• Journal of Korea Multimedia Society
• /
• v.19 no.3
• /
• pp.567-572
• /
• 2016

N-screen is an emerging technology to support multimedia multicasting, content sharing and content mobility. N-screen service providers should obtain the technology that provides the highest quality content seamlessly. Distributed nature of WiMedia distributed-MAC protocol can provide full mobility support, and achieves seamless medium access method in contrast to IEEE 802.15.3. So, in this paper, WiMedia distributed-MAC protocol is adopted and an asynchronous multicast transmission (AMT) technology is proposed to enhance performance of seamless N-screen wireless service based on distributed-MAC. The ACK frame transmissions are not required for multicast transmissions. By using this property in AMT, if a device is a multicast receiver, its reserved time slots can be reserved by the other devices with 1-hop distance. Furthermore, each N-screen device broadcasts and shares the information including an order in asynchronous traffic reservations to reduce conflicts in determining the transmission order of asynchronous N-screen packets. Therefore, AMT scheme expands the number of time slots available and throughputs for multicast and asynchronous traffic reservations when comparing with the distributed-MAC standard system. N-screen communications based on distributed-MAC with the proposed AMT shows a new framework for realizing N-screen wireless service with the full content mobility.

• ETRI Journal
• /
• v.33 no.3
• /
• pp.326-334
• /
• 2011

This paper outlines the time jitter effect of a sampling clock on a software-defined radio technology-based digital intermediate frequency (IF) transceiver for a mobile communication base station. The implemented digital IF transceiver is reconfigurable to high-speed data packet access (HSDPA) and three bandwidth profiles: 1.75 MHz, 3.5 MHz, and 7 MHz, each incorporating the IEEE 802.16d worldwide interoperability for microwave access (WiMAX) standard. This paper examines the relationship between the signal-to-noise ratio (SNR) characteristics of a digital IF transceiver with an under-sampling scheme and the sampling jitter effect on a multichannel orthogonal frequency-division multiplexing (OFDM) signal. The simulation and experimental results show that the SNR of the OFDM system with narrower band profiles is more susceptible to sampling clock jitter than systems with relatively wider band profiles. Further, for systems with a comparable bandwidth, HSDPA outperforms WiMAX, for example, a 5 dB error vector magnitude improvement at 15 picoseconds time jitter for a bandwidth of WiMAX 3.5 MHz profile.

• ETRI Journal
• /
• v.36 no.3
• /
• pp.385-395
• /
• 2014

In this paper, we consider a resource allocation scheme for millimeter wave-based wireless personal area networks using directional antennas. This scheme involves scheduling the reservation period of medium access control for IEEE 802.15.3c. Objective functions are considered to minimize the average delay and maximize throughput; and two scheduling algorithms-namely, MInMax concurrent transmission and MAxMin concurrent transmission-are proposed to provide a suboptimal solution to each objective function. These are based on an exclusive region and two decision rules that determine the length of reservation times and the transmission order of groups. Each group consists of flows that are concurrently transmittable via spatial reuse. The algorithms appropriately apply two decision rules according to their objectives. A real video trace is used for the numerical results, which show that the proposed algorithms satisfy their objectives. They outperform other schemes on a range of measures, showing the effect of using a directional antenna. The proposed scheme efficiently supports variable bit rate traffic during the reservation period, reducing resource waste.

• Journal of Sensor Science and Technology
• /
• v.17 no.3
• /
• pp.168-177
• /
• 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.

• Journal of Electrical Engineering and Technology
• /
• v.8 no.3
• /
• pp.658-665
• /
• 2013

While the chirp signal is extensively used in radar and sonar systems for target decision in wireless communication systems, it has not been widely used for positioning in indoor environments. Recently, the IEEE 802.15.4a standard has adopted the chirp spread spectrum (CSS) as an underlying technique for low-power and low-complexity precise localization. Chirp signal based ranging solutions have been established and deployed but their ranging performance has not been analyzed in multipath environments. This paper presents a ranging performance analysis of a chirp signal and suggests a method to suppress multipath error by using a type of non-linear chirp signal. Multipath ranging performance is evaluated using a conventional linear chirp signal and the proposed non-linear chirp signal. We verify the feasibility of both methods using two-ray multipath model simulation. Our results demonstrate that the proposed non-linear chirp signal can successfully suppress the multipath error.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.1C
• /
• pp.113-119
• /
• 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.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2009.04a
• /
• pp.467-470
• /
• 2009

