• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.604-607
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• 2013

A handoff call require more high QoS than that of a new call to satisfy continuity of communication on cellular networks. In case of a handoff call, after start connection of communication, the handoff call moves among cells. Therefore, Blocking of handoff call provides more bad service to respect to user. In this paper, we propose a 3 states guard channel schem to provide a stable environment of communication for a handoff call. The proposed scheme assigns the number of usable channels discriminatorily by distinguishing between of a new call and a handoff call. This scheme can reduce a handoff call blocking probability and improvement QoS of cellular networks. In this scheme, a handoff call classify by a partial handoff call and a full handoff call according to their handoff probability otherwise known as a previous guard scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.2
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• pp.189-197
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• 2016

Mobile ad-hoc networks (MANETs) experience frequent link disconnections due to non-uniform node distribution and mobility. Thus, end-to-end path establishment-based routing protocols cause frequent transmission failures in MANETs, resulting in heavy control messages for path reestablishment. While location-based MANET routing protocols, such as Greedy Perimeter Stateless Routing (GPSR), use location information to forward messages in a hop-by-hop routing fashion without an end-to-end path establishment procedure, such protocols encounter communication void problems when message forwarding to the next hop fails due to the absence of a relay node. Therefore, to solve this problem, this paper proposes a Delay Tolerant-GPSR (DT-GPSR) protocol, which combines Delay Tolerant Networking (DTN) technology with the GPSR protocol. The performance of DT-GPSR is compared with the performances of the original GPSR and PRoPHET routing protocols through simulation using NS-2. The simulation results confirm that DT-GPSR outperforms GPSR and PRoPHET in terms of the message delivery ratio and message delivery delay.

• Journal of Korea Technology Innovation Society
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• v.21 no.4
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• pp.1474-1492
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• 2018

This study empirically analyzes the direct effects of government support for SMEs (project success) and indirect effects (sales growth) focusing on the differences between financially difficult firms (so-called 'zombie' firms) and 'normal' firms. If the zombie firm has a problem in technology development (success of the project) and the economic resilience capability (sales growth), then excluding them from the government's R&D support programs would enhance the overall efficiency of the programs. If not, government R&D could complement the market failure and play a positive role in revitalizing marginal firms. In this study, we collected data about 7,575 firms who participated in seven government R&D programs in 2013 and 2014. As a result of the logistic regression analysis, we did not find evidence that the likelihood of success for zombie firms was lower than that for the normal firms. However, the tendency of sales growth after the project was smaller for the zombie firms than for the normal firms. For zombie firms, we also found that firms that succeeded in the project were more likely to increase sales than those that failed.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.31 no.6
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• pp.1137-1148
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• 2021

The main obstacle for implementing CSIDH-based cryptography is that it requires generating a kernel of a small prime order to compute the group action using Velu's formula. As this is a quite painstaking process for small torsion points, a new approach called radical isogeny is recently proposed to compute chains of isogenies from a coefficient of an elliptic curve. This paper presents an optimized implementation of radical isogenies and analyzes its ideal use in CSIDH-based cryptography. We tailor the formula for transforming Montgomery curves and Tate normal form and further optimized the radical 2- and 3- isogeny formula and a projective version of radical 5- and 7- isogeny. For CSIDH-512, using radical isogeny of degree up to 7 is 15.3% faster than standard constant-time CSIDH. For CSIDH-4096, using only radical 2-isogeny is the optimal choice.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3C
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• pp.83-91
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• 2005

We analyze the performance of an adaptive hybrid search code acquisition algorithm for direct-sequence code division multiple access (DS-CDMA) systems under slowly-moving mobile environments. The code acquisition algorithm is designed to provide the desired feature of constant false alarm rate (CFAR) to cope with nonstationarity of the interference in CDMA forward links. An analytical expression for the mean acquisition time is first derived and the probabilities of detection, miss, and false alarm are then obtained for frequency-selective Rayleigh fading environments. The fading envelope of a received signal is assumed to be constant over the duration of post-detection integration (PDI), considering slow fading environments. Finally, the performance of the designed code acquisition algorithm shall be evaluated numerically to examine the effect of some design parameters such as the sub-window size, size of the PDI, decision threshold, and so on, considering cdma2000 environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.5
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• pp.425-432
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• 2014

The Enhanced Distributed Channel Access (EDCA) function of IEEE 802.11e standard defines contention window (CW) for different Access Category (AC) limits to support Quality-of-Service (QoS). However, it have been remained the problem that the collision probability of transmission is increasing in congested network. Several different solutions have been proposed but the collision occurs among same priority queue within the same station to compete the channel access. This paper presents an APCA (Advanced Priority Collision Avoidance) algorithm for EDCA that increases the throughput in saturated situation. The proposed algorithm use reserved field's bits of FC(Frame Control) using IEEE 802.11e standard's RTS/CTS (Request to Send / Clear to Send) mechanism to avoid data collision. The simulation results show that the proposed algorithm improves the performance of EDCA in packet loss. Using Jain's fairness index formula, we also prove that the proposed APCA algorithm achieves the better fairness than EDCA method under network congested condition.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.147-156
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• 2004

