• 한국통신학회논문지
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• 제34권5A호
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• pp.421-428
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• 2009

Inter-cell coordination has been an emerging issue for mitigating inter-cell interference in broadband wireless access networks such as IEEE802.16 and 3GPP LTE (Long Term Evolution). This paper proposes uplink/downlink hybrid inter-cell coordination patterns for a TDD (Time Division Duplex)/MC-CDMA (Multi-Carrier Code Division Multiple Access) system. For the performance analysis, closed forms of inter-cell interferences are derived when uplink and downlink transmissions coexist over a multi-cell environment. In the analysis, we find an optimal ratio of downlink transmit powers of BSs (Base Stations) based on the target outage probability and the performance according to ratios of uplink/downlink transmit powers of MSs (Mobile Stations)/BSs is explored. Our numerical results show that interference mitigation utilizing the characteristics of the uplink and downlink power ratio is very effective in improving system performance in terms of QoS.

• International journal of advanced smart convergence
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• 제9권2호
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• pp.58-67
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• 2020

In this paper, we propose a data-driven-based beam selection scheme for massive multiple-input and multiple-output (MIMO) systems in ultra-dense networks (UDN), which is capable of addressing the problem of high computational cost of conventional coordinated beamforming approaches. We consider highly dense small-cell scenarios with more small cells than mobile stations, in the millimetre-wave band. The analog beam selection for hybrid beamforming is a key issue in realizing millimetre-wave UDN MIMO systems. To reduce the computation complexity for the analog beam selection, in this paper, two deep neural network models are used. The channel samples, channel gains, and radio frequency beamforming vectors between the access points and mobile stations are collected at the central/cloud unit that is connected to all the small-cell access points, and are used to train the networks. The proposed machine-learning-based scheme provides an approach for the effective implementation of massive MIMO system in UDN environment.

• 전자공학회논문지
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• 제51권4호
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• pp.27-32
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• 2014

단위행렬의 각 행을 공간부호로 사용하고 symmetric balance incomplete block design(BIBD) 부호를 스펙트럼부호로 사용한 2차원(2-D) 하이브리드 부호를 제안한다. 단위행렬의 각 행을 공간부호로 사용함으로써 수신기의 구조가 간단해지고 송수신단을 연결하는 방법도 간단해 짐을 알 수 있었다. 또한 비이상적 BIBD 부호를 스펙트럼부호로 사용하여 입력신호가 작을때도 효율적으로 동작할 수 있었다. 사용자 수에 따른 비트 오차율(BER) 분석을 통하여 제안하는 2-D 하이브리드 부호가 1차원(1-D) BIBD 부호에 비하여 최대사용자 수를 현저하게 증가시킬 수 있음을 알 수 있었다.

• 한국인터넷방송통신학회논문지
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• 제18권5호
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• pp.131-140
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• 2018

방송 스케줄링 기법은 데이터 방송 시스템의 성능을 향상시키기 위해서 필수적인 기술이다. 본 논문은 질의의 응답시간을 줄이기 위하여 다중 채널을 통한 데이터 방송의 문제를 연구하여 HDAMA로 명명된 새로운 하이브리드 데이터 방송 스케줄링 기법을 제안한다. 제안된 기법은 푸쉬기반 방송과 풀기반 방송의 장점을 결합하는 전략을 채택한다. HDAMA는 다중 데이터 질의의 특성을 반영하여 액세스 확률의 영향력을 적절하게 제어할 수 있고, 풀 데이터를 비교적 적시에 방송할 수 있기 때문에 질의 응답시간의 성능을 향상시킬 수 있다. 제안된 기법의 성능 평가를 위해 시뮬레이션이 수행되었다. 실험 결과에 따르면, 평균 응답시간의 성능에서 HDAMA는 다른 기법보다 우수한 성능을 보인다.

• Journal of Communications and Networks
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• 제11권6호
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• pp.615-625
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• 2009

Worldwide inter-operability for microwave access (WiMAX) is a promising technology that provides high data throughput with low delays for various user types and modes of operation. While much research had been conducted on physical and MAC layers, little attention has been paid to a comprehensive and efficient security solution for WiMAX. We propose a hybrid security solution combining identity-based cryptography (IBC) and certificate based approaches. We provide detailed message exchange steps in order to achieve a complete security that addresses the various kind of threats identified in previous research. While attaining this goal, efficient fusion of both techniques resulted in a 53% bandwidth improvement compared to the standard's approach, PKMv2. Also, in this hybrid approach, we have clarified the key revocation procedures and key lifetimes. Consequently, to the best of knowledge our approach is the first work that unites the advantages of both techniques for improved security while maintaining the low overhead forWiMAX.

