Byeong Man KIM Hyeon Soo KIM Wooyoung KIM
Message Sequence Chart (MSC) standardized by International Telecommunication Union is a graphical and textual language for specification of concurrent systems. It has been used formally as well as informally to specify behavior of real-time systems, in particular telecommunication switching systems. Formal verification of a system specification is crucial to ensure that implementation of the system works correctly. In particular, verification methods based on finite states have been widely used in telecommunication systems design. The methods determine global system states and transitions between them (i. e. , build a global state transition graph (GSTG)), and verify the system's desired properties, such as safety and liveness, on the GSTG. In this paper, we focus on construction of GSTGs from MSC specifications. We propose action dependency graph as an intuitive description of semantics of MSC specifications and present an algorithm to translate MSC specifications to action dependency graphs as well as an algorithm to construct a global state transition graph from an action dependency graph.
Doohyung CHO Kunsik PARK Jongil WON Sanggi KIM Kwansgsoo KIM
In this paper, Epitaxial (Epi) Junction Termination Extension (JTE) technique for silicon carbide (SiC) power device is presented. Unlike conventional JTE, the Epi-JTE doesn't require high temperature (about 500°C) implantation process. Thus, it doesn't require high temperature (about 1700°C) process for implanted dose activation and surface defect curing. Therefore, the manufacturing cost will be decreased. Also, the fabrication process is very simple because the dose of the JTE is controlled by epitaxy growth. The blocking characteristic is analyzed through 2D-simulation for the proposed Epi-JTE. In addition, the effect was validated by experiment of fabricated SiC device with the Single-Zone-Epi-JTE. As a result, it has blocking capability of 79.4% compared to ideal parallel-plane junction breakdown.
Jin-soo KIM Jae-Gon KIM Kwang-deok SEO
We propose an efficient selective block encoding scheme with motion information feedback in distributed video coding (DVC). The proposed scheme estimates the spatial and temporal matching costs for each block in the side information (SI) and for the blocks with high matching costs, the motion information is provided to the encoder side to selectively encode the motion-compensated frame difference signal. Experimental results show that the proposed scheme outperforms the recently developed DVC algorithms.
Jae-Young PARK Jong-Kyu SONG Chang-Soo JANG San-Hong KIM Won-Young JUNG Taek-Soo KIM
The holding voltage of high-voltage devices under the snapback breakdown condition has been known to be much smaller than the power supply voltage. Such characteristics cause high-voltage ICs to be susceptible to the transient latch-up failure in the practical system applications, especially when these devices are used as the ESD power clamp circuit. A new latchup-free design of the ESD power clamp circuit with stacked-bipolar devices is proposed and successfully verified in a 0.35 µm BCD (Bipolar-CMOS-DMOS) process to achieve the desired ESD level. The total holding voltage of the stacked-bipolar devices in the snapback breakdown condition can be larger than the power supply voltage.
Jun-Hee JANG Jung-Su HAN Sung-Soo KIM Hyung-Jin CHOI
To mitigate the asynchronous ICI (Inter-Cell Interference), SCM (Spatial Covariance Matrix) of the asynchronous ICI plus background noise should be accurately estimated for MIMO-OFDMA (Multiple-input Multiple-output-Orthogonal Frequency Division Multiple Access) system. Generally, it is assumed that the SCM of the asynchronous ICI plus background noise is estimated by using training symbols. However, it is difficult to measure the interference statistics for a long time and considering that training symbols are not appropriate for OFDMA system such as LTE (3GPP Long Term Evolution). Therefore, noise reduction method is required to improve the estimation accuracy. Although the conventional time-domain low-pass type weighting method can be effective for noise reduction, it causes significant estimation error due to the spectral leakage in practical OFDM system. Therefore, we propose a time-domain sinc type weighing method which can not only reduce noise effectively minimizing estimation error caused by the spectral leakage but also can be implemented using frequency-domain weighted moving average filter easily. We also consider the iterative CFR (Channel Frequency Response) and SCM estimation method which can effectively reduce the estimation error of both CFR and SCM, and improve the performance for LTE system. By using computer simulation, we show that the proposed method can provide up to 2.5 dB SIR (Signal to Interference Ratio) gain compared with the conventional method, and verify that the proposed method is attractive and suitable for implementation with stable operation.
