• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.6C
• /
• pp.429-437
• /
• 2008

Multiple-input multiple-output (MIMO) techniques can be used for the spectral efficiency enhancement of the cellular systems, which can be categorized into spatial multiplexing (SM) and spatial diversity schemes. MIMO systems suffer a severe performance degradation due to the intercell interference from the adjacent cells as the mobile terminal moves toward the cell boundary. Therefore for the spectral efficiency enhancement, an appropriate transmission scheme for the given channel environment and reception scheme which can mitigate the intercell interference are required. In this paper, we propose an adaptive signal transmission/reception scheme for the spectral efficiency improvement of $M_R{\times}M_T$ MIMO systems, present the decision criteria for the adaptive operation of the proposed scheme, and demonstrate the performance gain. The proposed scheme performs adaptive transmission using spatial multiplexing and spatial diversity, and adaptive reception using maximal ratio combining (MRC) and intercell spatial demultiplexing (ISD) when the spatial diversity transmission is used at the transmitter. Spatial multiplexing/demultiplexing is performed at the high signal-to-interference ratio (SIR) range, and the transmit diversity in conjunction with the adaptive reception uses either conventional MRC or ISD which can mitigate the $M_R-1$ interference signals, based on the mobile location. For the performance evaluation of the proposed adaptive scheme, the probability density function (pdf) of the effective SIR for the transmission/reception methods in consideration are derived for $M_R{\times}M_T$ MIMO systems. Using the results, the average effective SIR and spectral efficiency are presented and compared with simulation results.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.48 no.6
• /
• pp.489-493
• /
• 1999

In this paper, an analysis of microstrip-slotline transition is performed using a 3D vector Finite Element Method(FEM). Artificial anistropic absorber technique is employed to implement an matching boundary condition in FEM. On the base of the analysis, power divider/combiner is designed. The structure of the power combiner already developed are Branch-line coupler, Rat-race coupler, Wilkinson coupler, Lange coupler, etc. Which are all planar, If the frequency goes up, the coupling efficiency of these planar couplers is decreased on account of skin loss. Especially, in millimeter-wave band, the efficiency of more than two ways combiner is radically reduced, so that application in power amplifier circuit is almost impossible, Microstrip-slotline transition structure is a power combining technique integrated into wave-guide, so that the loss is small and the efficiency is high. Theoretically, we can mount several transistors into the power-combiner. This makes it possible to develop a high power amplifier. The numerically calculated performances of the device that is, we believe, the best are compared to the experimental results in Ka-Band(26.5GHz-40GHz).

• Journal of IKEEE
• /
• v.25 no.1
• /
• pp.133-138
• /
• 2021

We propose a Ku-band three-stack CMOS power amplifier to enhance the output power and efficiency. To minimize the dc power consumption, the driver stage is designed using common-source structure. To obtain high output power and utilize a voltage combining method, the power stage is designed using stack structure. To verify the proposed power amplifier structure, we design a Ku-band power amplifier using 65-nm RFCMOS process which provide nine metal layers. The P1dB, power-added efficiency, and gain are higher than 20 dBm, 23 dB, and 25%, respectively, while the operating frequency is 14 GHz-16 GHz.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.2A
• /
• pp.132-138
• /
• 2009

Cognitive radio is considered as a promising solution to scarce spectrum problem. The primary object of cognitive radio is to increase spectral efficiency, while causing limited interference to primary users who are using the spectrum. Hence, an essential part of cognitive radio systems is spectrum sensing which determines whether a particular spectrum is occupied or not by a primary user at a particular time. However, sensing decision of each individual secondary user alone may not be reliable enough due to shadowing and multipath fading of wireless channels. The so called hidden terminal problem makes the problem even worse, possibly yielding undesired interference to the primary users. Recently, cooperative spectrum sensing is emerging as a remedy to these problems of individual sensing. Cooperative sensing allows a group of secondary users to share local sensing information to extract a global decision with high fidelity. In this paper, we investigate a cooperative spectrum sensing algorithm based on hard decisions of local sensing outcomes. Specifically, we propose an effective scheme for combining local decisions by introducing weighting factors that reflect reliability of the corresponding secondary user. Through computer simulations, the performance of the proposed combining scheme is compared with that of the conventional scheme without weighting factors in various environments.

