-Squared Error) beam-forming technique based on the prior location information of threats and an optimization method for power allocation. In addition, the performance of the proposed method is evaluated and received signals of multiple threats are compared and analyzed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권6호
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• pp.2595-2618
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• 2018

In this paper, we investigate secure communication with the presence of multiple eavesdroppers (Eves) in a two-tier downlink dense heterogeneous network, wherein there is a macrocell base station (MBS) and multiple femtocell base stations (FBSs). Each base station (BS) has multiple users. And Eves attempt to wiretap a macrocell user (MU). To keep Eves ignorant of the confidential message, we propose a physical-layer security scheme based on cross-layer cooperation to exploit interference in the considered network. Under the constraints on the quality of service (QoS) of other legitimate users and transmit power, the secrecy rate of system can be maximized through jointly optimizing the beamforming vectors of MBS and cooperative FBSs. We explore the problem of maximizing secrecy rate in both non-colluding and colluding Eves scenarios, respectively. Firstly, in non-colluding Eves scenario, we approximate the original non-convex problem into a few semi-definite programs (SDPs) by employing the semi-definite relaxation (SDR) technique and conservative convex approximation under perfect channel state information (CSI) case. Furthermore, we extend the frame to imperfect CSI case and use the Lagrangian dual theory to cope with uncertain constraints on CSI. Secondly, in colluding Eves scenario, we transform the original problem into a two-tier optimization problem equivalently. Among them, the outer layer problem is a single variable optimization problem and can be solved by one-dimensional linear search. While the inner-layer optimization problem is transformed into a convex SDP problem with SDR technique and Charnes-Cooper transformation. In the perfect CSI case of both non-colluding and colluding Eves scenarios, we prove that the relaxation of SDR is tight and analyze the complexity of proposed algorithms. Finally, simulation results validate the effectiveness and robustness of proposed scheme.

• 한국전자파학회논문지
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• 제13권10호
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• pp.989-997
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• 2002

본 논문은 수신신호의 자기상관행렬로부터 얻어진 2개의 고유벡터를 이용하여 웨이트 벡터를 구함으로써 각도퍼짐이 존재하는 환경에서도 스마트 안테나의 성능을 향상시키는 새로운 방법을 제시하였다 기존의 고유치에 의거한 빔형성 기술은 가장 큰 고유치의 상응 고유백터 만을 사용하는 것에 비해 본 논문에서 제시하는 방법은 두개의 고유백터를 효율적으로 적용함으로써 각퍼짐이 많은 신호환경에서 특히 강인한 성능을 보인다. 본 논문에서 사용하는 고유벡터는 첫번째와 두번째로 가장 큰 고유값에 대응되는 벡터이며, 현재 상용화되고 있는 DSP로 구현 가능한 계산량(3.5$N_2$+ 12N)을 통해 정확하게 구해진다. 본 제안방법을 WCDMA 환경에서 모의 실험한 결과 넓은 각도퍼짐에도 성능이 우수하였으며, 고유함수 계산을 위한 상용 툴인 MATLABTM 프로그램의 고유함수를 이용하여 얻은 이론적인 성능값과도 큰 차이가 없음을 확인하였다.

• 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.

• Journal of Positioning, Navigation, and Timing
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• 제11권3호
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• pp.163-172
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• 2022

Typical anti-jamming technologies based on array antennas, Space Time Adaptive Process (STAP) & Space Frequency Adaptive Process (SFAP), are very effective algorithms to perform nulling and beamforming. However, it does not perform equally well for all types of jamming signals. If the anti-jamming algorithm is not optimized for each signal type, anti-jamming performance deteriorates and the operation stability of the system become worse by unnecessary computation. Therefore, jamming classification technique is required to obtain optimal anti-jamming performance. Machine learning, which has recently been in the spotlight, can be considered to classify jamming signal. In general, performing supervised learning for classification requires a huge amount of data and new learning for unfamiliar signal. In the case of jamming signal classification, it is difficult to obtain large amount of data because outdoor jamming signal reception environment is difficult to configure and the signal type of attacker is unknown. Therefore, this paper proposes few-shot jamming signal classification technique using meta-learning and transfer-learning to train the model using a small amount of data. A training dataset is constructed by anti-jamming algorithm input data within the GNSS receiver when jamming signals are applied. For meta-learning, Model-Agnostic Meta-Learning (MAML) algorithm with a general Convolution Neural Networks (CNN) model is used, and the same CNN model is used for transfer-learning. They are trained through episodic training using training datasets on developed our Python-based simulator. The results show both algorithms can be trained with less data and immediately respond to new signal types. Also, the performances of two algorithms are compared to determine which algorithm is more suitable for classifying jamming signals.