• Optical Science and Technology
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• v.5 no.1
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• pp.34-44
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• 2001

• Broadcasting and Media Magazine
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• v.6 no.3
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• pp.40-55
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• 2001

• Optical Science and Technology
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• v.8 no.1
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• pp.39-43
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• 2004

• Korean Journal of Optics and Photonics
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• v.9 no.5
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• pp.277-281
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• 1998

One dimensional inhomogeneous aperture modulation effects on the MTF of optical system was investigated. The lens under test was a doublet made in Korea. It has 10 mm effective diameter, 87.8 mm effective focal length. The ray-fans and spot diagrams were calculated and presented on the picture for on-axis and off-axis (field of view, $1^{\circ}$ and $2^{\circ}$). Aperture modulation was carried out by positioning a aperture modulator close contacter with the lens under test. We bought two modulators from Edmud Company in U.S.A. One was linear type and the other was stepped type. The MTFs were measured on the best of focus for each modulated aperture where the MTF has the highest value for 60 line/mm and were compared with one another. For on-axis, the MTFs of some modulated apertures had higher values than the MTF of unmodulated aperture in the high frequency region. In the case of off-axis, at the field of view $1^{\circ}$, the MTF values of some modulated aperture are improved prominently and some other one are disimproved. At the field of view $2^{\circ}$ most of the MTFs of modulated apertures had lower values than the MTF of unmodulated aperture except the MTFs of linear and inverse linear type aperture in the high frequency area. But the values of MTFs in high frequency region were too low for actual use.

• Journal of KIISE:Information Networking
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• v.37 no.3
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• pp.234-242
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• 2010

The demand on various broadcasting services has been greatly increasing in the area of mobile communication. In IEEE802.16e standard and mobile WiMAX, the multicast broadcast service (MBS) uses shared downlink channel for efficiently supporting a number of users. In this paper we propose a dynamic modulation and coding scheme with relay network to enhance the performance of MBS. The proposed approach employs the adaptive modulation and coding scheme for both the base station and relay station to achieve consistently high throughput. The result of computer simulation with NS-2 shows that the throughput and transmission time are significantly improved by using the proposed approach compared to the existing schemes having a fixed modulation level for the RSs.

• Korean Journal of Optics and Photonics
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• v.25 no.5
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• pp.279-285
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• 2014

We propose an electrically controllable terahertz wave modulator based on a metamaterial and vanadium dioxide ($VO_2$) thin film. A square loop shape is designed to play the roles of both a resonating metamaterial and a heater to electrically control the conductivity of $VO_2$. The transmission characteristics of the modulator were controlled by voltage. The transmission coefficient of the modulator was stably changed from 0.27 to 0.80 at 470 GHz according to the conductivity values of $VO_2$.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.1
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• pp.29-35
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• 2003

In this paper, we propose an improved image decryption system using a phase-encoded image and the principle of interference. An original image and a random image consist of only binary values. The phase-encoded original image is encrypted into a binary phase-only image by multiplying with a phase-encoded random key. Therefore the phase-encoded images have two phase values 0 or $\pi$. The proposed decryption technique is simply performed by interfering between a reference wave and a direct pixel-to-pixel mapping of the encrypted image with a decrypting key. Optical experiments confirmed that the proposed technique is a simple and robust architecture for optical encryption.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.127-131
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• 2009

본 논문에서는 디지털 통신에서 비트 전송율을 향상 시킬 수 있는 웨이브릿 편이 변조 시스템을 제안한다. 기존의 웨이브릿 편이 변조 시스템에서는 스케일링 함수(scaling function)를 1로, 웨이브릿(wavelet)을 0으로 할당하여 0과 1을 구분하였다. 제안한 방식은 스케일링 함수와 웨이브릿 그리고 이 두 신호를 반전시킨 4개의 반송파를 사용하여 변조한다. 즉, 웨이브릿은 00, 반전된 웨이브릿은 01, 스케일링 함수를 10, 반전된 스케일링 함수를 11로 할당하여 비트 전송률을 2배로 향상시키고자 한다. 복조시에는 4개의 상관기를 이용하여 원래의 2진 데이터(2비트)를 복원하였다. 모의실험 결과 제안한 방식이 기존의 웨이브릿 편이 변조 시스템에 비해 전송효율이 2배 향상되었음을 알 수 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.4C
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• pp.425-432
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• 2007

In this paper, we deals with automatic modulation classification capable of classifying incident signals without a priori information. The 7 key features which have good properties of sensitive with modulation types and insensitive with SNR variation are selected. The numerical simulations for classifying 9 modulation types using the these features are performed. The numerical simulations of the 4 types of modulation classifiers are performed the investigation of classification accuracy and execution time to implement the fast modulation classifier in software radio. The simulation result indicated that the execution time of DTC was best and SVC and MDC showed good classification performance. The prototype was implemented with DTC type. With the result of field trials, we confirmed the performance in the prototype was agreed with the numerical simulation result of DTC.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.11
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• pp.12-20
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• 2002

Serially concatenated multilevel coded modulation (SCMCM) is proposed in this paper. It is a combined scheme of the outer convolutional code and inner multilevel coded modulation (MCM) which is bandwidth-efficient coded modulation. And the performance of three schemes for decoding of the proposed SCMCM is compared and analyzed. As results of simulations, global iterative decoding with inner and outer code should be performed to improve the error performance as the number of iterations is increased. And the scheme which uses both local iterative multistage decoding in MCM and global iterative decoding with inner and outer code, called Scheme 3 in this paper, shows the best error performance among the three schemes considered in this paper. In addition, performance difference between this scheme and the others is increased as the signal to noise ratio (SNR) is increased. Therefore, Scheme 3 is considered to be the proper decoding scheme of SCMCM.