• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.2
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• pp.237-244
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• 2022

We measured the clutter loss (CL) and building entry loss (BEL) of signals in a low-rise high-density suburban environment. Three propagation models for BEL, CL, and a combination of BEL and CL were measured in the selected environment. We then derived the figures when the BEL was combined with the CL. At the two frequencies, the measured value of combination of BEL and CL is 27.55 dB and 26.12dB, respectively, and the differences between the measured value and the sum were -4.19 dB and 5.82 dB. Considering that the measurement was performed inside a building, such a difference seems to be small. Therefore, when BEL and CL were measured separately and summed, and then combined and summed, differences of -4.19 dB and 5.82 dB were apparent. This this result can be referenced when similar case of a propagation model was analyzed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.1
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• pp.201-209
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• 2014

This paper proposes a genetic algorithm to maximize the connectivity among the mobile nodes for the cooperative communication in ad-hoc networks. In general, as the movement of the mobile nodes in the networks increases, the amount of calculation for finding the solution would be too much increased. To obtain the optimal solution within a reasonable computation time for a high-density network, we propose a genetic algorithm to obtain the optimal solution for maximizing the connectivity. In order to make a search more efficient, we propose some efficient neighborhood generating operations of the genetic algorithm. We evaluate those performances through some experiments in terms of the maximum number of connections and the execution time of the proposed algorithm. The comparison results show that the proposed algorithm outperforms other existing algorithms.

• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2005.11a
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• pp.81-84
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• 2005

Various design schemes for network using wireless sensor nodes have been widely studied on the several application areas ranging from the real world information collection to environmental monitor. Currently, the schemes are focused on the design of sensor network for low power consumption, power-aware routing protocol, micro miniature operating system and sensor network middleware. The indoor localization system that identifies the location of the distributed nodes in a wireless sensor network requires features dealing with mobility, plurality and other environmental constraints of a sensor node. In this paper, we present an efficient location system to cope with mobility of multiple mobile nodes by designing a location handler that processes location information selectively depending on the nodes' density in a specific region. In order to resolve plurality of multiple mobile nodes, a routing method for the location system is also proposed to avoid the occurrence of overlapped location data.

• Transactions on Electrical and Electronic Materials
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• v.14 no.4
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• pp.203-207
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• 2013

P-type Si wafers were dipped in HF solution. The minority carrier lifetime (lifetime) increased after HF treatment due to the hydrogen termination effect. To investigate the film passivation effect, PECVD was used to deposit $SiN_x$ on both HF-treated and untreated wafers. $SiN_x$ generally helped to improve the lifetime. A thermal process at $850^{\circ}C$ reduced the lifetime of all wafers because of the dehydrogenation at high temperature. However, the HF-treated wafers showed better lifetime than untreated wafers. PERCs both passivated and not passivated by HF treatment were fabricated on the rear side, and their characteristics were measured. The short-circuit current density and the open-circuit voltage were improved due to the effectively increased lifetime by HF treatment.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.78-83
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• 2015

In this paper, when WLAN repeater of satellite communication package system as a novel wireless disaster communication network connected to LTE D2D mobile terminal, we analyzed radio channel interference from WLAN and WPAN system of adjacent same ISM band using Monte-Carlo method. In this study, WLAN cell radius was determined using Extended Hata Model considering practical environment, and simulated physical protection distance and density in the dense-mode to minimize interference from WLAN, Bluetooth, and ZigBee. Simulation results, WLAN repeater can be operated with 15 WLAN interferer over 130m distance, 23 Bluetooth interferer over 100m distance, and with 62 ZigBee interferer over 83m distance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.6
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• pp.1153-1160
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• 2003

In this paper, the performance of the UWB communication systems is analyzed in the presence of the Narrow Band Interference(NBI). UWB communication systems are modeled as using the Pulse Position Modulation(PPM). In this system, a Gaussian monocycle is used as the received pulses. The NBI is considered as a zero-mean random process with a constant spectral power density over its whole bandwidth. We obtain the mathematical expressions for describing the effect of the NBI on the UWB system. And it can be shown that the suppression of the effect of NBI on the UWB systems is available by adjusting the PPM related parameter.

• International Journal of Ocean System Engineering
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• v.1 no.4
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• pp.205-210
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• 2011

High data-rate underwater communications is demanded. This demand imposes stringent requirements on underwater communication equipment of phase-locked-loop (PLL). Phase noise in PLL is unwanted and unavoidable. In this paper, we investigate the PLL phase noise effect on high order QAM for underwater communication systems. The phase noise model using power spectral density is adopted for performance evaluation. The phase noise components considered in PLL are reference oscillator, voltage controlled oscillator (VCO), filter and divider. The filters in PLL noise are assumed to be second order active and passive low pass filters. Through simulation, we analyze the phase noise characteristics of the four components and then investigate the performance improvement factor of each component. Consequently, we derive specifications of VCO, phase detector, divider to meet performance requirement of high data-rate communication using QAM under phase noise influence.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.4
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• pp.633-654
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• 2010

High quality camera images, with good contrast and intensity, are needed to obtain the desired information. Images need to be enhanced when they are dark or bright. The histogram equalization technique, which flattens the density distribution of an image, has been widely used to enhance image contrast due to its effectiveness and simplicity. This technique, however, cannot be used to enhance images that are either too dark or too bright. In addition, it is difficult to perform histogram equalization in real-time using a general-purpose computer. This paper proposes a histogram equalization technique with AGC (Automatic Gain Control) to extend the image enhancement range. It is designed using VHDL (VHSIC Hardware Description Language) to enhance images in real-time. The system is implemented with an FPGA (Field Programmable Gate Array). An image processing system with this FPGA is implemented. The performance of this image processing system is measured.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.385-385
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• 2012

A two terminal N+/P/N+ junction device to replace the conventional selective transistor was studied as a bilateral switching device for spin transfer torque (STT) MRAM based on 3D device simulation. An N+/P/N+ junction structure with $30{\times}30nm$ area requires bi-directional current flow enough to write a data by a drain induced barrier lowering (DIBL) under a reverse bias at N+/P (or P/N+ junction), and high current on/off ratio of 106. The SiGe materials are widely used in hetero-junction bipolar transistors, bipolar compensation metal-oxide semiconductors (BiCMOS) since the band gap of SiGe materials can be controlled by changing the fraction and the strain epilayers, and the drift mobility is increased with the increasing Ge content. In this work, N+/P/N+ SiGe material based junction provides that drive current is increased from 40 to $130{\mu}A$ by increased Ge content from 10~80%. When Ge content is about 20%, the drive current density of SiGe device substantially increased to 2~3 times better than Si-based junction device in case of 28 nm P length, which is sufficient current to operation of STT-MRAM.

• Electronics and Telecommunications Trends
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• v.33 no.5
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• pp.24-32
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• 2018

With the advent of new convergence services, the requirements of 5G mobile communication systems are being newly derived. The 5G mobile communication system has been evolving to solve requirements that cannot be satisfied with existing 4G mobile communication systems, such as a high user experience transmission rate, short transmission delay, and high connection density. The evolution of a 5G mobile communication system to meet the new requirements is expected to be dominated by the UDN environment in which a number of small cells are concentrated. The 5G wireless backhaul system, which has advantages in terms of initial installation and operation cost, is expected to be an indispensable choice for connecting many small cells and core networks. This paper therefore looks at the frequency band characteristics and requirements applicable to 5G wireless backhaul systems that can accommodate new situations, and introduces key related technologies that can satisfy the 5G wireless backhaul requirements.. In addition, we describe the research and development trends of a 5G wireless backhaul system that is currently under development.