• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.12
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• pp.4835-4855
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• 2015

TV white space (TVWS) is showing promise to become the first widespread practical application of cognitive technology. In fact, regulators worldwide are beginning to allow access to the TV band for secondary users, on the provision that they access the geolocation database. Device-to-device (D2D) can improve the spectrum efficiency, but large-scale D2D communications that underlie TVWS may generate undesirable interference to TV receivers and cause severe mutual interference. In this paper, we use an established geolocation database to investigate the power allocation problem, in order to maximize the total sum throughput of D2D links in TVWS while guaranteeing the quality-of-service (QoS) requirement for both D2D links and TV receivers. Firstly, we formulate an optimization problem based on the system model, which is nonconvex and intractable. Secondly, we use an effective approach to convert the original problem into a series of convex problems and we solve these problems using interior point methods that have polynomial computational complexity. Additionally, we propose an iterative algorithm based on the barrier method to locate the optimal solution. Simulation results show that the proposed algorithm has strong performance with high approximation accuracy for both small and large dimensional problems, and it is superior to both the active set algorithm and genetic algorithm.

• ETRI Journal
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• v.37 no.5
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• pp.877-887
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• 2015

This paper is a first-hand summary on our comprehensive live trial of cellular-assisted device-to-device (D2D) communications currently being ratified by the standards community for next-generation mobile broadband networks. In our test implementation, we employ a full-featured 3GPP LTE network deployment and augment it with all necessary support to provide realtime D2D connectivity over emerging Wi-Fi-Direct (WFD) technology. As a result, our LTE-assisted WFD D2D system enjoys the required flexibility while meeting the existing standards in every feasible detail. Further, this paper provides an account on the extensive measurement campaign conducted with our implementation. The resulting real-world measurements from this campaign quantify the numerical effects of D2D functionality on the resultant system performance. Consequently, they shed light on the general applicability of LTE-assisted WFD solutions and associated operational ranges.

• Journal of Korea Multimedia Society
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• v.18 no.12
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• pp.1468-1474
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• 2015

Efficient spectrum sharing is an important issue in Device-to-Device (D2D) communications underlaying cellular networks as it can mitigate the interference to cellular users and improve the performance of the systems. In this paper, we formulate the radio resource allocation in D2D communications as a mixed nonlinear integer programing. We show the formulated problem is NP-hard and thus a polynomial time algorithm to solve is not possible. Since such a problem is very hard to obtain the optimal solution within a short running time, we instead propose a fast heuristic suboptimal algorithm to mitigate the interference caused to cellular users and improve the performance of the systems. Simulation results are provided to evaluate the performance of the proposed algorithm.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.06a
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• pp.363-365
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• 2013

최근 3D산업의 급성장으로 인해 3D콘텐츠 제작에 대한 관심이 확산되고 있다. 지금까지는 3D콘텐츠 제작을 영화나 애니메이션 같은 자연영상을 3D변환하는 것에 초점이 맞추어져 있었다. 자동 3D변환에서는 window 영상처럼 텍스트, 이미지, 로고 등의 혼합되어 있는 영상을 처리하는데 어려움이 있다. 특히 텍스트는 동일한 깊이맵을 얻지 못하면, 깨짐, 흔들림 등의 문제점이 발생한다. 해결방법으로 혼합 영상을 구분하고 영상 영역만을 탐색해서, 3D변환을 하고, 다른 영역은 2D로 처리함으로써 상기 문제점을 극복할 수 있다.

• Journal of IKEEE
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• v.15 no.4
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• pp.339-344
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• 2011

In this paper, we proposed an internal multi-band monopole antenna for mobile phone that can be used for smart phones. The proposed antenna has a small volume of $38{\times}8.5{\times}5\;mm^3$, ground size is $100{\times}60\;mm^2$, and covers the GSM900 (Global System for Mobile communications : 880-960 MHz), DCS (Digital Communications System : 1710-1880 MHz), K-PCS (Korea-Personal Communications Service : 1750-1870 MHz), US-PCS (US Personal Communications Service : 1850-1990 MHz), Bluetooth (2400-2483 MHz), Wibro (2300-2390 MHz) and WLAN (Wireless Local Area Network : 2400-2483.5 MHz) bands. The measured peak gains of the implemented antenna are 1.15 dBi at 920 MHz, 3.58 dBi at 1795 MHz, 3.46 dBi at 1810 MHz, 2.91 dBi at 1920 MHz, 5.18 dBi at 2345 MHz, 3.37 dBi at 2442 MHz.

