김학수 교수

A fully integrated passive and battery powered semi-active UHF RFID transponder chip supporting EPC Gen 2 protocol is presented. The proposed transponder works as a passive RFID tag when the generated RF-power is sufficient to operate, otherwise it operates in semi-active mode using battery power. The chip has re-writeable non-volatile memory bank formed by FeRAM and on-chip temperature sensor. The memory consists of EPC memory bank for EPC functionality and temperature bank for storing sensed d

In this paper, the beam design for signal-space interference alignment in slowly fading multiuser multiple-input multiple-output (MIMO) interference channels is considered. Based on a linear formulation for interference alignment, a predictive beam tracking algorithm is proposed using matrix perturbation theory. The proposed algorithm, based on a mixture of iteration and update, computes interference-aligning beamforming vectors at the current time by updating the previous beam vectors based on

The objective of this study was to establish a method to calibrate a large-scale laboratory rainfall simulator through developing and implementing an automated rainfall collection system to assess the reliability and accuracy of a rainfall simulator. The automated rainfall collection system was designed to overcome the limitations caused by the traditional manual measurement for obtaining the rainfall intensity and the spatial rainfall distribution in a large experimental area. The developed aut

We consider limited feedback for zero-forcing-based coordinated beamforming over time-varying channels. Most previous work on limited feedback focuses on the feedback rate of the channel state information (CSI), while assuming that feedback occurs for every channel use. This feedback update policy, however, may not be optimal for time-varying channels. To take channel variations into account, we propose a scheme that adjusts both the feedback rate and the feedback update period, depending on cha

The problem of beam tracking for zero-forcing coordinated beamforming in multiple-cell time-varying multiple-input multiple-output channels is considered. Based on null-space perturbation theory, an efficient update algorithm for block-diagonalization-based zero-forcing coordinated beam design is proposed and its performance is analyzed. In slowly-varying channels, the proposed algorithm well tracks the zero-forcing beam solution and significantly reduces computational complexity by simply updat

Stereoscopic conversion of two-dimensional (2-D) video is considered based upon image motions. In general, a stereoscopic camera with two imaging sensors is required for stereoscopic video, while the stereoscopic conversion directly converts 2-D video to 3-D stereoscopic video. Image motions that are needed to generate a stereoscopic image are computed by any motion estimation algorithms. However, it is well know that motion vectors are generally far from a true motion, thereby posing a difficul

The problem of interference alignment in time-varying MIMO interference channels is considered. To reduce complexity, an adaptive algorithm for beam vector design is proposed based on our previous work of least squares approach to beam design for interference alignment and matrix perturbation theory. The proposed algorithm calculates interference-aligning beam vectors by additive update of the previous value and reduces complexity significantly. Numerical results are provided to validate the pro

Abstract It is very important to obtain high reliability in the high‐voltage direct current (HVDC) system operation because of extremely high and huge power capacity. To guarantee the reliability IEC‐62501 standard requires valve test for the voltage source converter (VSC) HVDC system. This paper proposes a test circuit for modular multilevel converter (MMC)‐based HVDC valve. The proposed scheme has good features of adequate test current generation, considerably reduced power supply voltage, sim

This Paper proposes a current controller design method of grid connected inverter using an LCL filter without damping method. In case of a grid side current control, it is not necessary for the system to use the damping method if the ratio of the LCL filter resonant frequency to a system sampling frequency is larger than 1/6. However, if the grid impedance is changed, it is not sure whether the system is in the stable region or not. If an LPF (Low Pass Filter) is used in the feedback path of the

In this paper, a new amplify-and-forward (AF) relay systems using superimposed pilot signals is proposed for frequency selective fading channel environments. In the proposed scheme, the relay superimposes an additional pilot sequence on the received signal from the source, and forwards the combined signal to the destination. The superimposed pilot signal in this way enables the destination node to estimate the channel between the relay and destination (R-D), and this channel information is used

It was recently studied how to achieve the optimal degrees of freedom (DoF) in a multi-antenna full-duplex system with partial channel state information (CSI). In this paper, we revisit the DoF of a multiple-antenna full-duplex system using opportunistic transmission under the partial CSI, in which a full-duplex base station having M transmit antennas and M receive antennas supports a set of half-duplex mobile stations (MSs) having a single antenna each. Assuming no self-interference, we present

A new switching scheme for 3-phase interleaved bidirectional DC-DC converter is proposed. The proposed scheme provides soft switching condition for all the switches in both charging and discharging modes regardless of the output power level. Analysis and simulation are carried out for 3kW bidirectional DC-DC converter to charge and discharge a battery of an electric vehicle. Simulation results show the usefulness of the proposed scheme.

This paper proposes a new valve performance test circuit for MMC based HVDC power station. It is necessary for the valve test circuit to satisfy the standard in IEC-62501. The standard requires the valve current resembles the actual arm current of the HVDC system in operation. The arm current contains fundamental ac component, the second harmonic component, and dc component. Conventional valve test circuits provide only fundamental ac component, therefore, they are not suitable for the valve tes

ABSTRACT A laboratory‐based physical modeling environment has great potential to reproduce the complex physical hydrologic phenomena and understand the interactions of rainfall‐runoff processes in a visual and informative manner. In this study, a three‐layer physical modeling environment was developed to represent the dynamics of runoff production from the urban drainage system. The three‐layer physical modeling environment consists of a rainfall simulator (the 1st layer), a surface drainage net

It was recently studied how to achieve the optimal degrees of freedom (DoF) in a multi-antenna full-duplex system with partial channel state information (CSI). In this paper, we revisit the DoF of a multiple-antenna full-duplex system using opportunistic transmission under the partial CSI, in which a full-duplex base station having M transmit antennas and M receive antennas supports a set of half-duplex mobile stations (MSs) having a single antenna each. Assuming no self-interference, we present