본 논문에서는 유비쿼터스 기반 인프라를 이용한 실시간 유괴방지 시스템을 구축하였다. 급속한 사회 발전과 더불어 강력사건이 증가되고 있으며 그중에서 어린이 유괴 범죄 같이 질적으로 흉악한 범죄가 해마다 증가되고 있는 실정이다. 이러한 유괴 범죄를 예방하기 위하여 현재 GPS(Global Positioning System)을 이용한 위치인식 기술 및 이동통신 기지국을 이용한 위치인식 기술이 사용되고 있다. 단순히 위치인식 기술은 위험상황이 발생하였을 때, 상황을 정확히 인지하기 어려워 유괴된 어린이 44%가 1시간 이내 사망하고 74%가 3시간 이내 사망 한다는 통계를 감안하면 기존 시스템은 어린이 생명 보호 능력에 한계가 있다. 본 연구에서는 유비쿼터스 도시 기반 인프라를 구축하여 WPAN(Wireless Personal Area Network)환경에서 RF만으로 거리 측정이 가능한 IEEE 802.15.4a의 ISM Band CSS(Chirp Spread Spectrum)방식을 이용하여 보다 저 전력으로 정확한 위치정보 시스템을 적용하였다. 이에 CSS방식을 통하여 얻은 위치정보를 지능형 CCTV와 융합하여 CCTV가 단말기 위치로 자동 초점하는 시스템을 구성하였다. 도시통합운영센터에서 상황을 정확히 인지하고 신속하게 출동할 수 있도록 단말기 위치를 지속적으로 요원의 PDA 및 핸드폰으로 통보하고 현장 주변의 미디어 보드 표시와 음성 경고로 경찰의 적절한 대응 및 주변의 도움을 받을 수 있는 시스템을 구성하였다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.19 no.7
• /
• pp.67-72
• /
• 2005

If the PNC is shutting down or wants to leave the WPAN, it uses the handover process to give control to another device in the piconet. However when the PNC is selected, only the device capability information is checked in the WPAN standard specification and no detail criteria is described. In this paper, the PNC selection method with considering the number and density of device to maximize the piconet data throughput in the WPAN is studied. From the numerical analysis results, the considering with the devices concentration has higher data throughput compared with the uniform distribution. For the efficient performance, the device distribution within the piconet should be considered in the PNC selection.

• Journal of information and communication convergence engineering
• /
• v.12 no.2
• /
• pp.109-115
• /
• 2014

This paper presents a concurrent channel time allocation scheme used in the reservation period for concurrent transmissions in 60-GHz wireless personal area networks (WPANs). To this end, the proposed resource allocation scheme includes an efficient method for creating a concurrent transmission group by using a table that indicates whether individual streams experience interference from other streams or not. The coordinator device calculates the number of streams that can be concurrently transmitted with each stream and groups them together on the basis of the calculation result. Then, the coordinator device allocates resources to each group such that the streams belonging to the same group can transmit data concurrently. Therefore, when the piconet coordinator (PNC) allocates the channel time to the individual groups, it should allow for maximizing the overall capacity. The performance evaluation result demonstrates that the proposed scheme outperforms the random grouping scheme in terms of the overall capacity when the beamwidth is $30^{\circ}C$ and the radiation efficiency is 0.9.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38C no.11
• /
• pp.1074-1077
• /
• 2013

This paper analyzes the benefit of using directional antennas against eavesdropping attack in millimeter wave (mmWave)-based networks. All devices are equipped with a directional antenna or an omni-directional antenna in a single-hop communications. The probability of a device being detected by an eavesdropper is analyzed based on the exposure region of a device. The relative detection rate is introduced to represent the benefit of using directional antenna. Numerical results show that there exists an optimal number of devices that maximizes the detection probability and it varies according to the parameters such as antenna beamwidth. It shows that the use of directional antenna enables to protect the devices from the detection by an eavesdropper for almost the whole situation in mmWave band communication.