• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.3
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• pp.182-186
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• 2004

In this paper, 2.4GHz WLAN BPF(Band Pass Filter) which has two DGS(Defected Ground Structure) unit cells was simulated and manufactured. To do this, a unit DGS resonator with resonant frequency is designed. Then the BPF for WLAN with the center frequency of 2.4GHz md the bandwidth of 200MHz is designed using two DGS resonator, finally this circuit is fabricated. We also proposed the equivalent circuit of the BPF employing two DGS resonator. The BPF with DGS was obtained experimental results with network analyzer Agilent 8510C. The measured result shows good agreement with simulated data. Experimental results show the center frequency of 2.45GHz, the insertion loss of 1.08dB, and the 3-dB bandwidth of 470MHz(19.5%). Acceding to the measured values, it is found that the fabricated DGS BPF is available for wireless LAN.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.11a
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• pp.93-96
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• 2003

화상회의 시스템에서 대역폭의 이용률을 높이기 위한 연구로서 SARLM(Source Adaptive Receiver-Driven Multi-Layered Multicast)이 있다. 이 기법은 레이어의 병합(merging)과 분할(splitting)을 통해 새로운 레이어(layer)의 수와 각 레이어의 전송률을 결정하는데, 레이어의 병합 시 전체 수신자의 가용 대역폭(available bandwidth)의 이용률이 낮아지는 현상이 발생한다. 본 논문에서는 레이어의 병합 시 수신자의 가용 대역폭의 이용률을 개선한 기법을 제안한다. 제안하는 기법은 특정 레이어를 수신하는 수신자가 아주 적은 경우 하위 레이어의 수신자중 전송률의 많은 증가를 요청하는 수신자와 병합하고, 하위 레이어를 재그룹핑(regrouping) 한다. 실험 결과, 레이어의 병합 시 전체 수신자의 대역폭 이용률을 향상시킬 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.5
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• pp.1294-1303
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• 1996

In this paper, the microstrip anntenna with broad bandwidth is designed using parasitic element. In the designed cofiguration, parasitic element of the same resonating length but different width which is coupled to the nonradiating edge of a rectangular patch antenna. The driven element aloe is fed and the other part is operated as parasitic element. So the different patchs are resonating at differnt frequencies and this multiple resonance increase the bandwidth. The overall size of the antenna is not increased by adding parasitic element to a driven patch. Compared to the available wideband microstrip antennas, the designed antenna structure is bery compact. A theoretical explanation of the rectangular patch antenna coupled with prarsitic is analyzed by extending the theory of coupled microstrip lines. The theoretical and experimental results for a patch coupled with a single parasitic are presented.

• Journal of Electrical Engineering and information Science
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• v.3 no.1
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• pp.21-27
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• 1998

In this paper we apply routing algorithms in circuit switched networks to B-ISDN networks and investigate the performance. B-ISDN supports a wide range of services with hetrogeneous bandwidth requirements. We assume that the network supports D classes of traffic. It is modeled as a finite D dimensional Markov chain. A call is blocked on arrival if the required bandwidth is not available on the route. The shortest path routing, alternate routing and trunk reservation are considered for performance comparison. We also consider trunk reservation with restricted access control where the network reserves certain amount of bandwidths for one class of traffic that assumes a higher transmission priority. Through the method of successive iterations, we obtain the steady state equilibrium probabilities and call blocking probabilities for dynamic routing. The results can be used to design a B-ISDN network that improves network connection availability and efficiency while simultaneously reducing the network costs.

• ETRI Journal
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• v.32 no.4
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• pp.618-621
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• 2010

A low cross-polarization broadband stacked patch antenna is proposed. By means of the stacked patch configuration and probe-fed strip feed technique, the VSWR 1.2:1 bandwidth of the patch antenna is enhanced to 22% from 804 MHz to 1,002 MHz, which outperforms the other available patch antennas (<10%). Furthermore, the antenna has a cross-polarization level of less than -20 dB and a gain level of about 9 dBi across the operating bandwidth. Simulation results are compared with the measurements, and a good agreement is observed.

• Journal of Communications and Networks
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• v.8 no.3
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• pp.351-359
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• 2006

In this article, we present a new slow-start variant, which improves the throughput of transmission control protocol (TCP) Vegas. We call this new mechanism Gallop-Vegas because it quickly ramps up to the available bandwidth and reduces the burstiness during the slow-start phase. TCP is known to send bursts of packets during its slow-start phase due to the fast window increase and the ACK-clock based transmission. This phenomenon causes TCP Vegas to change from slow-start phase to congestion-avoidance phase too early in the large bandwidth-delay product (BDP) links. Therefore, in Gallop-Vegas, we increase the congestion window size with a rate between exponential growth and linear growth during slow-start phase. Our analysis, simulation results, and measurements on the Internet show that Gallop-Vegas significantly improves the performance of a connection, especially during the slow-start phase. Furthermore, it is implementation feasible because only sending part needs to be modified.

