• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.5
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• pp.568-575
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• 2011

In this paper, we propose a small broadband antenna for mobile device. The proposed antenna consists of a printed rectangular monopole antenna and a parastic element connected to ground using narrow meander line and it is designed on a FR-4 substrate that has a thickness of 0.8 mm and a dielectric constant of 4.4. The FR-4 substrate's size is 50 mm${\times}$90 mm comparable to the real mobile device. The fabricated antenna's size is 12.5 mm${\times}$10.5 mm${\times}$0.8 mm and the measurement shows -10 dB return loss bandwidth of 2,200~6,000 MHz and gains of 2.86~4.01 dBi. Accordingly, the proposed antenna can support mobile device for WiBro(2,300~2,380 MHz), WLAN(IEEE 802.11b/g/n: 2,400~2,480 MHz, IEEE 802.11a: 5,150~5,825 MHz), and mobile WiMAX(IEEE 802.16e : 2,500~2,690 MHz, 3,400~3,600 MHz) service bands.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2007.11a
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• pp.195-203
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• 2007

In this paper, an analytic model of sleep model operation in the IEEE 802.16e is investigated. A mobile subscribe. station (MSS) goes to sleep mode after negotiations with the base station (BS) and wakes up periodically for a short interval to check whether there is downlink traffic to it. If the arrival of traffic is notified, an MSS returns to wake mode. Otherwise, it again enters increased sleep interval which is double as the previous one. In order to consider the situation more practically, we propose the sleep mode starting threshold, during which MSS should await packets before it enters the sleep mode. By modifying the M/G/1 with multiple vacations model, energy consumption ratio(ECR) and average packet response time are calculated. Our analytic model provides potential guidance in determining the optimal parameters values such as sleep mode starting threshold, minimal sleep and maximal sleep window.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.583-583
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• 2006

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.47-52
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• 2006

In this paper, we suggested new network architecture to provide seamless service between the cellular system and new wireless broadband network such as IEEE 802.16e, called WiBro. The interworking technologies are very important issue because mobile operator should provide service connectivity between various wireless networks based on different access technologies. Moreover a change and modification on legacy network should be minimized for providing interworking with new wireless broad-band network. We implemented proposed interworking architecture between 3G cellular network and 802.16e network to provide seamless service including interworking unit in real test environment. Also, we performed performance evaluation in hybrid network environments.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.482-486
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• 2006

Fast 핸드오버는 단말이 기지국 간의 연결을 바꾸는 동안에 발생 하는 서비스 중단 시간을 줄이기 위해서 소개 되었다. 그러나, 새로운 Care of Address (CoA) 의 검증으로 인한 핸드오버 지연이나, 경로 최적화의 지연은 문제가 될 수 있다. 본 연구는 이러한 문제를 해결하기 위하여 향상된 Fast 핸드오버 방식을 소개 한다. 본 방식에서 단말은 이전 기지국과 연결 되어 있는 동안에 경로 최적화를 수행 하며, 새로운 CoA 의 검증을 필요로 하지 않는다.

• Journal of Communications and Networks
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• v.9 no.2
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• pp.141-149
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• 2007

Multiple-input multiple-output (MIMO) transmit pre-coding/beamforming can significantly improve system spectral efficiency. However, several obstacles prevent precoding from wide deployment in early wireless networks: The significant feedback overhead, performance degradation due to feedback delay, and the large storage requirement at the mobile devices. In this paper, we propose a precoding method that addresses these issues. In this approach, only 3 or 6 bits feedback is needed to select a precoding matrix from a codebook. There are fifteen codebooks, each corresponding to a unique combination of antenna configuration (up to 4 antennas) and codebook size. Small codebooks are prestored and large codebooks are efficiently computed from the prestored codebook, modified Hochwald method and Householder reflection. Finally, the feedback delay is compensated by channel prediction. The scheme is validated by simulations and we have observed significant gains comparing to space-time coding and antenna selection. This solution was adopted as a part of the IEEE 802.16e specification in 2005.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.4
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• pp.71-75
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• 2008

A folded monopole antenna is proposed for mobile communication applications. The proposed antenna covers CDMA and GSM at low frequency band, and it has a wide bandwidth (6.85 GHz) at high frequency band to cover GPS, DCS, USPCS, UHfS, WLAN (2.4, 5.2, 5.8 GHz), and the future application of IEEE 802.16e mobile WiMAX.

• Journal of Broadcast Engineering
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• v.13 no.1
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• pp.6-16
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• 2008

An instable wireless channel condition causes more packet losses and retransmissions due to interference, fading, station mobility, and so on. Therefore video streaming service over a wireless networks is a challenging task because of the changes in the wireless channel conditions and time-constraints characteristics of the video streaming services. To provide efficient video streaming over a wireless networks, QoS-enhanced MAC protocol, IEEE 802.11e, is standardized recently. Tn this paper, we propose a new network-adaptive H.264 video streaming mechanism in the IEEE 802.11e wireless networks. To improve the quality of video streaming services, video stream has to adapt to the changes in the wireless channel conditions. The wireless channel conditions are estimated by the packet loss probability and informed to the application layer by the cross-layering. According to the wireless channel information, the video streaming application filters out the low-priority data. This adaptation mechanism efficiently uses system resources because it drops the low-priority data in advance. Therefore, our cross-layer design can provide improved video streaming services to the end-user. Through the implementation and performance evaluation, we prove that the proposed mechanism improves the QoS of the video streaming by providing the smoothed playback.

• Journal of Advanced Navigation Technology
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• v.18 no.2
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• pp.142-150
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• 2014

In this paper, the performance analysis results of time/frequency synchronization and cell search algorithm are presented for aeronautical mobile airport communication systems (AeroMACS). AeroMACS is based on IEEE 802.16e mobile WiMAX standard and uses the aeronautical frequency band of 5GHz with the bandwidth of 5MHz. The simulation model of AeroMACS is designed and the performance evaluation is conducted with the various airport channel models such as apron (APR), runway (RWY), taxiway (TWY), and park (PRK). The proposed synchronization unit was designed in hardware description language (HDL) and implemented on FPGA. Also, the real-time operation was verified and evaluated using FPGA test system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1786-1795
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• 2006

Portable Internet extended from wireless LAN has a large cell size, similar to a wireless mobile communication. and can provide the seamless service which offers middle-low speed mobility. IEEE 802.16e, the international standard of Portable Internet, uses PKMv2 protocol for authorization and key exchange between a MSS and a BS. This paper proposes a new protocol based on PKMv2, which can provide that MSS is able to do fast authorization with a new BS when soft handover is occurred in a MSS. Our protocol can carry out fast authorization because of reducing the number of messages and parameter exchange, public key encryption and signature in wireless network more than the previous works. It also prevents eavesdropping from an external attacker and keeps the security against impersonation attacks for both a MSS and a BS.