김선정 교수

We investigate the performance of limited feedback zero forcing beamforming-based MU-MIMO in correlated channels when users have the opportunity to adapt their codebooks as a function of their own channel statistics (CDIT). An upper bound on the rate loss is derived in terms of the amount of feedback and the statistics of the channel. In order to maintain a constant rate loss with respect to the perfect CSIT case, it is shown that the number of feedback bits should scale linearly with the SNR (i

Herein, a controlled porous structure for photoactive gas sensors was fabricated using the gas-flow thermal evaporation and atomic layer deposition method. To control the porosity of the SnO2 matrix, Ar was introduced to the chamber to adjust the pressure from 0.1 to 1 Torr during thermal evaporation. Furthermore, nanoscale TiO2 layers were conformally deposited on the surface of porous SnO2 by atomic layer deposition as a selective active layer for HCHO. As a result, the sensor deposited at a p

Highly porous heterojunction films of SnO2/TiO2 were prepared using gas-flow thermal evaporation followed by atomic layer deposition (ALD). Highly porous SnO2 was fabricated by introducing an inert gas, Ar, during thermal evaporation. To build heterogeneous structures, the TiO2 layers were conformally deposited on porous SnO2 with a range of 10 to 100 cycles by means of ALD. The photocatalytic properties for different TiO2 thicknesses on the porous SnO2 were compared using the degradation of met

Multi-User (MU) Muliple Input-Multiple Output (MIMO) has become an essential technology to achieve IMT advanced requirements. Performance of limited feedback Multi-User MIMO in spatially and time correlated channels are investigated in this paper. A special attention is drawn to the case where users have the opportunity to adapt their codebooks as a function of their own channel statistics (i.e. transmit correlation, time correlation or channel imbalance in dual-polarized scenarios). New codeboo

Flexible spectrum utilization becomes one of the major agendas in the next generation wireless communications. A core technology to efficiently adjust spectrum is automatic modulation classification (AMC) which recently emerges in various future wireless research including military communications, cognitive radio and high-throughput wireless. AMC is essential for capturing over-the-air information, estimating a remained spectral resource and improving spectral efficiency in the corresponding wir

We have observed relaxation oscillations in an argon capacitive discharge connected to a peripheral grounded chamber through a slot with dielectric spacers. The oscillations, observed from time-varying optical emission of the main discharge chamber, show, for example, a high frequency (∼40kHz) relaxation oscillation at 100mTorr, with absorbed power near that for peripheral breakdown, and a low frequency (∼3Hz) oscillation, at higher absorbed power. The high frequency oscillation is found to igni

In a Multi-User MIMO (MU-MIMO) spatial multiplexing scheme, multiple users are scheduled in the same resource block (RB). However, due to the wide fluctuation of realistic traffic patterns, it could often occur that only a single or few users have active data that need to be sent. In 3GPP Long Term Evolution (LTE), Single-User MIMO (SU-MIMO) rank one preceding based Channel Quality Indicator (CQI) reporting mechanism is reused for MU-MIMO. This is optimum for MU-MIMO if single user is served. Ba

Recently, the interior permanent magnet (IPM) motors for electric vehicle (EV) traction motor are being extensively researched because of its high energy density and high efficiency. The traction motor for EV requires high power and high efficiency at the wide driving region. Therefore, it is essential to fully consider the characteristics of the motor from low speed to high-speed driving regions. Especially, when the motor is driven at high speed, a significant centrifugal force is applied to t

In this paper, the Box-Behnken design (BBD), which is a response surface method (RSM), was used to deduce a pole piece form that is able to effectively reduce the transfer torque ripple of a coaxial magnetic gear. A 2-D numerical analysis based non-linear finite element method (FEM) was used for the analysis between the response variables and the designed variables selected by the BBD. In addition, the reaction variable estimation equation based on the design variables was determined through a m

This paper presents a comparative study effective flux-modulator shape in coaxial magnetic gear for transfer torque ripple mitigation. Using a non-linear finite element method (FEM) based on 2-D numerical analysis, the transfer torque performances of the magnetic gear with proposed flux-modulators are analyzed and quantitatively compared based on the same structure.

본 논문에서는 인체부착형 Headset MIMO(Multiple-Input Multiple-Output) 안테나를 제안하고, 인체의 영향을 고려한 안테나 성능과 인체에 미칠 수 있는 영향에 대한 분석을 하였다. 제안된 MIMO 안테나는 접지면 위에 PIFA(planar inverted-F antenna) 형태의 두 안테나와 격리도 특성 개선을 위하여 안테나 사이에 위치한 isolator로 구성되어 있다. 근거리장에 인체가 존재할 때 안테나에 미치는 영향을 분석하기 위하여 시뮬레이션을 수행하고, 팬텀을 이용하여 시뮬레이션과 측정을 하였다. 측정 결과, MIMO 안테나의 성능을 평가하는 파라미터 중 하나인 상관 계수(Envelope Correlation Coefficient: ECC)는 ISM 대역에서 0.1 이하의 값을 가지므로 제안된 MIMO 안테나의 diversity 성능이 우수함을 입증하였다. 또한, 측정된 SAR(Specific Absorption Rate) 값은 공급전력 25