• The Journal of the Acoustical Society of Korea
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• v.20 no.7
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• pp.101-108
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• 2001

In this paper we focus on dynamic reservation slot allocation scheme for supporting QoS of a voice traffic in WATM MAC. Especially, voice traffic is the most important real-time object, and so we propose a new MAC protocol for voice traffic over WATM networks in the multimedia environment. According to the characteristics of voice traffic which is repeatedly in silent state and active state, new protocol allocates reservation slots dynamically with respect to the number of silent voice source of which starting time is stored to the state table in base station (BS). The simulation results show that the proposed protocol has better performance than slotted ALOHA in average access delay, collision rate, better than NC-PRMA(Non Collision Packet Reservation Multiple Access) in band width efficiency, and can provide a certain level of QoS requirement by the given slot assignment even though the number of voice terminals is increased.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.8
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• pp.1877-1884
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• 2014

Because of the limited power resource, we need a reliable low-power media access control technique suitable for unmaned remote sensor operation condition for the unmanned sensor processor to perform the task in the remote wireless network situation. Therefore CSMA/CA and X-MAC is generally considered to effectively transmit the signal in the low-power wireless network. In this paper, we propose the more efficient low-power LP-MAC Technique which consumes the minimum power and transmits the data faster in condition that the mobile nodes' joining to and leaving from the network which consists of the fixed nodes is fluid. The fixed nodes operate in an asynchronous mode to perform the network self-configuration and transmit data faster to the mobile node which is frequently join and leave the network. When the mobile node leaves the network, the network's operation mode will be synchronous mode to achieve the minimum power consumption, thus the minimum power operation becomes possible.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.69-79
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• 2001

비동기 및 차세대 이동통신 시스템의 진화 과정 상에서 RF관련 규격들의 변화에 대해 알아보았고, 비동기 시스템의 RF부를 제작하는데 사용하게 될 RF 부품 기술 동향을 단말기와 기지국의 경우로 나 누어 분석하였다. 또한 차세대인 4세대 시스템 RF 부의 진화 전망에 대해 간단히 알아보았다. 시스템 이 진화할수록, 요구되는 데이터 처리 능력으로 인 해 채널 대역폭은 점점 넓어지고, 기존 시스템과의 상호 간섭 방지를 위해 일반적인 RF 관련 규격 중 방사 규격과 요구되는 선형성이 엄격해진다. 앞으로 의 RF 부품의 기술적 진화는 직접 변환 방식의 부 품 개발로 단말기의 소형화, 저가격화를 이를 것이 고, 동작 주파수 영역을 0.8~5 GHz대로 하기 위한 광대역화, 선형화가 요구될 것이다. 또한 4 세대 시스템에서는 기존의 주파수 이용 개념과 무선 전송 기술에 변화를 주게 될 SDR 기반의 다중모드/복합 다중 접속 기술을 적용하게 될 것으로 예상된다.

• Annual Conference of KIPS
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• 2005.11a
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• pp.1195-1198
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• 2005

Radio Frequency Identification(RFID)를 이용한 물류 시스템은 바코드를 대체할 시스템으로 주목받고 있다. 이러한 RFID 를 이용한 물류 시스템이 실제로 적용하는 데에는 매우 큰 설치 비용이 문제로 제기된다. 이를 해결하기 위해 무선으로 연결되는 이동형 RFID 리더를 이용한다. 한편 동기화 모드 및 비동기화 모드로 전송되는 RFID 데이터의 특성과 기존의 라우팅 기법의 브로드캐스트에 따른 오버헤드를 줄이기 위해 재구성 가능한 클러스터 기반의 라우팅 기법이 적합하다. 따라서 RFID 창고 관리 시스템을 위한 재구성 가능한 클러스터 기반의 라우팅 기법을 제안한다.

• Journal of the Korean Professional Engineers Association
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• v.30 no.1
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• pp.125-136
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• 1997

The satellite communications system application to the Broadband ISDN(BISDN) is now being studied. Asynchronous transfer mode(ATM) is the target for BISDN and makes it possible to offer multimedia services on the simple network structure. This paper clarifies the required functions to the ATM interface between the terrestrial network and satellite TDMA system to compensate cell delay variation caused by satellite link, to improve the transmission efficiency, to do usage parameter control and to configure TDMA/ATM hardware interface.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9C
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• pp.905-912
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• 2007

This paper proposes an efficient estimation and compensation scheme of IQ imbalance for OFDM-based WLAN systems in the presence of symbol timing error. Since the conventional scheme assumes perfect time synchronization, the criterion of the scheme used to derive the estimation of IQ imbalance is inadequate in the presence of the symbol timing error and the system performance is seriously degraded. New criterion and compensation scheme considering the effect of symbol timing error are proposed. With the proposed scheme, the IQ imbalance can be almost perfectly eliminated in the presence of symbol timing error. The bit error rate performance of the proposed scheme is evaluated by the simulation. In case of 54 Mbps transmission mode in IEEE 802.11a system, the proposed scheme achieves a SNR gain of 4.3dB at $BER=2{\cdot}10^{-3}$. The proposed compensation algorithm of IQ imbalance is implemented using Verilog HDL and verified. The proposed IQ imbalance compensator is composed of 74K logic gates and 6K bits memory from the synthesis result using 0.18um CMOS technology.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.5
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• pp.95-103
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• 2009

An efficient symbol time synchronization scheme for IEEE 802.11n MIMO-OFDM based WLAN systems using cyclic shift diversity (CSD) preamble is proposed. CSD is used to prevent unintentional beamforming when the same preamble signal is transmitted through transmit antennas. However, it is difficult to find a proper starting-point of the OFDM symbol with the conventional algorithms because of time offset by multi-peaks which are result from cross-correlation of received CSD preamble with a known short training symbol. In addition, the performance of symbol time sync. is affected by AGC and packet detection position. In this paper, an optimal symbol time synch. algorithm which is composed of the boundary detection scheme between LTS and OFDM symbols, the verification scheme for enhancement of boundary detection accuracy, and the SNR-varying threshold estimation scheme is proposed. Simulation result show that the proposed algorithm has performance gains of 4.3dB in SNR compared to the conventional algorithms at the rate of 1% sync. failure probability for $2{\times}2$ MIMO-OFDM system and 18dB at 0.1% when maximum frequency offset exists. It also can be applied to $4{\times}4$ MIMO-OFDM system without any modification. Hence, it is very suitable for MIMO-OFDM WLAN systems using CSD preamble.

• Journal of Korea Multimedia Society
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• v.7 no.5
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• pp.713-720
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• 2004

In this paper we suggest error control scheme to improve CLR performance degradation on wireless ATM access networks which consist of access node and wireless channel. Based on the cell scale and hurst scale, traffic model of wireless ATM access network is analyzed. The CLR equation due to buffer overflow for wireless access node is derived for VBR traffic. the CLR equation due to random bit errors and burst errors for wireless channel is derived. Using the CLR equation for both access node and wireless channel, the CLR equation of wireless ATM access network is derived, and we evaluate the CLR performance on the wireless ATM access networks with conventional SR ARQ scheme and recommended error control scheme, that is, Type I Hybrid ARQ scheme. It is confirmed that CLR performance of the access networks with recommended error control schemes is superior to that of access networks with conventional error control scheme.