This paper presents an implementation and performance analysis of an access channel decoder which exploits a diversity gain due to the independent magnitude of received signals energy at each of antenna elements of a smart antenna BTS (Base-station Transceiver Subsystem) operating in CDMA2000 1X signal environment. Proposed access channel decoder consists of a searcher supporting 4 fingers, Walsh demodulator, and demodulator controller. They have been implemented with 5 of 1 million-gate FPGA's (Field Programmable Gate Array) Altera's APEX EP20K1000EBC652 and TMS320C6203 DSP (digital signal processing). The objective of the proposed access channel decoders is to enhance the data retrieval at co]1-site during the access period, for which the optimal weight vector of the smart antenna BTS is not available. Through experimental tests, we confirmed that the proposed access channel decoder exploitng the diversity technique outperforms the conventional one, which is based on a single antenna channel, in terms of detection probability of access probe, access channel failure probability, and $E_{b/}$ $N_{o}$ in Walsh demodulator.r.r.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1055-1064
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• 2017

Since a device such as a rocket motor requires very high reliability, a reasonable reliability design process is essential. However, Korea has implemented a design method for applying a safety factor to each component. In classic reliability analysis, input variables such as mean and standard deviation, used in the limit state function, are treated as deterministic values. Because the mean and standard deviation are determined by a small amount of data, this approach could lead to inaccurate results. In this study, reliability analysis is performed for bolted joints and o-ring seals, and the Bayesian approach is used to statistically estimate the input variables. The estimated variables and failure probability, calculated by the reliability analysis, are derived in the form of probability distributions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.3
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• pp.604-611
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• 2017

In wireless sensor networks, an energy efficient operation is important since the energy of the sensors is limited. This paper proposes an energy efficient method that reduces a packet generation with Matrix Completion method where sensor value matrix has low-rank and decreases a collision rate and an overhead by transmitting only sensor ID to a time slot corresponding to the sensor value. Computer simulations demonstrates that the proposed method shows 17% of transmission failure and 73% of the packet generation compared to a conventional CSMA/CS. Delay time of transmitting information of the proposed method exhibits 22% of the CSMA/CA and the MSE error after reconstructing sensor values by Singular Value Thresholding(SVT) in Fusion Center is 87% of the CSMA/CA.

• Proceedings of the Korean Society of Computer Information Conference
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• 2019.01a
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• pp.415-418
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• 2019

최근 사용자 대화형(user-interactive) 응용들은 OS에게 많은 양의 메모리를 빈번하게 요구한다는 특징을 보인다. 응용의 메모리 할당 요청이 발생하면 OS는 할당할 페이지의 초기화 작업을 필수적으로 수행하는데, 빈번하게 발생하는 페이지 초기화 작업이 응용의 성능을 저하시키고 있다. 기존 리눅스 기반 시스템은 페이지 초기화 지연을 단축하기 위해 CPU의 캐시에 매핑되어 있어서 초기 값을 빠르게 쓸 수 있는 페이지인 캐시-핫(cache-hot) 페이지를 우선적으로 할당한다. 하지만 기존 리눅스는 각 코어별로 캐시-핫 페이지를 인식하고 관리하며, 다른 코어가 관리하는 캐시-핫 페이지에는 접근할 수 없다. 이러한 정책 때문에 다른 코어가 공유 캐시(shared cache)에 매핑된 캐시-핫 페이지를 관리하고 있더라도, 이를 할당받지 못하고 캐시-콜드(cache-cold) 페이지를 할당받는 경우가 발생한다. 본 논문에서는 공유 캐시에 매핑된 것으로 추정되는 캐시-핫 페이지를 별도로 인식하고 공유 캐시에 매핑된 것으로 추정되는 캐시-핫 페이지를 모든 코어가 활용할 수 있게 하여, 응용이 캐시-핫 페이지를 할당받을 확률을 기존 기법보다 높이는 향상된 캐시-핫 페이지 할당 기법을 제안한다. 제안된 기법은 페이지 할당 요청이 발생하면 먼저 각 코어의 사유 캐시에 매핑된 것으로 추정되는 캐시-핫 페이지를 우선적으로 할당하고, 할당에 실패하면 공유 캐시에 매핑된 것으로 추정되는 캐시-핫 페이지를 할당한다. 이를 통해 캐시-핫 페이지를 할당받을 확률을 기존 기법보다 높이고, 결과적으로 평균 페이지 초기화 지연을 단축한다. 제안된 기법을 리눅스 커널 4.18.10버전 기반 환경에서 구현하여 실험한 결과, 평균 페이지 초기화 지연이 기존 리눅스 시스템과 비교하여 약 7% 단축되었다.