• ETRI Journal
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• 제35권1호
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• pp.120-130
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• 2013

This paper presents an analysis of resource assignment for multihop communications in millimeter-wave (mm-wave) wireless personal area networks. The purpose of this paper is to figure out the effect of using directional antennas and relaying devices (DEVs) in communications. The analysis is performed based on a grouping algorithm, categorization of the flows, and the relaying DEV selection policy. Three schemes are compared: direct and relaying concurrent transmission (DRCT), direct concurrent transmission (DCT), and direct nonconcurrent transmission (DNCT). Numerical results show that DRCT is better than DCT and DCT is better than DNCT for any antenna beamwidths under the proposed algorithm and policy. The results also show that using relaying DEVs increases the throughput up to 30% and that there is an optimal beamwidth that maximizes spatial reuse and depends on parameters such as the number of flows in the networks. This analysis can provide guidelines for improving the performance of mm-wave band communications with relaying DEVs.

• ETRI Journal
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• 제36권3호
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• pp.374-384
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• 2014

To achieve high-speed (giga-bit) connectivity for short-range wireless multimedia applications, the millimeter-wave (mmWave) wireless personal area networks with directional antennas are gaining increased interest. Due to the use of directional antennas and mmWave communications, the probability of non-interfering transmissions increases in a localized region. Network throughput can be increased immensely by the concurrent time allocation of non-interfering transmissions. The problem of finding optimum time allocation for concurrent transmissions is an NP-hard problem. In this paper, we propose two enhanced versions of previously proposed multi-hop concurrent transmission (MHCT) schemes. To increase network capacity, the proposed schemes efficiently make use of the free holes in the time-allocation map of the MHCT scheme; thus, making it more compact.

• ETRI Journal
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• 제36권3호
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• pp.385-395
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• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권11호
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• pp.2068-2086
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• 2011

Based on the quincunx sub-sampling grid, the New Interleaved Hierarchical INTerpolation (NIHINT) method is recognized as a superior pyramid data structure for the lossless and progressive coding of natural images. In this paper, we propose a new image interpolation algorithm, Edge Adaptive Hierarchical INTerpolation (EAHINT), for a further reduction in the entropy of interpolation errors. We compute the local variance of the causal context to model the strength of a local edge around a target pixel and then apply three statistical decision rules to classify the local edge into a strong edge, a weak edge, or a medium edge. According to these local edge types, we apply an interpolation method to the target pixel using a one-directional interpolator for a strong edge, a multi-directional adaptive weighting interpolator for a medium edge, or a non-directional static weighting linear interpolator for a weak edge. Experimental results show that the proposed algorithm achieves a better compression bit rate than the NIHINT method for lossless image coding. It is shown that the compression bit rate is much better for images that are rich in directional edges and textures. Our algorithm also shows better rate-distortion performance and visual quality for progressive image transmission.

• Journal of Communications and Networks
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• 제16권2호
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• pp.227-237
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• 2014

Throughput scaling laws for two coexisting ad hoc networks with m primary users (PUs) and n secondary users (SUs) randomly distributed in an unit area have been widely studied. Early work showed that the secondary network performs as well as stand-alone networks, namely, the per-node throughput of the secondary networks is ${\Theta}(1/\sqrt{n{\log}n})$. In this paper, we show that by exploiting directional spectrum opportunities in secondary network, the throughput of secondary network can be improved. If the beamwidth of secondary transmitter (TX)'s main lobe is ${\delta}=o(1/{\log}n)$, SUs can achieve a per-node throughput of ${\Theta}(1/\sqrt{n{\log}n})$ for directional transmission and omni reception (DTOR), which is ${\Theta}({\log}n)$ times higher than the throughput with-out directional transmission. On the contrary, if ${\delta}={\omega}(1/{\log}n)$, the throughput gain of SUs is $2{\pi}/{\delta}$ for DTOR compared with the throughput without directional antennas. Similarly, we have derived the throughput for other cases of directional transmission. The connectivity is another critical metric to evaluate the performance of random ad hoc networks. The relation between the number of SUs n and the number of PUs m is assumed to be $n=m^{\beta}$. We show that with the HDP-VDP routing scheme, which is widely employed in the analysis of throughput scaling laws of ad hoc networks, the connectivity of a single SU can be guaranteed when ${\beta}$ > 1, and the connectivity of a single secondary path can be guaranteed when ${\beta}$ > 2. While circumventing routing can improve the connectivity of cognitive radio ad hoc network, we verify that the connectivity of a single SU as well as a single secondary path can be guaranteed when ${\beta}$ > 1. Thus, to achieve the connectivity of secondary networks, the density of SUs should be (asymptotically) bigger than that of PUs.

