• The KIPS Transactions:PartB
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• v.13B no.4 s.107
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• pp.471-478
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• 2006

In this paper, two color contrast evaluation algorithms, W3C and NSSC algorithms are compared and investigated to select proper criteria of the color contrast of text-background color combinations in web documents. The relationship between the color contrast defined by existing formula and the readability rating is not perfect and there is quite a bit of variance, in particular, there is some substantial outlier. I modify the NSSC algorithm to apply all colors and compare the two algorithms to apply same color combinations of web safe colors. A new algorithm considering color temperature feeling as a component of the color contrast is proposed and implemented. As the results of this study, the existing two algorithms are not contradictory to each other, 82% of all color combinations of web safe colors are not proper combinations according to W3C guide which provide severe restriction to select colors in web documents compared to NSSC algorithm. Experimental test shows proposed algorithm is superior to the W3C algorithm with respect to the linearity of relationship between color contrast and readability rating. It means a color temperature feeling is an effective component of a color contrast. But to determine best contribution ratio of the color temperature feeling, further study is required and it is related to Hangul font style and size. The more popular a mobile color display is used, the more important accessibility factor a color contrast will be.

• The KIPS Transactions:PartA
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• v.12A no.3 s.93
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• pp.205-214
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• 2005

Flash memory is at high speed used as storage of personal information utilities, ubiquitous computing environments, mobile phones, electronic goods, etc. This is because flash memory has the characteristics of low electronic power, non-volatile storage, high performance, physical stability, portability, and so on. However, differently from hard disks, it has a weak point that overwrites on already written block of flash memory is impossible to be done. In order to make an overwrite possible, an erase operation on the written block should be performed before the overwrite, which lowers the performance of flash memory highly. In order to solve this problem the flash memory controller maintains a system software module called the flash translation layer(FTL). Of many proposed FTL schemes, the log block buffer scheme is best known so far. This scheme uses a small number of log blocks of flash memory as a write buffer, which reduces the number of erase operations by overwrites, leading to good performance. However, this scheme shows a weakness of low page usability of log blocks. In this paper, we propose an enhanced log block buffer scheme, FAST(Full Associative Sector Translation), which improves the page usability of each log block by fully associating sectors to be written by overwrites to the entire log blocks. We also show that our FAST scheme outperforms the log block buffer scheme.

• KIPS Transactions on Computer and Communication Systems
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• v.7 no.2
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• pp.49-58
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• 2018

A certificate is a means to certify users by conducting the identification of the users, the prevention of forgery and alteration, and non-repudiation. Most people use an accredited certificate when they perform a task using online banking, and it is often used for the purpose of proving one's identity in issuing various certificates and making electronic payments in addition to online banking. At this time, the issued certificate exists in a file form on the disk, and it is possible to use the certificate issued in an existing device in a new device only if one copies it from the existing device. However, most certificate duplication methods are a method of duplication, entering an 8-16 digit verification code. This is inconvenient because one should enter the verification code and has a weakness that it is vulnerable to security issues. To solve this weakness, this study proposes a method for enhancing security certificate duplication in a multi-channel using TCP and BLE. The proposed method: 1) shares data can be mutually authenticated, using BLE Advertising data; and 2) encrypts the certificate with a symmetric key algorithm and delivers it after the certification of the device through an ECC-based electronic signature algorithm. As a result of the implementation of the proposed method in a mobile environment, it could defend against sniffing attacks, the area of security vulnerabilities in the existing methods and it was proven that it could increase security strength about $10^{41}$ times in an attempt of decoding through the method of substitution of brute force attack existing method.

• The KIPS Transactions:PartC
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• v.14C no.2
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• pp.147-154
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• 2007

Network topology in ad hoc networks keeps changing because of node mobility and no limitation in number of nodes. Therefore, the scalability of routing protocol is of great importance, However, table driven protocols such as DSDV have been known to be suitable for relatively small number of nodes and low node mobility, Various protocols like FSR, OLSR, and PCDV have been proposed to resolve scalability problem but vet remain to be proven for their comparative superiority for scalability, In this paper, we compare and amine them by employing various network deployment scenarios as follows: network dimension increase's while keeping node density constant node density increases while keeping network dimension fixed, and the number of sessions increase with the network dimension and the number of nodes fixed. the DSDV protocol showed a low scalability despite that it imposes a low overhead because its convergence speed against topology change is slow, The FSR's performance decreased according to the increase of overhead corresponding to increasing number of nodes, The OLSR with the shortest convergence time among them shows a good scalability, but turned out to be less scalable than the PCDV that uses a clustering because of its relatively high overhead.

• The KIPS Transactions:PartC
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• v.17C no.3
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• pp.271-280
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• 2010

For the next generation mobile communication system, diverse wireless network techniques such as beyond 3G LTE, WiMAX/WiBro, and next generation WLAN etc. are proceeding to the form integrated into the All-IP core network. According to this development, Beyond 3G integrated into heterogeneous wireless access technologies must support the vertical handover and network to be used of several radio networks. However, unified management of each network is demanded since it is individually serviced. Therefore, in order to solve this problem this study is introducing the theory of Common Radio Resource Management (CRRM) based on Generic Link Layer (GLL). This study designs the structure and functions to support the vertical handover and propose the vertical handover algorithm of which policy-based and MCDM are composed between LTE and WLAN systems using GLL. Finally, simulation results are presented to show the improved performance over the data throughput, handover success rate, the system service cost and handover attempt number.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.2
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• pp.175-183
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• 2016

