Byeong-Gwon Kang

A nonunitary transfer matrix method for practical analysis of racetrack microresonator waveguide

We report that a nonunitary transfer matrix (NU-TM) method that we have developed is highly accurate and effective in analyzing and designing racetrack microresonator devices. Relatively poor output efficiency of a fabricated racetrack microresonator, unexplained by the conventional unitary transfer matrix (U-TM) method, are analyzed successfully by the NU-TM method. The track-length dependence, which is not obvious in the U-TM analysis, is clearly shown in the NU-TM analysis and is found to stem from the nonorthogonal phase difference between two branching waves in the directional coupling process. The results show excellent agreement with the results obtained by the finite-difference time-domain simulation method, thus confirming the validity and superior capability of the NU-TM method.

Prototype Design and Implementation of an Automatic Control System Based on a BCI

In recent years, automatic control based on brain–computer interfaces (BCIs) have attracted much attention as a useful tool to control external devices just by a user’s intent. A BCI system detects electrical signals produced from the human brain and converts them into control signals to operate a device by reading the user’s thoughts. In this paper, we propose a prototype of an automatic control system (ACS) that controls vehicle sensors through the application of a BCI to a vehicle system for remote sensor control. The proposed system is designed and implemented using several components, including a BCI device, a server system, a smart app, and a car control panel, so that it can be applied to smart car operations. The BCI device is used to transmit a user’s brain waves through an Arduino UNO board to a server system and it also provides a Bluetooth interface. The server system receives digital brain wave signals from the BCI device and presents them in a graph. The smart app receives normalized brain waves from the server system by the Bluetooth protocol and controls the smart car through a control panel by using brain wave information. The control panel of the smart car uses an ATMega128 board to operate the vehicle based on commands from the smart app through Bluetooth. The proposed BCI-based automatic control system (B-ACS) can be applied to short-range transport models for disabled users and it is expected to be of great assistance in improving the quality of their daily lives.

Design of RF switch with defected ground structure

A three-pole single throw switch with defected ground structure (DGS) is proposed. The equivalent circuit for the proposed switch structure is derived based on equivalent circuit of newly proposed DGS unit structure. The equivalent circuit parameters of DGS unit are extracted by using the circuit analysis method. The on/off aperation of the proposed switch is obtained by varying the capacitance in the ground metallic plane. The experimental results shows excellent insertion loss characteristic at on state and isolation characteristic at off state.

Analysis of ICT accessibility policy and implementation in South Korea

This paper introduces and describes the current ICT accessibility policy and program in South Korea including web accessibility, mobile accessibility and media accessibility for building an inclusive society. Although law and regulation describe the rights for vulnerable people to access many different formats of information technology, the assurance of ICT accessibility in technology and service has not been guaranteed. Several recommendations to promote ICT accessibility for vulnerable people are proposed in this paper.

A study on the implementation of a 3-dimensional positioning system on indoor environments

In this paper, we implemented a three dimensional positioning system with consideration of indoor wireless channel. A commercial modules are used for mobile and fixed node which is a product of German company Nanotron Co. Chirp spread spreading is adopted as modulation scheme to improve the ranging resolution and the module satisfies the IEEE standard 802.15.4a. The distance computation is based on received signal strength(RSS) levels and trilateration method. A testbed was set up to measure and compare the positioning estimation error of the used algorithm. The experiments results showed that the accuracy of location estimation was satisfied with the proposed method as much as 1m distance error in a wireless environment in an office building. We also propose a novel equation for distance estimation of three dimensional ranging system.

Upper bounds on the symbol-error probability of MPSK with phase error using pawula F-function IV

This letter presents an alternative derivation of the Case IV of Pawula F-function and an approximation for the corresponding probability density function (pdf) in the presence of the Tikhonov distributed phase error. The pdf of Case IV is used to obtain new upper bounds for the conditional and average symbol-error probabilities of M-ary phase shift keying with phase error over additive white Gaussian noise channels. Numerical results demonstrate the validity of the upper bounds.

A new design method for performance improvement of high power amplifier by using the matching circuit of defected ground structure

This paper describes a novel design method and the improvements of performance of a class AB power amplifier by using the equivalent circuit of Defected Ground Structure (DGS). The equivalent circuit of DGS has been used to optimize the output matching circuit for improving the performance of power amplifier. Design method for a power amplifier presented in this paper can provide the accurate design results to satisfy the optimum load condition and the desirable harmonic rejection, simultaneously. As a design example, we have designed a 20W power amplifier by the suggested design method. Measured results for the fabricated DGS power amplifier show pertinently the validity of this paper.

Design and implementations of a software defined radio scheme based modem for high-speed multimedia data service

In recent years, there has been much attention on software defined radio (SDR) schemes for high speed multimedia applications. It is required that the SDR system is flexible enough to support multiple air interfaces and signal processing functions at the same time. Also digital signal processors and FPGAs are widely used for implementation of these adaptive and flexible functions of a baseband modem for SDR applications. Meanwhile, it is known that the modulation schemes OCQPSK (orthogonal complex QPSK) and HPSK (hybrid PSK) are used for IMT-2000 services of synchronous systems and asynchronous systems, respectively. Thus, we designed and implemented an OCQPSK/HPSK modem using a DSP chip with consideration of SDR concepts. One modulation scheme is operated by adaptive selection between the two schemes, and 5 physical traffic channels differentiated by orthogonal codes are implemented in one DSP chip. Each channel has 1 Mbps data rates and 8 Mcps chip rates.

Design of Planer type Comb-Line Bandpass Filter And Design Parameter Extraction Using FE Analysis

In this paper, we present a design procedure of comb-line bandpass filter with asymmetrical coupled-lines, which has small size in comparison with other planar type filters to take full advantage of reducing the size of RF and microwave components. Based on a parallel coupled-line theory, we develop admittance inverter model for each asymmetric coupled-line pair. By combining equivalent circuits of the coupled-line section, the design formula, which means the J-inverter formula, for the presented filter is derived. Furthermore, a simple approach using 2-D static FE calculations is employed to extract the physical dimensions of asymmetric coupled-line for a comb-line band-pass filter. Fourth order comb-line bandpass filter with a microstrip multiple coupled-lines is designed by the aforementioned method. In addition, the comb-line filter has been simulated with 3-D EM software and fabricated for measurements. Excellent agreement between the simulation and measurement on the design filter shows the validity of the presented design and design-parameter extraction methods.

Impacts of Frequency Selectivity on the Error Performance of Time-Domain Equalizers in MIMO Systems

In this paper, we investigate the impacts of frequency selectivity on the error performance of time-domain equalizers in multiple-input multiple-output (MIMO) systems. Two types of time-domain equalizers are considered: linear equalizers and decision-feedback equalizers. Under the assumption of the perfect channel estimation at the receiver, the error performance of both linear and nonlinear equalizers is evaluated according to the frequency selectivity, i.e., the number of channel taps, by numerical simulations. The simulation results show that both linear and nonlinear equalizers achieve the error performance improvements as the number of channel taps increases. Therefore, in MIMO systems under frequency-selective fading channels, the diversity gain dominates the inter-symbol interference effects in terms of error performance and the increased frequency selectivity can provide the performance gain at the price of higher computational complexity.