• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권1호
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• pp.350-364
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• 2022

Traditionally, in multi-user multi-carrier systems, the neighboring subband will be gapped by one subcarrier, which is set as guard band to reduce multiple access interference (MAI) between neighboring subbands. The empty subcarrier for guard band will degrade the spectral efficiency of the whole system. In order to enhance the spectral efficiency of multi-user filter bank multiple carrier (FBMC) systems, a new subband allocation method is introduced, in which the neighboring subband is gapped by half subcarrier instead of one subcarrier. Meanwhile, in order to implement the proposed resource allocation scheme, an optimized FBMC prototype filter is designed to decrease the inter-subband interference to the neighboring subband. The detailed simulations about the comparison between the proposed spectrum assignment and traditional FBMC are given, as well as the performance in the different interference scenarios. The simulation results show that the combination of the proposed spectrum assignment scheme and the optimized filter has better performance compared to the traditional scheme. The proposed scheme can be used in the system which serves massive users to get higher spectrum efficiency.

• ETRI Journal
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• 제38권6호
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• pp.1153-1162
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• 2016

This paper addresses the resource allocation (RA) problem in multi-cell cognitive radio networks. Besides the interference power threshold to limit the interference on primary users PUs caused by cognitive users CUs, a proportional fairness constraint is used to guarantee fairness among multiple cognitive cells and the impact of imperfect spectrum sensing is taken into account. Additional constraints in typical real communication scenarios are also considered-such as a transmission power constraint of the cognitive base stations, unique subcarrier allocation to at most one CU, and others. The resulting RA problem belongs to the class of NP-hard problems. A computationally efficient optimal algorithm cannot therefore be found. Consequently, we propose a suboptimal RA algorithm composed of two modules: a subcarrier allocation module implemented by the immune algorithm, and a power control module using an improved sub-gradient method. To further enhance algorithm performance, these two modules are executed successively, and the sequence is repeated twice. We conduct extensive simulation experiments, which demonstrate that our proposed algorithm outperforms existing algorithms.

• Journal of the Optical Society of Korea
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• 제20권1호
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• pp.36-41
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• 2016

Visible Light Communication (VLC) using Light Emitting Diodes (LEDs) within the existing lighting infrastructure can reduce the implementation cost and may gain higher throughput than radio frequency (RF) or Infrared (IR) based wireless systems. Current indoor VLC systems may suffer from poor downlink resource allocation problems and small system throughput. To address these two issues, we propose an algorithm called a conflict graph scheduling (CGS) algorithm, including a conflict graph and a scheme that is based on the conflict graph. The conflict graph can ensure that users are able to transmit data without interference. The scheme considers the user fairness and system throughput, so that they both can get optimum values. Simulation results show that the proposed algorithm can guarantee significant improvement of system throughput under the premise of fairness.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권11호
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• pp.4387-4404
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• 2015

The energy-efficient design of sensing-based spectrum sharing of a multi-input and multi-output (MIMO) cognitive radio (CR) system with imperfect multiple antenna spectrum sensing is investigated in this study. Optimal resource allocation strategies, including sensing time and power allocation schemes, are studied to maximize the energy efficiency (EE) of the secondary base station under the transmit power and interference power constraints. EE problem is formulated as a nonlinear stochastic fractional programming of a nonconvex optimal problem. The EE problem is transformed into its equivalent nonlinear parametric programming and solved by one-dimension search algorithm. To reduce searching complexity, the search range was founded by demonstration. Furthermore, simulation results confirms that an optimal sensing time exists to maximize EE, and shows that EE is affected by the spectrum detection factors and corresponding constraints.

• Journal of Communications and Networks
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• 제12권5호
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• pp.449-458
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• 2010

In this paper, we present a distributed resource allocation algorithm for multi-cell uplink systems that increases the weighted sum of the average data rates over the entire network under the average transmit power constraint of each mobile station. For the distributed operation, we arrange each base station (BS) to allocate the resource such that its own utility gets maximized in a noncooperative way. We define the utility such that it incorporates both the weighted sum of the average rates in each cell and the induced interference to other cells, which helps to instigate implicit cooperation among the cells. Since the data rates of different cells are coupled through inter-cell interferences, the resource allocation taken by each BS evolves over iterations. We establish that the resource allocation converges to a unique fixed point under reasonable assumptions. We demonstrate through computer simulations that the proposed algorithm can improve the weighted sum of the average rates substantially without requiring any coordination among the base stations.

• 대한토목학회논문집
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• 제34권6호
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• pp.1911-1918
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• 2014

건설공사 프로젝트에서 인력 및 장비 등의 투입자원 증가는 공정간의 작업공간 간섭을 유발할 뿐만 아니라 프로젝트의 생산성과 품질에 영향을 미칠 수 있다. 이를 해결하기 위해 작업공간관련 연구가 수행되고 있으나, 단순히 공정들의 기하학적 위치만을 고려하여 작업공간을 검증하거나, 작업공간의 형상을 세부 작업별 분리된 형상이 아닌 일괄적 하나의 객체 형태로 생성하고 있다. 이러한 방식은 공정의 특성과 자원의 투입 시간에 따라 변화하는 작업공간의 크기를 반영하지 못하므로 합리적인 작업공간 충돌의 분석이 어렵게 된다. 이를 위해 본 연구에서는 공정과 자원의 특성에 적합한 작업공간의 형상과 크기를 생성할 수 있도록 작업공간의 3차원 모델 생성방법과 운용 시스템을 개발한다. 또한 이를 적용한 작업공간 간섭최적화 연계방안과 건설장비의 최적 이동경로 탐색 방법론을 개발하여 실무적 활용성을 검증한다.

