• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.1
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• pp.125-135
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• 2001

A 8$\times$4 microstrip antenna array is designed at 5.3 GHz and its characteristics are investigated with respect to the application in dual polarized synthetic aperture radars. The design is focused on the achievement of a wide bandwidth, a high polarization purity, a low loss, a good isolation and some mechanical requirements suitable for the application. The antenna is fed by a -3 dB tapered feed network, and is composed of dual polarized SSFIP (Strip-Slot-Foam-Inverted Patch) elements with honeycomb and shielding plane. Simulation results for the antenna array are presented and compared with measurements. It is observed that the antenna shows a bandwidth of 80 MHz, a polarization isolation better than 20 dB, an isolation of 40 dB, and good mechanical characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1065-1075
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• 2012

For the purpose of providing high data rate real-time services, radio transmission technologies (RTT) for ship ad-hoc network (SANET) based on the Recommendation ITU-R 1842-1 are designed. Physical layer parameters of SANET are contrived to meet the requirements of the specification. In order to improve the link reliability for SANET, in this paper, we investigate the performance of the SANET with the multiple antennas, where receive combining (RC), transmit diversity (TD), and beamforming (BF) are employed, respectively. Based on the analysis of the packet error rate (PER) under the highly correlated maritime wireless channel model, we select the efficient multiple antenna schemes for SANET to improve the link reliability. In addition, the optimal MCS levels for the single-carrier (SC) SANET with the bandwidth of 25 kHz, and the multi-carrier (MC) SANET with the bandwidth of 50 kHz and 100 kHz are finalized.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.4
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• pp.721-726
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• 2000

The remarkable progress of electronics and radio communications technology has made our life abundant. On the other hand, the countermeasure of EMC becomes more important socially according to the increased use of electromagnetic waves. It had been required that the absorbing ability of an electromagnetic wave absorber is mote than 20 dB, the bandwidth of which is required through 30 MHz to 1,000 MHB for satisfying the international standard about an anechoic chamber lot EMl/EMS measurement. From November of 1998, however, the CISPR11 has accepted the extended frequency band from 30 MHz to 18 GHz in the bandwidth of EMI measurement. In this paper, we proposed the cutting corn-shaped type satisfying the above requirements and carried out broadband design using the equivalent material constants method. Moreover, we have fabricated it and compared its characteristics with simulated one.

• Journal of Communications and Networks
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• v.4 no.3
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• pp.221-229
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• 2002

Adaptability is the most promising feature to be applied in future robust multimedia applications. In this paper, we propose the Direct Algorithm to improve the degree of satisfaction at heterogeneous receivers in multi-layered multicast video environments. The algorithm relies on a mechanism that dynamically controls the rates of the video layers and is based on feedback control packets sent by the receivers. The algorithm also addresses scalability issues by implementing a merging procedure at intermediate nodes in order to avoid packet implosion at the source in the case of large multicast groups. The proposed scheme is optimized to achieve high global video quality and reduced bandwidth requirements. We also propose the Direct Algorithm with a virtual number of layers. The virtual layering scheme induces intermediate nodes to keep extra states of the multicast session, which reduces the video degradation for all the receivers. The results show that the proposed scheme leads to improved global video quality at heterogeneous receivers with no cost of extra bandwidth.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.8
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• pp.3821-3841
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• 2019

Cloud radio access networks (C-RANs) have been regarded in recent times as a promising concept in future 5G technologies where all DSP processors are moved into a central base band unit (BBU) pool in the cloud, and distributed remote radio heads (RRHs) compress and forward received radio signals from mobile users to the BBUs through radio links. In such dynamic environment, automatic decision-making approaches, such as artificial intelligence based deep reinforcement learning (DRL), become imperative in designing new solutions. In this paper, we propose a generic framework of autonomous cell activation and customized physical resource allocation schemes for energy consumption and QoS optimization in wireless networks. We formulate the problem as fractional power control with bandwidth adaptation and full power control and bandwidth allocation models and set up a Q-learning model to satisfy the QoS requirements of users and to achieve low energy consumption with the minimum number of active RRHs under varying traffic demand and network densities. Extensive simulations are conducted to show the effectiveness of our proposed solution compared to existing schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.4
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• pp.881-902
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• 2024

