• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9A
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• pp.844-855
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• 2006

The communication system using multiple antennas improves link reliability or system capacity using tx & rx diversity, spatial multiplexing, and beamforming technique with services and characteristics of channel environment. This system is sensitive to spatial channel environment. In case of diversity, the lower correlation among links as a LoS environment, the better performance is acquired. In practical channel environment, However, there is high correlation, and there is high performance difference between ideal case and practical case. On the contrary, in case of beamforming, the higher correlation among links, the better performance is acquired. If we use the spatial adaptive transmission technique with spatial channel characteristics, we can get the system that maintains minimum link reliability and guarantees the overall system performance. In this paper, we propose the adaptive transmission and reception technique which use diversity or beamforming technique with channel characteristics.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2565-2567
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• 2004

본 논문에서는 빠르게 변화하는 이동 무선 채널 환경에서 심각한 성능 저하를 일으키는 인접 심볼 간섭(Inter-symbol interference: ISI)에 대처하기 위해 MLSE(Maximum Likelihood Sequence Estimztion) 등화기의 성능을 향상시키는 방법을 제안하였다. 기존의 MLSE 등화기는 비터비 알고리즘으로 어느 정도 계산량을 감소시켰지만, 정확한 채널 임펄스 응답을 필요로 하기 때문에, 시변 채널에서의 복잡한 채널 추정이 그 문제점으로 남아 있다. 이러한 문제점을 해결하기 위해서, 간단하고 향상된 칼만 필터 기반의 채널 추정기를 새롭게 제안하여 MLSE의 복잡성을 줄였다. 또한, 복잡한 채널 추정을 대신하여 페이딩 채널을 거쳐 수신된 데이터를 클러스터로 매핑하여 클러스터 중심 추정을 이용한 1-D CBSE(1-Dimensional Clustering-based Sequence Equalizer) 알고리즘에, 최소 길이를 지닌 훈련 시퀀스를 제안하여 개선된 1-D CBSE을 이용한 MLSE 등화 성능을 보여주었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.7
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• pp.1468-1476
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• 1997

In mobile communication systems, the Reduced State Sequence Estimation(RSSE) receiver must be able to track changes in the channel. This is carried out by the adaptive channel estimator. However, when the tentative decisions are used in the channel estimator, incorrect decisions can cause error propagation. This paper presents a new channel estimator using the path history in the Viterbi decoder for preventing error propagation. The selection of the path history in the Viterbi decoder for preventing error propagation. The selection of the path history for the channel estimator depends on the path metric as in the decoding of the Viterbi decoder in RSSE. And a discussion on the channel estimator with different adaptation algorithms such as Least Mean Square(LMS) algorithm and Recursive Least Square(RLS) algorithm is provided. Results from computer simulations show that the RSSE receivers using the proposed channel estimator have better performance than the other conventional RSSE receiver, and that the channel estimator with RLS algorithm is adequate for multipath fading channel.

• Journal of the Korea Society for Simulation
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• v.18 no.1
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• pp.1-7
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• 2009

In this paper, we obtain the optimal number of interfaces/channels in wireless mesh networks by simulation. The simulation study is done in static multi-channel multi-interface environment. When many nodes use a single interface and channel and contend for the channel, collisions of RTS/CTS results in network performance degradation. To avoid such degradation and reduce interferences between the adjacent nodes, use of multi-interface/channel is considered. 802.11a and 802.11b systems offer 12 and 3 orthogonal channels respectively and multi-interface/channel scheme could be applied. But rare research about the optimal number of interfaces/channels has been studied. Therefore, in this paper, simulation study for the optimal number of interfaces/channels in wireless mesh network is made.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.486-489
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• 2011

본 논문에서는 위성 DMB 환경에서 멀티채널 오디오 서비스를 제공할 수 있는 시스템을 제안한다. 위성 DMB 서비스는 2005 년부터 상용서비스를 시작한 이동멀티미디어방송 서비스로서, QVGA 급의 영상과 FM 음질의 오디오 서비스를 제공한다. 본 연구에서는 기존의 위성 DMB 시스템과 호환성을 유지하면서, 적은 비트율의 데이터를 추가하여 멀티채널 오디오 서비스를 제공하는 시스템에 대한 연구를 수행하였다. 이를 위하여 기존의 스테레오 오디오 시스템과 호환성을 가지면서도 적은 비트율의 데이터 추가만으로 멀티채널 오디오 신호의 재현이 가능한 멀티채널 오디오 부호화 기술을 적용하였고, 기존 위성 DMB 단말의 동작에 영향을 주지 않으면서, 멀티채널 오디오 서비스가 제공되는 것을 식별할 수 있도록 하는 시그널링 방법을 개발하여 적용하였다. 연구 결과의 검증을 위하여 위성 DMB 멀티채널 오디오 부호화기 및 단말을 개발하여 방송 실험을 수행하였고, 이를 통하여 제안한 방법으로 위성 DMB 환경에서 멀티채널 오디오 서비스를 효율적으로 제공할 수 있음을 증명하였다.