• Journal of Communications and Networks
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• 제7권1호
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• pp.76-86
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• 2005

Today's wireless access networks consist of several tiers that overlap each other. Provisioning of real time undisrupted communication to mobile users, anywhere and anytime through these heterogeneous overlay networks, is a challenging task. We extend the end-to-end approach for the handoff management in hybrid wireless data network by designing a fully mobile-controlled handoff for mobile devices equipped with dual mode interfaces. By handoff, we mean switching the communication between interfaces connected to different subnets. This mobile-controlled handoff scheme reduces the service disruption time during both horizontal and vertical handoffs and does not require any modification in the access networks. We exploit the IP diversity created by the dual interfaces in the overlapping area by simultaneously connecting to different subnets and networks. Power saving is achieved by activating both interfaces only during the handoff period. The performance evaluation of the handoff is carried out by a simple mathematical analysis. The analysis shows that with proper network engineering, exploiting the speed of mobile node and overlapping area between subnets can reduce service disruption and power consumption during handoff significantly. We believe that with more powerful network interfaces our proposal of dual interfaces can be realized.

• 정보처리학회논문지C
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• 제12C권2호
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• pp.223-228
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• 2005

현재 디지털 이동통신에서 사용되고 있는 DS(direct sequence)/CDMA 방식은 멀티미디어 통신과 같은 고속 데이터 전송에 적용할 경우 다중경로 페이딩 채널하에서 인접심볼간 간섭 및 다중접속간섭이 심해지는 문제점을 갖고 있다. 이러한 문제들을 보완하기 위해, 본 논문에서는 다원 접속 간섭을 억제하는 멀티코드 시스템에 인접 심볼간 간섭을 줄여주는 하이브리드 DS/FH(frequency hopping) SS(spread-spectrum)기술을 접목하여 멀티코드 하이브리드 DS/FH SS 시스템을 고안하였고, 기존의 멀티펀드 시스템이 가지는 문제점을 해결하고자 sub-code 기술을 이용하여 sub-code멀티코드 하이브리드 DS/FS SS 시스템을 제안하였다. 제안한 시스템의 성능을 분석하고자 다양한 채널 환경 하에서 컴퓨터 시뮬레이션을 실시하였다.

• ETRI Journal
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• 제35권5호
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• pp.786-796
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• 2013

In this paper, we propose a hybrid time-division multiplexing and dense wavelength-division multiplexing scheme to implement a cost-effective and scalable long-reach optical access network (LR-OAN). Our main objectives are to increase fiber plant utilization, handle upstream and downstream flow through the same input/output port, extend the reach, and increase the splitting ratio. To this end, we propose the use of an arrayed waveguide grating (AWG) and an erbium-doped fiber amplifier (EDFA) in one configuration. AWG is employed to achieve the first and second objectives, while EDFA is used to achieve the third and fourth objectives. The performance of the proposed LR-OAN is verified using the Optisystem and Matlab software packages under bit error rate constraints and two different approaches (multifiber and single-fiber). Although the single-fiber approach offers a more cost-effective solution because service is provided to each zone via a common fiber, it imposes additional losses, which leads to a reduction in the length of the feeder fiber from 20 km to 10 km.

• Journal of Gastric Cancer
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• 제11권4호
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• pp.230-233
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• 2011

Regarding the removal of a gastric bezoar, laparoscopic surgery was performed and it was shown that the laparoscopic approach is safe and feasible. However, the laparoscopic method has the risk of intraabdominal contamination, when the gastric bezoar is retrieved from the gastric lumen in the peritoneal cavity. We developed and applied a new procedure for the removal of the gastric bezoar using one surgical glove and two wound retractors as a fashion of intragastric single port surgery. Herein we present this new minimal invasive procedure, so named "hybrid access surgery" which involves the use of existing devices and overcomes the weakness of laparoscopic removal of the gastric bezoar. Our new procedure, combining the concept of intragastric and single port access, is acceptable and feasible to retrieve the gastric bezoar. In the future, this procedure may be one of the alternative procedures for retrieving gastric bezoar even when it is incarcerated in the pylorus.

• 한국통신학회논문지
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• 제35권1A호
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• pp.16-24
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• 2010

HSUPA(High Speed Uplink Packet Access)는 고속 스케줄링, HARQ, 짧은TTI등을 Node B에서 제공함으로써 HSDPA 에 대응되게 상향링크 쪽의 고속 데이터 전송률을 제공하는 WCDMA의 Rel 6 이동통신 기술이다. WCDMA 시스템의 RNC(Radio Network Controller)와 기지국인 Node B 간의 Iub 구간에서 혼잡을 검출하는 것은 사용자의 통신서비스 품질을 높이기 위해서 매우 중요하다. 이를 위해 TNL 혼잡 검출과 Node B의 링크 버퍼 관찰 방법을 제안하고 이를 통해 얻을 수 있는 패킷 수율에 대해 성능 분석을 하였다. 제안하는 방법을 통해 좁은 Iub 대역폭의 혼잡 검출은 패킷 수율 향상에 도움이 되는 것을 확인할 수 있었다.