• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권2호
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• pp.483-503
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• 2015

This paper analyzes the optimal user density and power allocation for Device-to-Device (D2D) communication underlaying cellular networks on multiple bands with the target of maximizing the D2D transmission capacity. The entire network is modeled by Poisson point process (PPP) which based on stochastic geometry. Then in order to ensure the outage probabilities of both cellular and D2D communication, a sum capacity optimization problem for D2D system on multiple bands is proposed. Using convex optimization, the optimal D2D density is obtained in closed-form when the D2D transmission power is determined. Next the optimal D2D transmission power is obtained in closed-form when the D2D density is fixed. Based on the former two conclusions, an iterative algorithm for the optimal D2D density and power allocation on multiple bands is proposed. Finally, the simulation results not only demonstrate the D2D performance, density and power on each band are constrained by cellular communication as well as the interference of the entire system, but also verifies the superiority of the proposed algorithm over sorting-based and removal algorithms.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2011년도 한국컴퓨터종합학술대회논문집 Vol.38 No.1(D)
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• pp.219-220
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• 2011

본 논문은 LTE-Advanced 망에서의 D2D(Device-to-Device) 통신을 효율적으로 하기 위한 주파수 할당 절차를 소개하고 그 메커니즘을 제안하였다. 제안한 메커니즘은 기지국에서 셀 내 주파수의 상태에 따라 주파수에 우선순위를 적용한 뒤, 높은 우선순위를 가지는 주파수를 D2D 통신에 할당한다. 성능평가에서는 D2D 통신, 주파수 할당 메커니즘을 적용하지 않은 D2D 통신, 주파수 할당 메커니즘을 적용한 D2D 통신의 처리량을 비교하여 제안한 메커니즘의 우수성을 증명하였다.

• Journal of Communications and Networks
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• 제16권5호
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• pp.568-577
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• 2014

We consider a mobile content delivery network (mCDN) in which special mobile devices designated as caching servers (caching-server device: CSD) can provide mobile stations with popular contents on demand via device-to-device (D2D) communication links. On the assumption that mobile CSD's are randomly distributed by a Poisson point process (PPP), an optimization problem is formulated to determine the probability of storing the individual content in each server in a manner that minimizes the average caching failure rate. Further, we present a low-complexity search algorithm, optimum dual-solution searching algorithm (ODSA), for solving this optimization problem. We demonstrate that the proposed ODSA takes fewer iterations, on the order of O(log N) searches, for caching N contents in the system to find the optimal solution, as compared to the number of iterations in the conventional subgradient method, with an acceptable accuracy in practice. Furthermore, we identify the important characteristics of the optimal caching policies in the mobile environment that would serve as a useful aid in designing the mCDN.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권8호
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• pp.3435-3454
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• 2016

Device-to-device (D2D) communication is a potential solution to the incessant increase in data traffic on cellular networks. The greatest problem is how to control the interference between D2D users and cellular mobile users, and between D2D users themselves. This paper proposes a solution for this issue by putting the full control privilege in cellular network using the software-defined networking (SDN) concept. A software virtual switch called Open vSwitch and several components are integrated into mobile devices for data forwarding and radio resource mapping, whereas the control functions are executed in the cellular network via a SDN controller. This allows the network to assign radio resources for D2D communication directly, thus reducing interference. This solution also brings out many benefits, including resource efficiency, energy saving, topology flexibility, etc. The advantages and disadvantages of this architecture are analyzed by both a mathematical method and a simple implementation. The result shows that implementation of this solution in the next generation of cellular networks is feasible.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권1호
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• pp.203-228
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• 2012

It is expected that device-to-device (D2D) communication is allowed to underlay future cellular networks such as IMT-Advanced for spectrum efficiency. This article studies the mechanisms of D2D communication and interference avoidance when the D2D subsystem reuses uplink resources and downlink spectrums with a cellular system, respectively. We firstly propose an effective scheme to establish and maintain D2D communication. Moreover, a novel method to deal with the resource allocation and interference avoidance issues by utilizing the network peculiarity of a hybrid network to share the uplink resource is proposed. Most research focuses on reusing the uplink spectrums, but how to share the downlink frequency bands is seldom addressed. To share the downlink spectrums and avoid the interference to the primary cellular devices, a labeled time slots based mechanism is proposed. Implementation details are described in a real cellular system and simulation results prove that satisfying performance can be achieved by using the proposed mechanisms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권4호
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• pp.1941-1960
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• 2019

