• 한국인터넷방송통신학회논문지
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• 제16권1호
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• pp.61-67
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• 2016

기회전송 증가 릴레이 시스템은 무선채널의 페이딩을 효과적으로 극복하고 무선 자원을 효율적으로 사용할 수 있는 장점을 갖는다. 그러나 지금까지 기회전송 증가 릴레이 시스템 연구에서는 릴레이의 위치가 공간적으로 고정되어 있는 것을 가정하였다. 일반적으로 모바일 환경에서는 사용자 터미널이 릴레이로 사용되는데, 사용자 터미널은 계속해서 움직이기 때문에 고정된 릴레이를 가정하는 것은 현실적이지 않다. 따라서 본 논문은 공간적으로 랜덤하게 분포된 사용자 터미널의 위치를 포아송 포인트 프로세스 (Poisson point process)로 모델링하고, 기회전송 증가 릴레이 시스템의 성능을 유도하였다. 유도 결과 릴레이가 랜덤하게 분포된 경우에도 릴레이가 고정된 경우와 마찬가지로 시스템의 성능이 향상되었으며, 릴레이의 밀도와 송수신 각도가 시스템의 성능에 영향을 주는 것을 알 수 있었다. 또한 최대비 결합과 선택결합 수신방법에 따른 시스템의 성능을 비교하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.574-578
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• 2004

In this paper, a nonlinear feedback system is analyzed for a surface micromachined resonant accelerometer. For this, a brief illustration of the plant dynamics is given. In the analysis, the periodic signal in the nonlinear feedback loop is obtained by the limit cycle point, which is best approximated via the describing function method. Considering the characteristic feature of plant dynamics, a simple phase shifted relay with finite slope is designed for the nonlinearity implementation. With a describing function for random plus sinusoidal input, we analyzed the effect of a white Gaussian noise on oscillation frequency. Finally, simulation and experimental result is given.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.850-852
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• 1996

High impedance fault (HIF) is defined as fault that general overcurrent relay can't detect or interrupt, Especially when HIF occur under 15 kV, energized high voltage conductor results in fire hazard, equipment damage or personal threat. Because most HIF occur arc, HIF detection using arc is to increase. Numerical arc model can be applied in an electromagnetic transients program (EMTP) to reproduce the dynamic and random characteristic of arcs for any insulator arrangement, current and system voltage. It allows the representation of any network configuration to be investigated, so the digital simulation of arc faults through air can be substitute for demanding power arc test.

• Journal of Communications and Networks
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• 제11권6호
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• pp.589-598
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• 2009

In wireless sensor networks, a node that reports information gathered from adjacent assets should relay packets appropriately so that its location context is kept private, and thereby helping ensure the security of the assets that are being monitored. Unfortunately, existing routing methods that counter the local eavesdropping-based tracing deal with a single asset, and most of them suffer from the packet-delivery latency as they prefer to take a separate path of many hops for each packet being sent. In this paper, we propose a routing method, greedy perimeter stateless routing-based source-location privacy with crew size w (GSLP-w), that enhances location privacy of the packet-originating node (i.e., active source) in the presence of multiple assets. GSLP-w is a hybrid method, in which the next-hop node is chosen in one of four modes, namely greedy, random, perimeter, and retreat modes. Random forwarding brings the path diversity, while greedy forwarding refrains from taking an excessively long path and leads to convergence to the destination. Perimeter routing makes detours that avoid the nodes near assets so that they cannot be located by an adversary tracing up the route path. We study the performance of GSLP-w with respect to crew size w (the number of packets being sent per path) and the number of sources. GSLP-w is compared with phantom routing-single path (PR-SP), which is a notable routing method for source-location privacy and our simulation results show that improvements from the point of the ratio of safety period and delivery latency become significant as the number of source nodes increases.

• Journal of Communications and Networks
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• 제15권5호
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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.

