• Journal of Satellite, Information and Communications
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• v.6 no.2
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• pp.51-59
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• 2011

To support seamless IPTV services in IP-based wireless network, delay or interruption time must be minimized because noticeable interruption will make IPTV service users unhappy. A number of protocols have been proposed for solving mobility problem. However effective seamless handover mechanism to support mobile IPTV services yet to be solved. Mobile WiMAX offers a wireless solution in the access networks that can support IPTV services. Goal of this paper is to identify some reasons of delay time during handover process in an IPv6 capable Mobile WiMAX and to perform handover delay of some optimization scenarios given by existing standardization and proposed improvement.

• Information and Communications Magazine
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• v.23 no.4
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• pp.60-70
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• 2006

• Communications of the Korean Institute of Information Scientists and Engineers
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• v.25 no.4 s.215
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• pp.5-14
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• 2007

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8A
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• pp.625-632
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• 2009

This paper presents the mobile IPTV system for the transmission of FGS-encoded video stream over WiMAX network. The proposed system is implemented to provide more subscribers with an improved mobile IPTV service considering the scarce resource constraint. The proposed system pursues an efficient tradeoff between the number of subscribers that receive the enhancement layer stream and their IPTV service quality. In the proposed system, some parts of the enhancement layer are transmitted with the modulation scheme and the coding rate adaptive to wireless link states of subscribers. Finally, experimental results are provided to show the performance of proposed mobile IPTV system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.9A
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• pp.790-795
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• 2011

The need for broadband wireless data networks such as IEEE 802.16e WiMAX systems increases as a variety of wireless information devices like smart phones are adopted rapidly in everyday life. Since most of mobile applications employ TCP as their transport layer protocol, the performance improvement of TCP in WiMAX systems is crucial. This paper proposes an efficient method to transmit uplink piggyback ACK packets by exploiting the uplink packet buffering which happens because of the resource allocation scheme of the WiMAX systems. The proposed method can support not only the ACK filtering but also the merging of the piggyback ACK packets. As a result, the bandwidth reduction in the piggyback ACK packet transmission leads to the improvement of the downlink throughput. The simulation results show that the bandwidth for the ACK packets reduces more than 90%, and the downlink throughput increases at least 30%.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.3
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• pp.103-110
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• 2010

This paper addressed the implementation of the systematic performance analysis of Quality of Service (QoS) by using OPNET simulator in the interworking architecture of IEEE 802.16e (mobile WiMAX) and IEEE 802.11e (WLAN) wireless network. Four simulation cases were provided in OPNET simulator and a voice traffic was simulated with various performance metrics, such as Mean Opinion Score (MOS), end-to-end delay and packet transmission ratio. Based on the simulation results, the MOS value presented better in WiMAX to WiMAX case compared to others in both static and mobility case. Meanwhile, end-to-end delay was not greatly affected by mobility in four cases. However, mobility was affected much in MOS value and packet transmission ratio in WLAN to WLAN case than in others.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12A
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• pp.998-1005
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• 2009

In the uplink of OFDMA (Orthogonal Frequency Division Multiple Access) based M-WiMAX(Mobile-Worldwide Interoperability for Microwave Access) system, linear phase shift is caused by signals transmitted from multiuser with different delay time and thus, MAI (Multiple Access Interference) occurs. MAI degrades the performance of ranging code detection and delay time estimation in the uplink. Therefore, in this paper, we propose ranging algorithm, applying SIC (Successive Interference Cancellation) to the conventional ranging algorithm, to minimize MAI and to improve ranging performance. The proposed ranging algorithm is verified through the Monte Carlo simulation, which shows the improved performance of ranging code detection and delay time estimation compared to the conventional algorithms. Through compared with random access of the 3GPP LTE, we can know limit of ranging performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.5
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• pp.40-46
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• 2007

In this paper, the effect of a Doppler Spread caused by a mobile station (MS) is analyzed for transparent mobile multi-hop relays (MMR) systems based on orthogonal frequency division multiplexing (OFDM). The exact expression of interchannel interference (ICI) power and the upper bounds of ICI power are derived for OFDM systems with cooperative MMR or non-coopeartive throughput enhancement (TE) MMR. Also, the exact signal-to-interference ratio (SIR) and its lower bound as well as ICI power and its upper bound, derived in this paper, are evaluated by computer simulation with the OFDM parameter set used for mobile WiMax (WiBro) systems.

• Information and Communications Magazine
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• v.24 no.5
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• pp.7-14
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• 2007

Mobile WiMAX의 도입으로 광대역 무선 이동통신 시스템에 대한 관심이 커지고 있는 상황이다. 이러한 Mobile WiMAX 시스템의 커버리지 확대등을 통한 시스템의 도입의 활성화등을 목적으로 IEEE802.16에서는 Relay Task Group을 만들어 모바일 와이맥스의 릴레이 확장을 도모하고 있다. 본 고에서는 Relay Task Group의 생성 및 현재까지의 논의되어서 포함된 PHY및 MAC 계층에서의 기술내용과 표준화 현황에 대해서 상세히 살펴보고자 한다.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.3-4
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• 2008

We propose an efficient uplink bandwidth request-allocation algorithm for variable-rate real-time service in IEEE 802.11 broadband wireless access networks. By introducing a notion of target delay under the framework of dual feedback, the proposed algorithm can assure the desired level of QoS while minimizing wastage of bandwidth allocation.