• Journal of Communications and Networks
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• v.16 no.1
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• pp.10-17
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• 2014

This work investigates two important performance metrics of underlay cooperative cognitive radio (CR) networks: Interference cumulative distribution function of licensed users and outage probability of unlicensed users. These metrics are thoroughly analyzed in realistic operating conditions such as imperfect fading channel information and strict transmit power constraint, which satisfies interference power constraint and maximum transmit power constraint, over Nakagami-m fading channels. Novel closed-form expressions are derived and subsequently validated extensively through comparisons with respective results from computer simulations. The proposed expressions are rather long but straightforward to handle both analytically and numerically since they are expressed in terms of well known built-in functions. In addition, the offered results provide the following technical insights: i) Channel information imperfection degrades considerably the performance of both unlicensed network in terms of OP and licensed network in terms of interference levels; ii) underlay cooperative CR networks experience the outage saturation phenomenon; iii) the probability that the interference power constraint is satisfied is relatively low and depends significantly on the corresponding fading severity conditions as well as the channel estimation quality; iv) there exists a critical performance trade-off between unlicensed and licensed networks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.10
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• pp.4823-4843
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• 2017

In this paper, an improved utility-based cross-layer dynamic subcarrier allocation (DSA) algorithm is proposed for single carrier frequency division multiple access (SC-FDMA) system, which adopts adaptive service rate control (ASRC) to eliminate the service rate waste and improve the spectral efficiency in heterogeneous network including non-real-time traffic and real-time traffic. In this algorithm, furthermore, a first in first out (FIFO) queuing model with finite space is established on the cross-layer scheduling framework. Simulation results indicate that by taking the service rate constraint as the necessary condition for optimality, the ASRC algorithm can effectively eliminate the service rate waste without compromising the scheduling performance. Moreover, the ASRC algorithm is able to further improve the quality of service (QoS) performance and transmission throughput by contributing an attractive performance trade-off between real-time and non-real-time applications.

• Proceedings of the Korean Society of Computer Information Conference
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• 2009.01a
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• pp.391-394
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• 2009

All-IP는 통신에 관련된 모든 개체가 IP를 사용하는 네트워크를 의미한다. All-IP 네트워크에서는 보안을 위해 통신 내용에 대한 암호화가 반드시 이루어져야 하며, 신뢰할 수 있는 3자 (trusted third party)는 서비스 중재 및 부가 서비스 제공을 위해 통신에 사용된 암호화 키를 획득할 수 있어야 한다. 이는 통신 개체가 다른 개체에게 암호화 키를 전달하는 메커니즘이 필요하다는 것을 의미한다. 우리는 본 논문을 통해, 통신 개체가 다른 개체에게 키를 전달하는 기법을 37에로 분류하고 각 기법에 대해 상세히 설명한다. 또한, 우리는 새로운 키 전달 프로토콜을 제안하고 3가지 운용 모드를 제시한다. 우리가 제안하는 프로토콜용 사용자의 필요에 따라 보안 기능을 선택적으로 운용할 수 있다. 성능평가 및 분석 결과에 따르면, 보안 가능과 성능은 뚜렷한 트레이드오프(trade-off) 관계가 있음을 알 수 있고, 기본적인 기능만을 운용할 경우 추가적인 오버헤드가 거의 없음을 알 수 있다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.3
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• pp.1091-1098
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• 2012

From the perspective of risk management, financial organization that have issued ELW require an efficient hedging methodology due to recently increased trade volume of ELW. This study presents an ELW hedging methodology using artificial neural network(ANN) to minimize hedging costs. The performance of the presented methodology in this study is examined by analysis utilizing the prices and volatilities of underlying assets, risk free interest rates, and maturities and computational experiments show that the proposed method is superior to existing dynamic delta hedging(DDH) technique in terms of hedging costs ranged from 25% to 250%.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.213-220
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• 2008

This paper analyzes a broadcasting technique for wireless multi-hop sensor networks that uses a form of cooperative diversity called opportunistic large arrays (OLAs). We propose a method for autonomous scheduling of the nodes, which limits the nodes that relay and saves as much as 32% of the transmit energy compared to other broadcast approaches, without requiring global positioning system (GPS), individual node addressing, or inter-node interaction. This energy-saving is a result of cross-layer interaction, in the sense that the medium access control (MAC) and routing functions are partially executed in the physical (PHY) layer. Our proposed method is called OLA with a transmission threshold (OLA-T), where a node compares its received power to a threshold to decide if it should forward. We also investigate OLA with variable threshold (OLA-VT), which optimizes the thresholds as a function of level. OLA-T and OLA-VT are compared with OLA broadcasting without a transmission threshold, each in their minimum energy configuration, using an analytical method under the orthogonal and continuum assumptions. The trade-off between the number of OLA levels (or hops) required to achieve successful network broadcast and transmission energy saved is investigated. The results based on the analytical assumptions are confirmed with Monte Carlo simulations.

