• 한국산업정보학회논문지
• /
• 제19권2호
• /
• pp.1-13
• /
• 2014

In IEEE 802.11p/1609-based vehicular networks, vehicles are allowed to exchange safety and control messages only within time periods, called control channel (CCH) interval, which are scheduled periodically. Currently, the length of the CCH interval is set to the fixed value (i.e. 50ms). However, the fixed-length intervals cannot be effective for dynamically changing traffic load. Hence, some protocols have been recently proposed to support variable-length CCH intervals in order to improve channel utilization. In existing protocols, the CCH interval is subdivided into safety and non-safety intervals, and the length of each interval is dynamically adjusted to accommodate the estimated traffic load. However, they do not consider the presence of hidden nodes. Consequently, messages transmitted in each interval are likely to overlap with simultaneous transmissions (i.e. interference) from hidden nodes. Particularly, life-critical safety messages which are exchanged within the safety interval can be unreliably delivered due to such interference, which deteriorates QoS of safety applications such as cooperative collision warning. In this paper, we therefore propose a new interference-aware Dynamic Safety Interval (DSI) protocol. DSI calculates the number of vehicles sharing the channel with the consideration of hidden nodes. The safety interval is derived based on the measured number of vehicles. From simulation study using the ns-2, we verified that DSI outperforms the existing protocols in terms of various metrics such as broadcast delivery ration, collision probability and safety message delay.

• Journal of Information Processing Systems
• /
• 제13권5호
• /
• pp.1229-1242
• /
• 2017

In this paper, an interference aware distributed multi-channel MAC (IDMMAC) protocol is proposed for wireless sensor and actor networks (WSANs). The WSAN consists of a huge number of sensors and ample amount of actors. Hence, in the IDMMAC protocol a lightweight channel selection mechanism is proposed to enhance the sensor's lifetime. The IDMMAC protocol divides the beacon interval into two phases (i.e., the ad-hoc traffic indication message (ATIM) window phase and data transmission phase). When a sensor wants to transmit event information to the actor, it negotiates the maximum packet reception ratio (PRR) and the capacity channel in the ATIM window with its 1-hop sensors. The channel negotiation takes place via a control channel. To improve the packet delivery ratio of the IDMMAC protocol, each actor selects a backup cluster head (BCH) from its cluster members. The BCH is elected based on its residual energy and node degree. The BCH selection phase takes place whenever an actor wants to perform actions in the event area or it leaves the cluster to help a neighbor actor. Furthermore, an interference and throughput aware multi-channel MAC protocol is also proposed for actor-actor coordination. An actor selects a minimum interference and maximum throughput channel among the available channels to communicate with the destination actor. The performance of the proposed IDMMAC protocol is analyzed using standard network parameters, such as packet delivery ratio, end-to-end delay, and energy dissipation, in the network. The obtained simulation results indicate that the IDMMAC protocol performs well compared to the existing MAC protocols.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2012년도 추계학술대회
• /
• pp.27-30
• /
• 2012

클러스터 기반 라우팅 프로토콜(CBRP, Cluster-Based Routing Protocol)은 각 클러스터 내에 헤더를 선출하고 클러스터 헤더는 모든 이동 노드들을 관리, 운영하기 때문에 전력 소모가 심하게 일어나게 된다. 기존의 CBRP는 각 노드의 잔여전력량을 고려하지 않고 헤더를 임의로 선출하기 때문에 클러스터 헤더의 평균 수명이 짧아지고 빈번하게 다른 헤더를 선출해야 하는 문제점을 가지고 있다. 본 논문에서는 클러스터 헤더를 선출할 때 클러스터 내 각 노드의 잔여전력량을 비교하여 잔여전력량이 가장 높은 노드를 클러스터 헤더로 선출하고 잔여전력량이 두 번째로 높은 노드를 보조 헤더로 선출한다. 선출된 클러스터 헤더의 잔여전력량이 낮아져 헤더 역할을 수행할 수 없게 되면 이웃 멤버 노드들에게 알림 메시지를 전송하여 미리 선출해둔 보조 헤더가 클러스터 헤더 역할을 하게 한다. 클러스터의 수명과 네트워크 전체의 수명을 연장시키면서 헤더 재선출로 인한 문제점을 줄이고 경로의 안정성을 높이는 개선된 프로토콜을 제안한다.

