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Deep-Fading Hole Avoidance for Secure Region Detection using Channel State Information
Suh, Jihwan,YOO, YONGJAE,Paek, Jeongyeup,박세웅 한국통신학회 2022 Journal of communications and networks Vol.24 No.6
One of the critical challenges in many wirelesssystems is the deep fading hole problem where signals interferedestructively to create an abrupt change in signal amplitude dueto multipath fading. In this work, we tackle this challenge in thecontext of secure region detection (SRD) problem. Specifically, wepropose SHARD, a novel hole avoidance technique that analyzeschannel state information (CSI) to significantly improve theaccuracy of CSI-based SRD. SHARD identifies potential fadingholes in CSI amplitude, and removes an unreliable portion of datawhile utilizing the remaining unaffected part. To compensate forthe loss of information, we define phase-distance for reliable useof time-varying CSI phase, and neighboring reference points areutilized for accurate matching. Our real-world experiments showthat SHARD can achieve a near-perfect 99.96% true-negativeratio (successfully rejecting devices not in the secure region)and an excellent true-positive of 98.01% for practical usage,significantly better than state-of-the-art prior work. We believeour ideas can be generalized to many RF-based localizationsystems to mitigate the deep fading hole problem and improvetheir accuracy.
Nanosize Particles of ZrVFe Alloy by Pulsed Laser Ablation in Ethanol
Kil, Daesup,Suh, Yongjae,Jang, Heedong,Lee, Jaechen,Song, Changbin,Kim, Wonbaek The Japan Institute of Metals 2005 Materials transactions Vol.46 No.11
<P>Nanosize powder of ZrVFe alloy has been prepared by a laser ablation method using a ZrVFe alloy as a target material. Ablation of the target alloy was carried out in a liquid container. The laser fluence, energy density at the target surface, was adjusted by manipulating the laser power and focus size to control the ablating conditions. The obtained colloidal dispersions of the nanoparticle were filtered and dried for characterization. The crystal structure of prepared nanoparticles maintained clear crystallinity and was the same as that of the original target alloy by comparison of the X-ray diffraction pattern. The particle sizes were distributed at around 100 nm depending on the used ablation conditions. The minimum average particle size of 71 nm was obtained at the laser fluence of 20.3 J/cm<SUP>2</SUP>, while the average size was not proportional to the laser fluence. The morphologies and oxidation state of the particle have been discussed for possible use of the ZrVFe powder as a getter material.</P>
FMS-AMS: Secure Proximity-based Authentication for Wireless Access in Internet of Things
Jeongyoon Heo,Yongjae Yoo,Jihwan Suh,Woojin Park,Jeongyeup Paek,Saewoong Bahk 한국통신학회 2020 Journal of communications and networks Vol.22 No.4
Proximity-based authentication enables wireless accesspoints (AP) to allow connection only to devices within a certain authentication range. This would be very convenient for allowing network access only to those within a physical boundary. However, anattacker not within the authentication range may deceive the APinto authenticating its proximity by eavesdropping with higher receiver gain and increasing its transmit power. This can be doneeasily using an amplifier or a directional antenna. To address thischallenge, we propose ‘Fixed MCS SNR (FMS)’ filtering schemebased on the intuition that high MCS requires high SNR, and amplifying the received signal strength does not necessarily improveSNR. We experimentally show that this is true in reality, and ourreal-world evaluation in various environments (14 locations) showsthat FMS scheme prevents ‘amplifier attacks’ in all cases. To further counter the false positives of FMS against ‘directional antennaattacks’ (avg. 35.7%), we also propose ‘Authentication Motionwith Signal strength gap (AMS)’ filtering scheme which defendsagainst both attacks in all cases at the cost of requiring the user tomake a simple motion. FMS or AMS scheme can be selected according to the application requirement to enhance the security ofproximity-based authentication in upcoming IoT.
Hee Dong Jang,Hankwon Chang,Yongjae Suh,Kikuo Okuyama 한국물리학회 2006 Current Applied Physics Vol.6 No.1l
Synthesis of silica (SiO2) nanoparticles from sprayed droplets of tetraethylorthosilicate (TEOS) by the ame spray pyrolysis was inves-tigated, and the particles were characterized by TEM, XRD, and BET method. TEOS concentration, maximum ame temperature, andparticle diameter. Spherical SiO2 nanoparticles ranged from 12 to 47 nm in average particle diameter were produced by through all theexperiments. As the TEOS concentration in the ame increased, the average particle diameter of the SiO2 nanoparticles having narrowsize distribution increased. Larger SiO2 nanoparticles were synthesized as hydrogen and oxygen ow rate decreased in the ame, respec-structure of all the product SiO2 nanoparticles was found as amorphous.
Laser Ablation법에 의한 ZrVFe 합금 나노분말 제조
길대섭,서용재,장희동,이재천,송창빈,김원백,Kil Daesup,Suh Yongjae,Jang Heedong,Lee Jaechen,Song Changbin,Kim Wonbaek 한국재료학회 2005 한국재료학회지 Vol.15 No.4
Nano-sized ZrVFe alloy powders were prepared by the ablation of powder compact in alcobol using a Nd-YAG pulsed Laser. The $Zr_{57}V_{35.}8Fe_{7.2}$ alloy commercially designated as ST707 has long been known as the ideal solution for various vacuum applications. The target for the ablation was sintered pellets of $Zr_{57}V_{35.}8Fe_{7.2}$ alloy powder. The alloy was prepared by arc melting and Hydride-DeHydride method. The ablated powders were mostly circular having fairly large size distribution smaller than 200 nm in all cases. The X-ray diffraction study revealed that the ablated alloy retained the crystal structure of the target alloy. Nevertheless, Fe and V contents in the ablated powder were lower than those in the target alloy. This was believed to result from the high vapour pressures of Fe and V compared to that of Zr. The size of the powders ablated at high energy fluence tends to decrease due at least partly to the breakdown of previously made ones.
Microbial production of ultrafine-grained magnetite by fermentation processes at room temperature.
Roh, Yul,Kim, Yumi,Lee, Sanghoon,Jang, Heedong,Suh, Yongjae American Scientific Publishers 2008 Journal of Nanoscience and Nanotechnology Vol.8 No.10
<P>A method of producing magnetite nanoparticles was developed through culturing a microorganism designated Haejae-1, Shewanella sp., in the presence of glucose and akaganeite (beta-FeOOH). Haejae-1 isolated from inter-tidal flat sediments was able to produce copious amount of ultrafine magnetite via glucose fermentation extracellularly under anaerobic conditions at room temperature, allowing for easy production, separation, and recovery of the magnetite. TEM observation revealed aggregates of small crystals of ultrafine magnetite which ranged in size from about 2 to 4 nanometers. Magnetic property by SQUID analysis showed the magnetite nanoparticles demonstrate superparamagnetic behavior. As a result, the method of the present study can be used to produce magnetite efficiently using inexpensive means at room temperature. The magnetite is a mineral of a great commercial value in that it is useful, e.g., in magnetic recording devices, drug carriers, and as toner for plain paper copiers.</P>