• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.3 s.106
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• pp.307-316
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• 2006

In this paper the analytical method, namely advanced minimum coupling loss(A-MCL), was proposed in order to analyze the coexistence of OFDM-based systems beyond 3G(B3G) with point-to point(PP) fixed service(FS) microwave systems. Our proposed method is based on a power spectral density(PSD) analysis. So it can be easily applicable to analyze the coexistence of OFDM-based systems B3G using flexible spectrum usage(FSU) with other systems, where the conventional MCL method cannot allocate transmit power partially to some subcarriers which overlap the band of a victim system. By applying the conventional MCL method and the A-MCL method, interfering power levels at the receiver of a interfered system are respectively calculated. A-MCL can calculate interference power more accurately than MCL by the maximum value of 4.5 dB. Therefore it can be concluded that our prosed method, namely A-MCL, is applicable to a sharing analysis of OFDM-based systems B3G.

• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2005.11a
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• pp.187-190
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• 2005

Ultra wideband (UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geolocation, and other applications. The energy of UWB signal is extremely spread from near DC to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional mobile wireless systems sharing the frequency bands such as WCDMA system. This paper experimentally evaluates the interference from two kinds of UWB sources, namely a direct-sequence spread-spectrum UWB source and an impulse radio UWB source, to a WCDMA digital transmission system. The average frame error rate degradations are presented. From these experimental results, we show that in all practical cases UWB system can coexist with WCDMA terminal without causing any dangerous interference.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.6
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• pp.11-22
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• 1996

We address an issue of channel sharing among users by using a random assignment-transmitter-based (RA-T) spread-spectrum transmission scheme which permits the contention mode only in the transmission of a header while avoiding collision during the data packet transmission. Once the header being successfully received, the data packet is ready for reception by switching to one of programmable matched-filters. But the receoption may be blocked due to limited number of matched-filters so that this effect is taken into account in our analysis. For realistic analysis, we integrate detection performance at the physical level with channel activity at the link level through a markov chain model. We also consider an acknowledgement scheme to notify whether the header is correctly detcted and the data packet can be processed continuously, which aims at reducing the interference caused unwanted data transmission. It is shown that receiver complexity can be greatly reduced by choosing a proper number of RA codes at the cost of only a little throughput degradation.

• Journal of Satellite, Information and Communications
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• v.8 no.1
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• pp.66-70
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• 2013

In this paper, Threshold setting method is proposed to improve detection probability for cooperative sensing. Even if cooperative users have all same false alarm rate, each user has different threshold due to pass ad-hoc channel. threshold level is related to detection probability. So, we select the highest threshold among cooperative users and then share threshold information for getting the high detection probability.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.1
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• pp.145-150
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• 2010

In this paper, the performance of cognitive radio network is analyzed in terms of Erlang capacity. To improve the Erlang capacity with respect to primary user (PU) and secondary user (SU) traffic, we propose an efficient radio resource management scheme utilizing the buffer for new SUs and interrupted SUs. Markov model is developed, and analyzed to derive the performances of the proposed spectrum sharing scheme in both primary system and secondary system. To determine the Erlang capacity region, the blocking probability, the forced termination probability and the non-completion probability are calculated. Simulation results provide insight into the advantages of the buffer utilization. It is observed that the supportable traffic loads of PU and SU can be increased significantly according to the buffer length.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.10
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• pp.2455-2472
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• 2012

Although underlay spectrum sharing has been shown as a promising technique to promote the spectrum utilization in cognitive radio networks (CRNs), it may suffer bad secondary performance due to the strict power constraints imposed at secondary systems and the interference from primary systems. In this paper, we propose a two-phase based cooperative transmission protocol with the interference cancellation (IC) and best-relay selection to improve the secondary performance in underlay models under stringent power constraints while ensuring the primary quality-of-service (QoS). In the proposed protocol, IC is employed at both the secondary relays and the secondary destination, where the IC-based best-relay selection and cooperative relaying schemes are well developed to reduce the interference from primary systems. The closed-form expression of secondary outage probability is derived for the proposed protocol over Rayleigh fading channels. Simulation results show that, with a guaranteed primary outage probability, the proposed protocol can achieve not only lower secondary outage probability but also higher secondary diversity order than the traditional underlay case.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.3
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• pp.1057-1073
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• 2015

In this paper, we consider cooperative D2D communications in cellular networks. More precisely, a cellular user leases part of its spectrum to facilitate the D2D communication with a goal of improving the energy efficiency of a D2D pair. However the D2D pair is untrusted to the cellular user, such resource sharing may result in the information of this cellular user unsecured. In order to motivate the cellular user's generosity, this D2D pair needs to help the cellular user maintain a target secrecy rate. To address this issue, we formulate a joint spectrum and power allocation problem to maximize the energy efficiency of the D2D communication while guaranteeing the physical layer security of the cellular user. Then, a theorem is proved to indicate the best resource allocation strategy, and accordingly, an algorithm is proposed to find the best solution to this resource allocation problem. Numerical results are finally presented to verify the validity and effectiveness of the proposed algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.3
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• pp.273-288
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• 2010

In this paper, we propose a cooperative multi-relay scheme for a secondary system to achieve spectrum access along with a primary system. In the primary network, a primary transmitter (PT) transmits the primary signal to a primary receiver (PR). In the secondary network, N secondary transmitter-receiver pairs (ST-SR) selected by a centralized control unit (CCU) are ready to assist the primary network. In particular, in the first time slot, PT broadcasts the primary signal to PR, which is also received by STs and SRs. At STs, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions of the available power to the primary and secondary signals respectively. The combined signal is then broadcasted by STs in a predetermined order. In order to achieve diversity gain, STs, SRs and PT will combine received replicas of the primary signal, using selection combining technique (SC). We derive the exact outage probability for the primary network as well as the secondary network. The simulation results are presented to verify the theoretical analyses.

• Electronics and Telecommunications Trends
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• v.27 no.6
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• pp.94-103
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• 2012

스마트폰, 태블릿 PC 등 정보 기술의 급속한 확대로 주파수 수요가 증가하여 세계 각국은 모바일 데이터 트래픽 수용을 위한 주파수 확보에 노력하고 있다. 미국은 원활한 주파수 확보를 통한 초고속 광대역 통신망의 확충이 통신 분야에서 미래 국제 경쟁력 확보에 필수적이라는 것을 인식하고, 새로운 대역에서 모바일 주파수를 확보하는 노력뿐 아니라 기존 대역에서 1차 사용자를 보호하며 공유할 수 있는 공유 주파수 자원의 확보도 추진하고 있다. 주파수 공유를 도입하면 필요한 주파수를 짧은 기간에 경제적인 가격으로 확보 가능하다는 장점이 있다. 본고는 미국에서 주파수 공유를 위해 도입하는 최근의 스펙트럼 정책 동향에 대해 기술하고자 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.10
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• pp.898-907
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• 2013

For D2D communications underlaying cellular networks, it is essential to consider the mutual interference between the existing cellular communications and D2D communications as well as the spectral efficiency, as they need to share the same frequency. Accordingly, a resource allocation scheme should be designed in such a way that minimizes the mutual interference and maximizes the spectrum utilization efficiency at the same time. In this paper, we propose a resource allocation scheme based on cooperation of the base station and D2D terminals. Specifically, a D2D terminal senses the cellular spectrum to recognize the interference condition, chooses the best cellular resource, and reports the information to the base station. The base station allocates D2D resource such that the corresponding D2D link and cellular link share the same resource. The performance of the proposed resource allocation scheme is ated through compu under 3GPP LTE-Advanced scenarios.