• Applied Chemistry for Engineering
• /
• v.26 no.3
• /
• pp.239-246
• /
• 2015

The hybridization of carbon nano-materials enhances the efficiency of each function of the resulting structure or composites. Also, the addition of non-carbon elements to nanomaterials modifies the electrochemical properties. Electrodes combining porous carbon nanofibers (CNFs) and metal oxides benefit from the combination of the double-layer capacitance of the CNFs and the pseudocapacitive character associated with the surface redox-type reactions. Consequently, they demonstrate superior supercapacitor performance in terms of high capacitance, high energy/power efficiency and high rate capability. This paper presents a comprehensive review of the latest advances made in the development and application of various metal oxide/CNF composites (CNFCs) to supercapacitor electrodes.

• International Journal of High-Rise Buildings
• /
• v.6 no.3
• /
• pp.271-277
• /
• 2017

Safety, livability, and efficiency are the three prominent problems of tall buildings, which are also the severe challenges to designers. We proposed the idea of building the sky town to solve these problems, which can be summarized in two sentences, one is tall building multi-storised, and another one is vertical facilities municipal-infrastructurised. The tall building can be horizontally cut into several multi-storey buildings by some large platforms. The platform extends a certain width to block the fire from spreading. Tall buildings are connected together as a group. One of them is a traffic core, which is used for vertical transportation and MEP. It connects to traffic center such as metro, while most of the other tall buildings' cores can be very much released, so as to achieve maximum efficiency of floor usable area and to give good traffic organization. By combining traffic core, platforms, and multi-storey buildings' inner traffic, a transportation network is formed. Finally, we refer to the design of Raffles City Chongqing to make a sketch of sky town.

• Journal of the Korean Society for Precision Engineering
• /
• v.23 no.1 s.178
• /
• pp.97-104
• /
• 2006

ELID(Electrolytic In-process Dressing) grinding is an excellent technique for mirror grinding of various advanced metallic or nonmetallic materials. A polishing process is also required for elimination of scratches present on ELID grinded surfaces. MAP(Magnetic Assisted Polishing) has been used as polishing method due to its high polishing efficiency and to its resulting in a superior surface quality. This study is describing an effective fabrication method combining ELID and MAP of nano-precision mirror grinding for glass-lens molding mould. It also presents some techniques for achieving the nanometer roughness of the hard metals, such as WC-Co, which are extensively used in precision tooling material.

• 유체기계공업학회:학술대회논문집
• /
• 2000.12a
• /
• pp.91-98
• /
• 2000

Developed is a computer program for the prediction of the aero-acoustic performance characteristics such as discharge pressure, efficiency, power and noise level in the basic design step of axial flow fan. The flow field and the aerodynamic performance of fan are analyzed by using the streamline curvature computing scheme with total pressure loss and flow deviation models. Fan noise is assumed to be generated due to the pressure fluctuations induced by wake vortices of fan blades and to radiate via dipole distribution. The vortex-induced fluctuating pressure on blade surface is calculated by combining thin airfoil theory and the predicted flow field data. The predicted aerodynamic performances, sound pressure level and noise directivity patterns of fan by the present computer program are favorably compared with the test data of actual fan. Furthermore, the present computer program is shown to be very useful in optimizing design variables of fan with high efficiency and low noise level and in analyzing their design sensitivities.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.7
• /
• pp.649-658
• /
• 2000

Thermodynamic modeling of low-pressure scroll compressor was developed by combining continuity and energy conservation equation. Suction gas heating was considered using energy balance inside the low pressure shell. Pressure, temperature and mass of refrigerant-22 as a function of orbiting angle were calculated by solving the governing equations using fourth order Rung-Kutta scheme. Motor efficiency was taken by experiments with a variation of frequency. The developed model was applied to the analysis of an inverter driven scroll compressor with a variation of frequency, pressure ratio and operating conditions. The model was verified with the experimental results at the same operating conditions. The developed model was adequate to predict performance of the inverter driven scroll compressor as a function of operating conditions. Calculated parameters from the model were discharge temperature, mass flow rate, power input, COP, and thermodynamic properties with respect to orbiting angle. To enhance the performance of a scroll compressor, it is essential to diminish leakage at low frequency level and improve the mechanical efficiency at high frequency level.

• Journal of the Korean Solar Energy Society
• /
• v.28 no.6
• /
• pp.15-23
• /
• 2008

The article deals with system technology of a new solar heating system which systematically combines exiting solar collector technology, auxiliary electrical water heating, floor heating system and well insulated construction method and its application of this system to apartment house heating system in the cold region, and also analyzed performance of the new system in terms of technical and economic feasibility. Results shows that energy efficiency approaches up to 50% of the energy consumption of local construction from 1980 to 1981. The implementation of "DQ technology" to floor heating system achieved from 79% to 85% of the energy-saving benefits comparing to other housing units which were supplied by the local district heating plant.