• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권7호
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• pp.1214-1229
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• 2011

Power control is a key technique in spectrum underlay cognitive network to guarantee the interference temperature limit of the primary users (PUs) and the quality of service of the secondary users (SUs). In this paper, a robust power control scheme via link gain pricing with $H_{\infty}$ estimator is proposed. The scheme guarantees the interference temperature of the PUs through operating in the network-centric manner, and keeps the fairness between the SUs through link gain pricing. Furthermore, the $H_{\infty}$ filter is also used in the proposed scheme to estimate the channel variation, and thus the power control scheme is robust to the severe channel fading. Plenty of simulations are taken, and prove its superior robust performance against the channel fading, and its effectiveness in guaranteeing the interference temperature limit of the PUs.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1992년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 19-21 Oct. 1992
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• pp.1051-1059
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• 1992

Two types of digital repetitive control systems are analyzed and designed to reduce the error spectrum including not only harmonic but also non-harmonic components. First, a novel gain scheduling algorithm is suggested for conventional and modified repetitive controller is scheduled to reduce the infinite norm of error in frequency domain. For this, the relative error transfer function is mewly defined as the ratio of the error spectrum for the system with a repetitive controller to the error spectrum for the system with a repetitive controller to the error spectrum for the system without a repetitive controller. Secondly, as an alternative of a repetitive control system with the gain scheduling, a repetitive control system with higher order repetitve function is analyzed and designed, where instead of equal weightings, weightings of the higher order repetitive function is determined in such a way that the infinite norm of relative error transfer function is minimized. To show the validities of proposed methods, computer simulation results are illustrated for a typical disk drive head positioning servo system.

• 한국전자파학회논문지
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• 제22권4호
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• pp.423-429
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• 2011

협력 스펙트럼 센싱은 스펙트럼 센싱의 신뢰성 및 정확도를 높이기 위해 다수의 CR 기기들이 정보를 공유하여 면허 사용자를 검출하는 방식이다. 이때, CR 기기의 센싱 결과를 융합하는 방식에 따라 경판정 방식(hard decision method)과 연판정 방식(soft decision method)으로 구별할 수 있다. 본 논문은 면허 사용자와 CR 기기 사이의 거리에 따른 가중치가 적용된 결합 방식(Distance based Weight Combining: DWC)을 사용하여 에너지 검출기반 협력 스펙트럼 센싱을 제안하고, 이에 따른 분석 및 모의 실험 결과를 나타낸다. 면허 사용자의 신호는 OFDM 기반의 시스템을 가정하였으며, 면허 사용자와 CR 기기 사이의 무선 채널은 가우시안(Gaussian) 채널로 모델링하였다. 에너지 검출법을 위한 임계값은 각 채널의 SNR(Signal to Noise Ratio)에 따라 다르게 적용되었으며, 각 채널의 잡음 신호의 평균값으로 가정하였다. DWC를 적용한 협력 스펙트럼 센싱을 수행한 결과, 거리에 따라 다양한 검출 확률을 나타낸 단일 센싱에 비해 비교적 안정된 검출 확률을 나타내는 것으로 알 수 있었으며, 동일 이득 결합을 반영하여 협력 스펙트럼 센싱을 수행한 것보다 우수한 스펙트럼 센싱을 나타내었다.

• Journal of Communications and Networks
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• 제16권2호
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• pp.140-145
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• 2014

In this paper, we propose an anti-interference cooperative spectrum sharing strategy for cognitive system, in which a secondary system can operate on the same spectrum of a primary system. Specifically, the primary system leases a fraction of its transmission time to the secondary system in exchange for cooperation to achieve the target rate. To gain access to the spectrum of the primary system, the secondary system needs to allocate a fraction of bandwidth to help forward the primary signal. As a reward, the secondary system can use the remaining bandwidth to transmit its own signal. The secondary system uses different bandwidth to transmit the primary and its own signal. Thus, there will be no interference felt at primary and secondary systems. We study the joint optimization of time and bandwidth allocation such that the transmission rate of the secondary system is maximized, while guaranteeing the primary system, as a higher priority, to achieve its target transmission rate. Numerical results show that the secondary system can gain significant improvement with the proposed strategy.

