• Korean journal of communication and information
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• v.46
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• pp.387-419
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• 2009

The concept of strategic group is defined as an aggregate of corporations utilizing similar strategies with similar resources. It becomes a kinds of contact point in the middle of corporation and industry between the industrial organization theory and the strategic management theory. This study tried to apply the strategic group model, which has been a main theory in the management studies, to program providing industry in Korea. This study shed lights upon research problems such as number of strategic groups, differences of strategic variables among the groups, finally differential performances according to strategic groups. 40 commercial broadcasting companies were analyzed to find answers. 9 strategic groups were drawn as a result of cluster analysis. Major variables which contribute to making groups were operating efficiency(4.05), pricing(3.83), size(number of system operator, 3.56), reliance on license revenue(2.58), horizontal integration(number of sister networks, 2.16) in order. An analysis of variance between performance variables has shown statistical significance regarding total net revenue per subscriber, however, insignificances statistically in regards to ratio of operating profit to net sales, cash Abstracts 687 flow ratio. Some studies in the past insisted that history variable played an important role to classifying strategic groups. However, this study found that the history didn't exert significant influence on either the group classification itself or performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.7 s.361
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• pp.17-22
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• 2007

OFDM (Orthogonal Frequency Division Multiplexing) is a special case of multicarrier transmission, where a single data stream is transmitted over a number of lower-rate subcarrier. One of the main reasons to use OFDM is to increase robustness against frequency-selective fading or narrowband interference. Unfortunately, an OFDM signal consists of a number of independently modulated subcarriers, which can give a large PAPR (Peak-to-Average Power Ratio) when added up coherently. In this paper, we investigate the performance of a simple PAPR reduction scheme, which requires no change of a receiver structure or no additional information transmission. The approach we employed is clipping in the time and frequency domains. The time-domain clipping is carried out with a predetermined clipping level while the frequency-domain clipping is done within EVM (Error Vector Magnitude). This approach is suboptimal with lower computational complexity compared to the optimal method. This evaluation is carried out on the OFDM system with an nonlinear amplifier. The simulation results demonstrated that the PAPR reduction algorithm is one of ways to reduce the effects of the nonlinear distortion of an HPA (High Power Amplifier).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6A
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• pp.405-419
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• 2012

In this paper, we propose a joint base station(BS) and relay precoders design in multi-relay aided multi-user all-multiple-input multiple-output(MIMO) system. The design criterion is to minimize user sum mean square error(SMSE) with relay sum power constraint(RSPC) where only local channel state information(CSI)s are available at relays. Local CSI at a relay is defined as the CSI of the channel which the relay itself accesses, out of among all the 1st hop and the 2nd hop channel in the system. With BS precoder structure which is concatenated with block diagonalization(BD) precoder, each relay can determine its own precoder using only local CSI. Proposed scheme is based on sequential iteration of two stages; stage 1 determines BS precoder and relay precoders jointly with SMSE duality, and stage 2 determines user receivers. Proposed scheme can be demonstrated theoretically to be always converge. We verify that proposed scheme outperforms simple amplify-and-forward(SAF), MMSE relay, and proposed schemes in [1] in terms of both SMSE and sum-rate performances.

• Journal of Navigation and Port Research
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• v.39 no.4
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• pp.293-297
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• 2015

Underwater acoustic communications has been limited use for military purposes in the past. However, the fields of underwater applications expend to detection, submarine and communication in recent. The excessive multipath encountered in underwater acoustic communication channel is creating inter symbol interference, which is limiting factor to achieve a high data rate and bit error rate performance. To improve the performance of a received signal in underwater communication, many researchers have been studied for channel coding scheme with excellent performance at low SNR. In this paper, we applied BCJR decoder based ( 2,1,7 ) convolution codes and to compensate for the distorted data induced by the multipath, we applying the turbo equalization method. Through the underwater experiment on the Gyeungcheun lake located in Mungyeng city, we confirmed that turbo equalization structure of BCJR has better performance than hard decision and soft decision of Viterbi decoding. We also confirmed that the error rate of decoder input is less than error rate of $10^{-1}$, all the data is decoded. We achieved sucess rate of 83% through the experiment.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.11
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• pp.3-11
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• 2015

An advanced receiver which can manage inter-cell interference is required to cope with the explosively increasing mobile data traffic. 3rd Generation Partnership Project (3GPP) has discussed network assisted interference cancellation and suppression (NAICS) to improve signal-to-noise-plus-interference ratio (SINR) and receiver performance by suppression or cancellation of interference signal from inter-cells. In this paper, we propose the advanced receiver based on soft decision to reduce the interference from neighbor cell in LTE-Advanced downlink system. The proposed receiver can suppress and cancel the interference by calculating the unbiased estimation value of interference signal using minimum mean square error (MMSE) or interference rejection combing (IRC) receiver. The interference signal is updated using soft information expressed by log-likelihood ratio (LLR). We perform the system level simulation based on 20MHz bandwidth of 3GPP LTE-Advanced downlink system. Simulation results show that the proposed receiver can improve SINR, throughput, and spectral efficiency of conventional system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.10
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• pp.1808-1814
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• 2008