The endurance reliability assessment of a highly complex mechanism is generally predicted by the fatigue life based on simple stress analysis. This study discusses various fatigue life assessment techniques for an automobile clutch snap ring. Finite element analyses were conducted to determine the structural stress on the snap ring. Structural stress that is insensitive in regards to the mesh size and type definition is presented in this study. The structural stress definition is consistent with elementary structural mechanics theory and provides an effective measure of a stress state that pertains to fatigue behavior of welded joints in the form of both membrane and bending components. Numerical procedures for both solid models and shell or plate element models are presented to demonstrate the mesh-size insensitivity when extracting the structural stress parameters. Conventional finite element models can be used with the structural stress calculations as a post-processing procedure. The two major implications from this research were: (a) structural stresses pertaining to fatigue behavior can be consistently calculated in a mesh-insensitive manner regardless of the types of finite element models; and (b) by comparing with the clutch snap-ring fatigue test data, we should predict the fatigue fractures of an automobile clutch snap ring using this method.

• KIISE Transactions on Computing Practices
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• v.21 no.1
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• pp.64-69
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• 2015

Place awareness is an essential for location-based services that are widely provided to smartphone users. However, traditional GPS-based methods are only valid outdoors where the GPS signal is strong and also require symbolic place information of the physical location. In this paper, environmental sounds and images are used to recognize important aspects of each place. The proposed method extracts feature vectors from visual, auditory and location data recorded by a smartphone with built-in camera, microphone and GPS sensors modules. The heterogeneous feature vectors were then learned by an ensemble learning method that learns each group of feature vectors for each classifier respectively and votes to produce the highest weighted result. The proposed method is evaluated for place recognition using a data group of 3000 samples in six places and the experimental results show a remarkably improved recognition accuracy when using all kinds of sensory data comparing to results using data from a single sensor or audio-visual integrated data only.

• KIPS Transactions on Software and Data Engineering
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• v.3 no.8
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• pp.321-328
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• 2014

In this paper, we present a MapReduce-based mobility pattern mining system which can predict efficiently the next place of mobile users. It learns the mobility pattern model of each user, represented by Hidden Markov Models(HMM), from a large-scale trajectory dataset, and then predicts the next place for the user to visit by applying the learned models to the current trajectory. Our system consists of two parts: the back-end part, in which the mobility pattern models are learned for individual users, and the front-end part, where the next place for a certain user to visit is predicted based on the mobility pattern models. While the back-end part comprises of three distinct MapReduce modules for POI extraction, trajectory transformation, and mobility pattern model learning, the front-end part has two different modules for candidate route generation and next place prediction. Map and reduce functions of each module in our system were designed to utilize the underlying Hadoop infrastructure enough to maximize the parallel processing. We performed experiments to evaluate the performance of the proposed system by using a large-scale open benchmark dataset, GeoLife, and then could make sure of high performance of our system as results of the experiments.

• KIPS Transactions on Computer and Communication Systems
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• v.6 no.9
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• pp.397-406
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• 2017

In case of using the existing encrypted algorithm for massive data encryption service under the cloud environment, the problem that requires much time in data encryption come to the fore. To make up for this weakness, a partial encryption method is used generally. However, the existing partial encryption method has a disadvantage that the encrypted data can be inferred due to the remaining area that is not encrypted. This study proposes a partial encryption method of increasing the encryption speed and complying with the security standard in order to solve this demerit. The proposed method consists of 3 processes such as header formation, partial encryption and block shuffle. In step 1 Header formation process, header data necessary for the algorithm are generated. In step 2 Partial encryption process, a part of data is encrypted, using LEA (Lightweight Encryption Algorithm), and all data are transformed with XOR of data in the unencrypted part and the block generated in the encryption process. In step 3 Block shuffle process, the blocks are mixed, using the shuffle data stored with the random arrangement form in the header to carry out encryption by transforming the data into an unrecognizable form. As a result of the implementation of the proposed method, applying it to a mobile device, all the encrypted data were transformed into an unrecognizable form, so the data could not be inferred, and the data could not be restored without the encryption key. It was confirmed that the proposed method could make prompt treatment possible in encrypting mass data since the encryption speed is improved by approximately 273% or so compared to LEA which is Lightweight Encryption Algorithm.

• The KIPS Transactions:PartC
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• v.11C no.6 s.95
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• pp.835-842
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• 2004

In this paper, we have analyzed the MC-DS/CDMA system with input signal synchronized completely through adjustment of the gain in the PLL loop, by using the hybrid SC/MRC-(2/3) technique, which is said to one of the optimal diversity techniques under the multi-path fading environment, assuming that phase error is defined to the phase difference between the received signal from the multi-path and the reference signal in the PLL of the receiver. Also, assuming that the regarded radio channel model for the mobile communication is subject to the Nakagami-m fading channel, we have developed the expressions and performed the simulation under the consideration of various factor, in the MC/DS-CDMA system with the hybrid SC.MRC-(2/3) diversity method, such as the Nakagami fading index(m), $the\;number\;of\;paths\;(L_p),$ the number of hybrid SC.MRC-(2/3) $diversity\;branches\;(L,\;L_c),$ the number of users (K), the number of subcarriers (U), and the gain in the PLL loop. As a result of the simulation, it has been confirmed that the performance improvement of the system can be achieved by adjusting properly the PLL loop in order for the MC/DS-CDMA system with the hybrid SC/MRC-(2/3) diversity method to receive a fully synchronized signal. And the value of the gain in the PLL loop should exceed 7dB in order for the system to receive the signal with prefect synchronization, even though there might be a slight difference according to the values of the fading index and the spread processing gain of the subcarrier.