• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.921-924
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• 2007

In this paper, we have implemented a ubiquitous healthcare system that can measure and check human's health in anytime and anywhere. The implemented prototype are composed of both front-end and back-end. The front-end have several groups: environment sensor group such as temperature, humidity, photo, voice sensor, health sensor group such as blood pressure, heart beat, electrocardiogram, spo2 sensor, gateway for wired/wireless communication, and RFlD reader to identify personal. The back-end has a serial forwarder to propagate measurment results, monitor program, and medical information server. The implemented sensor node constructs a sensor network using the Zigbee protocol and is ported the TinyOS. The data gathering base node is linux-based terminal that can transfer a sensed medial data through wireless LAN. And, the medical information server stores the processed medical data and can promptly notify the urgent status to the connected medical team. Through our experiments, we've confirmed the possibility of ubiquitous healthcare system based on sensor network using the Zigbee.

• Journal of KIISE:Information Networking
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• v.32 no.3
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• pp.391-403
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• 2005

Several nv6 mobility support protocols for mobile Internet services are proposed in IETP : Mobile Ipv6, Hierarchical Mobile Ipv6, and Fast Handovers over Mobile Ipv6. Recently, IEEE 802.11 network has also been widely deployed in public areas for mobile Internet services. In the near future, IPv6 mobility support over IEEE 802.11 network is expected to be a key function to actualize the All If-based mobile various services. For appropriate application of these protocols, the IPv6 mobility support protocols should be analyzed according to their characteristics in terms of signaling, handover latency, lost packets, and required buffer sire as well as the impact of lower layer such as IEEE 802.11 network. In this paper, we analyze the performance of the protocols over IEEE 802.11 network. We define a packet-level traffic model, a network system model, and a mobility model. From these models, we construct a framework for the performance analysis. We also make cost functions to formalize each protocol's performance. Lastly, we analyze the effect of varying parameters used to show diverse numerical results, and compare with each other. From the analysis results, it is concluded that each Protocol has contrary or contrastive advantages with other Protocols, so there is no protocol that holds a dominant position.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.8
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• pp.33-41
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• 2007

The IEEE 802.11 DCF channel access function allows single transmission inside two-hop network in order to avoid collisions and eliminate the hidden and exposed terminal problems. Singular transmission capability causes data frames waiting for the entire roundtrip time in the transmitter neighborhood, and results in increased frame latency and lower network throughput. Real-time and pervasive applications are severely affected for the lower medium utilization; especially with high network traffic. This work proposes a new scheme with the help of Frame Aggregation technique in IEEE802.11n and overcomes the single transmission barrier maintaining the basic DCF functionality. Proposed scheme allows parallel transmissions in non-interfering synchronized slots. Parallel transmissions bypass the conventional physical carrier sense and random Backoff time for several cases and reduce the frame latency and increase the medium utilization and network capacity.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.667-674
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• 2011

Data networks at sea will be overlapped networks with not only traditional carriers such as RF, satellites but also BWA like wireless LAN, WiBro, and WCDMA in near future. In this paper, an overlapped MANET model for data networks at sea, and a routing protocol (OMH-MW) selecting optimal transmission medium for each hop in routes are proposed. OMH-MW measures the optimality of each medium regarding the transmission characteristics of each application and those of the medium in together. The most suitable medium to each link is selected as the link in routes. Performances are compared with those of the MWR (Max-Win based Routing protocol searching optimal routes with only one medium).

• Journal of Navigation and Port Research
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• v.30 no.3 s.109
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• pp.189-195
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• 2006

Sea operation monitoring system is a system for the automatic ship operation that is used on the variety sea operations such as laying optical cables on the sea between the countries, laying cables on the seabed for a remote island, laying pipelines for the natural gas, and so forth. This system processes data which obtained through setting up environment and input from several sensors, and display GPS information with ENC data. And this system processes not only data of route file about sea operation, but also realtime information from PDA of client wirelessly connected with AP on wireless LAN. In addition, this system can improve efficiency of the operation as a result of enabling free movement within valid range. This paper design and implementation monitoring system from above appropriate to the embedded system, and improve competitive power of ship through prevention of a ship accident, to keep minimizing operation loads and support both the automatic ship operation and the safety voyage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6C
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• pp.457-464
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• 2005

Recently, Portable Internet being standardized provides fast movement with wider service range than wireless LAN does. If Portable Internet service starts, many people will use Portable Internet and thus wireless traffic is going to increase. In Portable Internet, it is important to reduce handover latency to provide user with satisfactory service when handover occurs. In IEEE 802.16e, MSS sends its own security context information to one Base Station which it will move to reduce handover latency. But this is not suitable in the situation that the BS doesn't know the security context. To reduce handover latency of proactive caching method that is to send security context information to adjacency Base Stations in advance has been proposed by[4]. In this paper we propose effective traffic management algorithm to reduce signaling network traffic caused by proactive caching method.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.04a
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• pp.1169-1172
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• 2011

