• 한국통신학회논문지
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• 제41권6호
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• pp.663-671
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• 2016

인터넷 트래픽양의 급증에 따라 고속 라우터의 수요가 많아졌다. 트래픽 통계 또는 보안 등의 목적으로 라우터에서 패킷을 측정해야 하는데 고속 라우터의 특성상 메모리공간이 제한적이다. RCC는 적은 메모리로 트래픽을 정확하고 효율적으로 측정하는 방법을 제시했다. RCC에서는 트래픽을 측정하는데 큰 Flow를 추가적인 Quadratic Probing 기반 해시 테이블에 누적하는 방법 사용한다. 그런데 Quadratic Probing은 적은 메모리 또는 메모리 사용률이 많은 상황에서 연산량이 많으며, 특히 갱신 또는 실시간 조회가 자주 발생하는 시스템에서 오버헤드가 크다. 이 논문에서는 RCC의 특성을 분석하고 실험을 통해 Quadratic Probing의 문제점을 증명하며 갱신 또는 조회에 효율적인 Cuckoo Hashing을 사용하여 RCC의 성능을 개선한다. 실험 결과에 따르면 RCC에서 Cuckoo Hashing을 사용할 때 메모리 사용률이 높은 상황에서도 높은 정확도를 보여주었고, 효율적으로 트래픽을 측정할 수 있었다.

• 대한조선학회논문집
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• 제51권4호
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• pp.274-282
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• 2014

Time series of the dynamic response of a slender marine structure was predicted using quadratic Volterra series. The wave-structure interaction system was identified using the NARX(Nonlinear Autoregressive with Exogenous Input) technique, and the network parameters were determined through the supervised training with the prepared datasets. The dataset used for the network training was obtained by carrying out the nonlinear finite element analysis on the freely standing riser under random ocean waves of white noise. The nonlinearities involved in the analysis were both large deformation of the structure under consideration and the quadratic term of relative velocity between the water particle and structure in Morison formula. The linear and quadratic frequency response functions of the given system were extracted using the multi-tone harmonic probing method and the time series of response of the structure was predicted using the quadratic Volterra series. In order to check the applicability of the method, the response of structure under the realistic ocean wave environment with given significant wave height and modal period was predicted and compared with the nonlinear time domain simulation results. It turned out that the predicted time series of the response of structure with quadratic Volterra series successfully captures the slowly varying response with reasonably good accuracy. It is expected that the method can be used in predicting the response of the slender offshore structure exposed to the Morison type load without relying on the computationally expensive time domain analysis, especially for the screening purpose.

• 전기학회논문지
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• 제61권3호
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• pp.451-458
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• 2012

This paper addresses the problem that policy iteration (PI) for continuous-time (CT) systems requires explorations of the state space which is known as persistency of excitation in adaptive control community, and as a result, proposes a PI scheme explorized by an additional probing signal to solve the addressed problem. The proposed PI method efficiently finds in online fashion the related CT linear quadratic (LQ) optimal control without knowing the system matrix A, and guarantees the stability and convergence to the LQ optimal control, which is proven in this paper in the presence of the probing signal. A design method for the probing signal is also presented to balance the exploration of the state space and the control performance. Finally, several simulation results are provided to verify the effectiveness of the proposed explorized PI method.

• 대한의용생체공학회:의공학회지
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• 제16권4호
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• pp.525-532
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• 1995

이 연구는 다음 두가지 사실에 기초를 두고 있다. 첫째, 혈관의 맥동은 전통적으로 동양의 한방에서 오랫동안 인체진단을 위해 사용되어져 왔다는 것이고, 둘째는 신체조직에서 파동의 비선형전파특성이 의용진단에 유용한 정보를 준다는 것이다. 따라서, 혈관의 벽을 전파하는 맥동파의 비선형전파특성은 의용진단을 위하여 효과적으로 이용될 수 있다는 것을 예측할 수 있다. 본 논문에서는, 혈관을 따른 두 지점에서 변위파형을 초음파 도플러 신호에 대한 직교검파에 의해 구하고, 여기에 바이스펙트럼해석과 볼테라모델전개를 적용하여 두지점 사이의 비선형 전달함수를 추정하며, 이것이 의용진단에 적용가능한지 모의샘플에 대하여 고찰하는 것을 목적으로 한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권7호
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• pp.3057-3075
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• 2020

End-to-end network delay plays an vital role in distributed services. This delay is used to measure QoS (Quality-of-Service). It would be beneficial to know all node-pair delay information, but unfortunately it is not feasible in practice because the use of active probing will cause a quadratic growth in overhead. Alternatively, using the measured network delay to estimate the unknown network delay is an economical method. In this paper, we adopt the state-of-the-art matrix completion technology to better estimate the network delay from limited measurements. Although the number of measurements required for an exact matrix completion is theoretically bounded, it is practically less helpful. Therefore, we propose an online adaptive sampling algorithm to measure network delay in which statistical leverage scores are used to select potential matrix elements. The basic principle behind is to sample the elements with larger leverage scores to keep the traits of important rows or columns in the matrix. The amount of samples is adaptively decided by a proposed stopping condition. Simulation results based on real delay matrix show that compared with the traditional sampling algorithm, our proposed sampling algorithm can provide better performance (smaller estimation error and less convergence pressure) at a lower cost (fewer samples and shorter processing time).