• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.10
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• pp.6296-6302
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• 2014

A new technique, which can increase the channel bandwidth in an optical wireless orthogonal frequency division multiplexing (OFDM) link based on a light emitting diode (LED), is proposed. The technique uses adaptive sampling to convert an OFDM signal to a sparse waveform. In compressive sensing (CS), a sparse signal that is sampled below the Nyquist/Shannon limit can be reconstructed successively with sufficient measurements. The data rate of the proposed CS-based visible light communication (VLC)-OFDM link increases from 30.72 Mb/s to 51.2 Mb/s showing an error vector magnitude (EVM) of 31 % at the quadrature phase shift keying (QPSK) symbol.

• Korean Journal of Remote Sensing
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• v.18 no.1
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• pp.53-59
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• 2002

The MSC is a payload on the KOMPSAT-2 satellite to perform the earth remote sensing. The instrument images the earth using a push-broom motion with a swath width of 15 km and a GSD(Ground Sample Distance) of 1 m over the entire FOV(Field Of View) at altitude 685 km. The instrument is designed to haute an on-orbit operation duty cycle of 20% over the mission lifetime of 3 years with the functions of programmable gain/offset and on-board image data compression/storage. The MSC instrument has one channel for panchromatic imaging and four channel for multi-spectral imaging covering the spectral range from 450nm to 900nm using TDI(Time Belayed Integration) CCD(Charge Coupled Device) FPA(Focal Plane Assembly). The MSC hardware consists of three subsystem, EOS(Electro Optic camera Subsystem), PMU(Payload Management Unit) and PDTS(Payload Data Transmission Subsystem) and each subsystems are currently under development and will be integrated and verified through functional and space environment tests. Final verified MSC will be delivered to spacecraft bus for AIT(Assembly, Integration and Test) and then COMSAT-2 satellite will be launched after verification process through IST(Integrated Satellite Test). In this paper, the introduction of MSC, the configuration of MSC electronics including electrical interlace and design of CEU(Camera Electronic Unit) in EOS are described. MSC Operation parameters induced from the operation concept are discussed and analyzed to find the influence of system for on-orbit operation in future.

• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.788-792
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• 2014

It has been a critical issue to reduce the size of spectrometers in many fields such as on-chip chemical and biological sensing. The proposed plasmonic channel-waveguide with a sub-micrometer width has a cutoff frequency which enables us to control wavelength dependent propagation properties. We focused on the capability of the waveguide for spectral-to-spatial mapping when the waveguide width changes gradually. In this paper, we propose a plasmonic tapered channel-waveguide structure as a compact spectrometer with a physical size of $0.24{\times}2.0{\times}0.20{\mu}m^3$. The scattering point just above the tapered waveguide moves linearly depending on the wavelength of the injecting light. The spectral-to-spatial mapping can be improved by increasing the tapered length.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1227-1236
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• 2001

A systematic analysis is made of suboptimal control for drag reduction. The influence of the amplitude of actuation (A) and the time scale of actuation ($\Delta$t(sub)a(sup)+) is evaluated. Two wall sensing variables are employed (∂w/∂y│(sub)w and ∂p/∂z│(sub)w) with two wall actuations (${\Phi}$$_2$and ${\Phi}$$_3$). To test the suboptimal control, direct numerical simulations of turbulent channel flow at Re(sub)$\tau$=100 are performed in a spectral domain. It is found that the effect of A and $\Delta$t(sub)a(sup)+∼1. The near-wall behaviors of flow structure are analyzed to characterize the drag reduction. The size effect of the sensor/actuator is examined.

• Journal of Sensor Science and Technology
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• v.17 no.5
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• pp.346-349
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• 2008

A metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector (PD) is proposed as an effective UV sensing device for integration with a GaN n-channel MISFET on auto-doped p-type GaN grown on a silicon substrate. Due to the high hole barrier of the metal-p-GaN contact, the dark current density of the fabricated MSM PD was less than $3\;nA/cm^2$ at a bias of up to 5 V. Meanwhile, the UV/visible rejection ratio was 400 and the cutoff wavelength of the spectral responsivity was 365 nm. However, the UV/visible ratio was limited by the sub-bandgap response, which was attributed to defectrelated deep traps in the p-GaN layer of the MSM PD. In conclusion, an MSM PD has a high process compatibility with the n-channel GaN Schottky barrier MISFET fabrication process and epitaxy on a silicon substrate.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.264-264
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• 2011

