• Journal of Korea Multimedia Society
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• v.21 no.4
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• pp.493-498
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• 2018

In this paper, we provide the performance analyses of a dual-hop amplify-and-forward(AF) relay transmission composed of asymmetric radio-frequence(RF) and free-space optical(FSO) links. In the mixed RF/FSO system, a relay is equipped with two receive antennas for RF signals and one additional transmit antenna for FSO signals. In order to improve a performance of RF link, a switch-and-stay (SSC) diversity technique is applied at the relay which can provide a proper link performance with a low complexity. Specifically, we offer the performance analyses of the proposed system in terms of outage probability and secrecy outage probability. In numerical examples, we compare the system performances with no diversity and selection combining systems and verify our analytical results via computer-based Monte-Carlo simulations.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1254-1255
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• 2008

Low cost TCO(Transparent Conductive oxide) thin films were prepared by 6" DC/RF magnetron sputtering systems. For the AZO preparation processes a 99.99% AZO target (Zn: 98 wt.%, $Al_2O_3$: 2 wt.%) was used. In order to verify the optical properties of the AZO thin films, the transparency was tested with sputtering conditions using UV-visible spectroscopy. As a result, we got the transmittance properties over 80% and low resistivity in the sputtering conditions of DC 200[W], Ar 30 [sccm], 1 [mtorr], 20 [min].

• Proceedings of the KIEE Conference
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• 2007.11a
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• pp.244-245
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• 2007

The RF inductive discharge of inductively couples plasma (ICP) continues to attract growing attention as an effective plasma source in many industrial applications, the best known of which are plasma processing and lighting technology. Although most practical ICPs operate at 13.56 [MHz] and 2.65 [MHz], the trend to reduce the operating frequency is clearly recognizable from recent ICP developments. in and electrodeless fluorescent lamp, the use of a lower operating frequency simplifies and reduces cost of RF matching systems and RF generators and can eliminate capacitive coupling between the inductor coil and plasma, which could be a strong factor in wall erosion and plasma contamination. In this study, electric and optical characteristics of electrodeless fluorescent lamp by changing ferrite position is discussed.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.12
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• pp.133-138
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• 2008

A 50-60GHz continuous-wave(cw) millimeter-wave(MMW) was converted(generated) by applying optical technology for future wireless and ubiquitous communications. The optical power of 22.5mW was injected into optical waveguide in this experiment. The generated MMW signals were radiated in a millimeter waveguide and detected through a millimeter detector on the inside of a millimeter waveguide in this experiment. The spectral linewidth of the MMW signals was less than 1 kHz. The power fluctuation of the MMW was less than 1.2 dBm over 50-60 GHz range.

• Journal of the Korean Vacuum Society
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• v.16 no.6
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• pp.453-457
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• 2007

Zinc oxide (ZnO) and Ga doped zinc oxide (GZO) with different thickness in range of 10nm to 100nm are prepared on glass substrate by RF magnetron sputtering at room temperature. The structural and optical properties of the thin films is evaluated. The structural properties of ZnO and GZO are investigated by Tunneling Electron Microscopy (TEM) and scanning electron microscopy (SEM). Optical properties are also investigated by UV-VIS-NIR spectrophotometer (200$\sim$1400nm). The much larger grain size of ZnO compared to GZO decreased the light scattering at the grain boundary and improved the transmittance. The transmittance of ZnO is higher than that of GZO through all of the ranges of wavelengths. In case of over 50nm, we found that the transmittance of ZnO is 20% higher than that of GZO.

• Proceedings of the Korean Vacuum Society Conference
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• 2007.08a
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• pp.285-285
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• 2007

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.9
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• pp.830-836
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• 2012

According to increasing the importance of underwater environments, the needs of UUV are growing. This paper represents the mechanism and algorithm of UUV docking system with 21-inch torpedo tubes for military submarines as a docking station. To improve the reliability of the docking, torpedo tubes launch a wired ROV and next the ROV combined with UUV is retrieved. For estimating the relative position between the ROV and UUV, in this paper, combining RF sensors and vision system is proposed. The RSSI method of RF sensors is used to estimate the distance and the optical image is combined for the directional information.

• Journal of the Korean Ceramic Society
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• v.49 no.5
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• pp.399-403
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• 2012

SnO thin films were fabricated by rf reactive sputtering on borosilicate substrates with an Sn target and Ar/$O_2$ gas mixture. The effect of rf power on the structural, electrical, and optical properties of SnO thin films was investigated with XRD, AFM, SEM, Hall effect measurements, and UV-Vis spectrometer. As a plasma power increased the crystallinity with a preferred orientation of SnO thin films was improved and the grain size slightly increased. However the grains were coalesced and excessively irregular in shape. The electrical conductivity of SnO thin films demonstrated a relatively low p-type conductivity of 0.024 $(Wcm)^{-1}$ at a higher power condition. Lastly, SnO thin films had poor optical transmittance in the visible range as a plasma power increased.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.98-106
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• 2009

This paper proposes an optical wireless transfer agent method which realizes the continuous and swift data transfer of optical wireless terminals in optical wireless networks. The unguided wireless channel generally shows frequent link disconnections and propagation delays due to weak wireless links. Specially speaking, optical wireless channels have more vulnerable links and roaming propagation delays relative to the weakness of the previous RF channels due to their low signal connectivity and small geographic coverage. Conventional optical wireless network protocols did not consider any fault models about physical link faults. Consequently, they have shown data transfer inefficiency for both data link control and physical wireless link control. To overcome these optical wireless environmental problems, this paper suggests a new wireless access point (or base station) agent system, which provides wireless or mobile clients with previous link layer protocols compensated.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.36-41
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• 2016

Visible Light Communication (VLC) using Light Emitting Diodes (LEDs) within the existing lighting infrastructure can reduce the implementation cost and may gain higher throughput than radio frequency (RF) or Infrared (IR) based wireless systems. Current indoor VLC systems may suffer from poor downlink resource allocation problems and small system throughput. To address these two issues, we propose an algorithm called a conflict graph scheduling (CGS) algorithm, including a conflict graph and a scheme that is based on the conflict graph. The conflict graph can ensure that users are able to transmit data without interference. The scheme considers the user fairness and system throughput, so that they both can get optimum values. Simulation results show that the proposed algorithm can guarantee significant improvement of system throughput under the premise of fairness.