• KSII Transactions on Internet and Information Systems (TIIS)
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• 제3권6호
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• pp.597-611
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• 2009

With the advent of ubiquitous computing society, many advanced technologies have enabled wireless sensor networks which consist of small sensor nodes. However, the sensor nodes have limited computing resources such as small size memory, low battery life, short transmission range, and low computational capabilities. Thus, decreasing energy consumption is one of the most significant issues in wireless sensor networks. In addition, numerous applications for wireless sensor networks are recently spreading to various fields (health-care, surveillance, location tracking, unmanned monitoring, nuclear reactor control, crop harvesting control, u-city, building automation etc.). For many of them, supporting security functionalities is an indispensable feature. Especially in case wireless sensor networks should provide a sufficient variety of security functions, sensor nodes are required to have more powerful performance and more energy demanding features. In other words, simultaneously providing security features and saving energy faces a trade-off problem. This paper presents a novel energy-efficient security architecture in an IEEE 802.15.4-based wireless sensor network called the Hybrid Adaptive Security (HAS) framework in order to resolve the trade off issue between security and energy. Moreover, we present a performance analysis based on the experimental results and a real implementation model in order to verify the proposed approach.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권4호
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• pp.800-818
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• 2013

Supporting video streaming over multi-hop wireless networks is particularly challenging due to the time-varying and error-prone characteristics of the wireless channel. In this paper, we propose a joint optimization scheme for video streaming over multi-hop wireless networks. Our coding scheme, called Joint Source/Network Coding (JSNC), combines source coding and network coding to maximize the video quality under the limited wireless resources and coding constraints. JSNC segments the streaming data into generations at the source node and exploits the intra-session coding on both the source and the intermediate nodes. The size of the generation and the level of redundancy influence the streaming performance significantly and need to be determined carefully. We formulate the problem as an optimization problem with the objective of minimizing the end-to-end distortion by jointly considering the generation size and the coding redundancy. The simulation results demonstrate that, with the appropriate generation size and coding redundancy, the JSNC scheme can achieve an optimal performance for video streaming over multi-hop wireless networks.

• 한국컴퓨터정보학회논문지
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• 제15권11호
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• pp.117-124
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• 2010

중앙 집중적 네트워크 관리 구조인 SNMP(Simple Network Management Protocol)를 무선 네트워크 관리에 적용하면 네트워크 과부하, AP에서의 NAT(Network Address Translation)로 인한 관리의 문제, 그리고 무선 노드의 성능 저하가 발생한다. 본 연구에서는 이러한 문제를 해결하기 위해 MA(Mobile Agent)를 도입한 유무선 네트워크 통합 관리 기법을 제안한다. 제안기법에서 유선 네트워크는 SNMP 기반으로 관리하고 무선 네트워크는 AP 또는 무선 노드에 SNMP를 MA 기반으로 구현하여 관리한다. 또한, SNMP 응답 메시지 내에 중복되는 OID 정보를 줄이는 방법도 제시한다. 분석을 통해 제안 기법이 제시된 문제를 해결하고 무선 노드에 대한 처리 시간이 개선됨을 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권5호
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• pp.959-975
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• 2011

Wireless mesh networks enlarge the wireless coverage area by interconnecting relatively stationary wireless routers (mesh routers). As wireless mesh networks are envisioned to provide high-bandwidth broadband Internet service to a large community of users, the Internet gateway, which acts as a central point of Internet attachment for the mesh networks, is likely to suffer heavily from the scramble for shared wireless resources because of aggregated traffic toward the Internet. It causes performance decrement on end-to-end transmissions. We propose a scheme to balance the load in a mesh network based on link quality variation to different Internet gateways. Moreover, under the mesh coverage, mobile nodes can move around and connect to nearby mesh routers while still keeping the connections to the Internet through the best gateway in terms of link quality. In this structure, gateways perform the balancing procedure through wired links. Information about gateways and mobile node's location is distributed appropriately so that every mesh router can quickly recognize the best gateway as well as the positions of mobile nodes. This distributed information assists mobile nodes to perform fast handoff. Significant benefits are shown by the performance analysis.

• Journal of Communications and Networks
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• 제11권3호
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• pp.287-296
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• 2009

Although asymptotic bounds of wireless network capacity have been heavily pursued, the answers to the following questions are still critical for network planning, protocol and architecture design: Given a three-dimensional (3D) network space with the number of active users randomly located in the space and using the wireless communication technology, what are the expected per-flow throughput, network capacity, and network transport capacity? In addition, how can the protocol parameters be tuned to enhance network performance? In this paper, we focus on the ultra wideband (UWB) based wireless personal area networks (WPANs) and provide answers to these questions, considering the salient features of UWB communications, i.e., low transmission/interference power level, accurate ranging capability, etc. Specifically, we demonstrate how to explore the spatial multiplexing gain of UWB networks by allowing appropriate concurrent transmissions. Given 3D space and the number of active users, we derive the expected number of concurrent transmissions, network capacity and transport capacity of the UWB network. The results reveal the main factors affecting network (transport) capacity, and how to determine the best protocol parameters, e.g., exclusive region size, in order to maximize the capacity. Extensive simulation results are given to validate the analytical results.

