• Journal of Internet Computing and Services
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• v.7 no.1
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• pp.173-178
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• 2006

In this paper, a channel estimation based on the time-domain windowing and its imperfectness in OFDM-based multiple-antenna transmission systems are analyzed with an emphasis on a preamble design for multi-channel separation, From the computer simulation results, the OFDM-CDMA system applying a space-time-frequency diversity with a full-rate full diversity code can give the diversity of D = 4 and D = 8 for both multi-user cases of maximum user and half user capacities, respectively

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.1200-1202
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• 2003

Satellite and aerial images are very useful means to monitor ecological and environmental situation. Nowadays more and more officials at Ministry of Environment in Korea need to access and use these image data through networks like internet or intranet. However it is very hard to manage and service these image data through internet or intranet, because of its size problem. In this paper very large image data service system for Ministry of Environment is constructed on web environment using image compression and web based image processing technology. Through this system, not only can officials in Ministry of Environment access and use all the image data but also can achieve several image processing effects on web environment. Moreover officials can retrieve attribute information from vector GIS data that are also integrated with the system.

• Proceedings of the Korea Information Processing Society Conference
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• 2019.10a
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• pp.211-212
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• 2019

Slicing Radio Access Network (RAN) can help in effectively utilizing the network bandwidth and to better manage the increasing traffic over interent. RAN slicing system discussed in this paper is based on an open-source slicing mechanism in which we write a JSON configuration file for slicing policy and send it to the FlexRAN controller. FlexRAN controlls the core networks (CNs) through OAI-RAN on the evolved packet core (EPC) component of this system. Each CN is responsible for handling a saperate RAN slice. The type of internet traffic is identified by the FlexRAN crontroller and is sent to the respective CN through OAI-RAN. CN handles the traffic according to the allocated bandwidth and in this way the internet traffic is sliced inside the EPC component.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.1
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• pp.365-382
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• 2021

This paper proposes a novel two-way relaying (TWR) approach for a two-relay wireless network based on non-orthogonal multiple access (NOMA), where two terminals exchange messages with a cellular base station (BS) via two intermediate relay stations (RSs). We propose a NOMA-based TWR approach with two relaying schemes, i.e., amplify-and-forward (AF) and decode-and-forward (DF), referred to as NOMA-AF and NOMA-DF. The sum-rate performance of our proposed NOMA-AF and NOMA-DF is analyzed. A closed-form sum-rate upper bound for the NOMA-AF is obtained, and the exact ergodic sum-rate of NOMA-DF is also derived. The asymptotic sum-rate of NOMA-AF and NOMA-DF is also analyzed. Simulation results show that the proposed scheme outperforms conventional orthogonal multiple access based transmission schemes. It is also shown that increasing the transmit power budget of the relays only cannot always improve the sum-rates.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.11
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• pp.4595-4610
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• 2020

In the practical communication environment, the accurate channel state information (CSI) is difficult to obtain, which will cause the mismatch of resource and degrade the system performance. In this paper, to account for the channel uncertainties, a robust power allocation scheme for a downlink Non-orthogonal multiple access (NOMA) heterogeneous network (HetNet) is designed to maximize energy efficiency (EE), which can ensure the quality of service (QoS) of users. We conduct the robust optimization model based on worse-case method, in which the channel gains belong to certain ellipsoid sets. To solve the non-convex non-liner optimization, we transform the optimization problem via Dinkelbach method and sequential convex programming, and the power allocation of small cell users (SCUs) is achieved by Lagrange dual approach. Finally, we analysis the convergence performance of proposed scheme. The simulation results demonstrate that the proposed algorithm can improve total EE of SCUs, and has a fast convergence performance.

• International journal of advanced smart convergence
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• v.13 no.2
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• pp.7-15
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• 2024

6G network technology represents the next generation of communications, supporting high-speed connectivity, ultra-low latency, and integration with cutting-edge technologies, such as the Internet of Things (IoT), virtual reality, and autonomous vehicles. These advancements promise to drive transformative changes in digital society. However, as technology progresses, the demand for efficient data transmission and energy management between smart devices and network equipment also intensifies. A significant challenge within 6G networks is the optimization of interactions between satellites and smart devices. This study addresses this issue by introducing a new game theory-based technique aimed at minimizing system-wide energy consumption and latency. The proposed technique reduces the processing load on smart devices and optimizes the offloading decision ratio to effectively utilize the resources of Low-Earth Orbit (LEO) satellites. Simulation results demonstrate that the proposed technique achieves a 30% reduction in energy consumption and a 40% improvement in latency compared to existing methods, thereby significantly enhancing performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2B
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• pp.192-202
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• 2004

In this paper we have proposed policy-based network management system architecture for Internet QoS support Mobile IP networks that is divided into four layers(application layer, information management layer, policy control layer, device layer), then we propose an implementation strategy of policy-based network management system to enforce various control and network management operations and a model of policy server using SCOPS(Simple Common Open Policy Service) protocol that is developed in this research. For policy-based mobile IP network management system implementation, we have derived four policy classes(access control, mobile IP operation, QoS control, and network monitoring) and we showed operation procedures for each policy scenarios. Finally we have implemented Internet QoS support policy-based mobile IP network testbed and management system and verified out DiffServ policy enforcement behaviors for a target class service that is arranged a specific bandwidth on network congestion conditions.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.6
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• pp.267-273
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• 2011

The importance of networking capability is gaining more weight for enterprise business and high-speed Internet access with guaranteed security management is essential to companies. This paper presents a unified network security management solution to support high-speed Internet access, active security management, traffic classification and control. The presented system provides firewall, VPN, intrusion detection, contents filtering, traffic management, QoS management, and history log functions in unified manner implemented in a single appliance device located at the edge of enterprise networks. This will enable cost effective unified network security solution to companies.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.2
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• pp.197-203
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• 2011

Ad-hoc networks do not rely on a preexisting infrastructure such as Access Points(AP) in wireless network infrastructure. Instead each node participates in routing by forwarding data for other nodes. It makes required broadcasting to transmit packets to the whole network. In that part, each node tries to transmit data without any information about the other nodes. Therefore it causes duplication of transmission and waste of power. This paper presents adaptive probabilistic broadcasting schemes based on packet reception counts to alleviate the broadcast storm problem for wireless ad hoc networks. In this algorithm, each node calculates efficiency broadcast probability. Simulation results for the proposed flood algorithm are also presented.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.6
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• pp.3000-3022
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• 2019

Full-duplex (FD) technologies enable wireless nodes to simultaneously transmit and receive signal using the same frequency-band. The FD modes could improve their physical layer throughputs. However, in the wireless ad hoc networks, the FD communications also produce new interference risks. On the one hand, the interference ranges (IRs) of the nodes are enlarged when they work in the FD mode. On the other hand, for each FD pair, the FD communication may cause the potential hidden terminal problems to appear around the both sides. In this paper, to avoid the interference risks, we first model the IR of each node when it works in the FD mode, and then analyze the conditions to be satisfied among the transmission ranges (TRs), carrier-sensing ranges (CSRs), and IRs of the FD pair. Furthermore, in the media access control (MAC) layer, we propose a specific method and protocol for collision avoidance. Based on the modified Omnet++ simulator, we conduct the simulations to validate and evaluate the proposed FD MAC protocol, showing that it can reduce the collisions effectively. When the hidden terminal problem is serious, compared with the existing typical FD MAC protocol, our protocol can increase the system throughput by 80%~90%.