• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3370-3392
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• 2017

Next Generation Beyond 4G/5G systems will rely on the deployment of small cells over conventional macrocells for achieving high spectral efficiency and improved coverage performance, especially for indoor and hotspot environments. In such heterogeneous networks, the expected performance gains can only be derived with the use of efficient interference coordination schemes, such as Fractional Frequency Reuse (FFR), which is very attractive for its simplicity and effectiveness. In this work, femtocells are deployed according to a spatial Poisson Point Process (PPP) over hexagonally shaped, 6-sector macro base stations (MeNBs) in an uncoordinated manner, operating in hybrid mode. A newly introduced intermediary region prevents cross-tier, cross-boundary interference and improves user equipment (UE) performance at the boundary of cell center and cell edge. With tools of stochastic geometry, an analytical framework for the signal-to-interference-plus-noise-ratio (SINR) distribution is developed to evaluate the performance of all UEs in different spatial locations, with consideration to both co-tier and cross-tier interference. Using the SINR distribution framework, average network throughput per tier is derived together with a newly proposed harmonic mean, which ensures fairness in resource allocation amongst all UEs. Finally, the FFR network parameters are optimized for maximizing average network throughput, and the harmonic mean using a fair resource assignment constraint. Numerical results verify the proposed analytical framework, and provide insights into design trade-offs between maximizing throughput and user fairness by appropriately adjusting the spatial partitioning thresholds, the spectrum allocation factor, and the femtocell density.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.6
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• pp.131-138
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• 2008

Mobile Ad hoc NETworks (MANETs) refer to autonomous networks in which wireless data communications are established between multiple nodes in a given coverage area without a base station or centralized administration. Because of node mobility and limited battery life, the network topology may changes frequently. Selecting the most reliable path during route discovery process is important to improve performance in ad hoc networks. In this paper, an enhanced routing protocol based on AODV(Ad hoc On-demand Distance Vector routing) by monitoring variation of receiving signal strength is proposed. New metric function that consists of node mobility and hops of path is used for routing decision. For preventing route failure by node movement during data transmission, a new route maintenance named as LRC (Local Route Change) is presented. If the node movement is detected, the routing agent switches path to its neighbor node in LRC. Simulation results show that the performance of the proposed routing scheme is superior to previous AODY protocol.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.4
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• pp.394-400
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• 2018

A heterogenous network is the one of key technologies for 5G, where one cell is divided into small cells in order to extend coverage and support high data rates. Divided cells aggravates the intercell interference problem as the cell edge increases. In order to avoid the intercell interference, it is the best to allocate the different spectrum for each cells. However, it also decreases the spectral efficiency. Therefore, the trade-off between the spectral efficiency gain and the signal quality loss by the interference should be considered for an efficient spectrum sharing in the heterogenous network. The adaptive modulation is the method to change the transmitted bit according to the channel quality, which is adopted as the standard in the most practical communication systems. It should be considered to applied the performance analysis into the practical systems. In this paper, the overall cell data rates is analyzed for the heterogenous network under the adaptive modulation. The Monte Carlo simulation results verify the correctness of the analysis.

• Proceedings of the KSMRM Conference
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• 2003.10a
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• pp.97-97
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• 2003

Contrast-enhanced MR angiography (CE-MRA) gradually occupies its position as a primary evaluation tool forsteno-occlusive disease of supra-aortic cervical arteries. It has several advantages over time-of-flight (TOF) technique such as shorter imaging time, less saturation effect, and less flow- and motion-related artifacts. Diverse methods of k-space sampling, imaging sequences, and strategies for image acquisitiontiming have been introduced since its early clinical application. Especially, methods of k-space sampling and image acquisition timing are very important to achieve maximal arterial enhancement and suppress venous signal while maintaining large scan coverage and high spatial resolution. In addition, regardless of several advantages over TOF technique, it still has a tendency to overestimate the degree of stenosis in patients with carotid or vertebralartery disease. In this exhibit, we will overview the current techniques of CE-MRA with special attention to methods of k-space sampling and image acquisition timing. We will also discuss diagnostic accuracy of CE-MRA in patients with supra-aortic cervical artery stenosis and artifacts frequently misinterpreted as steno-occlusive lesion on CE-MRA.

