• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6B
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• pp.508-516
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• 2006

The explosive growth of wireless network users and the existence of various wireless services have demanded high rate throughput as well as user's QoS guarantees. Towards this, this paper proposes QoS-oriented subcarrier allocation scheme considering the QoS provisioning of multiple users, which is major requirement for wireless network design point of view. This paper introduces joint RR/K&H combined with M-LWDF(Modified Largest Weighted Delay First) scheme throughout observing statistical channel behavior and real time queuing analysis for appropriate resource allocation tightly connected to multiuser scheduling. Accordingly, the system throughput can be enhanced, and the QoS demanded for delay sensitive services can be satisfied. Furthermore, the proposed scheme is applied for OFDMA(Orthogonal Frequency Division Multiple Access) systems to allocate sub-carriers in optimal way. The simulation results verify plausible performances of proposed resource allocation scheme via showing superior effective capacity under time-varying physical-layer channel behaviors.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.115-119
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• 2008

In this paper, the linearity of Doherty power amplifier has been improved by applying a new Photonic Bandgap(PBG) structure on the output of amplifier. The reposed spiral PBG structure is a two-dimensional(2-D) periodic lattice patterned on a dielectric slab that does not require nonplanar fabrication process. This structure has more broad stopband and high suppression performance than the conventional three cell PBG. Also, It has a sharp skirt property. We obtained the 3rd-order intermodulation distortion(IMD3) of -33dBc for CDMA applications with that of maintaining the constant power added efficiency(PAE), the IMD3 performance is improved as much as -8 dB compared with a Doherty power amplifier without PBG structure. Moreover, the physical length of PBG is shortened, therefore the whole amplifier circuit size is considerably reduced.

• Journal of the Economic Geographical Society of Korea
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• v.23 no.3
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• pp.262-275
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• 2020

Due to the pandemic caused by Corona 19, cities around the world have faced a change. As the global economic system weakens, localization is increasing in the product production and distribution system. In addition, consumption patterns have changed in urban where localization has been strengthened. As a result, the way physical places are consumed is also changing. Consumption of large multi-use facilities has drastically decreased, the speed of the collapse of the online and offline boundaries has been accelerated, and the consumption of amenities for sharing tastes has become more subdivided, specialized, and private. A big change also appeared in the urban scene, which is perceived as the concentration of urban amenities. Local scale and locality became important in the urban scene, and a new urban scene element called empathy emerged. Empathy aims to connect socially and emotionally to individuals consuming urban amenities. The pursuit of connectivity, taste consumption, and nostalgia. In this study, the space for cultural consumption based on empathy was named as empathetic space and the concept was explained. The importance of empathic space in the urban scene in the future post-corona situation was presented.

• 한국해양학회지
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• v.25 no.1
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• pp.1-7
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• 1990

Seawater temperature, salinity, inorganic nutrients and the standing crop of phytoplankton species of the 841 water samples from the upper 125 m at 15-40 stations on the 6 semiannual cruises in the southwestern waters of the East Sea (Korea) were studied during the period from September, 1981 to October, 1984, Among the 235 taxa identified two pennate diatioms, cylindrotheca closterium and Nitzschia delicatissima, were the most common and dominant species. The multiple regression analyses between net phytoplankton abundance (dependent variable) and associated environmental factors(independent variables) were applied to the samples from the surface mixed-layer. In spring the coefficients for the seawater temperature was 1. to 4.2 times greater than those for salinity, while the coefficients for the salinity was 2.1 to 3.4 times greater than those for seawater temperature in autumn. Distribution seawater temperature in spring, and salinity in autumn. Schematically the zone of high standing crops moved about on the T-S diagram in a cyclic manner. The distribution of phytoplankton standing crop was quite closely associated with the hydrographic conditions among various kinds of environmental factors studied.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.6
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• pp.35-43
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• 1999

We propose and analyze novel optical thyristor which can be used in free-space optical interconnection(FSOI). Novel optical thyristors are fully depleted optical thyristors(DOTs) using bottom mirror and/or multiple quantum wells (MQW), thereby its switching characteristics can be improved significantly. We obtain switching characteristics using coupled junction model associated with current oriented method. Emission characteristics of the DOT are obtained using thin film characteristic matrix and van Roosbroeck-Shockley relation. Compared to the performance using conventional DOT, the optical switching energy is decreased by a factor of 0.43 and the bit-rate is increased by a factor of 1.61 when the DOT with MQW and bottom mirror is employed for FSOI.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.4
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• pp.9-17
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• 1994

