• 한국인터넷방송통신학회논문지
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• 제9권4호
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• pp.87-97
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• 2009

A Mobile Ad hoc Network (MANET) is characterized by multi-hop wireless connectivity, frequently changing network topology with mobile nodes and the efficiency of the dynamic routing protocol plays an important role in the performance of the network. In this paper, the performance of five routing protocols for MANET is compared by using OPNET modeler: AODV, DSR, GRP, OLSR and TORA. The various performance metrics are examined, such as packet delivery ratio, end-to-end delay and routing overhead with varying data traffic, number of nodes and mobility. In our simulation results, OLSR shows the best performance in terms of data delivery ratio in static networks, while AODV has the best performance in mobile networks with moderate data traffic. When comparing proactive protocols (OLSR, GRP) and reactive protocols (AODV, DSR) with varying data traffic in the static networks, proactive protocols consistently presents almost constant overhead while the reactive protocols show a sharp increase to some extent. When comparing each of proactive protocols in static and mobile networks, OLSR is better than GRP in the delivery ratio while overhead is more. As for reactive protocols, DSR outperforms AODV under the moderate data traffic in static networks because it exploits caching aggressively and maintains multiple routes per destination. However, this advantage turns into disadvantage in high mobility networks since the chance of the cached routes becoming stale increases.

• International journal of advanced smart convergence
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• 제8권4호
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• pp.179-187
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• 2019

Vehicular density is usually low in a highway environment. Consequently, connectivity of the vehicular ad hoc networks (VANETs) might be poor. We are investigating the problem of deploying the approximation optimal roadside units (RSUs) on the highway covered by VANETs, which employs VANETs to provide excellent connectivity. The goal is to estimate the minimal number of deployed RSUs to guarantee the connectivity probability of the VANET within a given threshold considering that RSUs are to be allocated equidistantly. We apply an approximation algorithm to distribute RSUs locations in the VANETs. Thereafter, performance of the proposed scheme is evaluated by calculating the connectivity probability of the VANET. The simulation results show that there is the threshold value M of implemented RSUs corresponding to each vehicular network with N vehicles. The connectivity probability increases slowly with the number of RSUs getting larger.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2009년도 춘계학술발표대회
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• pp.1159-1162
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• 2009

브로드캐스팅 프로토콜은 무선 애드 혹 네트워크에서 컨트롤 메시지를 전체 노드에 전송하기 위한 목적으로 널리 사용된다. 전통적인 브로드캐스팅 프로토콜은 모든 노드가 처음 받은 메시지를 재전송 하기 때문에 극심한 중복전송과 충돌문제가 발생한다. 이러한 문제를 해결하기 위해 최근에 효율적으로 재전송노드를 줄이기 위한 브로드캐스팅 기법들이 제안되었지만 여전히 다수의 불필요한 재전송이 발생한다. 제안 기법은 1-홉 이웃노드의 위치정보를 이용하여 전파반경에 내접하는 정삼각형의 꼭짓점을 구하고 각 꼭짓점에 가장 가까운 이웃노드를 재전송노드로 선택한다. 우리는 먼저 재전송 노드를 최소화하기 위한 이상적인 모델을 제시하고 이상적인 모델에 근접하기 위한 방법을 설명한다. 시뮬레이션 결과를 통해 제안 기법이 기존의 효율적인 브로드캐스팅 프로토콜보다 성능이 우수하며 재전송 노드수가 lower bound에 근접하는 것을 보여준다.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2008년도 춘계학술발표대회
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• pp.706-709
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• 2008

With the increasing popularity of P2P file sharing and advancement of mobile technologies, mobile P2P has revealed its attraction. Anonymity has become an increasing requirement in mobile networks. To reduce receiving garbage files, file validation and filtering are other requirements in the mobile P2P environment. If there are effective file filtering and validation mechanism, nodes' battery duration will be saved. In this paper, we do an analysis of security and anonymity in P2P file sharing and exchange system in mobile ad hoc environment, and propose a new efficient anonymous protocol, which can provide anonymity by broadcasting with a probabilistic algorithm and hiding real hop count information, the file validation by the file's special hash value and file filtering mechanism through the collaboration of middle nodes.

