• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.5
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• pp.865-872
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• 2020

In the fifth generation (5G) mobile networks, non-orthogonal multiple access (: NOMA) has been considered as a promising technology, to increase the channel capacity. In NOMA, the multiple users share the channel resources and multiplex simultaneously. Recently, for the stronger channel user, it was reported that the bit-error rate (: BER) performance with interactive mobile users is degraded, compared to the BER of non-interactive users. In this paper, in order to improve such degraded BER performance, we propose the maximum-likelihood (: ML) receiver. First, the closed-form expression for the BER of the ML receiver is derived, and then it is shown that the BER of the ML receiver is improved, compared with the BER of the ideal perfect successive interference cancellation (: SIC) receiver. Additionally, based on the analytical expression, Monte Carlo simulations validates the above-mentioned results.

• Journal of Electrical Engineering and Technology
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• v.11 no.1
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• pp.86-92
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• 2016

Upon detecting a frequency event in a power system, the stepwise inertial control (SIC) of a wind turbine generator (WTG) instantly increases the power output for a preset period so as to arrest the frequency drop. Afterwards, SIC rapidly reduces the WTG output to avert over-deceleration (OD). However, such a rapid output reduction may act as a power deficit in the power system, and thereby cause a second frequency dip. In this paper, a hybrid reference function for the stable SIC of a doubly-fed induction generator is proposed to prevent OD while improving the frequency nadir (FN). To achieve this objective, a reference function is separately defined prior to and after the FN. In order to improve the FN when an event is detected, the reference is instantly increased by a constant and then maintained until the FN. This constant is determined by considering the power margin and available kinetic energy. To prevent OD, the reference decays with the rotor speed after the FN. The performance of the proposed scheme was validated under various wind speed conditions and wind power penetration levels using an EMTP-RV simulator. The results clearly demonstrate that the scheme successfully prevents OD while improving the FN at different wind conditions and wind power penetration levels. Furthermore, the scheme is adaptive to the size of a frequency event.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1A
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• pp.64-72
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• 2012

We consider multiuser multiple antenna two-way relaying systems in which all users exchange their data with their counterparts with the help of a relay. The systems complete all data exchanges in two time phases called multiple access phase and broadcasting phase for spectral efficiency and therby require an effective scheme reducing self-interference (SI) and multiuser interference (MUI). Different from the conventional scheme suppressing both SI and MUI at the relay, the proposed scheme adopts SI cancelation (SIC) at the users and renders the relay to suppress the MUI mainly considering the SIC output. We analyze the symbol error rate (SER) and the achievable diversity order of the proposed scheme when the multiple access phase is dominant in the performance and obtain simulation results on the SER and the sum rate under various conditions. The results show that the proposed scheme improves the symbol error rate and the sum rate remarkably at the cost of complexity increase.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1545-1547
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-Sic-$TiB_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_{2}O_{3}+Y_{2}O_3$. Phase analysis of composites by XRD revealed $\alpha$-SiC(6H), $TiB_2$, and YAG($Al_{5}Y_{3}O_{12}$). The relative density and the mechanical properties of composites were increased with increasing $Al_{2}O_{3}+Y_{2}O_3$ contents because YAG of reaction between $Al_{2}O_3$ and $Y_{2}O_3$ was increased. The Flexural strength showed the highest value of 432.5MPa for composites added with l2wt% $Al_{2}O_{3}+Y_{2}O_3$ additives at room temperature. Owing to crack deflection, crack bridging, phase transition and YAG of fracture toughness mechanism. the fracture toughness showed 7.1MPa${\cdot}m^{1/2}$. For composites added with l2wt% $Al_{2}O_{3}+Y_{2}O_3$ additives at room temperature The electrical resistivity and the resistance temperature coefficient respectively showed the lowest of 6.0${\sim}10^{-4}{\Omega}{\cdot}$ cm and 3.1${\times}10^{-3}/^{\circ}C$ for composite added with l2wt% $Al_{2}O_{3}+Y_{2}O_3$ additives at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of 25$^{\circ}C$ to 700$^{\circ}C$.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1474-1476
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-Sic-$ZrB_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_{2}O_{3}+Y_{2}O_{3}$. Phase analysis of composites by XRD revealed $\alpha$-SiC(6H), $ZrB_2$, and YAG($Al_{5}Y_{3}O_{12}$). The relative density of composites were increased with increasing $Al_{2}O_{3}+Y_{2}O_{3}$ contents. The flexural strength showed the highest value of 390.6MPa for composites added with 20wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature. Owing to crack deflection, crack bridging. phase transition and YAG of fracture toughness mechanism. the fracture toughness showed the highest value of 6.3MPa${\cdot}m^{1/2}$ for composites added with 24wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance (PTCR) in the temperature range of 25$^{\circ}C$ to 900$^{\circ}C$.

