• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.397-399
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• 2005

Handover is one of the most important factors that may degrade the performance of TCP connections and real-time applications in wireless data networks. We proposed a seamless handover with Motion Prediction in IEEE 802.16e-based broadband wireless access networks. By intergrating MAC and network layer handovers efficiently, this scheme minimizes the handover delay and eliminates packet losses during handover Simulations show that this scheme achieves loss-free packet delivery without packet duplication and increases TCP throughput significantly.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2006.06a
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• pp.318-321
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• 2006

현재 국내 국책사업으로 추진 중인 와이브로(WiBro) 기술 규격이 포함되어 있는 휴대인터넷 표준 규격인 IEEE 802.16e는 IP기반으로, 이동성이 뛰어나고 고속전송 기능의 특징을 가지고 있다. 또한 기지국간의 핸드오버(Handover)를 지원함으로써 이동성을 지원한다. 그러나 이러한 핸드오버 기법에 있어서 Replay 공격, Man-in-the-Middle 공격, Stolen-Verifier 공격 등에 취약한 문제점이 드러나고 있다. 본 논문은 이러한 기존 핸드오버 기법의 취약점을 개선하기 위해서 사용자의 인증서와 Timestamp값을 통한 IEEE 802.16e/와이브로 망에서 안전한 핸드오버 적용 방안에 대해 제안한다.

• Electronics and Telecommunications Trends
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• v.23 no.3
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• pp.10-18
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• 2008

IEEE 802.16m은 IEEE 802.16e 시스템과의 호환성을 유지하면서 차세대 4G 이동통신 규격으로 ITU-R에 IMT-Advanced 시스템을 위한 하나의 표준 규격으로 제안 및 채택하는 것을 목표로 한다. 2007년 Stage 1 단계인 요구사항 문서를 작성하였고, 2008년에는 Stage 2 단계인 시스템 기술 문서를 작성하고 있으며, 2009년에는 Stage 3 단계인 표준 규격을 작성할 예정이다. 주요 기술적 사항은 시스템 기술 문서를 작성하는 단계에서 결정되므로 2008년은 향후 802.16m 시스템에서 기술 주도권을 확보하는 데 있어 중요한 해가 된다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.355-358
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• 2007

In wireless mobile communication systems, priority of voice service through high speed data and multimedia transmission requires increased service diversification. Research is being carried out in this environment, on the call admission control techniques to guarantee the diversified service's QoS. SRN (Stochastic Reward Net) is an extended version of Petri nets, well know modeling and analysis tool. In this paper, we develop SRN call admission control model considering the 4 classes of services in the 4th generation IEE 802.16e mobile communication Technology.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.11 s.353
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• pp.95-117
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• 2006

In this paper, we describe the optimization of the link-level performance and the complexity of floating-point and fixed-point methods in IEEE 802.16e OFDMA/TDD mobile modem. In floating-point design, we propose the channel estimation methods for downlink traffic channel and select the optimized method using computer simulation. So we also propose efficent algorithms for time and frequency synchronization, Digital Front End and CINR estimation scheme to optimize the system performance. Furthermore, we describe fixed-point method of uplink traffic and control channels. The superiority of the proposed algorithm is validated using the performances of Detection, False Alarm, Missing Probability and Mean Acquisition Time, PER Curve, etc. For fixed-point design, we propose an efficient methodology for optimized fixed-point design from floating-point At last, we design fixed-point of traffic channel, time and frequency synchronization, DFE block in uplink and downlink. The tradeoff between performance and complexity are optimized through computer simulations.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.722-725
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• 2010

