Deock-Ho Ha

Characteristics of networks in financial markets

We investigate the financial network of the Korea Stock Exchange (KSE) using numerical simulations and scaling arguments. The frequency of degree and the edge density for a real stock market graph are mainly discussed from a numerical point of view. In particular, our frequency of degree follows approximately the power law distribution.

Programmable RF System for RF System-on-Chip

This paper proposes a new automatic programmable radio frequency (RF) system for a System-on-Chip (SoC) transceiver. We built a 5-GHz low noise amplifier (LNA) with an on-chip programmable RF system using 0.18-(m SiGe technology. This system is extremely useful for today’s RF IC devices in a complete RF transceiver environment. The programmable RF system helps it to provide DC output voltages, hence, making the compensation network automatic. The programmable RF system automatically adjusts performance of 5-GHz low noise amplifier with the processor in the SoC transceiver when the LNA goes out of the normal range of operation. The ACN compensates abnormal operation due to the unusual thermal variation or unusual process variation.

Automatic Image Quality Control System

A new automatic image quality control system for TFT-LCD (Thin Film Transistor Liquid Crystal Display) applications is proposed. Image quality factors such as gamma adjustment, flicker, brightness, and contrast are enhanced by proposed algorithm and system. Developed system utilizes programmable 6-point matching algorithm with reference gamma curve and automatic power setting algorithm. Proposed system showed significantly reduced gamma adjusting time, reduced flicker, high contrast and much less average gamma error than conventional manual method.

Analysis of wideband propagation characteristics for the high transmission rate in indoor radio channels

In this paper, the wideband propagation characteristics were analyzed by the frequency sweeping method. In order to investigate the possibility of a high transmission rate in indoor radio channels, we adopted a circularly polarized antenna in the indoor field tests under line-of-sight (LOS) and non-line-of-sight (NLOS) environments. We analyzed the effects of both human motions and transmission antenna heights. From the indoor field tests, it was found that amplitude deviation within the frequency bandwidth should be improved by circularly polarized waves under LOS conditions, due to removing the reflected wave with an odd number. Also it has been found that there exists an improvement of the amplitude deviation with polarization diversity reception under an NLOS environment. In addition, for the case where the transmission antenna height is changed up to the ceiling height, it has been found that there should be improvement of the wideband amplitude deviation for the high speed transmission system, using polarization diversity.

Design and fabrication of a microstrip antenna for S-DMB mobile phone handsets and UHF/RFID used in moving vehicles

In this paper, we proposed a microstrip antenna with S-DMB(Satellite Digital Multimedia Broadcasting) frequency band for mobile phone handsets. The proposed antenna can be also applied to the UHF/RFID for moving vehicles. The proposed antenna is implemented on a substrate, which is small enough to be installed in practical mobile phones, and it has sufficient impedance bandwidth and gain for the UHF frequency band. From the performance analysis results, it was found that the radiation pattern of proposed antenna shows superior performance and guarantees an acceptable frequency bandwidth which is wider than the existing products.

Structure of Correlations with Partially Surrogated Price Fluctuations

The well-known facts of financial markets support price fluctuations containing information on the complexity of the interactions among market participants. In this work, we present a new surrogate method to find the dependency of higher-order correlations on the magnitude of price fluctuations. By sorting returns into several groups with respect to the level of fluctuations, we show that large fluctuations characterize the structure of the temporal correlations of a financial time series. In particular, by investigating the positive and the negative parts separately, we confirm that the risk-averse behavior of traders is explicitly observed in financial markets.

MULTIFRACTALS ON SMALL-WORLD NETWORKS

We investigate the multifractals of the first passage time on a one-dimensional small-world network with reflecting and absorbing barriers. We analyze numerically the distribution of the first passage time at which the random walker arrives for the first time at an absorbing barrier after starting from an arbitrary initial site. Our simulation is found to estimate the fractal dimension D0 = 0.920 ∼ 0.930 for the different network sizes and random rewiring fractions. In particular, our simulation results are compared with the numerical computations for regular networks.

Performance of a novel XCP-OFDM system

This paper proposes an OFDM system that uses circularly polarized waves for improving the system performance. The circular polarization system has the characteristic that it cannot receive waves that are reflected an odd number of times. Using this characteristic, a modified OFDM system that uses cross-handed circular polarization (XCP-OFDM) is proposed. XCP-OFDM gives a much improved system performance due to a reduction of interference caused by reflected waves and interchannel interference. Both theoretical analysis and system simulation results are described.