• The Journal of the Acoustical Society of Korea
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• v.26 no.8
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• pp.426-431
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• 2007

In this paper we have studied the underwater vector channel modeling for MIMO(Multiple Input Multiple Output) to increase the performance and efficiency for ultrasound communication in underwater channel environments. Also we have analyzed the MIMO techniques using the proposed channel modeling. For underwater MIMO channel modeling. experiments were done in real channel environments and the data were analyzed to estimate parameters such as fading, Doppler, time delay, angle of arrival, and receiving power. These were used for modeling of underwater vector channel modeling for MIMO. Additionally, we have analyzed the performance of MIMO systems using our proposed channel models. As a result we could see that the BER has decreased severely with the same SNR when using the MIMO system.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.77-80
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• 2003

본 논문에서는 유비쿼터스 네트워킹을 위한 초고속 근거리 무선 전송기술로서 각광받고 있는 초광대역(Ultra Wideband : UWB) 통신 기술을 분석하고 실내 근거리 다중접속 환경 및 페이딩 환경에서의 시스템 성능을 분석하였다. 다중접속 간섭 환경은 UWB 시스템의 전송율과 간섭 수에 따른 시스템 성능을 분석하고, 페이딩 채널은 기존에 발표되었던 UWB 전파 실험을 통한 데이터를 바탕으로 Nakagami-m분포 모델을 이용하여 페이딩 지수 m에 따른 다양한 채널 환경을 고려하였다.

• Proceedings of the KSEEG Conference
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• 1999.04a
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• pp.248-250
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• 1999

• The KIPS Transactions:PartC
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• v.17C no.6
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• pp.471-484
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• 2010

In the wireless communication systems, the power consumption of a mobile device is very important issue due to its battery limitations. Hence most of the standards for wireless networks including a mobile WiMAX system are supporting their own power saving mode in way that a mobile device is able to reduce its energy usage while in the mode. However, those standards just define the arrangement of special time intervals, called a paging listening interval, during which the device needs to receive the paging-related control messages, and they do not specify how to effectively reduce the power in many different network environments. This means the amount of power spent by the device is very dependent on the implementations of individual device-vendors, and undesirable paging loss may happen according to the channel conditions. To reduce unnecessary power usage and the risk of paging loss, this paper proposes the effective frequency/BS selection algorithm applicable to a mobile device operating in the power saving mode, which serves the device with better BS based on the tracking for channel variation. This algorithm consists of the channel estimation phase during each paging listening interval, the tracking phase for the measured results, the frequency reselection phase based on the tracking activity, and the preferred BS reselection phase. Thus the proposed method can improve the paging performance while the device is moving in the network. Also the simulation result shows that the presented scheme is superior to other candidates in energy efficiency due to the channel-adaptive frequency/BS selection.

• Journal of Broadcast Engineering
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• v.14 no.4
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• pp.438-449
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• 2009

To analyze reception environments of ATSC Digital TV, CIR (Channel Impulse Response) analysis systems are widely applied. The receiving performances of conventional CIR analysis systems are not as good as those of commercial state-of-the-art receivers. There are difficulties in measuring and analyzing reception problems caused by multi-path interferences. To solve these problems, commercial DTV chip sets embedded CIR analysis system is proposed. Generally, commercial chip sets provide baseband (In-phase) channel data and field or segment sync data. For more precise analysis of measured I channel data, it is necessary to extract Q (quadrature) channel data components as well. This paper presents the technical requirements of CIR analysis system for DTV. In order to satisfy such requirements and measure more accurate magnitude and phase of CIR, a method to derive the quadrature data from the measured in-phase channel data is proposed. The proposed channel analysis system is implemented with a commercial DTV chip set and expedites the data analysis for use on DTV field test vehicles. Computer simulation and laboratory test results are provided to demonstrate the performance of the proposed channel analysis system.