• 한국통신학회논문지
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• 제33권12B호
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• pp.1050-1057
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• 2008

무선 메쉬 네트워크 (Wireless Mesh Network, WMN)는 최근 들어 무선 접속 네트워크에서 높은 네트워크 용량을 지원하기 위해 중요한 이슈로 대두되고 있다. WMN에서 주로 사용하는 네트워크 인터페이스 기술인 IEEE 802.11 표준에서는 IEEE 802.11b/g 또는 IEEE 802.11a와 같은 스펙에 따라 3개 또는 12개의 멀티채널을 지원한다. 하지만, WMN에서 채널 할당 알고리즘을 디자인 할 때 두 가지 중요한 문제, 즉 채널 의존성 문제와 채널 스캐닝 딜레이를 고려해야 한다. 채널 의존성 문제는 인터페이스의 동적인 채널 변경이 노드 연결성을 유지하기 위해 다른 인터페이스의 채널 변경을 일으키는 문제이다. 또한, 채널 스캐닝 밀레이는 인터페이스가 채널을 변경할 때마다 발생하며 성능에 영향을 미친다. 따라서, 본 논문에서는 멀티채널 WMN환경에서 이러한 문제점들을 위해 메쉬 게이트웨이로부터의 거리에 기반한 채널 할당 (Distance-Based Channel Assignment, DB-CA)을 제안한다. DB-CA에서는 서로 다른 채널을 사용하는 노드들이 통신을 하기 위해 채널 스캐닝을 수행하지 않고 오직 채널 스위칭만 수행하며, WMN의 메쉬 게이트웨이에 가까운 노드들이 사용하는 채널에 미칠 수 있는 간섭을 최소화 한다. 실험 결과를 통해 WMN에서 DB-CA가 기존 채널 할당 방식에 비해 향상된 성능을 나타냄을 확인하였다.

• 한국인터넷방송통신학회논문지
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• 제15권2호
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• pp.77-85
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• 2015

본 논문은 LTE-Advanced 환경에서의 eMBMS(evolved Multimedia Broadcast/Multicast Services) 기법을 위한 채널변경 대기시간 최소화 방안과 그 성능을 평가해 보고자 한다. 기존의 IGMP(Internet Group Management Protocol)을 이용한 MBMS 구성은 BM-SC(Broadcast Multicast Service Center)에서 eNB(evolevd Node B)까지는 멀티캐스트로, eNB에서 UE(User Equipment)까지는 브로드캐스트로 데이터를 전송한다. 때문에 채널 변경 시 IGMP Join Report를 BM-SC까지 전송해야 하며, 이후 eNB로부터 콘텐츠가 재송신되길 기다려야 한다. 이를 위해 가입자 채널 우선순위기법을 이용하여, UE가 즐겨 찾는 채널을 미리 브로드캐스트 함으로써 채널변경에 따른 대기시간을 최소화시킬 수 있다.

• 전자공학회논문지SC
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• 제47권6호
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• pp.51-57
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• 2010

본 논문에서는 다중 안테나 시스템에서의 전송률과 안정성 측면에서의 최적의 성능을 발휘하기 위해 채널 추정오차에 강인한 적응형 다중입출력(MIMO) 스위칭 알고리즘을 제안한다. 제안된 논문은 무선 채널의 추정 오차에 대한 강인성을 확보하기 위하여 가변형 패킷오류 예측 방식에 기반을 두었으며, 기존의 MIMO 스위칭 방식에 비해 스펙트럼 효율이 약 8% 이상 증대 됨을 확인할 수 있었다.

• 전자공학회논문지D
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• 제34D권8호
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• pp.52-61
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• 1997

In this paper it is proposed a new architecture for N*N optical packet switching system. It consists of active-splitter type pf packet router, travelling type of optical buffer memory for packet contention resoltuion and an electronic controller. the BER performance of the proposed switching system is analyzed with respect to channel crosstalks and amplified spontaneous emissio noise form switching elements and optical amplifiers respectively. Operational validity of the proposed switching system is also experimentally proved by realizing 2*2 optical packet switching system.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2009년도 추계학술발표대회
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• pp.679-680
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• 2009

Radio jamming attack is the most effective and easiest Denial-of-Service (DOS) attack in wireless network. In this paper, we proposed a multi-channel MAC protocol to mitigate the jamming attacks by using cognitive radio. The Cognitive Radio (CR) technology supports real-time spectrum sensing and fast channel switching. By using CR technologies, the legitimate nodes can perform periodic spectrum sensing to identify jamming free channels and when the jamming attack is detected, it can switch to un-jammed channel with minimum channel switching delay. In our proposed protocol, these two CR technologies are exploited for thwarting the jamming attacks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권9호
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• pp.4223-4239
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• 2016