• The Journal of the Korea Contents Association
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• v.11 no.2
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• pp.142-151
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• 2011

All medical information over sensor networks need to transmit and process securely in the u-Health services. The reliability of transmission between u-Health medical sensor devices and gateway is very important issue. When the user moves to other place with u-Health devices, its signal strength is going down and is far from the coverage of gateway. In this case, Malicious user can be carried out an intrusion under the situation. And also rogue gateway can be tried to steal medical information. Therefore, it needs mutual authentication between sensor devices and gateway. In this paper, we design a mutual authentication protocol which divided sessions from an authenticated session are updated periodically. And in order to reduce the traffic overhead for session authentication, we also introduce dynamic session management according to sampling rate of medical sensor type. In order to verify this, we implemented the programs for the test-bed, and got an overall success from three types of experiment.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.214-217
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• 2001

This paper presents an implementation methodology of common Rf- integrated PCS base station system which, is capable of providing PCS services for 3 PCS carriers concurrently and wireless system performance evaluation data is shown. We have built up a common PCS base station system using a commonization module, which is consisted of a multi-channel combiner, duplexer, LNA, power divider, feeder line, and a common set of antennas. It was shown that the performance of the system within the total 30MHz PCS frequency range is uniformly acceptable and measured signal quality and coverage are equivalent to that of the individual PCS base station. It is expected that PCS carriers are able to save a huge amount of installation and maintenance expenses by installing and sharing this base station system. This paper forms a groundwork for deploying efficient and economical IMT-2000 network.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2005.04a
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• pp.71-74
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• 2005

To introduce the four-dimensional computed tomography (4DCT, Light Speed RT, General Electric, USA) scanner newly installed in our department and evaluate its feasibility for gated radiotherapy. Respiratory signal measured by real-time position management (RPM$^{\circledR}$, Varian Medical, USA) was recorded in synchronization with the 4DCT scanner. 4DCT data were acquired in axial cine mode and sorted retrospective image based on respiratory phase. PTVs delineated from helical CT and 4DCT images were compared. The PTV delineated from conventional helical CT images was 2 cc larger than that from 4DCT images. Dose in PTV of the plan from retrospective CT was 99.3% (minimum=72.0%, maximum=106.5%) and that of helical CT plan was 95.2% (minimum=24.1%, maximum=106.4%) of prescribed dose. Comparing with DVHs of both plan, the coverage for 4CDT plan was 3.7% improved. It is expected that 4DCT could improve tumor control and reduce radiation toxicity for liver cancer.

• Journal of the Korea Society of Computer and Information
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• v.12 no.4
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• pp.149-158
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• 2007

A In the rapidly changing media environment, radio needs to be digitized in order to provide regular compatible service. Especially, most medium high frequency Medias have program contents thar are similar to the standard FM bandwidth, so digitizing radio will bring less effect than it is expected. However, the characteristics of radio medias are mobility, individuality, site-to-site, wide service coverage, immediate delivery and publicity, so it is necessary to study the future of radio media to provide continuous services, moreover, the main discussion regarding balanced development between medias will be the trend of the digitization of radio. Also it is easy and will cost less to change compared to other medias. AM was the first media to broadcast in Korea, and its network is spread all over Korea, also the receivers are the most widely distributed which means the signal reaches everywhere in Korea. In this study, the proper service model for AM digital radio is provided in this environment in which all Medias are rapidly digitizing due to the advancement of digital technology. The results of experimental are based on library study and KBS data of sound wave.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.709-730
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• 2017

To address the challenge of unprecedented growth in mobile data traffic, ultra-dense network deployment is a cost efficient solution to offload the traffic over some small cells. The overlapped coverage areas of small cells create more than one candidate access points for one mobile user. Signal strength based user association in IEEE 802.11 results in a significantly unbalanced load distribution among access points. However, the effective bandwidth demand of each user actually differs vastly due to their different preferences for mobile applications. In this paper, we formulate a set of non-linear integer programming models for joint user association control and user demand guarantee problem. In this model, we are trying to maximize the system capacity and guarantee the effective bandwidth demand for each user by soft-association control with a software defined network controller. With the fact of NP-hard complexity of non-linear integer programming solver, we propose a Kernighan Lin Algorithm based graph-partitioning method for a large-scale network. Finally, we evaluated the performance of the proposed algorithm for the edge users with heterogeneous bandwidth demands and mobility scenarios. Simulation results show that the proposed adaptive soft-association control can achieve a better performance than the other two and improves the individual quality of user experience with a little price on system throughput.

• Journal of Broadcast Engineering
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• v.13 no.5
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• pp.636-650
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• 2008

DTV has a great advantage as compared to Analog TV in picture quality under low reception field strength. Various high quality tuners have been developed to result in much smaller Noise Figure of the receivers and many trials for receiving DTV signal through indoor antenna. In this paper, results of intensive field tests on the indoor reception of DTV are presented. Tests were carried out around Seoul-Gyeonggi Metropolitan area. Commercial directional and omni-directional antennas and 5th generation receiver were used for reception availability tests. The effects of heights, locations, and types of the house as well as the distance to the transmitter on the reception performances are analyzed. Our test results will be applied to improve the indoor reception environment of DTV.