• ETRI Journal
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• v.44 no.2
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• pp.274-285
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• 2022

Retransmission in optical burst switching networks is a solution to recover data loss by retransmitting the dropped burst. The ingress node temporarily stores a copy of the complete burst and sends it each time it receives a retransmission request from the core node. Some retransmission schemes have been suggested, but uncontrolled retransmission often increases the network load, consumes more bandwidth, and consequently, increases the probability of contention. Controlled retransmission is therefore essential. This paper proposes a new controlled retransmission scheme for loss recovery, where the available bandwidth of wavelength channels and the burst lifetime are referred to as network conditions to determine whether to transmit a dropped burst. A retrial queue-based analysis model is also constructed to validate the proposed retransmission scheme. The simulation and analysis results show that the controlled retransmission scheme is more efficient than the previously suggested schemes regarding byte loss probability, successful retransmission rate, and network throughput.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.2
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• pp.114-124
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• 2009

In this paper, we propose a practical TCP friendly rate control scheme that considers the minimum channel bandwidth of the network when transporting SVC (scalable video coding) video over IP netowrks such as Internet. RTP and RTCP is mainly designed for use with UDP (User Datagram Protocol) for real-time video transport over the Internet. TCP-friendly rate control was proposed to satisfy the demands of multimedia applications while being reasonably fair when competing for bandwidth with conventional TCP applications. However the rate control model of the conventional TCP-friendly rate control scheme does not consider the minimum channel bandwidth of the network. Thus the estimated channel bandwidth by the conventional rate control model might be quite different from the real channel bandwidth when the packet loss ratio of the network is very large. In this paper, we propose a modified TCP-friendly rate control scheme that considers the minimum channel bandwidth of the network. Based on the modified TCP-friendly rate control, we assign the minimum channel bandwidth to the base layer bitstream of SVC video, and remaining available bandwidth is allocated to the enhancement layer of SVC video for the TCP friendly scalable video transmission. It is shown by simulations that the modified TCP-friendly rate control scheme can be effectively used for a wider range of controlled bit rates depending on the packet loss ratio than the conventional TCP-friendly control scheme. Furthermore, the effectiveness of the proposed scheme in terms of objective video quality is proved by comparing PSNR performance with the conventional scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.10
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• pp.2292-2302
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• 1997

In this paper, we propose a wireless MAC protocol named APRMA, which is capable of supporting the ABR type data service and maximizing channel utilization. In PRMA protocol, data terminals with random data packets cannot reserve slot. That is, slot reservation is applicable to the time constraint voice packet exclusively. But the reservation scheme has to be performed for loss sensitive data packet, and so data packets can get their quality of service. Therefore, in wireless MAC, reservation technique has to be used for both voice and data services. But in service aspects, if a fixed bandwidth is allocated to data terminals, time constraint voice packets may have a low efficiency. So in this study, the terminal which wants to request for ABR tyupe service, acquires a minimum bandwidth from system for thefirst time. If the system has extra available bandwidth, ABR terminals would acquire additional bandwidth slot by slot. As a result, APRMA protocol cansupporty the data service with loss sensitivity and maintain their channel utilization high. Also high priority services like voice can be satisfied with their QoS by APRMA.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2000.11a
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• pp.463-470
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• 2000

In this paper, we describe a wireless MAC protocol named APRMA(Abitrary Period Reservation Multiple Access), which is capable of supporting the ABR type data service and maximizing channel utilization. In original PRMA protocol, data terminals with random data packets cannot reserve slot. That is, slot reservation is applicable to the. time constraint voice packet exclusively. But the reservation scheme have to be performed for loss sensitive data packet, so data packets can get their quality of service. The aspects of service, if fixed bandwidth is allocated to data terminals, time constraint voice packets may have a low efficiency So in this study, the terminal which wants to request for ABR type service, acquires a minimum bandwidth from system for the first time. If the system have extra available bandwidth, ABR terminals would acquire additional bandwidth slot by slot. As a result, APRMA protocol can support the data service with loss sensitivity and maintain their channel utilization highly. Also high Priority services like voice can be satisfied with their QoS by APRMA.