• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.6
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• pp.3273-3308
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• 2017

Building appropriate trust evaluation models is an important research issue for security guarantee in social networks. Most of the existing works usually consider the trust values at the current time slot, and model trust as the stochastic variable. However, in fact, trust evolves over time, and trust is a stochastic process. In this paper, we propose a novel time-variant stochastic trust evaluation (TSTE) model, which models trust over time and captures trust evolution by a stochastic process. Based on the proposed model, we derive the time-variant bound of untrustworthy probability, which provides stochastic trust guarantee. On one hand, the time-variant trust level of each node can be measured by our model. Meanwhile, by tolerating nodes with relatively poor performance, our model can effectively improve the node resource utilization rate. Numerical simulations are conducted to verify the accuracy and consistency of the analytical bounds on distinguishing misbehaved nodes from normal ones. Moreover, simulation results on social network dataset show the tradeoff between trust level and resource utilization rate, and verify that the successful transmission rate can be improved by our model.

• Journal of Navigation and Port Research
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• v.32 no.9
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• pp.723-727
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• 2008

Sensing performances of evanescent field absorption (EFA) hetero-core fiber sensor has been presented based on EFA by changing the length and the core diameter of the single mode fiber. Experimental results have demonstrated a good feature in their relationship between the length and the core diameter of the single mode fiber. The sensor consists of 2 fiber optics which have the same cladding diameter of $125{\mu}m$ However one fiber optic used is single mode and has varying core diameter ranging from 3.3 to $5.6{\mu}m$. The other fiber is multimode type and has a thicker fixed core diameter of $62.5{\mu}m$. The 2 fiber optics are thermally spliced together. Experiments conducted to measure the resonance wavelength were carried out over a range of refractive index, to find the optimum sensing length Experiments show that core diameter of the single mode fiber and sensing length offects the linearity and sensitivity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.80-82
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• 2016

In this letter, we evaluate the performances of both GOOK and GFSK de/modulation techniques which are candidates for ULP communications in WPAN systems. For the performance evaluation, we define the system model for each of GOOK and GFSK de/modulations and perform computer simulations based on the proposed models. From the computer simulations, we show that GOOK de/modulation technique has 15 dB out-of-band emission gain and is robust over frequency offsets in terms of BER compared to GFSK de/modulation technique.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.05a
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• pp.873-875
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• 2014

In this paper, we propose the access control system based bluetooth using the MAC address of the smart device. Access control system that propose compares the smart device MAC address entry and exit and MAC address that is registered with the server. Depending on whether the match was compared, access control is performed. Result of the experiment, control of door is possible only by bluetooth pairing of the bluetooth module and smart device. Therefore, it does not require access to another tool.In addition, Action for access approval is omitted. Therefore, the access authorization procedure is simplified compared to existing access control systems, it is possible to improve the convenience.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.379-380
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• 2009

히스토그램 스트레칭이나 히스토그램 균등화 등 기존 대비 향상 기법들과 히스토그램 균등화 기반의 수많은 방법들은 저대비에 소수의 화소들이 넓게 퍼져 있는 영상에 대해서 만족할만한 결과를 내지 못한다. 따라서 본 논문은 군집화 방법을 이용한 새로운 영상 대비 향상 기법을 제안한다. 히스토그램의 군집수는 원영상의 히스토그램을 분석하여 얻을 수 있다. 히스토그램 성분들을 K-means 알고리즘을 이용하여 군집화한다. 그리고 히스토그램 군집 범위와 군집의 화소수 비율을 비교하여 히스토그램 스트레칭과 히스토그램 균등화를 선택적으로 적용한다. 실험 결과로부터 제안한 방법이 기존의 대비 향상 기법들보다 더 효과적임을 확인할 수 있었다.

