• KIPS Transactions on Computer and Communication Systems
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• v.3 no.9
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• pp.293-300
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• 2014

TDMA(Time Division Multiple Access) is a channel access scheme for shared medium networks. The shared frequency is divided into multiple time slots, some of which are assigned to a user for communication. Techniques for TDMA can be categorized into two classes: synchronous and asynchronous. Synchronization is not suitable for small scale networks because it is complicated and requires additional equipments. In contrast, in DESYNC, a biologically-inspired algorithm, the synchronization can be easily achieved without a global clock or other infrastructure overhead. However, DESYNC spends a great deal of time to complete synchronization and does not guarantee the maximum time to synch completion. In this paper, we propose a lightweight synchronization scheme, C-DESYNC, which counts the number of participating nodes with GP (Global Packet) signal including the information about the starting time of a period. The proposed algorithm is mush simpler than the existing synchronization TDMA techniques in terms of cost-effective method and guarantees the maximum time to synch completion. Our simulation results show that C-DESYNC guarantees the completion of the synchronization process within only 3 periods regardless of the number of nodes.

• Journal of the Korea Society for Simulation
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• v.20 no.4
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• pp.81-89
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• 2011

Underwater wireless network can be useful in various fields such as underwater environment observation, catastrophe prevention, ocean resources exploration, ocean organism research, and vessel sinking exploration. We need to develop an efficient design for Medium Access Control (MAC) protocol to improve multiple data communication in underwater environment. Aloha protocol is one of the basic and simple protocols, but it has disadvantage such as collision occurs oftenly in communication. If there is collision occured in RF communication, problem can be solved by re-sending the data, but using low frequency in underwater, the re-transmission has difficulties due to slow bit-rate. So, Time Division Multiple Access (TDMA) based MAC protocol is going to be used to avoid collisions, but if there is no data to send in existing TDMA, time slot should not be used. Therefore, this paper proposes dynamic TDMA protocol mechanism with reducing the time slots by sending short "I Have No Data" (IHND) message, if there is no data to transmit. Also, this paper presents mathematic analysis model in relation to data throughput, channel efficiency and verifies performance superiority by comparing the existing TDMA protocols.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.5 s.120
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• pp.496-502
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• 2007

In this paper, a slotted waveguide feeder for the electric field uniformity in multi-mode cavity is designed and fabricated. In case of the conventional feeder, a mode stirrer or a turntable is used for improving electric field uniformity in the multi-mode cavity. The proposed feeder has four slots, which have uniform radiation characteristic, on broad wall and shorted terminations at both ends. The electric field uniformity is simulated by CST's MWS(Microwave Studio) for the conventional and proposed feeders, respectively. The fabricated feeder shows the return loss of less than -20 dB at 2.45 GHz. To verify the validity of our proposal, the temperature distribution of the water samples in the multi- mode cavity is observed after a few minutes' heating. The proposed feeder is confirmed to have much better field uniformity in the multi-mode cavity than the conventional feeder.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.3
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• pp.336-344
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• 2011

The purpose of this study is to analyze the radiation-pattern characteristics above 1 GHz for the electromagnetic wave radiated from multi-slot such as ventilations, etc. on the enclosure of an EUT and so to make recommendations for suitable test methods. An experimental EUT was formed by putting a comb-generator at the center of a rectangular enclosure with 4 slots, and its radiation pattern was analyzed in the frequency range of 1~6 GHz. As analysis results, multi-lobe appears above 2 GHz and the number of multi-lobes is growing as the frequency increases. And real radiated-emission measurements were performed for the experimental EUT by scanning a receiving antenna in the height of 1~4 m and tilting toward maximum radiation, as well as setting the height of a receiving antenna to the central position of the EUT which is prescribed at the present standards. The measured results are +12.8 dB in the scanning and +16.4 in the scanning and tilting compared with the present standard test method. Therefore, the latter must be revised in order to consider the radiation pattern above 1 GHz.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.11
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• pp.846-850
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• 2009