Fast decision support systems and accurate diagnosis have become significant in the rapidly growing healthcare sector. As the number of disparate medical IoT devices connected to the human body rises, fast and interrelated healthcare data retrieval gets harder and harder. One of the most important requirements for the Healthcare Internet of Things (HIoT) is semantic interoperability. The state-of-the-art HIoT systems have problems with bandwidth and latency. An extension of cloud computing called fog computing not only solves the latency problem but also provides other benefits including resource mobility and on-demand scalability. The recommended approach helps to lower latency and network bandwidth consumption in a system that provides semantic interoperability in healthcare organizations. To evaluate the system's language processing performance, we simulated it in three different contexts. 1. Polysemy resolution system 2. System for hyponymy-hypernymy resolution with polysemy 3. System for resolving polysemy, hypernymy, hyponymy, meronymy, and holonymy. In comparison to the other two systems, the third system has lower latency and network usage. The proposed framework can reduce the computation overhead of heterogeneous healthcare data. The simulation results show that fog computing can reduce delay, network usage, and energy consumption.

• Journal of Information Processing Systems
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• v.7 no.2
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• pp.241-260
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• 2011

In earlier days, most of the data carried on communication networks was textual data requiring limited bandwidth. With the rise of multimedia and network technologies, the bandwidth requirements of data have increased considerably. If a network link at any time is not able to meet the minimum bandwidth requirement of data, data transmission at that path becomes difficult, which leads to network congestion. This causes delay in data transmission and might also lead to packet drops in the network. The retransmission of these lost packets would aggravate the situation and jam the network. In this paper, we aim at providing a solution to the problem of network congestion in mobile ad hoc networks [1, 2] by designing a protocol that performs routing intelligently and minimizes the delay in data transmission. Our Objective is to move the traffic away from the shortest path obtained by a suitable shortest path calculation algorithm to a less congested path so as to minimize the number of packet drops during data transmission and to avoid unnecessary delay. For this we have proposed a protocol named as Congestion Aware Selection Of Path With Efficient Routing (CASPER). Here, a router runs the shortest path algorithm after pruning those links that violate a given set of constraints. The proposed protocol has been compared with two link state protocols namely, OSPF [3, 4] and OLSR [5, 6, 7, 8].The results achieved show that our protocol performs better in terms of network throughput and transmission delay in case of bulky data transmission.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.6
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• pp.119-124
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• 2008

Transimpedance amplifier(TIA) is the most significant element to determine the performance of the optical receiver, and thus the TIA must satisfy tile design requirements of high gain and wide bandwidth. In f)is paper, we propose a novel single chip optical receiver that exploits an analog adaptive equalizer and a limiting amplifier to enhance the gain and bandwidth performance, respectively. The proposed optical receiver is designed by using a $0.13{\mu}m$ CMOS process and its post-layout simulations show $120dB{\Omgea}$ transimpedance gain and 5.88GHz bandwidth. The chip core occupies the area of $0.088mm^2$, due to utilizing the negative impedance converter circuit rather than using on-chip passive inductors.

• Journal of Internet Computing and Services
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• v.8 no.2
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• pp.77-87
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• 2007

A typical VOD service allows that a number of remote clients playback a desired video from a large collection of videos stored in one or more video servers. The main bottleneck for a VOD service is the network bandwidth connecting to the VOD server to the client due to the high bandwidth requirements. Many previous researches have shown that VOD server can be greatly improved through the use of multicast, broadcast, or P2P scheme. Broadcast is one of the most efficient techniques because it can transmit a stream to many users without additional network bandwidth. But the broadcast has long latency time. In order to overcome the drawback, in this paper, we propose P2Prefix broadcast scheme that can solve the service latency time, which is the problem of broadcast scheme, by using P2P caching as well as minimizing the client buffer requirement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.4
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• pp.750-760
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• 1994

In this paper we proposed a multiplexing scheme of real time and non-real traffics in which a congestion control is embedded. Real time traffics are assumed to be nonqueuable and have preemptive priority over non-real time traffics in seizing the common output link, whereas the non-real time traffics wait in the common buffer if the output link is not available for transmission. Real time traffics are encoded according to the bandwidth reduction strategy, paticularly when congestion occurs among non-real time traffics. This scheme provides us an efficient way for utilizing the costly bandwidth resources, by accommodation as many real time traffics as possible with gauranteeing its mimimum bandwidth requirements, and also resloving the congestion encountered among non-real time traffics. We describe the system as a Markov queueing system, provide the analysis by exploiting the matrix geometric method, and present the performance for various performance measures of interest. Some numerical results are also provided.