• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.10a
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• pp.668-670
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• 2017

Visible Light Communication, which is promising as a next generation near field wireless communications, has been increased study and application case due to the development of LED technology. However, there are few application cases to IoT service due to the necessity of separate equipment for communication and limitation of light transmission to obstacles. In this paper, it propose a portable VLC transceiver module that can be connected to USB OTG and dedicated application for control to realization position possible necessary technique. The string input from the dedicated application is sent to the VLC module via USB OTG to transmit and receive data between the modules. As string transmission experiment result, it is confirmed that ASCII code transmission between VLC transceiver modules is possible through control of the implemented dedicated application.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3455-3461
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• 2015

LTE and Wi-Fi networks provide wireless communication services to passengers in subway where the number of network access fluctuates according to passenger movement. While the number of network access increase, LTE can provide stable communication service but Wi-Fi suffers temporal access delay to network. This paper analyzes the increase in access delay of Wi-Fi network according to increasing user in subway section by making mathematical modeling of Wi-Fi network and simulation study. The access delay characteristics of Wi-Fi network is measured along an subway line and the results are compared to the theoretical study. These results can be applied to the connection method to build an efficient network structure between LTE and Wi-Fi interworking network and the future introduction of LTE-R.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.4
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• pp.1817-1823
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• 2011

OFDM Modulation is used for multimedia transmission At Urban Train. Recently the application field about data transmission is expanding the image as well. The case which the number of OFDM carrier is big is advantageous because multipass fading is big 18GHz wireless frequency. Existing WLAN which an ethernet transmission is possible is not suitable to a great distance transmission because number of carrier is 64. In this paper, we developed OFDM modem suitable to transmit broadband data at high speed train. A doppler compensation block added to offset the doppler effect. Therefore, the effectiveness is expected to be very big in field of urban train.

• Journal of KIISE:Information Networking
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• v.29 no.4
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• pp.333-345
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• 2002

As computers and networks become popular, distributing information on the Internet is common in our daily life. Also, the explosion of the Internet, of wireless digital communication and data exchange on Internet has rapidly changed the way we connect with other people. But secure mail is gaining popularity abroad and domestically because of their nature of providing security. That is. It has been used a variety of fields such as general mail and e-mail for advertisement. But, As the data transmitted on network can be easily opened or forged with simple operations. Most of existing e-mail system don't have any security on the transmitted information. Thus, security mail system need to provide security including message encryption, content integrity, message origin authentication, and non-repudiation. In this paper, we design and implement secure mail system with secure key agreement algorithm, non-repudiation service, and encryption capability to provide services for certification of delivery and certification of content as well as the basic security services.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.11
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• pp.2576-2583
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• 2015

In a full-duplex (FD) wireless cellular network, uplink (UL) users induce the severe inter-user interference to downlink (DL) users. Therefore, a user scheduling that makes a pair of DL user and UL user to use the same radio resource simultaneously influences the system performances significantly. In this paper, we first formulate an optimization problem for user scheduling to minimize the occurrence of outage, aiming to guarantee the quality of service of users, and then we propose a suboptimal user scheduling algorithm with low complexity. The proposed scheduling algorithm is designed in a way where the DL user with a worse signal quality has a higher priority to choose its UL user that causes less interference. Simulation results show that the FD system using the proposed user scheduling algorithm achieves the optimal performance and significantly decreases the outage probability compared with the conventional half-duplex cellular system.

• Journal of Internet Computing and Services
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• v.10 no.2
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• pp.65-73
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• 2009

IEEE802.11 Wireless LAN(WLAN) is being widely used in public space such as airport, and increases the networking boundary in campus and enterprise, and it has lastly attracted considerable attention for mesh network and converged network with other 3G mobile communication networks. In WLAN, load balancing among Access Points(AP) is an important issue for efficient resource management or supporting the Quality of Service(QoS) of traffic, but most researches focused on the AP selection in network entry or roaming of Stations(STA). In this paper, we propose an AP-Initiated Flow Redirection(FR) for AP load balancing by monitoring AP's availability in the true sense. When the AP's resource becomes almost saturated, that is used more than a specific threshold, the AP queries the roaming possible neighbor APs about their availability and calculates the distribution of traffic load with statistical methods such as entropy or chi-square. Finally, the AP decides flows and new APs for redirection and performs it. Our simulation results show that our FR mechanism increases the performance in the various views.