• Journal of information and communication convergence engineering
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• v.9 no.1
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• pp.16-20
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• 2011

In this paper, we designed and implemented an internal multi-band folded monopole antenna for mobile handset. The proposed antenna covers Global System for Mobile Communications (GSM900: 880~960 MHz), Digital Communications System (DCS: 1710~1880 MHz), US-Personal Communications Service (US-PCS: 1850~1990 MHz), Bluetooth(2400~2484 MHz), WiMAX(3400~3600 MHz), and Wireless Local Area Network (WLAN: 5150~5350 MHz, 5725~5875 MHz) band for Voltage Standing Wave Ratio $(VSWR)\;{\le}\; 3$. The measured peak gains of the implemented antenna are -1.78dBi at 920MHz, 2.72dBi at 1795MHz, 2.25dBi at 1920MHz, 2.34dBi at 2442MHz, 2.11 dBi at 3550MHz, and 2.04 dBi at 5250MHz.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.10
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• pp.2732-2749
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• 2023

Device-to-Device (D2D) communication has received increasing attention and been studied extensively thanks to its advantages in improving spectral efficiency and energy efficiency of cellular networks. This paper proposes a novel relay selection algorithm for multi-hop full-duplex D2D communications underlaying cellular networks. By selecting the relay of each hop in a reverse manner, the proposed algorithm reduces the heavy signaling overhead that traditional relay selection algorithms introduce. In addition, the social domain information of mobile terminals is taken into consideration and its influence on the performance of D2D communications studied, which is found significant enough not to be overlooked. Moreover, simulations show that the proposed algorithm, in absence of social relationship information, improves data throughput by around 70% and 7% and energy efficiency by 64% and 6%, compared with two benchmark algorithms, when D2D distance is 260 meters. In a more practical implementation considering social relationship information, although the proposed algorithm naturally achieves less throughput, it substantially increases the energy efficiency than the benchmarks.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.345-347
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• 2011

최근 3D 콘텐츠의 관심 증가는 Display 장치, 모바일 기기 등의 하드웨어적인 발전을 가져왔고, 이에 따른 입체 콘텐츠의 필요성이 대두되고 있다. 본 논문에서는 자동으로 2D영상을 3D입체영상으로 변환하는 기법을 제안한다. 영상에서 에지맵과 채도 영상을 추출하고 합성하여 깊이맵을 생성하고 필터를 통해 노이즈 제거 등 보정 작업하여 최종 깊이맵을 생성한다. 이 깊이맵을 이용해 2D영상의 시프트된 영상을 만들어 입체영상을 생성한다.

• ETRI Journal
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• v.35 no.2
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• pp.177-187
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• 2013

In this paper, we propose a dual-band multiple-input multiple-output (MIMO) antenna with high isolation for WLAN applications (2.45 GHz and 5.2 GHz). The proposed antenna is composed of a mobile communication terminal board, eight radiators, a coaxial feed line, and slots for isolation. The measured -10 dB impedance bandwidths are 10.1% (2.35 GHz to 2.6 GHz) and 3.85% (5.1 GHz to 5.3 GHz) at each frequency band. The proposed four-element MIMO antenna has an isolation of better than 35 dB at 2.45 GHz and 45 dB at 5.2 GHz between each element. The antenna gain is 3.2 dBi at 2.45 GHz and 4.2 dBi at 5.2 GHz.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.40-42
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• 2010

최근 3DTV 등의 3D 디스플레이의 공급으로 기존의 입체 콘텐츠뿐만 아니라, 일반 2D 영상도 자동적으로 입체 콘텐츠로 변환하여 3D로 시청할 수 있다. 이러한 콘텐츠를 시청할 때에 주로 사용하는 3D 디스플레이에는 자체적인 UI를 내장하고 있는데, 입체 모드에서의 이러한 UI를 3D로 변환하여 사용할 수 있는 3D UI기술에 대한 관심이 높아지고 있다. 본 논문에서는, 3D UI의 관심도 증가에 따라 좀 더 편리하고 이해도가 높은 3D UI의 개발 방법에 대하여 제안한다. Directshow를 이용하여, 문자와 UI 배경을 합성한다. 여기에 UI의 투명도, 시차, 밝기 등을 조절 가능하게 하여 사용자의 편의에 따라 선택할 수 있게 한다. 사전에 입체로 제작된 실험 영상을 실행하여 그 위에 메뉴 화면, 메뉴 글씨 등을 띄워 입체감 있는 3D UI를 제작, 증강을 체험할 수 있는 3D UI 플레이어를 구현한다.