1T-1C로 구성되는 기존의 dynamic random access memory (DRAM)는 데이터를 저장하기 위해 적절한 커패시턴스를 확보해야 한다. 따라서 커패시터 면적으로 인한 집적도의 한계에 직면해있으며, 이를 대체하기 위한 새로운 DRAM인 1T- DRAM이 연구되고 있다. 기존의 DRAM과 달리 silicon-on-insulator (SOI) 기술을 이용한 1T-DRAM은 데이터 저장을 위한 커패시터가 요구되지 않는다. 정공을 채널의 중성영역에 축적함으로서 발생하는 포텐셜 변화를 이용하며, 이때 발생하는 드레인 전류차를 이용하여 '0'과 '1'을 구분한다. 기존의 완전공핍형 평면구조의 1T-DRAM은 소스 및 드레인 접합부분에서 발생하는 누설전류로 인해 '0' 상태의 메모리 유지특성이 열화되는 단점을 가지고 있다. 따라서 메모리의 보존특성을 향상시키기 위해 소스/드레인 접합영역을 줄여 누설전류를 감소시키는 구조를 갖는 1T-DRAM의 연구가 필요하다. 또한 고유전율을 가지는 Si3N4를 이용한 oxide-nitride-oxide (ONO)구조의 게이트 절연막을 이용하면 동일한 두께에서 더 낮은 equivalent oxide thickness (EOT)를 얻을 수 있기 때문에 보다 저 전압에서 1T-DRAM 동작이 가능하여 기존의 SiO2 단일층을 이용한 1T-DRAM보다 동일 전압에서 더 큰 sensing margin을 확보할 수 있다. 본 연구에서는 누설전류를 감소시키기 위하여 소스 및 드레인이 채널위로 올려진 recessed channel 구조에 ONO 게이트 절연막을 적용한 1T-DRAM을 제작 및 평가하고, 본 구조의 1T-DRAM적용 가능성 및 ONO구조의 게이트 절연막을 이용한 sensing margin 개선을 확인하였다.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.825-827
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• 2003

Multi-Spectral Camera(MSC) is a payload on the KOMPSAT-2 satellite to perform the earth remote sensing. The instrument images the earth using a push-broom motion with a swath width of 15 km and a ground sample distance (GSD) of 1 m over the entire field of view (FOV) at altitude 685 Km. The instrument is designed to have an on-orbit operation duty cycle of 20% over the mission lifetime of 3 years with the functions of programmable gain/ offset and on-board image data compression/storage. The MSC instrument has one(1) channel for panchromatic imaging and four(4) channel for multi-spectral imaging covering the spectral range from 450nm to 900nm using TDI CCD Focal Plane Array (FPA). In this paper, the architecture and function of MSC hardware including electrical interface and the operation concept which have been established based on the mission requirements are described. And the design and the preparation of MSC system operation are analyzed and discussed.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.4
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• pp.195-201
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• 2011

Cognitive radio (CR), which is proposed as a technology that utilizes the frequency resources effectively, has studied to relive scarcity of the frequency resources. CR provides opportunistically under-utilize licensed frequency to the secondary user. However, in the wireless channels, due to the effect of fading and shadowing environments, spectrum sensing performance is compromised. Besides, to detect and classify various CR systems, a novel spectrum sensing algorithm is needed. Therefore, in this paper, we proposed the spectrum sensing algorithm with water marking scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2A
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• pp.124-131
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• 2009

Cognitive radio has been proposed to mitigate the spectrum scarcity problem by allowing the secondary users to access the under-utilized frequency bands and opportunistically transmit. Spectrum sensing, as a key technology in cognitive radio, is required to reliably detect the presence of primary users to avoid the harmful interference. However, it would be very hard to reliably detect the presence of primary users due to the channel fading, shadowing. In this paper, we proposed a distributed cooperative spectrum sensing scheme based on conventional DF (decode-and-forward) cooperative diversity protocol. We fist consider the cooperation between two secondary users to illustrate that cooperation among secondary users can obviously increase the detection performance. We then compare the performance of DF based scheme with another conventional AF (amplify-and-forward) protocol based scheme. And it is found that the proposed scheme based on DF has a better detection performance than the one based on AF. After that, we extend the number of cooperative secondary users, and demonstrate that increasing the cooperation number can significantly improve the detection performance.

• Korean Journal of Remote Sensing
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• v.29 no.1
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• pp.95-104
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• 2013

In this study, a novel method is proposed for retrieving relative surface temperature from single-channel middle infra-red (MIR, 3-5 ${\mu}m$) remotely sensed data. In order to retrieve absolute temperature from MIR data, it is necessary to accommodate at least atmospheric effects, surface emissivity and reflected solar radiance. Instead of retrieving kinematic temperature of each target, we propose an alternative to retrieve the relative temperature between two targets. The core idea is to minimize atmospheric effects by assuming that the differential at-sensor radiance between two targets experiences the same atmospheric effects. To reduce effective simplify atmospheric parameters, each atmospheric parameter was examined by MODTRAN and MIR emissivity derived from ASTER spectral libraries. Simulation results provided a required accuracy of 2 K for materials with a temperature of 300 K within 0.1 emissivity errors. The algorithm was tested using MODIS band 23 MIR day time images for validation. The accuracy of retrieved relative temperature was $0.485{\pm}1.552$ K. The results demonstrated that the proposed algorithm was able to produce relative temperature with a required accuracy from only single-channel radiance data. However, this method has limitations when applied to materials having very low temperatures using day time MIR images.