• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.12
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• pp.573-577
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• 2002

We designed wideband HTS antennas which consists of two triangle -radiation patches using a $YBa_2Cu_3O_{7-X}$ (YBCO) superconducting thin film. The major limitation of high-Tc superconducting (HTS) microstrip antennas is the narrow bandwidth due to the high Q and thin substrate. Defining bandwidth as the frequency range over which standing wave ratio (SWR) 2:1 or less, HTS antenna bandwidths are typically 0.85 % to 1.1 %. Thus considerable effort has been focused on developing antennas for broadband operation. To calculate input impedance and design of the broadband HTS antennas a moment method technique was used. The HTS antenna fabricated in this work was designed for K-band, which is useful band for satellite to satellite communications. The bandwidth obtained was a significant 6.7 % and the other measured performance of our HTS antenna, including the bandwidth, radiation Pattern, efficiency, standing wave ratio (SWR) and return losses was reported.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.523-526
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• 2002

We designed wideband HTS antennas which consists of two triangle-radiation patches using a YBa$_2$Cu$_3$O$\sub$7-x/ (YBCO) superconducting thin film. The major limitation of high-Tc superconducting (HTS) microstrip antennas is the narrow bandwidth due to the high Q and thin substrate. Defining bandwidth as the frequency range over which standing wave ratio (SWR) 2:1 or less, HTS antenna bandwidths are typically 0.85% to 1.1%. Thus considerable effort has been focused on developing antennas for broadband operation. To calculate input impedance and design of the broadband HTS antennas a moment method technique was used. The HTS antenna fabricated in this work was designed for K-band, which is useful band for satellite-to-satellite communications. The bandwidth obtained was a significant 6.7% and the other measured performance of our HTS antenna, including the bandwidth, radiation Pattern, efficiency, standing wave ratio (SWR) and return losses was reported.

• ETRI Journal
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• v.34 no.4
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• pp.613-616
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• 2012

A multi-spot-beam satellite is an attractive technique for future satellite communications since it can support high data rates by projecting high power density to each spot beam and can reuse a frequency in different cells to increase the total system capacity. In this letter, we propose a resource management technique adjusting the bandwidth of each beam to minimize the difference between the traffic demand and allocated capacity. This represents a reasonable solution for dynamic bandwidth allocation, considering a trade-off between the maximum total capacity and fairness among the spot beams with different traffic demands.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.747-748
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• 2013

This paper proposes a new dynamic polling method for XGPON1 (10-Gbps-capable passive optical network stage 1). XGPON1 system supports 2.5 Gbps for upstream and 10 Gbps for downstream. In XGPON1 system, if the polling frequency is high, then the efficiency of dynamic bandwidth allocation increases whereas the upstream bandwidth is wasted. The proposed method decreases the upstream bandwidth wastage owing to polling and efficiently increases the polling frequency.

• Journal of Communications and Networks
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• v.4 no.2
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• pp.97-101
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• 2002

Based on their shift and scale orthogonality properties, scaling and wavelet functions may be used as signaling functions having good frequency localization as determined by the fractional-out-of-band power (FOOBP). In this paper, application of Daubechies' wavelet and scaling functions as baseband signaling functions is described, with a focus on finding discretely realizable pulse-shaping transfer function circuits whose outputs approximate scaling and wavelet functions when driven by more conventional digital signaling waveforms. It is also shown that the inter-symbol interference (ISI) introduced by the approximation has negligible effect on the performance in terms of signal-to-noise ratio (SNR). Moreover, the approximations are often more bandwidth efficient than the original wavelet functions. These waveforms thus illustrate an example solution of a tradeoff between residual ISI and bandwidth efficiency as a signal design problem.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.4
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• pp.381-386
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• 2014

In this paper, the effect of slot antenna's location in the radiation performance and impedance bandwidth was analyzed. The proposed antenna was designed to operate at Wi-Fi band(2.4~2.5 GHz) when the slot antenna is located at the center of the ground plane, the proposed antenna has a bandwidth of 340 MHz(2.24~2.58 GHz) under voltage standing wave ratio of = 2 and achieves average realized efficiency of 69 % over Wi-Fi bands.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.484-491
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• 2000

It is necessary to apply SSB modulation method with high bandwidth efficiency to the DS-CDMA mobile communication systems in order to accommodate the increasing number of voice users as well as the broad band and high data rate service in the future. Even though the bandwidth efficiency increases if SSB modulation is applied to BPSK-DS/CDMA, its performance gets degraded because of the increased multiple access interference. Therefore for eliminating the increased multiple access interference, the SSB/BPSK-DS/CDMA with successive interference canceller(SIC) is proposed and its performance and capacity are analyzed. With the limited system bandwidth, it is shown that the SSB/BPSK-DS/CDMA with SIC can accommodate more capacity than the conventional BPSK-DS/CDMA with SIC.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.12
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• pp.1168-1173
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• 2012

In this paper, we propose a protection architecture of passive optical network (PON) system by using two optical line terminals (OLTs). Using this scheme, the network can sustain services to access area and restores normal operation in faulty conditions. Unlike existing systems, the proposed one increases the efficiency of the system by operating both OLTs using different wavelengths in normal condition. During protection mode, a Shared-bandwidth allocation scheme is employed to maximize the utilization efficiency. Performance analysis shows that the proposed scheme can provide reliability to Ethernet-based PON system very efficiently.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.10
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• pp.5058-5077
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• 2019

Traditional regenerating codes are designed to tolerate node failures with optimal bandwidth overhead. However, there are many types of partial failures inside the node, such as latent sector failures. Recently, proposed regenerating codes can also repair intra-node failures with node-level redundancy but incur significant bandwidth and I/O overhead. In this paper, we construct a new scheme of regenerating codes, called IR-RBT codes, which employs intra-node redundancy to tolerate intra-node failures and serve as the help data for other nodes during the repair operation. We propose 2 algorithms for assigning the intra-node redundancy and RBT-Helpers according to the failure probability of each node, which can flexibly adjust the helping relationship between nodes to address changes in the actual situation. We demonstrate that the IR-RBT codes improve the bandwidth and I/O efficiency during intra-node failure repair over traditional regenerating codes but sacrifice the storage efficiency.

• Korean Journal of Optics and Photonics
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• v.24 no.6
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• pp.297-310
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• 2013

With the explosive growth of internet data traffic due to the FTTH penetration, prevalence of smart devices and cloud network service, the demand for higher bandwidth is ever increasing with the pace of more than 40% annual growth. To accommodate ultra high bandwidth traffic, optical components in each hierarchy have progressed rapidly. WDM has begun to be deployed along with higher bandwidth service in the access network. Next-generation ROADM is under development for efficient network management in the metro network. For long-haul transmission, an advanced modulation scheme based on coherent transmission technology has been adopted to enhance spectral efficiency. In this paper, core components to meet the demands of high speed, high efficiency and low power consumption will be reviewed.