• 한국통신학회논문지
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• 제31권6A호
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• pp.603-610
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• 2006

본 논문은 다중 셀 OFDMA(Orthogonal Frequency Division Multiple Access) 시스템에서 외곽 지역 사용자들의 QoS(Quality of Service)를 보장하기 위해 두 단계로 이루어진 자원 할당 알고리즘을 제안한다. 다중 셀 환경에서 셀 외곽 지역에 위치한 사용자들은 인접 셀에서 발생하는 동일 채널 간섭에 의한 수신 SINR(Signal to Interference and Noise Ratio)의 열화가 셀 내부 지역의 사용자들에 비해 심각하다. 제안하는 기법은 인접한 셀들의 외곽 사용자들 간 배타적 부반송파 할당과 전력 재할당을 통해 동일 채널 간섭을 억제한다. 모의실험 결과 외곽 지역의 데이터 전송률을 600Kbps이상 향상시킴으로써 지역 간 불균형한 서비스 제공 현상을 완화시켜 사용자수와 사용자의 셀 내 위치에 대해 안정적인 데이터 전송률을 지원하였다.

• 한국통신학회논문지
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• 제39A권9호
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• pp.548-556
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• 2014

최근 급증하는 데이터 트래픽에 효율적으로 대응하기 위해 매크로 기지국 영역에 매크로 기지국과 같은 주파수를 사용하는 소형 기지국이 공존하는 이종망에 관한 연구가 활발하게 진행 중이다. 이때, 매크로셀로부터 소형셀로의 간섭을 줄이기 위해 시간 영역에서 ABS (Almost Blank Subframe)을 이용한 enhanced Inter-cell Interference Coordination (eICIC) 기법이 제안되어 있다. 그러나 간섭 문제 해결을 위해 데이터를 전송하지 않는 서브프레임들이 발생함으로써 매크로셀 입장에서는 자원 낭비 문제가 발생한다. 본 논문에서는 능동 안테나 시스템 (AAS)과 Genetic Algorithm (GA)을 이용하여 소형 셀 방향으로 안테나 이득을 줄인 매크로 기지국의 3D 섹터 빔을 형성하여 셀간의 간섭신호 세기가 감소 되도록 하고 데이터 전송에 모든 서브프레임을 이용하여 낭비되는 자원이 없도록 한다. LTE -Advanced 시스템 레벨 시뮬레이터를 통해 기존 eICIC 기법과의 성능을 비교 분석하며, 제안된 기법의 성능 향상을 확인한다.

• Journal of Communications and Networks
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• 제16권6호
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• pp.627-638
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• 2014

In this paper, we study the joint price and power allocation in spectrum sharing macro-femtocell networks. The proposed game theoretic framework is based on bi-level Stackelberg game where macro base station (MBS) works as a leader and underlaid femto base stations (FBSs) work as followers. MBS has fixed data rate and imposes interference price on FBSs for maintaining its data rate and earns revenue while FBSs jointly adjust their power for maximizing their data rates and utility functions. Since the interference from FBSs to macro user equipment is kept under a given threshold and FBSs compete against each other for power allocation, there is a need to determine a power allocation strategy which converges to Stackelberg equilibrium. We consider two cases for MBS power allocation, i.e., fixed and dynamic power. MBS can adjust its power in case of dynamic power allocation according to its minimum data rate requirement and number of FBSs willing to share the spectrum. For both cases we consider uniform and non-uniform pricing where MBS charges same price to all FBSs for uniform pricing and different price to each FBS for non-uniform pricing according to its induced interference. We obtain unique closed form solution for each case if the co-interference at FBSs is assumed fixed. And an iterative algorithm which converges rapidly is also proposed to take into account the effect of co-tier interference on interference price and power allocation strategy. The results are explained with numerical simulation examples which validate the effectiveness of our proposed solutions.

• 한국전자파학회논문지
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• 제18권9호
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• pp.1077-1082
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• 2007

본 논문에서는 3${\sim}$10 GHz대 통신용 초광대역 시스템이 3.5 GHz대 고정(fixed) WiMAX(Worldwide Interoperability for Microwave Access)에 미치는 간섭 영향에 대해 고찰하였고, WiMAX에 미치는 잠정적인 간섭을 줄이기 위해 초광대역 시스템의 송신 전력을 제어하는 방법을 제안하였으며, 몬테카를로 시스템 레벨 시뮬레이션을 통해 간섭 저감 효과를 분석하였다. 간섭 영향은 단위 면적 1$km^2$내에 존재하는 다수의 초광대역 시스템과 단일 WiMAX 수신기를 가정하였을 때, 초광대역 시스템의 간섭에 의한 WiMAX의 outage 확률로 평가하였으며, 결과의 일례로써 초광대역 시스템의 밀도가 20$devices/km^2$이고 송신 전력 제어 동적 출력 범위가 30 dB일 때, 송신 전력 제어 방법을 적용한 경우 간섭 저감 방법을 적용하지 않는 경우보다 초광대역 시스템의 간섭에 의한 WiMAX의 outage 확률이 42 % 감소되는 효과를 보였다. 결론적으로 제안된 송신 전력 제어 방법은 초광대역 시스템이 WiMAX에 미치는 간섭 영향을 저감시린 수 있음을 보였다.