Byungsoo KIM Kyesuk JUN Ihn Seok KIM
In this paper, the absorbing property of the discrete Green's function ABC, which was based on a powerful concept of the TLM method, has been improved by relocating loss process from the time domain to the space domain. The proposed scheme simply adds a loss matrix to the connection matrix in the basic TLM algorithm to make the formulation of the ABC more efficient. Various lengths of absorbing layers discretized for a WR-90 empty waveguide have been tested in terms of reflection property. An expression for an optimum absorbing property has been also derived with respect to the length of the layer. Comparison of the layer with the discrete Green's function ABC shows that the layer in this study has improved reflection property better than approximately 3 and 6 dB, respectively, when 50Δ
Woohyung LIM Chang Woo HAN Nam Soo KIM
In this letter, we propose a novel approach to feature compensation performed in the cepstral domain. Processing in the cepstral domain has the advantage that the spectral correlation among different frequencies is taken into consideration. By introducing a linear approximation with diagonal covariance assumption, we modify the conventional log-spectral domain feature compensation technique to fit to the cepstral domain. The proposed approach shows significant improvements in the AURORA2 speech recognition task.
Donghun AN Hoongee YANG Sunghyun YANG Youngsoo KIM Jonggwan YOOK Bongsoon KANG
This paper presents a simulation based method to predict the amount of frequency interference in a passive type RFID system. To judge occurrence of frequency interference, we use a parameter POI (probability of interference) that depends on several factors such as multiple access method, emission mask, the number of channel, etc. Due to its dependence on several factors, a Monte-carlo based simulation is suitably used. Through the simulation, we draw minimum separation distance between two readers and examine performance degradation due to aggregate interfering readers. Moreover, we present a reader deployment strategy based on the average POI of active readers operating in some area.
Ki-Sung SOHN Da-In HAN Ki-Ju BAEK Nam-Soo KIM Yeong-Seuk KIM
A new clock gating circuit suitable for shift register is presented. The proposed clock gating circuit that consists of basic NOR gates is low power and small area. The power consumption of a 16-bit shift register implemented with the proposed clock gating circuit is about 66% lower than that found when using the conventional design.
A shared buffer ATM switch loaded with bursty input traffic is modeled by a discrete-time queueing system. Also, the unbalanced and correlated routing traffic patterns are considered. An approximation method to analyze the queueing system under consideration is developed. To overcome the problem regarding the size of state space to be dealt with, the entire switching system is decomposed into several subsystems, and then each subsystem is analyzed in isolation. We first propose an efficient algorithm for superposing all the individual bursty cell arrival processes to the switch. And then, the maximum entropy method is applied to obtain the steady-state probability distribution of the queueing system. From the obtained steady-state probabilities, we can derive some performance measures such as cell loss probability and average delay. Numerical examples of the proposed approximation method are given, which are compared with simulation results.
The effect of feedback delay and channel estimation error on closed-loop transmit diversity (CTD) systems is investigated in time-selective Rayleigh fading channels. Based on a minimum mean square error (MMSE) channel estimator, the variance of the estimation error is formulated in terms of fading index and the number of transmit antennas. A bit error rate (BER) expression for the CTD system is analytically derived as a function of channel estimation error, feedback delay, and fading index. It is shown that the BER performance of the CTD system improves as the length of training symbols increases and/or the frame length decreases. In the CTD system, more accurate channel estimation scheme is required to achieve its full gain as the number of employed transmit antennas increases. It is also found that the CTD system is applicable to the slowly moving channel environments, such as pedestrians, but not for fast moving vehicles.
SooHong PARK MinHo LEE PyungSoo KIM Youngkeun KIM
This letter describes the current mechanism for IP address configuration in the wireless Internet and examines its drawbacks, and suggests a new mechanism of address configuration which provides a reduced message exchange for address configuration in the wireless Internet over the current 4-way message exchange when performing address configuration through DHCP. Analytic performance evaluation and comparison have shown that the proposed mechanism is faster in terms of delay than the existing mechanism including reduced packet loss when in motion.
Dongsoo KIM Jimin CHEON Gunhee HAN
The performance of an analog winner-take-all (WTA) circuit is affected by the corner error and the offset error. Despite the fact that the corner error can be reduced with large transconductance of the transistor, the offset error caused by device mismatch has not been completely studied. This paper presents the complete offset error analysis, and proposes low offset design guidelines and an offset cancellation scheme. The experimental results show good agreement with the theoretical analysis and the drastic improvement of the offset error.
