• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12C
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• pp.764-773
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• 2011

Despite enormous performance gain with multi-antenna transmission in the single cell environment, its gain diminishes out in the multi-cell environment due to interference. It is also very hard to solve the efficient downlink beamforming with low complexity in multi-cell environment. First, this paper shows that the asymptotically sum rate optimal downlink beamformings at low and high SNR are maximum ratio transmit (MRT) and zero forcing (ZF) beamforming in the multi-cell system, respectively. Secondly, exploiting the asymptotically optimal downlink beamforming, we develop simple two types of near optimal downlink beamforming schemes having the form of minimum mean squared error (MMSE) beamforming obtained from the dual uplink problem. For each type, three different subclasses are also considered depending on the computational complexity. The simulation results show that the proposed near optimum algorithms provide the trade-off between the complexity and the performance.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.519-522
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• 2004

수중 음향 탐지 시스템에서 빔 형성 기법은 탐지 성능에 큰 영향을 미치기 때문에 최적의 빔 설계는 오랫동안 많은 연구자들에 의해 연구되어 왔다. 실제로 최적의 빔 형성기를 구현할 때에는 각각의 센서에 대한 특성 고려와 파워를 효율적으로 전달하기 위한 정합회로의 설계가 필수적이다. 이전의 논문에서는 BeamCAD Tool을 이용한 최적 가중치의 계산, 센서 임피던스 측정 데이터와 Sensor Modeling Tool을 이용한 등가회로 모델링 그리고 Impedance Matching Tool을 이용한 정합회로 설계 기법에 대해서 소개하였다. 본 논문에서는 이러한 기법들과 함께 ABCD 전송 파라메터를 이용한 센서 가중치 보정 기법을 소개한다. 그리고 이러한 여러 기법들을 이용하여 최적빔 설계를 위한 가중회로를 구성하는 방법에 대해서 논의한다.

• Journal of Broadcast Engineering
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• v.23 no.5
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• pp.693-700
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• 2018

In this paper, we propose a wireless video transmission scheme, providing medium and long range communication in the 2.4GHz band with beamforming. With this scheme, it is shown that the transmission rate of 32Mbps and received signal power of -77dBm is achieved with 4 antennas of 5dBi and 16dBm transmit power at each antenna connection for the distance of 3.6km. The scheme also provides transmission distance of 20km for 10~12Mbps with the 4 omni-directional antennas of 5dBi.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.2
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• pp.9-16
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• 2012

In this paper, the beamforming and user scheduling scheme for device-to-device (D2D) underlaying celullar networks with partial channel state information is investigated. In the proposed scheme, cellular users whose channels are nearly orthogonal to the channel between base station and D2D receiver are selected for unitary beamforming so as to minimize the interference to the D2D receiver. The interference caused by underlaying D2D communication can be minimized by reducing the D2D transmitter's transmission power. To enhance the cellular users' throughput further, we also investigate codebook generation method in which each code vector belongs to multiple unitary code matrices. From simulation results, we show that the proposed beamforming and user scheduling scheme mitigates D2D interference to the cellular networks and the codebook generation method improves cellular users' throughput.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1A
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• pp.25-33
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• 2012

Random beamforming (RBF) uses the signal to interference plus noise ratio (SINR) feedback to select users in multiple-input multiple-output (MIMO) systems. A large number of users are required to obtain the gain of multi-user diversity for a downlink transmission. However, if the number is not large enough, it may be difficult to obtain multi-user diversity, leading to a rapid degradation in performance. To resolve this problem, we propose the beamforming matrix transformation and the user scheduling method. The beamforming matrix transformation scheme uses the SINRs of each users and have a better performance than conventional schemes over a small number of users. In addition, we propose the user scheduling scheme corresponding to the beamforming matrix transformation. In simulation results, we demonstrate that the sum-rate can be improved according to the number of users.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.1
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• pp.32-35
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• 2018

Massive multiple-input multiple-output (MIMO) transmission is an essential technique for achieving the high bandwidth efficiency required in 5G mobile communication systems. Various forms of arrays can be used as the number of antenna elements increases for massive MIMO transmission. In this letter, we propose a beamforming algorithm applicable to multiuser MIMO transmission using uniform circular arrays. By employing quasi-orthogonal beam pairs obtained from the inter-beam correlation information, we minimize inter-user interference and evaluate the resulting performance gain.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.300-304
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• 2015

This paper presents an omnidirectionally beam-steerable orthogonal loop resonator for wireless power transfer. The resonator is composed of two orthogonal loops. These connections of two loops and the current direction on the loops are determined by the control of switch. The magnetic field direction is determined by the vector sum of each loop current. The beam is steerable to eight directions by four switch modes. Using the suitable switch mode, the simulation and measurement efficiencies in the whole azimuthal direction are 56.3~60.0 %(deviation 3.7 %) and 41.2~48.7 %(deviation 7.5 %), respectively. The results show a little variation of transmission efficiency in the azimuthal direction.

• 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.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.12
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• pp.1632-1638
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• 2020

In this paper, we investigate a multi-beam satellite communication system where multiple terminals transmit information signals to the gateway via a satellite. The satellite is equipped with phased array antennas to form multiple spot beams of which bandwidths are not identically allocated. We formulate an optimization problem to maximize fairness of beam bandwidth allocation. In order to solve the problem, we propose two heuristic algorithms; iterative beam bandwidth allocation (IBBA) and request ratio-based beam bandwidth allocation (RRBBA) algorithms. The IBBA algorithm iteratively equalizes the ratio of allocated bandwidth of each beam to their resource request while the RRBBA algorithm allocates beam bandwidth calculated from the ratio. Simulation results show that the IBBA algorithm has close fairness performance to the optimum while the RRBBA algorithm has less performance than the IBBA algorithm at the price of reduced computational complexity.

• Journal of Broadcast Engineering
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• v.15 no.1
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• pp.122-132
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• 2010

AT-DMB system has been developed to increase data rate up to double of conventional T-DMB in the same bandwidth while maintaining backward compatibility. The AT-DMB system adopted hierarchical modulation which adds BPSK or QPSK signal as enhancement layer to existing DQPSK signal. The enhancement layer signal should be small enough to maintain backward compatibility and to minimize the coverage loss of conventional T-DMB service coverage. But this causes the enhancement layer signal of AT-DMB susceptible to fading effect in transmission channel. A turbo code which has improved error correction capability than convolutional code, is applied to the enhancement layer signal of the AT-DMB system for compensating channel distortion. However there is a need for other solutions for better reception of AT-DMB signal in receiver side without increasing transmitting power. In this paper, we propose adaptive array antenna system with Eigen-space beamforming algorithm which benefits beamforming gain along with diversity gain. We analyzed the reception performances of AT-DMB system in indoor and mobile environments when this new smart antenna system and algorithm is introduced. The computer simulation results are presented along with analysis comments.