• Review of KIISC
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• v.18 no.2
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• pp.40-48
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• 2008

미래의 광대역 무선망은 고주파수의 대역을 사용하여 신호의 감쇠가 높고, 높은 multi-path fading효과를 가지므로 전력제어가 필요하고 사용자에게 넓은 대역폭을 제공할 것으로 예측한다. 이를 위해 셀의 크기가 줄게 되고 BS의 수가 증가하여 네트워크 설치비용도 증가하게 될 것이다. 무선 메쉬 네트워크는 이런 문제를 해결하여 망구축과 운영을 쉽게 하고 영역 확장과 용량 확장을 유연하게 하며 저비용의 무선 bakhaul로 높은 신뢰성을 제공하는 특성을 가진다. 무선 메쉬 네트워크는 노드와 노드간의 무선 멀티-홉 통신을 이용하여 끊김 없는 연속적인 연결을 제공하는 네트워크 기술이다. 이 기술은 메쉬 라우터와 메쉬 클라이언트라는 노드로 구성되며 각 노드는 라우터인 동시에 호스트로 동작할 수 있다 앞서 언급한 바와 같이 자가 구성, 자가 복구의 능력을 가지고 저 비용으로 신뢰성 있는 네트워크 구축을 제공하기 때문에 무선랜이나 WiMAX, WPAN 등에서 채택되고 있다. 이 논문에서는 메쉬 네트워크의 구조와 특징을 자세히 설명하고 IEEE 802.11s와 IEEE 802.16j에서 진행되는 무선 메쉬 네트워크 관련 표준화를 살펴본 후 관련업체에서의 메쉬 네트워크 관련 개발 현황과 실제 구축 현황을 설명하고자 한다. 또한 무선 메쉬 네트워크에서 발생하는 여러 가지 보안 문제와 적용기술들을 짚어 보고자 한다.

• Journal of Information Processing Systems
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• v.7 no.2
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• pp.261-270
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• 2011

The IEEE 802.16 standard is supposed to provide a wide-range broadband wireless service, but it leaves the implementation of the wireless resource scheduler as an open issue. We have studied the scheduling problem and propose a two level scheduling (TLS) scheme with support for quality of service and fairness guarantees for downlink traffic in a WiMAX network. A central controller Base Station has a number of users, and each mobile subscriber station has different channel conditions. The same mobile subscriber station may have different service requirements at different times in the WiMAX network. Based on OPNET simulation, the results show our scheduling algorithm can increase the network throughput, maintain relative fairness, and lower delay over the round robin and weighted round robin algorithms.

• Electronics and Telecommunications Trends
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• v.24 no.5
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• pp.109-118
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• 2009

WBAN은 사람이 착용하는 옷이나 인체 내부 혹은 외부에 있는 여러 장치들을 상호 연결하여 통신할 수 있는 근거리 무선통신 기술로서 2005년부터 IEEE 802.15 TG16에서 표준화가 활발히 진행되고 있다. WBAN표준은 근거리, 저전력, 고신뢰성 무선통신을 위한 표준화를 목표로 하고 있으며, 용도에 따라 전송속도가 수 kbps$\sim$수십 Mbps 범위로서 의료용뿐만 아니라 비의료용 분야에 활용된다. 의료용은 체내에 이식되는 이식형과 인체 주변에 부착되는 착용형 장치에 활용되며, 비의료용은 데이터 전달이나 게임 응용 등 다양한 엔터테인먼트 분야에 활용된다. 본 고에서는 IEEE 802.15 TGl6에 제안된 WBAN 응용서비스와 이들 서비스의 요구사항을 분석하고, 일반인이 언제 어디서나 이용 가능한 미래의 헬스케어 서비스를 제공하기 위한 WBAN 구조를 살펴보고자 한다.

• IEMEK Journal of Embedded Systems and Applications
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• v.5 no.4
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• pp.185-194
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• 2010

In this paper, we propose an application layer-based vertical handover management protocol, called multihoming RTP (mhRTP), for real-time applications with seamless mobility across heterogeneous wireless access networks. The proposed multi-homing RTP provides a soft handover by utilizing multiple available wireless access network interfaces simultaneously. The newly available path is dynamically added to the ongoing session by the mhRTP session manager. Also the decision making of QoS-improving or QoS-guaranteed handover is possible based on the estimation of available bandwidth in each candidate network. The performances of the proposed mhRTP have been analyzed through a series of simulations on OPNET network simulator. From the performance analysis, we confirmed that the proposed mhRTP can provide QoS-guaranteed vertical handover with efficient session managements.