Chang Woo HAN Shin Jae KANG Nam Soo KIM
In this letter, we propose a novel approach to estimate three different kinds of phone mismatch penalty matrices for two-stage keyword spotting. When the output of a phone recognizer is given, detection of a specific keyword is carried out through text matching with the phone sequences provided by the specified keyword using the proposed phone mismatch penalty matrices. The penalty matrices associated with substitution, insertion and deletion errors are estimated from the training data through deliberate error generation. The proposed approach has shown a significant improvement in a Korean continuous speech recognition task.
Seonkeol WOO Hoongee YANG Sunghyun YANG Youngsoo KIM Jonggwan YOOK Bongsoon KANG
This letter presents a new TR-UWB receiver exploiting frequency components of UWB pulses. This is accomplished by separating frequency-components of UWB pulses into real and imaginary parts, independently correlating and effectively combining them. We analytically show this scheme improves the output SNR compared with a conventional one using complex correlation. This will also be justified by simulation results.
Two operations, polynomial multiplication and modular reduction, are newly induced by the properties of the modified Booth's algorithm and irreducible all one polynomials, respectively. A new and effective methodology is hereby proposed for computing multiplication over a class of fields GF(2m) using the two operations. Then a low complexity multiplexer-based multiplier is presented based on the aforementioned methodology. Our multiplier consists of m 2-input AND gates, an (m2 + 3m - 4)/2 2-input XOR gates, and m(m - 1)/2 4 1 multiplexers. For the detailed estimation of the complexity of our multiplier, we will expand this argument into the transistor count, using a standard CMOS VLSI realization. The compared results show that our work is advantageous in terms of circuit complexity and requires less delay time compared to previously reported multipliers. Moreover, our architecture is very regular, modular and therefore, well-suited for VLSI implementation.
Jeong-Mok KIM Zong-Soo LIM Joong-Chang CHUN Tae-Soo KIM
For the microwave level meter based on the FM-CW radar, we analyze the spectrum correlation of beat signals and propose a measurement algorithm using the fact that there exists a peak in the spectrum correlation of beat signals when range difference is sufficiently small. This algorithm can compensate the nonlinear effect of VCO frequency sweep, making it possible to determine the range difference in a precise manner even using a practical VCO. We present some experimental results to show the validity of this algorithm.
Jae-Won KIM Sun-Young JEON Hye-Soo KIM Jae-Woong YUN Sung-Jea KO
Vertical handoff is required to achieve anywhere and anytime internet access in the fourth generation (4G) network providing interoperability between universal mobile telecommunications system (UMTS) and wireless LAN (WLAN). However, video data can be lost due to latency caused by vertical handoff. To solve this problem, in this paper, we propose a video streaming technique supporting error concealment (EC) for video on demand (VOD) services that provides seamless playout at the client in vertical handoff. In the proposed method, the streaming server first predicts the client buffer status (CBS). Using the predicted CBS and the channel rate, the streaming server selects a proper video transmission method for vertical handoff between frame selective pre (FSP)-transmission and re-transmission. Performance evaluations are presented to demonstrate the effectiveness of the proposed method.
Doo Hwa HONG June Sig SUNG Kyung Hwan OH Nam Soo KIM
Decision tree-based clustering and parameter estimation are essential steps in the training part of an HMM-based speech synthesis system. These two steps are usually performed based on the maximum likelihood (ML) criterion. However, one of the drawbacks of the ML criterion is that it is sensitive to outliers which usually result in quality degradation of the synthesized speech. In this letter, we propose an approach to detect and remove outliers for HMM-based speech synthesis. Experimental results show that the proposed approach can improve the synthetic speech, particularly when the available training speech database is insufficient.
Youn-Soo KIM Eun Ju LEE Bong Soo KIM Hyung Seok KIM
ZigBee recently has been used a lot in wireless sensor networks because of its low power consumption and affordable chips. However, ZigBee's existing hierarchical routing algorithm has a disadvantage in that a node may communicate with a nearby node over several hops. In this letter we propose a Quasi-Hierarchical Routing (QHR) algorithm that can improve the ZigBee hierarchical routing method's inefficiency by using brief information on neighbors within radio range. The network simulation evaluates this QHR's performance by comparing it to other ZigBee routing schemes.