• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.311-315
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• 2006

Precision location and positioning of Asset within a network is an attractive feature with various applications, especially in indoor environments. Such a demand is met by the standard task group, IEEE 802.15.4a. Several methods, that is, pulse, chirp and chaotic communications have been proposed so far to satisfy the requirements of the standard. Among them, ultra wideband direct chaotic communications has advantageous features such as low hardware complexity, low cost, lower power consumption and flexible frequency band plan. In this paper, the feasibility of the ranging system using non-coherent chaotic transceiver is investigated by designing and implementing the system and the performance is proved by conducting location experiments in real indoor environments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권4호
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• pp.1276-1291
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• 2014

In the field of visible light communication (VLC), light-emitting diodes (LEDs) are used for transmitting data via visible light. In this study, we analyze pulse dual slope modulation (PDSM) as a means of delivering information in VLC. PDSM involves the modulation of symmetrical slope pulses to encode binary 0s and 1s, and owing to the moderately increasing and decreasing pulse shapes that are created, this method enables more spectral efficiency than the variable pulse position modulation (VPPM) technique currently adopted in IEEE 802.15.7. In particular, PDSM allows for the avoidance of intra-frame flicker by providing idle pulses in a spectrum-efficient way. A simple detection scheme is proposed for PDSMsignals, and its bit error rate (BER) is analyzed mathematically at varying slopes to validate the process through simulation. The BER performance of PDSM detection using dual sampling is compared to the performances of PDSM and VPPM using correlation detection. It is found that, when the probability of idle pulse transmission is less than 0.08 and higher than 0, the BER of dual sampling PDSM is lower than that of PDSM using correlation detection over the entire light intensity range.

• 한국통신학회논문지
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• 제34권1C호
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• pp.113-119
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• 2009

The training sequence with the appropriate length for equalization and initial synchronization is necessary before sending the pure data in the burst transmission type DS-UWB system. The length of the training sequence is one of the factors which make throughput decreased. The noble structure with the variable length of the training sequence whose length can be adaptively tailored according to the channel conditions (CM1,CM2,CM3,CM4) in the DS-USB systems is proposed. This structure can increase the throughput without sacrificing the performance than the method with fixed length of training sequence considering the worst case channel conditions. Simulation results under IEEE 802.15.3a channel model show that the proposed scheme can achieve higher throughput than a conventional one with the slight loss of BER performance. And this structure can reduce the computation complexity and power consumption with selecting the short length of the training sequence.

• Journal of Communications and Networks
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• 제14권5호
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• pp.501-509
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• 2012

This paper proposes a joint timing synchronization, channel estimation, and data detection for the impulse radio ultra-wideband systems. The proposed timing synchronizer consists of coarse and fine timing estimation. The synchronizer discovers synchronization points in two stages and performs adaptive threshold based on the maximum pulse averaging and maximum (MAX-PA) method for more precise synchronization. Then, iterative channel estimation is performed based on the discovered synchronization points, and data are detected using the selective rake (S-RAKE) detector employing maximal ratio combining. The proposed synchronizer produces two signals-the start signal for channel estimation and the start signal for start frame delimiter (SFD) detection that detects the packet synchronization signal. With the proposed synchronization, channel estimation, and SFD detection, an S-RAKE receiver with binary pulse position modulation binary phase-shift keying modulation was constructed. In addition, an IEEE 802.15.4a channel model was used for performance comparison. The comparison results show that the constructed receiver yields high performance close to perfect synchronization.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제16권1호
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• pp.50-54
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• 2010

컨테이너 보안 장치(CSD)는 기존 RFID Tag와 달리 컨테이너 내부에 장착하여 물리적 보안을 강화하였고 데이터를 이중으로 암호화함으로써 정보에 대한 보안을 강화한 장치이다. CSD는 배터리로 동작하기 때문에 전원을 효율적으로 사용해야 한다. 따라서 수면 기간과 채널 탐색기간을 반복하는 저전력 메커니즘이 필요하다. 그러나 이들 기간을 조절함에 따라 에너지의 효율성과 네트워크 연결성의 trade-off가 발생한다. 본 논문에서는 저전력 CSD를 구현함에 있어 비컨 주기와 채널 탐색 기간을 조절하여 이 문제를 해결하고자 하였다. 그 결과 95% 이상의 네트워크 연결성을 보장하고 일반적인 AA 배터리를 장착하여 최대 16일의 수명을 보장하는 것을 볼 수 있었다.