• Smart Structures and Systems
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• 제11권5호
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• pp.497-510
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• 2013

Quick, accurate damage monitoring is strongly required for damage assessment in the aftermath of a large natural disaster. Wireless sensor networks are promising technologies to acquire damage information in a citywide area. The wireless sensor networks, however, would be faced with difficulty to collect data in real-time and to expand the scalability of the networks. This paper discusses a scheme of network architecture to cove a whole city in multi-tier heterogeneous networks, which consist of wireless sensor networks, access networks and a backbone network. We first review previous studies for citywide damage monitoring, and then discuss the feature of multi-tier heterogeneous networks to cover a citywide area.

• 한국통신학회논문지
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• 제38B권6호
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• pp.454-472
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• 2013

무선 네트워크의 사용이 모바일 사용자로 점점 확대되고 무선 네트워크 기술의 발달로 다양한 무선 네트워크 시스템이 생겨났다. 무선 네트워크 시스템들은 중첩되어 있을 수 있으며 네트워크 간 전환을 필요로 한다. NGWN(Next Generation Wireless Networks)은 다양한 무선 네트워크를 통합하여 사용자에게 넓은 커버리지 영역과 최적화된 서비스를 제공한다. 기존의 핸드오프 관리 프로토콜은 NGWN의 응용프로그램에 핸드오프 지원을 보장하기에 충분하지 않다. CLH(Cross-Layer Handoff) 프로토콜 기법은 NGWN의 네트워크 내와 네트워크 간의 효율적인 핸드오프 관리를 위해 개발되었다. CLH은 무선 네트워크 환경에서 이동성관리를 지원하고 핸드오프 성능향상을 위해 모바일의 속도와 핸드오프 시그널링 지연 정보를 이용한다. 본 논문에서는 핸드오프 성능 분석을 위해 링크계층 및 네트워크계층의 민감도를 분석하고 이것을 기반으로 CLH 기법을 제안한다. CLH가 네트워크 내와 네트워크 간 핸드오프의 성능 향상을 높여준 다는 것을 본 논문의 다양한 이론적 분석을 통하여 평가하고 분석한다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 춘계종합학술대회
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• pp.671-674
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• 2007

유비쿼터스 센서 네트워크(Ubiquitous Sensor Networks)는 각종 센서에서 수집한 정보를 무선으로 수집할 수 있도록 구성한 네트워크를 말한다. 이러한 유비쿼터스 센서 네트워크에서 센서 노드는 한정된 전송 거리의 극복과 최적의 경로 설정으로 안정적인 데이터 전송이 중요하다. 이에 본 논문에서는 무선 메쉬 네트워크(Wireless Mesh Networks)를 이용한 센서 노드의 한정된 전송거리를 극복하고자 한다. 따라서 u-farm을 위한 환경감시 시스템은 무선 메쉬 네트워크의 MAP을 적용시켜 안정적인 데이터 전송이 이루어지도록 제안한다.

• 한국항행학회논문지
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• 제15권2호
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• pp.241-247
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• 2011

유선네트워크 환경에서의 Transmission Control Protocol(TCP) 패킷 손실은 대부분 네트워크의 혼잡에 의해서 발생한다. 하지만, 무선네트워크 환경에서는 무선 네트워크의 특징 중 하나인 높은 Bit Error Rate (BER)에 의한 손실이 대부분 일어난다. 네트워크는 무선 신호 품질에 의한 패킷 손실을 혼잡제어에 의한 손실로 판단하여, 혼잡제어 메커니즘이 빈번하게 수행된다. 무선 환경의 패킷 손실율을 이용하여 Explicit Wireless Loss Notification (EWLN) 알고리즘에서 발생될 수 있는 비효율적인 Congestion Window의 크기를 보다 효율적으로 재조정함으로써, 기존의 EWLN 알고리즘을 개선하는 알고리즘을 제안한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -1
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• pp.381-384
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• 2002

Orthogonal Frequency Division Multiplexing (OFDM), which employs orthogonal overlapping subcarriers to modulate the signals, has been attracted much attention in recent time as a favorable option for future generation wireless networks due to its ability to overcome many impairments in wireless channels. Since OFDM is a multi-carrier system adaptive modulation techniques can be effectively and efficiently used to enhance the system performance in terms of both BER and overall system capacity. This paper discusses a COFDM-CDMA system with adaptive modulation schemes for future generation wireless networks.