• ETRI Journal
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• v.45 no.5
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• pp.781-794
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• 2023

Uncrewed aerial vehicles (UAVs) have become a vital element in nonterrestrial networks, especially with respect to 5G communication systems and beyond. The use of UAVs in support of 4G/5G base station (uncrewed aerial vehicle base station [UAV-BS]) has proven to be a practical solution for extending cellular network services to areas where conventional infrastructures are unavailable. In this study, we introduce a UAV-BS system that utilizes a high-capacity wireless backhaul operating in millimeter-wave frequency bands. This system can achieve a maximum throughput of 1.3 Gbps while delivering data at a rate of 300 Mbps, even at distances of 10 km. We also present the details of our testbed implementation alongside the performance results obtained from field tests.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1B
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• pp.34-46
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• 2009

The remarkable growth of Korean telecommunication market has based on the introduction of competition as well as mobile technology like CDMA. It was well Down that such a conspicuous growth has been towed by mobile service rather than fixed telephone service. In telecommunications service the number of subscribers to mobile was over 40 millions in 2006 and also, while the traffic amount of fixed telephone has been more decreased, that of mobile, which already outnumbers the fixed, has been constantly increased and will be much more in future. It will accelerate the substitution of access and call demand of fixed service by mobile. This change of technology and demand does affect directly the market performance of telecommunications. And regulation has also an effect on market structure, which finally affects on market performance. In this paper we suppose the fixed and mobile telecommunications services are in a same industry. After reviewing the relations among the demand, cost, charge structure and revenue structure in the one fixed and mobile telecommunications market using the framework of an industrial structure analysis, we discuss the current issues of telecommunications regulation and implications for the future regulation.

• ETRI Journal
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• v.44 no.6
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• pp.915-924
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• 2022

In this paper, we present a two-stage scalable channel estimator (TSCE), a deep learning (DL)-based scalable, and robust channel estimator for wireless cellular networks, which is made up of two DL networks to efficiently support different resource allocation sizes and reference signal configurations. Both networks use the transformer, one of cutting-edge neural network architecture, as a backbone for accurate estimation. For computation-efficient global feature extractions, we propose using window and window averaging-based self-attentions. Our results show that TSCE learns wireless propagation channels correctly and outperforms both traditional estimators and baseline DL-based estimators. Additionally, scalability and robustness evaluations are performed, revealing that TSCE is more robust in various environments than the baseline DL-based estimators.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.10
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• pp.2529-2547
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• 2012

In this paper, we use a quadrotor-based mobile sink to gather sensor data from the terrestrial deployed wireless sensor network. By analyzing the flight features of the mobile sink node, we theoretically study the flight constraints of height, velocity, and trajectory of the mobile sink node so as to communicate with the terrestrial wireless sensor network. Moreover, we analyze the data amount which the mobile sink can send when it satisfies these flight constraints. Based on these analysis results, we propose a data acquisition approach for the mobile sink node, which is discussed detailed in terms of network performance such as the transmission delay, packet loss rate, sojourning time and mobile trajectory when given the flying speed and height of the mobile sink node. Extensive simulation results validate the efficiency of the proposed scheme.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.567-570
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• 2005

Recently, as mobile paradigms such as telematics or LBS (Location Based Service) have been being more diverse and mobile devices such as PDA (Personal Digital Assistance) or several telematics terminals have been being used more widely, mobile services, for example, mobile geographic information service have been being put more importance by people. In this paper, we propose to adopt S/W and data streaming mechanism as a method to improve performance of mobile geographic information service which is a representative of mobile services based on client-server architecture. The show the effectiveness of proposed methods, we design and implement S/W streaming prototype system and sample mobile geographic information service to be executed on the S/W streaming system.

• Journal of Distribution Science
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• v.15 no.12
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• pp.53-60
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• 2017

