• Proceedings of the Korea Information Processing Society Conference
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• 2009.04a
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• pp.1155-1158
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• 2009

모바일 서비스는 사용자보호를 위해 인증 및 암호화 기능이 필수적으로 제공되어야만 한다. 3GPP는 3 세대 이동통신 (UMTS)를 위한 인증보안구조인 AKA를 정의하였다. AKA에서는 인증벡터를 다수 개 생성하여 처리하는 기법을 채택하고 있으나 이러한 기법이 인증서버의 load 증가 및 방문서버의 저장공간 소모라는 문제점을 야기한다. 하지만 인증벡터를 다수 개 생성하는 기법은 단말의 핸드오버를 위한 필수불가결한 기법이다. 따라서 본 논문에서는 사용자의 이동패턴 및 인증요청 처리 속도에 따른 인증벡터의 동적 선택 알고리즘을 제안하여 이동통신 네트워크의 signaling load를 최소화하고자 한다. 이를 위해 확률 및 큐잉 이론이 도입되었으며, 시뮬레이션을 통해 수학적 분석을 검증한다. 또한 기존 관련연구에서 제안 하는 알고리즘과 비교 평가하였다.

• KSBB Journal
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• v.14 no.1
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• pp.96-102
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• 1999

Marine bacterium Bacillus cereus ASK202 produced an extracellular agarase (E.C.3.2.1.81) which showed a high level of enzyme activity in the presence of agar and agarose. In the optimal culture conditions, the agarase production increased 7.7 folds compared with the one obtained from the basal medium. Agarase production reached upto 160 units/L after 24hr of cultivation in a modified marine medium at $25^{\circ}C$. The degree of purification increased 31.5 folds with 27.8% yield through freeze drying, DEAE Sepharose CL-6B and Superose 6HR 10/30 column chromatography. The molecular weight of the purified agarase was determined to be 90,000 daltons by gel-permeation filteration. Optimal temperature and pH for the enzyme activity were $40^{\circ}C$ and 7.8, respectively. The enzyme was stable up to $50^{\circ}C$ and at a broad pH range of 5.0-10.0. The $\beta$-agarase was activated by $Zn(NO_3)_2$, and was inhibited by $CuSO_4$ and $SnCl_2$. The Km and Vmax values of this enzyme for agarose as a substrate was $2.4mg/m\ell$ and 13.6 mg/m$\ell$, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.8
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• pp.745-753
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• 2011

In this paper, the planar monopole antenna for multi-band service is proposed. The proposed antenna, which is a rectangular patch antenna with a U-shaped slit based on a monopole antenna for wide bandwidth characteristic, is designed and analyzed. The antenna size has been miniaturized by using the U-shaped slit. The frequency characteristics are modified and optimized by varying specific parameters. To obtain desired frequency bands, the U-shaped slit and patch lines have been applied. Whole antenna dimensions including the ground plane are $35{\times}50{\times}1\;mm^3$, and the antenna part size is $35{\times}27\;mm^2$. It is fabricated on the FR-4 substrate(${\epsilon}_r=4.4$) using a microstrip line of $50{\Omega}$ for impedance matching. For the measured results, the impedance bandwidth below a VSWR of 2 is 790~916 MHz, 1.74~2.14 GHz, and 2.36~3.13 GHz. The fabricated antenna is satisfied with the aimed impedance bandwidth in GSM/DCS/US-PCS/UMTS/Bluetooth/S-DMB applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.10
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• pp.1117-1127
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• 2012

In this paper, the monopole antenna for satisfying GSM900/DCS1800/PCS1900/UMTS2100 services is designed. We can get the characteristic of the low frequency bands by connecting the front patch to the back patch of the antenna and get the low frequency resonance band using a front patch slit. The proposed antenna total volume is $40{\times}98{\times}1.6\;mm^3$, and it is designed on the FR-4 substrate having a relative dielectric constant of 4.4. As measurement result after fabrication, showed that the resonant frequency bandwidths are 156 MHz(828~984 MHz), 708 MHz(1.476~2.184 GHz) based on the return loss of 10 dB, and the radiation patterns show as the omnidirectional shapes for the E-field and H-field. For analyzing the human effects, the proposed antenna is mounted on the mobile-phone case. The averaged peak SAR over 1 g and 10 g is simulated and measured when the input power is 0.25 W. We have checked the variation of the SAR values when the antenna is mounted 4 different directions, then checked the direction having a relatively higher SAR. The results also satisfied the limiting SAR values which are 1.6 W/kg and 2.0 W/kg averaged over 1 g and 10 g tissues respectively.

