• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권4호
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• pp.1330-1350
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• 2022

As a preprocessing operation of transmitter antennas, the hybrid precoding is restricted by the limited computing resources of the transmitter. Therefore, this paper proposes a novel hybrid precoding that guarantees the communication efficiency with low complexity and a fast computational speed. First, the analog and digital precoding matrix is derived from the maximum eigenvectors of the channel matrix in the sub-connected architecture to maximize the communication rate. Second, the extended power iteration (EPI) is utilized to obtain the maximum eigenvalues and their eigenvectors of the channel matrix, which reduces the computational complexity caused by the singular value decomposition (SVD). Third, the Aitken acceleration method is utilized to further improve the convergence rate of the EPI algorithm. Finally, the hybrid precoding based on the EPI method and the Aitken acceleration algorithm is evaluated in millimeter-wave (mmWave) massive multiple-input and multiple-output (MIMO) systems. The experimental results show that the proposed method can reduce the computational complexity with the high performance in mmWave massive MIMO systems. The method has the wide application prospect in future wireless communication systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제18권7호
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• pp.2047-2066
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• 2024

In order to improve the coverage and achieve massive spectrum access, non-orthogonal multiple access (NOMA) technology is applied in millimeter wave massive multiple-input multiple-output (mMIMO) communication network. However, the power assumption of active sensors greatly limits its wide applications. Recently, Intelligent Reconfigurable Surface (IRS) technology has received wide attention due to its ability to reduce power consumption and achieve passive transmission. In this paper, spectral efficiency maximum problem in the millimeter wave mMIMO-NOMA system with IRS is considered. The sparse RF chain antenna structure is designed at the base station based on continuous phase modulation. Furthermore, a joint optimization problem for power allocation, power splitting, analog precoding and IRS reconfigurable matrices are constructed, which aim to achieve the maximum spectral efficiency of the system under the constraints of user's quality of service, minimum energy harvesting and total transmit power. A three-stage iterative algorithm is proposed to solve the above mentioned non-convex optimization problems. We obtain the local optimal solution by fixing some optimization parameters firstly, then introduce the relaxation variables to realize the global optimal solution. Simulation results show that the spectral efficiency of the proposed scheme is superior compared to the conventional system with phase shifter modulation. It is also demonstrated that IRS can effectively assist mmWave communication and improve the system spectral efficiency.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 추계종합학술대회 논문집
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• pp.833-836
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• 1999

In this paper, a wideband MMIC LNA was designed using low Q matching network. Gains of 9.8~12.2 ㏈, and noise figures of 1.7~2.1 ㏈ were obtained from the fabricated wideband MMIC LNA in the frequency ranges of 1.5~2.5㎓. And maximum output power of 10.83 ㏈m were obtained at the center frequency of 2 ㎓. The chip size of the fabricated wideband MMIC low noise amplifier is 1.4 mm$\times$1.4 mm.

• 전기전자학회논문지
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• 제16권2호
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• pp.127-130
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• 2012

In this paper, we reported on a single balanced monolithic diode mixer using Marchand balun for millimeter-wave applications. The single balanced monolithic mixer was fabricated using drain-source-connected pseudomorphic high electron mobility transistor (PHEMT) diodes considering the PHEMT MMIC full process. The average conversion loss is 16 dB in the RF frequency range of 81~86 GHz at LO frequency of 75 GHz with LO power of 10 dBm. The RF-to-LO isolation characteristics are greater than -30 dB and the total chip size is $1.0mm{\times}1.35mm$.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권5호
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• pp.2102-2123
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• 2016

This paper considers a channel estimation scheme for millimeter-wave multiuser multiple-input multiple-output systems. According to the proposed method, parts of the beams are selected and the channel parameters are estimated according to the sparsity of channels and the orthogonality of the beams. Since the beams for each channel become distinct and the signal power increases with the increased number of antennas, the proposed approach is able to achieve good estimation performance. As a result, the sum rate can be increased in comparison with traditional approaches, and channels can be estimated with fewer pilot symbols. Numerical results verify that the proposed approach outperforms traditional approaches in cases with large numbers of antennas.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.857-860
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• 2005

