• 한국정보과학회논문지:정보통신
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• 제37권3호
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• pp.249-253
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• 2010

폭발적인 트래픽 양의 증가와 함께 ISM 대역과 같이 라이선스가 필요 없는 주파수 대역의 포화상태로 인하여 무선네트워크의 주파수 자원이 점점 부족해지고 있다. 그러나 반대로 라이선스 주파수 대역의 이용률은 극히 저조한 상태라는 것이 여러 실험결과를 통해 알려졌다. 이러한 라이선스 주파수의 비효율적인 측면을 완화하기 위해 최근 인지라디오 기술이 제안되고 있다. 인지라디오는 비록 라이선스가 없는 사용자라도 라이선스 사용자를 방해하지 않는 한에서 라이선스 주파수 대역을 사용할 수 있도록 하는 기술로써 라이선스 주파수 대역을 좀 더 효율적으로 사용할 수 있게 하는 기술이다. IEEE 802.22는 인지 라디오를 기반으로 하는 첫 번째 표준 무선네트워크이다. IEEE 802.22는 라이선스 사용자의 충분한 보호와 주파수 대역 사용의 효율성을 극대화 하기 위해 Two-Stage 채널 센싱 기법을 제안하고 있다. 본 논문에서는 Two-Stage 채널 센싱의 오버헤드를 분석하고 센싱에 사용되는 시간이 오버헤드에 미치는 영향을 알아보고자 한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권2호
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• pp.580-592
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• 2012

In this paper, a new compressive feedback (CF) scheme based on distributed compressed sensing (DCS) for time-corrected MIMO channel is proposed. First, the channel state information (CSI) is approximated by using a subspace matrix, then, the approximated CSI is compressed using a compressive matrix. At the base station, the approximated CSI can be robust recovered with simultaneous orthogonal matching pursuit (SOMP) algorithm by using forgone CSIs. Simulation results show our proposed DCS-CF method can improve the reliability of system without creating a large performance loss.

• 한국통신학회논문지
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• 제41권1호
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• pp.86-88
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• 2016

이전 연구에서 협력 스펙트럼 센싱을 위한 효율적인 보고 채널 전송 방식으로 이차 사용자의 센싱 결정을 융합 센터로 동시에 전달하는 방식이 제안된 바가 있다. 본 논문에서는 이 방식의 보고 채널에 대한 전송 오류를 경감하는 방안을 제시하고, 모의 실험을 통해 그 성능을 평가하고자 한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권10호
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• pp.4034-4053
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• 2015

In order to meet various requirements for transmission quality of both primary users (PUs) and secondary users (SUs) in cognitive radio networks, we introduce a channel bonding mechanism for PUs and a channel reservation mechanism for SUs, then we propose a novel spectrum allocation strategy. Taking into account the mistake detection and false alarm due to imperfect channel sensing, we establish a three-dimensional Markov chain to model the stochastic process of the proposed strategy. Using the method of matrix geometric solution, we derive the performance measures in terms of interference rate of PU packets, average delay and throughput of SU packets. Moreover, we investigate the influence of the number of the reserved (resp. licensed) channels on the system performance with numerical experiments. Finally, to optimize the proposed strategy socially, we provide a charging policy for SU packets.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권8호
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• pp.1754-1769
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• 2013

For the purpose of enhancing the spectrum efficiency, cognitive radio (CR) technology has been recently proposed as a promising dynamic spectrum allocation paradigm. In CR, spectrum sensing is the key capability of secondary users in a cognitive radio network that aims for reducing the probability of harmful interference with primary users. However, the individual CRs might not be able to carry out reliable detection of the presence of a primary radio due to the impact of channel fading or shadowing. This paper studies the cooperative spectrum sensing scheme as means of optimizing the sensing performance in AWGN and Rayleigh channels. Results generated from simulation provide evidence of the impact of channel condition on the complementary receiver operating characteristic (ROC). Based on the results, it was found that with constant local SNRs at the secondary users, the probability of missed detection ($P_m$) of cooperative spectrum sensing in a cognitive radio network, calculated using a closed form expression, can be significantly minimized. Thus, the paper illustrates that improvement of the detection performance of the CR network can be achieved by establishing a centralized cooperation among neighboring cognitive radio users. Finally, verification of the validity of the fusion schemes utilized for combining the individual CR decisions is provided.

• 한국ITS학회:학술대회논문집
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• 한국ITS학회 2010년도 춘계학술대회
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• pp.18-21
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• 2010

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2400-2413
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• 2019

Doubly-selective (DS) fading channel is often occurred in many orthogonal frequency division multiplexing (OFDM) communication systems, such as high-speed rail communication systems and underwater acoustic (UWA) wireless networks. It is challenging to provide an accurate and fast estimation over the doubly-selective channel, due to the strong Doppler shift. This paper addresses the doubly selective channel estimation problem based on complex exponential basis expansion model (CE-BEM) in OFDM systems from the perspective of distributed compressive sensing (DCS). We propose a novel DCS-based improved sparsity adaptive matching pursuit (DCS-IMSAMP) algorithm. The advantage of the proposed algorithm is that it can exploit the joint channel sparsity information using dynamic threshold, variable step size and tailoring mechanism. Simulation results show that the proposed algorithm achieves 5dB performance gain with faster operation speed, in comparison with traditional DCS-based sparsity adaptive matching pursuit (DCS-SAMP) algorithm.

