Jonghyun Lee

A novel smooth impact drive mechanism actuation method with dual-slider for a compact zoom lens system

In this paper, a novel actuation method for a smooth impact drive mechanism that positions dual-slider by a single piezo-element is introduced and applied to a compact zoom lens system. A mode chart that determines the state of the slider at the expansion or shrinkage periods of the piezo-element is presented, and the design guide of a driving input profile is proposed. The motion of dual-slider holding lenses is analyzed at each mode, and proper modes for zoom functions are selected for the purpose of positioning two lenses. Because the proposed actuation method allows independent movement of two lenses by a single piezo-element, the zoom lens system can be designed to be compact. For a feasibility test, a lens system composed of an afocal zoom system and a focusing lens was developed, and the passive auto-focus method was implemented.

Experiments and analysis of voice over Mobile IP

Supporting mobility in real-time applications such as Internet telephony is in demand as the mobile Internet becomes prevalent. A simple solution is to use Mobile JP in order to provide transparent handoffs to upper layer applications. However, due in part to the Mobile IPs limitations such as triangular routing delay and encapsulation overhead, application-layer solutions for mobile Internet telephony has been developed by extending Session Initiation Protocol (SIP). This work presents experimental results on Internet telephony based on Mobile IP and examines its feasibility by analyzing delay factors and increased network toads. We found that packet size in terms of number of frames per packet is important in optimizing the packet transmission delay and network load without hindering the interactivity in voice conversations. Our major contribution is to give a real experience on voice over Mobile IP and to raise a need of designing delay-aware and/or load-aware scheme for Internet telephony.

Joint estimation of the space-time distributed signal parameters

Understanding of wireless channel characteristics is important to be able to use the base-station smart antenna technology. Most channel parameter estimation algorithms that have been proposed, however, assume that incoming signal is generated by a point source, and some algorithms that consider distributed sources are limited to the space distribution. We propose an algorithm based on the maximum likelihood (ML) principle for the channel parameter estimation, and on the Neyman-pearson decision rule for deciding number of multipaths. The proposed algorithm is applied to field measurement data collected in three different type of urban areas, and we get some qualitative understanding for the effect of a high-rise building nearby a base station, the effect of a straight-lined road, and the effect of buildings surrounding a mobile.

Joint maximum-likelihood detection and estimation of space-time distributed multi-path parameters

Several parametric approaches for estimating the angular spread of a signal as well as its direction have been proposed previously. These approaches require that the number of signal sources should be less than the number of antennas. Furthermore, they usually consider the angle and the angular spread only. In this paper we extend the idea by modeling the received (CDMA) signal using reasonable distribution functions in terms of time as well as space parameters. The particular distributions of the angle and delay functions chosen herein are the Gaussian distribution. Our estimation algorithm based on the maximum likelihood (ML) method estimates the angles, the variance of the angular spreads, the time delay, the variance of the delay spreads, and finally the power of the individual multipath signals. The proposed method has been successfully applied to field measurement data collected in differnet regions throughout South Korea to extract representative channel parameters.

Deterministic fabrication of carbon nanotube probes using the dielectrophoretic assembly and electrical detection

We report the controlled dielectrophoretic assembly for the deterministic fabrication of carbon nanotube (CNT) probes. Electrical detection was applied to the dielectrophoretic assembly of CNT probes. Dielectrophoretic manipulation with an ac electric field of 5 MHz was used to form the CNT bridge across oppositely aligned tungsten tips (W-tips). A dc electric field was simultaneously applied to monitor the direct current flowing through the gap. The detected nanocurrent reveals that the CNT bridge is formed between W-tips in real time. We compared current data with bundle diameter of CNT probes in field emission scanning electron microscopy (FE-SEM) images. As the number of assembled CNTs increased, current was increased. With the obtained linear relationship, the number of the attached CNTs can be estimated without confirmation of the FE-SEM image. This combined use of the current detection method with dielectrophoretic manipulation will provide a reliable process for the fabrication of CNT probes.

