• 한국통신학회논문지
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• 제33권9B호
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• pp.775-785
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• 2008

We identify the problem of the current IEEE 802. lie HCCA (Hybrid Coordination Function Controlled Channel Access) scheduler and its numerous variations, that the queue information cannot be notified to the Hybrid Coordinator (HC) timely, therefore the uplink delay lengthens unnecessarily. We suggests a simple solution and a couple of implementation practices, namely the Adaptive Scheduler with RTS/CTS (ASR) and Adaptive Scheduler with Data/Ack (ASD). They are both further elaborated to emulate the Deficit Round Robin (DRB) scheduler. They are finally compared with existing exemplary schedulers through simulations, and shown to perform well.

• 한국멀티미디어학회:학술대회논문집
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• 한국멀티미디어학회 2000년도 추계학술발표논문집
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• pp.291-294
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• 2000

본 논문은 광대역 무선통신환경에서 3GPP(3rd Generation Partnership Project)에 기반한 비동기 IMT-2000 시스템의 송수신 시스템을 구성하여 기지국의 수신성능을 분석한다. 이동국과 기지국간의 Uplink채널 환경을 고려하였으며, 다중경로 페이딩(Multi-path Fading)채널과 다중접속간섭(Mult-Access Interference : MAI)에 의한 성능열화의 대책으로 Adaptive away 안테나와 동일채널 간섭제거기(Co-Channel Interference Canceler : CCI Canceller)를 직렬로 채용하였을 경우의 수신 성능을 수치해석을 통하여 분석하였다. Adaptive array 안테나는 방향성(Directivity : D=2.67) 이용하는 3-element array 안테나를 채용하였으며 성능분석 결과, Adaptive array 안테나와 간섭제거기를 직렬로 연결하였을 경우 다중접속간섭이 효과적으로 감소하여 수신성능이 큰 폭으로 향상됨을 알 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권11호
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• pp.5290-5304
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• 2016

With the growth of the massive amount of data, the failure probability of the cloud storage node is becoming more and more big. A single fault tolerance strategy, such as replication and erasure codes, has some unavoidable disadvantages, which can not meet the needs of the today's fault tolerance. Therefore, according to the file access frequency and size, an adaptive hybrid redundant fault tolerance strategy is proposed, which can dynamically change between the replication scheme and erasure codes scheme throughout the lifecycle. The experimental results show that the proposed scheme can not only save the storage space(reduced by 32% compared with replication), but also ensure the fast recovery of the node failures(increased by 42% compared with erasure codes).

• 인터넷정보학회논문지
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• 제19권2호
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• pp.9-15
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• 2018

This paper proposes an energy efficient adaptive relay station ON/OFF scheme with different frequency reuse factors (FRFs) to enhance the system throughput and reduce the transmission energy consumption for the transparent mode of 2-hop cellular relay networks (CRNs) based on orthogonal frequency division multiple access and time division duplex. In the proposed scheme, the base station turns on or off the relay stations (RSs) when they are overutilized and undertuilized based on the traffic density of the cell coverage, respectively. Through the simulation results, we show that the proposed scheme outperforms the conventional CRN in terms of the energy consumption with the same system throughput. Further, in order to increase the system throughput with low energy consumption, the best way is FRF 1 when the number of operating RSs is up to 4 and FRF 2 otherwise.

• 한국통신학회논문지
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• 제30권10C호
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• pp.976-982
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• 2005

In this paper, a channel-adaptive beamforming method is proposed for OFDMA (Orthogonal Frequency Division Multilexing Access) systems with smart antenna, in which the size of a cluster is determined adaptively depending on the frequency selectivity of the channel. The proposed method consists of 4 steps: initial channel estimation, refinement of channel estimates, region-splitting, and computation of weight vector for each region. In the proposed method, the size of a cluster for resource unit is determined adaptively according to a region-splitting criterion. It is shown by simulation that the proposed method shows good performances in both frequency-flat and frequency-selective channels.

• 한국통신학회논문지
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• 제27권3B호
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• pp.251-258
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• 2002

이 논문에서는 여러 반송파 직접수열 부호분할 다중접속 시스템에서 적응 부호율 길쌈부호화 방법을 살펴본다. 여러 가지 부호율을 쉽게 다를 수 있고 부호기와 복호기 얼개가 간단하도록 부호율 호환 구멍 뚫은 길쌈부호를(rate compatible punctured convolutional code: RCPC code) 쓴다. 데이터 처리량이 가장 많아지도록, 신호 대간섭과 잡음비 추정을 바탕으로 하는 적응 부호율 시스템을 제안한다. 제안한 적응 부호율 여러 반송파 직접수열부호분할 다중접속 시스템을 쓰면 주파수 대역 효율을 높이고 주파수 다양성을 얻을 수 있음을 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권1호
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• pp.287-304
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• 2012

Spectrum sensing is an important functionality for cognitive users to look for spectrum holes before taking transmission in dynamic spectrum access model. Unlike previous works that assume perfect knowledge of the SNR of the signal received from the primary user, in this paper we consider a realistic case where the SNR of the primary user's signal is unknown to both fusion center and cognitive radio terminals. A Kalman filter based adaptive Takagi and Sugeno's fuzzy system is designed to make the global spectrum sensing decision based on the observed energies from cognitive users. With the capacity of adapting system parameters, the fusion center can make a global sensing decision reliably without any requirement of channel state information, prior knowledge and prior probabilities of the primary user's signal. Numerical results prove that the sensing performance of the proposed scheme outperforms the performance of the equal gain combination based scheme, and matches the performance of the optimal soft combination scheme.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1998년도 학술발표대회 논문집 제17권 2호
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• pp.232-235
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• 1998

In this paper, we present the modified blind adaptive multiuser detector based on Constant Modulus Algorithm(CMA) for the demodulation of code-division multiple-access(CDMA) signals. Convergence issues are treated, and the performance of three algorithms is compared via computer simulations.

• 한국통신학회:학술대회논문집
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• 한국통신학회 2006년도 하계종합학술발표회 논문 초록집
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• pp.510-510
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• 2006

• 한국정보통신학회논문지
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• 제10권6호
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• pp.1060-1064
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• 2006

센서를 통해 수집된 데이터는 모든 정보를 취합하는 기지국으로 전송되게 된다. 센서들은 데이터를 전송하면서 지속적으로 주변 환경에 대한 데이터를 수집하여야 하기 때문에 에너지 소모가 크다. 본 논문에서는 수집된 데이터가 효율적으로 전송되어 트래픽 혼잡을 피하면서 에너지 효율성을 고려하는 기법을 제안한다. 트래픽이 증가하거나 감소할 때 전송률을 제어함으로써 Traffic 혼잡을 피하고, 기본적인 CSMA(Carrier Sense Multiple Access) 프로토콜에 최적의 옵션을 설정하여 각 센서에서 에너지 소모를 최소화는 기법이다. 시뮬레이션을 통해 최적의 CSMA 옵션과 제안된 트래픽 제어 기법을 적용하여 성능을 분석하고, 에너지 효율성과 효과적인 트래픽 제어 방법을 제시한다.