Purpose - This paper analyzes the effect of the handset subsidy and the Mobile Number Portability subscriber subsidy regulation, which are the main regulation adopted in "Law on the Improvement of the Mobile Terminal Distribution System" (Mobile Terminal Distribution Act), on the social surplus, the consumer surplus and profits of telecommunications carriers. We focus our analysis on whether the service charge competition is stimulated enough so that it can compensate for the loss of subsidies. Research design, data, and methodology - We use simple economic model to assess the impact of the handset subsidy and the Mobile Number Portability subscriber subsidy regulation. Unlike the former researches on this topic, we depart from using Hotelling model, and instead use the switching cost model, which uses switching cost as a parameter of market powers of telecommunications carriers. We also study the effect of the two different regulations when they are adopted both independently and concurrently. Results - If the market powers of telecommunications carriers are over certain threshold, contrary to the regulatory agency's assertion, the service charge competition would not be stimulated enough to compensate for the deduction in the subsidies, and thus the consumer surplus is compromised. Number Portability subsidy, especially, undermines the rival's market power and thus reduces the service charge. On the other hand, the regulations will also increase the profits of telecommunications carriers. However, social surplus is maximized when both of the regulations are present because the regulations reduces the frequency of switching handsets inefficiently. Conclusions - In enacting the Mobile Terminal Distribution Act, the telecommunications regulatory agency asserted that the regulation on subsidies will stimulate service charge competition, and in the long run, enhance the consumer surplus. However, contrary to the regulatory agency's assertion, subsidy regulation, especially the regulation on Number Portability subsidy, reduces consumer surplus. On the other hand, the Mobile Terminal Distribution Act can also increase the profits of telecommunications carriers because it decreases competition among the telecommunications carriers. However, the Mobile Terminal Distribution Act can increase the social surplus because it reduces inefficient switching of handsets.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10B
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• pp.929-935
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• 2006

When the Internet phone service, generally PC-to-Phone, first entered into the telecommunications service market, no regulatory issues were arisen to manage the service within the regulatory framework because of it's low quality, no phone number assignment and etc. However, almost the same quality, more applications and cheaper price compared with the fixed telecommunications service, have changed the regulator's policy allowing Internet phone service within market mechanism. While incumbent fixed telecommunications service enterprises had given with tremendous duties to continue the job categorized 'facilities-based telecommunication service provider', and which can be unreasonable and unfair if Internet phone service enterprises are allowed to enter into the fixed telecommunications market without any regulation. Thus, new regulatory framework has worked for the Internet phone service named the VoIP service generally in the fixed telecommunications market. Recently, VoIP is provided not only in the fixed telecommunications market but also in the mobile market as Wi-Fi phone is feasible in the wireless LAN environment. Furthermore, bundled service of Wi-Fi and cellular phone service will be launched soon, and the next version will be the mobile VoIP service operating like a cellular phone service. Hence, we will meet similar situation when the VoIP sewice enters into the fixed telecommunications service market. And, in this paper, we prospect the regulatory issues arising when the wireless or mobile VoIP service enterprises enter the mobile market, by analyzing possible scenarios.

• ETRI Journal
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• v.31 no.1
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• pp.92-94
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• 2009

We propose a system for mobile-phone fraud detection based on a bidirectional artificial neural network (bi-ANN). The key advantage of such a system is the ability to detect fraud not only by offline processing of call detail records (CDR), but also in real time. The core of the system is a bi-ANN that predicts the behavior of individual mobile-phone users. We determined that the bi-ANN is capable of predicting complex time series (Call_Duration parameter) that are stored in the CDR.

• Journal of the Korea Society of Computer and Information
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• v.15 no.5
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• pp.83-92
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• 2010

Along with the advance of industrial technology in mobile telecommunications and diversity in customer needs, today's Korean mobile telecommunication market has rapidly expanded due to stronger competition among businesses as well as increasing the number of subscribers. 3G roll-outs of mobile telecommunications service, so called "HSDPA" has seriously promoted marketing strategies among mobile telecommunication companies which led to move to the next generation customers. Understanding the competitive situation, mobile telecommunications companies are currently focusing on increasing sales per subscriber as well as increasing the number of subscribers as a solution to occupy the leading position in the mobile telecommunications industry in the future. The purpose of this study was to classify the customers in mobile telecommunications service with or without higher tendency of intention to subscribe and use the service using discriminant analysis. Through the discriminant analysis, discriminant function which classifying the critical user has been identified. The result of this study will give useful marketing strategies in competitive HSDPA mobile telecommunications market.

• International Journal of Contents
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• v.6 no.3
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• pp.59-64
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• 2010

The world mobile service is growing sharply and became bigger market than wired. So it is very needed to find the political way to promote mobile industry. The United States government recently decided to introduce new mobile policies for promoting mobile industry. Until now the telecommunications policies of the United States have affected policy developments for many countries including Korea. In this context, we studied the validity of introducing new mobile policies of the United States in Korea. We found that new mobile policies can cause the change of mobile market environment; mobile market power will be dispersed from network to content, application and devise, and new mobile market environment where consumers freely select and use network as well as content, application and devise will be made. Also we found empirically that if new policies are introduced in Korea, mobile industry will be promoted as Korean consumers use mobile services and goods quite actively in new mobile market. We think our results provide reasonable evidence to introduce new mobile policies in Korea.