• Journal of the Korean Operations Research and Management Science Society
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• v.21 no.1
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• pp.51-69
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• 1996

We consider a consumer self-selection model in which a regulated firm faces two market segments with differing valuation of quality of telecommunication services and examine some economic implications from the behaviors of the firm. In the context of a regulated monopolist, even though the results depend on the degree of privatization, the firm could lower the quality of the low-end model and reduce the price of the high-end in order to alleviate cannibalization. This justifies the provision of universal service policy in the telecommunications market. Based on this self-selection model, we also analyze an extended model of product introduction and show that the monopolist will introduce new product with the same introduction time of social planner. However, when we consider competition among firms, the market equilibrium may not guarantee the efficient time of product introduction.

• Journal of Communications and Networks
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• v.13 no.4
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• pp.377-384
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• 2011

Cooperative beamforming has previously been proven to be an efficient way to improve the cooperative diversity. This method generally requires all relay nodes to participate in beamforming, which can be seen as "all participate" cooperative beamforming. However, not all relay nodes have constructive impacts on the end-to-end bit error rate (BER) performance. Based on this observation, we propose a new cooperative scheme which only selects those "appropriate" relay nodes to perform cooperative beamforming. Such relay nodes can be simply determined with mean channel gains. Therefore, the selection complexity is significantly reduced as global instantaneous channel state information is not required. This scheme guarantees that energy is only allocated to the "appropriate" relay nodes, and hence provides superior diversity. We also prove that power allocation among source and selected relay nodes is a convex problem, and can be resolved with lower computational complexity. Simulation results demonstrate that our scheme achieves an essential improvement in terms of BER performance for both optimal and limited feedback scenarios, as well as high energy-efficiency for the energy-constrained networks.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2006.11a
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• pp.602-605
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• 2006

Recently, under recognition that ubiquitous computing is core paradigm to build up a state of new knowledge information and to strengthen the competitiveness of domestic information industry, governments, enterprises, and institutes in United States, Europe, and Japan devote all their energies to develop technologies concerned. In Korea, the government presents ubiquitous technologies as a main part of the next generation growth industry, and also other governmental agencies and enterprises concentrate their energies on early fruition of ubiquitous society. Accordingly, as a foundation research to apply ubiquitous environment which emerged as a next generation high-end telecommunication technology effectively to construction field, this paper will discuss about element technologies to realize changing aspects of construction process under ubiquitous environment and information services by stages.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.2 no.3
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• pp.48-60
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• 2003

With the rapid successful deployment of WLANs worldwide in numerous hotspots for high data rate, wireless access for data services has created the need to integrate the Cellular Networks with WLAN Networks. The integrated wireless environment will provide the end user a much better service experience along with a single subscription and a single bill. In this paper we focus on inter-working approaches, which combine WLANs and Cellular Networks into an integrated wireless environment capable of ubiquitous access to data services and very high data rates in hotspots areas. We first list the key requirements which are currently being standardized within the 30PP for integration with WLANs networks. We discuss two inter-working architectures namely loosely coupled and tightly coupled This paper will detail the loosely coupled inter-working approach while briefly discussing the tightly coupled inter-working. Finally, we will conclude that the loosely coupled approach is evolutionary and less intrusive than the tightly coupled approach.

• Journal of information and communication convergence engineering
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• v.10 no.2
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• pp.103-107
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• 2012

An end-launched adapter combining a coaxial loop within a rectangular waveguide has been analyzed and designed. The accurate electromagnetic modeling of input impedance for the adapter design has been developed using a modal analysis method. Also, design parameters to improve the end-launched adapter have been investigated. Numerical and experimental results of the proposed model have been compared with the results of previous works, and verified by an electromagnetic simulator of High Frequency Structure Simulator (HFSS). The input voltage standing wave ratios (VSWRs) are smaller than 2 over the wide frequency band from 7.5 GHz to 10.5 GHz.