• Broadcasting and Media Magazine
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• v.12 no.3
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• pp.14-36
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• 2007

다양한 무선 통신 서비스의 등장으로 주파수 자원의 수요가 급증하여 스펙트럼 이용 효율을 극대화하기 위한 새로운 기술 개발의 필요성이 대두되고 있으며, 이에 대한 기술로 Cognitive Radio (CR) 기술이 주목받고 있다. CR 기술은 선택된 주파수 대역에 최적의 QoS를 제공하기 위해서는 먼저 주파수 환경에 적응성을 갖는 스펙트럼 센싱 (Spectrum Sensing) 기술이 필요하며, CR 기술이 적용된 무선 브로드밴드 네트워크 (AWBN : Adaptive Wireless Broadband Network) 모듈은 최근 각광받고 있는 방통융합 솔루션의 Hot Issue인 QoS 보장 홈네트워크 기반의 멀티미디어 전송(TV Portal Service)용 네트워크에 최적화된 솔루션으로 활용될 것으로 기대하고 있을 뿐만 아니라, IEEE 802.22 그룹에서 연구되고 있는 비어있는 TV 대역 및 마이크로폰 대역에 활용될 뿐만 아니라, 기존의 Mobile WiMax에 의한 브로드밴드 네트워크에도 활용 가능하다. 본 고에서는 IEEE 802.22/16d 시스템 규격에 의해 개발된 AWBN 시스템 개발 내용을 기술한다.

• Journal of the Korea Computer Industry Society
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• v.10 no.5
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• pp.193-200
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• 2009

In this paper, the raid and fire preventable system using Zibee module with IEEE 802.15.4 wireless communication standard and multi-sensor was developed displaying raid and firing condition with wireless network. The raid preventable system is designed using a ultrasonhe waves sensor and infrared sensor. The fire preventable system is designed using a thermistor. The datas for raid and firing condition are communicated from enddevice to coordinator with wireless network and are displayed on PC monitor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12C
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• pp.1288-1296
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• 2006

This paper proposes a fast authentication scheme based on hierarchical key structure (HiFA) for roaming mobile nodes in both intra-domain and inter-domain. The full authentication procedure standardized in IEEE 802.11 and 802.16 is difficult to be applied to a handover since it needs a heavy operation and long delay time during a handover. Though a number of schemes were proposed to solve the problem, the existing schemes might degrade the security of authentication or impose heavy administrative burden on the Pome authentication server. The main contribution of this paper is to reduce the communication and computation overhead of the home authentication sewer without degrading the security strength of the fast roaming authentication using hierarchical authentication key structure. The proposed scheme iii this paper decentralizes the administrative burden of the home authentication server to other network entities such as a local authentication server or access point and supports the security separation of the authentication key among local authentication servers using hash key chain.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.1
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• pp.334-349
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• 2022

The effectiveness of Wi-Fi networks is greatly influenced by the optimization of contention window (CW) parameters. Unfortunately, the conventional approach employed by IEEE 802.11 wireless networks is not scalable enough to sustain consistent performance for the increasing number of stations. Yet, it is still the default when accessing channels for single-users of 802.11 transmissions. Recently, there has been a spike in attempts to enhance network performance using a machine learning (ML) technique known as reinforcement learning (RL). Its advantage is interacting with the surrounding environment and making decisions based on its own experience. Deep RL (DRL) uses deep neural networks (DNN) to deal with more complex environments (such as continuous state spaces or actions spaces) and to get optimum rewards. As a result, we present a new approach of CW control mechanism, which is termed as contention window threshold (CW_Threshold). It uses the DRL principle to define the threshold value and learn optimal settings under various network scenarios. We demonstrate our proposed method, known as a smart exponential-threshold-linear backoff algorithm with a deep Q-learning network (SETL-DQN). The simulation results show that our proposed SETL-DQN algorithm can effectively improve the throughput and reduce the collision rates.

• Journal of electromagnetic engineering and science
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• v.10 no.3
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• pp.104-116
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• 2010

With several advantages such as flexible downlink-to-uplink(DL-to-UL) ratio and flexible spectrum usage, Time Division Duplexing(TDD) is emerging as an alternate to Frequency Division Duplexing(FDD), especially in wireless broadband systems. We already have at least four different TDD systems in the industry: Time Division-Synchronous Code Division Multiple Access(TD-SCDMA), IEEE 802.16e-TDD, IEEE 802.16m-TDD, and Time Division-Long Term Evolution(TD-LTE). A disadvantage of TDD is that tight coordination such as time synchronization between adjacent operators is required to prevent interference between the adjacent TDD systems. In this paper, we investigate coexistence scenarios among the above four well-known TDD systems and calculate spectral efficiency(SE) loss in each scenario. Our findings are that SE loss can be significant if TDD ratios of the adjacent operators are considerably different. However, as long as the TDD ratios of the adjacent operators are similar, configurations in the systems permit perfect time synchronization between the two heterogeneous TDD systems, and the resulting SE loss is zero or reasonably low. We believe that the above findings and the configurations of the TDD systems recommended tominimize SE loss will be helpful for operators who deploy TDD systems in system parameter determination and cross-operator coordination.

• Journal of Satellite, Information and Communications
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• v.1 no.2
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• pp.89-94
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• 2006

ODFM(Orthogonal Frequency Division Multiplexing) technique is suitable for high speed data transfer both in wired/wireless channels, and is actively studied recently. Among them, WiBro based on IEEE 802.16 uses ODFM as its core technology, and is currently trying to expand market through commercialization. Therefore, if it's used for high speed moving object(KTX, airplane..etc) in near future, there is a possibility of ICI(inter-carrier interference) to occur due to DFS(Doppler Frequency Shift), a critical weak point of ODFM System. This study suggests 3 compensation techniques for Doppler effects in ODFM system operating through satellite, and confirms improved performance through constellation and BER curve.