• ETRI Journal
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• v.37 no.6
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• pp.1135-1142
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• 2015

Multilayered ZnO-$SnO_2$ heterostructure thin films consisting of ZnO and $SnO_2$ layers are produced by alternating the pulsed laser ablation of ZnO and $SnO_2$ targets, and their structural and field-effect electronic transport properties are investigated as a function of the thickness of the ZnO and $SnO_2$ layers. The performance parameters of amorphous multilayered ZnO-$SnO_2$ heterostructure thin-film transistors (TFTs) are highly dependent on the thickness of the ZnO and $SnO_2$ layers. A highest electron mobility of $43cm^2/V{\cdot}s$, a low subthreshold swing of a 0.22 V/dec, a threshold voltage of 1 V, and a high drain current on-to-off ratio of $10^{10}$ are obtained for the amorphous multilayered ZnO(1.5nm)-$SnO_2$(1.5 nm) heterostructure TFTs, which is adequate for the operation of next-generation microelectronic devices. These results are presumed to be due to the unique electronic structure of amorphous multilayered ZnO-$SnO_2$ heterostructure film consisting of ZnO, $SnO_2$, and ZnO-$SnO_2$ interface layers.

• Journal of Communications and Networks
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• v.15 no.5
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• pp.457-463
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• 2013

In recent days, cooperative diversity and communication security become important research issues for wireless communications. In this paper, to achieve low probability of interception (LPI) and high throughput in the cooperative single-carrier frequency division multiple access (SC-FDMA) system, a new physical layer transmission scheme is proposed, where a new encryption algorithm is applied and adaptive modulation is further considered based on channel state information (CSI). By doing so, neither relay node nor eavesdropper can intercept the information signals transmitted from user terminal (UT). Simulation results show above new physical layer transmission scheme brings in high transmission safety and secrecy rate. Furthermore, by applying adaptive modulation and coding (AMC) technique according to CSI, transmission throughput can be increased significantly. Additionally, low peak-to-average power ratio (PAPR) characteristic can still be remained due to the uniform distribution of random coefficients used for encryption algorithm.

• The Journal of the Korea institute of electronic communication sciences
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• v.1 no.1
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• pp.87-93
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• 2006

This is paper, with the development of computer and network communications technology, the technology of digital computer and modern communications has integrated into the field of intelligent home appliances, making them intelligentize with the function of a network information terminal. The paper introduces the Bluetooth SIG(Special Interesting Group) and the development of the standard of the Bluetooth. Researches the application model and the practical application of the Bluetooth technology, and the component elements of the Bluetooth. Finally deals with the outlook for the development of the Bluetooth technology.

• The Journal of the Korea Contents Association
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• v.4 no.4
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• pp.71-78
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• 2004

Dedicated Short Range Communications(DSRC) as a prominent communications candidate for Intelligent Transportation Systems(ITS) have been developed to support ITS applications such as value-added information service, e-commerce, electronic toll payment, etc. These various applications associated with electronic payment through unsecure communication channel of DSRC suffer from security threats. To ensure secure payment, we have adopted appropriate cryptographic mechanisms including encipherment, authentication exchange and digital signature. The cryptographic mechanisms require to use cryptographic keys established between two communication entities. In this paper, we propose a secure electronic payment system which is designed to have some functions for strong authentication, encryption, key agreement, etc. Especially, we adopt domestic developed cryptographic algorithms such as EC-KCDSA and SEED for digital signature and block cipher, respectively. We can show those mechanisms are appropriate for the secure electronic payment system for ITS services under the DSRC wireless environment in aspects of constrained computational resource use and processing speed.

• ETRI Journal
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• v.35 no.3
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• pp.406-413
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• 2013

In this paper, an orthogonal frequency division multiple access (OFDMA)-based minimum end-to-end delay (MED) distributed routing scheme for mobile backhaul wireless mesh networks is proposed. The proposed scheme selects routing paths based on OFDMA subcarrier synchronization control, subcarrier availability, and delay. In the proposed scheme, OFDMA is used to transmit frames between mesh routers using type-I hybrid automatic repeat request over multipath Rayleigh fading channels. Compared with other distributed routing algorithms, such as most forward within radius R, farthest neighbor routing, nearest neighbor routing, and nearest with forwarding progress, simulation results show that the proposed MED routing can reduce end-to-end delay and support highly reliable routing using only local information of neighbor nodes.