• 한국인터넷방송통신학회논문지
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• 제18권1호
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• pp.47-58
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• 2018

이기종 셀룰러 네트워크 (HCN)는 미래 5 세대 (5 세대) 무선 네트워크의 핵심 기술로서 가장 중요하다. 고려된 이기종 네트워크는 펨토셀 기지국 (BS)으로 중첩 된 임의로 매크로 셀 기지국 (MBS)으로 구성된다. 확률 적 기하학은 무선 ad hoc, 센서 네트워크 및 다중 계층 셀룰러 네트워크와 같은 무작위 토폴로지를 사용하여 네트워크를 모델링, 분석 및 설계하는 매우 강력한 도구이다. HCN은 미래의 5G 무선 네트워크를위한 기술 중 하나에 중점을 두어 다른 네트워크에 속한 다양한 BS를 배치함으로써 에너지 효율적으로 설계 될 수 있다. 본 논문에서는 능동 / 슬립 모드를 도입하여 셀룰러 네트워크의 BS가 효율적으로 전력을 소비 할 수 있도록 해주는 시스템을 끄고 켜는 방법을 제안한다. 이 모드는 MBS 및 FBS의 간섭 및 전력 소모를 개별적으로 줄일 수있다. 잘 셀룰러 네트워크의 에너지 효율성을 향상시킬 수 있다. 펨토 기지국 BS 밀도에 따라 Karush Kuhn Tucker (KKT) 조건을 해결할 수있는 처리량 정지 제약 조건 하에서 에너지 효율을 최대화하기위한 최적화 문제뿐만 아니라 MBS 및 FBS에 대한 전력 소모 최소화를 공식화한다. 우리는 또한 커버리지 홀을 피하기 위해 코디네이트 된 멀티 포인트 (CoMP)가 있거나없는 HCN 시나리오에서 커버리지 확률과 에너지 효율의 식을 제안하고 기종 알고리즘과 비교한다.

• 센서학회지
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• 제17권3호
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• pp.168-177
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• 2008

An indoor environmental monitoring system using IEEE 802.15.4 based wireless sensor network is proposed to monitor the amount of pollutant entering to the room from outside and also the amount of pollutant that is generated in indoor by the building materials itself or human activities. Small-size, low-power wireless sensor node and low power electrochemical sensor board is designed to measure the condition of indoor environment in buildings such as home, offices, commercial premises and schools. In this paper, two query models, the broadcasting query protocol and flooding query protocol, were designed and programmed as a query-based routing protocol in wireless sensor network for an environment monitoring system. The flooding query routing protocol in environment monitoring is very effective as a power saving routing protocol and reliable data transmission between sensor nodes.

• 전기전자학회논문지
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• 제11권4호
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• pp.322-330
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• 2007

Recent advances in wireless networks and low-cost, low-power design have led to active research in large-scale networks of small, wireless, low power sensors and actuators, In large-scale networks, lots of timing-synchronization protocols already exist (such as NTP, GPS), In ad-hoc networks, especially wireless sensor networks, it is hard to synchronize all nodes in networks because it has no infrastructure. In addition, sensor nodes have low-power CPU (it cannot perform the complex computation), low batteries, and even they have to have active and inactive section by periods. Therefore, new approach to time synchronization is needed for wireless sensor networks, In this paper, I propose Energy-Efficient Time Synchronization (EETS) protocol providing network-wide time synchronization in wireless sensor networks, The algorithm is organized two phase, In first phase, I make a hierarchical tree with sensor nodes by broadcasting "Level Discovery" packet. In second phase, I synchronize them by exchanging time stamp packets, And I also consider send time, access time and propagation time. I have shown the performance of EETS comparing Timing-sync Protocol for Sensor Networks (TPSN) and Reference Broadcast Synchronization (RBS) about energy efficiency and time synchronization accuracy using NESLsim.