• Current Optics and Photonics
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• 제5권2호
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• pp.114-120
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• 2021

Free-space optical (FSO) communication is considered to be a potential solution to congestion in the radio-frequency spectrum and last-mile-access bottleneck issues in future cellular communication networks, such as 5G and beyond. However, FSO link performance may degrade significantly due to irradiance fluctuations and random temporal fluctuations from atmospheric turbulence. Therefore, in this work the main objective is to reduce the effect of the atmospheric turbulence by considering a multihop FSO communication system with amplify-and-forward relaying supported by a radio-frequency (RF) link, which form a hybrid FSO/RF communication system. The FSO link is assumed to follow the gamma-gamma fading model, which represents strong turbulence. Also, the RF link is modeled by a Rayleigh distribution. The performance of the considered system, in terms of the outage probability and average bit-error rate (BER), is investigated and analyzed under various weather conditions and pointing errors. Furthermore, the effect of the number of employed relay nodes on the performance of the system is investigated. The results indicate that the considered system reduces outage probability and average BER significantly, especially for low channel quality. Finally, the closed-form expressions derived in this work are compared to the results of Monte Carlo simulations, for verification.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권6호
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• pp.2838-2858
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• 2019

Traditional channel models for vehicle-to-vehicle (V2V) communication usually assume fixed velocity in static scattering environment. In the realistic scenarios, however, time-variant velocity for V2V results in non-stationary statistical properties of wireless channels. Dynamic scatterers with random velocities and directions have been always utilized to depict the non-stationary statistical properties of the channel. In this paper, a non-stationary geometry-based cooperative scattering channel model is proposed for multiple-input multiple-output (MIMO) V2V communication systems, where a birth-death process is used to capture the appearance and disappearance dynamic properties of moving scatterers that reflect the time-variant time correlation and Doppler spectrum characteristics. Moreover, our model has more straight and concise to study the impact of the vehicular traffic density on channel characteristics and thus avoid complicated procedure in deriving the analytical expressions of the channel parameters and functions. The numerical results validate our analysis and demonstrate that setting important parameters of our model can appropriately build up more purposeful measurement campaigns in the future.

• 한국통신학회논문지
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• 제34권6A호
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• pp.506-514
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• 2009

센서 네트워크를 위한 MAC 프로토콜들은 전력 소모를 최소화하기 위해 낮은 듀티 사이클(Duty Cycle)을 사용한다. 그 중에서 RMAC [4]의 경우 Pioneer(PION) 프레임을 이용하여 한 주기 내에 여러 홉을 전송한다. 본 논문에서는 HE-MAC(Hop-Extended MAC)이라는 홉 연장 프로토콜을 제안한다. HE-MAC의 데이터 전송은 기존 RMAC과는 달리 한 주기 내에 전달될 수 있는 최대 홉 수 정보가 포함된 Explorer(EXP)를 이용하여 이루어진다. EXP의 정보와 Ready-to-Receive(RTR) 상태를 이용하여 RMAC에 비해 2홉을 늘림으로써 평균 전송 지연 시간을 감소시킨다. 또한, 적응적 슬립을 통하여 불필요한 전력 소모를 최소화할 뿐만 아니라 RMAC에서 나타나는 잦은 트래픽(Traffic)으로 인한 패킷 역전 문제를 해결한다. HE-MAC의 패킷 전송 지연시간을 수학적으로 분석하였으며, ns-2를 이용한 모의실험을 통해 성능평가를 하였다. 300개의 노드가 배치된 랜덤 토폴로지에서 HE-MAC은 RMAC에 비해 전력 소모량과 평균 전승 지연 시간을 14%, 20%만큼 감소시킨다.

• Animal cells and systems
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• 제9권3호
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• pp.139-144
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• 2005

The attractant (orange light) or repellent (white light) signal is transmitted from SRI (Sensory Rhodopsin I) via protein-protein interaction with its transducer Htrl (Halobacterial Transducer for Sensory Rhodopsin I) which in turn controls a cytoplasmic phospho-transfer pathway that modulates flagella motor switching in Halobacterium salinarum. Some mutations in both SRI and Htrl showed an unusual mutant phenotype called inverted signaling, in which the cell produces a repellent response to normally attractant light. Twelve mutations at the Glutamate 56 (E56) position in the second transmembrane helix of Htrl were introduced by site-specific random mutagenesis. Almost all E56 mutants showed orange-light inverted responses in pH and temperature-dependent manners except E56D and E56Y. Except for these two mutants, all mutants accelerated the $S_{373}$ decay compared to wild-type at $18^{\circ}C$. This supported that there is an interaction between SRI and the second transmembrane of Htrl. Also a structural model of Htrl based on the Tar crystal structure and the secondary structure prediction program proposed the E56 residue to be in the middle of the proton channel. The most important observation is that the E56 mutant provides the evidence that this residue is very sensitive for signal relay, which can be explained by the open and closed conformations of the channel (A and R conformations) in SRI, as was postulated by the unified conformational shuttling model for transport and signaling.