• The Transactions of the Korea Information Processing Society
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• v.6 no.2
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• pp.415-424
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• 1999

Systematic telecommunication network management is essential for operating large-scale integrated networks which consist of various network components manufactured by different vendors. ISO and ITU-T recommend the CMIP-based TMN architecture for this purpose. TMN uses GDMO for the definition of managed objects, and various GDMO compilers have been developed. However, the development of management objects by using these compilers is still a difficult task. In this paper, we present a GUI-based managed objects development environment, MODE. MODE divides managed object codes by system independent code(SIC) and system dependent cede(SDC). By providing development environments for SIC and SDC, MODE can ease the development of managed objects. To show the efficiency of MODE, we develop the managed objects of an ATM switch in MODE.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.3
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• pp.49-55
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• 2022

In the next generation mobile communication systems, hybrid massive multiple-input multiple output (MIMO) can be used to highly improve an achievable rate without increasing the number of RF chains. Recently, successive-interference-cancellation (SIC) based hybrid precoder design scheme was proposed to reduce the complexity. However, since this scheme uses simple diagonal matrix for baseband precoding, it cannot solve an interference problem between the transmitted streams. Also, there is a limitation for improving the data rate because of the use of one phase shifter for analog precoding. To solve these problems, in this paper we propose a digital precoding based on the SVD of the effective channel and an analog precoding using two phase shifters. Through simulation, we show that the proposed scheme has better achievable rate and SINR performances than the conventional one.

• Korean Journal of Remote Sensing
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• v.33 no.6_1
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• pp.901-915
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• 2017

Recently, global climate change has caused a catastrophic event in the Arctic Ocean, directly and indirectly. The air-sea interaction has caused the significant sea-ice reduction in the Arctic Ocean, and has been accelerating the Arctic warming. Many scientists are worried about the Arctic environment change, suggesting that many of anomalous events will produce direct or indirect biophysical effects on the Arctic. The aim of this study is to understand the inter-annual variability of the Arctic Ocean in wide-view using multi-satellite-derived measurements. Sea surface temperature (SST) and sea ice concentration (SIC) data were obtained from Optimum Interpolation Sea Surface Temperature (OISST) and ECMWF ERA-Interim, respectively. Chlorophyll-a concentration (CHL) was obtained from Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) and Aqua sensor from MODerate resolution Imaging Spectroradiometer (MODIS-Aqua) sensor which has continuously observed since 1998. From 1998 to 2016 summer in the Arctic Ocean which was defined as regions over $60^{\circ}N$ in this study, there were three consequences that CHL increase ($0.15mg\;m^{-3}\;decade^{-1}$), SST warming ($0.43^{\circ}C\;decade^{-1}$) and SIC decrease ($-5.37%\;decade^{-1}$). While SST and SIC highly correlated each other (r = -0.76), a relationship between CHL and SIC was very low ($r={\pm}0.1$) because of data limitations. And a relationship between CHL and SST shows meaningful results ($r={\pm}0.66$) with regional differences.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.1
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• pp.13-22
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• 2004

This paper drives the exact expression of bit error rate(BER) performance for successive interference cancellation(SIC) algorithm against multipath interference components in a high-speed downlink packet access(HSDPA) system of W-CDMA downlink and the BER performance is evaluated by numerical analysis. Numerical results showed that the average BER performance is rapidly saturated in terms of increasing the number of multipath and is revealed significant improvement for improvement Processing gain(PG). For example, the average BER Performance of the SIC algorithm is superior to the performance of conventional scheme by more than 7dB and 1.4dB for processing gain PG=54 and 128 under the two-path channel and average BER=$1.0{\times}10^{-3}$, respectively. This results also indicated that the average BER saturation is occurred at nearly one weight factor which is assigned to pilot and data channels. Likewise, the average BER performance is greatly degraded due to increasing the interference power in proportional to the number of multipath with increasing multicode K. And the smaller multipath fading channel gain is arrived later, the more the average BER performance is improved. The results of performance analysis in this paper indicated that the multipath interference cancellation is required to improve the BER performance in a HSDPA system under multicode for high-speed packet transmission, low spreading factor, and multipath fading channel.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.10
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• pp.769-778
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• 2017

In this paper, a self-interference signal cancellation(SIC) circult for In-band Full-Duplex has been developed and tested in RF/analog region. By use of this SIC circuit, a FM two-way radio has been developed working at FRS(Family Radio Service) band. The two-way radio device is transmitting the FM modulated signal and demodulating the wanted FM signal at the same time. A circulator is used to enable a single antenna to transmit and receive simuultaenously. The receiver circuit needs to cancel out the self-interference signal due to the transmit signal. A vector modulator(VM) is used to control the phase and magnitude of the esitmated signal. And in-phase and quadrature correlators are used to figure out the optimal coefficients of the VM to remove the self-interference signal according to the change of channel environment. In this work, SA58646 has been used as the FM transceiver, and the system is tested with a frequency of 465 MHz and a bandwidth of 12.5 kHz FM signal. The output power is 17.2 dBm at the antenna port, and the self intererence signal level is measured -49.2 dBm at the receiver end. Therefore the SIC level is measured by 66.4 dB.