• International Journal of Internet, Broadcasting and Communication
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• 제8권2호
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• pp.49-54
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• 2016

Data delivery is very challenging in VANETs because of its unique characteristics, such as fast topology change, frequent disruptions, and rare contact opportunities. This paper tries to explore the scope of 3G-assisted data delivery in a VANET within a budget constraint of 3G traffic. It is started from the simple S_Random (Srand) and finally reached the 3GSDD, i.e., the proposed algorithm. The performance evaluation of different algorithms is done through the two metrics delivery ratio and average delay. A third function utility is created to reflect the above two metrics and is used to find out the best algorithm. A packet can either be delivered via multihop transmissions in the VANET or via 3G. The main challenge is to decide which set of packets should be selected for 3G transmissions and when to deliver them via 3G. The aim is to select and send those packets through 3G that are most sensitive and requiring immediate attention. Through appropriate communication mechanism, these sensitive information are delivered via VANET for 3G transmissions. This way the sensitive information which could not be transmitted through normal VANET will certainly find its destination through 3G transmission unconditionally and with top priority. The delivery ratio of the packets can also be maximized by this system.

• Journal of Communications and Networks
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• 제11권6호
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• pp.574-588
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• 2009

Although much research has been conducted in the area of authentication in wireless networks, vehicular ad-hoc networks (VANETs) pose unique challenges, such as real-time constraints, processing limitations, memory constraints, frequently changing senders, requirements for interoperability with existing standards, extensibility and flexibility for future requirements, etc. No currently proposed technique addresses all of the requirements for message and entity authentication in VANETs. After analyzing the requirements for viable VANET message authentication, we propose a modified version of TESLA, TESLA++, which provides the same computationally efficient broadcast authentication as TESLA with reduced memory requirements. To address the range of needs within VANETs we propose a new hybrid authentication mechanism, VANET authentication using signatures and TESLA++ (VAST), that combines the advantages of ECDSA signatures and TESLA++. Elliptic curve digital signature algorithm (ECDSA) signatures provide fast authentication and non-repudiation, but are computationally expensive. TESLA++ prevents memory and computation-based denial of service attacks. We analyze the security of our mechanism and simulate VAST in realistic highway conditions under varying network and vehicular traffic scenarios. Simulation results show that VAST outperforms either signatures or TESLA on its own. Even under heavy loads VAST is able to authenticate 100% of the received messages within 107ms. VANETs use certificates to achieve entity authentication (i.e., validate senders). To reduce certificate bandwidth usage, we use Hu et al.'s strategy of broadcasting certificates at fixed intervals, independent of the arrival of new entities. We propose a new certificate verification strategy that prevents denial of service attacks while requiring zero additional sender overhead. Our analysis shows that these solutions introduce a small delay, but still allow drivers in a worst case scenario over 3 seconds to respond to a dangerous situation.

• 한국인터넷방송통신학회논문지
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• 제11권6호
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• pp.15-21
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• 2011

애드혹 네트워크에서는 협동 다이버시티를 적용하여 네트워크의 전력소모를 줄이고, 통달거리의 확장 및 시스템의 성능을 향상시키고 있다. 그러나 가장 큰 신호 대 잡음비(SNR, Signal-to-noise ratio)을 갖는 릴레이를 선택하여 송신하는 선택 릴레이 협동 다이버시티 방식은 느린 페이딩 채널에서 특정 릴레이가 계속 송신하므로 네트워크의 생존시간을 줄이게 된다. 그러므로 최근에 네트워크의 생존 시간을 늘이기 위하여 균일전력 릴레이 선택방식이 연구되었다. 본 논문에서는 소스-릴레이 및 릴레이-목적지간의 수신 신호 대 잡음비가 일정수준 이상이 되는 릴레이를 선택하여 송신할 수 있는 하는 이중 기회전송 협동 다이버시티(DOT, Double opportunistic cooperative diversity) 시스템에 균일전력 릴레이 선택방식을 적용하고 시스템의 성능을 유도하였다. 유도한 결과는 선택결합(SC, Selection combining) 방식과 최대비 합성결합(MRC, Maximal ratio combining) 방식과 비교하였다. 균일전력 릴레이 방식을 사용하였을 때 다른 방식에 비해서 시스템의 성능저하가 있었는데, 이는 네트워크의 생존 시간을 늘이기 위해서 릴레이에 균일한 송신기회를 주었기 때문으로 해석되었다.