• Journal of Korea Multimedia Society
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• v.9 no.2
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• pp.208-214
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• 2006

Participants of a NVE(networked virtual environment) may have different hardwares and network environments, and to guarantee the fairness, messages of participants should be synchronized. A solution for the synchronization problem is to wait for a certain amount of time until the server processes the message. It is not easy to determine a suitable waiting period because of the trade-off between the fairness and the responsiveness. In this paper we propose a method to decide a waiting period by considering only the participants with small network delays and perform experiments for the performance evaluation. Experiments show that the proposed method leads to significant improvement of responsiveness, while retaining fairness.

• Journal of Communications and Networks
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• v.16 no.5
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• pp.493-501
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• 2014

Coverage completeness is an important indicator for quality of service in wireless sensor networks (WSN). Due to limited energy and diverse working conditions, the sensor nodes have different lifetimes which often cause network holes. Most of the existing methods expose large limitation and one-sidedness because they generally consider only one aspect, either coverage rate or energy issue. This paper presents a novel method for coverage hole detection with residual energy in randomly deployed wireless sensor networks. By calculating the life expectancy of working nodes through residual energy, we make a trade-off between network repair cost and energy waste. The working nodes with short lifetime are screened out according to a proper ratio. After that, the locations of coverage holes can be determined by calculating the joint coverage probability and the evaluation criteria. Simulation result shows that compared to those traditional algorithms without consideration of energy problem, our method can effectively maintain the coverage quality of repaired WSN while enhancing the life span of WSN at the same time.

• Proceedings of the Korean Information Science Society Conference
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• 2010.06d
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• pp.360-365
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• 2010

In this paper, we present a distributed algorithm for detecting dynamic event regions in wireless sensor network with the consideration on energy saving. Our model is that the sensing field is monitored by a large number of randomly distributed sensors with low-power battery and limited functionality, and that the event region is dynamic with motion or changing the shape. At any time that the event happens, we need some sensors awake to detect it and to wake up its k-hop neighbors to detect further events. Scheduling for the network to save the total power-cost or to maximize the monitoring time has been studied extensively. Our scheme is that some predetermined sensors, called critical sensors are awake all the time and when the event is detected by a critical sensor the sensor broadcasts to the neighbors to check their sensing area. Then the neighbors check their area and decide whether they wake up or remain in sleeping mode with certain criteria. Our algorithm uses only 2 bit of information in communication between sensors, thus the total communication cost is low, and the speed of detecting all event region is high. We adapt two kinds of measure for the wake-up decision. With suitable threshold values, our algorithm can be applied for many applications and for the trade-off between energy saving and the efficiency of event detection.

• Proceedings of the Korean Information Science Society Conference
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• 2007.10c
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• pp.179-184
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• 2007

EPCglobal 네트워크란 EPC(Electronic Product Code)와 RFID(Radio Frequency Identification) 기술을 바탕으로 제품에 식별번호를 부여하고 정보를 저장할 수 있는 공간을 네트워크로 연동하여 공급자, 수요자, 소비가 제품에 관련된 정보를 알 수 있게 해주는 시스템을 말한다. 또한 EPCglobal 네트워크 아키텍처 프레임워크(EPCglobal network architecture framework)는 EPC를 사용하여 공급과 유통망 강화라는 업체간의 공동 목표를 위한 서비스하는 것이다. EPCglobal 네트워크 아키텍처 중 EPCIS(EPC Information System) 수집 애플리케이션, EPCIS 접근 애플리케이션에서 이벤트 정의 시 공통적인 의사소통을 위한 표준 어휘 정의가 필수적이며, 그 어휘 종류에는 표준 어휘(standard vocabulary)와 사용자어휘(user vocabulary)가 있다. 이 논문은 이 가운데 EPCglobal 네트워크 아키텍처의 표준 어휘 정의에 초점을 두고, 사용자 어휘는 부분적으로 정의하고자 한다. 따라서 이 논문은 EPCglobal 네트워크 프레임 아키텍처의 이벤트 정의 시 사용될 표준 어휘를 제안하고, XML 구현을 통해 실제 사용 가능한 환경을 제공할 것이다.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.1
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• pp.77-84
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• 2012

This paper describes the process of optimal resonant frequency design with full-bridge series-loaded resonant dc-dc converter in a high efficiency 3.3 kW on-board battery charger application for Electric Vehicles and Plug-in Hybrid Electric Vehicles. The optimal range of resonant frequency and switching frequency used for ZVS are determined by considering trade-off between loss of switching devices and resonant network with size of passive/magnetic devices. In addition, it is defined charging region of battery, the load of on-board charger, as the area of load by deliberating the characteristic of resonant. It is verified the designed frequency band by reflecting the defined area on resonant frequency.