• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.5
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• pp.1025-1030
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• 2011

To improve the performance of mobile communication systems, beamforming technology is being considered. However, the number of antenna should be more than four to implement beamforming technology. Therefore, the existing 2-Tx RU (radio unit) for $2{\times}2$ MIMO (multiple input multiple output) should be replaced by 4-Tx RU for beamforming function. In this paper, we propose a new method to implement 4-Tx beamforming RU reusing the existing 2-Tx RU. We think that our method is very useful from the viewpoint of cost and environment because the existing 2-Tx RUs can be reused.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.2
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• pp.289-294
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• 2014

In this paper, we investigate the user scheduling, transmit beamforming, and receive beamforming of uplink space division multiple access (SDMA) systems where multiple users are allowed to transmit their signal to a base station (BS) using the same frequency band simultaneously. The BS performs a receive beamforming using the predetermined pseudo-random pattern and select users with a specific criterion. Especially, in this paper, we propose the threshold-based transmit power control, in which a user decrease its transmit power according if its generating interference to other users's signal is larger than a predetermined threshold. Assuming that the TDD system is used, the channel state information (CSI) can be obtained at each user from pilot signals from the BS. Simulation results show that the proposed technique significantly outperforms the existing user scheduling algorithms.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2015.07a
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• pp.319-321
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• 2015

실시간으로 초고속 이동통신 서비스를 제공하기 위해 5 세대 이동통신 시스템에서는 초광대역(ultra wideband) 시스템 구축에 용이한 3-300GHz 밀리미터파 대역의 도입을 고려하고 있다. 그러나 밀리미터파 대역 신호는 상용 이동통신에서 사용되는 3GHz 이하의 대역에 비하여 전파특성이 열악하다. 이러한 밀리미터파 대역의 효과적인 활용을 위해 5 세대 이동통신 시스템에는 아날로그/디지털 빔포밍 기술을 결합한 하이브리드 빔포밍 기술을 고려하고 있다. 본 논문에서는 하이브리드 빔포밍 기술을 적용한 다중 안테나 상향링크 시스템에서 제로-포싱 (zero-forcing) 구조의 송수신기 설계 기법을 소개한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.10
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• pp.876-884
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• 2015

In this paper, a switched beamforming antenna system at 28 GHz frequency band is described for $5^{th}$ generation wireless communication. The butler matrix is used as a beamforming system and it produces linear spaced phase difference at four output ports. Array antenna is designed that can be steered in desired 4 different directions 28 GHz frequency band. Operation of designed butler matrix that composed of couplers and feedline is explained. The antenna system is designed in RO3003 substrate that has a height of 5 mil and dielectric constant of 3. The size of butler matrix is $20.3{\times}13.0mm^2$ and size of array antenna is $21.2{\times}19.9mm^2$. This system can be steered from $-34^{\circ}$ to $33^{\circ}$ and minimum sidelobe level is 12.9 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.3
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• pp.195-201
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• 2019

The effectiveness of the phased array antenna in wireless power transfer systems is due to its ability to form a beam pattern towards the desired direction. To maximize the efficiency of wireless power transfer through beamforming, the transmitter must recognize the information on the optimal transmission path. To achieve this, the transmitter usually transmits pilot signals periodically and the receiver extracts the optimal beamforming weights using the pilot signals. The receiver then feeds the beamforming weights back to the transmitter. In general, the amount of feedback increases with the number of antennas, which causes feedback overhead when there is a large number of antennas. In this paper, we propose a feedback simplification scheme based on the far-field approximation method. The simulation results are provided to validate the impact of the simplified feedback on the beam pattern.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.6
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• pp.501-504
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• 2017

In this paper, a hybrid beamforming antenna system using broadband butler matrix and phase shifter is proposed. In the previous works, an $8{\times}8$ butler matrix is used to overcome a drawback of the $4{\times}4$ butler matrix based switched beamforming which provides only 4 beam patterns. However the $8{\times}8$ butler matrix should be designed on the bi-layered substrate using via holes due to its complex structure. It causes performance degradation. To overcome these problems, the proposed hybrid beamforming antenna system is designed on the single side of the substrate for simple structure. By addition of two phase shifter, it provide various beam patterns. The proposed antenna system provides more than 10 dBi radiation gain in the ${\pm}45^{\circ}$ scanning range by 16 input combinations.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12A
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• pp.1165-1171
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• 2008

In this paper, a pilot emitting amplify-and-forward relay and its beamforming schemes, OBF (overall beamforming) and RBF (hop-by-hop beamforming), are proposed for two-hop relaying systems. The OBF performs beamforming with respect to a overall channel from a source node (SN) to a destination node (DN) through a relay node (RN), while the proposed RBF performs two independent beamformings: from the SN to the RN and from the RN to the DN. From our analytic and numerical results, it is shown that bit-error-rate (BER) performance of the proposed RBF is better than that of the OBF scheme since the RBF system can estimate channel more proper than the CBF system, which is verified by deriving and comparing the mean square errors of the channel estimation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.6
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• pp.1286-1291
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• 2013

Intensive researches on multiuser-based Massive MIMO are performed to increase the spectral efficiency. Although the Massive MIMO scheme based on huge number of antennas inevitably causes hardware and computational complexity in baseband and radio frequency (RF) elements, the problem can be mitigated without serious performance degradation by limiting the number of baseband and RF elements below the number of transmit antennas of base station and opportunistically selecting transmit antennas according to channel states. Accordingly, this paper proposes a simple antenna selection scheme for multiuser-based Massive MIMO systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.11
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• pp.2298-2304
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• 2015

In this paper, we provide a new approach which optimizes the vertical tilting angle of the base station for multi-cell multiple-input single-output (MISO) downlink active antenna systems (AAS). Instead of the conventional optimal algorithm which requires an exhaustive search, we propose simple and near optimal algorithms. First, we represent a large system approximation based vertical beamforming algorithm which is applied to the average sum rate by using the random matrix theory. Next, we suggest a signal-to-leakage-and-noise ratio (SLNR) based vertical beamforming algorithm which simplifies the optimization problem considerably. In the simulation results, we demonstrate that the performance of the proposed algorithms is near close to the exhaustive search algorithm with substantially reduced complexity.