• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.3
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• pp.638-646
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• 2005

In recent wireless communications, direct conversion transceiver or If sampling SDR-based receivers have being designed as an alternative to conventional transceiver topologies. In direct conversion receiver a.chitectu.e, the 1.equency/phase offset between the RF input signal and the local oscillator signal is a major impairment factor even though the conventional AFC/APC compensates the service deterioration due to the offset. To rover the limited tracking range of the conventional method and effectively aid compensation scheme in terms of I/Q channel imbalances, the frequency/phase offset compensation in RF-front end signal stage is proposed in this paper. In RF-front end, the varying phase offset besides the fixed large frequency/phase offset are corrected by using early-late phase compensator. A more simple frequency and phase tacking function in digital signal processing stage of direct conversion receiver is effectively available by an ingenious frequency/phase offset tracking method in RF front-end stage.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.8
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• pp.1853-1858
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• 2015

The existence communications of vessel focused on voice, FAX, ISDN, etc. using satellite on the existent most communications on the ships, and recently, the ships need high quality smart communication service environments. In the results of experiments using the existent system, it could access on board, but in the closed room of vessel, was impossible to access e-mail and smart apps except voice communication. In the present paper, we implemented a novel communication system that can access voice, text, e-mail, file, vessel monitoring apps, etc. It consists of a convergent communication terminal combined with satellite and communication for Smartphone, and smart communication environment on the closed room. As the results, we can access a variety of smart communication in anywhere on board.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.701-704
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• 2007

Recently, More and more consumer enjoy the finance service such as settling, account transferring, stocks investment, and so via mobile device. In the mobile environment, data transferring between the devices is formatted as XML. However, the common XML file is exposed to the attack such as hacking and malignity code, to satisfy security of mobile environment is very difficult. The problem is more seriously at the open platform such as WIPI that is developed by our country. So there is enough reason to propose one system to protect the import data. In this paper, we development the system to digital signature and signature the XML document in order to protect data, and the system is observing the recommendation of the XML Signature Syntax and Processing by W3C. When designing and composition the system, we use the digital signature algorithm RSA, DSA, KCDSA, and HMAC, etc. we test the system at the open WIPI platform.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.498-500
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• 2012

MVNOs(Mobile Virtual Network Operator) provide mobile services without the own spectrum license and they lease the wireless networks from mobile network operators. They provide more covered service simple resellers have served. Most of MVNO provided in Korea have facilities related to subscribers not lines and switches. Therefore interconnection between MVNO and the other operators is performed by mother mobile operators. Recently following to reform the Business Act of Telecommunications, MVNOs are allowed to interconnect directly to others and there are concerning problems to this. This paper reviewed the status of MVNO regulations for major countries and draw from implications for establishing the MVNO regulations in Korea.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.6
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• pp.849-854
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• 2018

Radio base stations, which are widely distributed across large areas, have many difficulties in managing them. Unmanned radio base stations in remote mountains are having a hard time accessing them in case of emergencies. Major telephone service providers only remotely control incoming and outgoing information and local small business partners responsible for maintaining actual facilities do not possess such technologies, so they are each checked during field visits. In this study, in order to process the sensor raw data and smoothing, we apply the particle filters and confirmed that the performance of sensor data accuracy is increased. Integrated system using temperature, humidity, fire condition, and power operation at a wide range of radio base stations under the real-time monitoring status is operated well. It show that all of the status of base station are monitored at the remote office using the cloud server through internet networking.

• The KIPS Transactions:PartC
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• v.9C no.4
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• pp.597-604
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• 2002

Changing group key is necessary for the remaining members when a new member joins or a member leaves the group in multicast communications. It is required to guarantee perfect forward and backward confidentiality. Unfortunately, in large groups with frequent membership changes, key changes become the primary bottleneck for scalable group. In this paper, we propose a novel approach for providing efficient group key distribution in large and dynamic groups. Unlike existing secure multicast protocols, our protocol is scalable to large groups because both the frequency and computational overhead of re-keying is determined by the size of a subgroup instead of the size of the whole group, and offers mechanism to prevent the subgroup managers with group access control from having any access to the multicast data that are transfered by sender. It also provides security service for preserving privacy in wireless computing environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7A
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• pp.560-568
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• 2012

Spectrum sensing and spectrum decision are the main functions that cognitive radios (CRs) have to perform in order to get the best available spectrum band for the establishment of a wireless communication. These problems are worsened in the presence of users with different demands and spectrum channels with different properties in a heterogeneous network. The primary objective in this work is to design and simulate a new spectrum decision algorithm for heterogeneous cognitive radio system. To this end, first, we consider all cognitive users are separated into different traffic classes according to their Quality of Service (QoS). The cognitive users within one traffic class perform spectrum sensing in centralized group-based cooperative spectrum sensing system and the users of different traffic classes share the sensing results. Second, we propose a novel use of the Analytic Hierarchy Process (AHP) to optimally select available bands according to user requirements and detected spectrum channel characteristics (SCC). In this paper, utility function is used as spectrum decision algorithm. Simulation results demonstrate that the proposed method shows can effectively select the best available spectrum channels with a low complexity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1B
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• pp.7-20
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• 2011

Recently, Proxy Mobile IPv6(PMIPv6) networks have been studied as the mobility management protocol to effectively use limited wireless resources. And the multicasting, which is core technology of the Internet broadcast system such as mobile IPTV, has been discussed mainly based on PMIPv6 network. However, multicasting based on PMIPv6 network causes disconnection of services because it does not solve problems of packet loss during binding and group joining procedure. Hence, we propose a seamless multicast scheme which prevents packet loss in PMIPv6 networks. The proposed scheme achieves lower latency than the existing scheme because it combines binding and group joining procedure, a1so it does not cause about packet losses due to performing buffering. We proved the performance using the simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.1057-1064
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• 2007

Cognitive radio(CR) technique which utilizes empty frequency bands allocated to private business but not being used temporally has been researched. According to the standard, CR users detect the primary user using the same channel, CR users should move to the another channel to guarantee the primary user's decodability. Thus, CR systems cannot use the same channel and support the CR user's QoS(Quality of Service) during the channel moving time. In this paper, we propose a radio resource sharing method that CR basestation controls the transmission power with the primary user's SNR(Signal to Noise Ratio) to increase the spectral efficiency of area and to minimize the outage of CR users. In addition, computer simulation demonstrates show that the proposed method improved spectral efficiency of area and decreased outage probability of CR users.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.90-94
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• 2007

The conventional single-reference station positioning is affected by systematic errors such as ionospheric and tropospheric delay, so that the rover must be located within 10 km from the reference station in order to acquire centimeter-level accuracy. The medium-range real-time kinematic has been proven feasible and can be used for high precision applications. However, the longer of the baseline, the more of the time for resolving the integral ambiguity is required. This is due to the fact that systematic errors can not be eliminated effectively by double-differencing. Recently, network approaches have been proposed to overcome the limitation of the single-reference station positioning. The real-time systematic error modeling can be achieved with the use of GPS network. For expanding the effective range and decreasing the density of the reference stations, Land Survey Bureau, Ministry of the Interior in Taiwan set up a national GPS network. In order to obtain the high precision positioning and provide the multi-goals services, a GPS network including 66 stations already been constructed in Taiwan. The users can download the corrections from the data center via the wireless internet and obtain the centimeter-level accuracy positioning. The service is very useful for surveyors and the high precision coordinates can be obtained real time.