• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6C
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• pp.512-522
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• 2005

In this paper, an optimal determination method of the subband-frame size and mode-switching level is proposed for adaptive OFDM-TDD systems in frequency-selective time-varying channels. The optimization problem considering frequency selectivity. user's mobility, and the signaling overhead caused by the mode change information is formulated in the maximum spectral efficiency sense satisfying the target BER. Assuming that subband-frame size is given, the mode-switching level is first optimized so that the spectral efficiency can be maximized satisfying the target BER. The subband-frame size among candidates is then determined, which maximizes the spectral efficiency. Simulation results show that the proposed scheme outperforms conventional schemes, in terms of the spectral efficiency and the BER.

• Journal of Biomedical Engineering Research
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• v.24 no.3
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• pp.217-231
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• 2003

Coded excitation with complementary Golay sequences is an effective means to increase the SNR and penetration of ultrasound imaging. in which the two complementary binary codes are transmitted successively along each scan-line, reducing the imaging frame rate by half. This method suffers from low frame rate particularly when multiple transmit focusing is employed, since the frame rate will be further reduced in proportion to the number of focal zones. In this paper. a new ultrasound imaging technique based on simultaneous multiple transmit focusing using modified orthogonal Golay codes is proposed to improve lateral resolution with no accompanying decrease in the imaging frame rate, in which a pair of orthogonal Golay codes focused at two different focal depths are transmitted simultaneously. On receive, these modified orthogonal Golay codes are separately compressed into two short pulses and individually focused. These two focused beams are combined to form a frame of image with improved lateral resolution. The Golay codes were modified to improve the transmit power efficiency (TPE) for practical imaging. Computer simulations and experimental results show that the proposed method improves significantly the lateral resolution and penetration of ultrasound imaging compared with the conventional method.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.37-40
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• 2007

효율적인 OFDM(Orthogonal frequency division multiplexing)의 동작을 위해 데이터의 시작 위치를 검출하는 프레임 동기 과정은 필수적인 요소이다. 본 논문에서는 OFDM 을 기반으로 한 이동 멀티미디어 통신 시스템에 적용가능한 새로운 프레임 동기 방법을 M-sequence 를 이용하여 설명하고 분석한다. 두 개의 반복되는 M-sequence 는 시간 영역에서 OFDM 의 프레임에 직접 더해지고, 수신단에서 M-sequence 의 자기상관 특성을 수행함으로 효과적인 프레임 동기를 얻을 수 있다. 이와 함께 주파수 옵셋 추정 알고리즘이 이루어 진다. 제안된 알고리즘은 비교적 단순하며 다중경로채널에서도 훌륭한 특성을 보여준다. 마지막으로 이 기술은 4G 이동 멀티미디어 통신 시스템에 적용할 수 있다.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.11a
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• pp.549-551
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• 2012

본 논문에서는 기존의 화소값 차영상 기법이 저속으로 움직이는 물체의 동작정보 감지에 취약한 점을 보완하기 위하여 실시간 영상 처리를 목적으로 연속된 프레임(Frame)에서 움직임이 있는 프레임을 찾아내고, 움직임 영역을 추출하는 움직임 검출에 관한 연구를 통해 웹캠 기반의 객체 감지시스템을 제안하였다. 제안 시스템은 단일 객체뿐 아니라 다중 객체의 움직임까지 파악할 수 있다는 장점을 가지고 있다.

• The KIPS Transactions:PartB
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• v.11B no.6
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• pp.701-708
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• 2004

Existing contents-based video retrieval systems search by using a single method such as annotation-based or feature-based retrieval. Hence, it not only shows low search efficiency, but also requires many efforts to provide system administrator or annotator with a perfect automatic processing. Tn this paper, we propose an agent-based, and automatic and unified semantics-based video retrieval system, which support various semantics-retrieval of the massive video data by integrating the feature-based retrieval and the annotation-based retrieval. The indexing agent embodies the semantics about annotation of extracted key frames by analyzing a fundamental query of a user and by selecting a key-frame image that is ed by a query. Also, a key frame selected by user takes a query image of the feature-based retrieval and the indexing agent searches and displays the most similar key-frame images after comparing query images with key frames in the database by using the color-multiple-partition histogram techniques. Furthermore, it is shown that the performance of the proposed system can be significantly improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6B
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• pp.495-507
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• 2006