In this paper, BER performance and error convergence speed of layered LDPC(Low Density Parity Check) decoder which supports IEEE 802.16e WiMAX standard is analyzed, and optimal design conditions for hardware implementation are derived. A LDPC decoder is modeled and simulated at AWGN channel with QPSK modulation by Matlab. The parity check matrix(PCM) for IEEE 802.16e standard which has block lengths of 576, 1440, 2304 and code rates of 1/2, 2/3A, 2/3B, 3/4A, 3/4B, 5/6 are used. Fixed-point simulation results show that fixed-point bit-width should be more than 8 bits for acceptable decoding performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9A
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• pp.888-897
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• 2007

In this paper, we propose an uplink dynamic resource allocation algorithm to increase sector throughput and fairness among users in 802.16e OFDMA TDD system. In uplink, we address the difference between uplink and downlink channel state information in 802.16e OFDMA TDD system. The simulation results show that not only an increment of 10% of sector throughput but higher level of fairness is achieved by round-robin using the FLR and the rate / margin adaptive inner closed-loop power control algorithm. The FLR algorithm determines the number of sub-channels to be allocated to the user according to the user's position. Also, we get 31.8% more sector throughput compared with the round-robin using FLR by FASA algorithm using uplink channel state information. User selection, sub-channel allocation, power allocation algorithms and simulation methodology are mentioned in Part I.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6A
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• pp.445-457
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• 2009

Recently, there are growing interests in femto-cell for providing indoor users with various broadband multimedia services more efficiently. The technical issues regarding femto-cell such as interference management, self-organization, and resource allocation are now being intensively studied and investigated by researchers worldwide. In this paper, two novel schemes of neighboring cell list(NCL) management are proposed for the IEEE 802.16e system where a macro-cell and huge number of femto-cells coexist. The proposed schemes, named MS location-based neighboring cell list management and BS type-based neighboring cell list management, enable a mobile station(MS) to perform fast scanning and efficient handover by means of preselecting the candidate target femto-cells with high possibility for handover. The simulation result shows that the proposed schemes improve the MS's handover-related performance in terms of scanning power and scanning time compared with the conventional managements scheme of IEEE 802.16e system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.1
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• pp.25-34
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• 2010

The IEEE 802.16-2004 standard has a security sub-layer in the MAC layer called, Privacy Key Management (PKM). However, several researches have been published to address the security vulnerabilities of IEEE 802.16-2004. After the IEEE 802.16-2004 standard, a new advanced and revised standard was released as the IEEE 802.16e-2005 amendment which is foundation of Mobile WiMAX network supporting handoffs and roaming capabilities. PKMv2 in Mobile WiMAX includes EAP authentication, AES-based authenticated encryption, and CMAC or HMAC message protection. However, Mobile WiMAX still has a problem of security architecture such as a disclosure of security context in network entry, a lack of secure communication in network domain, and a necessity of efficient handover supporting mutual authentication because Mobile WiMAX security has mainly concentrated on between SS and BS communication. Based on the investigation results, we propose a novel mobile WiMAX security architecture, called RObust and Secure MobilE WiMAX (ROSMEX), to prevent the new security vulnerabilities.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.270-272
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• 2007

인터넷의 급속한 성장에 따라 사용자들은 이동중에도 인터넷을 이용하고자 하는 수요가 증하고 있다. IEEE 802.16 시스템은 이러한 사용자들의 요구를 충족할 수 있는 시스템으로 이동중에도 인터넷을 사용할 수 있도록 하는 기술이다. 하지만 이동 중에 발생하는 핸드오프에 대한 QoS는 보장되고 있지 못하다. 본 논문에서는 핸프오프시에 등록걸차를 간소화 시켜줌으로써 지연시간을 줄여주고, 데이터 손실과 약간의 끊김현상을 줄여주고자 한다. 이 메커니즘으로 핸프오프가 발생할 때 BS간 전환을 보다 빨라게 해주어 사용자들은 이동중에도 다양한 서비스를 끊김없이 받을 수 있으며. 핸프오프 전에 받고 있던 QoS도 그대로 유지할 수 있어 보다 나은 무선 인터넷 사용을 할 수 있을 것이라 사료된다.