• Korean Journal of Optics and Photonics
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• v.33 no.1
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• pp.11-21
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• 2022

We have investigated the optimal design of an aperiodic optical phased array (OPA) for use in light detection and ranging applications. Three optimization algorithms - particle-swarm optimization (PSO), a genetic algorithm (GA), and a pattern-search algorithm (PSA) - were employed to obtain the optimal arrangement of optical antennas comprising an OPA. The optimization was performed to obtain the minimal side-lobe level (SLL) of an aperiodic OPA at each steering angle, using the three optimization algorithms. It was found that PSO and GA exhibited similar results for the SLL of the optimized OPA, while the SLL obtained by PSA showed somewhat different features from those obtained by PSO and GA. For an OPA optimized at a steering angle <45°, the SLL value averaged over all steering angles increased as the angle of optimization decreased. However, when the angle of optimization was larger than 45°, low average SLL values of <13 dB were obtained for all three optimization algorithms. This implies that an OPA with high signal quality can be obtained when the arrangement of the optical antennas is optimized at a large steering angle.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.4
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• pp.530-536
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• 1993

In adaptive antenna, recently Gooch suggested a new adaptive system using equation error method, but the system demands inverse model about the pole part and thus does not guarantee stability. In this paper, algorithm is proposed that has a basis on Popov's extra-stability theory. And system is developed of output error method. In addition, the result obtained by applying proposed algorithm to system of output error method is compared with that of Gooch model.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.501-505
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• 2003

There are many antenna array errors. They will distort the array beam pattern and result in an increased sidelobe level. A calibration technique is proposed for correcting the antenna array errors such as mutual coupling and unequal feeder characteristics. These are modeled as a matrix representing the interaction between the radiating elements. The matrix is estimated from the measured array response vectors. The antenna array errors are corrected by modifying the beamforming weight vector. It is verified by the electromagnetic simulation and experiment that the proposed technique reduces the sidelobe level and increases the antenna gain.

• Information and Communications Magazine
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• v.22 no.9
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• pp.175-186
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• 2005

향후 수년 내에 흠, 오피스 및 핫스팟 영역에서 초고속 멀티미디어의 서비스 수요가 폭발적으로 증가할 것으로 전망됨에 따라 IEEE 802.11에서는 200-500Mbps급의 차세대 초고속 무선랜 표준으로서 IEEE 802.11n의 표준안을 제정하는 작업을 진행하고 있다. 새로운 표준에는 무선통신의 다양한 기술들이 표준으로 채택될 전망이다. 논의되고 있는 기술들로는 물리계층에서의 다중 안테나의 사용, 송신 빔 형성, 듀얼 밴드 그리고 LDPC (Low Density Parity Check) 등의 기술과 MAC (Media Access Control) 계층에서의 집합 전송, 블록 전송, 링크 적응 기법 등의 채택이 논의되고 있다. 기존의 무선랜 시스템에서 널리 사용되어온 IEEE 802.11a/b/g와의 호환성을 보장한다. 또한 차세대 무선랜은 차량용 통신 장치를 위한 고속 이동성을 보장하는 표준인 IEEE 802.11p에 대한 논의도 함께 이루어지고 있다. 본 고에서는 표준회의에서 논의되고 있는 후보 기술들과 차세대 무선랜의 기술동향을 살펴본다.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.109-110
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• 2007

The sum-rate capacity of multi-antenna broadcast channels recently has attracted much research interests. However, those effort mainly has focused on a single-cell system. In this paper, we consider a multi-cell system where a transmitter uses zero-forcing beamforming with multiple antennas. We select a linear zero-forcing weight that maximizes the sum-rate when intercell interference exists. With numerical investigation, we will show the sum-rate gain achieved by the proposed method gets larger when the number of interfering cells increases.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.689-692
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• 2003

In this paper, we propose an adaptive beamforming algorithm for array antenna. The proposed beamforming algorithm, based on Block LMS (Block - Least Mean Squares) algorithm, has a variable step size from coefficient update. This method shows some advantages that the convergence speed is fast and the calculation time can reduced using a block LMS algorithm from frequency domain. As the adaptive parameter approaches a stationary state, it could reduce the number of filter coefficient update with the help of various step size. In this paper we compared the efficiency of the proposed algorithm with a standard LMS algorithm which is a representative method of adaptive beamforming.

• Proceedings of the KIEE Conference
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• 2004.05a
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• pp.56-58
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• 2004

In this paper, we propose an adaptive beamforming algorithm for array antenna. The proposed beamforming algorithm is based on EDS (Euclidean Direction Search) algorithm. Generally LMS algorithm has a much slower rate of convergence, but its low computational complexity and robustness make it a representative method of adaptive beamforming. Although the RLS algorithm is known for its fast convergence to the optimal Wiener solution, it still suffers from high computational complexity and poor performance. The proposed EDS algorithm has a rapid convergence better than LMS algorithm, and has a computational more simple complexity than RLS algorithm. In this paper we compared the efficiency of the EDS algorithm with a standard LMS algorithm.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.10
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• pp.1-9
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• 2008

In this paper, a simple and efficient three cell based clustered-cell coordination is proposed with well hewn zero-forcing beamforming (ZF-BF) with a semi-orthogonal user selection (SUS) as transmission and scheduling scheme. For a modified Wyner's channel model with two classes of user groups for a hexagonal cellular system, the upper bound of asymptotic sum rate scaling of ZF-BF in a proposed coordination is shown to be proportional to the number of transmit antennas and double logarithms of the number of users. The numerical results verify the efficiency of the proposed cell coordination. It is also numerically shown that ZF-BF with the SUS in CCCT actually achieves the upper bound of asymptotic sum rate sum rate scaling.

• Journal of Broadcast Engineering
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• v.11 no.4 s.33
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• pp.521-532
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• 2006

Recently, many research initiatives have been underway to improve reception performance of ATSC based DTV signal in mobile channel by adopting multiple antennas. In this paper, we propose a new mobile channel model which can be applicable to any array geometry. And then we propose new channel estimation algorithm which uses PN5l1 sequence in field synch. The proposed algorithm is to estimate channel by correlating the input signal in If frequency band and finding maximum peak, which does not need complicated synchronization circuit. Finally, we propose new receiver structures which can be implemented at the front-end of the existing receiver with no modification. With computer simulation, we verify the performance of the proposed model and verify the performance of the receiver structure with computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.997-1005
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• 1998

This paper presents a modified on-off algorithm based on the gradient method for providing the phase of each antenna element more accurately and simply compared to the conventional on-off algorithm. The sup4erisority of theproposed method is due to the fact that the proposed method finds the increase and decrease of the array output power more accurately by utilizing the gradient of array output power with respect to the instantaneous phase of array element. The array antenna adopting to the proposed method formsmaximum beam-pattern along the direction of the desired signal by aligning the phase of every antenna enement. The proposed method is applied to both linear and two-dimentional aray for analyzing the result. The capability of the real-time processing of the proposed technique is confirmed by implementing the proposed algorithm with TMS320C30 Evaluation Module. Since the computational load required to form the beam-pattern per snapshot is small, the proposed method is suitable for the mobile communication system of which the response must be fast. By the results obtained from the application of the proposed method to the CDMA mobile communication environment, it is vreified that the performance of the received signal is consideralbly improved.