• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.24 no.1
• /
• pp.75-86
• /
• 2014

Demand for the femtocell is largely credited to the surge in a more always best connected communication conscious public. 3GPP defines new architecture and security requirement for Release 9 to deal with femtocell, Home eNode B referred as HeNB. In this paper, we analyze the HeNB security with respect to mutual authentication, access control, and secure key agreement. Our analysis pointed out that a number of security vulnerabilities have still not been addressed and solved by 3GPP technical specification. These include eavesdropping, man-in-the-middle attack, compromising subscriber access list, and masquerading as valid HeNB. To the best of our knowledge, any related research studying HeNB security was not published before. Towards this end, this paper proposes an improved authentication and key agreement mechanism for HeNB which adopts proxy-signature and proxy-signed proxy-signature. Through our elaborate analysis, we conclude that the proposed not only prevents the various security threats but also accomplishes minimum distance from use-tolerable authentication delay.

• Journal of Communications and Networks
• /
• v.15 no.3
• /
• pp.312-320
• /
• 2013

Home evolved Node-B (HeNB), also called a femtocell or a femto base station, is introduced to provide high data rate to indoor users. However, two main problems arise in femtocell networks: (1) Small coverage area of HeNB, which results in limited cell-splitting gain and ping-pong handover (HO) problems and (2) high inter-femtocell interference because HeNBs may be densely deployed in a small region. In this study, an efficient cooperation mechanism called an HeNB-aided virtual-HO (HaVHO) scheme is proposed to expand the coverage area of femtocells and to reduce inter-femtocell interference. The cooperation among neighbor HeNBs is exploited in HaVHO by enabling an HeNB to relay the data of its neighbor HeNB without an HO. The HaVHO procedure is compatible with the existing long term evolution specification, and the information exchange overhead in HaVHO is relatively low. To estimate the signal to interference plus noise ratio improvement, the area average channel state metric is proposed, and the amount of user throughput enhancement by HaVHO is derived. System-level simulation shows that HaVHO has a better performance than the other four schemes, such as lesser radio link failure, lesser ping-pong handover, lesser short-stay handover, and higher user throughput.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.10 no.3
• /
• pp.53-60
• /
• 1973

Calculations of the temperature coefficients of the elastic surface wave velocity and delay time were performed for the propagation along the X axis of rotated Y cut plane of the LiNbO3 and LiTaO3. Measurements of the temperature dependence of delay time of the elastic surface wave were also performed for the propagation along the X axis of a 130" rotated Y cut plane of the LiNb03 at the temperature range from liquid He to room temperature. Experimental value 70$\times$10-6/$^{\circ}C$ of the temperature coefficient of the delay time of the elastic surface wave agrees well with the calculated value 72.7$\times$10-a/$^{\circ}C$. The temperature coefficient of delay time of elastic surface wave propagating along the X axis of a 130$^{\circ}$ rotated Y cut plane o( the LiNbO3 is approximately 16$\times$10-6/$^{\circ}C$ at the near temperature of liquid He.d He.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.16 no.2
• /
• pp.15-18
• /
• 1979

Deposited film of a transition metal, Ti was diffused into LiNbO3 crystals to form integrated optical waveguides. By suppressing L O out -diffusion, single-mode waveguides could be constructed. Measurements on characteristics were performed by using the prise coupling technique and a He-Ne laser. ( λ = 0.6328 $\mu$m)

• Nuclear Engineering and Technology
• /
• v.18 no.2
• /
• pp.92-96
• /
• 1986

The $^{93}Nb(n,n\alpha)^{89m}Y$, $^{93}Nb(n,{\alpha})^{90m}Y$ and $^{93}Nb(n,2n)^{92m}Nb$ cross sections at a neutron energy of 14.6 MeV have been measured relative to the $^{27}Al(n,p)^{27}Mg$ and $^{27}Al(n,{\alpha})^{24}Na$ cross sections. A small accelerator utilizing $T(D,n)^4He$ reaction was used as a neutron source and the neutron energy spread is about 0.4MeV at the sample. All induced activities were measured with a 70cc HPGe detector in the same geometry.