In addition to RBL function, which is used to applying for spam e-mail filtering, as an effective way to deal with the recently widespread spam types, this paper proposes how to extract URL that was comprised in the original e-mail, apply it to RBL, and expand it. The BotNet, which is used to using for sending spam mails these days, has a problem that it is not able to solve with the distributed addresses of sent mails in spam e-mails. In general, as these spam e-mails are sent from the infected Zombi PC of individual user, the sent address itself is not efficient and is meaningless to use in RBL. As an effective way to filter spam e-mail sent by BotNet, this paper analyzes URLs that contained in the original spam e-mail and proposes how to effectively improve filter rate, based on the distribution data of URL site tempting users. This paper proposes the sending mechanism of spam e-mails from BotNet and the methods to realize those types of spam e-mails. In order to gather analyzable spam e-mails, this paper also carries out an experiment by configuring trap system of spam e-mail. By analyzing spam e-mails, which have been received during the certain period of experiment, this paper shows that the expanded RBL method, using URLs that contained in spam e-mails, is effective way to improve the filter distribution of spam e-mail.

• The Journal of the Convergence on Culture Technology
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• v.5 no.4
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• pp.277-282
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• 2019

This study analyzed the determinants of the financial Soundness of savings banks. In particular, empirical analysis was carried out on how the loan deposit ratio correlates with financial soundness after restructuring. As the restructuring of savings banks was finalized in 2014, asset management changed and it is time to analyze the financial characteristics of savings banks. In summary, the relationship between the savings bank lending rate and the NPL ratio is estimated to have a negative value at the 1% significance level. In other words, the higher the mortgage rate, the lower the substandard and below ratio. It can be said that it is not easy for a savings bank to build an aggressive loan portfolio. In other words, the more difficult it is to finance loans through savings deposits, the more likely the risk aversion tends to be. The higher the corporate loan ratio, average interest expense, and economic growth rate, the higher the risk index. The larger the asset size and the higher the loan growth rate, the lower the risk index. Increasing the mortgage rate may reduce risk-seeking behavior, but it does not mean that it is unconditionally positive for savings banks. Therefore, the loan deposit rate regulation should reduce the incentives for excessive asset expansion and manage preemptive soundness through lending portfolio management.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.20 no.2
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• pp.43-55
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• 2010

${\mu}TESLA$ broadcast authentication protocol have been developed by many researchers for providing authenticated broadcasting message between receiver and sender in sensor networks. Those cause authentication delay Tree-based ${\mu}TESLA$[3] solves the problem of authentication delay. But, it has new problems from Merkel hash tree certificate structure. Such as an increase in quantity of data transmission and computation according to the number of sender or parameter of ${\mu}TESLA$ chain. ${\mu}TPCT$-based ${\mu}TESLA$[4] has an advantages, such as a fixed computation cost by altered Low-level Merkel has tree to hash chain. However, it only use the sequential values of Hash chain to authenticate ${\mu}TESLA$ parameters. So, It can't ensure the success of authentication in lossy sensor network. This paper is to propose the improved method for Tree-based ${\mu}TESLA$ by using XOR-based chain. The proposed scheme provide advantages such as a fixed computation cost with ${\mu}$TPCT-based ${\mu}TESLA$ and a message loss-tolerant with Tree-based ${\mu}TESLA$.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.3
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• pp.59-66
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• 2021

Humans mainly recognize surrounding objects using visual and auditory information among the five senses (sight, hearing, smell, touch, taste). Major research related to the latest object recognition mainly focuses on analysis using image sensor information. In this paper, after emitting various chirp audio signals into the observation space, collecting echoes through a 2-channel receiving sensor, converting them into spectral images, an object recognition experiment in 3D space was conducted using an image learning algorithm based on deep learning. Through this experiment, the experiment was conducted in a situation where there is noise and echo generated in a general indoor environment, not in the ideal condition of an anechoic room, and the object recognition through echo was able to estimate the position of the object with 83% accuracy. In addition, it was possible to obtain visual information through sound through learning of 3D sound by mapping the inference result to the observation space and the 3D sound spatial signal and outputting it as sound. This means that the use of various echo information along with image information is required for object recognition research, and it is thought that this technology can be used for augmented reality through 3D sound.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.5
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• pp.719-730
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• 2021

We have demonstrated a sandwich-type ZnO-based piezoelectric energy harvesting nanogenerator, namely ZCZ-NG device, composed of symmetrically stacked layers of ZnO/carbon tape/ZnO structure. Especially, we have adopted a conductive double-sided adhesive carbon tape in an effort to fabricate a high-quality ZCZ-NG device, leading to its superior output performance in terms of the peak-to-peak output voltage. Effects of the device size, ZnO layer thickness, and bending strain rate on the device performance have been investigated by measuring the output voltage. Moreover, to evaluate the effectiveness of the fabricated ZCZ-NG devices, we have experimentally implemented a sensor network testbed which can utilize the output voltages of ZCZ-NG devices. This sensor network testbed consists of several components such as Arduino-based transmitter and receiver nodes, wirelessly transmitting the sensed information of each node. We hope that this research combining the ZnO-based energy harvesting devices and IoT sensor networks will contribute to the development of more advanced energy harvester-driven IoT sensor networks in the future.