Selective establishment of pseudo reservations for QoS guarantees in mobile Internet

In this paper, we propose a new mechanism for supporting seamless QoS guarantees in mobile Internet, called selective establishment of pseudo reservations (SEP). SEP addresses the issues of the conventional approaches such as excessive reservation requirements due to establishment of multiple advance reservations. It significantly reduces the number of required advance reservations by employing a movement detection scheme using link-layer functionalities. SEP requires fewer functional and structural changes in the current Internet components and protocols since all enhanced features are integrated into leaf base stations (BSs). Experimental results show that SEP outperforms the conventional approaches such as HMRSVP in reservation session loss and completion rates as the offered load in the network becomes high and the average number of handoffs increases during a reservation session.

Angular distribution estimation of the arriving signal using a mechanically steered fixed beam antenna

A method of estimating the spatio-temporal channel parameter is proposed. Using a mechanically rotating antenna which has a narrow beam width, we show how to estimate the distribution of the incoming signal in the directions of the angle and delay. With the proposed method, the estimation problem is represented as a deconvolution problem which can be converted as a matrix equation with constraints. We also show the results of the proposed method tested with field data.

Musical instruments recognition using hidden Markov model

A new musical instrument recognition technique based on a hidden Markov model (HMM) is proposed. The spectral envelope is the key information of instrument characteristic and timbre. We decompose an instrument sound into sinusoidal components (harmonics) and noise components and estimate the amplitudes of the harmonics component. We want to express the spectral envelope effectively using estimated amplitude, therefore, we define three kinds of features and apply a recognition procedure to each feature. The HMM model used is continuous single Gaussian output HMM. To evaluate the performance of the recognition technique, the proposed technique is applied to classify the real instrumental sound of MUMS (MacGill University Master Samples). The recognition success ratio is more than 70%.

Concurrency control in multidatabase systems: a performance study

Abstract A multidatabase system (MDBS) is a federation of multiple autonomous local database systems (LDBSs). Over the years, it has been recognized that the most challenging issue of concurrency control in an MDBS has been a concern about how to resolve indirect conflicts and thereby to ensure global serializability (GSR), without sacrificing the local autonomy. Even though the global serializability issue is well understood and many concurrency control algorithms have been proposed, it is noticeable that the performance trade-offs of those algorithms are not yet understood. To address issues about the performance of concurrency control algorithms in an MDBS, we examine two MDBS concurrency control algorithms through simulation: optimistic ticket method (OTM) and global ticket method (GTM) that we have proposed. In OTM, the GSR is assured by way of accessing a local object (ticket), by which any indirect conflicts that may cause non-serializable execution are resolved. The global transaction manager (Global_TM) in GTM maintains a global variable (ticket), which is similar to timestamp, and the commit order of a GT is predefined by the order of assigned global ticket value. We examine the performance trade-offs of the two concurrency control methods (CCMs) with respect to ensuring GSR in particular. To ensure GSR, the (GTs) are expected to frequently restart in OTM and block in GTM. In this study, we also investigate the implications of time-out interval on the performance as we assume that the time-out approach is used as a global deadlock resolution method for both algorithms. Our experimental results showed that GTM outperforms OTM in cases that short time-out values are given. However, in case that the time-out value relatively becomes long, our results demonstrated that OTM outperforms GTM.

Analysis on electric energy of EAP generator using Smartpice

In this research we proposed the circuit for storing electric energy by converting mechanical energy at capacitor using EAP Pad. We used the Smartspice program which is a circuit analysis program for checking level of electric energy. We mainly analyzed into 4 effecting factors to electric energy, and 4 factors are firstly applied voltage, secondly the capacitor of source part and the capacitor of capacitor part, thirdly capacitor of EAP and its change of capacitor value, and for last an applied frequency. For addition, research for EAP generators are needed electric power to circuit at all time till now. But different from that, this research focused on not all time.