본 연구는 고가의 인프라 구축이라는 제약 때문에 현재까지 기초적인 수준에 머물러있는 홈 네트워크의 문제점을 극복하고자 제안된 스마트폰 중심의 개인환경서비스(PES : Personal Environment Service)를 연구하였다. 개인환경서비스는 스마트폰과 무선랜, 블루투스 등의 모듈이 탑재된 가전기기와 근거리 무선통신으로 사용자의 선호도를 저장하고 있는 프로파일을 교환하여 가전기기를 자동으로 설정해 주며 프로파일은 서비스 서버에도 전송되어 지속적으로 갱신, 사용자에게 편리한 생활을 제공해 준다. 본 연구는 이러한 스마트폰 중심의 개인환경서비스의 데모 시스템 구조 및 시연 시스템을 구축하였다. 데모시스템의 스마트폰 플랫폼은 구글 사의 안드로이드 2.2 (Froyo) 버전이며, 지능형 가전기기와는 블루투스 통신을 통해 사용자와 서비스 프로파일을 교환한다. 가전기기는 PC, 난방기기, 가스렌지, TV, 라디오 총 5가지를 구현하였는데 실제 가전기기를 구현할 수 없는 한계로 인해 PC를 제외한 가전기기는 블루투스 임베디드 보드에 LCD 디스플레이를 설치한 모의(pseudo) 가전기기로 대체하였다. 스마트폰에 저장되어 있는 사용자 프로파일은 각각의 가전기기별 선호도를 환경설정을 통해 설정할 수 있게 하였고, 선호도를 설정하면 가전기기는 블루투스 통신으로 스마트폰의 사용자 프로파일을 전송받아 자동 설정해 준다. 서비스 서버는 스마트폰과 가전기기의 모든 로그를 전송받아 패턴분석 과정을 거쳐 사용자의 프로파일을 자동으로 설정해주어서 사용자는 개인에게 최적화된 생활환경을 제공받게 된다. 개인환경서비스는 현재 표준화 규격 개발을 위해 제조업체, 이동통신사, 연구소, 대학교 등에서 활발히 연구 중에 있으며, 향후에는 현재까지 개발된 데모 시스템을 토대로 프로토콜을 연구, 수립하여 표준화 규격 개발에 기여할 예정이다.

• Journal of the Korea Society for Simulation
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• v.23 no.4
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• pp.65-74
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• 2014

IEEE 802.11n standard has introduced the new schemes in MAC and PHY layers to improve network throughput. Frame aggregation and Block ACK are mainly defined to increase the efficiency of the MAC layer. There exists still problem in IEEE 802.11n. When block ACK request and/or response frames are missing or received in error, the sender does not know the status (success/failure) of each frame in the aggregated large frame and retransmits all the frames. This can cause a lower network performance. To solve this problem, we propose a new effective scheme, called reduced retransmission of MPDUs (RRM) scheme. In the proposed scheme, when a sender does not receive a block ACK response frame, it just transmits a next data frame and requests a block ACK. Therefore, it can retransmits the erroneous frames. Performance of the proposed scheme is investigated by simulation. Our results show that the proposed scheme is very effective and improves the performance under a wide range of channel error conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.1
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• pp.38-40
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• 2014

In this paper, proposed method achieves delay reduction and throughput improvement by utilizing token-ring method in infrastructure network. Access Point gives token passing effect by successively transmitting ACK frame including a node's Association ID. Not only can this method considerably reduce time for medium access, but also improve throughput. Furthermore, AP offers more frequent medium access opportunity to node having highest data queue among nodes associated by AP. these method can evenly offer medium access opportunity according to Queue's volumes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.12
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• pp.2401-2409
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• 2015

This paper proposes the improved handoff mechanism for IEEE 802.11 wireless LANs. When a wireless mobile node moves out of the coverage of its currently associated AP(Access Point) and needs to be re-associated with a new AP, a handoff procedure is initiated. Channel scanning process during a handoff procedure occupies over 90% of total handoff latency. Long latency leads to many packet losses and service discontinuity, which degrades wireless network performance. This paper describes about the new mechanism to improve handoff performance by skipping channel scanning during a handoff procedure. In oerder for that, acquires neighboring AP information such as its address, location, channel number in use, the number of associated nodes before handoff, and delivers the information to its associated mobile nodes. The mobile nodes can reduce handoff latency and perform more exact handoff using the delivered AP information. We have conducted simulations to analyze our proposal's performance and confirmed that handoff latency and the number of handoff occurrences are decreased.