• 전기학회논문지
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• 제58권1호
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• pp.147-154
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• 2009

This paper presents a grating~integrated SPR (Surface Plasmon Resonance) sensor chip for simple and inexpensive biomolecule detection. The grating-integrated SPR sensor chip has two sensing channels having a nano grating for SPR coupling. An external mirror is used for multi channel SPR sensing. The present sensor chip replaces bulky and expensive optical components, such as fiber-optic switches or special shaped prisms, resulting in a simple and inexpensive wavelength modulated multi-channel SPR sensing system. We fabricate a SPR sensor chip integrated with 835 nm-pitch gratings by a micromolding technique to reduce the fabrication cost. In the experimental characterization, the refractive index sensitivity of each sensing channel is measured as $321.8{\pm}8.1nm$/RI and $514.3{\pm}8.lnm$/RI, respectively. 0.5uM of the target biomolecule (streptavidin) was detected by a $1.13{\pm}0.16nm$ shift of the SPR dip in the 10%-biotinylated sample channel, while the SPR dip in the reference channel for environmental perturbation monitoring remained at the same position. From the experimental results, multi-channel biomolecule detection capability of the present grating-integrated SPR sensor chip has been verified. On the basis of the preliminary experiments, we successfully measured the binding reaction rate for the $2\;nM{\sim}200\;nM$ monoclonal-antibiotin, thus verifying biomolecule concentration detectability of the present SPR sensor chip. The binding reaction rates measured from the present SPR sensor chip agredd well with those from a commercialized SPR sensor.

• 한국통신학회논문지
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• 제34권6A호
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• pp.484-493
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• 2009

최근 한정된 주파수의 사용 효율성을 높이기 위해 Cognitive Radio 시스템의 허가 주파수 대역 사용을 제한적으로 용인하는 CR 기술이 각광받고 있다. CR 기술에서 최우선적으로 고려되어야 할 사항은 주 사용자의 통신을 보호하는 것이다. 즉 CR 사용자는 주 사용자의 출현을 인지하는 즉시 현재 채널의 사용을 중지해야 하며, 이러한 상황을 사전에 고려하여, 운용이 가능한 주파수 대역을 폭넓게 확보해야 한다. 이를 위해 CR 사용자는 지속적인 스펙트럼 센싱을 수행한다. CR 사용자가 스펙트럼을 센싱하는 동안에는 이용 중인 서비스가 일시적으로 중단되는 현상이 발생한다. 본 논문에서는 주 사용자를 보호하기 위한 CR 센싱 요구조건을 만족하는 전제 하에, CR 사용자의 QoS를 최대한 보장하면서 스펙트럼 센싱을 수행하도록 하는 채널 센싱 스케쥴링 방법을 제안한다. 이를 위해, 센싱할 채널의 개수와 센싱 주기를 CR 센싱 요구조건의 주요 지표로 이용하였고, CR 사용자의 QoS 보장 요구사항은 패킷 지연과 손실 측면에서 분석하였다. 위의 센싱 스케쥴링 방법을 수치 분석을 통해 여러 파라미터들을 다양하게 변화시킴으로서, 다양한 환경에서 QoS를 만족시킬 수 있는 적합한 파라미터를 구할 수 있었다. 그리고 성능 평가를 통해 채널을 연속적으로 센싱하는 방법과 두 가지 측면, Delay와 성공적으로 전송한 패킷의 수를 비교하였을 때 우수한 성능을 나타냄을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권7호
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• pp.2212-2230
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• 2014

Cognitive radio (CR) users, known as secondary users (SUs), should avoid interference with primary users (PUs) who own the licensed band, while trying to access it; when the licensed band is unused by the PUs. To detect PUs, spectrum sensing should be performed over in-band channels that are currently in use by SUs. If PUs return to access the band, SUs need to vacate it, disrupting the SUs' communication unless a non-utilized band is discovered. Obtaining a non-utilized band in a short period facilitate seamless communication for SUs and avoid interference on PUs by vacating from the channel immediately. Searching for a non-utilized band can be done through proactive out-of-band (OB) sensing. In this paper, we suggest a proactive OB sensing scheme that minimizes the time required to discover a non-utilized spectrum in order to continue communication. Although, the duration spent on OB sensing reduces the throughput of the CR networks that can be achieved on band being utilized, the lost throughput can be compensated in the new discovered band. We demonstrate that, the effect of our proposed scheme on the throughput owing to OB sensing is insignificant, while exhibiting a very short channel discovery time.