• Journal of Welding and Joining
• /
• v.26 no.1
• /
• pp.76-82
• /
• 2008

The effect of Nb addition on the precipitation and precipitate coarsening behavior was investigated in Ti and Ti + Nb steel weld HAZ. A dilatometer equipped with a He-quenching system was used to simulate the weld thermal cycle. Compared to $TiC_yN_{1-y}$ precipitate in a Ti containing steel, $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle with addition of Nb is precipitated in a Ti + Nb containing steel. Meanwhile, precipitate coarsening occurred more easily in Ti + Nb steel, which may be because the high temperature stability of $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle is deteriorated by the Nb addition.

• Korean Journal of Optics and Photonics
• /
• v.9 no.6
• /
• pp.423-427
• /
• 1998

Two wave mixing experiments in $LiNbO_3$, $BaTiO_3$ are carried out, and the characteristics as optical information processing device are investigated. Examined crystals are commonly used ones, such as 0.03% mol Ce-doped $BaTiO_3$, 0.03% mol Fe-doped $LiNbO_3$, and 6% mol MgO-doped $LiNbO_3$. $Ar^+$ ion laser is used as the writing beam, and He-Ne Laser is used as the reading beam. The recording-decay and erasing characteristics of diffraction gratings, the time constants, and also the angular selectivities are measured for each crystals and compared.

• Journal of the Korean Vacuum Society
• /
• v.12 no.S1
• /
• pp.28-32
• /
• 2003

Both $LiNbO_3$ and $KTiOPO_4$ samples were implanted with 350 keY $H^+$ and $He^+$ ions at different doses ranging from $1 ${\times}$\times10^{16}$ to of $5 ${\times}$\times10^{16}$ ions/$\textrm{cm}^2$. Single and multi-energy implantations were performed at room temperature. Mono-mode or a few modes in both $LiNbO_3$ and $KTiOPO_4$ waveguides were observed. The effect of temperature on the refractive index profiles of $LiNbO_3$ and $KTiOPO_4$ waveguids was studied. The temperature covered from room temperature, $200^{\circ}C$, 194.5 K (dry ice) and 77K (liquid nitrogen). Different mechanisms are needed to interpret the observed behavior. A n, increased mono-mode $LiNbO_3$ waveguide was formed by multi-energy keV $He^+$ ions.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.12
• /
• pp.3679-3683
• /
• 2010

Niobium oxide ($Nb_2O_5$) and phosphated $Nb_2O_5$ were synthesized and used as catalysts for sorbitol dehydration to isosorbide. The characterization results of $N_2$ adsorption, XRD and $NH_3$-TPD revealed that the phosphoric acid modification could well prevent the crystallization of $Nb_2O_5$. And the amorphous phosphated $Nb_2O_5$ catalysts kept the relatively large surface area and stable acidity at high calcination temperature. The catalytic results showed that the selectivity to isosorbide could be dramatically enhanced over phosphated $Nb_2O_5$. The excellent catalytic performance with 100.0% sorbitol conversion and 62.5% isosorbide selectivity were obtained over the 0.8P/NBO-400 catalyst. Comparing with $Nb_2O_5$ catalysts, phosphated $Nb_2O_5$ catalysts regenerated through a simple calcination process showed no significant activity loss after recycling three runs.

• Proceedings of the Optical Society of Korea Conference
• /
• 2000.02a
• /
• pp.286-287
• /
• 2000

최근에 광연결(optical interconnection)을 위한 목적으로 LiNbO$_3$(0.03 mol% Fe doped)결정에 광굴절(photorefractive) 도파로를 기록하는 방법이 소개되고$^{(1-2)}$ 있는데 제작 방법과 원리는 다음과 같다. 17mW 출력의 He-Ne 레이저광을 렌즈로 통과시켜 빔의 크기를 줄인 후 초점은 LiNbO$_3$크리스털에 입사하는 반대편 면에 맞추어 입사시킨다. 그림 1에서 +y방향으로 초점이 입사면을 통과할 때까지 크리스털을 이동시켜 도파로를 만든다. 이 때 이동하는 방법은 10ms 노광시킨 후 15$mu extrm{m}$씩 불연속적으로 움직여 나간다. (중략)