In this paper, we consider an amplify-and-forward (AF) full-duplex relay network (FDRN) using simultaneous wireless information and power transfer, where a battery-free relay node harvests energy from the received radio frequency (RF) signals from a source node and uses the harvested energy to forward the source information to destination node. The time-switching relaying (TSR) protocol is studied, with the assumption that the channel state information (CSI) at the relay node is imperfect. We deliver a rigorous analysis of the outage probability of the proposed system. Based on the outage probability expressions, the optimal time switching factor are obtained via the numerical search method. The simulation and numerical results provide practical insights into the effect of various system parameters, such as the time switching factor, the noise power, the energy harvesting efficiency, and the channel estimation error on the performance of this network. It is also observed that for the imperfect CSI case, the proposed scheme still can provide acceptable outage performance given that the channel estimation error is bounded in a permissible interval.

• 전자공학회논문지S
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• 제34S권4호
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• pp.1-11
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• 1997

In this paper, modeling of the communication channel occupancy characteristics at the base station in the wide area radio trunking syste has been performed. Using the results, mathematical analysis for the switching capacity at the network switch has also been done. Specificatlly, we propose a G/M/m queueing model for the single service area modeling, and analyze changes in call blockingprobabilities accoridng to changes in the burstness characteristics of group paging calls. As a result, we have observe dthat the channel occupancy variations become larger as the burstness characteristics become more apparent, to make the call blocking probability higher. Next, based on the single service area analysis, we have anayzed mathematically the average switching capacity required to serve mobile subscribers for a wide area radio trunking sytem, where multiple switching port assignments are required when the people in the same group are distributed over several base stations. Accordingly, we have observed that the average and the variance of switching channel occupancy are closely related to the mobility characteristics of subscribers, and that we need a netowrk switch having bigger capacity as subscribers show wider distribution. Especially, with the call dropping probability within 0.2%, a switch having about 5 to 6 times bigger can be required, compared with the one when the mobility of subscribers is mostly restricte dto a single service area.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권12호
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• pp.6098-6122
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• 2018

Cache-based side-channel attacks have achieved more attention along with the development of cloud computing technologies. However, current host-based mitigation methods either provide bad compatibility with current cloud infrastructure, or turn out too application-specific. Besides, they are defending blindly without any knowledge of on-going attacks. In this work, we present CacheSCDefender, a framework that provides a (Virtual Machine Monitor) VMM-based comprehensive defense framework against all levels of cache attacks. In designing CacheSCDefender, we make three key contributions: (1) an attack-aware framework combining our novel dynamic remapping and traditional cache cleansing, which provides a comprehensive defense against all three cases of cache attacks that we identify in this paper; (2) a new defense method called dynamic remapping which is a developed version of random permutation and is able to deal with two cases of cache attacks; (3) formalization and quantification of security improvement and performance overhead of our defense, which can be applicable to other defense methods. We show that CacheSCDefender is practical for deployment in normal virtualized environment, while providing favorable security guarantee for virtual machines.

• Journal of Communications and Networks
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• 제11권3호
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• pp.279-286
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• 2009

This paper proposes an adaptive mode switching algorithm between two strategies in multiple antenna cellular networks:A single-user mode and a multi-user mode for the broadcast channel. If full channel state information is available at the base station, it is known that a multi user transmission strategy would outperform all single-user transmission strategies. In the absence of full side information, it is unclear what the capacity achieving method is, and thus there are few criteria to decide which of the myriad possible methods performs best given a system configuration. We compare a single user transmission and a multi user transmission with linear receivers in this paper where the transmitter and the receivers have multiple antennas, and find that neither strategy dom inates the other. There is instead a transition point between the two strategies. Then, the mode switching point is determined both ana lytically and numerically for a multiple antenna cellular downlink with correlation between transmit antennas.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권7호
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• pp.3433-3446
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• 2019

Aiming at the high complexity of traditional single-channel demodulation algorithm for PCMA signals, a new demodulation algorithm based on neural network is proposed to reduce the complexity of demodulation in the system of non-cooperative PCMA communication. The demodulation network is trained in this paper, which combines the preprocessing module and decision module. Firstly, the preprocessing module is used to estimate the initial parameters, and the auxiliary signals are obtained by using the information of frequency offset estimation. Then, the time-frequency characteristic data of auxiliary signals are obtained, which is taken as the input data of the neural network to be trained. Finally, the decision module is used to output the demodulated bit sequence. Compared with traditional single-channel demodulation algorithms, the proposed algorithm does not need to go through all the possible values of transmit symbol pairs, which greatly reduces the complexity of demodulation. The simulation results show that the trained neural network can greatly extract the time-frequency characteristics of PCMA signals. The performance of the proposed algorithm is similar to that of PSP algorithm, but the complexity of demodulation can be greatly reduced through the proposed algorithm.