• 한국컴퓨터정보학회논문지
• /
• 제18권1호
• /
• pp.63-71
• /
• 2013

클러스터 기반 라우팅 프로토콜(CBRP, Cluster-Based Routing Protocol)은 각 클러스터 내에 헤더를 선출하고 클러스터 헤더가 모든 이동 노드들을 관리, 운영하기 때문에 전력 소모가 심하게 일어나게 된다. 각 노드의 잔여 전력량을 고려하지 않고 헤더를 임의로 선출하기 때문에 클러스터 헤더의 평균 수명이 짧아지고 빈번하게 다른 헤더를 선출해야 하는 문제점을 가지고 있다. 본 논문에서는 잔여전력량을 고려하여 헤더 재선출로 인한 라우팅 지연을 줄이고, 클러스터뿐만 아니라 전체 네트워크의 수명을 연장시키는 새로운 헤더 선출기법을 제안한다. 제안 기법에서는 잔여전력량을 고려하여 헤더와 보조 헤더를 선출한다. 선출된 클러스터 헤더의 잔여전력량이 낮아져 헤더 역할을 수행할 수 없게 되면 미리 선출해둔 보조 헤더가 클러스터 헤더 역할을 수행하도록 함으로써 빈번한 헤더 재선출로 인한 문제점을 줄인다. 또한 잔여전력량이 높은 노드가 헤더로 선출되기 때문에 각 클러스터의 모든 노드는 전력이 균등하게 소비되어 네트워크 전체의 수명을 연장시킨다.

• 비교문화연구
• /
• 제38권
• /
• pp.89-113
• /
• 2015

This paper explores the work of mourning of 9/11 in the United States, focusing on the project of building the National September 11 Memorial managed by the Lower Manhattan Development Corporation(LMDC) and the War on Terror declared by the George W. Bush administration in the wake of 9/11. This paper first looks at the project of building the Natioanl September 11 Memorial and considers what was at stake in achieving this project. It also examines the limitations of the project. This paper argues that, in spite of the efforts to mourn the victims in significant and meaningful ways, the work of mourning in the memorial project fails at least in two respects. First, the memorial project "began so soon" right after 9/11 that the victims' families were not given enough time to mourn their loved ones. Second, the project were permeated with American nationalism and patriotism, which made the 316 non-American victims of 9/11 invisible and forgotten. Then, it goes on to examine the War on Terror because the War on Terror epitomized the failure of mourning due to these causes. In his address to the nation delivered on the very day of 9/11, President George W. Bush stated that "America was targeted for the attack because we're the brightest beacon for freedom and opportunity in the world" and that the terrorists failed to threaten America into chaos. He also stated that America is in "the war against terrorism." These statements were a futile reassertion of the illusion of American invulnerability and a prohibition of mourning in favor of violent military responses to 9/11. American nationalism also underlies Bush's official naming of September 11 as "Patriot Day." The victims were sacrificed because they were at the site when terrorists attacked, which implies that their death had nothing to do with American patriotism. Naming September 11 as Patriot Day was an act of imbuing the absurdity of the victims' death with a false meaning and an act of forgetting the non-American victims. The failure of the work of mourning of 9/11 consisted in the inability to recognize human vulnerability and interdependence and the inability to mourn not only American victims but also non-American victims killed in 9/11 and the War on Terror. A meaningful and significant mourning could be possible when we realizes that all human beings are exposed to one another and their lives are interdependent on one another. September Eleventh Families for Peaceful Tomorrows well demonstrated this kind of mourning. When most Americans supported violent retaliations, Peaceful Tomorrows made pleas for nonviolent responses to 9/11. Turning their grief into action for peace, its members work "to create a safer and more peaceful world for everyone," not only for Americans. Their effort to mourn in meaningful and nonviolent ways delivers the message that a disaster like 9/11 should not happen anywhere.