• 방송공학회논문지
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• 제14권1호
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• pp.89-92
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• 2009

본 논문에서는 위치인식기반 WPAN에 적용 가능한 무선인지 기술 중에서 BBA 기반의 전력할당기법에 논의한다.. Cognitive Radio 환경을 벗어난 서비스영역 밖에 있는 CR사용자의 관점에서 통신이 가능하게 하는 방법을 찾는 것이 관점이다. CR에서는 서비스 영역 밖에서는 통신을 하지 못하도록 규정을 하고 있다. 그 이유는 주사용자가 서비스를 제공받는데 피해나 간섭의 영향을 최소화하기 위해서이며, 이런 것이 선행되지 않고서는 값비싼 주파수라는 자원을 공유하기를 꺼려 하기 때문이다. 하지만 이와 같은 피해를 주지 않게 보장을 한다면 CR사용자는 서비스 영역 밖에서도 충분히 서비스를 제공받을 수 있게 된다. 그 방법을 BBA(Bi-directional Beamforming Antenna), 즉 지향성 양방향 안테나를 이용하여 가능한 방법을 제시하려 한다.

• 한국콘텐츠학회논문지
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• 제8권8호
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• pp.28-36
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• 2008

주파수 자원 가치는 무선통신의 발전과 함께 더욱 커지고 있다. 하지만 앞으로 정보화 사회에서는 주파수 자원의 수요가 공급에 비하여 매우 많기 때문에 주파수 부족 현상이 심각하게 대두된다. 따라서 사용되지 않고 있는 주파수 자원을 효율적으로 이용하기 위한 기술로서 최근 각광을 받고 있는 Cognitive Radio(CR) 기술이 필요한 시점이다. 본 논문은 임베디드 보드에서 CR 기반의 효율적인 Spectrum Sensing 기법을 적용하였다. 현재 이론적으로 제시되어 있는 여러 Spectrum Sensing 기법들에 대해 살펴보고 이 기법들을 CR 환경이 구현된 임베디드 플랫폼에 적용시켜 MAC 메시지를 통해 성능을 검증하였다.

• ETRI Journal
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• 제34권2호
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• pp.175-183
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• 2012

Conventional synchronization algorithms for impulse radio require high-speed sampling and a precise local clock. Here, a phase-locked loop (PLL) scheme is introduced to acquire and track periodical impulses. The proposed impulse PLL (iPLL) is analyzed under an ideal Gaussian noise channel and multipath environment. The timing synchronization can be recovered directly from the locked frequency and phase. To make full use of the high harmonics of the received impulses efficiently in synchronization, the switching phase detector is applied in iPLL. It is capable of obtaining higher loop gain without a rise in timing errors. In different environments, simulations verify our analysis and show about one-tenth of the root mean square errors of conventional impulse synchronizations. The developed iPLL prototype applied in a high-speed ultra-wideband transceiver shows its feasibility, low complexity, and high precision.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권8호
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• pp.3821-3841
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• 2019

Cloud radio access networks (C-RANs) have been regarded in recent times as a promising concept in future 5G technologies where all DSP processors are moved into a central base band unit (BBU) pool in the cloud, and distributed remote radio heads (RRHs) compress and forward received radio signals from mobile users to the BBUs through radio links. In such dynamic environment, automatic decision-making approaches, such as artificial intelligence based deep reinforcement learning (DRL), become imperative in designing new solutions. In this paper, we propose a generic framework of autonomous cell activation and customized physical resource allocation schemes for energy consumption and QoS optimization in wireless networks. We formulate the problem as fractional power control with bandwidth adaptation and full power control and bandwidth allocation models and set up a Q-learning model to satisfy the QoS requirements of users and to achieve low energy consumption with the minimum number of active RRHs under varying traffic demand and network densities. Extensive simulations are conducted to show the effectiveness of our proposed solution compared to existing schemes.

• 전기전자학회논문지
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• 제25권1호
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• pp.53-63
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• 2021

여러 분야에서 전파 장비가 복잡해지고 다양해지면서 주파수 간섭으로 인한 문제가 빈번하게 발생하고 있다. 특히, 국내의 상황은 협소한 영토에서 전파환경이 우수한 특정 고지대에 다수의 시스템이 밀집해 있으며, 동일 대역의 고출력 신호를 송신하는 레이다 시스템이 근거리에 배치되어 운용되는 경우도 발생하고 있다. 본 논문에서는 실제 전파간섭 현상에 대하여 간섭의 형태를 구분하고 적절한 신호간섭 파라미터를 도출하였다. 이것을 간섭기법에 반영하여 간섭신호의 전력밀도를 예측하고 실 측정을 통하여 유효성을 검증한 결과를 바탕으로 간섭시스템과 피해시스템의 운용시나리오를 분석하여 간섭을 최소화 할 수 있는 방법을 제안한다.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2011년도 하계학술대회
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• pp.137-140
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• 2011

A precoding strategy is one of the representative interference management techniques in cognitive radio (CR) network which is a typical interference-limited environment. The interference minimization approach to precoding is an appropriate scheme to mitigate the interference efficiently while it may cause the capacity loss of the desired channel. The precoding scheme for the maximal capacity of the desired channel improves the capacity of the desired channel while it increases the interference power and finally causes the capacity loss of the interfered users. Therefore, we propose a precoding scheme which satisfies these two conflicting goals and manages the interference signal in such an interference-limited environment. The proposed scheme consists of two steps. First, the precoder nulls out the largest singular value of the interference channel to mitigate the dominant interference signal based on the interference minimization approach. Second, the transmitter calculates the sum capacities per mode and selects a mode to maximize the sum capacity. In the second step, each mode consists of the right singular vectors corresponding to the singular values except the largest singular value eliminated in the first step. Simulation results show that the proposed precoding scheme not only efficiently mitigate the interference signal, but also has the best performance in terms of the sum capacity in a MIMO-based CR network.