• Journal of electromagnetic engineering and science
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• v.4 no.3
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• pp.128-136
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• 2004

In this paper,. with the aim of achieving the expected performance improvement for a polarization diversity system, we analyzed two-branch polarization diversity at the receiving end of a mobile link which a transmitter emits circularly polarized wave. In this analysis, to calculate the correlation coefficient considered by XPD(cross polarization discrimination) between the two received signals, a simple theoretical model of circular polarization diversity is adopted. From the analysis results, it is clearly seen that the correlation coefficient of circular polarization diversity evaluated by the XPD is less than that of conventional linear polarization diversity. And also, we designed and implemented a circular polarization diversity system with micro-strip antenna. By using the circular polarization diversity system, we analyzed the measured data in indoor NLOS(Non-Line-Of-Sight) environments. From this analysis results, it is also clearly seen that the diversity effect of circular polarization diversity system shows better performance compared to the conventional linear diversity system by about 3 dB high.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.821-824
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• 1993

This paper deals with a $3{\phi}$ rectifier unit for telecommunication system. The rectifier unit is developed to Cope with the step-up of the AC input voltatage from 220V to 380V. By using a buck-type converter in the front-end, it keeps the input power factor high and reduces the voltage ripple in the dc output. It also has a very wide voltage regulation range, which lets the unit be applied for both the 220V and 380V input system. The study includes the power conversion scheme, control strategy, snubber circuit and finally, experimental results.

• Journal of Communications and Networks
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• v.17 no.1
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• pp.58-66
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• 2015

Aeronautical communication networks (ACN) is an emerging concept in which aeronautical stations (AS) are considered as a part of multi-tier network for the future wireless communication system. An AS could be a commercial plane, helicopter, or any other low orbit station, i.e., Unmanned air vehicle, high altitude platform. The goal of ACN is to provide high throughput and cost effective communication network for aeronautical applications (i.e., Air traffic control (ATC), air traffic management (ATM) communications, and commercial in-flight Internet activities), and terrestrial networks by using aeronautical platforms as a backbone. In this paper, we investigate the issues about connectivity, throughput, and delay in ACN. First, topology of ACN is presented as a simple mobile ad hoc network and connectivity analysis is provided. Then, by using information obtained from connectivity analysis, we investigate two communication models, i.e., single-hop and two-hop, in which each source AS is communicating with its destination AS with or without the help of intermediate relay AS, respectively. In our throughput analysis, we use the method of finding the maximum number of concurrent successful transmissions to derive ACN throughput upper bounds for the two communication models. We conclude that the two-hop model achieves greater throughput scaling than the single-hop model for ACN and multi-hop models cannot achieve better throughput scaling than two-hop model. Furthermore, since delay issue is more salient in two-hop communication, we characterize the delay performance and derive the closed-form average end-to-end delay for the two-hop model. Finally, computer simulations are performed and it is shown that ACN is robust in terms of throughput and delay performances.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.8
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• pp.318-330
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• 2003

The advantages of "VPN over Internet" are cost-effectiveness and flexibility However, the disadvantages are the lack of sufficient QoS mechanism and transmission capacity for high bandwidth service. Given this increasing demand for high bandwidth Internet and QoS assurances in "PN over Internet", IP/GMPLS based control plane combined with a high bandwidth capacity of DWDM optical network is seen as a very favorable approach for the realization of future "OVPN over IP/GMPLS over DWDM" Within OVPN for providing QoS guaranteed multimedia service over the NGOI(Next Generation Optical Internet) based on the "IP/GMPLS over DWDM" concept, differentiated QoS framework is one of the key issues to implement OVPN over DWDM-based NGOI. Keeping in mind that IETF(Internet Engineering Task Force) and ITU-T(International Telecommunication Union) are standardizing IP/GMPLS over DWDM protocol framework as a solution for the NGOI, in this paper, we suggest Optical-LSP establishment and QoS maintenance scheme based on DOQS(Differentiated Optical QoS Service) classes, which are the key issue of DOQS protocol framework for assuring end-to-end QoS in "OVPN over IP/GMPLS over DWDM".

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.9
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• pp.107-115
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• 2013

Smart appliances with multi-media and telecommunication equipments provide users complicated convenience functions. On the contrary, 8-bit controller-based low performance electronics still cannot afford such multimedia and telecommunication. If we find a way to have low-end electronics connected and provide complicated functions, they can be also made "smart". Fortunately, 8-bit controllers used in low-end appliances have UART, which can be connected to any of BlueTooth, Wi-Fi and ZigBee communication modules which can, in turn, communicate with smart devices. Any communication module can be attached to the low-end electronics due to the variety of smart devices' connectivity at the other side. Although the convenience functions seem complicated, they are actually macros in a script form composed of micro commands which implement the base functions of appliances. Since the kinds of the base functions are not that many, the low-end electronic appliances will become "smart" if their control program can be extended to execute sequentially the micro commands in any combination. Such simple innovation has not seen the world, until now due to the overhead of the additionally required hardware such as display devices and buttons. The high-quality display and touch screen functionalities of smart devices can replace the required hardware, and remove the overhead completely. In fact, the low-end appliances become smart as if an "evolution kit" is newly equipped.