• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3B
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• pp.390-397
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• 2010

This paper presents an effective IPTV channel control algorithm considering network utilization and channel zapping time. The proposed algorithm keeps maximum average channel zapping time of each subscriber in the tolerable range with low network bandwidth usage by adjusting the type of each channel and the number of additional intra frames inserted into each channel. Finally, experimental results are provided to show the performance of the proposed algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4A
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• pp.356-368
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• 2011

While most of the public radio spectrum bands are allocated to licensed users, cognitive radio has been considered as a promising technology for the efficient spectrum utilization. In this new technology, secondary users opportunistically use the temporally underutilized licensed bands as long as they do not give the harmful interference to primary users. In this paper, we focus on the infra-structured network condition in which the cognitive radio network consists of a cognitive radio base station and multiple secondary users. Upon detecting a primary user, the entire cognitive radio network generally switches to another available channel, even if most of the on-going communications still does not interfere with the primary user. Moreover, the network re-entry process on a new channel causes the service disruption of the on-going communications. For this reason, in this paper, we propose a relaying scheme for efficient frequency usage, in which the secondary user out of the interference range of a primary user performs as a relaying node for the secondary user possibly interfering with a primary user. The entire spectrum switching is not required, and thus, we can avoid the service disruption of the on-going communications as much as possible.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2011.06a
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• pp.173-175
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• 2011

적극적인 관제 및 책임 관제구역 도입의 필요성과 안전항행을 위한 정보제공 및 업무 효율성 증진 방안 강구로 현재 섹터 관제를 시행하고 있으며 선박의 충돌사고 예방 및 해양환경보호에 큰 역할을 하고 있는 것이 사실이다. 하지만 일반적 형태와 상이한 부산항의 관제섹터 변경구역에서의 현 문제점과 합리적인 VHF채널 운영방안을 제시한다.

• 한국IT서비스학회:학술대회논문집
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• 2009.05a
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• pp.327-330
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• 2009

무선랜 (WLAN)과 지그비 (Zigbee)는 동일한 2.4GHz대의 비면허 주파수 대역(ISM-Band)을 사용하기 때문에 네트워크 간의 주파수 간섭이 발생한다. 더욱이 지그비의 경우 무선랜의 채널과 중첩되지 않는 채널은 단 두 개 채널에 불과하기 때문에 무선랜의 주파수 간섭을 받을 경우 통신 지연 시간의 증가가 불가피 하다. 이에 본 논문에서는 지그비와 무선랜 간의 주파수 간섭으로 인해 발생하는 통신 지연 시간 최소화를 위한 빠른 채널 변경 알고리즘을 제안한다. 이와 더불어 제안 알고리즘의 성능 분석을 위해 모의실험을 수행하였고, 그 결과 제안 알고리즘의 통신 지연 시간이 감소됨을 확인하였다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1952_1953
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• 2009

전력선 채널 잡음은 전력선에 연결되어 있는 전기기기들에 의하여 변화하는 특성을 갖으며, 이러한 잡음 특성을 극복하기 위한 한가지 방법으로 DS/SS 방식을 적용하는 방법이 있다. 그러나 저속 DS/SS 전력선 모뎀의 경우 낮은 데이터전송률 때문에, 잡음 특성을 개선하기 위하여 Chip 수가 큰 PN code를 적용하기 어렵다. 따라서 본 논문에서는 전원 전압에 동기되어 잡음의 양이 변화하는 것에 따라 PN code를 변경하는 방법[1]을 적용하고자 하였다. 전력선 채널의 잡음은 비교적 부하가 고정적인 가로등 전력선 채널로 한정하여 잡음을 모델링 하였으며, 전원전압에 맞추어 잡음의 양에 따라 PN code 길이를 변경하는 FSK 방식의 DS/SS 시스템을 구성하여 시뮬레이션 하였다. 시뮬레이션 결과 적용된 시스템이 전력선 채널에서 효과적 성능을 발휘함을 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12B
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• pp.1050-1057
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• 2008