• 한국산학기술학회논문지
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• 제11권9호
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• pp.3571-3577
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• 2010

본 논문에서는 예상 위치좌표 탐색기법과 이를 균등거리비율 개념인 AEDR(Algorithm for localization using the concept of Equivalent Distance Rate)에 적용한 위치인식 보정 알고리즘인 E&E(Equivalent distance rate & Estimated location coordinator exploration)를 제안 한 후 실험을 통해 성능을 분석하였다. 실험결과, E&E는 4개의 시나리오에서 SDS-TWR의 위치인식 보정성능을 0.60m에서 0.34m로 0.26m 만큼 향상시켰고, E&E는 설정된 시나리오에 따라 기존에 제안된 AEDR과 비교한 결과 위치인식 보정 성능비율이 최대 15% 만큼 우수함을 확인하였다. 또한 E&E의 전체 성능실험 중 99%에서 위치인식 오차가 1m 이내로 측정되었는데 이 정도의 위치인식 보정 성능이라면 제안하는 알고리즘인 E&E는 다양한 위치인식 응용분야에 충분히 적용 가능 할 것으로 판단된다.

• 한국산업정보학회논문지
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• 제17권7호
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• pp.1-8
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• 2012

본 논문에서는 유비쿼터스 환경 구축을 위한 센서 네트워크에서 효율적으로 데이터를 전송할 수 있는 멀티홉(multi-hop) 릴레이 (Relay) 전송 시스템을 고려한다. ISM 주파수 대역을 사용하는 DBO-CSS (Differentially Bi-Orthogonal Chirp Spread Spectrum) 방식의 확산대역 신호 중 하나인 첩 (Chirp) 신호를 이용하여 구축된 센서 네트워크를 기반으로 센서 거리 및 사물 위치인식을 위한 효율적인 릴레이 프로토콜을 제안한다. 효율적인 네트워킹 접속을 위하여 Zone information packet, Hop information packet, Tag information packet 및 Application serial packet 의 4종류의 패킷구조를 설계하여 구현하였으며, 구축된 센서 네트워크를 기반으로 사물의 위치인식의 효율성을 높이기 위한 구현 알고리즘을 제안하였다. 최종적으로 $15m{\times}15m$ 멀티셀 및 10 홉으로 구성된 테스트베드 시스템에서 제안한 프로토콜의 성능의 우수성을 검증한다.

• 한국전자통신학회논문지
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• 제11권8호
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• pp.735-742
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• 2016

저속 WPAN은 저속, 저전력, 저비용의 단거리 무선 네트워킹 기술이다. 저속 WPAN에서는 경쟁 기반의 CSMA/CA 알고리즘을 사용하여 디바이스들의 무선 채널 접속을 제어하기 때문에 프레임 전송시 언제라도 충돌이 발생할 수 있으며 이로 인해 네트워크 성능이 심각하게 저하될 수 있다. 본 논문에서는 저속 WPAN의 CSMA/CA 과정에서 프레임 충돌율을 줄이기 위해 네트워크 상황에 따라 백오프 구간을 동적으로 변화시키는 알고리즘을 제안한다. 시뮬레이션 수행 결과, CSMA/CA 과정에서 제안하는 동적 백오프 알고리즘은 백오프 구간을 정적으로 유지했을 경우에 비해 프레임 전달율과 지연 시간 측면에서 안정적이면서도 우수한 성능을 보이는 것을 확인하였다.

• 센서학회지
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• 제17권3호
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• pp.168-177
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• 2008

An indoor environmental monitoring system using IEEE 802.15.4 based wireless sensor network is proposed to monitor the amount of pollutant entering to the room from outside and also the amount of pollutant that is generated in indoor by the building materials itself or human activities. Small-size, low-power wireless sensor node and low power electrochemical sensor board is designed to measure the condition of indoor environment in buildings such as home, offices, commercial premises and schools. In this paper, two query models, the broadcasting query protocol and flooding query protocol, were designed and programmed as a query-based routing protocol in wireless sensor network for an environment monitoring system. The flooding query routing protocol in environment monitoring is very effective as a power saving routing protocol and reliable data transmission between sensor nodes.

• 대한임베디드공학회논문지
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• 제1권2호
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• pp.104-112
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• 2006

ZigBee is the emerging industrial standard for ad hoc networks based on IEEE 802.15.4. It is used for low data rate and low power wireless network applications. Expected applications of ZigBee include wireless sensor networks for remote monitoring, home control, and industrial automation. Since one of the most important design goals of ZigBee is to reduce the installation and running costs, the ZigBee stack is embedded in the cheap and small micro-controller unit. The hierarchical routing algorithm is used for ZigBee end devices which have very limited resources. Using the block addressing scheme, end devices can send data to the destination without a routing table. However, hierarchical routing has the problem that the packets follow the tree hierarchy to the destination even if the destination is located nearby. In this paper, we propose a scheme to improve the hierarchical routing algorithm in ZigBee networks by employing the neighbor table that is originally used together with the routing table. We suggest selecting the neighbor node that has the minimum remaining hops to the destination as the next hop node. Simulation result shows that the proposed scheme saves more than 30% of the hop counts compared with the original hierarchical routing.