• 한국정보과학회논문지:정보통신
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• 제37권2호
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• pp.142-149
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• 2010

본 논문에서는 IEEE 802.11 WLAN과 IEEE 802.16 WMAN 무선 네트워크가 같은 공간에서 공유대역(shared band)을 사용하는 상황에서 공존이 가능하도록 802.16 MAC 프로토콜의 수정을 제안한다. 제안하는 WMAN MAC 프로토콜은 WLAN을 고려하여 BS(Base Station)와 SS(Subscriber Station)가 통신할 때 WLAN의 통신을 지연시켜 충돌을 피하는 방식으로 동작한다. 즉, BS에서 SS로 데이터를 전송하는 하향 서브 프레임(downlink subframe)에서는 SS가 할당받은 버스트(burst) 구간에서 CTS(Clear To Send)를 사용하여 WLAN의 전송을 막고, SS에서 BS로 데이터를 전송하는 상향 서브 프레임(uplink subframe)에서는 BS가 CTS를 사용하여 WLAN의 통신을 지연시킨다. 제안하는 프로토콜은 WLAN과의 충돌을 방지하여 전송효율을 높일 수 있으며, 이를 시뮬레이션에 의해 분석한다.

• Journal of Communications and Networks
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• 제14권2호
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• pp.179-187
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• 2012

Power saving is one of the most important features that extends the lifetime of portable devices in mobile wireless networks. The IEEE 802.16e mobile broadband wireless access system adopts a power saving mechanism with a binary truncated exponent algorithm for determining sleep intervals. When using this standard power saving scheme, there is often a delay before data packets are received at the mobile subscriber station (MSS). In order to extend the lifetime of a MSS, the battery energy must be used efficiently. This paper presents a dynamically alternating sleep interval scheduling algorithm as a solution to deal with the power consumption problem. We take into account different traffic classes and schedule a proper sequence of power saving classes. The window size of the sleep interval is calculated dynamically according to the packet arrival rate. We make a tradeoff between the power consumption and packet delay. The method achieves the goal of efficiently reducing the listening window size, which leads to increased power saving. The performance of our proposed scheme is compared to that of the standard power saving scheme. Simulation results demonstrate the superior performance of our power saving scheme and its ability to strike the appropriate performance balance between power saving and packet delay for a MSS in an IEEE 802.16e mobile broadband wireless access system.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(1)
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• pp.81-84
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• 2000

This paper has been studied the design of 16-QAM demodulator used in broadband wireless local loop subscriber station. In B-WLL systems, transmission signal experience the inter symbol interference(ISI) due to multipath, frequency offset of RF/IF local oscillator and phase offset. In this paper, we discuss the effective data recovery algorithm for 16-QAM demodulator to compensate the distorted signal from ISI, frequency offset and phase offset.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 춘계종합학술대회
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• pp.872-875
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• 2005

무선랜을 확장한 휴대인터넷은 그 셀크기가 이동통신처럼 크고 중저속의 이동성을 지원하면서 이음매 없는 (seamless) 서비스를 제공할 수 있다. 휴대인터넷 국제 표준인 IEEE 802.16e에서는 단말과 기지국간 권한인증 및 키 교환을 위해서 PKMv2(Privacy Key Management) 프로토콜을 사용하고 있다. 본 연구에서는 먼저, WMAN(Wireless Metropolitan Area Network) 표준인 IEEE 802.16 표준을 기반으로 이동성을 지원하는 IEEE 802.16e 표준과 TTA 휴대인터넷 표준을 바탕으로 휴대인터넷의 전체 보안구조를 파악하였다. 그리고 MSS(Mobile Subscribe Station)가 서비스를 제공받는 BS(Base Station)를 옮겨갈 경우 인증 및 키 교환을 위한 기존의 프로토콜을 분석하였다.

• 정보보호학회논문지
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• 제6권4호
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• pp.3-38
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• 1996

The mobile station shall convolutionally encode the data transmitted on the reverse traffic channel and the access channel prior to interleaving. Code symbols output from the convolutional encoder are repeated before being interleaved except the 9600 bps data rate. All the symbols are then interleaved, 64-ary orthogonal modulation, direct-sequence spreading, quadrature spreading, baseband filtering and QPSK transmission. The sync, paging, and forward traffic channel except the pilot channel in the forward CDMA channel are convolutionally encoded, block interleaved, spread with Walsh function at a fixed chip rate of 1.2288 Mcps to provide orthogonal channelization among all code channels. Following the spreading operation, the I and Q impulses are applied to respective baseband filters. After that, these impulses shall be transmitted by QPSK. Authentication in the CDMA system is the process for confirming the identity of the mobile station by exchanging information between a mobile station and the base station. The authentication scheme is to generate a 18-bit hash code from the 152-bit message length appended with 24-bit or 40-bit padding. Several techniques are proposed for the authentication data computation in this paper. To protect sensitive subscriber information, it shall be required enciphering ceratin fields of selected traffic channel signaling messages. The message encryption can be accomplished in two ways, i.e., external encryption and internal encryption.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.89-92
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• 2005

