• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.9
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• pp.1343-1349
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• 2013

In optical fiber communications, several newly-developed signal formats are used to obtain the best performance within limited spectral bandwidth. CSRZ (carrier-suppressed return-to-zero) format is one of the new signal formats, which has better spectral efficiency and better robustness to dispersion than RZ (return-to-zero) format. Thus it is widely used for demonstrating high-speed optical communication systems. In an earlier research, we proposed a clock-extraction method of CSRZ signal to monitor chromatic dispersion. However, the clock-frequency component extracted by the clock-extraction method can be affected by the bandwidth of a transmitter or a receiver. Therefore, in this paper, we investigate the effect of bandwidth on the chromatic dispersion monitoring of CSRZ signal based on clock-frequency component. As a result, we propose a couple of robust clock-extraction methods to monitor chromatic dispersion in CSRZ signal.

• Journal of Internet Computing and Services
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• v.11 no.1
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• pp.49-57
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• 2010

Today, internet traffic is rapidly increasing by the appearance of a large number of website thru a numerous internet service provider and the introduction of advanced teaching methods like utilizing ICT(Information and Communication Technology) education. At these actualities, it is requested to increase internet bandwidth in the scene of school; however, it is difficult to resolve the request quickly because of the government's budget and technical problems. In this circumstance, this paper proposes a method to raise the efficiency of internet operations with the current bandwidth. In order to achieve the purpose of this paper, the analysis of internet traffic has been done by the traffic currently being used in school, and an internet bandwidth distribution model differ from the existing standpoint is developed with the analyzed result. It can be used to predict the increase in the bandwidth which may be requested at school in the future, and it can support the office of education for appropriate bandwidth allocation at schools and reduction of school budget in telecommunication. Also, it can be adopted as a future oriented reference model for network policy.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.10
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• pp.31-40
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• 2013

In this paper, the spatial modulation (SM) multi-input multi-output (MIMO) system is proposed for indoor wireless local area networks (WLANs) with improved spectral efficiency. SM is suitable for high speed WLANs with avoiding the inter channel interference (ICI). Only one transmit antenna is activated in SM at each symbol interval. Therefore, it fails to attain the maximum coding gain of MIMO. The space time block code (STBC)-SM MIMO system can attain the maximum diversity gain at the expense of spectral efficiency. The proposed Golden-SM MIMO system uses the Golden code to improve the coding gain and spectral efficiency at the same time. The Golden code is adapted for STBC-SM and it makes the new code book for transmission symbols. The performance of the proposed system is compared with the conventional systems with computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5A
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• pp.484-492
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• 2006

A multi-code biorthogonal code keying(MBCK) system consists of multiple waveform coding block, and the sum of output codewords is transmitted. Drawback of MBCK is that it requires amplifier with high linearity because its output symbol is multi-level. MBCK with constant amplitude preceding blcok(CA-MBCK) has been proposed, which guarantees sum of orthogonal codes to have constant amplitude. Redundant bits of CA-MBCK for constant amplitude coding are not only used to make constant amplitude signal but also used to improve the bit error rate(BER) performance at receiver. In this paper, we proposed a transmission scheme which combine CA-MBCK with $Q^{2}PSK$ to improve bandwidth efficiency of CA-MBCK. The BER performance of the scheme is same that of CA-MBCK in additive white gaussian noise(AWGN). And we showed that BER performance of the proposed system can be improved using redundant bits of constant amplitude preceding.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.48 no.4
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• pp.1-11
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• 2011

In order to obtain more clear x-ray images, an antiscatter grid, which can absorb the scattered rays, is employed. The artifacts due to the grid pattern are, however, visible, and thus should be removed by employing digital filters. For over exposed x-ray images, the strength of the grid artifacts are too big to be removed if fixed-bandwidth filters are employed. In this paper, for an efficient grid artifact reduction, we analyze the characteristics of the image formation and image saturation as the x-ray exposure increases. We can notice that, as the saturation begins to occur, the maximum of the artifact component decreases contrary to increasing exposure amount. We propose then an adaptive filtering algorithm for reduction of the grid artifacts, where the significant-signal bandwidth of the artifact component is used to choose appropriate filter bandwidths. The proposed algorithm is tested for real x-ray digital images, and can efficiently remove the grid artifacts.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.5
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• pp.506-514
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• 2008