Recently, wireless sensor networks have found their way into a wide variety of applications and systems with vastly varying requirements and characteristics such as environmental monitoring, smart spaces, medical applications, and precision agriculture. The sensor nodes are battery powered. Therefore, the energy is the most precious resource of a wireless sensor network since periodically replacing the battery of the nodes in large scale deployments is infeasible. Energy efficient mechanisms for gathering sensor readings are indispensable to prolong the lifetime of a sensor network as long as possible. There are two energy-efficient approaches to prolong the network lifetime in sensor networks. One is the compression scheme to reduce the size of sensor readings. When the communication conflict is occurred between two sensor nodes, the sender must try to retransmit its reading. The other is the MAC protocol to prevent the communication conflict. In this paper, we propose a novel approaches to reduce the size of the sensor readings in the MAC layer. The proposed scheme compresses sensor readings by allocating the time slots of the TDMA schedule to them dynamically. We also present a mathematical model to predict latency from collecting the sensor readings as the compression ratio is changed. In the simulation result, our proposed scheme reduces the communication cost by about 52% over the existing scheme.

• Journal of Advanced Navigation Technology
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• v.22 no.4
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• pp.336-341
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• 2018

In this paper, we designed and implemented an ultra wideband (UWB) antenna with 5G mobile communication and WLAN bands rejection characteristics. The proposed antenna consists of a planar radiation patch with two slots, parasitic elements on both sides of the strip line and ground plane on back side. The upper n-type slot contributes for 5G mobile communication band (3.42~3.70 GHz) rejection and the lower n-type slot contributes for wireless local area network (WLAN) band (5.15~5.825 GHz) rejection. Parasitic elements were used in order to satisfy the voltage standing wave ratio (VSWR) less than or equal to 2.0 for UWB band (3.10~10.60 GHz) except two rejection bands. The Ansoft's high frequency structure simulator (HFSS) was used for antenna design and simulations. The simulated antenna showed dual rejection bands of 3.36~3.71 GHz and 5.13 ~ 5.92 GHz in UWB band, and measured result for the implemented antenna showed dual rejection bands of 3.40~3.72 GHz and 5.08~5.858 GHz. Simulated and measured VSWRs are less than or equal to 2.0 for all UWB band except dual rejection bands.

• The Journal of Korean Academy of Prosthodontics
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• v.56 no.3
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• pp.206-211
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• 2018

Purpose: Recently, a method of forming a slot in the prosthesis lingual has been introduced to solve the occlusal and aesthetic disadvantages of screw-retained prosthesis in the manufacture of implant-fixed prosthesis and to ensure retrievability in cement retained prostheses. The purpose of this study is to investigate the effect of the internal gap on the removal of the prosthesis in the preparation of cement-retained implant prostheses with lingual slots. Materials and methods: Titanium abutment and internal gap of the zirconia prosthesis to be attached to the upper part were set to 30, 35, and $50{\mu}m$, respectively. Three for each type total 15 were produced for each type. The zirconia prosthesis formed a retrievable cement-type slot with a space of 1 mm at the location where the titanium abutment meets the shelf area. Autocatalytic resin cement was used for bonding of abutment and zirconia prosthesis, and the maximum removal stress value was measured in units of Ncm by using the customized equipment of the cemented specimen. The Kruskal-Wallis test was used to compare the three groups by statistical analysis (${\alpha}=.05$), modified by post hoc test the Mann-Whitney U-test and the Bonferroni correction method were used to compare the two methods (${\alpha}=.017$). Results: There was no statistically significant difference in removal stress between the $30{\mu}m$ group and the $35{\mu}m$ group in the internal gap (P = .032), and there was a significant difference between the $30{\mu}m$ group and the $50{\mu}m$ group, between the $35{\mu}m$ group and the $50{\mu}m$ group (P < .017). Conclusion: Thus, the internal gap of computer-aided design affected the retention between the zirconia prosthesis and the titanium abutment.