• The Journal of the Acoustical Society of Korea
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• 제27권1E호
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• pp.1-10
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• 2008

A noise suppression algorithm is proposed for nonstationary noisy environments. The proposed algorithm is different from the conventional approaches such as the spectral subtraction algorithm and the minimum statistics noise estimation algorithm in that it classifies speech and noise signals in time-frequency bins. It calculates the ratio of the variance of the noisy power spectrum in time-frequency bins to its normalized time-frequency average. If the ratio is greater than an adaptive threshold, speech is considered to be present. Our adaptive algorithm tracks the threshold and controls the trade-off between residual noise and distortion. The estimated clean speech power spectrum is obtained by a modified gain function and the updated noisy power spectrum of the time-frequency bin. This new algorithm has the advantages of simplicity and light computational load for estimating the noise. This algorithm reduces the residual noise significantly, and is superior to the conventional methods.

• Journal of the Optical Society of Korea
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• 제12권4호
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• pp.337-345
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• 2008

This article presents the RSOA-based re-modulation schemes for practical application to the WDM-PON link. Emphasis is put on the three methods for reducing the residual downstream signal in the upstream transmission; the simplest one is to use the RSOA gain-saturation property, the second uses selective filtering of the adiabatic-chirped DFB-LD output spectrum, and the last uses a dynamic RSOA gain control by varying its driving current according to the incident binary signal. The reflection sensitivity in the proposed re-modulation link is also qualitatively presented in the cases of using two different types of seed light: coherent light from DFB-LD array and spectrum-sliced incoherent ASE light. We show experimental results of an error-free bidirectional gigabit transmission over 20 km at -30 dB reflection with the spectrum-sliced ASE seed light.

• 한국ITS학회:학술대회논문집
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• 한국ITS학회 2010년도 춘계학술대회
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• pp.37-42
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• 2010

• 한국광학회지
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• 제29권1호
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• pp.32-39
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• 2018

The impact of the amplified spontaneous emission (ASE) on the gain recovery time of a bulk semiconductor optical amplifier (SOA) is investigated. The gain-recovery time is obtained by determining the time evolution of the gain, carrier density, and ASE in an SOA, after the propagation of a short pump pulse and continuous-wave (CW) probe of gain dynamics. In the simulation, a wide-band-semiconductor model, which can be characterized by the material gain coefficient over a wide wavelength range, is used, because the gain bandwidth of a practical SOA is very wide. The pump pulse and counterpropagating CW probe field are considered in the simulation, with the ASE noise spectrum equally divided.

• 대한전자공학회논문지TC
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• 제47권7호
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• pp.45-50
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• 2010

본 논문은 면허사용자와 CR기기 사이의 거리에 따른 가중치가 적용된 결합방식 (Distance based weight combining : DWC)을 사용하여 에너지 검출 기반 협력 스펙트럼 센싱을 제안하고 이에 따른 분석 및 모의실험 결과를 나타낸다. 면허사용자의 신호는 OFDM기반의 시스템을 가정하였으며 면허 사용자와 CR 기기 사이의 무선 채널은 가우시안 (Gaussian) 채널로 모델링 하였다. 에너지 검출법을 위한 임계값은 각 채널의 SNR (Signal to Noise Ratio)에 따라 다르게 적용되었으며 각 채널의 잡음신호의 평균값으로 가정하였다. DWC를 적용한 협력 스펙트럼 센싱을 수행한 결과 거리에 따라 다양한 검출확률을 나타낸 단일 센싱에 비해 비교적 안정된 검출확률을 나타내는 것으로 알 수 있었으며, 동일이득 결합을 반영하여 협력스펙트럼 센싱을 수행한 것 보다 우수한 스펙트럼 센싱을 나타내었다.

• 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.