• Journal of KIISE:Information Networking
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• v.33 no.1
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• pp.38-48
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• 2006

For extending of hot-spot of WLAN, (2) proposes internetworking scheme between wireless LAN (WLAN) and mobile ad-hoc network (MANET), which employ the same layer-2 protocol with different mode. Compared to internetworking schemes between UMTS (Universal Mobile Telecommunications Systems) and WLAN (3-4), the scheme from (2) has relatively low overhead and latencies because WLAN and MANET are physically and logically similar to each other. However, the mode switching algorithm proposed in r2] for internetworking between WLAN and MANET only considers signal strength and determines handoff, and mobile nodes following a zigzag course in pollution area may perform handoff at short intervals. Furthermore, (2) employs mobile IPv6 (MIPv6) at base, which brings still high delay on handoff and overhead due to signal message exchange. In this paper, we present optimized internetworking scheme between WLAN and MANET, modified from (2). To settle ping-pong handoff from (2), we propose adaptive mode switching algorithm. HMIPv6 is employed for IP connectivity and mobility service in WLAN, which solves some shortcomings, such as high handoff overhead and vulnerable security. For routing in MANET, OLSR is employed, which is a proactive Protocol and has optimally reduced signal broadcasting overhead. OLSR operates with current P protocol compatibly with no change or modification. The proposed internetworking scheme based on adaptive mode switching algorithm shows better performance than scheme from (2).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3558-3562
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• 2010

The exact fundamental frequency (pitch) extraction is important in speech signal processing. However the exact pitch extraction from speech signal is very difficult due to the effect of formant and transitional amplitude. So in this paper, the pitch is detected after flattening the spectrum in frequency region by proposed algorithm for minimized harmonics variance value. Experimental result showed the proposed method appeared an outstanding performance in compared with LPC, Cepstrum. Also, the results show the proposed method is better than conventional method.

• Proceedings of the Korean Information Science Society Conference
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• 2007.10d
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• pp.62-65
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• 2007

3GPP(3rd Generation Partnership Project) 주도의 유럽형 3세대 이동통신인 UMTS 시스템에서 제공하는 멀티미디어 방송 서비스(Multimedia Broadcast/Multicast Service)는 무선 네트워크상에서 동일한 정보를 하나의 링크를 통해 다수의 사용자에게 제공하는 point-to-multipoint 서비스이다. 콘텐츠가 무료로 제공되면 임의의 사용자들이 콘텐츠가 제공되는 채널에 액세스할 수 있다. 그러나 채널 액세스가 가입(subscription)기반이면, 가입하지 않은 사용자들은 콘텐츠를 이용할 수 없어야 한다. 이를 위해 사용자를 인증하고 안전한 방법으로 콘텐츠를 전송할 수 있는 보안 서비스가 필요하다. 본 논문은 MBMS의 전반적인 개요를 설명하여 앞으로 논의될 내용인 MBMS 보안구조에 대한 배경지식을 제공한다. 또한 브로드캐스트와 멀티캐스트 모드 각각에 대한 MBMS 구조를 설명하고, 멀티캐스트 모드에서의 보안 기능과 키관리 기법, 콘텐츠 보호 기술에 대해 상세히 분석한다.

• Journal of information and communication convergence engineering
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• v.1 no.4
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• pp.183-188
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• 2003

The $4^{th}$ generation mobile communications, through several radio access networks such as WLAN, Bluetooth, UMTS, GPRS, CDMA 1X, and IMT-2000 in the same area offering different type of coverage, will support interactive multimedia services in additions to wider bandwidths, higher bit rates, and service portability. Regardless of various radio access networks, they will also support robust security mechanisms, as well as seamless mobility and common authentication. In this paper, we give an overview of WLAN security and examine its security problems. We also explain the enhanced security schemes, such as port-based authentication, EAP, and IEEE 802.1X. For secure wireless communications, several possible security solutions are offered and evaluated in various respects to improve WLAN security. This paper will make a contribution to provide more secure wireless communications to cellular operators embracing WLAN technology as a means to generate new revenues based on data services.

• The KIPS Transactions:PartD
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• v.11D no.4
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• pp.951-958
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• 2004

This paper describes problems when visited ISP subscriber gets dynamic IP address in home ISP for wireless internet service on GPRS network. We propose a specific DHCP relay for wireless internet service of visited ISP subscriber on GPRS network. We designed and implemented the specific DHCP relay and installed it in ISP testbed. We show the allocated dynamic IP address using specific DHCP relay for visited ISP subscriber on GPRS network. Now we think it is possible the visited ISP subscriber can access wireless internet service on GPRS network using specific DHCP relay, and UMTS system can be managed IP address for subscriber roaming.

• Proceedings of the Korea Information Processing Society Conference
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• 2000.10b
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• pp.1609-1612
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• 2000

무선망에서 기존의 회선 서비스뿐만 아니라 패킷 서비스 및 영상 서비스 등을 수용하는 데 있어서 고려되어야 할 것들 중 하나는 무선 자원의 활용이다. 특히 패킷 서비스의 경우 가변적인 패킷의 길이와 양으로 효율적인 무선 자원관리를 어렵게 하는 요소를 지니고 있다. 즉, 무선 자원을 효율적으로 운용하기 위해서는 동적인 무선 자원할당 메커니즘이 중요한 역할을 한다. UMTS 표준 문서에서는 계층 2 전송 프로토콜인 RLC (Radio Link Control) 버퍼의 양만을 측정하여 무선 자원 할당이 제어가 되도록 권고하고 있다. 하지만 트래픽 양의 변화가 큰 VBR 트래픽의 경우, 이와 같은 방법은 갑자기 증가하거나 감소하는 트래픽 양에 적응하기 힘들고 이는 무선 자원의 효율성을 저하시키며, QoS 제공도 어렵다. 본 논문에서는 먼저 트래픽 특성을 알 수 있는 토큰 버켓 모델을 RLC에 적용하고, 동적 무선 자원 할당을 위해 RLC 버퍼의 양뿐만 아니라 예상되는 유입 트래픽 양을 측정 및 보고하는 메커니즘을 제안한다.