• The Korean Journal of Air & Space Law and Policy
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• no.spc
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• pp.137-163
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• 2007

The air market in Asia has already entered upon the age of limitless competition. It means a very important moment in Asia air market. Each Asian country thus has put a lot of effort into a development plan and support to their hub airport. In order to achieve such a plan, first of all we should build closer cooperation system between the two countries Japan and Korea. The Korea and Japan are very fast growing in the northeast countries within the global air transport market. Air passenger and cargo traffic volumes between Korea and Japan have increased dramatically, since the 1990s. In response to such a trend, both countries have opened new airports and expanded existing facilities in the hopes of laying claims to the main international hub airport in Asia. Apart from the trend, air transportation between Korea and Japan's metropolitan areas is the only transportation in substance, even if they are located very closely in geographical position. The air transportation between the two countries shows that it is necessary to get fast and more convenient because of the economic and cultural interchange and exchange concentrated on the metropolitan areas, and that will promote the economic growth of Korea and Japan. However, within the air transportation industry field, there have no sufficient seats/slots to supply the air demand from the capital cities of each country, as well as no counterplan for some problems regarding capacityand sustain ability of metropolitan airports. Thus, it is necessary for us to consider in all aspects and solve them to improve air transportation between Korea and Japan. This paper is to try to demonstrate this matter and from all angles, that is, in legal and political aspects, facilities and given environmental conditions and cooperation between Korea and Japan. I think that it is indeed a great necessary and convenient for many Korean and Japanese tourists to conclude a new 'Open Sky Agreement' between Japan and Korea in order to the prepare the increase of the shuttle flight between Haneda-Gimpo and opening of air route newly for shuttle flight between Haneda and Cheongju as well as opening of air route for shuttle flight between Haneda-Shanghai Hongqiao International Airport and Beijing International Airport for the 2008 Beijing Olympic Games. Furthermore it is a great desirable thing for us to conclude a new 'Open Sky Agreement' in cooperation reciprocally among the Japan, China and Korea for opening the new air route by the shuttle flight.

• The korean journal of orthodontics
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• v.40 no.5
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• pp.294-303
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• 2010

Objective: This study was designed to measure the surface roughness at the slot floor of various ceramic brackets. Methods: One kind of stainless steel bracket ($Succes^{(R)}$), two kinds of monocrystalline brackets (Inspire $Ice^{(R)}$, $Perfect^{(R)}$) and two kinds of polycrystalline brackets (Crystalline $V^{(R)}$, $Invu^{(R)}$) were examined. Atomic force microscopy (AFM) was used to measure the surface roughness of each bracket. Data acquisition and processing were performed using $SPIP^{TM}$. Results: The differences in values of Sa, Sq, and Sz in $Invu^{(R)}$ and Inspire $Ice^{(R)}$ were not statistically different from the control group $Succes^{(R)}$. The values of Sa, Sq, and Sz of $Perfect^{(R)}$ and Crystalline $V^{(R)}$ were greater than those of $Succes^{(R)}$. Differences of all the Sa, Sq, and Sz values between $Perfect^{(R)}$ and Crystalline $V^{(R)}$ were not statistically significant. Conclusions: It is concluded that the slot surfaces of $Succes^{(R)}$, Inspire $Ice^{(R)}$, and $Invu^{(R)}$ were smooth compared to those of Crystalline $V^{(R)}$ and $Perfect^{(R)}$.

• Radiation Oncology Journal
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• v.23 no.2
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• pp.123-130
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• 2005

Purpose: We wanted to improve the setup reproducibility of breast cancer patients when utilizing a commercially available breast board for radiation therapy. The breast board was modified by using a new head rest and 2 types of board fixation devices. Materials and Methods: A conventional head/neck rest was modified to be positioned in various slots of the breast board, and it was fabricated 1 cm thinner to provide more comfort to a patient when the patient's neck was rotated. This rest improves the uncertainty of the daily setup. Also, the sagging problems at the left and right sides became negligible with the two types of board fixation devices: (1) the stair type, and (2) the arm type. The first device consists of an upper/lower holder with 4 stair-types of grooves and 4 rectangular Inserts. In order to cover the whole range of vertical setup of the breast board, 4 rectangular inserts were needed, and each covered 10 steps. The arm-type fixation device was also fabricated and attached to the breast board, It had two aluminum bars that were fixed by utilizing a lock-type of screw. These devises were evaluated with two volunteers in order to prove the effectiveness of the improved setup accuracy. Results; The developed cranio-caudal fixation device demonstrated that it could reduce the cranio-caudal error by nearly $55\%$ compared to the old device. As for left-and-right inclination, the stair-type and arm-type fixation devices can reduce the relative inclination by nearly $80\%$ and $90\%$, respectively, compared to the breast board without the fixation device. Conclusion: It was verified that the developed devices were effective for positioning the patients and for avoiding inclination of the breast board.