• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.3
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• pp.321-330
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• 2010

In this paper, the theoretical background and the specific implementation method of a compressive receiver for RFID signal detection as well as the design method of DDL(Dispersive Delay Line) and chirp LO are described. DDL, which is one of the main components of the compressive receiver, is designed to have $13{\mu}s$ dispersive delay time and 6 MHz bandwidth using the SAW technique based on $LiNbO_3$ material. The chirp LO is designed using DDS(Direct Digital Synthesizer). Also the compressive receiver is fabricated to be installed into the RFID reader. Test results show the maximum frequency error of 25 kHz for single signal input, the receiver sensitivity of -44 dBm, and the maximum frequency error is 75 kHz for 6 multi-tone input signals. These results indicate that the fabricated compressive receiver is working well even in dense RFID operating environments.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.3
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• pp.343-348
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• 2011

With the rapid and wide-spread use of mobile communications much attention has been focussed on propagation in the urban area crowed with buildings. It is often surrounded by hills, forests, and mountains. The importance of surface scattering interference between transmitters and receivers on the rough surfaces has been interested and investigated. Therefore, a prediction method is necessary to estimate the influence of rough surfaces on microwave radio propagation. Moreover, most of the mobile communications are performed based on the digital communication system rather than the analog one. In this case, we must pay more careful attention to the signal delay caused by the phase delay due to the multi-path propagation. In this paper we have analyzed numerically scattering of electromagnetic waves from Composite structures by using FVTD (Finite Volume Time Domain) method. We consider two different types of rough surfaces such as periodic and composite structures.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.4
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• pp.55-60
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• 2002

This paper presents a technique for the preparation of vertically grown CNTs by ICPHFCVD(inductively coupled plasma hot filament chemical vapor deposition) below $580^{\circ}C$. Purification of the CNTs(carbon nanotubes) using RE(radio frequency) plasma in a one step process, based on the different etching property of the Ni-tip, amorphous carbon and carbonaceous materials is also discussed. After purifying the grown materials. CNTs shown the multi walled and hollow typed structure. The typical outer and inner diameters or CNT were 50 nm and 25 nm, respectively. The graphitic wall was composed of 82 layers and the distance between wall and wall was 0.34 nm. From the results of TEM observation, the Ni catalyst at the tip of the carbon nanotubes were effectively removed by using a RF plasma etching, continuously.

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.865-868
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• 2007

Recently, wireless LANs are often applied in home or office because of its various of convenience. Frequency range of wireless LANs specified by IEEE 802.11b is at 2.4 GHz. The bluetooth, the microwave oven, and the PDA(Personal Digital Assistants) uses, however, the same frequency band. So problems will be produced in these environments, such as multi-pass interference and system-to-system interference. These problems can be eliminated by using EM wave absorber. In this paper, we designed and fabricated EM wave absorber using MnZn-Ferrite, Sendust, and CPE( Chlorinated Polyethylene). The EM wave absorber with the ratio of material (MnZn-Ferrite : Sendust : CPE = 64 : 16 : 20 wt.%) has thickness of 3.7 mm and absorption ability more than 17 dB at 2.4 GHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.13-23
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• 2007

In this paper, a packet scheduling scheme that supports real-time traffic having multi-level delay constraints in OFDMA systems is proposed. The proposed scheme pursues to satisfy the delay constraint first, and then manage the residual radio resource in order to enhance the overall throughput. A parameters named tolerable delay time (TDT) is newly defined to deal with the differentiated behaviors of packet scheduling according to the delay constraint level. Assuming that the packets violating the delay constraint are discarded, the proposed scheme is evaluated in terms of the packet loss probability, throughput, channel utilization. It is then compared with existing schemes for real-time traffic support such as the Exponential Scheduling (EXP) scheme, the Modified Largest Weighted Delay First (M-LWDF) scheme, and the Round robin scheme. The numerical results show that the proposed scheduling scheme performs much better than the aforementioned scheduling schemes in terms of the packet loss probability, while slightly better in terms of throughput and channel utilization.