• Journal of the Optical Society of Korea
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• 제8권4호
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• pp.149-155
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• 2004

Newly developed modal transmission-line theory(MTLT) is used to analyze rigorously the optical power distribution in grating-assisted directional couplers(GADCs) with three guiding channels. By defining a novel coupling efficiency ${\eta}$ amenable to the rigorous analytical solutions of modal transmission-line theory, we explicitly evaluate the power coupling and distribution of TM modes. The results reveal that the incident power is sensitively partitioned through three output channels in terms of such grating parameters as the grating period, the duty cycle, and the operating wavelength.

• 드라이브 ㆍ 컨트롤
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• 제15권1호
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• pp.1-9
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• 2018

The spool displacement of directional control valve can be considered as the standard signal to measure the bandwidth frequency of a directional control valve. When the spool displacement is not available, the metering-orifice system is implemented in this research as an alternative way of measuring the 90 degrees phase bandwidth frequency of the hydraulic directional control valve. The inertia effect on the transmission line oil induces the phase lead of the valve load pressure when compared with the phase of spool displacement. The capacitance effect of the oil induces the phase lag of the valve load pressure. The phase of the load pressure can be adjusted to be the same as that of the spool displacement by controlling the opening area of the metering orifice. A series of experiments were conducted to verify the effectiveness of the metering orifice. The 90 degrees phase bandwidth frequency measured from the valve load pressure was significantly deviated in some cases from the frequency of the spool displacement. The metering orifice was hard to be applied to measure the -90 degrees phase bandwidth frequency of the high precision.

• 한국통신학회논문지
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• 제36권3A호
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• pp.278-286
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• 2011

지향성 안테나는 네트워크의 공간 재사용 기술이 발전함에 따라 Ad Hoc 네트워크에서 널리 사용되고 있다. 그러나 확장된 전송영역은 이웃하는 수신 노드 간에 충돌을 일으키고, 이것은 지향성 안테나의 전송능력을 충분히 사용하지 못하게 하는 원인이 된다. 본 논문에서는 지향성 안테나를 위한 새로운 전력제어 MAC프로토콜을 제안한다. 이 프로토콜을 지원하기 위하여 이웃하는 수신 노드들 중에서 간섭 노드의 집합을 찾아내기 위한 기법을 개발한다. 그리고 전력 제어 알고리즘을 이용하여 최소 전송 전력을 계산한 후, 데이터를 전송한다. 이 프로토콜의 시뮬레이션 결과, 네트워크 성능이 향상되었으며 전력 소비가 감소하였음을 알 수 있었다.

• 한국광학회지
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• 제16권2호
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• pp.162-167
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• 2005

나노 크기 양자우물구조로 구성된 광통신용 방향성결합기를 모드전송선천 이론을 이용하여 설계하였다. 그 타당성과 유용성을 보이기 위하여 나노 결합기의 그 전파특성과 결합특성을 서로 다른 유효질량으로 구성된 이중 양자우물구조에서 분석하였다. 그 수치해석 결과 전체 전자에너지가 83.9 meV일 때, 결합길이 295.3 nm에서 최대 결합효율을 나타내었다. 더욱이, 이중 양자우물구조 사이의 장벽(barrier) 두께가 증가함에 따라 협대역(narrowband) 필터로 동작하였다.

• 한국산학기술학회논문지
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• 제13권1호
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• pp.317-321
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• 2012

본 논문에서는 높은 지향성을 갖는 방향성 결합기의 특성을 연구하였다. 방향성 결합기는 이동통신 기지국의 송신단에서 신호의 크기나 주파수 혹은 안테나에서의 반사 등을 확인하기 위해 사용된다. 높은 지향성을 갖는 방향성 결합기를 개발하기 위해 시뮬레이션을 통해 특성을 분석하였고 이를 바탕으로 방향성 결합기를 제작 분석하였다. 제작된 결합기는 약 31dB 정도의 높은 지향성 특성을 보였다.