In wireless local area networks (WLANs), the successful design of scheduling algorithm is a key factor in guaranteeing the various quality of service (QoS) requirements for the stringent real-time constraints of multimedia services. In this paper we propose a multipolling-based dynamic scheduling algorithm for providing delay guarantees to multimedia traffics such as MPEG streams. The dynamic algorithm exploits the characteristics of MPEG stream, and uses mini frames for feedback control in order to deliver dynamic parameters for channel requests from stations to the point coordinator (PC) operating at the access point (AP). In this scheme, the duration of channel time allocated to a station during a superframe is changed dynamically depending on the MPEG frame type, traffic load and delay bound of the frame, etc. Performance of the proposed scheme is investigated by simulation. Our results show that compared to conventional scheme, the proposed scheme is very effective and has high performance while guaranteeing the delay bound.

• Proceedings of the KAIS Fall Conference
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• 2010.05a
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• pp.319-322
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• 2010

본 논문에서는 특징기반 검색을 이용하여 대용량의 비디오 데이터에 대한 사용자의 다양한 의미검색을 지원하는 에이전트 기반에서의 자동화되고 통합된 비디오 의미기반 검색 시스템을 제안한다. 사용자의 기본적인 질의를 분석하고 질의에 의해 추출된 키 프레임의 이미지를 사용자가 선택함으로써 인덱싱 에이전트는 추출된 키 프레임의 주석에 대한 의미를 더욱 구체화시킨다. 또한, 사용자에 의해 선택된 키 프레임은 특징기반 검색의 질의 이미지가 되고 인덱싱 에이전트는 제안하는 다중 분할 칼라 히스토그램 기법을 통해 질의 이미지와 데이터베이스의 키 프레임들을 비교한 후 가장 유사한 키 프레임 이미지를 검색하여 사용자에게 디스플레이한다. 제안하여 구현된 시스템은 현저히 향상된 성능을 보였다.

• Journal of the Korea Society of Computer and Information
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• v.18 no.4
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• pp.79-85
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• 2013

In SIP(Session Initiation Protocol) environment, the presence server should process SIP SUBSCRIBE request messages including multiple presence resources addresses from users, and also precess massive notification messages from the subscribed presence resources. The load of the presence server increases as number of users increase, and it limits system extendability. Therefore a new multiple presence servers architecture has been suggested in this research. In this architecture presence servers can be added dynamically and each server's load can be controlled effectively as number of users increase. Each presence server can monitor current load status of entire presence system by using presence event notification package which newly has been suggested in this paper. When a particular presence server's load increases over predefined limit, the presence service processing is distributed by selecting a server which has the smallest load, or by generating a new server dynamically. In this system the overall load of the entire system can be controlled optimally and extendability of the system can be increased. For this purpose a new presence event notification package and presence information data format have been suggested. The performance of the proposed system has been evaluated by experiments. They shows 44.3% increase in SUBSCRIBE message processing time, and 43.1% increase in Notification message processing time.

• Journal of Broadcast Engineering
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• v.8 no.1
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• pp.72-79
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• 2003

The Eureka-147 Digital Audio Broadcasting(DAB) system is the new international standard for mobile broadcasting services including high-quality audio, program associated data and other multimedia data. In this paper, we design the transport frame structures for the mobile multimedia services by using the configuration of the Eureka-147 DAB multiplex and MPEG system specifications, and then compare their performances in terms of functionality and overhead. Especially, we suggest and analyze the effective transport structures, which are improved in the efficiency of media multiplexing architecture, by removing the functionally overlapped parts between DAB and MPEG systems. In addition, we evaluate the transmission environments of various DAB data channels and demonstrate the transmission error effects on the low bit rate video stream.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1C
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• pp.54-62
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• 2012

A Wi-Fi mesh network providing multi-hop wireless connections based on IEEE 802.11 PHY/MAC technology has recently received a significant attention as a network infrastructure that interconnects RFID systems and wireless sensor networks (WSNs). However, the current IEEE 802.11 contention-based MAC protocol cannot fully utilize the network capacity due to eithor frame collisions or unused network resources. In this paper, we propose a novel multi-channel scheduling MAC (MCS-MAC) protocol for Wi-Fi mesh networks. Under the secondary interference model of Wi-Fi mesh networks, the MCS-MAC protocol can maximize the network throughput via activation of collision-free links that has a maximal link weight. Through the simulations, we show that the throughput of the MCS-MAC protocol is at least three times higher than that of existing MAC protocols in Wi-Fi mesh networks.