For the past years, wireless communications environment have developed with explosive demand of internet service and increase of subscriber. Anytime anywhere, we can access internet service and recently, we can access internet with portable terminal using wireless communications. So several schemes have been proposed for the efficient service. In this paper, we may improve performance of wibro system using adaptive antennas scheme at the base station (BS) and mobile station(MS),operating jointly. In wibro system, the joint use of transmit beamforming at BS and receive beamforming at MS is improved the SINR and increased the capacity compared to conventional system[1],[2].

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.115-118
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• 1998

ATM(Asynchronous Transfer Mode)을 기반으로한 BSC(Base Station Controller)를 이용한 무선 이동통신망에서는 크게 MSC, BSC, BTS로 구성 되어진다. BSC는 MSC(Mobile Switch Center)와의 STM-1급 (155.52Mbps) 정합이 이루어지며, 여러 BTS(Base Transceiver Subsystem)와 T1(1.544Mbps)/E1(2.048Mbps)급 정합이 이루어져 호연결, 관리, 제어 및 MT(Mobile Terminal)의 soft-handoff를 담당한다. BSC내의 저속 가입자 I/F에서는 BTS와 BSC내의 ATM switch와의 정합을 수행하면서 VPI/VCI변환, BSC 내부 cell format으로 변환, 그리고 UPC(Usage Parameter Control)등이 이루어진다. 본 논문에서는 ATM switch를 이용한 BSC 내부의 저속 가입자 I/F의 구현에 관해서 살펴본다.

• 정보학연구
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• 제12권2호
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• pp.1-12
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• 2009

China first started its mobile phone services in 1987, and the number of users has exponentially increased so that it reached 700 millions in January 2009. Currently China's 2G(GSM) users is 650 millions. These 2G (GSM) services have an advantage of the capability to use the mobile phone with a SIM (Subscriber Identity Modul) card, one kind of smart cards, inserted into it. However, due to the security vulnerability of SIM cards being used within China's 2G (GSM) services, SIM cards cloning. Problems concerning mobile phone surveillance towards a designated person by illegal cloning ESN and IMSI have recently risen to be a massive social issue within Korea as well. These studies have experimented the possibility of SIM cards clone in various mobile communication corporations using 2G (GSM) in China, and hence discovered the security vulnerability such as the incoming outgoing, SMS service and additional services on mobile phones using clone SIM cards.

• 한국통신학회논문지
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• 제25권3B호
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• pp.577-583
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• 2000

An efficient echo cancellation method, which controls the echo caused from the PSTN, is proposed. In our situation, the PSTN is connected to the mobile subscriber and the base-station which use different bit-rate CVSD(continuously variable slope delta modulation) coders and echo canceller is installed at the location of the base-station. By using the symmetry of the coder pairs. the proposed method shortens the echo pate length and reduces the nonlinear distortion inherent in the coders. And it is implemented in the decoded signal region, so fitted to the general-purpose DSP implementation. We also proposed a echo cancellation method using the combined bit-stream so as to implement without the multipliers onto the VLSI. It has an improved echo cancellation performance by reducing the high frequency noises in the coders. And it has an reduced complexity by reducing the excitation rate of the bit-stream.

• Journal of Communications and Networks
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• 제9권3호
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• pp.247-253
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• 2007

In this paper, downlink capacity of time duplex division (TDD) based cellular wireless networks utilizing fixed hopping stations is investigated. In the network, a number of fixed subscriber stations act as hopping transmission stations between base stations and far away subscribers, forming a cellular and ad hoc mobile network model. At the radio layer, TDD code division multiple access (CDMA) is selected as the radio interface due to high efficiency of frequency usage. In order to improve the system performance in terms of downlink capacity, we propose different time slot allocation schemes with the usage of fixed hopping stations, which can be selected by either random or distanced dependent schemes. Performance results obtained by computer simulation demonstrate the effectiveness of the proposed network to improve downlink system capacity.