Unmanned aerial vehicles (UAVs), acting as mobile base stations (BSs), can be deployed in the typical fifth-generation mobile communications (5G) scenarios for the purpose of substantially enhancing the radio coverage. Meanwhile, UAV aided underlay device-to-device (D2D) communication mode can be activated for further improving the capacity of the 5G networks. However, this UAV aided D2D communication system is more vulnerable to eavesdropping attacks, resulting in security risks. In this paper, the D2D receivers work in full-duplex (FD) mode, which improves the security of the network by enabling these legitimate users to receive their useful information and transmit jamming signal to the eavesdropper simultaneously (with the same frequency band). The security communication under the UAV coverage is evaluated, showing that the system's (security) capacity can be substantially improved by taking advantage of the flexible radio coverage of UAVs. Furthermore, the closed-form expressions for the coverage probabilities are derived, showing that the cellular users (CUs)' secure coverage probability in downlink transmission is mainly impacted by the following three factors: its communication area, the relative position with UAV, and its eavesdroppers. In addition, it is observed that the D2D users or DUs' secure coverage probability is relevant to state of the UAV. The system's secure capacity can be substantially improved by adaptively changing the UAV's position as well as coverage.

• 대한의용생체공학회:의공학회지
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• 제41권2호
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• pp.75-83
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• 2020

In large-scale hospitals, the department of biomedical engineering should always provide quick repair service for damaged medical devices to guarantee continuous patient treatment. However, in actual circumstances, there are so many time-consuming issues that delays device repair for weeks or even months; therefore, it is required to prepare alternative ways for quick repair service. In this study, we first mentioned about the regulation issues in Korea about the 3D printing-based medical device repair, and then introduced the results of our preliminary study that evaluated the feasibility of 3D printing-based medical device repair before real-field application. Results of the study demonstrated that, in all of the 23 cases, parts for repair that were manufactured by 3D-printing were successfully fixed and connected to the main body of the original device, and showed sufficient rigidity for protecting internal parts of the device. Considering the experimental results, medical device repair by applying 3D printing technology can be a promising alternative in cases when regular repair process is not available or takes too much time.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권4호
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• pp.1481-1500
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• 2016

Device-to-Device (D2D) communication underlaying macro-small cell networks, as one of the promising technologies in the era of 5G, is able to improve spectral efficiency and increase system capacity. In this paper, we model the cross- and co-tier D2D communications in two-tier macro-small cell networks. To avoid the complicated interference for cross-tier D2D, we propose a mode selection scheme with a dedicated resource sharing strategy. For co-tier D2D, we formulate a joint optimization problem of power control and resource reuse with the aim of maximizing the overall outage capacity. To solve this non-convex optimization problem, we devise a heuristic algorithm to obtain a suboptimal solution and reduce the computational complexity. System-level simulations demonstrate the effectiveness of the proposed method, which can provide enhanced system performance and guarantee the quality-of-service (QoS) of all devices in two-tier macro-small cell networks. In addition, our study reveals the high potential of introducing cross- and co-tier D2D in small cell networks: i) cross-tier D2D obtains better performance at low and medium small cell densities than co-tier D2D, and ii) co-tier D2D achieves a steady performance improvement with the increase of small cell density.

• 전자공학회논문지
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• 제52권5호
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• pp.33-47
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• 2015

셀룰러 네트워크에서 기지국의 과부하를 줄이고 주파수 부족 현상을 완화시킬 수 있는 D2D(Device-to-Device) 통신에 대한 연구가 활발히 진행되고 있다. 하지만 셀룰러 네트워크의 상향링크 주파수 자원을 공유함으로써 상호간의 간섭은 증가하게 된다. 본 논문에서는 셀룰러와 D2D 사이의 간섭을 줄이기 위하여 새로운 하이브리드 수신기 FSC(Full Suppression Cancellation)를 제안한다. 제안한 수신기는 IRC(Interference Rejection Combining)와 SIC(Successive Interference Cancellation)를 결합하여 간섭을 억제 및 제거 할 수 있다. 시스템 레벨 시뮬레이션은 3GPP LTE-A 시스템의 20MHz 대역을 기반으로 이루어 졌으며, 시뮬레이션 결과 제안한 수신기를 통해 기존 수신기보다 SINR, 전송률 및 스펙트럼 효율 측면에서 성능 향상을 가져다주는 것을 확인하였다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.835-837
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• 2002

The 17" Backlight Unit (BLU) employing twelve EEFLs (External Electrode Fluorescent Lamp) has been developed for LCD-TV The characteristics of the EEFL BLU without dual brightness enhancement film (DBEF) were equivalent to those of CCFL (Cold cathode Fluorescent Lamp) BLU employing eight CCFLs with DBEF. Luminance, power consumption and uniformity were 12,000nits, 32watt and 80%, respectively. The inverter of EEFL Backlight Unit is composed of 2 transformers and driven by the sinusoidal waveform.