Ki-Man Kim

Acoustic intruder detection system for home security

We propose a new algorithm to detect an intruder in a small room. The basic idea of the proposed method is to estimate the variation of features of the room acoustic transfer function.

Basic RF Characteristics of the Microstrip Line Employing Periodically Perforated Ground Metal and Its Application to Highly Miniaturized On-Chip Passive Components on GaAs MMIC

In this study, highly miniaturized on-chip impedance transformers employing periodically perforated ground metal (PPGM) were developed for application to broadband low-impedance matching. In order to realize a broadband operation by using an equal ripple transfer characteristic over a passband, a three-section transformer was designed by mapping its reflection coefficient to the Chebyshev function. The three-section transformer showed a good RF performance over a broadband (1.5-13 GHz) including ultra-wideband. The size of the three-section transformer was 0.129 mm2, which is 2.3% of the size of the transformer fabricated by a conventional microstrip line. Using the PPGM structure, a highly miniaturized on-chip Wilkinson power divider with a low port impedance of 13 Omega was also developed, and its size is 0.11 mm2, which is 6% of the size of the one fabricated by the conventional microstrip line. In addition, in this study, the PPGM structure was theoretically characterized using a conventional capacitive loaded periodic structure. Using the theoretical analysis, basic characteristics of the transmission line with PPGM were also investigated in order to evaluate its suitability for application to a development of miniaturized on-chip passive components. According to the results, it was found that the PPGM structure is a promising candidate for application to a development of miniaturized on-chip components on monolithic microwave integrated circuits

A Study on the Cooperative Diversity Technique with Amplify and Forward for Underwater Wireless Communication

In this paper, we introduce the application of the cooperative diversity in underwater wireless communication. Cooperative diversity creates a virtual sensor array between source and destination, thereby influence the space diversity benefits of multiple-input/multiple-output (MIMO) system. In this paper, we consider the amplify-and-forward (AF) protocols in cooperative diversity for underwater wireless communication. For AF protocol in cooperative diversity, each relay node is amplifying the received signal from the source node and retransmits to destination node. We used the Ray mode model base on underwater channel parameter between each node for assume the underwater channel. Simulation results of the AF cooperative diversity in underwater wireless communication show the better performance than the direct transmission. As a result, we acquired more enhanced result of about 5 dB than other comparison technique.

Quick audio retrieval using multiple feature vectors

This paper concentrated on the content-based audio retrieval and proposed a quick audio search algorithm. In the previous work, the time-series audio search method with the upper bound proof was generally used. However, the searching speed of a time-series search method is very poor at real time. Therefore, in present paper the preprocessing stage is introduced for this defect. And to enhance the search accuracy we use the multiple feature vectors of audio signal. Through the experiment, the results of retrieval performance are presented.

A new spectral enhancement algorithm in MP3 audio

This paper proposes a new blind method of spectral (high frequency) enhancement of MP3 audio. Due to the protocol constraint, the audio bandwidth of MP3 is restricted to 16 kHz at 128 kbps and 12 kHz at 64 kbps. Although band-restricted MP3 audio provides savings of storage space and network bandwidth, it suffers a major problem of a loss in high frequency fidelity such as localization, ambient information, and bright nature of audio. In contrast to previous works, this paper suggests a couple of new approaches such as dynamic cut-off finding, harmonic compensation and the gain-controlled high frequency compensation. Furthermore, the proposed algorithm requires less computational power with better high frequency enhancement capability compared to the previous works. The proposed algorithm is implemented on TI TMS67I3 DSP platform and tested with IFP 800 model MP3 player. Audio quality of the proposed algorithm is reported and compared using spectrum analysis

Experimental Study on Isolation Characteristics Between Adjacent Microstrip Lines Employing Periodically Perforated Ground Metal for Application to Highly Integrated GaAs MMICs

Using a periodically perforated ground metal (PPGM) on GaAs monolithic microwave integrated circuit (MMIC), a microstrip line structure with a high isolation characteristic between lines was developed. The high isolation characteristic was originated from a resonance between adjacent microstrip lines employing PPGM. According to experimental results, a much better isolation characteristic was observed from the adjacent microstrip lines employing PPGM compared with conventional microstrip lines, and the frequency range for high isolation was easily controlled by changing the PPGM structure. Above results indicate that microstrip lines employing PPGM are very useful for application to compact signal/bias lines of highly integrated MMIC requiring a high isolation characteristics between lines.

Passive-range estimation using dual focused beamformers

The passive-range estimation technique using a single focused beamformer has been studied under the sea. However, there are not many more methods in the case of closed multisource environments. In this paper, we propose the technique using dual focused beamformers to estimate the ranges of a closed multisource, and compare the proposed technique with the previous method. The proposed method is verified via computer simulation under the simplified multipath underwater channel model.

MIMO underwater communication with sparse channel estimation

In the area of underwater communications, MIMO (Multiple Input Multiple Output) techniques for increasing the data rates have been studied. The advantage of MIMO techniques is to increase the channel capacity, and it does not use additional frequency or transmit power. In this paper, we propose a sparse channel estimation method for MIMO underwater communication. The proposed method is comprised of the dominant channel tap position detection based on L1-norm minimization, channel regeneration, and LMS (Least Mean Square) channel estimation. To prove the performance of the proposed method, the simulations were conducted. The channels for simulation were generated by Bellhop model, and the sound speed profile that was really measured in sea was used. The range between sources and receivers is 1 km. In simulation results, the channel tracking speed of the proposed method was faster than the conventional method. The BER (Bit Error Rate) performance was improved about 10% at 15dB of SNR (Signal-to-Noise Ratio).

Design of OFDM System for High Speed Underwater Communication

The performance of underwater acoustic communication system is influenced on channel characteristic. Especially, an important feature of the underwater acoustic communication is multipath propagation and Doppler spread cause by the surface and bottom reflections. In this paper, we study the application of high speed data transmission in underwater to use the OFDM (Orthogonal Frequency Division Multiplexing) technique for robust the reverberation and multi-path. We use the clipping method for overcome the performance reduce in high PAPR (Peak-to-Average Power Ratio). We confirm the performance of communication in underwater to use the model for actually underwater channel simulation model and experiment in small water tank. As a result of experiment in small water tank, we acquired the BER of modulation techniques.

A Simplified Subspace Fitting Method for Estimating Shape of a Towed Array

Although the existing array shape estimation methods using reference sources demonstrate good performance, most of the methods require at least two reference sources 2RS in known locations and the reference sources must be in far field. This communication proposes a simplified subspace fitting method that uses only a single reference source 1RS. In the proposed method, the horizontal and vertical positions of each sensor are modeled by applying fixed intersensor spacing and sensor angles, so that the unknown parameters of the cost function are reduced. Furthermore, the Cramer-Rao lower bound (CRLB) is investigated for the proposed method. The results of the numerical experiments indicate that the proposed method is practical for estimating the shape of a towed array.