• International Journal of Computer Science & Network Security
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• v.23 no.1
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• pp.120-124
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• 2023

Strong surface waves among collinearly arranged patch antenna arrays pose unwanted inter element coupling particularly when high permittivity dielectric materials are used. In order to avert those waves, a novel Defected Ground Structure (DGS) is carved out systematically between two E-plane patch antenna elements. The introduced low profile μ shaped structure consequently improves impedance bandwidth and reflection coefficient by suppressing surface waves considerably. Parametric simulation results are analyzed and discussed.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2008.11a
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• pp.181-184
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• 2008

The paper describes a Layered Modulation using the SVC signals and studies the properties of the modulation with respect to several parameters by the computer simulation. The SVC signals will include a base layer signal and an enhancement signal, and the base layer signal is the more important one in its channel robustness. The parameters will include a carrier frequency, a bandwidth, power level, modulation type and code rate. We analyze the demodulating and decoding process of the Layered Modulation system through several scatter plots. And then we discuss the affect of the layer signal power difference to the BER performance, which also proves the base layer signal is more important than the enhancement layer signal.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.55-58
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• 2007

An adaptive subcarrier allocation scheme based on comparative superiority of opportunity cost between groups is proposed for the enhancement of system capacity and its simple implementation at the base station of a multiuser OFDM system. The proposed algorithm is similar to the blockwise or the decentralized subcarrier allocation algorithm proposed by Xiaowen et al and Alen et al, respectively. In the proposed algorithm, however, all subcarriers are grouped according to the coherence bandwidth and the comparative superiority concept, which swaps the groups between users if the system capacity is increased, is adopted for the enhancement of system capacity. In addition, the proposed algorithm provides a simple solution for the conflict problem among users by reallocating only the conflicted groups and unassigned groups instead of reallocating entire groups. Simulation results demonstrate that the proposed algorithm increases the system capacity effectively over a static, an adaptive blockwise, and a decentralized subcarrier allocation algorithms.

• ETRI Journal
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• v.26 no.5
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• pp.384-390
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• 2004

We propose a new bandwidth-efficient technique that achieves high data rates over a wideband wireless channel. This new scheme is targeted for a multiple-input multiple- output orthogonal frequency-division multiplexing (MIMO-OFDM) system that achieves transmit diversity through a space frequency block code and capacity enhancement through the iterative joint processing of zero-forcing detection and maximum a posteriori (MAP) decoding. Furthermore, the proposed scheme is compared to the coded Bell Labs Layered Space-Time OFDM (BLAST-OFDM) scheme.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.89-90
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• 2007

In this paper, we propose Doherty amplifier with proper drain bias line. By $\lambda$/4 microstrip line, IMD is eliminated. Also output power of amplifier is reduced in wanted bandwidth. For linearity improvement, we design drain bias with narrow $\lambda$/4 microstrip line. We observe that gain characteristics improve 1dB and $3^{rd}/5^{th}$ IMD characteristics reduce 5dB/10dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.2 s.117
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• pp.126-135
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• 2007

This paper proposes a new miniaturization method for a parallel coupled line filter with enhanced bandwidth characteristics. A previous method incorporated several advantages, such as size reduction through the use of only a small number of capacitors, in addition to grounding, suppression of harmonic characteristics, and improved skirt characteristics for the parallel coupled line filter, which is conventional in the field of RE filters due to its design and fabrication simplicity. However, the previous method also has disadvantages related to the bandwidth shrinkage of the miniaturized filters. In this paper, the amount of bandwidth shrinkage is analyzed in terms of the relationship between the loaded Q(quality factor) and the group delay of a resonator. Moreover, the reduction in the bandwidth is solved by a design with new design equations. To show the validity of the proposed method, a hairpin filter with a center frequency of 5.2 GHz and an fractional bandwidth(FBW) of 10% was scaled down to half its original dimension by the proposed method with the enhanced bandwidth characteristics. The measured result shows a high level of agreement with theoretical results.

• The Journal of the Acoustical Society of Korea
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• v.30 no.4
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• pp.190-196
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• 2011

Bandwidth extension is a technique to improve speech quality and intelligibility, extending from 300-3400 Hz narrowband speech to 50-7000 Hz wideband speech. This paper designs an artificial bandwidth extension (ABE) module embedded in the AMR (adaptive multi-rate) decoder, reducing LPC/LSP analysis and algorithm delay of the ABE module. We also introduce a fast search codebook mapping method for ABE, and design a low power BWE technique based on the AMR decoder. The proposed ABE method reduces the computational complexity and the algorithm delay, respectively, by 28 % and 20 msec, compared to the traditional DTE (decode then extend) method. We also introduce a weighted classified codebook mapping method for constructing the spectral envelope of the wideband speech signal.

• The Journal of the Acoustical Society of Korea
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• v.36 no.1
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• pp.70-77
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• 2017

Bandwidth extension is a technique to improve speech quality, intelligibility and naturalness, extending from the 300 ~ 3,400 Hz narrowband speech to the 50 ~ 7,000 Hz wideband speech. In this paper, an Artificial Bandwidth Extension (ABE) module embedded in the Opus audio decoder is designed using the information of narrowband speech to reduce the computational complexity of LPC (Linear Prediction Coding) and LSF (Line Spectral Frequencies) analysis and the algorithm delay of the ABE module. We proposed a spectral envelope extension method using DBN (Deep Belief Network), one of deep learning techniques, and the proposed scheme produces better extended spectrum than the traditional codebook mapping method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.3
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• pp.305-316
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• 1998

The impedance matching network with the simplfied real frequency technique (SRFT) is proposed as a method for bandwidth enhancement of microstrip antenna. The validity of the technique is based on the relative frequency insensitivity of the radiation pattern and gain characteristics as compared to the resonant behaviour of the input impedance. The most significant feature of this technique is that there is no need to find any analytical description of the antenna and generator, and it only utilizes directly real frequency generator and load data over the prescribed frequency band. Furthermore, it is not necessary to invent an analytic form of the system transfer function to assume a matching network topology in advance. In this paper, the transmission line model is used to investigate the rectangular microstrip antenna, and based on the Fano's bandwidth-enlargement theory, the SRFT is introduced to design the matching networks of microstrip antennas in order to obtain a constant gain over the frequency band of interest. Two representative microstrip antnnas with different structure are fabricated and tested. From these procedures, it is obtained that the proposed impedance matching networks of microstrip antenna improve the impedance bandwidth nearly three times compared to the antenna without them.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.2
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• pp.252-258
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• 2017

In this paper, the bandwidth and gain enhancement of a double-dipole quasi-Yagi antenna (DDQYA) using a modified balun and two directors is studied. The proposed DDQYA consists of two strip dipoles with different lengths, a ground reflector, which are connected through a coplanar strip line, and two directors. The modified balun is used to increase the bandwidth, whereas two directors are appended to the DDQYA to enhance the gain in the middle and high frequency band. The effects of the length and width of the first director on the antenna performance are analyzed, and final design parameters to obtain a gain over 7 dBi at 1.60-2.90 GHz band are obtained. A prototype of the proposed DDQYA is fabricated on an FR4 substrate, and the experimental results show that the antenna has a frequency band of 1.57-3.00 GHz for a VSWR < 2, and measured gain ranges 7.1-7.8 dBi at 1.60-2.90 GHz band.