• Journal of Satellite, Information and Communications
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• v.7 no.1
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• pp.75-81
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• 2012

This study is to design the transmitter and receiver of short range UWB(Ultra Wide Band) imaging radar that is able to display high resolution radar image for front area of a UGV(Unmanned Ground Vehicle). This radar can help a UGV to navigate autonomously as it detects and avoids obstacles through foliage. The transmitter needs two transmitters to improve the azimuth resolution. Multi-channel receivers are required to synthesize radar image. Transmitter consists of high power amplifier, channel selection switch, and waveform generator. Receiver is composed of sixteen channel receivers, receiver channel converter, and frequency down converter, Before manufacturing it, the proposed architecture of transceiver is proved by modeling and simulation using several parameters. Then, it was manufactured by using industrial RF(Radio Frequency) components and all other measured parameters in the specification were satisfied as well.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.10
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• pp.4002-4014
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• 2015

ITU-R M.1842-1, as a well-known specification dedicated to maritime mobile applications, has standardized wireless transmission protocols according to the particular characteristics of a maritime communications scenario. A time division multiple access (TDMA) frame structure, along with modulation schemes to achieve a high data rate, has been described clearly in ITU-R M.1842-1. However, several specification items are still under "to be decided" status, which brings ambiguity to research works. In addition, the current version of ITU-R M.1842-1 is focused mainly on maritime transmissions in open-sea areas, where the cyclic prefix (CP) is set to zero and only 16-QAM is used in the multi-carrier (MC) system. System performance might be dramatically degraded in coastline areas due to the inter-symbol interference (ISI) caused by selective fading. This is because there is a higher probability that the signal will be reflected by obstacles in coastline areas. In this paper, we introduce the transmission resource block (TRB) dedicated to ITU-R M.1842-1 for a ship ad-hoc network (SANET), where the pilot pattern of TRB is based on the terrestrial trunked radio (TETRA). After that, we evaluated SANET performance under the maritime channel model in a coastline area. In order to avoid noise amplification and to overcome the ISI caused by selective fading, several strategies are suggested and compared in the channel estimation and equalization procedures, where the link-level simulation results finally validate our proposals.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.7
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• pp.3412-3432
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• 2019

Recent advances in radio frequency (RF) power transfer provide a promising technology to power sensor nodes. Adoption of mobile chargers to replenish the nodes' energy has recently attracted a lot of attention and the mobility assisted energy replenishment provides predictable and sustained power service. In this paper, we study the joint optimization of mobile charging and data gathering in sensor networks. A wireless multi-functional vehicle (WMV) is employed and periodically moves along specified trajectories, charge the sensors and gather the sensed data via one-hop communication. The objective of this paper is to maximize the uplink throughput by optimally allocating the time for the downlink wireless energy transfer by the WMV and the uplink transmissions of different sensors. We consider two scenarios where the WMV moves in a straight line and around a circle. By time discretization, the optimization problem is formulated as a 0-1 programming problem. We obtain the upper and lower bounds of the problem by converting the original 0-1 programming problem into a linear programming problem and then obtain the optimal solution by using branch and bound algorithm. We further prove that the network throughput is independent of the WMV's velocity under certain conditions. Performance of our proposed algorithm is evaluated through extensive simulations. The results validate the correctness of our proposed theorems and demonstrate that our algorithm outperforms two baseline algorithms in achieved throughput under different settings.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.628-631
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• 2014

Recently, the proliferation of new applications, e.g., mobile TV, Internet gaming, large file transfer, and the various of user terminals, e.g., smart phones and notebooks, has dramatically increased user traffic and network load. In order to meet this traffic growth, vendors and cellular operators are working on the development of new technologies and cellular standards. Within them, small cell deployment has been heralded as one of most promising way to increase both coverage and capacity of future cellular network. Small cell technology enables to improve capacity of cellular radio network by tight cooperation between small cell and macro cell in multi-tier network where small cells are densely deployed within macro cell coverage. In this paper, we describe the deployment scenarios for cooperation between macro cell and small cells and state-of-the-art technologies related to dense small cell deployment. Then, we also provide design principles and standardization trends for small cell enhancement in 3GPP.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.68.1-68.1
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• 2019

Turbulence plays a crucial role in controlling star formation as it produces density fluctuation as well as non-thermal pressure against gravity. Therefore, turbulence controls the mode and tempo of star formation. However, despite a plenty of previous studies, the properties of turbulence remain poorly understood. As part of the Taeduk Radio Astronomy Observatory (TRAO) Key Science Program (KSP), "mapping Turbulent properties In star-forming MolEcular clouds down to the Sonic scale (TIMES; PI: Jeong-Eun Lee)", we mapped the Orion A and the Ophiuchus clouds, in three sets of lines (13CO 1-0/C18O 1-0, HCN 1-0/HCO+ 1-0, and CS 2-1/N2H+ 1-0) with a high-velocity resolution (~0.1 km/s) using the TRAO 14-m telescope. The mean Trms for the observed maps are less than 0.25 K, and all these maps show uniform Trms values throughout the observed area. These homogeneous and high signal-to-noise ratio data provide the best chance to probe the nature of turbulence in two different star-forming clouds, the Orion A and Ophiuchus clouds. We present comparisons between the line intensities of different molecular tracers as well as the results of a Principal Component Analysis (PCA).