• Journal of Communications and Networks
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• 제7권3호
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• pp.377-384
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• 2005

The purpose of this research is to develop and evaluate a traffic engineering architecture that uses local state information. This architecture is applied to an Internet protocol radio access network (RAN) that uses multi-protocol label switching (MPLS) and differentiated services to support mobile hosts. We assume mobility support is provided by a protocol such as the hierarchical mobile Internet protocol. The traffic engineering architecture is router based-meaning that routers on the edges of the network make the decisions onto which paths to place admitted traffic. We propose an algorithm that supports the architecture and uses local network state in order to function. The goal of the architecture is to provide an inexpensive and fast method to reduce network congestion while increasing the quality of service (QoS) level when compared to traditional routing and traffic engineering techniques. We use a number of different mobility scenarios and a mix of different types of traffic to evaluate our architecture and algorithm. We use the network simulator ns-2 as the core of our simulation environment. Around this core we built a system of pre-simulation, during simulation, and post-processing software that enabled us to simulate our traffic engineering architecture with only very minimal changes to the core ns-2 software. Our simulation environment supports a number of different mobility scenarios and a mix of different types of traffic to evaluate our architecture and algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권6호
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• pp.1023-1041
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• 2010

In cognitive radio networks, cooperative spectrum sensing schemes are proposed to improve the performance of detecting licensees by secondary users. Commonly, the cooperative sensing can be realized by means of hard decision fusion (HDF) or soft decision fusion (SDF) schemes. The SDF schemes are superior to the HDF ones in terms of the detection performance whereas the HDF schemes are outperforming the SDF ones when the traffic overhead is taken into account. In this paper, a hybrid SFD-HDF cluster-based approach is developed to jointly exploit the advantages of SFD and HDF schemes. Different SDF schemes have been proposed and compared within a given cluster whereas the OR-rule base HDF scheme is applied to combine the decisions reported by cluster headers to a common receiver or base station. The computer simulations show promising results as the performance of the proposed scenario of hybridizing soft and hard fusion schemes is significantly outperforming other different combinations of conventional SDF and HDF schemes while it noticeably reduces the network traffic overhead.

• 한국통신학회논문지
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• 제35권3B호
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• pp.474-484
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• 2010

본 연구에서는 항공화물 터미널 내에서의 항공화물 관리를 위해 RFID(Radio Frequency Identification, 무선인식)를 기반으로 하는 실시간 모니터링시스템개발을 소개한다. 시스템의 개발에 앞서 필요한 기능을 구현하고 개발 프레임워크를 구성하기 위해 인천공항 화물 터미널을 대상으로 요구사항을 분석하였으며 요구사항 분석에 따라 실시간 관리 기능을 구현하기 위해 RFID 기술에 대한 도입 방안을 연구하였다. RFID 기술의 적용 가능성을 실험하기 위해 인천공항 화물 터미널에서 RFID 장비들에 대한 성능을 실험하였고 예상되는 문제점들에 대한 분석을 위해 동일한 지점에서의 전파환경을 분석하였다. 위의 연구 결과들을 토대로 항공화물에 대한 모니터링 솔루션의 전체적인 시스템 구성은 EPC 네트워크를 기반으로 하였으며 시스템 구현의 유연성 및 확장성을 고려하여 시스템 아키텍처에 비즈니스 모델에 대한 시스템적인 정의를 위한 BPM(Business Process Modeling)솔루션을 도입하고 모니터링 솔루션은 웹 기반으로 개발하였다.

• 대한전자공학회논문지
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• 제27권4호
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• pp.491-501
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• 1990

Recently, four speech coding techniques, namely, SBC-APCM(sub-band coding adaptive PCM), RPE-LPC(regualr pulse excitation linear predictive codec), MPE-LTP(multi-pulse excited long-term prediction) and CELP (code-excited linear prediction) are proposed for digital mobile radio applications. However, a performance comparison of these coders in the Rayleigh fading environment has not been made yet. In this paper, the performances of the four spech coders in the random bit error and burst error environment are investigated. For the channel coding of SBC-APCM, RPE-LPC and MPE-LTP, the sensitivity of output bit stream is measured and a bit selective forward error correction is provided acording to the measured bit sensitivity. And for an attempt to improve the performance of CELP, an optimum quantizer is applied for transmitting scalar quantities in CELP. However, an improvement over the conventional approach is found to be negligible. For the channel coding of CELP, Reed-Solomon code, Golay code, convolutional code of rate 1/2 shows the best performance. Finally, from the simulation results, it is concluded that CELP is the best candidate for digital mobile radio and is followed by MPE-LTP, SBC-APCM and RPE-LPC.