• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.5
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• pp.1229-1234
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• 2012

Vehicular communications have been receiving much attention in intelligent transport systems (ITS) by combining communication technology with automobile industries. In general, vehicular communications can be used for vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication by adopting IEEE802.11p/1609 standard which is commonly known as wireless access in vehicular environments (WAVE). WAVE system transmits signal in 5.9GHz frequency band with orthogonal frequency division multiplexing (OFDM) signaling. In this paper, we consider physical layer issues in vehicular communications. We first overview the physical (PHY) layer of WAVE standard and properties of 5.9GHz signals, and then physical layer issues to provide reliable communication link are discussed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5A
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• pp.317-324
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• 2012

Physical layer network coding (PNC) was first introduce by Zhang et al. for two-way relay channels (TWRCs). By utilizing the PNC, we can complete two-way communications within two time slots, instead of three time slots required in non-PNC systems. Recently, the upper and lower bounds for a bit error rate (BER) of PNC have been analyzed for fading channels. In this paper, we derive an exact BER of the PNC for the TWRC over fading channels. We determine decision regions based on the nearest neighbor rule and partition them into several wedge areas to apply the Craig's polar coordinate form for computing the BER. We confirm that our derived analysis accurately matches with the simulation results.

• Proceedings of the Korean Information Science Society Conference
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• 2010.06b
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• pp.465-470
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• 2010

현재 사이버 물리 시스템을 통해 IT와 교통, 항공, 의료, 화학등 많은 분야들이 융합되어 Cyber Element와 Physical Element가 상호 작용하는 대규모 시스템 구축에 많은 연구가 이루어 지고 있다. 하지만 정적인 제어 구조를 가진 기존 시스템들의 통합으로 인해 새롭게 구축되는 대규모 시스템은 복잡도가 크게 증가하여 제어 구조에 관한 명세가 새롭게 이루어져야 하는 문제가 발생하고 있으며 해결하기 위해 사이버 물리 시스템에서는 일시적인 동적 제어가 가능한 미들웨어에 대한 요구가 증가하고 있다. 이에 본 논문에서는 사이버 물리 시스템을 위한 장치 간 동적 제어를 제공할 수 있는 미들웨어를 개발하기 위하여 하위 계층에서는 Star형, 상위 계층에서는 Flat한 계층 구조를 가진 하이브리드 계층 구조를 제안한다. 또한 미들웨어 구성요소들에 대한 특성 및 기능을 정의하고, XML(eXtensible Markup Language)을 이용하여 다양한 상황과 각 구성요소들의 기능에 따라 확장성과 유연성 있는 제어 메시지를 설계한다.

• Journal of Broadcast Engineering
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• v.13 no.1
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• pp.17-24
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• 2008

At the view of Application layer, there are many researches to achieve the cross-layer optimization with Physical layer. Scalable video coding is good example. Although it is necessary to consider the session layer which lies halfway between two layers, the research about that is insufficient. We present a feasible solution of dynamic session control for scalable video coding over IMS.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.11
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• pp.1214-1219
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• 2010

In this paper, a software radio system, supporting the physical layer of IEEE 802.15.4 standard, has been developed using USRP(Universal Software Radio Peripheral) board and GNU Radio package of an open source development kit for software radio. The software radio system supports the standards of BPSK and OQPSK modulations for 868/915 MHz band and OQPSK modulation for 2.45 GHz band. To verify the operation of the developed system, it has been tested under the standard signals according to the frequency band and packet structures for the transmitting and receiving operation. At 2.4 GHz, the Smart RF EV board and CC2430 modules are used to check the proper operation of the software radio system. The system performance test shows that the emission power spectrum, the eye-pattern, and PER(Packet Error Rate) meet the standard. It has been confirmed that the developed system supports the PHY layer of IEEE 802.15.4.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9B
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• pp.785-791
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• 2006

A CF-Poll frame which contains the channel reservation time can be piggybacked in QoS-Data frame to increase the channel efficiency in HCCA. However, if any QSTA in the network uses the low physical transmission rate, the QoS-Data frame which includes the CF-Poll frame must be transmitted by the minimum transmission rate. Therefore, it can cause the decrease of the channel efficiency and the increase of the frame transmission delay for other traffic streams when any QSTA has the low physical transmission rate. In this paper, we define this phenomenon as the piggyback problem at the low physical transmission rate and evaluate the effect of this problem. In the simulation results, when a CF-Poll piggyback is used, the delay is increased about 25% if any QSTA has the low physical transmission rate, while the delay is decreased about 7.8% if all QSTA has the high physical transmission rate. We also found that the gain of the CF-Poll piggyback mechanism is achieved when all QSTA has higher physical transmission rate than 24 or 36Mbps.

• Journal of Satellite, Information and Communications
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• v.8 no.1
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• pp.1-7
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• 2013

Currently satellite communication systems usually use the ACM(Adaptive Coding and Modulation) to extend the link availability and to increase the bandwidth efficiency. However, when ACM system is used for satellite communications, we should carefully consider TCP congestion control to avoid network congestions. Because MODCODs in ACM are changed to make a packet more robust according to satellite wireless link conditions, bandwidth of satellite forward link is also changed. Whereas TCP has a severe problem to control the congestion window for the changed bandwidth, then packet overflow can be experienced at MAC or PHY interface buffers. This is a reason that TCP in transport layer does not recognize a change of bandwidth capability form MAC or PHY layer. To overcome this problem, we propose the adaptive congestion control scheme of TCP for supporting ACM in Satellite PEP (Performance Enhancing Proxy) systems. Simulation results by using ns-2 show that our proposed scheme can be efficiently adapted to the changed bandwidth and TCP congestion window size, and can be useful to improve TCP performance.

• Journal of Satellite, Information and Communications
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• v.12 no.3
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• pp.50-53
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• 2017

Satellite communications are vulnerable to malicious eavesdroppers and interceptors due to wide coverage and broadcasting applications. However, technologies for securing satellite networks have yet to be more articulated beyond high-layer packet encryption. As attempts for jamming and spoofing attacks spread out, it is extremely critical to invest on the development of physical layer security solutions. In this paper, we review current technologies for satellite communication network security both in high and physical layers. We also present recent research results on physical layer security in the fields of information theory and wireless networks. We suggest a future direction for satellite communication security, including a cross-layer approach.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.585-588
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• 2000

광대역 무선 서비스에 대한 수요가 증가함에 따라 이미 제정되었거나 현재 제정중인 무선 LAN 표준안으로는 ETSI BRAN의 HIPERLAN, IEEE 802.11, MMAC-PC등이 있다 이러한 표준안들은 상위계층은 서로 다른 반면, 5 GHz 대역에서 OFDM 방식을 사용하는 공통된 물리계층을 정의하고 있다. 본 논문에서는 이중 HIPERLAN/2 물리계층의 구조 및 파라미터를 설명하고 그 성능을 분석한다.

• Information and Communications Magazine
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• v.31 no.2
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• pp.98-104
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• 2014

최근 안전한 무선 통신 시스템을 위하여 기존의 암호학적인 접근에서 벗어나 다양한 방식의 물리 계층 보안 기술이 제안되고 있다. 본고에서는 현재 사용되고 있는 암호학 기반의 키 생성 기술을 간략히 설명하고, 물리 계층 보안 기술 중 하나인 무선 채널 특성을 이용한 비밀키 생성 원리 및 기술 동향을 소개한다.