• Journal of Internet Computing and Services
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• v.17 no.6
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• pp.25-31
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• 2016

Recently, with greatly improving the wireless communication technology, new services are created using smart sensors, i.e., machine-to-machine (M2M) and Internet of Things (IoT). In this paper, we propose a novel IoT device (IoTD) personalization method that adopt Small-cell Access Points (SAPs) to control IoTDs using user equipments (UEs), e.g., smart phones and tablet PC, from service users. First, we introduce a system architecture that consists of UE, IoTD, and SAP and propose the IoTD personalization method with two procedures, i.e., IoTD profile registration procedure and IoTD control procedure. Finally, through simulations, we evaluated the system performance of the proposed scheme and it is shown that the proposed scheme outperforms the conventional scheme in terms of the packet delay, packet loss probability, and normalized throughput.

• Journal of Korea Spatial Information System Society
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• v.10 no.3
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• pp.67-78
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• 2008

With the rapid development of wireless communication and mobile equipment, many applications for location-based services have been emerging. Moving objects such as vehicles and ships change their positions over time. Moving objects have their moving path, called the trajectory, because they move continuously. To monitor the trajectory of moving objects in a large scale database system, an efficient Indexing scheme to processed queries related to trajectories is required. In this paper, we focus on the issues of minimizing the dead space of index structures. The Minimum Bounding Boxes (MBBs) of non-leaf nodes in trajectory-preserving indexing schemes have large amounts of dead space since trajectory preservation is achieved at the sacrifice of the spatial locality of trajectories. In this thesis, we propose entry relocating techniques to reduce dead space and overlaps in non-leaf nodes. we present performance studies that compare the proposed index schemes with the TB-tree and the R*-tree under a varying set of spatio-temporal queries.

• Journal of Advanced Navigation Technology
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• v.22 no.4
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• pp.288-294
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• 2018

The entertainment system of the aircraft has changed its paradigm in the form of using passenger electronic devices instead of using a fixed monitor. This has simplified the on-board equipment while the risk of safety has increased with the electric charging of portable electronic devices. Unlike personal portable electronic devices that do not have a transmission function, the use of Wi-Fi enabled electronic devices(T-PED) is allowed and the battery is required to be charged in the cabin. In this study, we used the NASA Aviation Safety Reporting System to investigate the effects of changes in wireless environment and entertainment service. Based on this, we analyzed the risks of personal electronic devices by sharing event occurrence cases caused by in-flight electronic equipment or passenger portable electronic devices(especially smart phones) from the viewpoint of aircraft safety management. This analysis includes identification of potential hazards and risk assessment, and finally the strategies for risk mitigation for safe use of portable electronic devices are suggested.

• The KIPS Transactions:PartC
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• v.17C no.2
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• pp.189-196
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• 2010

The LEACH does not use flooding method for data transmission and this makes low power consumption. So performance of the WSN is increased. On the other hand, QoS based algorithm which use restricted flooding method in WSN also achieves low power consuming rate by reducing the number of nodes that are participated in routing path selection. But when the data is delivered to the sink node, the LEACH choose a routing path which has a small hop count. And it leads that the performance of the entire network is worse. In the paper we propose a QoS based energy efficient clustering and routing algorithm in WSN. I classify the type of packet with two classes, based on the energy efficiency that is the most important issue in WSN. We provide the differentiated services according to the different type of packet. Simulation results evaluated by the NS-2 show that proposed algorithm extended the network lifetime 2.47 times at average. And each of the case in the class 1 and class 2 data packet, the throughput is improved 312% and 61% each.