We reported 94 GHz, low conversion loss, and high isolation single balanced active-gate mixer based on 70 nm gate length InGaAs/InAlAs metamorphic high electron mobility transistors (MHEMTs). This mixer showed that the conversion loss and isolation characteristics were 2.5 ${\sim}$ 2.8 dB and under -30 dB, respectively, in the range of 93.65 ${\sim}$ 94.25 GHz. The low conversion loss of the mixer is mainly attributed to the high-performance of the MHEMTs exhibiting a maximum drain current density of 607 mA/mm, a extrinsic transconductance of 1015 mS/mm, a current gain cutoff frequency ($f_t$) of 330 GHz, and a maximum oscillation frequency ($f_{max}$) of 425 GHz. High isolation characteristics are due to hybrid ring coupler which adopted dielectric-supported air-gapped microstrip line (DAML) structure using surface micromachined technology. To our knowledge, these results are the best performance demonstrated from 94 GHz single balanced mixer utilizing GaAs-based HEMTs in terms of conversion loss as well as isolation characteristics.

• 한국군사과학기술학회지
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• 제15권2호
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• pp.161-168
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• 2012

In this paper, we have experimentally studied on phase characteristics of airborne radome for ELINT directional finding system, because it is difficult to find theoretical solutions for phase error of the radome. Especially, we described the millimeter wave band radome that was fabricated with cyanate-ester material and its thickness was 2mm. We presented the phase error about millimeter band radome. That phase error is about 30 degrees for parallel and perpendicular polarization in the K-Ka band. That is reasonable value for the ELINT directional finding system.

• 한국통신학회논문지
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• 제41권8호
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• pp.890-895
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• 2016

최근 빠른속도로 발전하는 무선통신기술로 인하여 스마트 기기의 사용이 날로 증가하고 있다. 이에 따른 데이터 트래픽의 문제가 날로 증가함에 따라 네트워크의 용량 증대를 위하여 아직 개척되지 않은 새로운 영역인 6GHz 이상의 대역에 대한 연구가 진행되었다. 밀리미터파(Millimeter Wave, MmWave) 통신은 6GHz 이상의 대역을 이용하여 초당 기가비트의 데이터 전송률 달성을 가능하게 한다. 작은 파장으로 인한 경로 손실을 극복하기 위해 대량의 안테나 배열을 사용하여 이득을 높인다. 본 논문에서는 하이브리드 빔포밍(Hybrid beamforming)을 이용한 프리코딩 과정에서 시스템의 스펙트럼 효율(Spectral efficiency)을 최대화 하는 알고리즘을 제시하였다. 또한 스펙트럼 효율이 최대가 되는 빔 수의 최적화 방법을 수식을 통해 제안하였다. 제안한 방법으로 스펙트럼 효율을 최대화 하는 것을 확인하였다.

• 대한전자공학회논문지TC
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• 제48권11호
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• pp.89-94
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• 2011

본 논문에서는 밀리미터파 Tuner system을 이용하여 밀리미터파 탐색기에 적용 가능한 W-band MMIC 저잡음 증폭기를 구현하였다. 저잡음 증폭기를 위해 구현된 MHEMT의 측정결과 692mA/mm의 드레인 전류 밀도, 726mS/mm의 최대전달컨덕턴스를 얻었으며, RF 특성으로 전류이득차단주파수는 195GHz, 최대공진주파수는 305GHz의 양호한 성능을 나타내었다. 제작된 W-band 저잡음 증폭기의 측정결과 94GHz에서 7.42dB의 우수한 S21 이득 특성을 얻었으며, 잡음 지수의 측정결과 94.2GHz에서 2.8dB의 잡음 특성을 얻었다.

• 융합신호처리학회논문지
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• 제18권1호
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• pp.21-24
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• 2017

밀리미터파 영상시스템은 위험한 은닉 물체를 탐지하는 분야에 활용되고 있다. 능동형 시스템은 외부 RF 신호원이 필요하지만 수동형은 인체와 물체의 온도차에 의한 흑체복사 성질을 이용하므로 실내외에서 사용이 가능하다. 그러나 일반적으로 수동형 밀리미터파 영상은 온도분해능과 신호레벨이 낮고 잡음의 영향이 크다. 본 논문에서 은닉 물체까지의 거리 추정을 위한 수동형 스테레오 3mm 밀리미터파 영상에 관한 연구를 수행한다. 수평, 수직 편광 밀리미터파 영상시스템에서 획득한 두 쌍의 스테레오 영상을 이용하여 은닉물체를 k-means 클러스터링 알고리즘으로 몸체영역과 분할하고 물체의 중심 위치를 이용하여 거리를 추정한다. 실험에서 성공적으로 거리를 추정할 수 있음을 확인한다.