It is well recognized recently that ultrasonic technique is one of the most widely used methods of nondestructive evaluation to characterize material properties of nonconventional engineering materials. Therefore it is very important to understand physical phenomenon on propagation behavior of elastic wave in these materials, which is directly associated with ultrasonic signals in the test. In this study, the theoretical analysis on multi-scattering of harmonic elastic wave due to the particulate with interface between matrix and fiber in metal matrix composites(MMCs) was done on the basis of Lax's quasi-crystalline approximation and extinction theorem. SiC particulate (SiCp) reinforced A16061-T6 composite material was chosen for this analysis. From this analysis, frequency dependences of phase velocity and amplitude attenuation of effective plane wave due to the change of volume fraction of SiC particulate were clearly found. It was also shown that the interface condition between matrix and fiber in MMCs gives a direct effect on the variation of phase velocity of plane wave in MMCs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.772-772
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• 2001

In this paper, we proposed the image-based 3D ray-tracing indoor propagation model using patch scattering model which can calculate the scattering phenomenon of the indoor structures. A patch scattering model for modeling indoor structures defines a scattering phenomenon by using RCS(Radar Cross Section) about rectangular patch without complex calculation, for example generating image antennas about each indoor structures. RCS is simply defined as a ratio of scattering power to incident power, and we use bistatic PCS which is simplified numerically by Physical Optics. Also, a simple indoor compensation factor is defined as empirical constant from measured data instead of complex numerical expression because basic patch scattering model cannot include important multipath components, so we san use patch scattering model in indoor environment using indoor compensation factor.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.722-733
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• 2001

In this paper, we proposed the image-based 3D ray-tracing indoor propagation model using patch scattering model which can calculate the scattering phenomenon of the indoor structures. A patch scattering model for modeling indoor structures defines a scattering phenomenon by using RCS(Radar Cross Section) about rectangular patch without complex calculation, for example generating image antennas about each indoor structures. RCS is simply defined as a ratio of scattering power to incident power, and we use bistatic PCS which is simplified numerically by Physical Optics. Also, a simple indoor compensation factor is defined as empirical constant from measured data instead of complex numerical expression because basic patch scattering model cannot include important multipath components, so we san use patch scattering model in indoor environment using indoor compensation factor.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.270-276
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• 2018

Fifth-generation communications are approaching, and they will require broadband antennas that include the existing LTE frequency band (1.7 GHz to 2.7 GHz) and the newly allocated frequency band (3.4 GHz to 3.7 GHz). Many kinds of antennas satisfy the required broadband characteristics, including the dual-element folded dipole antenna proposed in this paper. A zigzag line was used to make the antenna more compact. This was accomplished by reducing the physical length while maintaining the electrical length. To validate the proposed antenna, a prototype was fabricated using PCB (${\epsilon}_r$:4.4, Height: 1.6 mm) and its performance was evaluated. Results obtained by simulation and experiment showed good agreement.

• The Korean Journal of Ecology
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• v.23 no.5
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• pp.369-375
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• 2000

Although urban soils must be well understood in order to ensure their conservation and optimum use, these intensively managed and disturbed soils have not been extensively investigated up to now. Urban soils from forest, lawn, streetside, and bare ground and under pavement in Inchon had high bulk density as a result of widespread trampling-induced soil compaction. The various urban soils including forests showed lower water content and higher temperature as compared with rural forest soil. Chemically, soils from urban areas had an unusual neutral pH and low organic matter content. Total bacterial numbers in urban soils was only 5∼50% of that in the rural forest soil. An analysis of stepwise multiple regression revealed that soil organic matter was the most important predictor variable on total bacterial number. The dehydrogenase activity of most urban soils was not significantly different from that of rural forest soil, whereas the microbial activity of soils under pavement was lower. Our investigations show that inadequate organic matter of highly compacted soils has adversely affected the abundance of microorganisms involving nutrient cycling in urban soils.