• Journal of Industrial Convergence
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• v.20 no.1
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• pp.63-68
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• 2022

In schools and corporate buildings, public WiFi Access Points are installed on the ceilings of hallways. In the case of an architectural structure in which a WiFi signal enters through a steel door made of a material with high signal attenuation, Internet connection is frequently cut off or fails when the door is closed. To solve this problem, our research implements an economical and portable WiFi extender using a Raspberry Pi and an auxiliary battery. Commercially available WiFi extenders have limitations in the location where the power plug is located, and WiFi extension using the WiFi hotspot function of an Android smartphone is possible only in some high-end models. However, because the proposed device can be installed at the position where the Wi-Fi reception signal is the best inside the door, the WiFi range can be extended while minimizing the possibility of damage to the original signal. Experimental results show that it is possible to eliminate the shadows of radio waves and to provide Internet services in the office when the door is closed, to the extent that web browsing and real-time video streaming for 720p are possible.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.9
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• pp.891-897
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• 2006

The coverage of the NDGPS is nationwide currently and by 2007 more than 2 NDGPS signal will be available in most of Korean peninsula both coastal area and inland. The role of NDGPS beacon is transmitting pseudorange corrections however if range or pseudorange can be measured from NDGPS beacon signal, it might be possible to construct an independent regional navigation system: The range from NDGPS beacon signal can be used as additional measurements to remove GPS shadow area and to improve accuracy and reliability of GPS. Furthermore, by adding Loran-C, a regional radio navigation system without GPS can be possible. In this paper, a feasibility study on the regional positioning system using NDGPS and LORAN-C are given. The results show that the NDGPS and LORAN-C can be used as a ground based regional navigation system if requirements such as synchronization of NDGPS network, dual coverage of NDGPS, navigation algorithm for both NDGPS and LORAN-C measurements and an efficient ASF compensation method are met.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.1
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• pp.94-106
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• 2020

Recently, the radio navigation method utilizing the GPS(Global Positioning System) satellite information is widely used as the method to measure the position of objects. As GPS applications become wider and fields based on various positioning information emerge, new methods for achieving higher accuracy are required. In the case of autonomous vehicles, the INS(Inertial Navigation System) using the IMU(Inertial Measurement Unit), and the DR(Dead Reckoning) algorithm using the in-vehicle sensor, are used for the purpose of preventing degradation of accuracy of the GPS and to measure the position in the shadow area. However, these positioning methods have many elements of problems due not only to the existence of various shaded areas such as building areas that are continually enlarged, tunnels, underground parking lots and but also to the limitations of accumulation-based location estimation methods that increase in error over time. In this paper, an efficient positioning method in a large underground parking space using Fingerprint method is proposed by placing the AP(Access Points) and directional antennas in the form of four anchors using WLAN, a popular means of wireless communication, for positioning the vehicle in the GPS shadow area. The proposed method is proved to be able to produce unchanged positioning results even in an environment where parked vehicles are moved as time passes.

• Journal of the Korean Association of Geographic Information Studies
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• v.8 no.4
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• pp.143-154
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• 2005

This paper proposes the location acquisition methods and LBS(location-based services) system using RFID(radio frequency identification) tags with location information in ubiquitous city. Location information is checked using RFID tags attached to various buildings. stores and road signs. And various LBSs are provided based on the location information. Traditionally, when the location information is obtained by a GPS, the precision of the location information may deteriorate due to geographical displacement of a satellite and GPS receivers, for example shadow zone by building, in-door environment, and heavy cloud. The objective of this paper is to provide a ULID(universal location identification) data structure, a ULID-based location acquisition method and an LBS system, in which precise location information is extracted using RFID tags attached to various buildings, stores and road signs and ULID and also danger of information leakage is minimized so that an LBS of ubiquitous environment can be provided to a user.

• Journal of Chest Surgery
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• v.23 no.5
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• pp.929-935
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• 1990

Violence in our society, combined with improving transport system, resulted in increased numbers of patients with cardiac wounds reaching the hospital alive. Most patients with penetrating cardiac injury, rather than blunt injury, present with a syndrome of either hemorrhagic shock or cardiac tamponade. And they should be operated upon as soon as possible. Often the atrioventricular valves and other important cardiac structures are also damaged by the penetrating instruments or missile. Both intracardiac communications and atrioventricular fistulas may result in significant left-to-right shunts accompanied by congestive heart failure, necessitating surgical correction. Usually, retained cardiac foreign bodies, which are almost always bullets or fragments of missiles, may lie within a cardiac chamber or in the myocardium. Emboli of bullets or other missiles from distant sites to the right side of the heart are numerous enough to require attention. Recently we experienced a case with intracardiac foreign body due to penetrating cardiac injury. A 19 year-old man was admitted to our hospital due to penetrating anterior chest wound by iron segment. The roentgenogram of the chest revealed a radio-opaque metallic shadow in left lower chest around the cardiac apex, mild blunting of left costophrenic space, but no cardiomegaly. During operation the foreign body was noted to be present in the cardiac chamber by the portable C-arm fluoroscopy. But during the manipulation it moved into left inferior pulmonary vein from left ventricle by way of left atrium. So we could manage to remove it from left inferior pulmonary vein by direct approach to the vein. It was iron segment, sized 0.lcm x0.6cmx0.5cm, with sharp margins. The patient had an uneventful postoperative recovery except for chylopericardium and was discharged.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.8
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• pp.2894-2909
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• 2015