Wireless Mesh Networks (WMNs) have recently become a hot issue to support high link capacity in wireless access networks. The IEEE 802. I 1 standard which is mainly used for the network interface technology in WMNs supports up to 3 or 12 multiple channels according to the IEEE 802.11 specification. However, two important problems must be addressed when we design a channel assigmnent algorithm: channel dependency problem and channel scanning delay. The former occurs when the dynamic channel switching of an interface leads to the channel switching of other interfaces to maintain node connectivity. The latter happens per channel switching of the interface, and affects the network performance. Therefore, in this paper, we propose the Distance-Based Channel Assigmnent (DB-CA) scheme for multi-channel WMNs to solve such problems. In DB-CA, nodes just perform channel switching without channel scanning to communicate with neighboring nodes that operate on different channels. Furthermore, DB-CA minimizes the interference of channels being used by nodes near the gateway in WMNs. Our simulation results show that DB-CA achieves improved performance in WMNs.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.4
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• pp.1005-1014
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• 2010

When reader collect tags, we found that they tend to get together to specific interface in Multi-Interface Multi-Channel 2.4GHz Active RFID system. To solve this problem, we designed the LP-Combind and AP-Balanced protocol for load distribution between interfaces, then verified its superiority of the performance through the simulation. There are three problems to implement designed protocols in hardware of firmware-level. first, tag selects randomly the channel of reader and reader need the method which can change the channel of tags. second, reader has the synchronization problem between reader and tag. third, reader has problem that MCU of reader have to operate simultaneously dual interface. To slove this problems, we designed the message and implemented method for tag channel change and the protocol in order to adjust synchronization between reader and tag, Therefore, we compared and analyzed the performance of protocols by experiment. If LP windows size is same, the performance of LP-Combined protocol and AP-Balanced protocol which lower collision probability by its load distribution is more outstanding than single interface protocol performance.

• Journal of Advanced Navigation Technology
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• v.6 no.3
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• pp.203-210
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• 2002

In this paper, the BER performance of IEEE 802.11a OFDM WLAN system is obtained by simulation and it is shown that the proposed modified channel estimation algorithm improves the channel estimation performance of the system. The wireless channel used in channel simulation includes AWGN and delay spread channel implemented by TDL model. At first, the performance of OFDM WLAN system according to data rate and coding rate defined in standard is evaluated in AWGN channel. Then, imperfect channel estimation in indoor wireless channel is considered. After the performance of conventional channel estimation scheme using only two long training symbols is evaluated, and that of proposed modified channel estimation scheme using additional 8 short training symbol is compared with it. From the simulation results, it is shown that modified channel estimation scheme provides reduced channel estimation error and improves the channel estimation performance due to noise averaging effect with the same preamble format as defined in specification.

• The Journal of the Korea Contents Association
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• v.8 no.1
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• pp.272-281
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• 2008

A layer channel, which can express effects on 3D image, is inserted to use it on application rendering effectively. The current method of effect rendering requires individual sources in storage and image processing, because it uses individual and mixed management of images and effects. However, we can save costs and improve results in images processing by processing both image and layer channels together. By changing image format to insert a layer channel in image and adding a hide function to conceal the layer channel and control to make it possible to approach image and layer channels simultaneously during loading image and techniques hiding the layer channel by changing image format with simple techniques, like alpha blending, etc., it is developed to improve reusability and be able to be used in all programs by combining the layer channel and image together, so that images in changed format can be viewed in general image viewers. With the configuration, we can improve processing speed by introducing image and layer channels simultaneously during loading images, and reduce the size of source storage space for layer channel images by inserting a layer channel in 3D images. Also, it allows managing images in 3D image and layer channels simultaneously, enabling effective expressions, and we can expect to use it effectively in multimedia image used in practical applications.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2003.07a
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• pp.11-16
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• 2003

본 논문에서는 새로운 공개키 다중채널 broadcast encryption scheme(이하 PK-MCBE라 부른다)을 제안한다. 일반적인 broadcast encryption은 하나의 채널스트림을 전송하는 반면 PK-MCBE는 다수채널의 컨텐츠 스트림을 전송한다. 본 논문에서 제안하는 방식에서 수신자는 단지 하나의 비밀키만을 필요로 하며 한번 받은 비밀키는 변경되지 않는다. 제안하는 방식에서는 각 채널당 송신자가 전송하는 메세지의 공통부분을 한번만 전송하여 전체 전송 메세지의 길이를 줄일 수 있다. 또한 배신자(traitors)를 추적하여 효과적으로 강제 탈퇴시킬 수 있다.