At coverage boundaries of cellular systems including the recent WiBro standard which operate with full frequency reuse for increased spectral efficiency, interference signals from the base stations(BS) of adjacent cells degrade the receiver performance. In this paper, a detection method for multiple-antenna mobile stations(MS) is proposed for downlink performance improvement at coverage boundaries of cellular systems. For the performance verification, we obtain the probability density function(pdf) of the effective signal-to-interference and noise ratio(SINR) according to the variation of the interference signals from adjacent cells as well as the number of MS antennas, and calculate the transmission efficiency. We also verify the performance of proposed method with simulation results, to demonstrate a significant performance improvement is achieved over the maximal ratio combining(MRC) and spatial demultiplexing(SD) methods in terms of the effective SINR and the spectral efficiency.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.11_12
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• pp.654-662
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• 2005

Mobile portable devices for wireless network solely depend on a limited battery power. Therefore, we need to design for wireless communication protocols with an energy efficiency. TCP-Westwood is one of the most important approaches on TCP performance improvement in wireless environments that estimates the available bandwidth by using the sampling mechanism. The advantage is that data can be transmitted efficiently using the estimation of available bandwidth. However, when the sender with TCP-Westwood is in a wireless environment, it does not consider of the sampling mechanism operation. In this thesis, a new energy saving transport protocol, called E2TP(Energy Efficient Transport Protocol), is proposed to solve problems which occur when the sender with TCP-Westwood is in a wireless environment. Also, when there are packet loss while doing frequent link error in a wireless environment, E2TP provides the instantaneous segment size adjustment for a more efficient data retransmission. The simulation result proves that the proposed E2TP has better performance in energy efficiency and throughput than both TCP and TCP-Westwood.

• Journal of KIISE
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• v.44 no.11
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• pp.1219-1230
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• 2017

Real-time streaming services over the Internet have increased with the explosive growth of the various mobile platforms, with a focus on smart phones, and the demand for them is growing. In addition, the bandwidth occupied by the streaming services over the Internet had already surpassed 50% in 2010. Because of the shortage of network bandwidth for multimedia services traffic, restrictions on quality and capacity will become more and more serious. CCN is a future Internet architecture that improves how existing host-based Internet architecture handles content-oriented structure, but it is designed for the transmission of general contents and is not suitable for transmitting real-time streaming contents. In this paper, we focus on the inefficient aspects of CCN and propose a hierarchical grade-based scheme for real-time service for a more efficient environment in real-time streaming services. Experiments have shown better performance in terms of bandwidth, network load, and reliability.

• The KIPS Transactions:PartC
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• v.12C no.6 s.102
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• pp.891-900
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• 2005

This paper studies network recovery methods for WDM optical mesh networks, concentrating on improving spare resource utilization. The resource efficiency can be obtained by sharing spare resources needed for network recovery. To improve the sharability of spare resources in WDM networks, methods to share backup paths us well as spare capacity should be studied. The proposed method in this paper uses multiple ring-covers and this method provides fast and simple recovery operation by exploiting the characteristics of logical ring topology, and also provides efficient resource utilization by using multiple distributed backup paths to improve the sharability of overall spare resources in the networks. This method can provide layered reliability to network service by enabling hierarchical robustness against multiple failures. The performance results show that the proposed method provide improved resource efficiency for single failure and enhanced robustness for multiple failures.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.4
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• pp.825-840
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• 2015

Adaptive bitrate (ABR) streaming technology has become an important and prevalent feature in many multimedia delivery systems, with content providers such as Netflix and Amazon using ABR streaming to increase bandwidth efficiency and provide the maximum user experience when channel conditions are not ideal. Where such systems could see improvement is in the delivery of live video with a closed loop cognitive control of video encoding. In this paper, we present streaming camera system which provides spatially and temporally adaptive video streams, learning the user's preferences in order to make intelligent scaling decisions. The system employs a hardware based H.264/AVC encoder for video compression. The encoding parameters can be configured by the user or by the cognitive system on behalf of the user when the bandwidth changes. A cognitive video client developed in this study learns the user's preferences(i.e. video size over frame rate) over time and intelligently adapts encoding parameters when the channel conditions change. It has been demonstrated that the cognitive decision system developed has the ability to control video bandwidth by altering the spatial and temporal resolution, as well as the ability to make scaling decisions.