As the number of mobile devices such as smart phones and tablets explodes, the need for new services or applications is also rapidly increasing. Smart class application is one of the emerging applications, in which most of contents are distributed to all members of a class simultaneously. It is highly required to select relay nodes to cover shadow area of radio as well as extend coverage, but existing algorithms in a smart class environment suffer from high control packet overhead and delay for exchanging topology information among all pairs of nodes to select relay nodes. In addition, the relay selection procedure should be repeated in order to adapt to the dynamic topology changes caused by link status changes or device's movement. This paper proposes the learning based relay selection algorithm to overcome aforementioned problems. The key idea is that every node keeps track of its relay quality in a fully distributed manner, where RQI (Relay Quality Indicator) is newly defined to measure both the ability of receiving packets from content source and the ability of successfully relaying them to successors. The RQI of each node is updated whenever it receives or relays broadcast packet, and the node having the higher RQI is selected as a relay node in a distributed and run-time manner. Thus, the proposed algorithm not only removes the overhead for obtaining prior knowledge to select relay nodes, but also provides the adaptability to the dynamic topology changes. The network simulation and experimental results prove that the proposed algorithm provides efficient and reliable content distribution to all members in a smart class as well adaptability against network dynamics.

• Journal of IKEEE
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• v.24 no.1
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• pp.90-96
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• 2020

As various communication services have emerged due to the development of mobile communication technology, there is a need for a wideband antenna supporting multiple communication services with one antenna. In this paper, we propose a planar slot wideband antenna that can support all the communication services of 3.1~4.99GHz, the low frequency band of 5G, in addition to the existing communication services such as WiFi, LTE 2300/2500, and WiMAX. Through the simulation, the optimized antenna design parameters were obtained, and the antenna was fabricated to implement an antenna with a frequency bandwidth of 1.96~6.01GHz (S11 <-10dB) and presented the radiation pattern and gain of the antenna. The proposed antenna is a multi-band antenna that can provide all the services of LTE, Wifi, WiMAX, and 5G low frequency bands. It can be used as a repeater antenna in radio shadow area such as buildings, dense areas, and ships.

• The KIPS Transactions:PartC
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• v.16C no.1
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• pp.57-64
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• 2009

In order to efficiently provide IP based Wireless Broadband services in Mobile WiMAX, schemes for more efficiently utilizing a limited bandwidth in radio links are needed. Robust Header Compression (ROHC), a standard header compression scheme proposed by IETF, Bi-directional Optimistic (O) mode provides higher compression efficiency and robustness compared with Payload Header Suppression (PHS) which is an optional header compression scheme for mobile WiMAX [1, 2]. However, if consecutive packet losses occur because of a Shadow Region of Mobile WiMAX or bit errors, header decompression failure rate of the ROHC O mode increases due to inconsistency of the compression information between the Compressor and the Decompressor. Therefore, a complementary mechanism is needed. In this paper, we propose an approach for the dynamic adjustment of an optimistic parameter, which has an effect on both the compression efficiency and the robustness, for improving the performance of ROHC O mode. We also analyze the performance of the proposed approach using an OPNET simulator.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.450-450
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• 2006

Organic light-emitting diodes (OLED) as pixels for flat panel displays are being actively pursued because of their relatively simple structure, high brightness, and self-emitting nature [1, 2]. The top-emitting diode structure is preferred because of their geometrical advantage allowing high pixel resolution [3]. To enhance the performance of TOLEDs, it is important to deposit transparent top cathode films, such as transparent conducting oxides (TCOs), which have high transparency as well as low resistance. In this work, we report on investigation of the characteristics of an indium tin oxide (ITO) cathode electrode, which was deposited on organic films by using a radio-frequency magnetron sputtering method, for use in top-emitting organic light emitting diodes (TOLED). The cathode electrode composed of a very thin layer of Mg-Ag and an overlaying ITO film. The Mg-Ag reduces the contact resistivity and plasma damage to the underlying organic layer during the ITO sputtering process. Transfer length method (TLM) patterns were defined by the standard shadow mask for measuring specific contact resistances. The spacing between the TLM pads varied from 30 to $75\;{\mu}m$. The electrical properties of ITO as a function of the deposition and annealing conditions were investigated. The surface roughness as a function of the plasma conditions was determined by Atomic Force Microscopes (AFM).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.3
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• pp.465-470
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• 2007

This paper is designed and producted the microstrip patch antenna which used aperture coupled feed structure, and had a comparatively hish gain and headband characteristic with a PCS substitution repeater antenna. The proposed antenna transformed a coupled slot into a H-type in order to improve a characteristic of a general aperture coupled feed antenna. It is this H-type form slot reduces back lobe from the antenna backside at the same time that a coupling between a power feed and patches is iccreased, and to have maximized a gain of an antenna. As a result of having measured the antenna which the VSWR was 1.5 or below and tied up the gain than 7.5dBi in the $1750{\sim}1870$[MHz] that was a PCS substitution, and a beamwidth became in $80^{\circ}$ and radio waves shadow was local, but accomplishment did PCS mobile communication service in building me smoothly, but confirmed what practical use can become.